JP5710997B2 - Fatigue limit identification system and fatigue limit identification method - Google Patents

Description

  The present invention relates to an infrared thermography apparatus that applies a repeated stress to an object to be measured, and distributes an average temperature rise caused by energy dissipation inside the material or a frequency component of 1, 2, 3 times the generated stress amplitude within a certain region. The fatigue limit specifying system and the fatigue limit specifying method using the dissipative energy measuring means to measure by the above.

  Conventionally, as a method for specifying a fatigue limit or a fatigue fracture location, for example, methods described in Non-Patent Documents 1 to 4 have been reported. FIG. 30 (a) shows the temperature rise of an XC55 (carbon steel containing 0.55% carbon) steel test piece measured by an infrared thermography apparatus for the conventional method for identifying a fatigue point described in Non-Patent Document 1. It is the image which showed distribution of quantity. From the image shown in FIG. 30 (a), the temperature rise location of the XC55 steel test piece can be known. Non-Patent Document 1 states that a tensile fracture-compression load is periodically applied to an XC55 steel test piece at 100 Hz, and fatigue failure occurs at a measured temperature rise location.

  FIG. 30B shows a method for specifying the fatigue limit stress value shown in Non-Patent Document 1. FIG. 30 (b) shows the result of measuring the amount of temperature rise by stepwise changing the periodic tensile-compressive load applied to the XC55 steel test piece with the infrared thermography apparatus used in FIG. 30 (a). . FIG. 30B shows a state in which the gradient of the temperature rise with respect to the stress changes near the stress of 380 MPa. Non-Patent Document 1 describes that the point at which the slope changes (that is, the point where two straight lines intersect) substantially matches the fatigue limit of the XC55 steel specimen.

  Non-Patent Document 2 shows an application example to an automobile part such as a crankshaft, and shows a state in which the gradient of the temperature rise with respect to the load changes as in Non-Patent Document 1. Non-Patent Document 2 also states that the point at which the slope changes (that is, the point where two straight lines intersect) substantially matches the fatigue limit of the crankshaft.

  Non-Patent Document 3 shows how the slope of the temperature rise with respect to stress changes in the rotational bending test for XC55 steel, which is widely used for automotive parts, and the point where two straight lines intersect is fatigued. It states that it almost matches the limit.

  In Non-Patent Document 4, the notch specimen is used to plot the point at which the slope of the temperature rise with respect to the stress changes as in Non-Patent Document 1, and the stress at the point where two straight lines intersect and one straight line is the stress. A method for identifying fatigue limit stress is described in which the intersection at which the difference in stress at the point of intersection with the axis is the minimum is the fatigue limit.

M.M. P. Luong, “Fatigue limit evaluation of metals using an infrared thermotechnique”, Mechanics of Materials 28, 1998, p. 155-163 Tatsuya Yao, “Fatigue Limit Prediction by Stress Image and Dissipation Energy Measurement by Infrared Thermography”, Nondestructive Inspection, 2002, Vol. 51, No. 6, p. 333-337 M.M. P. Luong, “Infrared thermal scanning of fatigue in metals”, Nuclear Engineering and Design, 158: p. 363-376, 1995 F. Cira, G. et al. Curti, R.A. Sesana, “A new iterative method for the thermal retardation of fatigue limits in steels”, International Journal of Fatigue, 27: p. 453-459, 2005

  However, although there have been many reports on the method and system for identifying the fatigue limit by measuring the dissipated energy, there are a number of reports that have been made, but it is appropriate for the measurement of the dissipative energy, how to draw two straight lines, and the fatigue limit 2 Each method was used by researchers to determine how to find the intersection of straight lines. For this reason, the method for identifying the fatigue limit stress by measuring dissipative energy is greatly affected by the shape, material, processing, etc. of the measurement object, and there is no standard method for determining the specific method, resulting in a large measurement error. There was a thing.

  For these reasons, regarding the method for identifying the fatigue limit stress value by measuring dissipated energy, it is necessary to measure under appropriate conditions, such as how to determine the fatigue limit stress from the measured value, and obtain an appropriate value. There are many unclear points such as parameters for the analysis.

  Therefore, an object of the present invention is to solve the above problems, and to clarify a measurement condition for dissipating energy measurement, and to identify a fatigue limit specifying system and a fatigue limit specifying method capable of appropriately specifying a fatigue limit stress. Is to provide.

  The present invention is directed to a fatigue limit identification system and a fatigue limit identification method. In order to achieve the above object, the fatigue limit specifying system of the present invention measures the minute temperature change of the object to be measured and the vibrator that repeatedly applies stress to the object to be measured. An infrared thermography device that obtains a temperature image and an information processing device that processes the temperature image of the measurement object obtained from the infrared thermography device. The information processing apparatus includes a step of measuring the dissipated energy of the measurement object, a step of evaluating the stress concentration factor of the measurement object, a value of the stress concentration factor obtained from the step of evaluating the stress concentration factor, and the dissipated energy. And a step of specifying a fatigue limit from the measurement result obtained from the step of measuring In the process of measuring the dissipation energy, when a constant repeated external force was applied, it was repeatedly vibrated until the area of the hysteresis loop became constant in a hysteresis loop state in which the relationship between the amount of change in temperature and the amount of strain was closed. Measure the dissipated energy in a stable state.

An outline of the fatigue limit specifying system and the fatigue limit specifying method is shown in FIG. Referring to FIG. 1 (a), the steps of measuring the dissipated energy in the fatigue limit specifying system and the fatigue limit specifying method of the present invention include a step of capturing an image while gradually increasing the load, and a step of acquiring the captured image. It is divided into a process of performing image processing by fast Fourier transform at a specific frequency and a process of measuring a distortion change amount from a pixel shift amount by an image correlation method. Further, the temperature image obtained in the image processing step by the fast Fourier transform is a step of detecting the maximum pixel range a of the next principal stress sum, and is included in the principal stress sum image shown in FIG. A maximum pixel range a of the principal stress sum is detected. Then, in the detected maximum pixel range a, the strain change amount separately obtained in the step of measuring the strain change amount and the temperature change amount obtained in the step of performing image processing by fast Fourier transform are extracted, and the strain is extracted. A strain variation-temperature variation curve (FIG. 1C) is created in a step of creating a graph of the temperature variation with respect to the variation.

  The strain change-temperature change curve shown in FIG. 1C is a hysteresis loop state where the strain change-temperature change curve is closed in the next step, and whether the area of the hysteresis loop is constant or not. If it is determined and the area of the hysteresis loop is constant regardless of the number of repetitions, it is determined as the adaptive range. For the maximum pixel range a of the principal stress sum from the image obtained by the fast Fourier transform, the dissipated energy obtained as the load applied to the measurement object increases or the stress amplitude increases is shown in FIG. Is plotted as shown in

  On the other hand, if the strain change-temperature change curve is not a closed hysteresis loop and the area is not stable, it is determined as a non-adaptive range, and the process returns to the image capture process, where the strain change-temperature change curve is The condition that the hysteresis loop state and the area of the hysteresis loop are constant is obtained repeatedly. In this way, if the strain change amount-temperature change amount curve is in a closed hysteresis loop state and the hysteresis loop area is constant, the process proceeds to the next statistical processing & intersection extraction step. In the statistical processing & intersection extraction step, several approximate lines B and C are drawn by performing statistical processing by the least square method using at least three or more points in the graph shown in FIG. When the approximate straight line A indicating the state with the lowest dissipated energy is used as a reference, loads A1 ′ and A2 ′ corresponding to the fatigue limit are obtained from the intersections A1 and A2 at which the drawn approximate straight lines intersect with the approximate straight line A, respectively. .

  The present invention is directed to a fatigue limit identification system and a fatigue limit identification method. In order to achieve the above object, the fatigue limit specifying system of the present invention measures a minute temperature change of a measurement object, a vibrator that repeatedly applies a load or stress to the measurement object, and measures the measurement object. An infrared thermography device that obtains a temperature image of an object, and an information processing device that processes the temperature image of the measurement object obtained from the infrared thermography device. The information processing apparatus includes a step of measuring the dissipated energy of the measurement object, a step of evaluating the stress concentration factor of the measurement object, a value of the stress concentration factor obtained from the step of evaluating the stress concentration factor, and the dissipated energy. And a step of specifying a fatigue limit from the measurement result obtained from the step of measuring. In the process of measuring the dissipated energy, the dissipated energy is measured in a stable state in which a repeated frequency component twice as large as the generated stress amplitude is repeatedly vibrated when a constant external force is applied. .

  An outline of the fatigue limit specifying system and the fatigue limit specifying method is shown in FIG. With reference to FIG. 2A, the steps of measuring the dissipated energy in the fatigue limit specifying system and the fatigue limit specifying method of the present invention include the steps of capturing an image while gradually increasing the load, and the generated stress for the captured image. Performing image processing by fast Fourier transform for each specific cycle at a frequency twice the amplitude, detecting the maximum pixel range a of the principal stress sum, and performing image processing by fast Fourier transform for each specific cycle with respect to the number of cycles. A step of graphing the amount of temperature change obtained by the step of performing, a step of specifying an adaptive cycle range b in which the amount of change in temperature is constant from the graph of the amount of temperature change with respect to the number of cycles shown in FIG. A process of performing image processing by fast Fourier transform in a specified cycle range, a process of graphing dissipated energy, and a graph It consists step of extracting statistical processing and intersection by the least squares method using the at least three points in the.

FIG. 2B shows a graph of the temperature change obtained by the process of performing image processing by fast Fourier transform for each specific cycle. As shown in FIG. 2B, the amount of temperature change, which is a double frequency component, decreases exponentially in the range where the number of repeated stresses applied is small. On the other hand, in a range where the number of repetitions is large, the temperature change amount is almost constant and stable (that is, the gradient of the temperature change amount falls within a predetermined range). In this way, when a constant repeated external force is applied, the load frequency A1 ′, A2 ′ corresponding to the fatigue limit is appropriately obtained by measuring the repeated frequency component twice the generated stress amplitude in a stable state. It becomes possible. For example, in the graph of FIG. 2B, since the temperature change amount becomes constant after 400 cycles or more, the number of adaptive range cycles is specified as 400 cycles or more. Next, image processing by fast Fourier transform is performed at a frequency twice as high as the stress frequency component, using the specified image in the range of 400 cycles or more. The data processed by the fast Fourier transform is shown in the same manner as in FIG. 1 (d). By performing statistical processing by the least square method using at least three points in the graph, several approximate lines B and C are drawn. It is burned. Based on the approximate straight line A indicating the state with the lowest dissipated energy, load loads A1 ′ and A2 ′ corresponding to the fatigue limit are obtained from the intersections A1 and A2 at which the drawn approximate straight lines intersect with the approximate straight line A, respectively. It is done.

  The present invention is directed to a fatigue limit identification system and a fatigue limit identification method. In order to achieve the above object, the fatigue limit specifying system of the present invention measures the minute temperature change of the object to be measured and the vibrator that repeatedly applies stress to the object to be measured. An infrared thermography device that obtains a temperature image and an information processing device that processes the temperature image of the measurement object obtained from the infrared thermography device. The information processing apparatus includes a step of measuring the dissipated energy of the measurement object, a step of evaluating the stress concentration factor of the measurement object, a value of the stress concentration factor obtained from the step of evaluating the stress concentration factor, and the dissipated energy. The step of specifying the fatigue limit from the measurement result obtained from the step of measuring the energy, and the step of measuring the dissipative energy is 1 or 3 times the generated stress amplitude when a constant repeated external force is applied. The dissipated energy is measured in a stable state where vibration is repeatedly applied until the repetition frequency component of becomes a constant change amount.

  The outline of the fatigue limit specifying system and the fatigue limit specifying method has the same configuration as in FIG. With reference to FIG. 2A, the steps of measuring the dissipated energy in the fatigue limit specifying system and the fatigue limit specifying method of the present invention include the steps of capturing an image while gradually increasing the load, and the generated stress for the captured image. Image processing by fast Fourier transform for each specific cycle at a frequency of 1 or 3 times the amplitude, step of detecting the maximum pixel range of the principal stress sum, and image by fast Fourier transform for each specific cycle with respect to the number of cycles A step of graphing the temperature change amount obtained by the processing step, and a step of specifying an adaptive cycle range b in which the temperature change amount changes constantly from the graph of the temperature change amount with respect to the number of cycles shown in FIG. A process to perform image processing by fast Fourier transform in the specified cycle range, and a process to graph the dissipation energy When comprised of the step of extracting statistical processing and intersection by the least squares method using the at least three points in the graph. FIG. 3A shows a graph of the amount of temperature change obtained by fast Fourier transform, which is one time the generated stress amplitude, in the process of performing image processing by fast Fourier transform for each specific cycle. Moreover, when the temperature change amount obtained by the fast Fourier transform of three times the generated stress amplitude is graphed, it is shown as in FIG.

