JP2017215258A - Method for measuring stress distribution - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method in which a stress distribution can be measured at a practicable level in a noncontact manner without applying black coating material to a surface of a measured body.SOLUTION: A method for measuring a stress distribution according to the present invention, includes: a first procedure for sticking a blackbody tape 3 on a surface of a measured body TP to which a load is added; a second procedure for imaging the surface of the measured body with the blackbody tape stuck, by an infrared imaging device 1 and measuring a temporal change of a temperature distribution of the measured body; a third procedure for calculating a temporal change of a stress distribution of the measured body on the basis of the measured temporal change of the temperature distribution of the measured body and a predetermined relational formula between a temporal change in temperature and a temporal change in stress; and a fourth procedure for correcting the temporal change of the stress distribution of the measured body calculated in the third procedure using a correction factor of the blackbody tape obtained by calculation beforehand.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a method for measuring a stress distribution of a measurement object to which a load is applied by a so-called thermoelastic stress measurement method.

  Conventionally, for example, a thermoelastic stress measurement method using an infrared imaging device (thermography) has been proposed as a method for non-contact measurement of a stress distribution of a measurement object to which a load is applied, such as a structure such as a bridge or a crane. (For example, refer to Patent Document 1). The thermoelastic stress measurement method uses the thermoelastic effect that a temperature change occurs when the measured object undergoes elastic deformation in an adiabatic manner, and continuously measures the image of the measured object using an infrared imaging device. Measure the temporal change in the temperature distribution of the body (change in the temperature distribution within a predetermined time), and measure the temporal change in the measured temperature distribution as the temporal change in the stress distribution of the measured object (the temperature distribution within the predetermined time). Change).

  When using this thermoelastic stress measurement method to measure the temporal change in the temperature distribution of the measured object, the heat (infrared) around the measured object is reflected by the surface of the measured object and received by the infrared imaging device. There is a case. In other words, the temporal change in the temperature distribution of the measured object measured using the infrared imaging device is caused by a factor other than the temperature change caused by the thermoelastic effect (infrared intensity change emitted from the measured object). Temperature changes may be included. Since the temperature change caused by the thermoelastic effect is extremely small, if the infrared reflectance on the surface of the object to be measured is large, the temperature change caused by the thermoelastic effect is buried in the change in the infrared reflection intensity on the surface of the object to be measured. Therefore, there is a possibility that the change in stress distribution of the measured object cannot be calculated with high accuracy.

For this reason, when using the thermoelastic stress measurement method, a method has been proposed in which a black paint is applied to the surface of the object to be measured and the infrared reflectance on the surface of the object to be measured is reduced (emissivity is increased) (for example, , See Patent Document 2).
However, depending on the use of the object to be measured, it may be necessary to return the surface of the object to be measured to its original state after applying the black paint to the surface of the object to be measured and finishing the measurement of the stress distribution. However, since the black paint cannot be removed quickly or completely over time, the stress distribution can be measured accurately without contact without applying black paint to the surface of the object to be measured. Is desired.

  Patent Documents 3 and 4 propose a technique for attaching a black body tape to the surface of the measured object in order to measure the accurate temperature of the measured object. The technology is not intended for thermoelastic stress measurement methods that measure very small temperature changes caused by the thermoelastic effect.

JP 2006-98283 A Japanese Patent Laying-Open No. 2015-1392 JP 2000-230914 A JP 2001-281061 A

  The present invention has been made to solve the above-described problems of the prior art, and measures stress distribution at a non-contact and practical level without applying black paint to the surface of the object to be measured. It is an object to provide a possible method.

In order to solve the above problems, the present inventors do not apply a black paint to the surface of the object to be measured as in the past in order to reduce the reflectance of infrared rays on the surface of the object to be measured (increase the emissivity). Instead, the inventors focused on attaching a detachable black body tape so that the surface of the object to be measured can be returned to the original state after the measurement of the stress distribution is completed.
In general, the thickness of the black paint is about 10 μm, whereas the thickness of the black body tape is as large as about 100 to 200 μm. Therefore, the infrared radiation radiated by the black body tape is absorbed by the black body tape and attenuated. However, it is considered that the intensity of infrared rays received by the infrared imaging device (that is, infrared rays transmitted through the black body tape) decreases. As described above, since the temperature change caused by the thermoelastic effect is extremely small, the temperature change caused by the thermoelastic effect due to the absorption of infrared rays in the black body tape (the change in the intensity of infrared rays emitted from the measured object). In general, it is generally considered that there is a possibility that the change in the stress distribution of the object to be measured cannot be accurately calculated.
In addition, the change in temperature distribution that can be measured by the infrared imaging device may actually be a change in temperature distribution of the black body tape. In this case, the black body tape does not reach the same temperature as the measured object due to the influence of the heat capacity according to the thickness of the black body tape, and the change in the temperature distribution of the black body tape is measured. It is considered that there is a possibility that the change, and hence the change in the stress distribution of the measurement object, cannot be calculated with high accuracy.
Furthermore, due to both the absorption of infrared rays in the black body tape and the heat capacity of the black body tape, there is a possibility that the change in the temperature distribution of the measurement object, and hence the change in the stress distribution of the measurement object, may not be accurately calculated. Conceivable.
However, as a result of intensive studies by the present inventors, a correction coefficient for the black body tape is calculated in advance, and the change in stress distribution of the measured object calculated by the thermoelastic stress measurement method is corrected using this correction coefficient. It was found that the change in stress distribution can be calculated at a sufficiently practical level.

