JPS621205B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method and apparatus that can easily measure the distribution of stress applied to an object to be measured.

Measuring the magnitude of stress that occurs in each part of various machines and structures is a safe and reliable method by selecting the shape of each part, the dimensions of the materials used, the materials, etc. when designing the machine or structure. This is extremely important to enable economical design. Various methods have therefore been developed to measure stress distribution. The main conventional methods include, for example, methods in which stress is measured by gluing a resistance wire etc. to the object to be measured and detecting the strain occurring in the object from changes in the resistance value of the resistance wire, and optical methods. The transparent resin makes it easy to measure.
There are methods such as creating a model that is close to the real thing, actually applying a load to this model, and measuring the stress distribution. However, the former method not only requires specialized skills to bond the resistance wire to the object to be measured, but is also troublesome. Therefore, in order to measure the stress distribution by gluing resistance wires to multiple locations on the object to be measured,
Requires considerable labor and equipment. Furthermore, the latter method requires the creation of a model close to the object to be measured, making it impossible to easily measure the stress distribution.

The present invention solves the shortcomings of such conventional stress measurement methods and provides a novel method that can quickly and easily measure the stress distribution of a measured object to which a time-varying load is applied without contact. The present invention will be described in detail below with reference to the drawings.

When the temperature of the surface of the test sample was measured when compressive and tensile loads were repeatedly applied to the test sample, the inventor found that the surface temperature did not simply increase in areas where stress was concentrated, but that the surface temperature increased with the application of load. It has been found that periods in which the temperature rises above the ambient temperature and periods in which it falls below the ambient temperature are alternately repeated. That is, when a load with a sinusoidal waveform as shown in Figure 1a is applied to a sample, the surface temperature of the stress concentration area of the sample is higher than the ambient temperature with a sinusoidal waveform synchronized with the load application as shown in Figure 1b. As a result, periods when the temperature is lower than the ambient temperature and periods when the temperature is lower than the ambient temperature are alternately repeated.

This is because heat generation occurs at the stress concentration area during the period when compressive force is applied, and heat absorption occurs during the period when tensile force is applied, and this heat generation and heat absorption are repeated in a relatively short cycle, so there is no effect on the surroundings. The surface temperature of the stress concentration area changes in an adiabatic state in which heat diffusion or heat inflow from the surroundings is cut off. For example, if only compressive force is applied in a rectangular waveform as shown in Figure 1c, only a temperature rise in the rectangular waveform synchronized with it will occur as shown in Figure 1d,
It was also confirmed that when only a tensile force was applied as shown in figure e, only a temperature drop occurred as shown in figure f. As a result of repeated experiments under various conditions, it was found that there is a proportional relationship between the amount of temperature change and the stress change (more precisely, the amount of displacement due to stress).

Figures 2a and 2b show relationship diagrams of load--temperature change and ambient temperature--temperature change determined through experiments. Based on this relationship, by repeatedly applying a load to the object to be measured and detecting the range of change in surface temperature at a specific point at that time, it is possible to know the stress applied to the specific point. This method allows you to find out the stress value at one point, and by gradually moving the measurement point and finding the stress values at many different points, you can find out the stress distribution. When measuring point by point, the load must be changed at least once to measure one point.For example, to measure 200 horizontal points and 200 vertical points in a certain area, for a total of 40,000 points, Assuming that the load change period is 33 milliseconds (frequency 30Hz), it takes 6.6 seconds to horizontally scan 200 points, and a total of 1320 seconds to scan one screen (frame).

Although the time required is much shorter than the conventional method of installing resistance wires, it is still not completely satisfactory.

By the way, during the half cycle of the compressive load during which the repeated load shown in Figure 1a is applied, the stress value at each point on the surface of the object other than the measurement point also changes as well as the measurement point. It shows a temperature increase (from ambient temperature) according to the stress value at each point, and a temperature decrease (from the ambient temperature) according to the stress value at each point during the half cycle of tensile loading.
It shows. Therefore, in the method described above, in which stress values are measured point by point and the measurement points are gradually moved, information other than the measurement points that are changing at the same time while measuring each point is lost. The efficiency of information usage is extremely poor. Therefore, it is inevitable that the measurement will take a long time.