As shown in FIGS. 3A and 3B, the temperature change amount, which is a frequency component of 1 or 3 times, increases exponentially in a range where the number of repeated stresses applied is small. On the other hand, in a range where the number of repetitions is large, the temperature change amount is almost constant and stable (that is, the gradient of the temperature change amount falls within a predetermined range). In this way, when a constant external force is applied, the load loads A1 ′ and A2 ′ corresponding to the fatigue limit are properly measured by measuring a repetition frequency component that is one or three times the generated stress amplitude in a stable state. It becomes possible to ask for. For example, in the graphs of FIGS. 3A and 3B, since the temperature change amount is constant after 400 cycles or more, the adaptive range cycle number is specified as 400 cycles or more. Next, image processing by fast Fourier transform is performed at a frequency 12 times or 3 times the stress frequency component, using the specified image in the range of 400 cycles or more. The data processed by the fast Fourier transform is shown in the same manner as in FIG. 1 (d). By performing statistical processing by the least square method using at least three points in the graph, several approximate lines B and C are drawn. It is burned. When the approximate straight line A indicating the state with the lowest dissipated energy is used as a reference, load loads A1 ′ and A2 ′ corresponding to the fatigue limit are obtained from the intersections A1 and A2 where the drawn approximate straight lines intersect with the approximate straight line A, respectively. It is done.

  In the process of measuring the dissipated energy of the present invention, the obtained temperature image is subjected to fast Fourier transform with a frequency component that is twice or three times the repeated stress frequency by an information processing device, and the temperature change of the fast Fourier transformed temperature image. A temperature change amount is extracted in a region where the quantity distribution shows the maximum.

  In the process of measuring the dissipated energy, the information processing device performs fast Fourier transform with a frequency component twice or three times the generated stress amplitude, and shows the region where the temperature change distribution of the temperature image subjected to fast Fourier transform shows the maximum 4 shows. The region where the color in the range enclosed by the square in FIG. 4 is white is the maximum temperature change amount. By plotting the temperature of this maximum portion for each load, a graph as shown in FIG. 1D is obtained, and the fatigue limit can be obtained from this graph.

  The step of measuring the dissipated energy of the present invention is to extract the amount of temperature rise with respect to a specific time in the region where the principal stress sum generated by the stress repeatedly applied to the measurement object is maximum by the information processing device. Features.

  FIG. 5 is a diagram showing a temperature rise amount with respect to a specific time in a region where the principal stress sum generated by the stress repeatedly applied to the measurement object in the step of measuring the dissipation energy is maximum. When stress is repeatedly applied to the measurement object for a certain time and the temperature for the specific time is plotted in a region where the principal stress sum is maximum, the temperature rises as shown in FIG. This temperature fluctuation rise is first-order approximated by the least square method, and the difference between the values of the first and last frames of the first-order approximated line is defined as the average temperature difference ΔT. When this average temperature difference ΔT is obtained for each load, and the load is plotted on the horizontal axis and ΔT is plotted on the vertical axis, a graph similar to FIG. 1D is obtained, and the fatigue limit can be obtained from this graph.

  The step of specifying the fatigue limit of the present invention is characterized by mainly using data in a stress range corresponding to high cycle fatigue.

Here, the stress range corresponding to high cycle fatigue will be described with reference to FIG. FIG. 6 is a diagram showing a complete fatigue curve in which the horizontal axis represents the number of repetitions and the vertical axis represents the stress amplitude. In this figure, σ _B is the tensile strength, σ _PB is the upper discontinuous stress, σ _PH is the lower discontinuous stress, σ _K is the critical stress, σ _W is the fatigue limit, and _NK is the critical number of cycles. In FIG. 6, the stress range σ corresponding to high cycle fatigue is σ _W ≦ σ ≦ σ _K.

  In the step of specifying the fatigue limit of the present invention, the temperature change amount obtained by fast Fourier transform at a frequency that is one time the repetition frequency of the stress applied to the object to be measured is calculated, and the temperature change amount or main stress with respect to the testing machine load. A load or stress range in which the sum does not rapidly increase or decrease is mainly used. In FIG. 7A and FIG. 7B, the test machine load is plotted on the horizontal axis and the principal stress sum is plotted on the vertical axis.

  Here, the range in which the temperature change amount or the principal stress sum with respect to the testing machine load does not rapidly increase or decrease is the range of the adaptive load range α shown in FIG. 7A or 7B.

  The step of specifying the fatigue limit of the present invention calculates the amount of temperature change obtained by fast Fourier transformation at a frequency twice the repetition frequency of the stress applied to the object to be measured. It is characterized by mainly using a load or stress range in which the temperature change amount obtained by fast Fourier transform at a frequency twice as high as the temperature change amount obtained by fast Fourier transform at the frequency does not involve a sudden increase or decrease.

  Here, the range in which the temperature change amount obtained by fast Fourier transform at a frequency twice as fast as the temperature change amount obtained by fast Fourier transform at the frequency of the principal stress sum or the repetition frequency is not accompanied by a sudden increase or decrease is shown in FIG. ) Or the range of the adaptive stress range α shown in FIG.

  It should be noted that the temperature change amount with respect to the test machine load or the temperature change amount obtained by fast Fourier transform at a frequency twice as fast as the temperature change amount obtained by fast Fourier transform at a frequency that is one time the repetition frequency that is the principal stress sum is not specified. (A) When the temperature change amount obtained by fast Fourier transform at a frequency twice the test machine load shown in FIG. 9 (b) is plotted, and the range in which the temperature change amount does not rapidly increase or decrease can be specified. May be determined by a graph in which the amount of temperature change obtained by fast Fourier transform at a frequency twice that of the testing machine load is plotted.

The step of measuring the dissipative energy of the present invention is a graph plotting the temperature change amount against the stress in the region where the temperature change amount of the temperature image processed in the step of measuring the dissipative energy is maximum. , n-n> statistical treated approximate line by the least square method in the first data range _{a n} and dispersing the respective a approximate line _{B n-n 'n, B} ' and _n-n, dispersion and dispersion a _'n The fatigue limit is obtained by the intersection of at least two approximate lines determined by n satisfying the minimum of the sum of B ′ _N−n .

10, 3 ≦ n ≦ N-n approximate line A _n was determined while increasing one by one n in the range of _the horizontal axis of the load or stress amplitude corresponding to the intersection of _{B N-n,} each approximation line A _n, it is a diagram obtained by subtracting the approximate line when the sum of the variances a _'n and B' _n-n of _{B n-n} are minimized. The dispersions A ′ _n and B ′ _{N−n at} this time are each represented by the formula (1).

Where n: number from minimum load, N: measurement point within adaptive load or stress range α, as shown in FIG. 10, determined by n satisfying the minimum of the sum of variance A ′ _n and variance B ′ _N−n The fatigue limit can be accurately obtained from the intersection of at least two approximate lines.

  As described above, the fatigue limit specifying system and the fatigue limit specifying method of the present invention are the stress obtained in the process of evaluating the stress concentration factor as a process, the step of measuring the dissipation energy, and the step of evaluating the stress concentration factor. And a step of specifying a fatigue limit from the measurement result obtained from the step of measuring the value of the concentration factor and the dissipated energy. Thereby, it is possible to measure the fatigue progress state of the measurement object, and improve the estimation accuracy of the fatigue limit by appropriately measuring the energy related to fatigue. Furthermore, by analyzing and processing data necessary for specifying the fatigue limit by measuring dissipative energy, it is possible to clarify the range applicable as the fatigue limit specifying method.

  In addition, for the dissipated energy measurement means and the measured temperature data for each pixel, image processing is performed for a specific frequency component, and in the process of specifying the fatigue limit, the appropriate statistical processing adaptive range is limited, thereby dissipating by the statistical processing method. It is possible to provide an energy fatigue limit identification system and a fatigue limit identification method with high accuracy.

(A) The figure which shows the outline | summary of the algorithm of the fatigue limit specific | identification system of this invention (b) The figure which shows the largest pixel range a of a principal stress sum in the principal stress sum image of this invention (c) Strain variation | change_quantity of this invention -Diagram showing temperature variation curve (d) Diagram showing dissipated energy obtained with an increase in load or stress amplitude applied to the measurement object of the present invention (A) The figure which shows the outline | summary of the algorithm of the fatigue limit specific system of this invention (b) The figure which shows the temperature change amount of 2f component for every specific cycle of this invention (A) The figure which shows the temperature change amount of the 1f component for every specific cycle of this invention (b) The figure which shows the temperature change amount of the 3f component for every specific cycle of this invention The figure which shows the temperature variation distribution of the Fourier-transformed temperature image of this invention The figure showing the temperature rise amount with respect to the specific time of this invention The figure which shows the complete fatigue curve of this invention (A) The figure which shows the range where the main stress sum of this invention does not accompany rapid increase / decrease (b) The figure which shows the range where the main stress sum of this invention does not accompany rapid increase / decrease (A) The figure which shows the range where the temperature change amount which carried out the fast Fourier transform by the double frequency of this invention does not accompany rapid increase / decrease. (B) The temperature change amount which carried out the fast Fourier transform by the double frequency of this invention. Diagram showing range without increase / decrease (A) A temperature change amount obtained by fast Fourier transform at twice the frequency of the present invention is shown. (B) A temperature change amount obtained by fast Fourier transform at twice the frequency of the present invention. Shows an approximate line when the sum of the variances A _'n and B' _N-n of the approximation line A _{n, B N-n} of the present invention is minimized The figure which shows the fatigue limit specific system outline | summary of this invention The figure which shows the state which fixed the measuring object 1b in Embodiment 1 of this invention to the fatigue testing machine 1a. It shows the shape and brief review of the measurement object 1b is a test piece having a radius of curvature rh ₀ in the first embodiment of the present invention The figure explaining the principle of the dissipated energy measurement of this invention (A) The figure which plotted the dissipation energy with respect to the strain amount in Embodiment 1 of this invention for every repetition frequency of the stress amplitude applied to a test piece (b) The specific cycle of the dissipation energy with respect to the load in Embodiment 1 of this invention The figure plotted for every (c) The figure which shows the result of having plotted the fatigue limit with respect to the area change rate of the hysteresis loop of the temperature variation | change_quantity with respect to the distortion amount in Embodiment 1 of this invention (d) In Embodiment 1 of this invention The figure which showed the range of the number of adaptive cycles (e) The figure which plotted the value signal-processed with the repetition vibration frequency component (2f) of 2 times with respect to the load in Embodiment 1 of this invention for every specific cycle (f) This The figure which plotted the temperature change waveform of the elastic deformation range and the plastic deformation range with respect to the repetition frequency in Embodiment 1 of invention (A) The figure which plotted 2f component with respect to the repetition frequency of the stress amplitude applied to the test piece in Embodiment 2 of this invention (b) The 2f component with respect to the repetition frequency of stress amplitude in Embodiment 2 of this invention was plotted FIG. (C) is a diagram showing the result of plotting the fatigue limit for the double repeated excitation frequency component (2f) in the second embodiment of the present invention. (D) The range of the adaptive cycle number in the second embodiment of the present invention. The figure shown (e) The figure which plotted the value signal-processed with the repetition vibration frequency component (2f) of 2 times with respect to the load in Embodiment 2 of this invention for every specific cycle (A) The figure which plotted the 1f component with respect to the repetition frequency of the stress amplitude in Embodiment 3 of this invention (b) The figure which plotted the 3f component with respect to the repetition frequency of the stress amplitude in Embodiment 3 of this invention (c) This The figure which plotted the 1f and 3f component with respect to the repetition frequency added to the measuring object in Embodiment 3 of invention (d) The figure which showed the range of the adaptive cycle number of the 1f component in Embodiment 3 of this invention (e) The figure which showed the range of the adaptive cycle number of 3f component in Embodiment 3 of this invention (f) The value which carried out the signal processing by the twice repeated vibration frequency component (2f) with respect to the load in Embodiment 3 of this invention is shown. Figure plotted for each specific cycle (A) The figure which shows the dissipative energy image extracted by carrying out the fast Fourier transform of 2f component in Embodiment 4 of this invention (b) The figure which plotted 2f component with respect to the load in Embodiment 4 of this invention (A) The figure which shows the dissipative energy image extracted by carrying out the fast Fourier transform of the 3f component in Embodiment 4 of this invention (b) The figure which plotted the 3f component with respect to the load in Embodiment 4 of this invention (A) The figure which shows the average temperature difference image which pulled the image averaged for every pixel in the specific cycle in Embodiment 5 of this invention (b) The average temperature difference with respect to the load in Embodiment 5 of this invention was plotted Figure (A) The figure which plotted 2f component with respect to the load in Embodiment 6 of this invention, and shows how a fatigue limit changes in and out of the high cycle fatigue range (b) The load in Embodiment 6 of this invention Showing how the fatigue limit changes in and out of the high cycle fatigue range (A) The figure which plotted the 2f component with respect to the load in Embodiment 7 of this invention, and showed how the fatigue limit changes within and outside the adaptive range when the principal stress sum increases abruptly (b) FIG. 9 is a graph plotting the 2f component against the load in the seventh embodiment of the present invention, and shows how the fatigue limit is outside the adaptive range when the principal stress sum decreases rapidly or does not increase proportionally even when the load is increased. Figure showing how it changes (A) Plot of 2f component against principal stress sum in Embodiment 8 of the present invention, showing how the fatigue limit changes inside and outside the adaptive range when the temperature change amount of 2f component increases rapidly. (B) A graph plotting the 2f component against the load in Embodiment 8 of the present invention, in which the temperature change amount of the 2f component rapidly decreases or does not increase proportionally even if the principal stress sum is increased. Of how the fatigue limit changes inside and outside the adaptation range (A) approximate line A _n drawn from the least squares method in the ninth embodiment of FIG. (B) The present invention plotting the dissipated energy to the test machine load in a ninth embodiment of the present _invention, the dispersion A of _{B N-n 'n} and B' _n-n approximate line a _n in the embodiment 9 of FIG. (c) the present invention, plotted on the vertical axis the sum of _the horizontal axis the load corresponding to the intersection of _{B n-n,} each approximation and plots dissipated energy against tester load line a _n, (d) of FIG invention the sum of the dispersion a _'n and B' _n-n of _{B n-n} plotted on the vertical axis (A) The figure which showed the relationship between the curvature radius of a notch and the area of 1 pixel in Embodiment 10 of this invention (b) The curvature radius and plastic range of a notch in Embodiment 10 of this invention, and 1 pixel The figure which showed the fatigue limit with respect to a relative ratio (c) The figure which showed the fatigue limit with respect to the plastic range in Embodiment 10 of this invention, and the relative ratio of 1 pixel (A) In each embodiment of this invention, the figure which shows the result of having measured the dissipated energy using the test piece whose curvature radius of a notch part is 2.0 mm (b) In each embodiment of this invention, The figure which shows the result of having measured the dissipation energy using the test piece whose curvature radius of a notch part is 1.0 mm (c) In each embodiment of this invention, the test piece whose curvature radius of a notch part is 0.6 mm (D) The figure which shows the result of having measured the dissipation energy using the test piece whose curvature radius of a notch is 0.2 mm in each embodiment of this invention (A) The figure which shows the fatigue SN curve calculated | required using the test piece whose curvature radius of a notch part is 2.0 mm in each embodiment of this invention. (B) In each embodiment of this invention, a notch The figure which shows the fatigue SN curve calculated | required using the test piece whose curvature radius of a part is 2.0 mm (c) In each embodiment of this invention, using the test piece whose curvature radius of a notch part is 2.0 mm The figure which shows the calculated | required fatigue SN curve (d) The figure which shows the fatigue SN curve calculated | required using the test piece whose curvature radius of a notch part is 2.0 mm in each embodiment of this invention. The figure which shows the result of the fatigue limit load amplitude calculated | required from the fatigue SN curve by the fatigue test by the result of the dissipation energy measurement in each embodiment of this invention The figure explaining the material applicable as a measuring object in each embodiment of this invention (A) The figure which shows distribution of the temperature rise amount of the steel test piece calculated | required with the identification method of the conventional fatigue limit stress value (b) The figure which shows the identification method of the conventional fatigue limit stress value

