JP7506324B2 - Fracture prediction method, fracture prediction device, fracture prediction program, and recording medium - Google Patents

Description

The present invention relates to a fracture prediction method and fracture prediction device for components joined at spot welds, as well as a fracture prediction program and a recording medium.

In recent years, the automotive industry has been faced with an urgent need to develop a body structure that can reduce the impact of a collision. In this case, it is important that the structural components of the vehicle absorb the impact energy. The main structure for absorbing the impact energy during a vehicle collision is a structure in which steel plates are formed by press forming or the like, and then the components are spot welded to create a closed cross section. The spot welds must be strong enough to maintain the closed cross section of the components without easily breaking even under the complex deformation and load conditions that occur during a collision. In order to study and design such vehicle body structures through simulation, it is necessary to be able to accurately predict the breakage of spot welds in vehicle collision simulations.

Japanese Patent No. 4150383 Japanese Patent No. 4133956 Japanese Patent No. 4700559 Patent No. 4418384 Patent No. 6330967 Japanese Patent No. 6202232

Tensile tests using shear joint, cross joint, and L-joint test pieces are used as a simple method for measuring the fracture strength of spot welds. The shear joint test measures the strength when the test piece is primarily subjected to shear force, leading to fracture. The cross joint test measures the strength when the test piece is primarily subjected to axial force, leading to fracture. The L-joint test measures the strength when the test piece is primarily subjected to moment, leading to fracture. Patent documents 1 to 4 discuss methods for predicting fracture of spot welds for each input format.

However, when considering the collision deformation of a full vehicle model of an automobile, for example, various input loads are applied to the components, causing complex deformation. Therefore, the input applied to the spot weld is not a shear force, axial force, or moment applied alone, but a combination of these inputs.

For example, Patent Documents 1, 2, and 3 disclose methods for determining whether a spot weld has broken based on a cross tensile test and a shear tensile test, and Patent Documents 4 and 5 disclose methods for determining whether a spot weld has broken based on an L-shaped tensile test. However, no technology has yet been devised for cases where axial and shear forces are applied in combination, or where a moment is also applied in combination.

Patent Document 6 also discloses a method for acquiring a parameter called effective width (the width at which a spot weld bears a load according to the component shape) used in fracture prediction depending on the direction of the load applied to the spot weld. However, this only deals with cases where the direction of the load applied to the spot weld changes depending on the component shape (for example, the longitudinal direction or lateral direction of the component), and does not disclose any technology for cases where a spot weld is subjected to a complex input (axial force, shear force, moment).

The present invention has been made in consideration of the above problems, and aims to provide a fracture prediction method and fracture prediction device, as well as a fracture prediction program and recording medium, that can accurately predict fracture of spot welds that model spot welds with high precision, for example when predicting the collision deformation of automobile components on a computer.

In order to solve the above problems, we have intensively studied and come up with the following aspects of the invention. The gist of the present invention is as follows:

1. A method for predicting fracture of a spot weld in a case where members joined by a spot weld are deformed and a load is applied to the spot weld, leading to fracture, comprising:
A first step of acquiring a first breaking value, a second breaking value, and a third breaking value applied to the spot weld at a breaking load;
A second step of creating plot points having axial force component values and shear force component values of the first fracture value and the second fracture value on a plane having two axes of axial force and shear force, and acquiring a limit line including at least these two plot points as a first fracture limit line;
A third step of creating plot points having axial force component values and moment component values of the first fracture value and the third fracture value on a plane having two axes of axial force and moment, and acquiring a limit line including at least these two plot points as a second fracture limit line;
A fourth step of creating plot points having shear force component values and moment component values of the second fracture value and the third fracture value on a plane having two axes of shear force and moment, and obtaining a limit line including at least these two plot points as a third fracture limit line;
A fifth step of acquiring a limit line including at least the first fracture value and the second fracture value as a fourth fracture limit line in a space having three axes of axial force, shear force, and moment;
A sixth step of acquiring a surface of a three-dimensional space formed by three axes of a shear force, an axial force, and a moment, and the first fracture limit line, the second fracture limit line, the third fracture limit line, and the fourth fracture limit line as a fracture limit surface;
A seventh step of obtaining a calculated axial force component, a calculated shear force component, and a calculated moment component applied to the spot weld in a deformation simulation of the member;
an eighth step of determining whether or not a fracture has occurred in the spot weld of the component based on whether or not a calculated fracture point having the calculated axial force component, the calculated shear force component, and the calculated moment component exceeds the fracture limit surface;
A fracture prediction method comprising:

2. The second step includes:
The fracture prediction method according to 1., characterized in that plot points having axial force component values and shear force component values of the first fracture value and the second fracture value are created on a plane having axial force and shear force as two axes, and a straight line including at least these two plot points is obtained as the first fracture limit line.

3. The second step includes:
A tensile test was performed using a cross joint type and a pure shear joint type test piece having the same material and plate thickness as the member and the same nugget diameter of the spot weld as the member,
2. The fracture prediction method according to 2., characterized in that axial force component values and shear force component values of the first fracture value and the second fracture value are obtained by a simulation analysis that reproduces the tensile test.

4. The second step includes:
Tensile tests were conducted using test pieces of cross joint type and pure shear joint type with multiple materials, plate thicknesses, and nugget diameters of spot welds.
2. The fracture prediction method according to claim 2, characterized in that an axial force component value and a shear force component value of the first fracture value and the second fracture value are obtained using a database that accumulates information obtained by a simulation analysis that reproduces the tensile test.

5. The first and second steps include:
A tensile test is performed using two or more joint test pieces that are made of the same material and have the same plate thickness as the member, have the same nugget diameter as the spot welds as the member, and can apply axial and shear forces to the spot welds in a composite manner;
The fracture prediction method according to 1., characterized in that a fracture value is obtained by a simulation analysis that reproduces the tensile test, two or more plot points having axial force component values and shear force component values of the fracture value are created, and an approximation line obtained by linearly approximating these plot points is obtained as a first fracture limit line, and an intersection of this approximation line and the axial force axis is obtained as the first fracture value, and an intersection of this approximation line and the shear force axis is obtained as the second fracture value.

6. The third step includes:
The fracture prediction method according to 1., characterized in that plot points having axial force component values and moment component values of the first fracture value and the third fracture value are created on a plane having axial force and moment as two axes, an elliptical approximation including these two points is created, and the elliptical approximation is obtained as the second fracture limit line.

7. The third step includes:
Tensile tests were performed using test pieces of a cross joint type and an L-joint type, which were made of the same material and had the same plate thickness as the member and had the same nugget diameter of the spot weld as the member,
The fracture prediction method according to 6., characterized in that axial force component values and moment component values of the first fracture value and the third fracture value are obtained by a simulation analysis that reproduces the tensile test.

8. The first step comprises:
Tensile tests were conducted using test pieces of cross joint type and L-joint type with multiple materials, plate thicknesses, and nugget diameters of spot welds.
6. The fracture prediction method according to claim 6, characterized in that an axial force component value and a moment component value of the first fracture value and the third fracture value are obtained using a database that accumulates information obtained by a simulation analysis that reproduces the tensile test.

9. The fracture prediction method according to any one of 6. to 8., characterized in that the third fracture value is a value obtained by projecting the L-joint fracture load value plotted on a plane having axial force and moment as two axes onto a moment axis.