Therefore, the object to be measured is horizontally scanned with a radiation thermometer during the period when the compressive load is applied, and temperature data (high temperature values) at, for example, 200 points along the scanning line are acquired at once by this horizontal scanning. Then, during the period when the tensile load is applied, horizontally scan the same position with a radiation thermometer, and by this second horizontal scan, the temperature data (low temperature values) at the same 200 points along the same scanning line are calculated as one. If we obtain the difference between the temperature data obtained during compressive loading (when temperature rises) and the temperature data during tensile load (when temperature decreases) obtained in this way, we can calculate the difference between 200 points along the scanning line. Data corresponding to the temperature difference between compressive load and tensile load, that is, stress, can be obtained. In this way, stress data for 200 points can be obtained at once during one cycle of load application, and the measurement time can be reduced by an order of magnitude.

The most basic embodiment of the present invention based on this idea will be described in detail below with reference to the drawings.

FIG. 3 is a schematic diagram of such an embodiment. In the figure, 1 is a vibrator. Although the vibrator 1 is not shown, it is driven by a hydraulic mechanism or the like driven by a motor or the like. It has pistons 2, 3 that periodically reciprocate and mechanisms 5, 6 for fixing the object to be measured. The object to be measured 4 is stimulated by the vibrator 1, for example, as shown in FIG. 4a.
A load as shown in is applied. However, in the figure, a portion larger than the 0 level represents a compressive load, and a portion smaller than the 0 level represents a tensile load. 7 is a synchronization signal generation circuit, and the synchronization signal generation circuit 7 receives, for example, a signal obtained by detecting the movement of the piston of the vibrator 1 or the rotation of a motor, or a signal attached to the object to be measured. Based on such signals, the circuit 7 generates a small signal as shown in FIG. This circuit generates a synchronization pulse having a time width t. The synchronization pulse from the synchronization signal generating circuit 7 is supplied to an optical scanning mechanism 8. The optical scanning mechanism 8 has a scanning mirror and its driving source as main components, and oscillates the mirror based on a synchronization signal having a short time width shown in FIG. The image is scanned, for example, on line H of the object to be measured 4 as shown in FIG. 4c. However, in FIG. 4c, the vertical axis represents the distance from the scanning start point on line H, and the horizontal axis represents time. The output signal from the infrared detector 9 is supplied to a linearity correction circuit 11 via an amplifier 10. The linearity correction circuit corrects the signal of the infrared detector 9 into a signal proportional to the temperature of the detection point of the object to be measured. The linearity correction circuit 11 is connected to one input terminal of a direct subtraction circuit 15, and is also connected to an A/D converter 12 and a memory 1.
3. Connected to the other input terminal of the subtraction circuit 15 via the D/A converter 14. The output signal of the subtraction circuit 15 is supplied to the vertical deflection coil 17Y of the cathode ray tube 16. Reference numeral 18 denotes a controller, and the controller 18 is supplied with a synchronization signal as shown in FIG. , a synchronizing signal such as that shown in FIG. 4d, obtained by removing every other pulse of the pulse signal shown in FIG. 4b, is supplied to the scanning signal generating circuit 19. As a result, the scanning signal generating circuit 19 generates a scanning signal as shown in FIG.
Supply to 7X.