The present invention has been completed based on the above-mentioned findings of the present inventors.
That is, in order to solve the above-described problem, the present invention provides a first procedure in which a black body tape is applied to the surface of a measurement object to which a load is applied, and the black body tape is applied in the first procedure. A second procedure for imaging the surface of the measured object with an infrared imaging device and measuring a temporal change in the temperature distribution of the measured object, and a temporal change in the temperature distribution of the measured object measured by the second procedure And a predetermined relational expression between a temporal change in temperature (temperature change within a predetermined time) and a temporal change in stress (stress change within a predetermined time), the temporal distribution of the stress distribution of the measured object A third procedure for calculating a change, and a fourth procedure for correcting a temporal change in the stress distribution of the measured object calculated by the third procedure using a correction coefficient calculated in advance for the blackbody tape. Stress distribution measurement characterized by including The law provides.

According to the stress distribution measuring method according to the present invention, by performing the first to third procedures, the temporal change in the stress distribution of the measured object with the black body tape attached to the surface is the heat It is calculated by an elastic stress measurement method. That is, the temporal change in stress is calculated for each pixel constituting the captured image captured by the infrared imaging device, but since the captured image is composed of pixels arranged two-dimensionally, the stress distribution (two-dimensional distribution) The temporal change of is calculated. In addition, the following formula | equation (A) can be illustrated as a predetermined relational expression in a 3rd procedure.
Δσ = −1 / K · ΔT / T (A)
In the above formula (A), ΔT represents a temporal change in temperature (temperature change within a predetermined time), Δσ represents a temporal change in stress (stress change within a predetermined time), and T represents a temperature of the object to be measured. , K means a thermoelastic coefficient. The thermoelastic coefficient K is a physical property value determined by the material of the object to be measured. For example, when the object to be measured is formed of a steel material, K = 3.5 × 10 ⁻¹² [Pa ⁻¹ ].
According to the stress measurement method of the present invention, the temporal change in the stress distribution of the measurement object is corrected by using the correction coefficient calculated in advance by executing the fourth procedure. That is, the temporal change in the stress distribution of the measured object is corrected by dividing the temporal change in the stress calculated for each pixel constituting the captured image captured by the infrared imaging device, for example, by the correction coefficient. It will be.
According to the stress distribution measuring method according to the present invention, it is possible to measure a temporal change of the stress distribution at a non-contact and practical level without applying a black paint to the surface of the object to be measured. If the initial value of the stress distribution is grasped (including not only when the stress distribution is actually measured and grasped, but also when it can be assumed), the stress distribution temporally changes to this initial value. By adding, the absolute value of the stress distribution after the lapse of a predetermined time can also be measured. When the initial value of the stress distribution is zero, the temporal change of the stress distribution itself corresponds to the absolute value of the stress distribution after a predetermined time has elapsed. The term “measurement of stress distribution” as used in the present invention is a concept that includes both the case of measuring only the temporal change of the stress distribution and the case of measuring the absolute value of the stress distribution after a predetermined time has elapsed.

In the present invention, it is considered that if the thickness of the black body tape applied to the surface of the object to be measured changes, the amount of infrared absorption in the black body tape (the amount of infrared transmission through the black body tape) also changes.
Therefore, preferably, the correction coefficient used in the fourth procedure is expressed by a function having the thickness of the black body tape as a variable. In the fourth procedure, the correction coefficient of the black body tape pasted in the first procedure is used. The correction coefficient corresponding to the thickness is selected, and correction is performed using the selected correction coefficient.

According to the preferable method described above, even if the thickness of the black body tape changes (including the case where the total thickness changes due to the overlap of two or more black body tapes), appropriate correction is possible and practical. The stress distribution can be measured at the level.
In addition, as the thickness of the pasted black body tape, the design value may be used, or the thickness of the black body tape actually attached to the measured object may be measured using a film thickness meter or the like. good.