10. A device for predicting fracture of a spot weld when a member joined by a spot weld is deformed, a load is applied to the spot weld, and the spot weld is fractured, comprising:
a breaking value acquisition unit that acquires a first breaking value, a second breaking value, and a third breaking value that are applied to the spot welded portion when a breaking load is applied;
Plot points having axial force component values and shear force component values of the first fracture value and the second fracture value are created on a plane having two axes of axial force and shear force, and a limit line including at least these two plot points is obtained as a first fracture limit line;
Plot points having axial force component values and moment component values of the first fracture value and the third fracture value are created on a plane having two axes of axial force and moment, and a limit line including at least these two plot points is obtained as a second fracture limit line;
Plot points having shear force component values and moment component values of the second rupture value and the third rupture value are created on a plane having two axes of shear force and moment, and a limit line including at least these two plot points is obtained as a third rupture limit line;
A limit line including at least the first fracture value and the second fracture value is obtained as a fourth fracture limit line in a space having three axes of axial force, shear force, and moment.
A breaking limit line acquisition unit;
a fracture limit surface acquisition unit that acquires a surface of a three-dimensional space formed by three axes of shear force, axial force, and moment, and the first fracture limit line, the second fracture limit line, the third fracture limit line, and the fourth fracture limit line as a fracture limit surface;
a deformation simulation execution unit that acquires a calculated axial force component, a calculated shear force component, and a calculated moment component applied to the spot weld in a deformation simulation of the member;
a fracture determination unit that determines whether or not a fracture has occurred in the spot weld of the member based on whether or not a calculated fracture point having the calculated axial force component, the calculated shear force component, and the calculated moment component exceeds the fracture limit surface;
A fracture prediction device comprising:

11. The breaking limit line acquisition unit
The fracture prediction device according to item 10. is characterized in that plot points having axial force component values and shear force component values of the first fracture value and the second fracture value are created on a plane having axial force and shear force as two axes, and a straight line including at least these two plot points is obtained as the first fracture limit line.

12. A tensile test was carried out using test pieces of a cross joint type and a pure shear joint type, which were made of the same material and plate thickness as the above-mentioned member and had the same nugget diameter of the spot weld as the above-mentioned member;
The breaking limit line acquisition unit is
12. The fracture prediction device according to 11., characterized in that an axial force component value and a shear force component value of the first fracture value and the second fracture value are obtained by a simulation analysis that reproduces the tensile test.

13. Tensile tests were conducted using test pieces of cruciform joint type and pure shear joint type with multiple materials, plate thicknesses, and nugget diameters of spot welds.
12. The fracture prediction device according to claim 11, characterized in that the fracture limit line acquisition unit acquires axial force component values and shear force component values of the first fracture value and the second fracture value using a database that accumulates information obtained by a simulation analysis that reproduces the tensile test.

14. A tensile test is carried out using two or more joint test pieces that are made of the same material and plate thickness as the member, have the same nugget diameter as the spot welds as the member, and can apply axial and shear forces to the spot welds in a composite manner;
The break value acquisition unit and the break limit line acquisition unit are
The fracture prediction device according to 10. is characterized in that a fracture value is obtained by a simulation analysis that reproduces the tensile test, two or more plot points having axial force component values and shear force component values of the fracture value are created, an approximation line obtained by linearly approximating these plot points is obtained as a first fracture limit line, and an intersection of this approximation line with the axial force axis is obtained as the first fracture value, and an intersection of this approximation line with the shear force axis is obtained as the second fracture value.

15. The breaking limit line acquisition unit is
The fracture prediction device according to item 10. is characterized in that plot points having axial force component values and moment component values of the first fracture value and the third fracture value are created on a plane having axial force and moment as two axes, an elliptical approximation including these two points is created, and the second fracture limit line is obtained.

16. Tensile tests were conducted using test pieces of cross joint type and L-joint type, which were made of the same material and plate thickness as the above-mentioned member and had the same nugget diameter of the spot weld as the above-mentioned member,
The breaking limit line acquisition unit is
15. The fracture prediction device according to claim 15, characterized in that axial force component values and moment component values of the first fracture value and the third fracture value are obtained by a simulation analysis that reproduces the tensile test.

17. Tensile tests were conducted using test pieces of cross joint type and L-joint type with multiple materials, plate thicknesses, and nugget diameters of spot welds.
15. The fracture prediction device according to claim 15, characterized in that the fracture value acquisition unit acquires axial force component values and moment component values of the first fracture value and the third fracture value using a database that accumulates information obtained by a simulation analysis that reproduces the tensile test.

18. The fracture prediction device according to any one of 15 to 17, characterized in that the third fracture value is a value obtained by projecting the L-joint fracture load value plotted on a plane having axial force and moment as two axes onto a moment axis.

19. A program for predicting fracture of a spot weld when a member joined by a spot weld is deformed, a load is applied to the spot weld, and the spot weld is fractured, comprising:
A first step of acquiring a first breaking value, a second breaking value, and a third breaking value applied to the spot weld at a breaking load;
A second step of creating plot points having axial force component values and shear force component values of the first fracture value and the second fracture value on a plane having two axes of axial force and shear force, and obtaining a limit line including at least these two plot points as a first fracture limit line;
A third step of creating plot points having axial force component values and moment component values of the first fracture value and the third fracture value on a plane having two axes of axial force and moment, and obtaining a limit line including at least these two plot points as a second fracture limit line;
A fourth step of creating plot points having shear force component values and moment component values of the second fracture value and the third fracture value on a plane having two axes of shear force and moment, and obtaining a limit line including at least these two plot points as a third fracture limit line;
A fifth step of acquiring a limit line including at least the first fracture value and the second fracture value as a fourth fracture limit line in a space having three axes of axial force, shear force, and moment;
A sixth step of acquiring a surface of a three-dimensional space formed by three axes of a shear force, an axial force, and a moment, and the first fracture limit line, the second fracture limit line, the third fracture limit line, and the fourth fracture limit line as a fracture limit surface;
A seventh step of acquiring a calculated axial force component, a calculated shear force component, and a calculated moment component applied to the spot weld in a deformation simulation of the member;
an eighth step of determining whether or not a fracture has occurred in the spot weld of the component based on whether or not a calculated fracture point having the calculated axial force component, the calculated shear force component, and the calculated moment component exceeds the fracture limit surface;
A fracture prediction program characterized by causing a computer to execute the above.

20. The second step comprises:
19. The fracture prediction program according to claim 19, characterized in that plot points having axial force component values and shear force component values of the first fracture value and the second fracture value are created on a plane having two axes of axial force and shear force, and a straight line including at least these two plot points is obtained as the first fracture limit line.

21. A tensile test was carried out using test pieces of a cross joint type and a pure shear joint type, which were made of the same material and plate thickness as the above-mentioned member and had the same nugget diameter of the spot weld as the above-mentioned member;
The second step includes:
20. The fracture prediction program according to claim 20, characterized in that an axial force component value and a shear force component value of the first fracture value and the second fracture value are obtained by a simulation analysis that reproduces the tensile test.

22. Tensile tests were conducted using test pieces of cruciform joint type and pure shear joint type with multiple materials, plate thicknesses, and nugget diameters of spot welds.
20. The fracture prediction program according to claim 20, characterized in that the second step acquires axial force component values and shear force component values of the first fracture value and the second fracture value using a database that accumulates information obtained by a simulation analysis that reproduces the tensile test.

