JP7520409B2 - Method and device for detecting internal defects - Google Patents

Description

The present invention relates to a method and device for detecting internal defects.

Conventional non-destructive inspection methods include an ultrasonic flaw detector (see Patent Document 1) and an inspection system that uses radiation (see Patent Document 2).

JP 2016-61760 A JP 2017-219382 A

The non-destructive testing method described in the above patent document is a method for identifying cavities inside an object to be tested.

However, defects such as unwelded areas that occur during welding that do not result in cavities are difficult to detect using conventional non-destructive testing methods.

The purpose of the present invention is to make it possible to non-destructively detect the presence of internal defects, such as unwelded areas without cavities, in processed materials.

The method for detecting internal defects according to the first aspect includes a calculation step of calculating the residual stress distribution on the surface of the processed material from the known inherent strain distribution of the processed material, a measurement step of measuring the residual stress distribution on the surface of the processed material, which is the object of internal defect detection, and a determination step of comparing the calculated value of the residual stress distribution calculated in the calculation step with the actual measured value of the residual stress distribution measured in the measurement step to determine the presence or absence of an internal defect.

This method of detecting internal defects is a method in which when any one of the mechanical boundary conditions, geometric boundary conditions, and material properties is unknown, the unknown information is estimated based on the other information. Specifically, when the inherent strain that causes residual stress is known as a mechanical boundary condition, and the material properties (material quality) are known, the residual stress distribution in the processed material depends on the geometric boundary conditions. This method estimates the presence or absence of internal defects such as unwelded areas from the measured residual stress values.

When the processed material is a welded joint material, and the inherent strain distribution is uniform in the weld line direction due to the joining without welding oscillation, the inherent strain distribution of the entire joint material can be determined by extracting a portion of the end of the joint material during welding and examining the inherent strain distribution. This makes it possible to know the residual stress distribution over the entire joint material. Furthermore, if the relationship between various welding methods and inherent strain distribution is available in a database, the inherent strain distribution for the welding conditions can be known. In the calculation step, the residual stress distribution on the surface of the processed material can be obtained from this known inherent strain distribution.

In the measurement step, the residual stress distribution on the surface of the processed material, which is the target of internal defect detection, can be measured non-destructively, for example, at the welding site, using, for example, a commercially available portable X-ray diffraction device.

In the judgment step, if the calculated residual stress distribution on the surface of the processed material obtained from the known inherent strain distribution is equal to the actual measured residual stress distribution, it can be judged that the processed material has no internal defects such as unwelded areas and is properly joined. Also, if there is a gap between the calculated residual stress distribution on the surface of the processed material obtained from the known inherent strain distribution and the actual measured residual stress distribution, it can be judged that there is an internal defect such as an unwelded area somewhere.

In this way, this method of detecting internal defects makes it possible to non-destructively determine whether or not there is an internal defect.

In the second aspect, in the method for detecting internal defects according to the first aspect, the calculation step calculates the residual stress distribution on the surface of the processed material assuming an internal defect of any position and size from the known inherent strain distribution of the processed material, and the determination step further estimates the position and size of the internal defect by an optimal calculation that finds, from the residual stress distributions calculated in the calculation step, a residual stress distribution that is closest to the actual residual stress distribution measured in the measurement step.

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

In the determination step, an optimal calculation is performed to find the residual stress distribution calculated in the calculation step that is closest to the actual residual stress distribution measured in the measurement step. This makes it possible to estimate the position and size of the internal defect.

The internal defect detection device according to the third aspect has 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 that measures the residual stress distribution on the surface of the processed material that is the object of internal defect detection, and a determination unit that compares the calculated value of the residual stress distribution calculated by the calculation unit with the actual measured value of the residual stress distribution measured by the measurement unit to determine the presence or absence of an internal defect.

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

When the processed material is a welded joint material, and the inherent strain distribution is uniform in the weld line direction due to the joint not having welding oscillation, the inherent strain distribution of the entire joint material can be determined by extracting a portion of the end of the joint material during welding and examining the inherent strain distribution. This makes it possible to know the residual stress distribution over the entire joint material. Furthermore, if the relationship between various welding methods and inherent strain distribution is available in a database, the inherent strain distribution for the welding conditions can be known. The calculation unit can obtain the residual stress distribution on the surface of the processed material from this known inherent strain distribution.

The measurement unit can be, for example, a commercially available portable X-ray diffraction device. This measurement unit can non-destructively measure the residual stress distribution on the surface of the processed material, which is the target for internal defect detection.

In the judgment 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 actual measured value of the residual stress distribution, it can be determined that the processed material has no internal defects such as unwelded areas and is properly joined. Also, 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 actual measured value of the residual stress distribution, it can be determined that there is an internal defect such as an unwelded area somewhere.