Embodiments of the present invention will be described below with reference to the drawings.
(Embodiment 1)
A fatigue limit specifying system and a fatigue limit specifying method according to Embodiment 1 of the present invention will be described. FIG. 11 is a diagram showing a fatigue limit specifying system according to Embodiment 1 of the present invention. In FIG. 11, a high-precision infrared camera (hereinafter simply referred to as an infrared camera) 1c measures the temperature of a measurement object 1b fixed to a fatigue tester 1a. As the infrared camera 1c, a Silver 480M manufactured by Cedip was used. The temperature image measured by the infrared camera 1c is subjected to data processing by the information processing apparatus 1d having fast Fourier transform means. A monitor 1e is connected to the information processing apparatus 1d. Further, as the fatigue testing machine 1a, a hydraulic servo fatigue testing machine (Shimadzu Corporation, Servo Pulser, 10 kN) was used. The load amplitude of the fatigue testing machine 1a was measured by changing the tensile load every 0.5 kN from 0 kN to 8.5 kN by load control. The measurement frequency was fixed at 25 Hz. Moreover, the state which fixed the test piece which is the measuring object 1b to the fatigue testing machine 1a in FIG. 12 is shown. Figure 13 is a diagram showing the shape and dimensions of the test piece that is the measuring object 1b having a radius of curvature rh _0. In FIG. 13, B is the width of the test piece, d is the notch depth (notch), b is half the width of the minimum cross section of the stress concentration portion, and t is the thickness.

  Next, the principle of dissipated energy measurement will be described with reference to FIG. The test piece subjected to repeated load generates a repeated temperature change 2a having the same frequency as the excitation frequency by the vibrator due to the thermoelastic effect, but in addition, an average temperature rise 2c is generated due to energy dissipation inside the material. However, the temperature change 2a due to the thermoelastic effect and the average temperature rise 2c due to the dissipative energy are smaller than the temperature change 2b due to disturbance. For this reason, the temperature variation ΔT of the test piece is expressed as (Equation 2) as follows.

ΔT = 2b−T _c + 2c + 2a (Equation 2)
ΔT: Temperature change 2b: External factor (wind and ambient temperature change)
_Tc : heat conduction (high temperature and low temperature work to make uniform)
2c: Dissipated energy (temperature rise in repeated cycles)
2a: Thermoelastic effect

  In the actual measurement of dissipated energy, the temperature of the test piece is measured with an infrared thermography apparatus, and at the same time, a synchronous input signal, which is a control signal from the fatigue testing machine 1a, is taken in, and fast Fourier transform is performed on a specific frequency component based on the synchronous input signal. By performing infrared stress image processing by conversion (Fast Fourier Transform), the influence of disturbance is excluded, and only the temperature change due to the thermoelastic effect of the test piece is measured. Dissipation of temperature rise (2c) in repeated cycles by separating and measuring the amount of temperature rise due to the dissipated energy inside the material based on the mechanical phenomenon of each repeated cycle from the temperature rise / fall due to the thermoelastic effect An energy measurement image can be drawn. The information processing apparatus 1d can also draw a dissipated energy measurement image using a temperature image acquired in advance.

  FIG. 4 is a dissipated energy image obtained by fast Fourier transform with twice the frequency component. In the region where the principal stress sum is maximum near the fatigue limit of 5.7 kN, the dissipated energy is the largest, and the dissipated energy against the amount of strain in this region is plotted for each number of repetitions of the stress amplitude applied to the specimen. The results obtained are shown in FIG. From the result of FIG. 15A, it can be seen that the relationship of the temperature change amount to the strain amount is a closed hysteresis loop state, and the area of the hysteresis loop is almost constant regardless of the number of repetitions.

  However, in the hysteresis loop state in which the relationship of the temperature change amount to the strain amount shown in FIG. 15A is closed and the area of the hysteresis loop is almost constant regardless of the number of repetitions, how much accurate fatigue is required. It is unclear whether the limit can be determined. Therefore, in order to investigate how constant the hysteresis loop area is to determine the fatigue limit accurately, FIG. 15 (b) shows the area change rate with respect to the number of repeated cycles of stress or load applied to the test piece. The results plotted for each load applied to the test specimen are shown. However, the area change rate shown here is a value obtained by calculating the average area of the hysteresis loop of 10 cycles every 100 cycles and dividing the average area obtained in the previous 100 cycles by the average area obtained in the next 100 cycles. It is.

  When the stress or load applied to the test piece is lower than 6.0 kN based on the result of FIG. 15B, the deformation is in the elastic range, and the relationship between the amount of temperature change and the amount of strain is almost proportional and linear. For this reason, damage due to fatigue hardly accumulates and fatigue does not progress, so that the area change rate hardly changes even if the number of cycles is changed. From this result, it shows a hysteresis loop in which the amount of temperature change with respect to the strain amount is closed, and as a method of judging whether the area of the hysteresis loop has become almost constant regardless of the number of times stress or load is applied to the specimen It was found that it was necessary to judge within the stress or load range (fatigue progress stress or load range) with a state where the area change rate of the hysteresis loop changed depending on the stress applied to the test piece or the number of repetitions of the load. . That is, in the case of FIG.15 (b), it has confirmed that it was necessary to pay attention to the area change rate in the range of 6.0 kN-8.5 kN.

Next, it was confirmed to what extent the rate of change of the area of the hysteresis loop of the temperature change amount with respect to the strain amount can be specified accurately if the rate of change is constant. FIG. 15 (c) shows the result of plotting the fatigue limit against the area change rate obtained in FIG. 15 (b). The results of FIG. 15C are plotted in a load range (here, a range of 6.0 kN to 8.5 kN) in which the area change rate of the hysteresis loop changes depending on the stress applied to the test piece or the number of repetitions of the load. Is. From the result of FIG. 15 (c), it was confirmed that when the area change rate of the hysteresis loop exceeds 10%, the estimated fatigue limit decreases, and it is estimated on the risk side from the viewpoint of safety. Therefore, the correct fatigue limit of 5.7 kN can be accurately obtained when the area change rate of the hysteresis loop is 10% or less.

  From the above results, in order to specify the fatigue limit with high accuracy, the change in the area of the hysteresis loop of the temperature change with respect to the strain amount involves a state that changes depending on the stress applied to the test piece or the number of repetitions of the load. It should be within the stress or load range and repeatedly apply stress or load to the test piece until the area change rate is 10% or less (ie stable state) and perform signal processing using the measured or measured data. I understood. The above-mentioned adaptation range is indicated by hatching in FIG. Judging from the shaded area in FIG. 15D, it is clear that signal processing may be performed using data measured or measured at a cycle number of 400 cycles or more.

  FIG. 15 (e) shows the stress amplitude frequency 2 applied to the test piece corresponding to the load on the horizontal axis and the dissipated energy on the vertical axis in order to confirm whether the measurement conditions obtained based on the above results are correct. A value obtained by signal processing with a double repeated excitation frequency component (2f) is plotted for each specific cycle. The appropriate condition is that the area change rate of the hysteresis loop of the temperature change amount with respect to the strain amount is within the stress or load range with the state changing depending on the stress applied to the test piece or the number of repetitions of the load. The dissipated energy obtained by performing signal processing on the basis of data measured at 400 cycles or more, which is a range of the number of repetitions satisfying a condition of 10% or less, is plotted for each load. FIG. 15E also plots the results of less than 400 cycles, which is the appropriate measurement condition range, for reference. From the above results, when the number of cycles is less than 400 cycles, the amount of change in temperature relative to the amount of strain cannot be measured in a stable state, and thus it is estimated as a load lower than the actual fatigue limit. On the other hand, at 400 cycles or more, since the temperature change with respect to the strain can be measured in a stable state, the dissipated energy (2f component) curve obtained by FFT processing with twice the frequency component also overlaps, resulting in actual fatigue. A value close to the limit is estimated.

  From the above results, the area change rate of the hysteresis loop of the temperature change amount with respect to the strain amount is within the stress or load range with the state changing depending on the stress or load repetition number applied to the test piece. The fatigue limit can be estimated with high accuracy by performing signal processing using data measured or measured at a number of repetitions that satisfies the condition of 10% or less. However, even if the area change rate is 10% or more, the estimated fatigue limit is 20% and the decrease is about 10%, so if the measurement with high accuracy is not required, the area change rate is The approximate fatigue limit can be estimated even if the number of repetitions satisfying the condition of 10% or less is not exceeded.

In addition, as a method for obtaining an appropriate measurement condition, a method for simply determining other than a method for monitoring an area change rate of a hysteresis loop of a temperature change amount with respect to a strain amount, a temperature change with respect to the number of repetitions as shown in FIG. A waveform plot may be used. In FIG. 15 (f), in the case of a low load or stress that only causes elastic deformation, only a temperature change due to the thermoelastic effect results in a sine wave as indicated by a dotted line. On the other hand, when a high load or stress (above the fatigue limit) is reached, temperature change due to the thermoelastic effect and energy due to plastic deformation are generated. Therefore, the temperature change is added by the generated energy, and the waveform is drawn as a solid line. . Since the temperature change amount that is the vertical axis of the hysteresis curve shown in FIG. 15 (a) corresponds to the temperature change amount due to plastic deformation, the stable state of plastic shakedown is found by monitoring the temperature change due to plastic deformation, It is possible to find an appropriate measurement state capable of estimating the fatigue limit with high accuracy. That is, when the number of repetitions is small with a load or stress exceeding the fatigue limit, the shape of the waveform shown by the solid line changes. On the other hand, when the number of repetitions increases and the plastic shake-down state becomes stable, the shape of the waveform shown by the solid line becomes constant regardless of the number of repetitions. The waveform shape is monitored, the correlation coefficient of the waveform shape is obtained every several hundred cycles, and if the correlation coefficient is 0.7 or more, it can be determined that it can be used as a measurable cycle number. It is clear that this correlation coefficient should be set high in order to measure with higher accuracy.

In order to improve the measurement accuracy based on the appropriate conditions obtained by this fatigue limit specifying method, a system for discriminating whether or not the temperature change with respect to the strain can be measured in a stable state is shown in FIG. The system was constructed using the algorithm shown in. As a result, it is possible to determine whether the relationship between the amount of change in temperature and the amount of strain is a closed hysteresis loop state, and improve the accuracy of the fatigue limit identification method by always measuring in an appropriate state. I was able to. This result shows that the test pieces having different stress concentration coefficients, in which the curvature radius of the notch portion is changed to rh ₀ = 5.0 mm, 1.0 mm, 0.6 mm, 0.2 mm, and 0.1 mm, are applied to the fatigue testing machine 1a. Even when the dissipated energy is measured while gradually increasing the load, the fatigue limit can be accurately estimated by measuring in a state where the temperature change relative to the strain amount is stable, as in the case of the curvature radius of 2.0 mm. did it.