23. A tensile test is carried out using two or more joint test pieces that are made of the same material and plate thickness as the member, have the same nugget diameter as the spot welds as the member, and can apply axial and shear forces to the spot welds in a composite manner;
The first and second steps include:
19. The fracture prediction program according to claim 19, characterized in that a fracture value is obtained by a simulation analysis that reproduces the tensile test, two or more plot points having axial force component values and shear force component values of the fracture value are created, an approximation line obtained by linearly approximating these plot points is obtained as a first fracture limit line, and an intersection of this approximation line with the axial force axis is obtained as the first fracture value, and an intersection of this approximation line with the shear force axis is obtained as the second fracture value.

24. The third step comprises:
19. The fracture prediction program according to claim 19, characterized in that plot points having axial force component values and moment component values of the first fracture value and the third fracture value are created on a plane having axial force and moment as two axes, an elliptical approximation including these two points is created, and the elliptical approximation is obtained as the second fracture limit line.

25. A tensile test was carried out using a cross joint type and an L joint type test piece that were made of the same material and plate thickness as the above-mentioned member and had the same nugget diameter of the spot weld as the above-mentioned member,
The third step comprises:
24. The fracture prediction program according to item 24, characterized in that axial force component values and moment component values of the first fracture value and the third fracture value are obtained by a simulation analysis that reproduces the tensile test.

26. Tensile tests were conducted using test pieces of cross joint type and L-joint type with multiple materials, plate thicknesses, and nugget diameters of spot welds.
The fracture prediction program according to claim 24, characterized in that the first step obtains axial force component values and moment component values of the first fracture value and the third fracture value using a database that accumulates information obtained by a simulation analysis that reproduces the tensile test.

27. The fracture prediction program according to any one of claims 24 to 26, characterized in that the third fracture value is a value obtained by projecting an L-joint fracture load value plotted on a plane having axial force and moment as two axes onto a moment axis.

28. A computer-readable recording medium having a fracture prediction program according to any one of 19. to 27. recorded thereon.

According to the present invention, for example, when predicting the collision deformation of automobile components on a computer, it is possible to accurately predict the fracture of spot welds that are modeled after spot welding with high precision.

FIG. 2 is a schematic diagram showing a cruciform joint tensile test. FIG. 1 is a schematic diagram showing a pure shear type joint tensile test. FIG. 2 is a schematic diagram showing a shear joint tensile test. FIG. 1 is a schematic diagram showing a KS2 test piece. FIG. 1 is a schematic diagram showing a KS2 tensile test. FIG. 2 is a perspective view showing each fracture point on a first plane having two axes of axial force and shear force. FIG. 1 is a perspective view showing an overview of an L-joint type tensile test. FIG. 2 is a schematic diagram showing a U-shaped peel type tensile test. FIG. 4 is a schematic characteristic diagram showing each breaking point on a second plane having an axial force and a moment as two axes. FIG. 11 is a characteristic diagram showing each breaking point on a third plane having two axes of shear force and moment. FIG. 1 is a characteristic diagram showing a CTS break point, a pure shear break point, and break points at different angles obtained from a KS2 test on a third plane having two axes of shear force and moment. 1 is a block diagram showing a fracture prediction device according to a first embodiment. FIG. FIG. 2 is a flow diagram showing a fracture prediction method according to the first embodiment. FIG. 4 is a characteristic diagram showing a first fracture limit line obtained in the first embodiment. FIG. 4 is a characteristic diagram showing a second fracture limit line obtained in the first embodiment. FIG. 11 is a characteristic diagram showing a third fracture limit line obtained in the first embodiment. FIG. 4 is a characteristic diagram showing a fracture limit surface obtained in the first embodiment. FIG. 2 is a block diagram showing a fracture prediction device according to a modified example of the first embodiment. FIG. 11 is a flowchart showing a fracture prediction method according to a modified example of the first embodiment. FIG. 11 is a schematic diagram showing a hat member two-point bending test, a hat member shape, and spot welding positions of the second embodiment. 13 is a schematic diagram (the top diagram is a photograph) showing the result of three-point bending of the hat member of the second embodiment and the location of spot welding fracture. FIG. 2 is a schematic diagram showing the internal configuration of a personal user terminal device.

[Basic outline of the present invention]
The present inventors conducted studies using a specified test piece in order to establish a fracture prediction method that takes into account a case in which multiple types of inputs are applied in combination to a spot weld, which is a joint between components.

Here, of the multiple types of inputs (axial force, shear force, moment), we focused on axial force and shear force to obtain the CTS fracture value and pure shear fracture value applied to the spot weld at the fracture load. Specifically, we conducted joint tensile tests using test pieces of the cross joint type shown in Figure 1 and the pure shear joint type shown in Figure 2, which were made of the same material and thickness as the component to be fractured, and obtained the fracture load (maximum load) of the spot weld.

Then, a finite element analysis (FEM analysis) was performed using an FEM model that reproduced the joint tensile test, and a forced tensile displacement was applied to the FEM model until the load at the point where the forced tensile displacement was applied reached the fracture load (maximum load) of each joint obtained from the experiment. The axial force component, shear force component, and moment component generated at the spot weld at that time were obtained and used as the CTS fracture value and pure shear fracture value. Of the values obtained in this way, the axial force component value and shear force component value were plotted on a plane with the axial force and shear force as the two axes, and the CTS fracture point (shear force component value is approximately zero) and pure shear fracture point (axial force component value is approximately zero) were obtained.

Furthermore, a shear joint tensile test was conducted using other shear joint type TSS test pieces, as shown in Figure 3, made of the same material and plate thickness as the above-mentioned components, to obtain the breaking load (maximum load) of the spot weld. 201 to 203 in Figure 3 are the same as 201 to 203 in Figure 2.

Then, an FEM analysis was performed using an FEM model that reproduced the joint tensile test, and a forced tensile displacement was applied to the FEM model until the load at the point where the forced tensile displacement was applied reached the breaking load (maximum load) obtained from the experiment. The axial force component, shear force component, and moment component generated at the spot weld at that time were obtained and taken as the TSS breaking value. Of the values obtained in this way, the axial force value and shear force value were plotted on the above plane as the axial force component value and shear force component value at the TSS breaking point.

Next, the inventors carried out a joint tensile test using the KS2 test piece as shown in FIG.
A KS2 test piece 221 is used, which is made by placing KS2 test pieces 211 and 212, which have a U-shaped cross-sectional shape made of the same material and plate thickness as the above-mentioned members back to back and joining the central portion 213 by spot welding.

As shown in Figure 5, the inventor attached the KS2 test piece 221 to a specified tensile testing machine at different angles, applied a tensile force F downward in Figure 5, performed joint tensile tests, and obtained the breaking load (maximum load) of the spot weld. The installation angles of the KS2 test piece 221 (the angle of the joint surface of the KS2 test pieces 211 and 212 relative to the tensile force direction) were 0°, 30°, 60°, and 90°. 0° is a test that is almost equivalent to a shear joint tensile test using a TSS test piece, and 90° is a test that is almost equivalent to a cross joint tensile test using a CTS test piece.

An FEM model that replicated the KS2 test was then created and subjected to FEM analysis. A forced tensile displacement was applied to the FEM model until the load at the point where the forced tensile displacement was applied reached the breaking load (maximum load) of each joint obtained from the experiment. The axial force component, shear force component, and moment component generated at the spot weld at that time were obtained, and the axial force and shear force values obtained in this way were plotted on the above plane as the axial force component and shear force component values of each breaking point.