In the present invention, when the area of the measured object for measuring the temporal change of the stress distribution is wide, it may be necessary to attach two or more black body tapes to the surface of the measured object. At this time, in order not to create an area where the black body tape is not attached (so as not to create a gap between adjacent black body tapes), the adjacent black bodies are not simply attached side by side. It is preferable that the tape is attached so as to have an overlapping portion.
Therefore, preferably, in the first procedure, the black body tape is pasted on the surface of the measured object so that two or more black body tapes overlap each other, and in the fourth procedure, the 2 For a portion where two or more black body tapes are overlapped, the correction coefficient corresponding to the total thickness of the two or more black body tapes is selected and corrected using the selected correction coefficient.

According to the preferable method described above, it is possible to appropriately correct a portion where two or more black body tapes overlap, and to measure the stress distribution at a practical level.
In addition, as a total thickness of two or more black body tapes (total value of thicknesses of the respective black body tapes), a design value may be used, or two or more sheets actually attached to a measurement object may be used. The total thickness of the black body tape may be measured using a film thickness meter or the like.

When the correction coefficient used in the present invention is expressed by a function having the thickness of the black body tape as a variable, the correction coefficient is expressed by a power function of the thickness of the black body tape, and the time distribution of the stress distribution of the measured object calculated in the third procedure is calculated. The present inventors have found that if the change is corrected by dividing by this correction factor, a more appropriate correction is possible, and the temporal change of the stress distribution can be measured at a more practical level. .
Therefore, preferably, when the correction coefficient used in the fourth procedure is CR and the thickness of the black body tape is t, the correction coefficient CR is expressed by the following equation (1), and In four procedures, the temporal change of the stress distribution of the measurement object calculated in the third procedure is corrected by dividing by the correction coefficient CR.
CR = a · t ^b (1)
In the above formula (1), a and b are predetermined constants.

  According to the preferable method described above, more appropriate correction can be performed, and the stress distribution can be measured at a more practical level.

In the present invention, although various correction coefficient calculation methods are conceivable, it is preferable to calculate, for example, as follows.
That is, preferably, the correction coefficient used in the fourth procedure is that the strain sensor is attached to the surface of the test body, and a load of a predetermined condition is applied to the test body to which the strain sensor is attached, so that the strain sensor A first preparatory procedure for detecting a temporal change, and calculating a temporal change in a stress of a portion of the test body to which the strain sensor is attached based on the detected temporal change of the strain; and a surface of the test body The black body tape is affixed to the test body, a load having the same condition as the predetermined condition is applied to the test body to which the black body tape is affixed, and the surface of the test body is imaged by the infrared imaging device, and the test Measuring the temporal change of the temperature distribution of the body, and calculating the temporal change of the stress distribution of the specimen based on the temporal change of the measured temperature distribution of the specimen and the predetermined relational expression; The calculated stress distribution of the specimen A second preparatory procedure for extracting a temporal change in stress of a part of the test specimen that is the same as a part to which the strain sensor is attached from a temporal change; and a temporal change in stress of the test specimen extracted by the second preparatory procedure. Calculated by a third preparation procedure for determining the correction coefficient so as to coincide with the temporal change in stress of the specimen calculated by the first preparation procedure when a change is corrected using the correction coefficient. Is done.

According to said preferable method, the time change of the stress of a test body is calculated in a 1st preparatory procedure using a strain sensor. Further, in the second preparation procedure, the temporal change in the stress of the specimen is calculated using the infrared imaging device. Then, in the third preparation procedure, the correction coefficient is calculated by comparing both calculation results. Specifically, when the temporal change in the stress of the specimen calculated by the first preparation procedure is considered as a true value, and the temporal change in the stress of the specimen extracted by the second preparation procedure is corrected using the correction coefficient In addition, the correction coefficient is determined so that the corrected value matches the true value.
Therefore, according to the preferable method described above, the temporal change in the stress distribution of the measurement object after correction using the correction coefficient in the fourth procedure is the time of the stress distribution of the measurement object calculated using the strain sensor. It can be expected that it can be calculated with the same accuracy as that of the target change.
In addition, a strain gauge can be illustrated as a strain sensor used with said preferable method. Moreover, it is preferable that the test body used by said preferable method is formed from the same kind of material as a to-be-measured body.

  According to the present invention, the stress distribution can be measured at a non-contact and practical level without applying a black paint to the surface of the object to be measured.

It is a mimetic diagram showing a schematic structure of a stress distribution measuring device for performing a stress distribution measuring method concerning one embodiment of the present invention. It is a flowchart which shows roughly the procedure of the stress distribution measuring method which concerns on one Embodiment of this invention. It is explanatory drawing explaining the preparation procedure of the stress distribution measuring method which concerns on one Embodiment of this invention. It is a figure which shows an example of correction coefficient CR 'calculated in the 3rd preparatory procedure of the stress distribution measuring method which concerns on one Embodiment of this invention, and determined correction coefficient CR. It is a figure which shows typically an example of the captured image of an infrared imaging device when a black body tape is affixed on the surface of a to-be-measured body so that it may have a part with which 2 or more black body tapes overlap. It is a figure which shows an example of the result of having measured the time change of the stress distribution of a to-be-measured body by the stress distribution measuring method which concerns on one Embodiment of this invention.