In this way, this internal defect detection device can non-destructively determine whether or not there is an internal defect.

In the fourth aspect, in the internal defect detection device according to the third aspect, the calculation unit calculates the residual stress distribution on the surface of the processed material assuming an internal defect of any position and size from the known inherent strain distribution of the processed material, and the determination unit further estimates the position and size of the internal defect by optimal calculation to find, from the residual stress distributions calculated by the calculation unit, a residual stress distribution that is closest to the actual residual stress distribution measured by the measurement unit.

In this internal defect detection device, the calculation section calculates the residual stress distribution on the surface of the processed material assuming an internal defect of any position and size from the known inherent strain distribution of the processed material.

The determination unit performs an optimal calculation to find the residual stress distribution calculated by the calculation unit that is closest to the actual residual stress distribution measured by the measurement unit. This makes it possible to estimate the position and size of the internal defect.

According to the present invention, when an internal defect such as an unwelded portion without a cavity is present in a processed material, its presence can be detected non-destructively.

FIG. 1 is a block diagram showing an internal defect detection device. 2A is a perspective view showing a bonding material with a weld formed on the surface side, FIG. 2B is a perspective view showing a bonding material with the weld removed and the surface side processed to be flat, and FIG. 2C is a perspective view showing one side of the bonding material of FIG. 2B cut at the center of the weld. FIG. 3 is an FEM model diagram of the bonding material shown in FIG. 1 is a plan view showing measurement positions of surface residual stress in a bonding material, and an FEM model diagram showing an end face of the bonding material. FIG. FIG. 5 is a diagram 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 .

Below, an embodiment of the present invention will be described with reference to the drawings. In the drawings, the arrow FR indicates the front of the vehicle, the arrow UP indicates the upper side of the vehicle, and the arrow RH indicates the right side of the vehicle.

In FIG. 1, the internal defect detection device 10 according to this embodiment has a calculation unit 11, a measurement unit 12, and a judgment unit 13.

The calculation unit 11 is, for example, a computer that calculates the residual stress distribution on the surface 14A of the welded joint material 14 from the known inherent strain distribution of the welded joint material 14, which is an example of a processed material. The calculation unit 11 calculates the residual stress distribution when the joint material 14 does not have a welding defect, which is an example of an internal defect, by using, for example, the finite element method (FEM). In addition, the calculation unit 11 is capable of calculating the calculated value of the residual stress distribution on the surface 14A of the joint material 14 assuming a welding defect of any position and size. In this case, the calculation unit 11 determines the residual stress distribution under each condition while changing the position and size of the welding defect.

The inherent strain distribution of the joining material 14 can be obtained, for example, by extracting and examining a portion 14B (Figure 2 (B)) of the end of the joining material 14 that has no welding defects. If the relationship between various welding methods and the inherent strain distribution is available as a database, the inherent strain distribution for the welding conditions can be easily obtained.

In FIG. 2, the joining material 14 in this embodiment is, for example, two metal plates 16, 18 butt-welded together. In FIG. 2(A), a linear weld bead is formed at the welded portion 20, and an excess is formed on the surface 14A side of the joining material 14. FIG. 2(B) shows the state in which this excess has been scraped off and the surface 14A side of the joining material 14 has been machined flat. FIG. 2(C) shows one side of the joining material 14 in FIG. 2(B) cut at the center (dotted line L) of the welded portion 20, for example the metal plate 18 side.

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

A welding 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 where the welding is insufficient, such as a cavity (gap) that occurs in the welded portion 20. In this embodiment, an example of a welding defect will be described as an unwelded portion.

The measuring unit 12 is a part that measures the residual stress distribution on the surface 14A of the joining material 14. The measuring 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 with the actual measured value of the residual stress distribution measured by the measurement unit 12 to determine the presence or absence of a welding defect. The determination unit 13 may further estimate the position and size of the welding defect by an optimal calculation that finds one that is closest to the actual measured value of the residual stress distribution measured by the measurement unit 12 from among the many residual stress distributions calculated by the calculation unit 11 while changing the position and size of the welding defect.

(Action)
This embodiment is configured as described above, and its operation will be described below. When any one of the mechanical boundary conditions, the geometric boundary conditions, and the material properties is unknown, the internal defect detection device 10 according to this embodiment estimates the unknown information based on the other information. Specifically, when the inherent strain that causes the residual stress is known as the mechanical boundary condition, and the material properties (material quality) are known, the residual stress distribution of the joining material 14 depends on the geometric boundary condition. This detection device estimates the presence or absence of a welding defect such as an unwelded portion from the actual measured value of the residual stress distribution.