The above results are shown in Figure 6. On a plane with the shear force and axial force as the two axes, it was found that the TSS break point and each break point with a different angle obtained from the KS2 test are interpolated between the CTS break point and the pure shear break point, and these points can be approximated by a straight line.

Obtaining multiple breaking points with different angles using KS2 tests etc. requires a considerable amount of effort and is not easy. On the other hand, CTS breaking points, pure shear breaking points, TSS breaking points etc. can be obtained relatively easily in a short amount of time.

In light of this knowledge, the inventors came up with the idea of obtaining at least two points, the CTS fracture point and the pure shear fracture point, and obtaining a first fracture limit line based on these fracture points. It is believed that the first fracture limit line obtained in this way accurately defines the fracture limit when a shear force and an axial force are applied to a component in a composite manner. In this way, it is possible to easily obtain a first fracture limit line that accurately represents the composite fracture limit when an axial force and a shear force are applied to a test piece, without obtaining each fracture point by a KS2 test or the like.

On the other hand, based on this knowledge, two or more break points for each angle of the CTS break point, pure shear break point, TSS break point, and KS2 test are obtained, and the limit line obtained by linearly approximating these break points is almost equivalent to the first break limit line obtained from the CTS break point and pure shear break point, so this may be used as the first break limit line. Also, the intersection of the limit line obtained by linear approximation in this way with the axial force axis may be used as the first break value, and the intersection with the shear force axis may be used as the second break value.

Furthermore, the present inventors have attempted to expand the consideration of the composite fracture limit.
Here, of the multiple types of inputs (axial force, shear force, moment), we focus on the axial force and moment, and obtain the CTS fracture value, LTS fracture value, and fracture value from a U-peel test applied to the spot weld at the time of fracture load, and use these to obtain a second fracture limit line on a plane (second plane) with the axial force and moment as the two axes.

The second breaking limit line is created as follows.
In order to obtain the LTS fracture value applied to the spot weld at the fracture load, a joint tensile test was conducted using an L-joint type test piece as shown in FIG. 7, which was made of the same material and had the same plate thickness as the component to be fractured, and the fracture load (maximum load) of the spot weld was obtained.

Then, a finite element analysis (FEM analysis) was performed using an FEM model that reproduced the joint tensile test, and a forced tensile displacement was applied to the FEM model until the load at the location where the forced tensile displacement was applied reached the fracture load (maximum load) of each joint obtained from the experiment. The axial force component, shear force component, and moment component generated at the spot weld at that time were obtained and used as the LTS fracture value (the shear force component value was approximately zero). Of the values obtained in this way, the axial force value and moment value were plotted on the second plane described above to obtain the LTS fracture point. The CTS fracture value described above (the moment component value was approximately zero) was also plotted on the second plane to obtain the CTS fracture point.

Furthermore, a joint tensile test was conducted using a U-shaped peel type test piece shown in Figure 8, which was made of the same material and thickness as the above-mentioned members, to obtain the breaking load (maximum load) of the spot weld. The test piece used was a U-shaped joint type test piece 401, as shown in Figure 8, in which a pair of base materials 401a, 401b with a U-shaped cross section are placed back to back and joined at a spot weld 402. A tensile test was conducted on this test piece in the direction indicated by the tensile direction 403 until the test piece broke. At this time, the breaking load of the test piece in the tensile direction 403 was measured.

Then, an FEM analysis was performed using an FEM model that reproduced the joint tensile test, and a forced tensile displacement was applied to the FEM model until the load at the point where the forced tensile displacement was applied reached the fracture load (maximum load) obtained from the experiment. The axial force component, shear force component, and moment component generated at the spot weld at that time were obtained and taken as the U-shaped peel fracture value. Of the values obtained in this way, the axial force value and moment value were plotted on the above plane as the axial force component value and moment component value at the U-shaped peel fracture point.

The above results are shown in Figure 9. It was found that on a plane with axial force and moment as the two axes, the fracture points obtained from the U-peel test were located on the same curve, interpolating between the LTS fracture point and the CTS fracture point. Furthermore, it was found that this curve can be expressed using an elliptical approximation.

Obtaining the breaking point by the U-peel test requires time-consuming preparation of test pieces, whereas the LTS breaking point, CTS breaking point, etc. can be obtained relatively easily in a short time.
In view of this finding, the inventors have come up with the idea of obtaining at least two points, the LTS break point and the CTS break point, or three points, the LTS break point, the CTS break point, and the U-shaped peel break point, and further obtaining a curve including these points to obtain a second fracture limit line. To obtain a more accurate result, the second fracture limit line may be obtained as an elliptical curve using an elliptical approximation formula.

Furthermore, since it is considered that a moment larger than the moment in the tensile test using the L-shaped joint type is not generated, substantially the same results can be obtained even if the point obtained by projecting the LTS fracture point onto the moment axis is used as the third fracture value. In other words, the second fracture limit line can be obtained by obtaining two points, the point obtained by projecting the LTS fracture point onto the moment axis and the CTS fracture point, or the three points obtained by projecting the LTS fracture point onto the moment axis, the CTS fracture point, and the U-shaped peel fracture point, and obtaining a curve including these points. In addition, to obtain more accurate results, the second fracture limit line may be obtained as an elliptical curve using an elliptical approximation formula.
The second fracture limit line obtained in this manner is considered to accurately define the fracture limit when an axial force and a moment are applied to a member in combination.

Here, out of the multiple types of inputs (axial force, shear force, moment), we focus on shear force and moment, obtain the pure shear fracture value and LTS fracture value applied to the spot weld at the time of fracture load, and use these to obtain the third fracture limit line on a plane (third plane) with the shear force and moment as the two axes.

The third breaking limit line is created as follows.
As shown in Figure 10, the shear force component value and moment component value of the pure shear fracture value are plotted on the third plane, and the shear force component value and moment component value of the LTS fracture value are plotted on the moment axis of the third plane (the shear force component value is almost zero). Then, the straight line connecting these two points is obtained as the third fracture limit line. It is considered that the third fracture limit line obtained in this way accurately defines the fracture limit when a shear force and a moment are applied to the member in a composite manner.

Furthermore, in a space with three axes of axial force, shear force, and moment, a straight line connecting the CTS fracture point and the pure shear fracture point applied to the spot weld at the time of fracture load is obtained as the fourth fracture limit line.

The fourth fracture limit line is created as follows.
When the above CTS fracture value, pure shear fracture value, and shear force component value and moment component value of each fracture point with different angles obtained from the KS2 test are plotted on the third plane, it can be seen that they are plotted on a straight line connecting the CTS fracture value and the pure shear fracture value, as shown in FIG. 11. It is known that the axial force component value and the shear force component value of these fracture points are located on a straight line connecting the CTS fracture value and the pure shear fracture value even on a plane with axial force and shear force as two axes, as shown in FIG. 6. From the above, it can be said that these fracture points are located on a straight line connecting the two points of the CTS fracture value and the pure shear fracture value even in a space with axial force, shear force, and moment as three axes. The straight line connecting the two points of the CTS fracture value and the pure shear fracture value obtained in this way is obtained as the fourth fracture limit line.

The surface of the three-dimensional space formed by the three axes of shear force, axial force, and moment, and the first, second, third, and fourth fracture limit lines obtained as described above, is obtained as the fracture limit surface (the surface surrounded by the second, third, and fourth fracture limit lines is a convex curved surface). The fracture limit surface obtained in this way is considered to accurately define the fracture limit when axial force, shear force, and moment are applied to the test specimen in a combined manner.

