JP7290213B2 - Internal defect detection method and internal defect detection apparatus - Google Patents

Description

The present invention relates to an internal defect detection method and an internal defect detection apparatus.

As examples of conventional non-destructive inspection methods, an ultrasonic flaw detector (see Patent Document 1) and an inspection system using radiation (see Patent Document 2) are disclosed.

JP 2016-61760 A JP 2017-219382 A

The non-destructive inspection method according to the above-described patent document is a method for identifying the internal cavity of the inspection object.

However, when a defect such as an unwelded portion that occurs during joining by welding does not cause a cavity, it has been difficult to detect it by the conventional non-destructive inspection method.

SUMMARY OF THE INVENTION An object of the present invention is to enable non-destructive detection of the presence of internal defects such as unwelded portions without cavities in a workpiece.

A method for detecting internal defects according to a first aspect includes a calculation step of calculating a residual stress distribution on the surface of the processed material from a known inherent strain distribution of the processed material, and measuring the residual stress distribution on the surface of the processed material. and a determining step of comparing the calculated value of the residual stress distribution calculated in the calculating step with the measured value of the residual stress distribution measured in the measuring step to determine whether or not there is an internal defect.

This internal defect detection method is a method of estimating the unknown information based on other information when any one of mechanical boundary conditions, geometric boundary conditions, and material properties is unknown. . Specifically, when the inherent strain that causes residual stress is known as a mechanical boundary condition and the material properties (material) are known, the residual stress distribution of the workpiece depends on the geometric boundary conditions. . This method estimates the presence or absence of an internal defect such as an unwelded portion from the measured residual stress value.

When the processed material is a welded joint material, and if the inherent strain distribution is uniform in the weld line direction due to joining without welding oscillation, a part of the end of the joint material is extracted during welding and the inherent strain is measured. By examining the distribution, the inherent strain distribution of the entire joint material becomes clear. Therefore, it is possible to know the residual stress distribution over the entire bonding material. In addition, when the relationship between various welding methods and inherent strain distribution is obtained as a database, the inherent strain distribution for welding conditions can be known. In the calculation step, the residual stress distribution on the surface of the workpiece can be obtained from such a known inherent strain distribution.

In the measurement step, the residual stress distribution on the surface of the processed material can be non-destructively measured, for example, even at the welding site by using, for example, a commercially available portable X-ray diffractometer.

In the determination step, if the calculated value of the residual stress distribution on the surface of the processed material obtained from the known inherent strain distribution is equal to the measured value of the measured residual stress distribution, there is an internal defect such as an unwelded portion in the processed material. Therefore, it can be determined that the joint is correctly joined. In addition, if there is a gap between the calculated value of the residual stress distribution on the surface of the processed material obtained from the known inherent strain distribution and the measured value of the residual stress distribution, an internal defect such as an unwelded part somewhere It can be determined that there is

Thus, according to this internal defect detection method, it is possible to non-destructively determine whether or not there is an internal defect.

A second aspect is the internal defect detection method according to the first aspect, wherein in the calculating step, an internal defect of an arbitrary position and size is assumed from a known inherent strain distribution of the processed material. The residual stress distribution on the surface of is calculated, and in the determination step, from among the residual stress distributions calculated in the calculation step, an optimum calculation is performed to find the one that is close to the measured value of the residual stress distribution measured in the measurement step. , to estimate the location and size of the internal defect.

In this internal defect detection method, in the calculation step, the residual stress distribution on the surface of the processed material assuming an internal defect of arbitrary position and size is calculated from the known inherent strain distribution of the processed material.

In the determination step, optimum calculation is performed to find out the residual stress distribution calculated in the calculation step that is close to the measured value of the residual stress distribution measured in the measurement step. This makes it possible to estimate the position and size of the internal defect.

An internal defect detection device according to a third aspect includes a calculation unit that calculates a residual stress distribution on the surface of the processed material from a known inherent strain distribution of the processed material, and a residual stress distribution on the surface of the processed material. and a determination unit that compares the calculated value of the residual stress distribution calculated by the calculation unit and the measured value of the residual stress distribution measured by the measurement unit, and determines whether or not there is an internal defect.