  From the above results, it is possible to accurately determine the fatigue limit by using the fatigue limit identification method in which the relationship between the amount of change in temperature and strain is closed and the hysteresis loop area is measured in a constant state regardless of the number of repetitions. Judgment system for measuring in a hysteresis loop state in which the relationship between the amount of change in temperature and the amount of strain, which is an important criterion in the fatigue limit identification method, can be estimated, and in which the area of the hysteresis loop is constant regardless of the number of repetitions By constructing, it becomes possible to always obtain the fatigue limit with high accuracy.

(Embodiment 2)
An overview of the fatigue limit specifying system and the fatigue limit specifying method in Embodiment 2 of the present invention will be described. FIG. 11 is a diagram showing a fatigue limit specifying system according to Embodiment 2 of the present invention. The configuration of the fatigue limit specifying system is the same as that of the first embodiment. In FIG. 11, a high-precision infrared camera (hereinafter simply referred to as an infrared camera) 1c measures the temperature of a measurement object 1b fixed to a fatigue tester 1a. As the infrared camera 1c, a Silver 480M manufactured by Cedip was used. The temperature image measured by the infrared camera 1c is subjected to data processing by the information processing apparatus 1d having fast Fourier transform means. A monitor 1e is connected to the information processing apparatus 1d. Further, as the fatigue testing machine 1a, a hydraulic servo fatigue testing machine (Shimadzu Corporation, servo pulser, 10 kN) was used. The load amplitude of the fatigue testing machine 1a was measured by changing the tensile load every 0.5 kN from 0 kN to 8.5 kN by load control. The measurement frequency was fixed at 25 Hz. Moreover, the state which fixed the test piece which is the measuring object 1b to the fatigue testing machine 1a in FIG. 12 is shown. Figure 13 is a diagram showing the shape and dimensions of the test piece that is the measuring object 1b having a radius of curvature rh _0. In FIG. 13, B is the width of the test piece, d is the notch depth (notch), b is half the width of the minimum cross section of the stress concentration portion, and t is the thickness.

  In the actual measurement of dissipated energy, the temperature of the test piece is measured with an infrared thermography apparatus, and at the same time, a synchronous input signal, which is a control signal from the fatigue testing machine 1a, is taken in, and fast Fourier transform is performed on a specific frequency component based on the synchronous input signal. By performing infrared stress image processing by conversion (Fast Fourier Transform), the influence of disturbance is excluded, and only the temperature change due to the thermoelastic effect of the test piece is measured. Dissipation of temperature rise (2c) in repeated cycles by separating and measuring the amount of temperature rise due to the dissipated energy inside the material based on the mechanical phenomenon of each repeated cycle from the temperature rise / fall due to the thermoelastic effect An energy measurement image can be drawn.

  As the measurement object 1b, a test piece having a curvature radius of 2.0 mm shown in FIG. 13 was used. The range in which the dissipated energy is extracted from the measured image is the region where the principal stress sum is maximum, and the temperature change amount of the image obtained by fast Fourier transform with the double frequency component shown in FIG. 4 is the largest. It is a range. FIG. 16A is a diagram in which the horizontal axis represents the number of repetitions of the stress amplitude applied to the test piece, and the vertical axis represents the result of fast Fourier transform with the repeated excitation frequency component (2f component) twice the stress amplitude frequency. It is. From the result of FIG. 16 (a), it can be seen that the 2f component is not stable in a range where the number of repetitions of the stress amplitude applied to the measurement object 1b is small, and thus an appropriate value cannot be obtained.

  However, it is unclear to what extent a constant fatigue limit can be obtained in a constant state within the cycle number range in which the 2f component shown in FIG. 16 (a) is stable. Therefore, in order to investigate how constant the fatigue limit can be obtained accurately, the rate of change of the 2f component with respect to the number of cycles applied to the stress or load applied to the test piece is obtained, and for each load applied to the test piece. The plotted results are shown in FIG. However, the rate of change of the 2f component shown here is calculated by calculating the average value of the 2f component of 10 cycles every 100 cycles, and obtaining the average value of 10 cycles obtained in the previous 100 cycles in the next 100 cycles. It is the value divided by the average value of the cycle.

  When the stress or load applied to the test piece is lower than 6.0 kN from the result of FIG. 16B, the deformation is in the elastic range, so that damage due to fatigue hardly accumulates and fatigue does not progress, so the 2f component The rate of change hardly changes even if the number of cycles is changed. From this result, as a method of determining whether the value processed with the 2f component has become almost constant regardless of the number of stresses or loads repeated on the test piece, the stress or 2f component applied to the test piece It was found that it was necessary to make a judgment within the stress or load range (fatigue progress stress or load range) with the state changing depending on the number of load repetitions. That is, in the case of FIG. 16B, it has been confirmed that it is necessary to pay attention to the rate of change of the 2f component within the range of 6.0 kN to 8.5 kN.

  Next, it was confirmed to what extent the rate of change of the 2f component was constant and the fatigue limit could be specified accurately. FIG. 16C shows the results of plotting the fatigue limit against the change rate of the 2f component obtained in FIG. The results of FIG. 16C are plotted in a load range (here, a range of 6.0 kN to 8.5 kN) in which the rate of change of the 2f component changes depending on the stress applied to the test piece or the number of repeated loads. It is. From the result of FIG. 16 (c), it was confirmed that the fatigue limit estimated that the rate of change of the 2f component exceeds 10% is reduced, and that it is a risk side estimation from the viewpoint of safety. Therefore, the correct fatigue limit of 5.7 kN can be accurately obtained by the number of repetitions at which the rate of change of the 2f component becomes 10% or less.

  From the above results, in order to specify the fatigue limit with high accuracy, the 2f component is changed within the stress or load range in which the change of the 2f component changes depending on the stress applied to the test piece or the number of repetitions of the load. It was found that the measurement should be performed at a number of cycles that satisfies the condition that the rate of change of 10% or less is satisfied, or signal processing may be performed using the measured data. The above-described adaptive range is indicated by hatching in FIG. Judging from the shaded area in FIG. 16D, it is clear that signal processing may be performed using data measured or measured at a cycle number of 400 cycles or more.

FIG. 16 (e) shows the stress amplitude frequency 2 applied to the test piece corresponding to the load on the horizontal axis and the dissipated energy on the vertical axis in order to confirm whether the measurement conditions obtained based on the above results are correct. A value obtained by signal processing with a double repeated excitation frequency component (2f) is plotted for each specific cycle. Appropriate conditions include 400 cycles or more that satisfy the condition that the rate of change of the 2f component is 10% or less within a stress or load range with a state that changes depending on the number of times stress or load is applied to the test piece. The dissipated energy obtained by signal processing based on the data measured in is plotted for each load. Further, in FIG. 16 (e), the results of less than 400 cycles that are the appropriate measurement condition range are also plotted for reference.

  In FIG. 16 (e), when less than 400 cycles, the 2f component with respect to the number of repetitions of the stress amplitude applied to the test piece could not be measured in a stable state, and therefore, dissipated energy was generated more than necessary from a low load. Estimated as a load lower than the fatigue limit. On the other hand, at 400 cycles or more, since the 2f component can be measured in a stable state, the curves of the dissipated energy (2f component) obtained by FFT processing with twice the frequency component overlap, which is almost the same value as the actual fatigue limit. Is estimated. From the above results, it is possible to estimate the fatigue limit with high accuracy by performing signal processing using data measured or measured more than the number of repetitions in which the double frequency component (2f component) is a constant change amount. it is obvious.

  However, even if the rate of change of the double frequency component (2f component) is 10% or more, the estimated fatigue limit is moderate, with a rate of change of 20%. If not required, the approximate fatigue limit can be estimated even if the number of repetitions satisfying the condition that the area change rate is 10% or less is not exceeded.

  It should be noted that as a method for obtaining appropriate measurement conditions, it is possible to simply determine the frequency component (2f component) twice the number of repeated cycles of load or stress as a method for simply determining the repetition as shown in FIG. You may utilize the plot of the temperature change waveform with respect to frequency | count. In FIG. 15 (f), in the case of a low load or stress that only causes elastic deformation, only a temperature change due to the thermoelastic effect results in a sine wave as indicated by a dotted line. On the other hand, when a high load or stress (above the fatigue limit) is reached, temperature change due to the thermoelastic effect and energy due to plastic deformation are generated. Therefore, the temperature change is added by the generated energy, and the waveform is drawn as a solid line. . Since the temperature change amount, which is the vertical axis of the 2f component shown in FIG. 16A, corresponds to the temperature change amount due to plastic deformation, the stable state of plastic shakedown is found by monitoring the temperature change due to plastic deformation, It is possible to find an appropriate measurement state capable of estimating the fatigue limit with high accuracy. That is, when the number of repetitions is small with a load or stress exceeding the fatigue limit, the shape of the waveform shown by the solid line changes. On the other hand, when the number of repetitions increases and the plastic shakedown state becomes stable, the shape of the waveform indicated by the solid line becomes constant. The waveform shape is monitored, the correlation coefficient of the waveform shape is obtained every several hundred cycles, and if the correlation coefficient is 0.7 or more, it can be determined that it can be used as a measurable cycle number. It is clear that this correlation coefficient should be set high in order to measure with higher accuracy.

In order to further improve the measurement accuracy of this fatigue limit specifying method, a system was constructed using the algorithm shown in FIG. As a result, it is possible to determine whether the repetitive frequency component twice the generated stress is generated with a constant amount of change, and it is possible to always measure in an appropriate state, and the accuracy of the fatigue limit identification method Was able to improve. This result shows that the fatigue testing machine 1a is obtained by using test pieces having different stress concentration coefficients in which the curvature radius of the notch is changed to rh ₀ = 5 mm, 1.0 mm, 0.6 mm, 0.2 mm, and 0.1 mm. Even when the dissipated energy is measured while gradually increasing the load, the measurement is performed in a state in which the repetition frequency component twice the generated stress amplitude is a constant change amount as in the case of the curvature radius of 2.0 mm. Thus, the fatigue limit could be estimated accurately.

  From the above results, it is possible to estimate the fatigue limit with high accuracy by using a fatigue limit identification method that repeatedly vibrates and measures until the repetition frequency component twice the generated stress reaches a certain amount of change. By constructing a system using a judgment algorithm for measuring a repetition frequency component twice the generated stress, which is an important judgment criterion, with a constant change amount, it becomes possible to always obtain the fatigue limit with high accuracy.

(Embodiment 3)
An overview of the fatigue limit specifying system and the fatigue limit specifying method in Embodiment 3 of the present invention will be described. FIG. 11 is a diagram showing a fatigue limit specifying system according to Embodiment 3 of the present invention. The configuration of the fatigue limit specifying system is the same as that of the first embodiment. In FIG. 11, a high-precision infrared camera (hereinafter simply referred to as an infrared camera) 1c measures the temperature of a measurement object 1b fixed to a fatigue tester 1a. As the infrared camera 1c, a Silver 480M manufactured by Cedip was used. The temperature image measured by the infrared camera 1c is subjected to data processing by the information processing apparatus 1d having fast Fourier transform means. A monitor 1e is connected to the information processing apparatus 1d. Further, as the fatigue testing machine 1a, a hydraulic servo fatigue testing machine (Shimadzu Corporation, servo pulser, 10 kN) was used. The load amplitude of the fatigue testing machine 1a was measured by changing the tensile load every 0.5 kN from 0 kN to 8.5 kN by load control. The measurement frequency was fixed at 25 Hz. Moreover, the state which fixed the test piece which is the measuring object 1b to the fatigue testing machine 1a in FIG. 12 is shown. Figure 13 is a diagram showing the shape and dimensions of the test piece that is the measuring object 1b having a radius of curvature rh _0. In FIG. 13, B is the width of the test piece, d is the notch depth (notch), b is half the width of the minimum cross section of the stress concentration portion, and t is the thickness.

  In the actual measurement of dissipated energy, the temperature of the test piece is measured with an infrared thermography apparatus, and at the same time, a synchronous input signal, which is a control signal from the fatigue testing machine 1a, is taken in, and fast Fourier transform is performed on a specific frequency component based on the synchronous input signal. By performing infrared stress image processing by conversion (Fast Fourier Transform), the influence of disturbance is excluded, and only the temperature change due to the thermoelastic effect of the test piece is measured. Dissipation of temperature rise (2c) in repeated cycles by separating and measuring the amount of temperature rise due to the dissipated energy inside the material based on the mechanical phenomenon of each repeated cycle from the temperature rise / fall due to the thermoelastic effect An energy measurement image can be obtained.