In a joining material 14 without welding oscillation, the inherent strain distribution may be roughly uniform in the direction of the weld line. In this case, the inherent strain distribution of the entire joining material 14 can be determined by extracting a portion 14B (FIG. 2(B)) of the end of the joining material 14 during welding and examining the inherent strain distribution. This makes it possible to know the residual stress distribution over the entire joining material 14. Furthermore, if the relationship between various welding methods and inherent strain distribution is available as a database, the inherent strain distribution for the welding conditions can be easily obtained. The calculation unit 11 can obtain the residual stress distribution on the surface 14A of the joining material 14 from such a known inherent strain distribution.

The measurement unit 12 can be, for example, a commercially available portable X-ray diffraction device. Portable X-ray diffraction devices are suitable for performing measurements at the welding site. Note that a fixed X-ray diffraction device may also be used. This measurement unit 12 can non-destructively measure the residual stress distribution on the surface 14A of the joining material 14.

When the calculated value of the residual stress distribution on the surface 14A of the joining material 14 obtained from the known inherent strain distribution is equal to the actual measured value of the residual stress distribution, the judgment unit 13 can judge that the joining material 14 has no defects such as unwelded parts and is properly joined. Also, when there is a gap between the calculated value of the residual stress distribution on the surface 14A of the joining material 14 obtained from the known inherent strain distribution and the actual measured value of the residual stress distribution, it can be judged that there is a welding defect such as an unwelded part somewhere.

The calculation unit 11 may calculate the residual stress distribution on the surface 14A of the joining material 14 assuming a welding defect of any position and size from the known inherent strain distribution of the joining material 14. In this case, the residual stress distribution is obtained under each condition while changing the position and size of the welding defect.

The determination unit 13 may also perform an optimal calculation to find a residual stress distribution that is closest to the actual residual stress distribution measured by the measurement unit 12 from among the many residual stress distributions calculated by the calculation unit 11 while changing the position and size of the welding defect. This makes it possible to estimate not only the presence or absence of a welding defect, but also its position and size.

In this way, the internal defect detection device 10 can non-destructively determine whether or not there is a welding defect in the joining material 14. As an example, when spot-welded material is viewed from the opposite side of the welded surface, it may be difficult to tell by visual inspection whether it is properly welded. However, according to this embodiment, it is possible to non-destructively inspect whether spot-welded material is properly welded, and if there is an unwelded portion, its position and size can be estimated.

(Method of detecting internal defects)
In FIG. 1, the method for detecting internal defects includes a calculation step S1 for calculating a residual stress distribution on a surface 14A (FIG. 2) of the joining material 14 from a known inherent strain distribution of the welded joining material 14, a measurement step S2 for measuring the residual stress distribution on the surface 14A of the joining material 14, and a determination step S3 for comparing the calculated value of the residual stress distribution calculated in the calculation step S1 with the actual measured value of the residual stress distribution measured in the measurement step S2 to determine the presence or absence of an internal defect.

In the calculation step S1, the residual stress distribution on the surface 14A of the joining material 14 may be calculated assuming an internal defect of any position and size from the known inherent strain distribution of the joining material 14. In addition, in the determination step S3, the position and size of the internal defect may be estimated by an optimal calculation that finds, from the residual stress distributions calculated in the calculation step S1, a residual stress distribution that is close to the actual measurement value of the residual stress distribution measured in the measurement step S2.

(Test Example)
Fig. 3 shows an FEM model of the joining material 14 shown in Fig. 2(C). Fig. 4 shows a measurement position 22 of residual stress on the surface 14A of the joining material 14, and an FEM model of the end surface of the joining material 14. The joining material 14 has a length of 110 mm, a width of 40 mm on one side, and a thickness of 5 mm. The origins of the x-axis, y-axis, and z-axis are set at the corners on the bottom side, left side, and front side of the joining material 14, and the range of 0 ≤ y ≤ 8 mm as viewed from the surface 14A corresponds to the welded part 20. Based on these figures, a specific example of a method for detecting internal defects will be described.

Here, it is unknown that the unwelded portion 24 (FIG. 4) occurs at a position of 25 mm≦x≦30 mm, y=8 mm, 3 mm≦z≦4 mm. The inherent strain distribution of the joining material 14 is known. In the calculation step S1 (FIG. 1), the residual stress distribution of the surface 14A (y=10 mm, z=5 mm) of the joining material 14 when the unwelded portion occurs at a position of, for example, y=8 mm, 3 mm≦z≦4 mm, 15 mm≦x≦100 mm (in 5 mm increments) is calculated. This residual stress is calculated at multiple measurement positions 22 in the x direction. Specifically, the residual stress is calculated at the positions of x=10 mm, x=20 mm, x=30 mm, x=40 mm, x=50 mm, x=60 mm, x=70 mm, x=80 mm, x=90 mm, and x=100 mm. 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.