When any one of mechanical boundary conditions, geometric boundary conditions, and material properties is unknown, this internal defect detection device estimates the unknown information based on other information. Specifically, when the inherent strain that causes residual stress is known as a mechanical boundary condition and the material properties (material) are known, the residual stress distribution of the workpiece depends on the geometric boundary conditions. . This detection device estimates the presence or absence of an internal defect such as an unwelded portion from the measured value of the residual stress distribution.

When the processed material is a welded joint material, and if the inherent strain distribution is uniform in the weld line direction due to joining without welding oscillation, a part of the end of the joint material is extracted during welding and the inherent strain is measured. By examining the distribution, the inherent strain distribution of the entire joint material becomes clear. Therefore, it is possible to know the residual stress distribution over the entire bonding material. In addition, when the relationship between various welding methods and inherent strain distribution is obtained as a database, the inherent strain distribution for welding conditions can be known. The calculator can obtain the residual stress distribution on the surface of the processed material from such a known inherent strain distribution.

For example, a commercially available portable X-ray diffraction device can be used as the measurement unit. This measuring unit can non-destructively measure the residual stress distribution on the surface of the workpiece.

In the judging section, if the calculated value of the residual stress distribution on the surface of the processed material obtained from the known inherent strain distribution is equal to the measured value of the measured residual stress distribution, there is an internal defect such as an unwelded portion in the processed material. Therefore, it can be determined that the joint is correctly joined. In addition, if there is a gap between the calculated value of the residual stress distribution on the surface of the processed material obtained from the known inherent strain distribution and the measured value of the residual stress distribution, an internal defect such as an unwelded part somewhere It can be determined that there is

Thus, according to this internal defect detection apparatus, it is possible to non-destructively determine whether or not there is an internal defect.

A fourth aspect is the internal defect detection device according to the third aspect, wherein the calculation unit assumes an internal defect at an arbitrary position and size from a known inherent strain distribution of the processed material In the determination unit, the residual stress distribution calculated by the calculation unit is further calculated by the optimum calculation to find one that is close to the measured value of the residual stress distribution measured by the measurement unit. , to estimate the location and size of the internal defect.

In this internal defect detection apparatus, the calculation unit calculates the residual stress distribution on the surface of the processed material assuming an internal defect at an arbitrary position and size from the known inherent strain distribution of the processed material.

The judging unit performs optimum calculation to find out the residual stress distribution calculated by the calculating unit that is close to the actual measured value of the residual stress distribution measured by the measuring unit. This makes it possible to estimate the position and size of the internal defect.

ADVANTAGE OF THE INVENTION According to this invention, when an internal defect, such as an unwelded part without a cavity, exists in a workpiece, the existence thereof can be detected in a non-destructive manner.

1 is a block diagram showing an internal defect detection device; FIG. (A) is a perspective view showing a bonding material in which an excess build-up is formed on the surface side. (B) is a perspective view showing the bonding material from which the surplus is scraped off and the surface side is processed to be flat. (C) is a perspective view showing one side of the bonding material of FIG. 2(B) cut at the center of the welded portion. 3 is an FEM model diagram of the bonding material shown in FIG. 2(C); FIG. FIG. 2 is a plan view showing the measurement position of residual stress on the surface of the bonding material, and an FEM model diagram showing the end surface of the bonding material. FIG. 5 is a graph showing the root mean square of the difference between the measured value and the calculated value of the residual stress distribution at each measurement point in FIG. 4;

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments for carrying out the present invention will be described based on the drawings. In the drawings, arrow FR indicates the front of the vehicle, arrow UP indicates the upper direction of the vehicle, and arrow RH indicates the right direction of the vehicle.

In FIG. 1 , an internal defect detection apparatus 10 according to the present embodiment includes a calculation unit 11 , a measurement unit 12 and a determination unit 13 .

The calculator 11 is, for example, a computer that calculates the residual stress distribution on the surface 14A of the joint material 14 from the known inherent strain distribution of the welded joint material 14 as an example of the processed material. The calculation unit 11 calculates the residual stress distribution when there is no welding defect, which is an example of an internal defect, in the joining material 14 using, for example, the finite element method (FEM). In addition to this, the calculation unit 11 can calculate the calculated value of the residual stress distribution on the surface 14A of the joining material 14 assuming a welding defect of arbitrary position and size. In this case, the calculator 11 obtains the residual stress distribution under each condition while changing the position and size of the weld defect.