  As the measurement object 1b, a test piece having a curvature radius of 2.0 mm shown in FIG. 13 was used. The range in which the dissipated energy is extracted from the measured image is the region where the principal stress sum is maximum, and the temperature change amount of the image obtained by fast Fourier transform with the double frequency component shown in FIG. 4 is the largest. It is a range. FIG. 17A is a diagram in which the horizontal axis represents the number of repetitions of the stress amplitude applied to the test piece, and the vertical axis represents the result of fast Fourier transform with a repeated excitation frequency component (1f component) that is one time the stress frequency. is there. From the result of FIG. 17A, it can be seen that the 1f component is not stable in a range where the number of repetitions of the stress amplitude applied to the measurement object 1b is small, and thus an appropriate value cannot be obtained. FIG. 17B is a graph in which the horizontal axis represents the number of repetitions of the stress amplitude applied to the test piece, and the vertical axis represents the result of fast Fourier transform with a repeated excitation frequency component (3f component) three times the stress frequency. is there. From the result of FIG. 17 (b), it can be seen that in the range where the number of repetitions of the stress amplitude applied to the measurement object 1b is small, the 3f component is not stable as well as the 1f component, so that an appropriate value cannot be obtained.

  Note that the 1f component and the 3f component do not show an extreme decrease at a low load as seen in the 2f component. Therefore, as a method for determining whether or not the value subjected to signal processing at 2f has become almost constant regardless of the number of repetitions of stress or load applied to the test piece, the repetition of stress or load applied to the test piece by the 2f component Although it was possible to judge within a stress or load range that varies depending on the number of times (fatigue progress stress or load range), the method cannot be used with the 1f component and the 3f component. Therefore, in the 1f component and the 3f component, a load or stress corresponding to 1/2 of the tensile strength is taken as a guideline based on a general concept of fatigue strength, and the 1f component or the 3f component is a load with a load or stress higher than that. By clarifying the range that can be regarded as being almost constant regardless of the number of repetitions, a condition that allows the fatigue limit to be specified with high accuracy was obtained.

  The result of FIG. 17 (c) is a result of examining the rate of change for each repeated cycle of the 1f component and the 3f component in a range of a load of 5.5 kN or more corresponding to 1/2 of the tensile strength. The rate of change shown here is calculated by calculating the average value of the 1f component or 3f component of 10 cycles every 100 cycles, and the average value obtained in the previous 100 cycles is the value of the 1f component or 3f component obtained in the next 100 cycles. It is the value divided by the average value. From the result of FIG. 17C, it was found that the fatigue limit can be accurately estimated when the rate of change is in the range of 10% or less. That is, in order to specify the fatigue limit with high accuracy, the condition that the rate of change of the 1f component or the 3f component is 10% or less in a range equal to or greater than a load or stress corresponding to 1/2 of the tensile strength is used. It has been found that signal processing may be performed using data measured or measured at a number of cycles that satisfy or more. The range of the number of cycles of the 1f component and the 3f component satisfying the above conditions is the hatched range shown in FIGS. 17D and 17E, and signal processing is performed using data measured or measured at 400 cycles or more. Just do it.

  FIG. 17 (f) shows the number of repetitions of the stress amplitude applied to the test piece in this region near the fatigue limit of 5.7 kN in order to confirm whether the proper measurement conditions obtained based on the above results are correct. It is the result of having plotted 2f component for every load load. From the results of FIG. 17D and FIG. 17E, the number of repetitions in which the 1f component and the 3f component become constant change amounts is both 400 cycles or more.

  From the above results, it was confirmed that the fatigue limit can be estimated with high accuracy by performing signal processing using data measured or measured at the number of repetitions at which the 1f component or 3f component is a constant change amount or more. If the cycle is less than 400 cycles, the 2f component with respect to the number of repetitions of the stress amplitude applied to the specimen cannot be measured in a stable state, so dissipated energy is generated more than necessary from a low load, and the load is lower than the actual fatigue limit. It is estimated. On the other hand, since the 2f component can be measured stably at 400 cycles or more, the dissipated energy (2f component) curves obtained by FFT processing with twice the frequency component also overlap and almost match the actual fatigue limit. The value to be estimated.

  However, even if the rate of change of 1x frequency component (1f component) or 3x frequency component (3f component) is 10% or more, the estimated fatigue limit is reduced by about 10% at a rate of change of 20%. Therefore, if high-precision measurement is not required, the approximate fatigue limit can be estimated even if the number of repetitions does not exceed the condition that satisfies the area change rate of 10% or less.

  In addition, as a method for obtaining an appropriate measurement condition, a method for simply ascertaining other than a method for monitoring a 1f component or a 3f component with respect to the number of repeated cycles of load or stress, a temperature change with respect to the number of repetitions as shown in FIG. A waveform plot may be used. In FIG. 15 (f), in the case of a low load or stress that only causes elastic deformation, only a temperature change due to the thermoelastic effect results in a sine wave as indicated by a dotted line. On the other hand, when a high load or stress (above the fatigue limit) is reached, temperature change due to the thermoelastic effect and energy due to plastic deformation are generated. Therefore, the temperature change is added by the generated energy, and the waveform is drawn as a solid line. . Since the temperature change amount, which is the vertical axis of the 1f and 2f components shown in FIGS. 17 (a) and 17 (b), is proportional to the temperature change amount due to plastic deformation, the temperature change due to the plastic deformation is monitored for plasticity. It is possible to find a stable state of shakedown, and to find an appropriate measurement state that can estimate the fatigue limit with high accuracy. That is, when the number of repetitions is small with a load or stress exceeding the fatigue limit, the shape of the waveform shown by the solid line changes. On the other hand, when the number of repetitions increases and the plastic shakedown state becomes stable, the shape of the waveform indicated by the solid line becomes constant. The waveform shape is monitored, the correlation coefficient of the waveform shape is obtained every several hundred cycles, and if the correlation coefficient is 0.7 or more, it can be determined that it can be used as a measurable cycle number. It is clear that this correlation coefficient should be set high in order to measure with higher accuracy.

In order to further improve the measurement accuracy of this fatigue limit specifying method, a system was constructed using the algorithm shown in FIG. As a result, it is possible to determine whether it is in a stable state by repeatedly oscillating until the repetition frequency component of 1 or 3 times the generated stress amplitude reaches a certain amount of change, and can always measure in an appropriate state. The accuracy of the fatigue limit identification method could be improved. In addition, this result is a fatigue test using test pieces having different stress concentration factors, in which the radius of curvature of the notch is changed to rh ₀ = 5.0 mm, 1.0 mm, 0.6 mm, 0.2 mm, and 0.1 mm. When dissipating energy is measured while gradually increasing the load when mounted on the machine 1a, the generated stress amplitude is repeated 1 time (1f component) or 3 times (3f component) as in the case of a curvature radius of 2.0 mm. The fatigue limit could be accurately estimated by measuring the frequency component with a constant variation.

  From the above results, it is possible to estimate the fatigue limit with high accuracy by using a fatigue limit specifying method that repeatedly vibrates and measures until the repetition frequency component of 1 or 3 times the generated stress amplitude reaches a constant change amount. By constructing a system using a judgment algorithm to measure the repetition frequency component of 1 or 3 times the generated stress amplitude, which is an important judgment criterion in the limit identification method, with a constant change amount, the fatigue limit is always accurately determined. It becomes possible to ask.

(Embodiment 4)
An outline of the fatigue limit specifying system and the fatigue limit specifying method in Embodiment 4 of the present invention will be described. As the fatigue limit specifying system of the fourth embodiment, the measurement object 1b is fixed to the fatigue testing machine 1a as shown in FIG. 12 using FIG. The load amplitude of the fatigue testing machine 1a was measured by changing the tensile load every 0.5 kN from 0 kN to 8.0 kN by load control. The measurement frequency was fixed at 25 Hz. Further, as the measurement object 1b, the curvature radius rh ₀ = 2.0 mm of the shape shown in FIG. 13, the width B of the test piece B = 15 mm, the notch depth (notch) d = 2.5 mm, the stress concentration portion A test piece of SUS304 having a notch with a minimum cross-sectional width of 2b = 6.0 mm and a thickness of 3.0 mm was used.

  The number of repetitions, which is a condition for performing measurement with high accuracy, is a hysteresis loop state in which the relationship between the temperature change amount and the strain amount studied in the first embodiment is closed, and the area of the hysteresis loop is constant regardless of the number of repetitions. A range satisfying the condition of the state, a range satisfying the condition that the repetition frequency component twice the generated stress studied in the second embodiment is a constant change amount, and one time the generated stress amplitude studied in the third embodiment Alternatively, the range where the three-fold repetition frequency component satisfies the constant change amount was the same condition as the number of repetitions of 400 cycles or more. Therefore, the number of repetitions was examined with 400 cycles or more.

  FIG. 18A is a dissipative energy image extracted by fast Fourier transform of a repetition frequency component (2f component) twice the generated stress amplitude. A region indicated by a white square in FIG. 18A indicates a region having the highest temperature change amount (that is, a region having the highest dissipation energy), and corresponds to a position of 0.5 mm from the notch bottom. The temperature change distribution of the dissipative energy is highest in the white square near the notch bottom and decreases as the distance from the notch bottom increases. In order to investigate the influence of the extracted energy on the fatigue limit identification accuracy due to the dissipated energy, the dissipated energy is extracted at positions 0.5 mm, 1.0 mm, and 2.0 mm from the notch bottom. The image by the fast Fourier transform was taken and analyzed with a frequency component twice as large as the generated stress. FIG. 18B is a diagram in which a load is plotted on the horizontal axis and a 2f component is plotted on the vertical axis. As is clear from the result of FIG. 18 (b), the fatigue limit estimated as the distance from the position of 0.5 mm where the dissipated energy of the notch bottom is the highest is increased from 1.0 mm to 1.5 mm. It is seen and changes to a dangerous side in terms of fatigue strength.

Further, FIG. 19A is a dissipative energy image extracted by fast Fourier transform of a repetition frequency component (3f component) three times the generated stress amplitude. Similarly to FIG. 18 (a), the region indicated by the white square in FIG. 19 (a) shows the region having the highest temperature change amount (that is, the region having the highest dissipation energy), and is 0.5 mm from the notch bottom. Corresponds to position. The temperature change distribution of the dissipative energy is highest in the white square near the notch bottom and decreases as the distance from the notch bottom increases. In order to investigate the influence of the extracted energy on the fatigue limit identification accuracy due to the dissipated energy, the dissipated energy is extracted at positions 0.5 mm, 1.0 mm, and 2.0 mm from the notch bottom. The image by fast Fourier transform was taken and analyzed with a frequency component of 3 times the generated stress.

FIG. 19B is a diagram in which a load is plotted on the horizontal axis and a 3f component is plotted on the vertical axis. As is clear from the result of FIG. 19 (b), the fatigue limit estimated as the distance from the 0.5 mm position where the dissipated energy of the notch bottom is the highest is increased from 1.0 mm to 1.5 mm. It will shift to a dangerous side in terms of fatigue strength. 18B and 19B, the radius of curvature of the notch was changed to rh ₀ = 5.0 mm, 1.0 mm, 0.6 mm, 0.2 mm, and 0.1 mm. Even when dissipated energy is measured while gradually increasing the load using specimens with different stress concentration factors, the stress amplitude is twice as large as when the radius of curvature is 2.0 mm. The image measured in a state where the repetition frequency component of 3 times is generated at a constant change amount is subjected to FFT processing with the repetition frequency component of 2 times or 3 times, and the data of the region indicating the maximum of the obtained temperature change image is obtained. By extracting, the fatigue limit could be estimated accurately.

  Based on the above results, in the region where the fast Fourier transform is performed with the frequency component twice or three times the stress frequency applied to the object to be measured, By extracting the amount, the fatigue limit can be accurately estimated, and the region where the temperature change distribution of the repetition frequency component that is twice or three times the generated stress amplitude, which is an important criterion for determining the fatigue limit, shows the maximum. However, it is clear that it is possible to always obtain the fatigue limit with high accuracy by constructing a system for extracting the temperature change amount.

(Embodiment 5)
An outline of the fatigue limit specifying system and the fatigue limit specifying method in Embodiment 5 of the present invention will be described. As the fatigue limit specifying system of the fifth embodiment, the measurement object 1b is fixed to the fatigue testing machine 1a as shown in FIG. 12 using FIG. The load amplitude of the fatigue testing machine 1a was measured by changing the tensile load every 0.5 kN from 0 kN to 8.0 kN by load control. The measurement frequency was fixed at 25 Hz. Further, as the measurement object 1b, the curvature radius rh ₀ = 2.0 mm of the shape shown in FIG. 13, the width B of the test piece B = 15 mm, the notch depth (notch) d = 2.5 mm, the stress concentration portion A test piece of SUS304 having a notch with a minimum cross-sectional width of 2b = 6.0 mm and a thickness of 3.0 mm was used.

  The number of repetitions, which is a condition for performing measurement with high accuracy, is a hysteresis loop state in which the relationship between the temperature change amount and the strain amount studied in the first embodiment is closed, and the area of the hysteresis loop is constant regardless of the number of repetitions. A range satisfying the condition of the state, a range satisfying the condition that the repetition frequency component twice the generated stress studied in the second embodiment is a constant change amount, and one time the generated stress amplitude studied in the third embodiment Alternatively, the range where the three-fold repetition frequency component satisfies the constant change amount was the same condition as the number of repetitions of 400 cycles or more. Therefore, the number of repetitions was examined with 400 cycles or more.