Meanwhile, in the measurement step S2 (Fig. 1), the residual stress distribution is measured, and the actual measurement value is obtained for each measurement position 22. The calculated and actual measurements of the residual stress can be compared with each other. In the judgment step S3, if the actual measurement value differs from the calculated value without the unwelded portion, it can be estimated that an unwelded portion exists in the joining material 14. In the judgment step S3, it is also possible to obtain the root mean square (RMS) of the difference between the calculated value and the actual measurement value. In the calculation step S1 (Fig. 1), a large number of residual stress distributions are calculated when the location where the unwelded portion is thought to exist is changed, that is, when the positional conditions of the unwelded portion are changed, and the positional conditions with the smallest difference (RMS) from the actual measurement value are selected, so that the positional conditions of the unwelded portion can be estimated.

Figure 5 shows the RMS of the difference between the measured and calculated residual stress distribution at the position y=10mm, z=5mm when the position of the unwelded part is changed to 15mm≦x≦20mm (x=17.5mm), 20mm≦x≦25mm (x=22.5mm), 25mm≦x≦30mm (x=27.5mm), 30mm≦x≦35mm (x=32.5mm), 35mm≦x≦40mm (x=37.5mm), 40mm≦x≦45mm (x=42.5mm). In this figure, the RMS is 0 MPa at 25mm≦x≦30mm (x=27.5mm). In other words, the calculated value when the unwelded part is assumed to be at the position 25mm≦x≦30mm, y=8mm, 3mm≦z≦4mm is closest to the measured value. 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, the position and size of the weld defect can be estimated by optimal calculation, which finds the residual stress distribution closest to the actual measured value measured by the measurement unit 12 from among the many residual stress distributions calculated by the calculation unit 11 while changing the position and size of the weld defect.

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

(Quality evaluation of welded structures)
In fields directly related to human life, such as bullet train bogies and aircraft materials, there is a high demand for safety. Therefore, a relatively high level of quality assurance is required. If an unwelded portion exists in a welded portion, the unwelded portion can be regarded as a type of crack, and there is a problem that the crack expands the stress and the crack growth rate becomes relatively high. This embodiment makes it possible to nondestructively evaluate quality, thereby ensuring even greater reliability for structures that require a high level 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 identified. Furthermore, according to this embodiment, welding defects can be detected regardless of the shape of the joining material, so inspection is possible even for shapes that are relatively difficult to measure with ultrasonic waves. Furthermore, internal peeling that cannot be seen from the surface of a component is difficult to measure with ultrasonic waves, but this embodiment makes it possible to detect it. It is also possible to identify voids that occur in welds.

[Other embodiments]
An example of an embodiment of the present invention has been described above, but the embodiment of the present invention is not limited to the above, and it goes without saying that various modifications can be made without departing from the spirit and scope of the present invention.

The processed materials are not limited to the welded joint material 14, but also include pressure-welded materials, surface-modified materials, plastically processed materials, localized heat-input processed materials (flexural iron), heat-treated materials, and heavily processed materials. Pressure-welded materials include friction stir welded materials, lap resistance welded materials, and butt resistance welded materials. Surface-modified materials include peened materials, carburized materials, nitriding materials, thermal sprayed materials, and sputter-coated materials. Plastically processed materials include cold-worked materials and hot-worked materials. And heat-treated materials include quenched materials, tempered materials, and annealed materials. In the above embodiment, it is possible to detect internal defects in such various processed materials.

10: Internal defect detection device 11: Calculation unit 12: Measurement unit 13: Determination unit 14: Joining material (processed material)
14A Surface 24 Unwelded area (internal defect)
S1: Calculation step S2: Measurement step S3: Judgment step

Claims (2)

A calculation step of calculating a residual stress distribution on a surface of the processed material assuming an internal defect of any position and size from a known inherent strain distribution of the processed material;
A measuring step of measuring a residual stress distribution on a surface of the processed material which is an object of internal defect detection;
a determination step of comparing the calculated value of the residual stress distribution calculated in the calculation step with the actual measured value of the residual stress distribution measured in the measurement step to determine whether or not there is an internal defect;
A method for detecting an internal defect comprising: A calculation unit that calculates a residual stress distribution on a surface of a processed material assuming an internal defect of any position and size from a known inherent strain distribution of the processed material;
A measuring unit that measures a residual stress distribution on a surface of the processed material which is an object of internal defect detection;
a determination unit that compares the calculated value of the residual stress distribution calculated by the calculation unit with the actual measured value of the residual stress distribution measured by the measurement unit to determine whether or not there is an internal defect;
An internal defect detection device having