Hereinafter, a stress distribution measurement method according to an embodiment of the present invention will be described with reference to the accompanying drawings as appropriate.
FIG. 1 is a schematic diagram showing a schematic configuration of a stress distribution measuring apparatus for executing a stress distribution measuring method according to an embodiment of the present invention.
As shown in FIG. 1, the application target of the stress distribution measurement method according to the present embodiment is a measurement object TP to which a load is applied. In this embodiment, the to-be-measured body TP is a welded structure having the weld bead B, and the end B1 of the weld bead B that can be a fracture starting point is used as a stress distribution measurement region. The to-be-measured body TP of this embodiment is attached to a fatigue testing machine (not shown). When measuring the stress distribution, one end (the lower end shown in FIG. 1) is constrained and the other end (the figure). A repetitive load (tensile load or compressive load) having a predetermined frequency is applied to the upper end shown in FIG.

  As shown in FIG. 1, the stress distribution measuring apparatus 100 according to the present embodiment is connected to the infrared imaging apparatus 1 and the infrared imaging apparatus 1, and the temporal change of the stress distribution is based on the image signal output from the infrared imaging apparatus 1. And an arithmetic unit 2 that calculates

  The infrared imaging device 1 includes a two-dimensionally arranged infrared detection element such as InSb and an imaging optical system, and forms an infrared ray emitted from the measurement target TP on each infrared detection element via the imaging optical system. Then, it is converted into an electrical signal and output to the arithmetic unit 2 as an image signal of a predetermined frame rate that constitutes the captured image.

The arithmetic device 2 locks in a signal waveform corresponding to a temperature change caused by a thermoelastic effect to be measured from the image signal input from the infrared imaging device 1. That is, only a predetermined frequency component is extracted from the image signal input from the infrared imaging device 1. Specifically, a reference signal having the same frequency as the repeated load applied by the fatigue tester is input to the arithmetic device 2 from the fatigue tester. Then, the arithmetic device 2 synchronously detects the image signal input from the infrared imaging device 1 with the reference signal input from the fatigue testing machine, and uses only the image signal component having the same frequency as the reference signal or the same frequency as the reference signal. By extracting only the image signal of the narrow frequency band including it, the S / N ratio of the temperature change caused by the thermoelastic effect to be measured is improved.
The arithmetic unit 2 determines the temporal distribution of the temperature distribution of the measured object TP according to the magnitude of the image signal component extracted as described above and the correspondence between the magnitude of the image signal component stored in advance and the temperature. A change (temporal change in temperature distribution for each pixel constituting the captured image captured by the infrared imaging device 1) is calculated. In addition, as will be described later, the arithmetic device 2 is based on the temporal change in the temperature distribution of the measured object TP and a predetermined relational expression between the temporal change in temperature and the temporal change in stress. The time change of the stress distribution of TP is calculated. Furthermore, as will be described later, the arithmetic device 2 corrects the temporal change in the calculated stress distribution of the measured object TP.

  The infrared imaging device 1 has a function to calculate a temporal change in the stress distribution of the measured object TP (the temporal change in the stress distribution of the measured object TP, which is a feature of the present invention, will be described later). The computing device 2 can be configured using a commercially available device for executing the thermoelastic stress measurement method. An example of such a commercially available apparatus is an “infrared stress measurement system” sold by Ken Automation. The arithmetic device 2 according to the present embodiment executes a correction procedure described later in a personal computer that has built-in software for calculating the temporal change of the stress distribution of the measurement object TP included in the commercial device as described above. The program can be installed and configured.

Hereinafter, a stress distribution measuring method using the stress distribution measuring apparatus 100 having the above configuration will be described.
FIG. 2 is a flowchart schematically showing the procedure of the stress distribution measuring method according to the embodiment of the present invention. FIG. 3 is an explanatory diagram illustrating a preparation procedure for the stress distribution measurement method according to the embodiment of the present invention.
As shown in FIG. 2, the stress distribution measuring method according to the present embodiment includes a preparation procedure (S1 in FIG. 2), a first procedure (S2 in FIG. 2), a second procedure (S3 in FIG. 2), and a third procedure. (S4 in FIG. 2) and the fourth procedure (S5 in FIG. 2). Hereinafter, each procedure will be described sequentially.

<Preparation procedure>
As shown in FIG. 2, in the preparation procedure, a correction coefficient for the black body tape is calculated in advance (S1 in FIG. 2). Specifically, in this preparation procedure, a first preparation procedure to a third preparation procedure described below are executed.