Specific embodiments are described in detail below with reference to the drawings.

[First embodiment]
Fig. 12 is a block diagram showing a fracture prediction device according to the first embodiment Fig. 13 is a flow chart showing a fracture prediction method according to the first embodiment.

As shown in FIG. 12 , the fracture prediction device according to this embodiment includes a fracture point acquisition unit 11, each fracture limit line acquisition unit 12, a fracture limit surface acquisition unit 13, a deformation simulation execution unit 14, and a fracture determination unit 15.
In the fracture prediction method according to the present embodiment, as shown in FIG. 13, steps S11 to S14 and step S15 are performed, and then fracture determination is made in step S16.

In this embodiment, using the component to be subjected to fracture judgment, fracture prediction is performed for the spot weld when the components joined at the spot weld are deformed, a load is applied to the spot weld, and the spot weld breaks.

First, tensile tests are performed using test pieces of the cross joint type, pure shear joint type, and L-joint type (step S11).

In the tensile test, a cross joint type test piece is used to measure the axial force applied to the spot weld when the breaking load is applied, a shear joint type test piece is used to measure the pure shear force applied to the spot weld when the breaking load is applied, and an L-joint type test piece is used to measure the moment applied to the spot weld when the breaking load is applied. These test pieces are made of the same material and thickness as the above-mentioned components that are the subject of the fracture judgment, and have the same nugget diameter of the spot weld.

FIG. 1 is a perspective view showing an outline of a tensile test using a cross joint type.
The test specimen is made by stacking two steel plates, which are base materials 102, and spot welding them to form a nugget 101. A tensile test is performed on this test specimen in the direction indicated by the arrow 103 until the test specimen breaks. At this time, the breaking load (maximum load) of the test specimen in the tensile direction 103 is measured.

FIG. 2 is a perspective view showing an outline of a tensile test using a pure shear joint type.
The test piece is made by stacking two steel plates, which are base materials 202, and spot welding them to form a nugget 201. When a tensile test is performed using a shear joint test piece, the steel plate warps and rotates at the spot weld when viewed from the side, generating not only shear force but also axial force. In this embodiment, a tensile test is performed in a state where the shear joint test piece is sandwiched between predetermined thick plates 204 and 205 so that the steel plate does not warp or rotate, and the breaking load of the test piece in the tensile direction 203 in FIG. 2 is measured.

FIG. 7 is a perspective view showing an outline of a tensile test using an L-shaped joint type.
The test piece is bent into an L-shape to form a flange portion 302 with a length L2, and the base materials 301a and 301b are aligned in opposite directions and spot welded to form a nugget 304. Both ends 303a and 303b are pulled until the periphery of the nugget 304 breaks, and the breaking load (maximum load) is measured.

Following the tensile test, in step S12, an FEM analysis is performed to reproduce the joint tensile test using an FEM model. In the FEM analysis, a forced tensile displacement is applied until the load at the portion that provides the tensile boundary condition becomes the same as the breaking load (maximum load) obtained from the experiment. The breaking point acquisition unit 11 acquires, through the FEM analysis in step S12, the CTS breaking value, which is the first breaking value corresponding to the tensile test using the cross joint type, the pure shear breaking value, which is the second breaking value corresponding to the tensile test using the pure shear joint type, and the LTS breaking value, which is the third breaking value corresponding to the tensile test using the L-shaped joint type.

As shown in Figure 14, the break point acquisition unit 11 plots the CTS break value and the pure shear break value as the CTS break point (N _CTS , 0) and the pure shear break point (0, S _pure ) on a plane with axial force and shear force as two axes (n axis, s axis).

The break point acquisition unit 11 plots the CTS break value and the LTS break value as the CTS break point (N _CTS , 0) and the LTS break point (N LTS , M _LTS ), respectively, on a plane with axial force and moment as two axes (n _-axis , m-axis) as shown in Fig. 15. Here, since it is considered that no moment greater than the moment in a tensile test using an L-joint type will occur, the point where the LTS break point is projected onto the moment axis is defined as the LTS break point (0, M _LTS ) on the plane with shear force and moment as two axes (s-axis, m-axis).

As shown in Figure 16, the break point acquisition unit 11 plots the LTS break value and the pure shear break value as the LTS break point (0, M _LTS ) and the pure shear break point (S _pure , M _pure ), respectively, on a plane with the shear force and moment as two axes (s axis, m axis).

Next, the fracture limit line acquisition unit 12 acquires a straight line connecting the CTS fracture point and the pure shear fracture point as a first fracture limit line L1, a curve passing through the CTS fracture point (0, M _LTS ) and the LTS fracture point as a second fracture limit line L2, and a straight line connecting the LTS fracture point (0, M _LTS ) and the pure shear fracture point as a third fracture limit line L3 (step S13). The first fracture limit line L1, the second fracture limit line L2, and the third fracture limit line L3 are displayed in a space with the axial force, the shear force, and the moment as the three axes.

The fracture limit line L1 obtained in the above manner is shown in Fig. 14. The fracture limit line L1 obtained in this manner accurately defines the composite fracture limit due to the axial force and shear force that are compositely applied to the member to be fractured.
The fracture limit line L2 obtained in the above manner is shown in Fig. 15. The fracture limit line L2 obtained in this manner almost accurately defines the composite fracture limit due to the axial force and moment applied in a composite manner to the member to be subjected to fracture judgment.
The fracture limit line L3 obtained in the above manner is shown in Fig. 16. The fracture limit line L3 obtained in this manner almost accurately defines the composite fracture limit due to the shear force and moment compositely applied to the member to be fractured.

Furthermore, in step S13, the fracture limit line acquisition unit 12 acquires a straight line connecting at least the CTS fracture point and the pure shear force point in a space having three axes of axial force, shear force, and moment as the fourth fracture limit line L4.

Next, as shown in FIG. 17, the fracture limit surface acquisition unit 13 acquires the surface of the three-dimensional space formed by the three axes of shear force, axial force, and moment, and the first fracture limit line L1, the second fracture limit line L2, the third fracture limit line L3, and the fourth fracture limit line L4 obtained as described above as a fracture limit surface S (step S14). Here, in the fracture limit surface, the surface surrounded by the second fracture limit line L2, the third fracture limit line L3, and the fourth fracture limit line L4 becomes a convex curved surface. In FIG. 17, the second fracture limit line L2' for an arbitrary shear force is shown by a dashed line. The fracture limit surface obtained in this way accurately defines the fracture limit when an axial force, a shear force, and a moment are applied in combination to the member to be fractured.

Meanwhile, the deformation simulation execution unit 3 performs a deformation simulation analysis using FEM using an FEM model of the component to be subjected to fracture judgment, and obtains the axial force component, shear force component, and moment component applied to the spot weld of the component (step S15).

Then, the fracture determination unit 5 plots the input points consisting of the acquired axial force components, shear force components, and moment components in a space in which the fracture limit surface has been created, with the axial force, shear force, and moment components as the three axes, and determines whether or not a fracture has occurred in the spot weld of the component depending on whether or not the input points exceed the fracture limit surface (step S16).

As described above, according to this embodiment, since the actual collision deformation of a component that is the subject of fracture judgment is caused by the combined application of input loads of shear force, axial force, or moment, it is possible to easily and accurately predict whether or not a fracture will occur in the component, which is closer to reality, by analyzing the case in which these three types of inputs are combinedly applied to the component.
According to this embodiment, for example, when predicting the deformation of an automobile component due to a collision on a computer, it is possible to accurately predict the fracture of a spot welded portion in which the spot weld is modeled with high precision.