The inherent strain distribution of the joint material 14 can be obtained, for example, by extracting and examining a portion 14B (FIG. 2B) of the end of the joint material 14 without welding defects. If the relationship between various welding methods and inherent strain distribution is obtained as a database, the inherent strain distribution for welding conditions can be easily obtained.

In FIG. 2, the joining material 14 in this embodiment is, for example, two metal plates 16 and 18 butt-welded. In FIG. 2(A), a weld bead extending linearly is formed in the welded portion 20, and an extra weld is formed on the surface 14A side of the bonding material 14. In FIG. FIG. 2(B) shows a state in which the surplus is scraped off and the surface 14A side of the bonding material 14 is flattened. FIG. 2(C) shows one side of the bonding material 14 of FIG. 2(B) cut at the center of the welded portion 20 (one-dot chain line L), for example, the metal plate 18 side.

The welded joining material 14 includes fusion welding material, resistance spot welding material, laser spot welding material, projection welding material, and seam welding material.

A weld defect is an example of an internal defect, such as an unwelded portion formed without a cavity in the welded portion 20, or a portion of insufficient welding such as a cavity (void) generated in the welded portion 20. . In this embodiment, an example of a weld defect is described as an unwelded portion.

The measuring part 12 is a part that measures the residual stress distribution on the surface 14A of the bonding material 14 . The measurement unit 12 may be, for example, a commercially available portable X-ray diffraction device or a fixed X-ray diffraction device.

The determination unit 13 is, for example, a computer that compares the calculated value of the residual stress distribution calculated by the calculation unit 11 and the actual measurement value of the residual stress distribution measured by the measurement unit 12 to determine the presence or absence of welding defects. Further, the determination unit 13 finds a residual stress distribution that is close to the measured value of the residual stress distribution measured by the measurement unit 12 from among many residual stress distributions calculated by the calculation unit 11 while changing the position and size of the weld defect. A best fit calculation may estimate the location and size of the weld defect.

(action)
This embodiment is configured as described above, and the operation thereof will be described below. When any one of mechanical boundary conditions, geometric boundary conditions, and material properties is unknown, the internal defect detection apparatus 10 according to the present embodiment uses the unknown information based on other information. presume. Specifically, when the inherent strain that causes residual stress is known as a mechanical boundary condition and the material properties (material) are known, the residual stress distribution of the bonding material 14 depends on the geometric boundary conditions. do. This detection device estimates the presence or absence of welding defects such as unwelded parts from the measured values of the residual stress distribution.

In the joint material 14 without welding oscillation, the inherent strain distribution may be generally uniform in the weld line direction. By extracting and examining the inherent strain distribution, the inherent strain distribution of the entire bonding material 14 becomes clear. Therefore, the residual stress distribution in the entire bonding material 14 can be known. Moreover, when the relationship between various welding methods and the inherent strain distribution is obtained as a database, the inherent strain distribution for the welding conditions can be easily obtained. The calculator 11 can obtain the residual stress distribution of the surface 14A of the bonding material 14 from such a known inherent strain distribution.

As the measurement unit 12, for example, a commercially available portable X-ray diffraction device can be used. A portable X-ray diffraction device is suitable for performing measurements at a welding site. A fixed X-ray diffraction device may also be used. The residual stress distribution on the surface 14A of the bonding material 14 can be non-destructively measured by the measurement unit 12. FIG.

In the determination unit 13, when the calculated value of the residual stress distribution on the surface 14A of the bonding material 14 obtained from the known inherent strain distribution is equal to the measured value of the measured residual stress distribution, the unwelded part etc. of the bonding material 14 It can be determined that there is no defect in the joint and that it is joined correctly. In addition, if there is a gap between the calculated value of the residual stress distribution on the surface 14A of the bonding material 14 obtained from the known inherent strain distribution and the measured value of the residual stress distribution, there may be an unwelded portion somewhere. It can be determined that there is a welding defect.

Note that the calculation unit 11 may calculate the residual stress distribution on the surface 14A of the bonding material 14 assuming a welding defect of arbitrary position and size from the known inherent strain distribution of the bonding material 14 . In this case, the residual stress distribution under each condition is determined while changing the position and size of the weld defect.

In addition, the determination unit 13 finds a residual stress distribution that is close to the measured value of the residual stress distribution measured by the measurement unit 12 from among many residual stress distributions calculated by the calculation unit 11 while changing the position and size of the weld defect. Optimal calculations may be performed. This makes it possible to estimate not only the presence or absence of a weld defect, but also its position and size.