FIG. 20A shows an image obtained by averaging a temperature image of 400 cycles to 600 cycles for each pixel from an image of averaging temperature images of 900 to 1000 cycles of the stress amplitude applied to the measurement object 1b for each pixel. It is the figure which showed the difference of the subtracted average temperature. Similarly to FIGS. 18A and 19A, the region indicated by the white square in FIG. 20A indicates the region where the amount of temperature change is the highest (that is, the region where the dissipated energy is the highest). 0 from the bottom.
It corresponds to a position of 5 mm. The temperature change distribution of the dissipative energy is highest in the white square near the notch bottom and decreases as the distance from the notch bottom increases. FIG. 20B is a diagram in which a load is plotted on the horizontal axis and a temperature difference is plotted on the vertical axis. In the data of FIG. 20B, the white circle is a result of plotting the difference in average temperature at a position of 0.5 mm in the vicinity of the notch bottom where the dissipated energy is the highest. When the fatigue limit is estimated from this result, it agrees with the fatigue limit of 5.7 kN obtained from the fatigue test, and it was proved that the fatigue limit can be estimated even using the difference in average temperature.

Further, in order to investigate how the position where the dissipated energy obtained from the difference in average temperature extracts affects the accuracy of identifying the fatigue limit due to the dissipated energy, the extracted position of the dissipated energy is set to the position 0. Differences in average temperature were calculated and analyzed while increasing the load at 5 mm, 1.0 mm, and 2.0 mm. From the result of FIG. 20B, the estimated fatigue limit tends to increase as the distance from the 0.5 mm position where the dissipated energy at the notch bottom is the highest, 1.0 mm and 1.5 mm, and the fatigue limit is increased. Transition to the danger side. Note that the results shown in FIG. 20B show that the test pieces having different stress concentration coefficients were obtained by changing the curvature radius of the notch portion to rh ₀ = 5 mm, 1.0 mm, 0.6 mm, 0.2 mm, and 0.1 mm. Even when the dissipated energy was measured while gradually increasing the load, the dissipated energy image obtained by extracting the average temperature difference as in the case of the radius of curvature of 2.0 mm. This shows that the fatigue limit can be accurately estimated by using the value indicating the maximum temperature difference.

  From the above results, it is also possible to accurately extract the amount of temperature rise with respect to a specific time (that is, the difference in average temperature) in the region where the amount of temperature change generated by the stress repeatedly applied to the measurement object is maximum. By constructing a system that can estimate the fatigue limit and extract the difference in average temperature, it is possible to always obtain the fatigue limit with high accuracy.

(Embodiment 6)
An overview of the fatigue limit specifying system and the fatigue limit specifying method in Embodiment 6 of the present invention will be described. As the fatigue limit specifying system of the sixth embodiment, the measurement object 1b was fixed to the fatigue testing machine 1a as shown in FIG. 12 using FIG. The load amplitude of the fatigue testing machine 1a was measured by changing the tensile load every 0.5 kN from 0 kN to 8.0 kN by load control. The measurement frequency was fixed at 25 Hz. Moreover, as the measurement object 1b, the curvature radius rh ₀ = 2.0 mm, 5.0 mm of the shape shown in FIG. 13, the width B of the test piece B = 15 mm, the notch depth (notch) d = 2.5 mm, A test piece of SUS304 having a notch of 2.0 mm, minimum cross-sectional width 2b = 6.0 mm, and thickness 3.0 mm of the stress concentration portion was used.

  The number of repetitions, which is a condition for performing measurement with high accuracy, is a hysteresis loop state in which the relationship between the temperature change amount and the strain amount studied in the first embodiment is closed, and the area of the hysteresis loop is constant regardless of the number of repetitions. A range satisfying the condition of the state, a range satisfying the condition that the repetition frequency component twice the generated stress studied in the second embodiment is a constant change amount, and one time the generated stress amplitude studied in the third embodiment Alternatively, the range where the three-fold repetition frequency component satisfies the constant change amount was the same condition as the number of repetitions of 400 cycles or more. Therefore, the number of repetitions was examined with 400 cycles or more.

  FIG. 21A is a diagram in which a load is plotted on the horizontal axis and a 2f component is plotted on the vertical axis. The approximate line indicated by the solid line is a line drawn by the method of least squares using data of the stress amplitude range of high cycle fatigue. Moreover, the approximate line shown with a broken line is the line drawn by the least square method using even the data of the stress amplitude range of the low cycle fatigue which is the range beyond the stress amplitude of the high cycle fatigue. As is clear from this result, using the fatigue amplitude range data for high cycle fatigue matches the fatigue limit obtained from the fatigue test, but if the data for the low cycle fatigue range is included, the fatigue limit is determined from the fatigue test. It is estimated to be higher than the obtained fatigue limit, and shifts to a dangerous side in terms of fatigue strength.

  Further, FIG. 21B is a diagram in which a load is plotted on the horizontal axis and a difference in average temperature is plotted on the vertical axis. The approximate line indicated by the solid line is a line drawn by the method of least squares using data of the stress amplitude range of high cycle fatigue. Moreover, the approximate line shown with a broken line is the line drawn by the least square method using even the data of the stress amplitude range of the low cycle fatigue which is the range beyond the stress amplitude of the high cycle fatigue. Similar to the result of FIG. 21 (a), this result agrees with the fatigue limit obtained from the fatigue test when the data of the fatigue amplitude range of high cycle fatigue is used. The limit is estimated to be higher than the fatigue limit obtained from the fatigue test.

  From the above results, it is clear that the fatigue limit can be accurately measured by mainly using data in the stress range corresponding to high cycle fatigue in the process of identifying the fatigue limit from the results extracted in the process of measuring the dissipation energy. It is. Furthermore, by constructing a system for detecting data within the fatigue amplitude range of high cycle fatigue, it is possible to always obtain the fatigue limit with high accuracy.

(Embodiment 7)
An outline of the fatigue limit specifying system and the fatigue limit specifying method in Embodiment 7 of the present invention will be described. As the fatigue limit specifying system of the seventh embodiment, the measurement object 1b was fixed to the fatigue testing machine 1a as shown in FIG. 12 using FIG. The load amplitude of the fatigue testing machine 1a was measured by changing the tensile load every 0.5 kN from 0 kN to 8.0 kN by load control. The measurement frequency was fixed at 25 Hz. Further, as the measurement object 1b, the curvature radius rh ₀ = 2.0 mm of the shape shown in FIG. 13, the width B of the test piece B = 15 mm, the notch depth (notch) d = 2.5 mm, the stress concentration portion A test piece of SUS304 having a notch with a minimum cross-sectional width of 2b = 6.0 mm and a thickness of 3.0 mm was used.

  The number of repetitions, which is a condition for performing measurement with high accuracy, is a hysteresis loop state in which the relationship between the temperature change amount and the strain amount studied in the first embodiment is closed, and the area of the hysteresis loop is constant regardless of the number of repetitions. A range satisfying the condition of the state, a range satisfying the condition that the repetition frequency component twice the generated stress studied in the second embodiment is a constant change amount, and one time the generated stress amplitude studied in the third embodiment Alternatively, the range where the three-fold repetition frequency component satisfies the constant change amount was the same condition as the number of repetitions of 400 cycles or more. Therefore, the number of repetitions was examined with 400 cycles or more.

  FIG. 22A is a diagram in which the abscissa represents the load and the ordinate represents the 2f component, which is the dissipated energy, in which the principal stress sum increases abruptly. Approximation including data in the range where the principal stress sum does not suddenly increase / decrease (adaptive range α) and data in the range where the principal stress sum suddenly increases / decreases (outside the adaptive range) It is the figure which showed how the value of a fatigue limit changes when drawing a line. The range (adaptation range α) in which the main stress sum does not rapidly increase or decrease is determined from FIG. 7A in which the horizontal axis represents the tester load and the vertical axis represents the main stress sum, and the main stress sum is 823 MPa. The load corresponds to 8.2 kN. The fatigue limit estimated using the data within the adaptive range of FIG. 22A is 5.7 kN, which is consistent with the fatigue limit 5.7 kN obtained from the fatigue test. On the other hand, the fatigue limit estimated from outside the applicable range is 7.0 kN, and the fatigue limit is considerably shifted to the dangerous side.

FIG. 22B is a diagram in which the horizontal axis represents the load, and the vertical axis represents the 2f component, which is the dissipated energy. The principal stress sum rapidly decreases or does not increase proportionally even if the load is increased. FIG. Approximation including data in the range where the principal stress sum does not suddenly increase / decrease (adaptive range α) and data in the range where the principal stress sum suddenly increases / decreases (outside the adaptive range) We compared how the fatigue limit value changes when a line is drawn. The range (adaptation range α) in which the principal stress sum does not increase or decrease suddenly is determined from FIG. 7 (b) in which the horizontal axis represents the tester load and the vertical axis represents the principal stress sum. The total load is 840MPa and the testing machine load is 8.3.
It corresponds to kN. The fatigue limit estimated using the data within the adaptive range in FIG. 22B is 6.4 kN, which is the same as the fatigue limit obtained from the fatigue test, 6.4 kN.

On the other hand, the fatigue limit estimated from the data including the outside of the adaptation range is 6.7 kN, and the fatigue limit shifts to the danger side. Note that the results shown in FIGS. 22A and 22B differ from each other in the stress concentration factor when the radius of curvature of the notch is changed to rh ₀ = 1.0 mm, 0.6 mm, 0.2 mm, and 0.1 mm. Even when the dissipated energy is measured while gradually increasing the load by attaching it to the fatigue testing machine 1a using the test piece, the amount of temperature change relative to the testing machine load or the curvature radius is 5.0 mm or 2.0 mm. This shows that the fatigue limit can be accurately estimated by mainly using the range in which the main stress sum does not rapidly increase or decrease.

  Based on the above results, the temperature change amount obtained by fast Fourier transform at a frequency twice the repetition frequency of the stress applied to the object to be measured is calculated. It is clear that the fatigue limit can be accurately estimated by mainly using the non-existing range. Furthermore, the temperature change amount calculated by fast Fourier transform at twice the repetition frequency of the stress applied to the measurement object is calculated, and the temperature change amount or the main stress sum with respect to the testing machine load does not increase or decrease rapidly. By building a system that detects and detects within the appropriate range, it is always possible to accurately determine the fatigue limit.

(Embodiment 8)
An outline of the fatigue limit specifying system and the fatigue limit specifying method in Embodiment 8 of the present invention will be described. As the fatigue limit specifying system of the eighth embodiment, the measurement object 1b is fixed to the fatigue testing machine 1a as shown in FIG. 12 using FIG. The load amplitude of the fatigue testing machine 1a was measured by changing the tensile load every 0.5 kN from 0 kN to 8.0 kN by load control. The measurement frequency was fixed at 25 Hz. Further, as the measurement object 1b, the curvature radius rh ₀ = 2.0 mm of the shape shown in FIG. 13, the width B of the test piece B = 15 mm, the notch depth (notch) d = 2.5 mm, the stress concentration portion A test piece of SUS304 having a notch with a minimum cross-sectional width of 2b = 6.0 mm and a thickness of 3.0 mm was used.

  The number of repetitions, which is a condition for performing measurement with high accuracy, is a hysteresis loop state in which the relationship between the temperature change amount and the strain amount studied in the first embodiment is closed, and the area of the hysteresis loop is constant regardless of the number of repetitions. A range satisfying the condition of the state, a range satisfying the condition that the repetition frequency component twice the generated stress studied in the second embodiment is a constant change amount, and one time the generated stress amplitude studied in the third embodiment Alternatively, the range where the three-fold repetition frequency component satisfies the constant change amount was the same condition as the number of repetitions of 400 cycles or more. Therefore, the number of repetitions was examined with 400 cycles or more.

  FIG. 23 (a) is a graph in which the horizontal axis plots the temperature change amount obtained by fast Fourier transform at a frequency that is one repetition of the principal stress sum, and the vertical axis plots the 2f component that is the dissipated energy. This is the case when the sum increases. Approximation including data in the range where the principal stress sum does not suddenly increase / decrease (adaptive range α) and data in the range where the principal stress sum suddenly increases / decreases (outside the adaptive range) It is the figure which showed how the value of a fatigue limit changes when drawing a line. The range (adaptation range α) in which the temperature change amount obtained by fast Fourier transform at twice the frequency does not increase or decrease rapidly is determined from FIG. 8A in which the principal stress sum is plotted on the horizontal axis and the dissipated energy is plotted on the vertical axis. The principal stress sum is 823 MPa, which corresponds to a tester load of 8.2 kN. The fatigue limit estimated using the data within the adaptive range in FIG. 23A is 5.7 kN, which is consistent with the fatigue limit 5.7 kN obtained from the fatigue test. On the other hand, the fatigue limit estimated from outside the applicable range is a stress of 667 MPa and a load of 7.0 kN, and the fatigue limit is considerably shifted to the dangerous side.