In such a configuration, if a load as shown in FIG. The image of the infrared detector 9 is scanned over the line H of the object to be measured 4 as shown in FIG. As a result, the infrared rays emitted from each point on the line H are sequentially guided to the infrared detector 9 via the optical scanning mechanism 8. The scanning alternately overlaps in the period indicated by A in FIG. 4b, when the largest compressive load is applied to the object to be measured 4, and the period indicated by B in FIG. 4b, when the largest tensile load is applied. By scanning during period A, a temperature signal as shown in FIG. 5a is obtained from the detector 9, and by scanning during period B, a temperature signal as shown in FIG. 5b is obtained from the detector 9. Controller 1
8 is based on the supply of the synchronization signal shown in FIG. 4b and a write command signal as shown in FIG. 4f and FIG. 4g.
A read command signal as shown in FIG. 1 is supplied to the memory 13. As a result, the signal shown in FIG. 5a obtained by scanning during period A is stored in the memory 13 via the linearity correction circuit 11 and the A/D converter 12. When the signal shown in FIG. 5b is supplied to the subtraction circuit 15 via the linearity correction circuit 11 during scanning in period B, the fifth signal stored in the memory 13 is
The signal shown in FIG. a is read out from the memory 13 and supplied to the subtraction circuit 15 via the D/A converter 14. Therefore, the subtraction circuit outputs a signal obtained by subtracting both signals as shown in FIG. 5c.
It is supplied to the vertical deflection coil 17Y of the cathode ray tube 16. At this time, in synchronization with the supply of the signal, the cathode ray tube 16
The horizontal deflection coil 17Y includes a scanning signal generation circuit 1.
9 supplies a scanning signal as shown in FIG. 4e, the cathode ray tube 16 displays a stress distribution waveform along the line H of the object to be measured 4 as shown in FIG.

For example, when bending stress is applied to the object to be measured, compressive stress may be applied to one side of the object and tensile stress may be applied to the other side. The displayed waveform is represented by a waveform above the 0 level and a waveform below the 0 level, respectively. Therefore, by observing this waveform, it is possible to accurately know the distribution of stress applied to the object 4 to be measured, including its type.

In the above-described embodiment, the difference signal between the signals obtained when the line H of the object to be measured 4 is scanned once each in periods A and B is guided to the cathode ray tube to measure the stress distribution along the line H of the object to be measured 4. However, in order to improve the accuracy of stress distribution measurement, the stress distribution can also be displayed based on a signal obtained by scanning line H multiple times in periods A and B as described below.

FIG. 7 is for explaining such an embodiment, and in this figure, the same components as in FIG. 3 are given the same numbers. In FIG. 7, 12a and 12b are A/D converters, and the output signals from these A/D converters are passed through first and second adder circuits 21a and 21b, respectively.
The data is supplied to the memories 13a and 13b. First,
The output signals of the second memories 13a and 13b are sent to the subtraction circuit 1 via D/A converters 14a and 14b, respectively.
5 and the addition circuit 21
a, 21b. 20 is a controller which supplies write and read command signals as shown in FIG. 4 f and h to the first memory 13a, and also supplies write and read command signals as shown in FIG.
The write and read command signals as shown in
is supplied to the memory 13b. If the line H of the object to be measured 4 is periodically scanned under the supply of such a signal, the first signal detected by scanning in period A will be stored in the memory 13a, but the period The signal detected by the second scan in A is added together with the signal read out from the memory 13a in the adding circuit 21a, and then stored in the memory 13a. Therefore, assuming that the line H is scanned, for example, 2n times, the memory 13a stores a signal obtained by integrating n signals obtained by scanning the line H n times in the period A. In exactly the same way, a signal obtained by integrating n signals obtained by scanning line H n times in period B is stored in the memory 13b. When such integrated signals based on a predetermined number of scans are stored in these memories 13a and 13b, the controller 20
3a and 13b are supplied with the same periodic readout command signal, and a signal is sent to the scanning signal generation circuit 19 in synchronization with the supply of the readout command signal,
A periodic scanning signal synchronized with the readout is sent from the circuit 19 to the horizontal deflection coil 17X of the cathode ray tube 16.
supply to. As a result, a signal obtained by subtracting the integrated value signal of the memory 13b from the integrated value signal of the memory 13a is periodically supplied to the cathode ray tube 16 in synchronization with the scanning signal. , the stress distribution waveform of line H whose S/N ratio has been improved by a factor of √ is displayed based on the signal.

In the embodiment described above, the scanning of the line H for improving the S/N ratio was performed only during the period when the load applied to the object to be measured 4 was at its maximum, but one horizontal scan could be performed faster. Therefore, scanning may be performed even during a period when the load is not at its maximum, and the detection signals during this period may be integrated.