As described above, according to the internal defect detection device 10, it is possible to non-destructively determine whether or not there is a welding defect in the joint material 14. FIG. As an example, the spot weld material may not be properly welded by visual inspection when viewed from the opposite side of the weld surface. However, according to the present embodiment, it is possible to non-destructively inspect whether or not the spot welding material is properly welded, and if there is an unwelded part, its position and size can be estimated.

(Method for detecting internal defects)
In FIG. 1, the internal defect detection method includes a calculation step S1 of calculating the residual stress distribution on the surface 14A (FIG. 2) of the joint material 14 from the known inherent strain distribution of the welded joint material 14; The measurement step S2 for measuring the residual stress distribution on the surface 14A of the surface 14A, the calculated value of the residual stress distribution calculated in the calculation step S1, and the measured value of the residual stress distribution measured in the measurement step S2 are compared to determine whether there is an internal defect and a judgment step S3 for judging.

In the calculation step S1, the residual stress distribution on the surface 14A of the bonding material 14 assuming an internal defect of arbitrary position and size may be calculated from the known inherent strain distribution of the bonding material 14 . Further, in the determination step S3, the position and size of the internal defect are determined by optimum calculation for finding out the residual stress distribution calculated in the calculation step S1 that is close to the measured value of the residual stress distribution measured in the measurement step S2. can be estimated.

(Test example)
FIG. 3 shows an FEM model of the bonding material 14 shown in FIG. 2(C). FIG. 4 shows an FEM model of the residual stress measurement position 22 on the surface 14A of the bonding material 14 and the end face of the bonding material 14. As shown in FIG. The bonding material 14 has a length of 110 mm, a width of 40 mm on one side, and a thickness of 5 mm. Assuming that the origins of the x-, y-, and z-axes are set at the corners of the bottom, left, and front sides of the bonding material 14, the welded portion 20 corresponds to the range of 0≦y≦8 mm when viewed from the front surface 14A. A specific example of the internal defect detection method will be described based on these figures.

Here, it is unknown that the unwelded portion 24 (FIG. 4) is formed at a position of 25 mm≦x≦30 mm, y=8 mm, and 3 mm≦z≦4 mm. The inherent strain distribution of the bonding material 14 is known. In the calculation step S1 (FIG. 1), the surface 14A (y= 10mm, z=5mm) are calculated respectively. This residual stress is calculated at a plurality of measurement positions 22 in the x direction. Specifically, the residual stress Calculate The calculated values are as shown in Tables 1 and 2. In Tables 1 and 2, σx indicates the residual stress in the x-axis direction, and σy indicates the residual stress in the y-axis direction.

On the other hand, in the measurement step S2 (FIG. 1), the residual stress distribution is measured and the measured values at each measurement position 22 are obtained. Calculated and measured values of residual stress can be compared with each other. In determination step S3, if the measured value is different from the calculated value indicating that there is no unwelded portion, it can be estimated that the bonding material 14 has an unwelded portion. It is also possible to obtain the root mean square (RMS) of the difference between the calculated value and the measured value in decision step S3. In the calculation step S1 (FIG. 1), a large number of residual stress distributions are calculated in advance when the location where the unwelded portion is thought to occur is changed, that is, when the positional condition of the unwelded portion is changed, and the measured values and the The position of the unwelded portion can be estimated by selecting the position condition with the smallest difference (RMS).

In Fig. 5, the positions of the unwelded parts are 15 mm ≤ x ≤ 20 mm (x = 17.5 mm), 20 mm ≤ x ≤ 25 mm (x = 22.5 mm), 25 mm ≤ x ≤ 30 mm (x = 27.5 mm), 30 mm ≤ x ≤35mm (x=32.5mm), 35mm≤x≤40mm (x=37.5mm), 40mm≤x≤45mm (x=42.5mm) at y=10mm, z=5mm The RMS of the difference between the measured and calculated residual stress distribution is shown. In this figure, the RMS is 0 MPa at 25 mm≦x≦30 mm (x=27.5 mm). In other words, the calculated values when it is assumed that the non-welded portions occur at the positions of 25 mm≦x≦30 mm, y=8 mm, and 3 mm≦z≦4 mm are closest to the measured values. From this, it can be seen that the position of the unwelded portion 24 is 25 mm≦x≦30 mm (x=27.5 mm), y=8 mm, and 3 mm≦z≦4 mm.