(First preparation procedure)
As shown in FIG. 3A, in the first preparation procedure, the strain sensor 4 is attached to the surface of the test body TP1. As a preferable configuration, the test body TP1 of the present embodiment is formed of the same material as the measurement target TP, and is provided with a circular hole TPa. In this embodiment, a strain gauge is used as the strain sensor 4, and this strain gauge is attached near the circular hole TPa of the test body TP1. The strain sensor 4 is connected to the data logger 5 in order to continuously record the output signal of the strain sensor 4.
In the first preparation procedure, the test body TP1 to which the strain sensor 4 is attached as described above is attached to, for example, a fatigue tester (not shown), and a load under a predetermined condition is applied to the test body TP1 to cause the strain sensor 4 to perform strain. Detect changes in time. Specifically, the temporal change of the distortion is detected based on the output signal of the distortion sensor 4 continuously recorded in the data logger 5. More specifically, in this embodiment, the difference between the maximum value and the minimum value of distortion is detected. As a load of the predetermined condition added to the test body TP1, a repeated load (tensile load or compressive load) at a predetermined frequency can be exemplified as in the case of the measured body TP.
Then, in the first preparation procedure, the temporal change in the stress of the part to which the strain sensor 4 of the test body TP1 is attached is calculated based on the detected temporal change in the strain. Specifically, when the Young's modulus determined by the material of the test body TP1 is E, the temporal change in strain is Δε, and the temporal change in stress is Δσ _T , the temporal change in stress Δσ according to the following equation (B): _T is calculated.
Δσ _T = E · Δε (B)
In this embodiment, the temporal change Δσ _T of the stress is calculated for each of a plurality of load conditions in which the maximum load and the minimum load applied to the specimen TP1 are changed to various values.

(Second preparation procedure)
As shown in FIG. 3B, in the second preparation procedure, the black body tape 3 is attached to the same surface of the specimen TP1 used in the first preparation procedure. Specifically, after removing the strain sensor 4 from the test body TP1, the black body tape 3 is attached to the surface of the test body TP1 including the portion where the strain sensor 4 is attached. However, the present invention is not limited to this, and it is also possible to execute the second preparation procedure first and then execute the first preparation procedure. When the second preparation procedure is executed first, the strain sensor 4 may be attached after the blackbody tape 3 is removed.
In the second preparation procedure, the test body TP1 to which the black body tape 3 is adhered as described above is attached to the same fatigue tester (not shown) as in the first preparation procedure, and the test body TP1 has a predetermined first preparation procedure. The surface of the test specimen TP1 is imaged by the infrared imaging device 1 with the same load condition (a plurality of load conditions in which the maximum load and the minimum load applied to the test specimen TP1 are changed to various values). The arithmetic device 2 measures a temporal change in the temperature distribution of the specimen TP1 based on the image signal input from the infrared imaging device 1. That is, the temporal change in temperature is measured for each pixel constituting the captured image captured by the infrared imaging device 1. Next, the arithmetic device 2 calculates a temporal change in the stress distribution of the test specimen TP1 based on the measured temporal change in the temperature distribution of the test specimen TP1 and a relational expression represented by the following formula (A). . That is, the temporal change in stress is calculated for each pixel constituting the captured image captured by the infrared imaging device 1.
Δσ = −1 / K · ΔT / T (A)
In the above formula (A), ΔT represents a temporal change in temperature, Δσ represents a temporal change in stress, T represents the temperature of the specimen TP1, and K represents a thermoelastic coefficient. The thermoelastic coefficient K is a physical property value determined by the material of the test body TP1, and for example, when the test body TP1 is made of a steel material, K = 3.5 × 10 ⁻¹² [Pa ⁻¹ ].
Further, in the second preparation procedure, the arithmetic unit 2 determines the time of stress at the same part of the specimen TP1 as the part where the strain sensor 4 is attached in the first preparation procedure from the temporal change of the stress distribution of the specimen TP1 calculated. To extract changes. Specifically, among the temporal changes in the stress distribution of the calculated specimen T1, that is, the temporal changes in the stress of all the pixel areas constituting the captured image, the pixel area corresponding to the part where the strain sensor 4 is attached The time variation of the stress (for example, the average time variation of the stress in the pixel region corresponding to the portion where the strain sensor 4 is attached) is extracted.
In this embodiment, as a preferable configuration, the thickness of the black body tape 3 to be attached to the surface of the test body TP1 is changed, and the second preparation procedure is repeatedly performed. Similar to the preparation procedure, for each of a plurality of load conditions, the temporal change in the stress of the part of the specimen TP1 that is the same as the part to which the strain sensor 4 is attached is extracted.

In addition, as the black body tape 3 to be used, for example, a black body tape manufactured by Ichinen TASCO can be exemplified.
Moreover, it is preferable that the frequency of the load (repetitive load) applied to the specimen TP1 in the first preparation procedure and the second preparation procedure is 5 Hz or more. If the frequency of the load is too small, when the temporal change in the temperature distribution of the test body TP1 is measured in the second preparation procedure, the heat generated by the thermoelastic effect diffuses before the measurement, thereby causing the temperature generated by the thermoelastic effect. This is because the change may not be measured accurately. Moreover, it is preferable that the magnitude | size of the load added to test body TP1 in a 1st preparation procedure and a 2nd preparation procedure shall be 10 Mpa or more converted into a stress amplitude. If the applied load is too small, when measuring the temporal change of the temperature distribution of the test body TP1 in the second preparation procedure, there is a possibility that the temperature change exceeding the temperature detection resolution of the infrared detection element included in the infrared imaging device 1 does not occur. Because there is.