FIG. 8 is a time chart for explaining such an embodiment. When the load applied to the object to be measured 4 is as shown in FIG. Provide a synchronization signal as shown in . As a result, the optical scanning mechanism 8 is activated on the basis of the synchronization signal for example 15 times each during a half cycle in which a compressive load and a tensile load are applied as shown in FIG. 8c.
Scanning is performed once at a time. Each scan is performed in such a short period that the load applied to the object to be measured hardly changes. In synchronization with such scanning, a write command signal and a read command signal are supplied to the first memory 13a at the timing shown in FIG. 8d from the controller 20 shown in FIG. A write command signal and a read command signal are supplied to the second memory 13b at the timing shown in e, and the detection signals obtained by scanning during the period when the compressive load is applied to the object to be measured are integrated in the memory 13a. Then, the detection signals obtained by scanning during the period when the tensile load is applied to the object to be measured are integrated in the memory 13b. For example, if the line H of the object to be measured is scanned over m periods of periodic load, these memories 13a, 1
In 3b, detection signals obtained when each line H is scanned 15 m times are integrated. Therefore, the controller 20 supplies the same periodic readout signal to these memories 13a and 13b, and also sends a signal to the scanning signal generation circuit 19 in synchronization with the supply of the periodic readout command signal. 16
A scanning signal synchronized with the supply of the read command signal is supplied to the read command signal. As a result, the cathode ray tube 16 stores the integrated value of the first memory 13a into the second memory 13b.
The stress distribution waveform of line H of the object to be measured 4 based on the signal obtained by subtracting the integrated value of is displayed.

In this embodiment, the signal supplied to the subtraction circuit 15 is detected by scanning during the period in which the maximum compressive load is applied, as shown at P7 in FIG. 8c, as shown in FIG. 5a. This is a signal obtained by integrating the temperature signal shown in FIG. By the way, in order to find the maximum value of stress generated at each point on the scanning line, P
The temperature detection signal obtained by scanning when the compressive load reaches its maximum as shown in 7, and the temperature detection signal obtained by scanning when the tensile load reaches its maximum as shown by r7 in Fig. 8c. It is necessary to find the difference signal between the temperature detection signal and the temperature detection signal, but for the reasons mentioned above, this difference signal cannot be derived by simply dividing the output signal of the subtraction circuit 15 by the number of integrations of 15 m, and is generally calculated as follows. All you have to do is ask. That is, in FIG. 8c, the ratio between the average value of the compressive load in each scan when the scans from P1 to P15 were performed and the maximum compressive load value of the scan P7 is calculated, and the ratio is stored in the memory 13a.
Divide the integrated signal stored in , by this ratio, and further calculate the ratio of the average compressive load value when scanning r1 to r15 and the maximum tensile load value during scanning r7. In search of memory 13
The desired temperature difference signal is obtained by dividing the integrated signal stored in b by this ratio, and dividing the difference signal between the two divided signals by the number of integrations of 15 m. In the embodiment shown in FIG. 8, the applied load has a sinusoidal waveform, and the scanning timing is uniformly distributed and sufficiently dense with respect to the waveform, so the ratios are approximately 2/π. Become. Therefore, the signal obtained by multiplying the output signal of the subtraction circuit 15 by π/2·(1/15m) becomes the desired signal.

In the embodiment described above, the line H of the object to be measured 4 is scanned one-dimensionally to measure the stress distribution of the line H. However, the scanning line may be sequentially shifted perpendicularly to the line H. It is also possible to display the two-dimensional stress distribution of the object to be measured 4.