(Modification)
A modification of the first embodiment described above will now be described.
Fig. 18 is a block diagram showing a fracture prediction device according to this modified example, and Fig. 19 is a flow chart showing a fracture prediction method according to this modified example.

In this modified example, similar to the present embodiment described above, a component that is the subject of fracture judgment is used to predict fracture of a spot weld when the components joined at the spot weld deform and a load is applied to the spot weld, leading to fracture.
In this modification, the first embodiment is further expanded to disclose fracture prediction when three elements, axial force, shear force, and moment, are applied to a member in a composite manner.

In this modification, step S17 is performed instead of step S11, which is the first step of the present embodiment and involves performing a tensile test and FEM analysis.
In step S17, the fracture limit line acquisition unit 5 uses the fracture point database to acquire a CTS fracture value, which is the first fracture value corresponding to a tensile test using a cross joint type, a pure shear fracture value, which is the second fracture value corresponding to a tensile test using a pure shear joint type, an LTS fracture value, which is the third fracture value corresponding to a tensile test using an L-joint type, and other shear joint types, a TSS fracture value, fracture values at each angle in the KS2 test, and even a U-peel fracture value.

The fracture point database stores the results of tensile tests performed using a cross joint type, pure shear joint type, L joint type, TSS joint type, KS2 joint type, and U-peel joint type for a variety of materials, plate thicknesses, and nugget diameters of spot welds, as well as data on CTS fracture values, pure shear fracture values, LTS fracture values, TSS fracture values, fracture values for each angle in the KS2 test, and even U-peel fracture values obtained by FEM analysis in which the tensile tests are reproduced using an FEM model.
In this modified example, by utilizing this break point database, the CTS break value, pure shear break value, and LTS break value for the test piece corresponding to the component can be obtained efficiently in an easy and short time.

Second Embodiment
The effects of the first embodiment will be described below in comparison with a comparative example.

In this example, as shown in Figure 20, a three-point bending test was performed on a hat-shaped component with a height of 60 mm and a width of 120 mm. In the hat-shaped component, the hat-shaped cross-section steel plate and the flat steel plate serving as the back plate are spot-welded at 20 points on one side, for a total of 40 points on both sides. The spot pitch is 40 mm, and the flange width is 15 mm.

The material and thickness of the hat-shaped member are 1500 MPa tensile strength steel plate and 1.4 mm plate thickness for both the hat-shaped cross section steel plate and the flat steel plate. The nugget diameter of the spot weld is 4.7 mm. The hat-shaped member was supported by a fixed jig, the distance between the fulcrums of the fixed jig was set to 700 mm, and a 3-point bending test was performed by pressing an impactor with a radius of 50 mm against the flat steel plate side with a stroke of 150 mm.

In addition, using the same steel plate with a tensile strength of 1500 MPa and a thickness of 1.4 mm as the hat-shaped component, spot welding was performed so that the nugget diameter of the spot weld was 4.7 mm, and test pieces of cross joint type, pure shear joint type, and L-shaped joint type were produced. Tensile tests were performed on each joint to obtain the breaking load (maximum load).

Next, an FEM analysis was performed to reproduce the joint tensile test using an FEM model. In the FEM analysis, a forced tensile displacement was applied until the load at the part that provided the tensile boundary condition became the same as the breaking load (maximum load) obtained from the experiment. The CTS breaking point, which is the first breaking value corresponding to the tensile test using the cross joint type, the pure shear breaking point, which is the second breaking value corresponding to the tensile test using the pure shear joint type, and the LTS breaking point, which is the third breaking value corresponding to the tensile test using the L-shaped joint type, were obtained.

Furthermore, the obtained data on the CTS break point, pure shear break point, and LTS break point were loaded into the program according to the present invention to obtain a break limit line, and a break limit surface was obtained from the obtained break limit line.

Furthermore, an FEM model was created that reproduced the three-point bending experimental conditions of the hat-shaped component, and the program according to the present invention was incorporated to obtain the axial force components, shear force components, and moment components applied to each spot weld during deformation. Input points consisting of the obtained axial force components, shear force components, and moment components were plotted in a space with the fracture limit surface created, with the axial force, shear force, and moment components as the three axes. The presence or absence of fracture in the spot weld of the component was determined based on whether the input point exceeded the fracture limit surface.

The comparative program did not create a fracture limit surface, but instead acquired the axial force component, shear force component, and moment component applied to each spot weld during deformation. It simply compared the axial force component with the axial force value at the CTS fracture point, the shear force component with the shear force value at the pure shear fracture point, and the moment component with the moment value at the LTS fracture point, and determined whether or not a fracture had occurred at the spot weld based on whether any of the component values exceeded the fracture limit value.

Figure 21 shows the deformation state of the hat member and the fracture occurrence status of the spot welds after the impactor was pressed 150 mm. In the experiment, it was confirmed that fractures occurred in the spot welds in three places on one side (six places on both sides), and the back plate was curled up.

On the other hand, when FEM analysis incorporating the program of the present invention was used to predict the fracture of spot welds, it predicted spot weld fractures in three places on one side (six places on both sides) at the same locations as in the experiment, with a 100% agreement rate with the experiment (agreement rate = 40/40). On the other hand, when FEM analysis incorporating the program of the comparative example was used to predict the fracture of spot welds, it predicted spot weld fractures in three places on one side (six places on both sides) at the same locations as in the experiment, but in addition, it erroneously determined that spot weld fractures had occurred in two places on one side (four places on both sides) even in places where no fractures occurred in the experiment, with a 90% agreement rate with the experiment (agreement rate = 36/40).

These results show that the accuracy of spot weld fracture prediction is insufficient in conventional technology, which does not take into account the fact that complex inputs are applied to spot welds in actual components. In contrast, it has been confirmed that the use of the present invention makes it possible to accurately predict fracture at spot welds even in complex deformation states in which axial force, shear force, and moment are applied to the spot welds in a complex manner, as in actual components.

[Third embodiment]
The components of the fracture prediction device described above, that is, the fracture point acquisition units 11 and 16, the fracture limit line acquisition unit 12, the fracture limit surface acquisition unit 13, the deformation simulation execution unit 14, and the fracture determination unit 15 shown in Fig. 12 and Fig. 18, may be realized by dedicated hardware. Also, each of the above components may be configured by a memory and a CPU (Central Processing Unit), and may realize the functions of each component by loading a program for realizing the functions of each component into the memory and executing the program.

In addition, a program for implementing the functions of each of the above components (steps S11, S17 to S16 shown in Figures 13 and 19) may be recorded on a computer-readable recording medium, and the program recorded on the recording medium may be read into a computer system and executed to execute the processing of each of the above components. Note that the term "computer system" here includes hardware such as the OS and peripheral devices.

Furthermore, if the WWW system is used, the "computer system" may also include the home page providing environment (or display environment).
In addition, the term "computer-readable recording medium" refers to portable media such as flexible disks, optical magnetic disks, ROMs, and CD-ROMs, and storage devices such as hard disks built into computer systems. Furthermore, the term "computer-readable recording medium" may also include devices that dynamically hold a program for a short period of time, such as a communication line when transmitting a program via a network such as the Internet or a communication line such as a telephone line, and devices that hold a program for a certain period of time, such as volatile memory inside a computer system that serves as a server or client in such cases. Furthermore, the above-mentioned program may be one that realizes part of the above-mentioned functions, or may be one that can realize the above-mentioned functions in combination with a program already recorded in the computer system.