(Third preparation procedure)
In the third preparation procedure, when the temporal change in the stress of the specimen TP1 extracted in the second preparation procedure is corrected using the correction coefficient CR, the temporal change in the stress of the specimen TP1 calculated in the first preparation procedure. The correction coefficient CR for the black body tape 3 is determined so as to match the above.
Specifically, in this embodiment, the temporal change Δσ of the stress of the specimen TP1 under one load condition extracted for each thickness of the blackbody tape 3 by the second preparation procedure is calculated by the first preparation procedure. By dividing by the temporal change Δσ _T of the stress of the test body TP1 under the one load condition, the correction coefficient is calculated for each thickness of the black body tape 3 and under the one load condition. This correction coefficient is calculated for all load conditions, averaged, and a correction coefficient CR ′ for each thickness of the blackbody tape 3 is calculated. In the present embodiment, each correction coefficient CR ′ is approximated by the least square method or the like, and the correction coefficient CR expressed by a function having the thickness t of the black body tape 3 shown in the following equation (1) as a variable is represented. decide.
CR = a · t ^b (1)
In the above formula (1), a and b are predetermined constants, and t is the thickness of the blackbody tape 3.

  FIG. 4 is a diagram illustrating an example of the correction coefficient CR ′ calculated in the third preparation procedure and the determined correction coefficient CR. In the example shown in FIG. 4, the correction coefficient CR is determined using the four correction coefficients CR ′ for the thickness t = t1 to t4 of the blackbody tape 3. In the example shown in FIG. 4, the correction coefficient CR is expressed as a power function of t using constants a> 0 and b <0. According to the knowledge of the present inventors, the most appropriate correction is possible by expressing the correction coefficient CR as a power function of the thickness t of the black body tape 3. However, the present invention is not limited to this. For example, the correction coefficient CR can be expressed as a linear function of the thickness t of the black body tape 3.

  In the stress distribution measurement method according to the present embodiment, after performing the preparation procedure including the first to third preparation procedures described above and calculating in advance the correction coefficient CR for the blackbody tape 3 (S1 in FIG. 2). ), The first procedure (S2 in FIG. 2) is executed. As long as at least the type of the black body tape 3 to be attached to the measurement target TP is not changed, the above preparation procedure (first to third preparation procedures) is executed once. However, there is no need to execute repeatedly.

<First procedure>
As shown in FIGS. 1 and 2, in the first procedure, the black body tape 3 is attached to the surface of the measurement target TP to which a load is applied (S2 in FIG. 2). As described above, in this embodiment, since the end B1 of the weld bead B included in the measurement target TP is used as a stress distribution measurement region, the surface of the end B1 of the weld bead B is formed as shown in FIG. The black body tape 3 is pasted so as to cover it.
In addition, when the measurement area | region of the to-be-measured body TP is wide, it may be necessary to affix two or more black body tapes 3 on the surface of the to-be-measured body TP. At this time, in order not to generate a region where the black body tape 3 is not attached (so as not to generate a gap between the adjacent black body tapes 3), the regions are adjacent to each other instead of simply being attached side by side. The black body tape 3 is preferably attached so as to have an overlapping portion.

<Second procedure>
As shown in FIG. 1 and FIG. 2, in the second procedure, the measured object TP with the black body tape 3 attached as described above is attached to a fatigue testing machine (not shown), a load is applied, The surface of the measurement object TP is imaged by the infrared imaging device 1, and the temporal change of the temperature distribution of the measurement object TP is measured by the arithmetic device 2 (S3 in FIG. 2). That is, the arithmetic device 2 measures a temporal change in temperature for each pixel constituting the captured image captured by the infrared imaging device 1.

<Third procedure>
As shown in FIG. 2, in the third procedure, the arithmetic device 2 performs a temporal change in the temperature distribution of the measurement target TP measured in the second procedure, a temporal change in temperature, and a temporal change in stress. Based on the predetermined relational expression, the temporal change in the stress distribution of the measured object TP is calculated (S4 in FIG. 2). That is, the arithmetic unit 2 calculates the stress distribution of the measured object TP based on the temporal change of the temperature distribution of the measured object TP measured by the second procedure and the relational expression expressed by the above-described equation (A). Calculate the change over time.