In this way, from among many residual stress distributions calculated by the calculation unit 11 while changing the position and size of the weld defect, the optimum calculation is performed to find the residual stress distribution that is close to the measured value of the residual stress distribution measured by the measurement unit 12. , the position and size of the weld defect can be estimated.

Since this embodiment is an approach that determines geometric boundary conditions, it is not necessarily limited to detection of unwelded portions, but can also be applied to dimensional evaluation of structures with unknown internal shapes. For example:

(Quality evaluation of welded structures)
There are high demands for safety in fields that are directly related to human life, such as Shinkansen bogies and aircraft materials. Therefore, a relatively high level of quality assurance is required. If there is an unwelded portion in the welded portion, the unwelded portion can be regarded as a kind of crack, so there is a problem that the stress is magnified by the crack and the crack growth rate becomes relatively high. According to this embodiment, the quality can be evaluated non-destructively, so that even higher reliability can be ensured for structures that require a high degree of safety, such as bullet trains and automobiles.

(Non-destructive detection of internal defects in industrial products)
This embodiment is a method for determining the geometric boundary conditions of an object when the inelastic strain distribution that causes residual stress is known, and the internal shape can also be specified. Further, according to the present embodiment, welding defects can be detected without depending on the shape of the bonding material, so even shapes that are relatively difficult to measure by ultrasonic measurement can be inspected. Furthermore, it is considered difficult to measure by ultrasonic measurement even internal delamination that cannot be detected from the surface of the member, but it can be detected according to the present embodiment. Moreover, it is also possible to specify the voids generated in the welded portion.

[Other embodiments]
An example of the embodiment of the present invention has been described above, but the embodiment of the present invention is not limited to the above, and can be modified in various ways without departing from the spirit of the present invention. Of course there is.

The processed material is not limited to the welded joining material 14, but also includes pressure-welded materials, surface-modifying materials, plastically-worked materials, local heat-input-worked materials (flexible iron), heat-treated materials, heavily-worked materials, and the like. Pressure welding consumables include friction stir weld consumables, lap resistance weld consumables, and butt resistance weld consumables. Surface modification materials include peening materials, carburizing materials, nitriding materials, thermal spraying materials, and sputter coating materials. Plastic-worked materials include cold-worked materials and hot-worked materials. The heat-treated materials include quenched materials, tempered materials, and annealed materials. In the above embodiment, it is possible to detect such internal defects in various workpieces.

10 Internal defect detection device 11 Calculation unit 12 Measurement unit 13 Judgment unit 14 Joining material (processing material)
14A surface 24 unwelded part (internal defect)
S1 Calculation step S2 Measurement step S3 Judgment step

Claims (2)

a calculation step of calculating a residual stress distribution on the surface of the processed material from the known inherent strain distribution of the processed material;
a measuring step of measuring residual stress distribution on the surface of the processed material;
a determination step of comparing the calculated value of the residual stress distribution calculated in the calculation step with the measured value of the residual stress distribution measured in the measurement step to determine whether there is an internal defect;
has
In the calculation step, from the known inherent strain distribution of the processed material, calculating the residual stress distribution on the surface of the processed material assuming an internal defect of arbitrary position and size,
In the determination step, the position and size of the internal defect are further determined by optimum calculation for finding, from among the residual stress distributions calculated in the calculation step, those that are close to the measured values of the residual stress distribution measured in the measurement step. Estimated internal defect detection method. a calculation unit that calculates the residual stress distribution on the surface of the processed material from the known inherent strain distribution of the processed material;
a measurement unit for measuring residual stress distribution on the surface of the processed material;
a determination unit that compares the calculated value of the residual stress distribution calculated by the calculation unit and the measured value of the residual stress distribution measured by the measurement unit and determines whether there is an internal defect;
has
The calculation unit calculates the residual stress distribution on the surface of the processed material assuming internal defects of arbitrary positions and sizes from the known inherent strain distribution of the processed material,
The determination unit further determines the position and size of the internal defect by performing optimum calculation to find out the residual stress distribution calculated by the calculation unit that is close to the actual measurement value of the residual stress distribution measured by the measurement unit. Detecting device for presumed internal defects.

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