As a specific example, the model conversion device, the model conversion method, and the section collapse prediction method shown in this embodiment are implemented by a computer function 500 as shown in FIG.
The computer function 500 includes a CPU 501, a ROM 502, and a RAM 503. It also includes a controller (CONSC) 505 for an operation unit (CONS) 509, and a display controller (DISPC) 506 for a display (DISP) 510 serving as a display unit such as a CRT or LCD. It also includes a controller (DCONT) 507 for a hard disk (HD) 511 and a storage device (STD) 512 such as a flexible disk, and a network interface card (NIC) 508. These functional units 501, 502, 503, 505, 506, 507, and 508 are connected to each other via a system bus 504 so as to be able to communicate with each other.

The CPU 501 executes software stored in the ROM 502 or HD 511, or software supplied from the STD 512, thereby controlling each component connected to the system bus 504 in an overall manner. That is, the CPU 501 reads out and executes a processing program (structure design support program) for performing the operations described above from the ROM 502, HD 511, or STD 512, thereby performing control for realizing the operations in this embodiment. The RAM 503 functions as the main memory or work area of the CPU 501.

The CONSC 505 controls instruction input from the CONS 509. The DISPC 205 controls the display of the DISP 510. The DCONT 507 controls access to the HD 511 and STD 512 which store the boot program, various applications, user files, network management program, and the above-mentioned processing programs in this embodiment. The NIC 508 exchanges data bidirectionally with other devices on the network 513.
Instead of using a normal computer terminal device, a specific computer specialized for the fracture prediction device may be used.

Reference Signs List 1, 5, 11 Breaking point acquisition section 2, 12 Breaking limit line acquisition section 3, 14 Deformation simulation execution section 4, 15 Breaking judgment section 13 Breaking limit surface acquisition section 101, 201, 304 Nugget 102, 202, 401a, 401b Base material 103, 203, 403 Tensile direction 204, 205 Thick plate 211, 212, 221 KS2 test piece 302 Flange portion 303a, 303b Both ends 401 U-shaped joint type test piece 402 Spot welded portion

Claims (28)