<4th procedure>
As shown in FIG. 2, in the fourth procedure, the computing device 2 uses the correction coefficient CR for the blackbody tape 3 that has been calculated in advance for the blackbody tape 3 in the above-described preparation procedure. The temporal change in the stress distribution of the measuring body TP is corrected (S5 in FIG. 2).
Specifically, in the present embodiment, as described above, the correction coefficient CR is represented by a function having the thickness of the blackbody tape 3 represented by the expression (1) as a variable. A correction coefficient CR corresponding to the thickness of the black body tape 3 attached in the first procedure is selected, and correction is performed using the selected correction coefficient CR. More specifically, the arithmetic device 2 corrects the temporal change in the stress distribution of the measured object TP calculated by the third procedure by dividing it by the correction coefficient CR.
In addition, as a thickness of the affixed black body tape 3, a design value may be used, or the thickness of the black body tape 3 actually affixed to the measurement target TP is measured using a film thickness meter or the like. You may do it. Then, for example, by manually inputting the design value or the actual measurement value of the thickness of the black body tape 3 to the arithmetic device 2, the arithmetic device 2 can be configured to select the correction coefficient CR according to the input thickness. is there.
As the film thickness meter for actually measuring the thickness of the black body tape 3, for example, when the measured object TP is a magnetic material, an electromagnetic induction type film thickness meter can be preferably used. As an electromagnetic induction type film thickness meter, “Electromagnetic film thickness meter LE-370” manufactured by Kett Science Laboratory can be exemplified. Moreover, when the to-be-measured body TP is a nonmagnetic material, for example, an eddy current film thickness meter can be used.

In the first procedure, when the black body tape 3 is pasted on the surface of the measurement object TP so that two or more black body tapes 3 overlap, the arithmetic device 2 has two or more black body tapes 3. For the overlapping portion, a correction coefficient CR corresponding to the total thickness of two or more blackbody tapes 3 is selected, and correction is performed using the selected correction coefficient CR.
The portion where the black body tape 3 overlaps can be determined by, for example, displaying a captured image (monochrome image) captured by the infrared imaging device 1 on a monitor screen provided in the arithmetic device 2 and visually observing it. . That is, as shown in FIG. 5, since the degree of shading differs between the portion where the black body tape 3 overlaps and the portion where it does not overlap, it can be determined by viewing the captured image displayed on the monitor screen. FIG. 5 schematically shows an example in which two blackbody tapes 3 overlap in the vicinity of the center of the captured image. Then, for example, using a pointing device such as a mouse on the monitor screen, it is possible to manually indicate the overlapping portion and the non-overlapping portion of the black body tape 3 in the captured image, and the total thickness of the overlapping portion and What is necessary is just to input the thickness of the part which does not overlap into the arithmetic unit 2 manually. In the example shown in FIG. 5, t = t1 is input as the thickness t of the non-overlapping portion, and t = 2 · t1 that is the thickness of two sheets is input as the thickness t of the overlapping portion. Thereby, the arithmetic unit 2 selects the correction coefficient CR (CR2 in the example shown in FIG. 5) according to the input total thickness t = 2 · t1 for the overlapping portions, and for the non-overlapping portions. The correction coefficient CR (CR1 in the example shown in FIG. 5) corresponding to the input thickness t = t1 can be selected.

According to the stress distribution measurement method according to the present embodiment described above, the correction coefficient CR for the blackbody tape 3 is calculated in advance by executing the preparation procedure. Moreover, the temporal change of the stress distribution of the measurement object TP in a state where the black body tape 3 is attached to the surface is calculated by the thermoelastic stress measurement method by executing the first procedure to the third procedure. It will be. Further, by executing the fourth procedure, the temporal change in the stress distribution of the measurement object TP is corrected using the correction coefficient CR for the blackbody tape 3 calculated in advance.
Therefore, according to the stress distribution measuring method according to the present embodiment, it is possible to measure the temporal change of the stress distribution at a practical level without contact without applying black paint to the surface of the measurement object TP. If the initial value of the stress distribution is known, the absolute value of the stress distribution after a predetermined time can be measured by adding the temporal change of the stress distribution to the initial value.