FIG. 9 is for explaining such an embodiment, and the same components as in FIG. 3 are given the same numbers. In this embodiment, it is assumed that a compressive load and a tensile load that change in a rectangular shape as shown in FIG. A synchronizing signal as shown in FIG. 10b is taken out and supplied to the optical scanning mechanism 22. Optical scanning mechanism 2
2 can be scanned in the horizontal direction for scanning the line H in this embodiment, and can also be scanned in the vertical scanning direction perpendicular to this direction. The optical scanning mechanism 22 scans the image of the infrared detector 9 on the object to be measured 4 in the horizontal direction in response to a synchronization signal from the synchronization signal generation circuit 21, as shown in FIG. The synchronization signal is also supplied to the controller 26, and the controller 26 controls the storage/arithmetic unit 24 based on the synchronization signal, as well as the scanning signal generation circuit 27 and the optical scanning mechanism 22. That is, based on the supply of the synchronization signal, the controller 26 sends a synchronization signal as shown in FIG. 10d to the optical scanning mechanism 22, and causes the optical scanning mechanism 22 to vertically scan in steps as shown in FIG. 10e. . Therefore, the same horizontal scanning line of the object 4 to be measured is horizontally scanned six times by the optical scanning mechanism 22, and then vertically scanned one step at a time. The signal obtained from the detector 9 by such scanning is A/D
The data is supplied to a storage/arithmetic unit 24 via a converter 23, and the storage/arithmetic unit 24 includes a controller 26.
Since the control signal of Integrate the difference signal between the integrated signal of detection signals obtained by horizontal scanning and the integrated signal of detection signals obtained by three consecutive scans during the period when a tensile load is applied to the object to be measured. The signal divided by the number of times 3 is the first signal of the storage arithmetic unit 24.
is stored in a series of memory addresses corresponding to the scan.
The integrated signal of the signals obtained in the first three scans and the integrated signal of the signals obtained in the subsequent three scans when scanning the second and third horizontal scanning lines in exactly the same way. A signal obtained by dividing the difference signal between the two lines by three is stored in a series of memory addresses corresponding to the second and third scanning lines of the memory/arithmetic unit 24. When horizontal and vertical scanning of a certain range of the object 4 to be measured is completed in this way, the storage/arithmetic device 24 stores image signals corresponding to each horizontal scanning line of the object 4 to be measured as described above.

Therefore, the controller 26
4 to repeatedly read out the image signals stored corresponding to each horizontal scanning line, and supply a signal synchronized with the reading to the scanning signal generating circuit 27. The scanning signal generating circuit 27 generates periodic horizontal and vertical scanning signals synchronized with the readout of the image signal by supplying the signals, and supplies them to the horizontal and vertical deflection coils 17X and 17Y of the cathode ray tube 16. the result,
The image signal from the storage/arithmetic unit 24 is supplied to the grid G of the cathode ray tube 16 via the D/A converter 25, and a two-dimensional image of the object to be measured 4 as shown in FIG. 11 is displayed on the screen of the cathode ray tube 16. The stress distribution is displayed as a brightness modulation signal.

In this embodiment, the two-dimensional stress distribution of the object to be measured 4 is displayed on the cathode ray tube 16 in a brightness modulated manner. By supplying it to the 16 vertical deflection coils 17Y, the two-dimensional stress distribution of the object to be measured can be displayed on the cathode ray tube 16 in an amplitude modulated manner.

In the series of embodiments described above, the signal representing stress was converted into a digital signal and stored, but analog image storage means such as a scan converter or a photograph may also be used.

Further, as for the direction of the load, it may be applied only in the compression direction or the tension direction as shown in FIG.

Furthermore, the present invention is equally applicable to objects to be measured to which repeated loads are applied, even if the loads are not applied repeatedly by a vibrator, such as parts of machines in operation. can.

Furthermore, in the above-mentioned embodiment, an example was described in which a load is repeatedly applied to the object to be measured, but the load applied to the object to be measured only changes at a high speed and does not change repeatedly. In this case, the same line of the object to be measured is scanned at least once in a short period of time when different loads are applied,
By obtaining a difference signal between the two detection signals based on the scanning, the stress distribution of the object to be measured can be measured. Furthermore, even if a recorder is used in place of the display device, exactly the same results can be obtained.

As described above, according to the present invention, the one-dimensional or two-dimensional stress distribution of the object to be measured can be measured quickly and easily without contact.