FIG. 23B is a diagram in which the horizontal axis represents the load, and the vertical axis represents the 2f component, which is the dissipated energy. The temperature change amount obtained by fast Fourier transform at twice the frequency rapidly decreases, or the load is It is a figure in case it does not increase in proportion even if it increases. When the approximate line is drawn using the data of the range (adaptive range α) in which the temperature change amount after the fast Fourier transform at twice the frequency does not increase or decrease rapidly, the temperature change amount by the fast Fourier transform at the double frequency Compared how the fatigue limit value changes when an approximate line is drawn, including data in a range with a sudden increase or decrease (out of the applicable range). The range (adaptive range α) in which the temperature change amount obtained by fast Fourier transform at twice the frequency does not involve a rapid increase / decrease is determined from FIG. 8B in which the horizontal axis represents the principal stress sum and the vertical axis represents the dissipated energy. The main stress sum is 825 MPa, which corresponds to the testing machine load of 8.3 kN in FIG. The fatigue limit estimated using the data within the adaptive range of FIG. 23B is a stress of 597 MPa and a load of 6.4 kN, which is consistent with the fatigue limit obtained from the fatigue test of 6.4 kN.

The results shown in FIGS. 23A and 23B are different from each other in the stress concentration coefficient when the curvature radius of the notch is changed to rh ₀ = 1.0 mm, 0.6 mm, 0.2 mm, and 0.1 mm. Even when the dissipated energy is measured while gradually increasing the load using a test piece attached to the fatigue testing machine 1a, the fast Fourier transform is performed at a frequency twice that of the testing machine load as in the case of a curvature radius of 2.0 mm. It is shown that the fatigue limit can be accurately estimated by mainly using the range in which the temperature change amount does not involve a sudden increase or decrease.

  Based on the above results, the temperature change amount obtained by fast Fourier transformation at a frequency twice the repetition frequency of the stress applied to the measurement object is calculated, and the fast Fourier transformation is performed at a frequency one time the repetition frequency which is the principal stress sum. It is clear that the fatigue limit can be accurately estimated by mainly using a range in which the temperature change amount obtained by fast Fourier transform at a frequency twice that of the temperature change amount is not accompanied by a sudden increase or decrease. Furthermore, it detects the range in which the temperature change amount that has been fast Fourier transformed at a frequency twice that of the temperature change amount that has been fast Fourier transformed at a frequency that is one time the repetition frequency, which is the principal stress sum, is not accompanied by a sudden increase or decrease. By constructing a system for analyzing the above, it becomes possible to always obtain the fatigue limit with high accuracy.

(Embodiment 9)
The outline of the fatigue limit specifying system and the fatigue limit specifying method in Embodiment 9 of the present invention will be described. As the fatigue limit specifying system of the ninth embodiment, the measurement object 1b is fixed to the fatigue testing machine 1a as shown in FIG. 12 using FIG. The load amplitude of the fatigue testing machine 1a was measured by changing the tensile load every 0.5 kN from 0 kN to 8.0 kN by load control. The measurement frequency was fixed at 25 Hz. Further, as the measurement object 1b, the curvature radius rh ₀ = 2.0 mm of the shape shown in FIG. 13, the width B of the test piece B = 15 mm, the notch depth (notch) d = 2.5 mm, the stress concentration portion A test piece of SUS304 having a notch with a minimum cross-sectional width of 2b = 6.0 mm and a thickness of 3.0 mm was used.

  The number of repetitions, which is a condition for performing measurement with high accuracy, is a hysteresis loop state in which the relationship between the temperature change amount and the strain amount studied in the first embodiment is closed, and the area of the hysteresis loop is constant regardless of the number of repetitions. A range satisfying the condition of the state, a range satisfying the condition that the repetition frequency component twice the generated stress studied in the second embodiment is a constant change amount, and one time the generated stress amplitude studied in the third embodiment Alternatively, the range where the three-fold repetition frequency component satisfies the constant change amount was the same condition as the number of repetitions of 400 cycles or more. Therefore, the number of repetitions was examined with 400 cycles or more.

FIG. 24A is a diagram in which the test machine load is plotted on the horizontal axis and the dissipated energy is plotted on the vertical axis. The approximate curve 1 and approximate curve 2 in FIG. 24A are two approximate curves drawn when n = 3. For example, when n = 2, the approximate line A ₃ is obtained by the least square method using two points from the minimum load, and the approximate curve B _N-3 is obtained by the least square method using the remaining points except the first three points. The intersection of two approximate curves can be obtained. A load corresponding to the thus 3 ≦ n ≦ N-n approximate line A _n was determined while increasing one by one n in the range _of, the intersection of _{B N-n} on the horizontal axis, the approximate line A _n, B _{N When} the sum of _−n variances A ′ _n and B ′ _N−n is plotted on the vertical axis, it can be drawn as shown in FIG. The variances A ′ _n and B ′ _{N−n at} this time are each calculated by Expression (1).

  FIG. 24B shows the range in which the principal stress sum shown in the seventh embodiment is not accompanied by a sudden increase or decrease, or the temperature change amount obtained by fast Fourier transform at twice the frequency shown in the eighth embodiment shows a sudden increase or decrease. Regardless of the range not accompanied, it is the sum of the variances of the approximate line 1 and the approximate line 2 which are two approximate lines obtained by the least square method using all the plotted data. From the result shown in FIG. 24B, the intersection at which the sum of the variances of the two approximate lines is minimized is 7.3 kN, which is not consistent with the fatigue limit of 5.7 kN obtained from the fatigue test. Therefore, the data in the range in which the principal stress sum shown in the seventh embodiment is not accompanied by a sudden increase or decrease or the temperature change amount obtained by fast Fourier transform at twice the frequency shown in the eighth embodiment is not accompanied by a sudden increase or decrease. The sum of the variances of the approximate line 1 and the approximate line 2 which are two approximate lines obtained by the least square method was obtained.

Figure 24 (c), similarly to FIG. 24 (b), the approximate line _{A n,} the horizontal axis the load corresponding to the intersection of _{B N-n,} each approximate line _{A n,} dispersion A of _{B N-n} ' The sum of _n and B ′ _N−n is plotted on the vertical axis. From the result of FIG. 24C, the intersection at which the sum of the variances of the two approximate lines is minimized is 5.7 kN. FIG. 24D is a diagram in which the test machine load is plotted on the horizontal axis and the dissipated energy is plotted on the vertical axis, and the approximate line when the sum of the variances of the two approximate lines 1 and 2 is minimized. 1 and approximate line 2 are shown. The intersection point 5.7 kN obtained from FIGS. 24C and 24D coincides with the fatigue limit 5.7 kN obtained from the fatigue test, and the fatigue limit can be obtained with high accuracy.

The results shown in FIGS. 24A and 24B are obtained by changing the curvature radius of the notch to rh ₀ = 5.0 mm, 1.0 mm, 0.6 mm, 0.2 mm, and 0.1 mm. When dissipating energy is measured while gradually increasing the load using specimens with different concentration factors, the frequency is twice that of the tester load as in the case of a radius of curvature of 2.0 mm. Statistic by the least squares method in the data range of N−n> 1, where N is the total number of data in the range where the temperature change amount obtained by the fast Fourier transform in FIG. treated approximate line _{a n} and the approximate line _{B n-n} disperse each a _'n, B' and _n-n, is determined by n which the sum of _{'n-dispersion} B' dispersion a _n-n meets the minimum By the intersection of at least two approximate lines It is clear that the fatigue limit can be estimated with high accuracy.

(Embodiment 10)
An overview of the fatigue limit specifying system and the fatigue limit specifying method in Embodiment 10 of the present invention will be described. As the fatigue limit specifying system of the tenth embodiment, the measurement object 1b is fixed to the fatigue testing machine 1a as shown in FIG. 12 using FIG. The load amplitude of the fatigue testing machine 1a was measured by changing the tensile load every 0.5 kN from 0 kN to 8.0 kN by load control. The measurement frequency was fixed at 25 Hz. Further, as the measurement object 1b, the curvature radius rh ₀ of the shape shown in FIG. 13 is changed from 0.1 mm to 5.0 mm, the test piece width B = 15 mm, and the notch depth (notch) d = 2. SUS304 test piece was used in which the notch depth (notch) d was changed in accordance with the radius of curvature, assuming that the minimum cross-sectional width 2b = 6.0 mm and the thickness 3.0 mm were constant. . The plastic range is changed by changing the radius of curvature rh ₀ of the shape shown in FIG. 13 from 0.1 mm to 5.0 mm, and how the area corresponding to the plastic range and the size of one pixel of the infrared camera are affected. It was investigated. FIG. 25A shows the relationship between the plastic range of the notch portion of the test piece and the size of one pixel of the infrared camera. Note that the plastic range and the size of one pixel were obtained based on the radius of curvature of the notch portion of the test piece.

  As for the number of repetitions, which is a condition for performing measurement with high accuracy, fast Fourier transform is performed with the double repeated excitation frequency component (2f component) studied in the second embodiment, but in a constant state regardless of the number of repetitions. A range satisfying a certain condition, a range satisfying a condition in which a repetition frequency component twice as large as the generated stress studied in the second embodiment satisfies a constant change amount, and one or three times the generated stress amplitude studied in the third embodiment. The range of conditions where the double repetition frequency component becomes a constant change was studied.

  FIG. 25B shows a relative ratio obtained by dividing the radius of curvature of the notch of the test piece and the plastic range by the area corresponding to one pixel of the infrared camera on the horizontal axis, and the 2f component of dissipated energy on the vertical axis. It is the figure which plotted the fatigue limit calculated | required from the calculated | required fatigue limit and the fatigue test. As the radius of curvature of the notch of the test piece decreases, the plastic range due to stress concentration also decreases. As the plastic range becomes smaller than the area corresponding to the spatial resolution per pixel of the infrared camera, the fatigue limit obtained from the fatigue test and the fatigue limit obtained from the infrared ray tend to be shifted. This is considered to be a result indicating a measurement limit in estimating the fatigue limit of the infrared camera. From this result, it was found that if the area of the plastic range is about 7 times or more than the area corresponding to the spatial resolution per pixel of the infrared camera, the fatigue limit can be measured accurately. In addition, the spatial resolution of the infrared camera used this time is 0.35 μm × 0.35 μm, and it is physically more than 3 times the length of one pixel (2) compared with the width of the notch (2 times the radius of curvature = diameter). It was found that the fatigue limit can be accurately measured.

Further, this time, the radius of curvature rh ₀ of the test piece to be measured is set to 2.0 mm, and 1 pixel, 2 pixels × 2 pixels, 3 pixels × 3 pixels, and the measurement target pixel are used to apparently increase one pixel of the infrared camera. By increasing the area and averaging, the area of the plastic range and the area ratio of the pixel to be measured were changed and examined. FIG. 25C shows a relative ratio obtained by dividing the area of the plastic range by the area corresponding to one pixel of the infrared camera on the horizontal axis and the fatigue limit obtained from the 2f component of the dissipated energy on the vertical axis and a fatigue test. It is the figure which plotted the fatigue limit. Also from this result, it was found that the fatigue limit can be accurately measured if the relative ratio obtained by dividing the area of the plastic range by the area corresponding to one pixel of the infrared camera is 7 times or more. From the above results, it is clear that the fatigue limit can be measured with high accuracy if one pixel of the infrared camera is about 1/7 or less with respect to the plastic range.

Next, an example of the step of evaluating the stress concentration coefficient K and the step of specifying the fatigue limit in each embodiment described above will be briefly described. The step of evaluating the stress concentration factor K in each embodiment of the present invention specifies whether the stress concentration factor K is less than a predetermined value. The process for evaluating the stress concentration factor will be described below. The stress concentration factor K is expressed by the following (Equation 3).
K = σ _m / σ ₀ (Equation 3)
σ _m : Maximum stress (notch bottom) σ ₀ : Nominal stress (stress when there is no notch)

If the notch shape of the test piece is clear and data is accumulated from past studies, it is possible to estimate the stress concentration factor K from the shape to some extent, but basically it is experimental. It is necessary to measure using a mechanical method. As a method for evaluating the stress concentration factor K in a non-destructive manner, a mathematical analysis method using a simulation such as a finite element method and an experimental mechanical method such as a photoelastic method or a moire method are generally used. In addition, as a method of nondestructive evaluation from actual measurement, a strain gauge is attached as much as possible, the maximum stress σ _m and the nominal stress σ ₀ are obtained from measurement by stress distribution, and calculated from (Equation 3) There is a method of measuring the two-dimensional stress distribution of the principal stress sum from the thermoelastic effect using a simple infrared camera, obtaining the maximum stress σ _m and the nominal stress σ ₀ , and calculating from (Equation 3).

Simulation analysis methods such as the finite element method, photoelasticity method, and moire method need to prepare a special model for measurement, so models with large individual differences such as welding and fastening parts are faithfully modeled. Not suitable to do. The measurement by the strain gauge method can be evaluated easily and with high accuracy, but it is necessary to increase the number of measurement points in order to obtain the stress distribution, which is a large-scale measurement such as a measuring instrument. On the other hand, the infrared stress measurement method does not require the preparation of a special model, and can be measured without contact regardless of the material. For those having a small radius, the range in which the heat insulation condition capable of adapting the thermoelastic effect is narrowed, so that the maximum stress is measured low and the stress concentration factor is also low.

  As a result, the stress concentration factor can be obtained by calculating the stress distribution of the principal stress sum from the stress measurement using the thermoelastic effect using a high-accuracy infrared camera, confirming a simple value, and then dissipating energy. It is desirable to specify the fatigue limit by measurement. In addition, when the stress concentration factor by infrared stress measurement is close to a predetermined value (for example, 3), or when the stress concentration part is close to the end and the measurement accuracy is lowered due to the edge effect by the infrared camera, infrared stress measurement is performed. It is desirable to accurately obtain the stress concentration factor by measuring with several strain gauges attached to the stress concentration portion of the stress distribution obtained from the above.