Hereinafter, an example (Test 1 and Test 2) of the result of measuring the temporal change of the stress distribution of the measurement object TP shown in FIG. 1 by the stress distribution measurement method according to the present embodiment will be described.
As test 1, the measurement object TP shown in FIG. 1 has a frequency of 10 Hz, a maximum load of 60.6 [kN], and a minimum load of 3.0 [kN] (stress ratio R = 0.05, load change ΔP). = 57.6 [kN]) was applied, and the temporal change in the stress distribution at the end B1 of the weld bead B was measured by the stress distribution measurement method according to this embodiment. The black body tape 3 used in Test 1 had a thickness t = 0.14 mm and a correction coefficient CR = 0.33. Then, an average stress temporal change Δσ ′ (Δσ before correction) in a pixel region corresponding to a portion to which a later-described strain sensor 4 is attached in the captured image captured by the infrared imaging device 1 was calculated. Further, the strain sensor 4 is attached to the end B1 of the weld bead B of the measurement object TP, and the repeated load under the same conditions as described above (frequency 10 Hz, maximum load 60.6 [kN], minimum load 3.0 [kN]). Was added to calculate the time change Δσ _T of the stress.
Further, as test 2, the measured object TP shown in FIG. 1 has a frequency of 10 Hz, a maximum load of 45.5 [kN], and a minimum load of 2.3 [kN] (stress ratio R = 0.05, load A cyclic load (tensile load) of change ΔP = 43.2 [kN]) was applied, and the temporal change in the stress distribution at the end B1 of the weld bead B was measured by the stress distribution measurement method according to this embodiment. The black body tape 3 used in Test 2 had a thickness t = 0.14 mm and a correction coefficient CR = 0.33. Then, an average stress temporal change Δσ ′ in a pixel region corresponding to a part to which a later-described strain sensor 4 is attached in the captured image captured by the infrared imaging device 1 was calculated. Further, the strain sensor 4 is attached to the end B1 of the weld bead B of the measured object TP, and a repeated load under the same conditions as described above (frequency 10 Hz, maximum load 45.5 [kN], minimum load 2.3 [kN]). Was added to calculate the time change Δσ _T of the stress.

FIG. 6 shows the results of Test 1 and Test 2. As shown in FIG. 6, when the temporal change Δσ _T of the stress measured using the strain sensor 4 is considered as a true value, the measurement error (= (Δσ′−ΔσT) in both Test 1 and Test 2 / ΔσT × 100) is 10% or less, and it was confirmed that the stress distribution could be measured at a practical level.

DESCRIPTION OF SYMBOLS 1 ... Infrared imaging device 2 ... Arithmetic unit 3 ... Black body tape 100 ... Stress distribution measuring device TP ... Measurement object

Claims (5)

A first procedure for attaching a black body tape to the surface of a measurement object to which a load is applied;
A second procedure for imaging the surface of the measurement object to which the black body tape is attached by the first procedure with an infrared imaging device, and measuring a temporal change in the temperature distribution of the measurement object;
Based on the temporal change of the temperature distribution of the measured object measured by the second procedure and a predetermined relational expression between the temporal change of temperature and the temporal change of stress, the stress distribution of the measured object A third procedure for calculating temporal changes;
A fourth procedure for correcting a temporal change in the stress distribution of the measured object calculated by the third procedure using a correction coefficient calculated in advance for the black body tape;
A stress distribution measuring method comprising: The correction coefficient used in the fourth procedure is represented by a function having the thickness of the black body tape as a variable,
The said 4th procedure WHEREIN: The said correction coefficient according to the thickness of the black body tape stuck by the said 1st procedure is selected, It correct | amends using this selected correction coefficient. Stress distribution measurement method. In the first procedure, the black body tape is pasted on the surface of the object to be measured so that two or more black body tapes overlap each other.
In the fourth procedure, for the portion where the two or more blackbody tapes overlap, the correction coefficient corresponding to the total thickness of the two or more blackbody tapes is selected, and the selected correction coefficient is used. The stress distribution measuring method according to claim 2, wherein the stress distribution measuring method is corrected. When the correction coefficient used in the fourth procedure is CR and the thickness of the black body tape is t, the correction coefficient CR is expressed by the following equation (1):
4. The stress distribution according to claim 2, wherein in the fourth procedure, the temporal change of the stress distribution of the measurement object calculated by the third procedure is corrected by dividing by the correction coefficient CR. 5. Measuring method.
CR = a · t ^b (1)
In the above formula (1), a and b are predetermined constants. The correction coefficient used in the fourth procedure is
A strain sensor is attached to the surface of the test body, a load with a predetermined condition is applied to the test body to which the strain sensor is attached, and a temporal change in strain is detected by the strain sensor, and a temporal change in the detected strain is detected. A first preparatory procedure for calculating a temporal change in stress of a portion of the specimen to which the strain sensor is attached;
The black body tape is affixed to the surface of the test body, a load having the same condition as the predetermined condition is applied to the test body to which the black body tape is affixed, and the surface of the test body is applied with the infrared imaging device. The temporal change of the temperature distribution of the test specimen is measured to measure the temporal distribution of the stress distribution of the specimen based on the measured temporal change of the temperature distribution of the specimen and the predetermined relational expression. A second preparatory procedure for calculating a change, and extracting a temporal change in stress of a part of the test body that is the same as a part to which the strain sensor is attached, from the temporal change of the stress distribution of the test body calculated;
When the temporal change of the stress of the specimen extracted by the second preparation procedure is corrected using the correction coefficient, the temporal change of the stress of the specimen calculated by the first preparation procedure is matched. A third preparatory procedure for determining the correction factor;
The stress distribution measuring method according to claim 1, wherein the stress distribution measuring method is calculated by:

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