[Brief explanation of the drawing]

Fig. 1 is a waveform diagram for explaining the principle of the present invention, Fig. 2 is a diagram showing the relationship between load and temperature change, and the relationship between ambient temperature and temperature change, and Fig. 3 is a diagram showing the relationship between the load and temperature change, and Fig. 3 is a diagram for implementing the present invention. FIG. 4 is a schematic diagram showing an example of a device for the purpose of scanning, FIG. FIG. 6 is a diagram illustrating a detected temperature waveform, FIG. 6 is a diagram illustrating a display waveform on a cathode ray tube, and FIG. 7 is a diagram illustrating another example of an apparatus for carrying out the present invention. , FIG. 8 is a diagram for establishing still another embodiment of the present invention, FIG. 9 is a diagram for showing still another example of the apparatus for carrying out the present invention, and FIG. 10 is a diagram for explaining the applied load. FIG. 11 is a diagram illustrating a two-dimensional stress distribution image of a cathode ray tube. 1: Vibrator, 2, 3: Piston, 4: Measured object, 5, 6: Fixing mechanism, 7: Synchronous signal generation circuit,
8: Optical scanning mechanism, 9: Infrared detector, 10:
Amplifier, 11: Linearity correction circuit, 12,
12a, 12b, 23: A/D converter, 13, 1
3a, 13b: Memory, 14, 14a, 14
b, 25: D/A converter, 15: subtraction circuit, 1
6: Cathode ray tube, 17X, 17Y: Deflection coil, 1
8, 20, 26: Controller, 19, 27: Scanning signal generation circuit, 24: Storage arithmetic device.

Claims (1)

[Claims] 1. Applying a load that changes over time to the object to be measured,
The object to be measured is horizontally scanned in synchronization with this load application at a speed where the load change can be virtually ignored, and the infrared radiation emitted from each scanning point is detected. acquiring and storing a first signal representing a temperature distribution on a desired line of the object to be measured on one side when a load is applied;
Obtaining a second signal representing a temperature distribution substantially on the same line as the line on the other side when the different loads are applied, determining a difference signal between the first and second signals, and displaying or recording the difference signal. A stress distribution measurement method characterized by: 2. Claim 1, wherein the load that changes over time is a load that changes repeatedly.
Stress distribution measurement method described in section. 3. The scanning line of the object to be measured is sequentially moved approximately perpendicular to the line to scan different lines, and the difference signals obtained corresponding to each of the different lines are guided to a display device and displayed on the object. Claim 1 or 2, which measures the two-dimensional stress distribution of the measurement object.
Stress distribution measurement method described in section. 4. The stress distribution measuring method according to claim 3, wherein the difference signal is supplied to the display device as a luminance modulation signal. 5. The stress distribution measuring method according to claim 1 or 3, wherein the difference signal is supplied to the display device as an amplitude modulated signal. 6. Scanning the line multiple times during at least one of the two different load application periods, and integrating the detection signal obtained by substantially scanning the difference signal multiple times. 4. A stress distribution measuring method according to claim 1 or 3, characterized in that the stress distribution is determined using a signal obtained by applying a signal. 7. Claim 6, characterized in that the same load is applied to the object to be measured during the period in which each of the plurality of scans is performed, and the load is a maximum load or a minimum load. The stress distribution measurement method described. 8. The stress distribution measuring method according to claim 6, wherein a changing load is applied to the object to be measured during a period in which each of the plurality of scans is performed. 9. The stress distribution measuring method according to any one of claims 1 to 8, wherein the load is a compressive load and/or a tensile load. 10. The stress distribution measuring method according to any one of claims 1 to 8, wherein the load is a load obtained by superimposing a variation on a constant load. 11 A load applying means for applying a periodically changing load to the object to be measured, a circuit for obtaining a signal synchronized with changes in the load applied to the object to be measured, and a circuit for horizontally and vertically scanning the object to be measured. In this way, an infrared imaging means that detects the infrared rays emitted from each scanning point of the object to be measured and obtains a signal corresponding to the temperature value, and two different timings for applying loads based on the signals from the circuit. control means for causing the infrared imaging means to horizontally scan a straight line of the object at least once and sequentially shift the scanning line of the object to vertically scan the object; storage means for storing one of two detection signals obtained by the infrared imaging means for each horizontal scanning line of the body; one detection signal stored in the storage means and the other detection; A stress distribution measuring device comprising: a subtraction means for obtaining a difference signal from a signal; and a means for displaying or recording the difference signal obtained for each horizontal scanning line.