  For specimens that are clear and simple, such as specimens, it is desirable to estimate the stress concentration factor from relational expressions derived from past data and simulation analysis, and to specify the fatigue limit by measuring dissipated energy .

For example, a test piece in which seven types of stress concentration factors were changed by changing the curvature radius rh ₀ of the notch of the test piece having a notch shape as shown in FIG. 13 to 0.1 mm to 5 mm was used. Note that the width B, the notch depth (notch) d, the half width b of the minimum cross section of the stress concentration portion, and the thickness t were fixed to 3 mm, respectively.

For these specimens, the inflection points obtained from the measurement results of the dissipated energy measured by changing the load amplitude and the fatigue limit load obtained from the mechanical fatigue test using the same specimen are stressed. An example of the result of comparison for each concentration factor is shown in FIGS. 26 (a) to 26 (d) are attached to the fatigue testing machine 1a with test pieces in which the radius of curvature of the notch is changed to rh ₀ = 2.0 mm, 1.0 mm, 0.6 mm, and 0.2 mm, The result of dissipating energy while gradually increasing the load is shown. On the other hand, FIGS. 27A to 27D show, in the fatigue testing machine 1a, test pieces in which the radius of curvature of the notch is changed to rh ₀ = 2.0 mm, 1.0 mm, 0.6 mm, and 0.2 mm. It is the fatigue SN curve obtained by attachment.

Furthermore, the fatigue limit load amplitude obtained from the results of the measured dissipative energy and the fatigue SN curve by the fatigue test, which were studied by adding three types of curvature radius of the notch, rh ₀ = 5 mm, 0.5 mm, and 0.1 mm. The results are shown in FIG. As shown in FIG. 28, when the stress concentration factor is 3 and the stress concentration factor is 3 or more, the fatigue limit load obtained from the load amplitude value corresponding to the first inflection point obtained from the dissipated energy measurement and the fatigue SN curve is obtained. The amplitude value matches. When the stress concentration factor is less than 3, the load amplitude value corresponding to the inflection point after the first stage obtained from the dissipated energy measurement and the fatigue limit load amplitude value obtained from the fatigue SN curve coincide. From this, it is clear that the load amplitude value agrees with the fatigue limit load amplitude value obtained from the fatigue SN curve.

  Further, the step of specifying the fatigue limit in the fatigue limit specifying system and the fatigue limit specifying method of the present invention includes measuring the dissipated energy when the stress concentration factor obtained in the step of evaluating the stress concentration factor is a predetermined value or more. The first stage of the intersection obtained in the process is used, and if it is less than a predetermined value, the first stage and the subsequent stages are used. By performing data processing in such a system, it is possible to specify an appropriate fatigue limit.

In addition, materials that can be applied as measurement objects in the fatigue limit identification system in each embodiment of the present invention will be described. FIG. 29 is a diagram illustrating a measurement result of a measurement target composed of a material in which the main component of the measurement target is iron, particularly carbon steel (SPCC) or austenitic stainless steel. For each material, the inflection point of the dissipated energy by the infrared camera and the fatigue limit load obtained from the fatigue SN curve by the fatigue test were compared for each material. In the fatigue limit identification system according to each embodiment, an infrared camera 1c (Cedip's Silver 480M) was used, and the obtained image was subjected to image processing using fast Fourier transform (FFT). Further, as the fatigue testing machine 1a, a hydraulic servo fatigue testing machine (Shimadzu Corporation, servo pulser, 10 kN) was used. In addition, the curvature radius and stress concentration factor of the notch part of the test piece which is the measurement object 1b used at this time are as shown in FIG.

  As is clear from the results of FIG. 29, in the case of carbon steel and austenitic stainless steel, as in the case of SUS304, when the stress concentration factor is 3 or more, the load corresponding to the first inflection point obtained from the measurement of dissipated energy Fatigue limit load amplitude value obtained from the fatigue SN load obtained from the fatigue level load amplitude value obtained from the first stage after the first stage after the amplitude value agrees with the fatigue limit load amplitude value obtained from the fatigue SN curve and the stress concentration factor is less than 3. The load amplitude value matches. Therefore, it is clear that it can be applied as a fatigue limit specifying method. In addition, it was confirmed that the location where the fatigue test broke and the location with the highest temperature identified from the dissipated energy measurement with an infrared camera coincided.

  Furthermore, by converting the tester load into the sum of principal stresses, it was confirmed that relative comparison was possible even when there were a plurality of locations where the dissipated energy was generated as in the case of SUS304, and it was possible to identify the fatigue fracture location. From the above results, the fatigue limit specifying system according to each embodiment of the present invention is composed of a material whose main component is iron, particularly carbon steel, austenitic stainless steel as a method for specifying the fatigue limit. It is clear that it can be applied to materials and is also effective as a method for identifying fatigue fracture locations.

  Each processing procedure performed by the information processing apparatus described in each embodiment of the present invention includes predetermined program data stored in a storage device (ROM, RAM, hard disk, etc.) that can execute the above-described processing procedure. It may be realized by being interpreted and executed by the CPU. In this case, the program data may be introduced into the storage device via the storage medium, or may be directly executed from the storage medium. Note that the storage medium refers to a semiconductor memory such as a ROM, a RAM, or a flash memory, a magnetic disk memory such as a flexible disk or a hard disk, an optical disk memory such as a CD-ROM, a DVD, or a BD, and a memory card. The storage medium is a concept including a communication medium such as a telephone line or a conveyance path.

  In each embodiment of the present invention, each functional block constituting the information processing apparatus is typically realized as a program that operates on a CPU (or processor), but part or all of the functions are implemented. May be realized as an LSI which is an integrated circuit. These LSIs may be individually made into one chip, or may be made into one chip so as to include a part or all of them. The name used here is LSI, but it may also be called IC, system LSI, super LSI, or ultra LSI depending on the degree of integration.

  Further, the method of circuit integration is not limited to LSI's, and implementation using dedicated circuitry or general purpose processors is also possible. An FPGA (FIELD PROGRAMMABLE GATE ARRAY) that can be programmed after manufacturing the LSI or a reconfigurable processor that can reconfigure the connection and setting of circuit cells inside the LSI may be used.

Further, if integrated circuit technology comes out to replace LSI's as a result of the advancement of semiconductor technology or a derivative other technology, it is naturally also possible to carry out function block integration using this technology. Biotechnology can be applied.

  The present invention is to construct a fatigue limit specifying system equipped with an algorithm for extracting appropriate measurement conditions and appropriate processing ranges to enable measurement under appropriate conditions and statistical processing based on the appropriate ranges of acquired data. It is useful for identifying the fatigue limit with high accuracy, making it possible to judge the safety and life prediction of products and parts in a short time, and to prevent unsafe events in advance.

a Maximum pixel range of principal stress sum 1a Hydraulic servo fatigue tester 1b Test piece 1c Infrared camera 1d Information processing device (PC for image processing)
1e Monitor 2a Repeated temperature change at the same frequency as the excitation frequency 2b Temperature change of disturbance 2c Average temperature due to energy dissipation inside the material

Claims (8)

A fatigue limit identification system,
A vibrator that repeatedly applies stress to the measurement object;
An infrared thermography device for measuring a minute temperature change of the measurement object and obtaining a temperature image of the measurement object;
An information processing device that processes a temperature image of the measurement object obtained from the infrared thermography device;
The information processing apparatus includes:
Measuring a dissipated energy of the measurement object, and a step of evaluating the stress concentration factor of the measurement object, and the obtained values of the stress concentration factor from step of evaluating the stress concentration factor, the dissipated energy And a step of identifying the fatigue limit from the measurement result obtained from the step of measuring,
The step of measuring the dissipated energy is a hysteresis loop in which the relationship between the amount of temperature change and the amount of strain is closed in a region where the principal stress sum is maximum when a constant external force is applied to the object to be measured. A fatigue limit specifying system that measures the dissipated energy in a stable state in which the hysteresis loop is repeatedly vibrated until the area of the hysteresis loop becomes constant. A fatigue limit identification system,
A vibrator that repeatedly applies stress to the measurement object;
An infrared thermography device for measuring a minute temperature change of the measurement object and obtaining a temperature image of the measurement object;
An information processing device that processes a temperature image of the measurement object obtained from the infrared thermography device;
The information processing apparatus includes:
The step of measuring the dissipation energy of the measurement object, the step of evaluating the stress concentration factor of the measurement object, the value of the stress concentration coefficient obtained from the step of evaluating the stress concentration coefficient, and the dissipation energy And a step of identifying the fatigue limit from the measurement result obtained from the step of measuring,
In the step of measuring the dissipated energy, when a constant external force is applied to the object to be measured, a repetition frequency component twice the stress amplitude is a constant rate of change in a region where the principal stress sum is maximum. A fatigue limit identification system that measures the dissipated energy in a stable state that is repeatedly vibrated until. A fatigue limit identification system,
A vibrator that repeatedly applies stress to the measurement object;
An infrared thermography device for measuring a minute temperature change of the measurement object and obtaining a temperature image of the measurement object;
An information processing device that processes a temperature image of the measurement object obtained from the infrared thermography device;
The information processing apparatus includes:
The step of measuring the dissipation energy of the measurement object, the step of evaluating the stress concentration factor of the measurement object, the value of the stress concentration coefficient obtained from the step of evaluating the stress concentration coefficient, and the dissipation energy And a step of identifying the fatigue limit from the measurement result obtained from the step of measuring,
The step of measuring the dissipated energy includes a repetition frequency component that is one or three times the stress amplitude in a region where the principal stress sum is maximum when a constant repeated external force is applied to the measurement object. A fatigue limit specifying system that measures the dissipated energy in a stable state in which vibration is repeatedly applied until a constant rate of change is reached . The step of specifying the fatigue limit is a graph plotting the temperature change amount against the stress of the region where the temperature change amount of the temperature image processed in the step of measuring the dissipated energy is maximum, and the total number of data is N, n-n> statistical treated approximate line by the least square method in the first data range _{a n} and dispersing the respective a approximate line _{B n-n 'n, B} ' and _n-n, wherein said dispersion a _'n an intersection of at least two or more approximate line sum of the variances B _'n-n is determined by n which satisfies the minimum, and obtains the fatigue limit, according to any one of claims 1 to 3 Fatigue limit identification system.
However, n = 3, 4,..., N−n> 1. A method implemented by an information processing apparatus that processes a temperature image of a measurement object obtained from an infrared thermography apparatus,
The step of measuring the dissipation energy of the measurement object, the step of evaluating the stress concentration factor of the measurement object, the value of the stress concentration coefficient obtained from the step of evaluating the stress concentration coefficient, and the dissipation energy And a step of identifying the fatigue limit from the measurement result obtained from the step of measuring,
The step of measuring the dissipated energy is a hysteresis loop in which the relationship between the amount of temperature change and the amount of strain is closed in a region where the principal stress sum is maximum when a constant external force is applied to the object to be measured. A fatigue limit specifying method of measuring the dissipated energy in a stable state in which the hysteresis loop is repeatedly vibrated until the area of the hysteresis loop becomes a constant state. A method implemented by an information processing apparatus that processes a temperature image of a measurement object obtained from an infrared thermography apparatus,
A step of measuring the dissipative energy of the measurement object; a step of evaluating a stress concentration factor of the measurement object; a value of the stress concentration coefficient obtained from the step of evaluating the stress concentration coefficient; And a step of identifying the fatigue limit from the measurement result obtained from the step of measuring,
In the step of measuring the dissipated energy, when a constant external force is applied to the object to be measured, a repetition frequency component twice the stress amplitude is a constant rate of change in a region where the principal stress sum is maximum. A fatigue limit specifying method for measuring the dissipative energy in a stable state in which vibration is repeatedly applied until A method implemented by an information processing apparatus that processes a temperature image of a measurement object obtained from an infrared thermography apparatus,
The step of measuring the dissipation energy of the measurement object, the step of evaluating the stress concentration factor of the measurement object, the value of the stress concentration coefficient obtained from the step of evaluating the stress concentration coefficient, and the dissipation energy And a step of identifying the fatigue limit from the measurement result obtained from the step of measuring,
The step of measuring the dissipated energy includes a repetition frequency component that is one or three times the stress amplitude in a region where the principal stress sum is maximum when a constant repeated external force is applied to the measurement object. A fatigue limit specifying method for measuring the dissipated energy in a stable state in which vibration is repeatedly applied until a constant rate of change is reached . The step of specifying the fatigue limit is a graph plotting the temperature change amount against the stress of the region where the temperature change amount of the temperature image processed in the step of measuring the dissipated energy is maximum, and the total number of data is N, n-n> statistical treated approximate line by the least square method in the first data range _{a n} and dispersing the respective a approximate line _{B n-n 'n, B} ' and _n-n, wherein said dispersion a _'n 8. The fatigue limit is determined by an intersection of at least two approximate lines determined by n satisfying the minimum of the variance B ′ _N−n , according to claim 5 . Fatigue limit identification method.
However, n = 3, 4,..., N−n> 1.

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