A method for predicting fracture of a spot weld in a case where a load is applied to a spot weld due to deformation of members joined by a spot weld, leading to fracture of the spot weld, comprising:
A first step of acquiring a first breaking value, a second breaking value, and a third breaking value applied to the spot weld at a breaking load;
A second step of creating plot points having axial force component values and shear force component values of the first fracture value and the second fracture value on a plane having two axes of axial force and shear force, and acquiring a limit line including at least these two plot points as a first fracture limit line;
A third step of creating plot points having axial force component values and moment component values of the first fracture value and the third fracture value on a plane having two axes of axial force and moment, and acquiring a limit line including at least these two plot points as a second fracture limit line;
A fourth step of creating plot points having shear force component values and moment component values of the second fracture value and the third fracture value on a plane having two axes of shear force and moment, and obtaining a limit line including at least these two plot points as a third fracture limit line;
A fifth step of acquiring a limit line including at least the first fracture value and the second fracture value as a fourth fracture limit line in a space having three axes of axial force, shear force, and moment;
A sixth step of acquiring a surface of a three-dimensional space formed by three axes of a shear force, an axial force, and a moment, and the first fracture limit line, the second fracture limit line, the third fracture limit line, and the fourth fracture limit line as a fracture limit surface;
A seventh step of obtaining a calculated axial force component, a calculated shear force component, and a calculated moment component applied to the spot weld in a deformation simulation of the member;
an eighth step of determining whether or not a fracture has occurred in the spot weld of the component based on whether or not a calculated fracture point having the calculated axial force component, the calculated shear force component, and the calculated moment component exceeds the fracture limit surface;
A fracture prediction method comprising: The second step comprises:
The fracture prediction method according to claim 1, characterized in that plot points having axial force component values and shear force component values of the first fracture value and the second fracture value are created on a plane having axial force and shear force as two axes, and a straight line including at least these two plot points is obtained as the first fracture limit line. The second step comprises:
A tensile test was performed using a cross joint type and a pure shear joint type test piece having the same material and plate thickness as the member and the same nugget diameter of the spot weld as the member,
The fracture prediction method according to claim 2, characterized in that axial force component values and shear force component values of the first fracture value and the second fracture value are obtained by a simulation analysis that reproduces the tensile test. The second step comprises:
Tensile tests were conducted using test pieces of cross joint type and pure shear joint type with multiple materials, plate thicknesses, and nugget diameters of spot welds.
The fracture prediction method according to claim 2, characterized in that an axial force component value and a shear force component value of the first fracture value and the second fracture value are obtained using a database that accumulates information obtained by a simulation analysis that reproduces the tensile test. The first and second steps include:
A tensile test is performed using two or more joint test pieces that are made of the same material and have the same plate thickness as the member, have the same nugget diameter as the spot welds as the member, and can apply axial and shear forces to the spot welds in a composite manner;
The fracture prediction method according to claim 1, further comprising the steps of: obtaining a fracture value by a simulation analysis that reproduces the tensile test; creating two or more plot points having axial force component values and shear force component values of the fracture value; linearly approximating the plot points to obtain an approximation line as a first fracture limit line; and obtaining an intersection of this approximation line with an axial force axis as the first fracture value and an intersection of this approximation line with a shear force axis as the second fracture value. The third step is
The fracture prediction method according to claim 1, characterized in that plot points having axial force component values and moment component values of the first fracture value and the third fracture value are created on a plane having axial force and moment as two axes, an elliptical approximation including these two points is created, and the elliptical approximation is obtained as the second fracture limit line. The third step is
Tensile tests were performed using test pieces of a cross joint type and an L-joint type, which were made of the same material and had the same plate thickness as the member and had the same nugget diameter of the spot weld as the member,
The fracture prediction method according to claim 6, characterized in that the axial force component values and moment component values of the first fracture value and the third fracture value are obtained by a simulation analysis that reproduces the tensile test. The first step comprises:
Tensile tests were conducted using test pieces of cross joint type and L-joint type with multiple materials, plate thicknesses, and nugget diameters of spot welds.
The fracture prediction method according to claim 6, characterized in that an axial force component value and a moment component value of the first fracture value and the third fracture value are obtained using a database that accumulates information obtained by a simulation analysis that reproduces the tensile test. The fracture prediction method according to any one of claims 6 to 8, characterized in that the third fracture value is a value obtained by projecting the L-joint fracture load value plotted on a plane having axial force and moment as two axes onto the moment axis. A device for predicting fracture of a spot weld when a member joined by a spot weld is deformed, a load is applied to the spot weld, and the spot weld is fractured, comprising:
a breaking value acquisition unit that acquires a first breaking value, a second breaking value, and a third breaking value that are applied to the spot welded portion when a breaking load is applied;
Plot points having axial force component values and shear force component values of the first fracture value and the second fracture value are created on a plane having two axes of axial force and shear force, and a limit line including at least these two plot points is obtained as a first fracture limit line;
Plot points having axial force component values and moment component values of the first fracture value and the third fracture value are created on a plane having two axes of axial force and moment, and a limit line including at least these two plot points is obtained as a second fracture limit line;
Plot points having shear force component values and moment component values of the second rupture value and the third rupture value are created on a plane having two axes of shear force and moment, and a limit line including at least these two plot points is obtained as a third rupture limit line;
A limit line including at least the first fracture value and the second fracture value is obtained as a fourth fracture limit line in a space having three axes of axial force, shear force, and moment.
A breaking limit line acquisition unit;
a fracture limit surface acquisition unit that acquires a surface of a three-dimensional space formed by three axes of shear force, axial force, and moment, and the first fracture limit line, the second fracture limit line, the third fracture limit line, and the fourth fracture limit line as a fracture limit surface;
a deformation simulation execution unit that acquires a calculated axial force component, a calculated shear force component, and a calculated moment component applied to the spot weld in a deformation simulation of the member;
a fracture determination unit that determines whether or not a fracture has occurred in the spot weld of the member based on whether or not a calculated fracture point having the calculated axial force component, the calculated shear force component, and the calculated moment component exceeds the fracture limit surface;
A fracture prediction device comprising: The breaking limit line acquisition unit is
The fracture prediction device according to claim 10, characterized in that plot points having axial force component values and shear force component values of the first fracture value and the second fracture value are created on a plane having axial force and shear force as two axes, and a straight line including at least these two plot points is obtained as the first fracture limit line. Tensile tests were conducted using test pieces of a cross joint type and a pure shear joint type, which were made of the same material and plate thickness as the member and had the same nugget diameter of the spot weld as the member,
The breaking limit line acquisition unit is
The fracture prediction device according to claim 11, characterized in that axial force component values and shear force component values of the first fracture value and the second fracture value are obtained by a simulation analysis that reproduces the tensile test. Tensile tests were conducted using test pieces of cross joint type and pure shear joint type with multiple materials, plate thicknesses, and nugget diameters of spot welds.
The fracture prediction device according to claim 11, characterized in that the fracture limit line acquisition unit acquires axial force component values and shear force component values of the first fracture value and the second fracture value using a database that accumulates information obtained by a simulation analysis that reproduces the tensile test. A tensile test is carried out using two or more joint test pieces that are made of the same material and have the same plate thickness as the member, have the same nugget diameter as the spot welds as the member, and can apply axial and shear forces to the spot welds in a composite manner;
The break value acquisition unit and the break limit line acquisition unit are
The fracture prediction device according to claim 10, characterized in that a fracture value is obtained by a simulation analysis that reproduces the tensile test, two or more plot points having axial force component values and shear force component values of these fracture values are created, and an approximation line obtained by linearly approximating these plot points is obtained as a first fracture limit line, and an intersection of this approximation line with the axial force axis is obtained as the first fracture value, and an intersection of this approximation line with the shear force axis is obtained as the second fracture value. The breaking limit line acquisition unit is
The fracture prediction device according to claim 10, characterized in that plot points having axial force component values and moment component values of the first fracture value and the third fracture value are created on a plane having axial force and moment as two axes, an elliptical approximation including these two points is created, and the elliptical approximation is obtained as the second fracture limit line. Tensile tests were carried out using test pieces of a cross joint type and an L-joint type, which were made of the same material and plate thickness as the member and had the same nugget diameter of the spot weld as the member,
The breaking limit line acquisition unit is
The fracture prediction device according to claim 15, characterized in that the axial force component values and moment component values of the first fracture value and the third fracture value are obtained by a simulation analysis that reproduces the tensile test. Tensile tests were conducted using test pieces of cross joint type and L-joint type with multiple materials, plate thicknesses, and nugget diameters of spot welds.
The fracture prediction device described in claim 15, characterized in that the fracture value acquisition unit acquires axial force component values and moment component values of the first fracture value and the third fracture value using a database that accumulates information obtained by a simulation analysis that reproduces the tensile test. The fracture prediction device according to any one of claims 15 to 17, characterized in that the third fracture value is a value obtained by projecting the L-joint fracture load value plotted on a plane having axial force and moment as two axes onto the moment axis. A program for predicting fracture of a spot weld when a member joined by a spot weld is deformed, a load is applied to the spot weld, and the spot weld is fractured, the program comprising:
A first step of acquiring a first breaking value, a second breaking value, and a third breaking value applied to the spot weld at a breaking load;
A second step of creating plot points having axial force component values and shear force component values of the first fracture value and the second fracture value on a plane having two axes of axial force and shear force, and obtaining a limit line including at least these two plot points as a first fracture limit line;
A third step of creating plot points having axial force component values and moment component values of the first fracture value and the third fracture value on a plane having two axes of axial force and moment, and obtaining a limit line including at least these two plot points as a second fracture limit line;
A fourth step of creating plot points having shear force component values and moment component values of the second fracture value and the third fracture value on a plane having two axes of shear force and moment, and obtaining a limit line including at least these two plot points as a third fracture limit line;
A fifth step of acquiring a limit line including at least the first fracture value and the second fracture value as a fourth fracture limit line in a space having three axes of axial force, shear force, and moment;
A sixth step of acquiring a surface of a three-dimensional space formed by three axes of a shear force, an axial force, and a moment, and the first fracture limit line, the second fracture limit line, the third fracture limit line, and the fourth fracture limit line as a fracture limit surface;
A seventh step of acquiring a calculated axial force component, a calculated shear force component, and a calculated moment component applied to the spot weld in a deformation simulation of the member;
an eighth step of determining whether or not a fracture has occurred in the spot weld of the component based on whether or not a calculated fracture point having the calculated axial force component, the calculated shear force component, and the calculated moment component exceeds the fracture limit surface;
A fracture prediction program characterized by causing a computer to execute the above. The second step includes:
The fracture prediction program according to claim 19, characterized in that plot points having axial force component values and shear force component values of the first fracture value and the second fracture value are created on a plane having axial force and shear force as two axes, and a straight line including at least these two plot points is obtained as the first fracture limit line. Tensile tests were conducted using test pieces of a cross joint type and a pure shear joint type, which were made of the same material and plate thickness as the member and had the same nugget diameter of the spot weld as the member,
The second step includes:
The fracture prediction program according to claim 20, characterized in that axial force component values and shear force component values of the first fracture value and the second fracture value are obtained by a simulation analysis that reproduces the tensile test. Tensile tests were conducted using test pieces of cross joint type and pure shear joint type with multiple materials, plate thicknesses, and nugget diameters of spot welds.
The fracture prediction program according to claim 20, characterized in that the second step obtains axial force component values and shear force component values of the first fracture value and the second fracture value using a database that accumulates information obtained by a simulation analysis that reproduces the tensile test. A tensile test is carried out using two or more joint test pieces that are made of the same material and have the same plate thickness as the member, have the same nugget diameter as the spot welds as the member, and can apply axial and shear forces to the spot welds in a composite manner;
The first and second steps include:
The fracture prediction program according to claim 19, characterized in that a fracture value is obtained by a simulation analysis that reproduces the tensile test, two or more plot points having axial force component values and shear force component values of these fracture values are created, and an approximation line obtained by linearly approximating these plot points is obtained as a first fracture limit line, and an intersection of this approximation line with the axial force axis is obtained as the first fracture value, and an intersection of this approximation line with the shear force axis is obtained as the second fracture value. The third step comprises:
The fracture prediction program according to claim 19, characterized in that plot points having axial force component values and moment component values of the first fracture value and the third fracture value are created on a plane having axial force and moment as two axes, an elliptical approximation including these two points is created, and the elliptical approximation is obtained as the second fracture limit line. Tensile tests were carried out using test pieces of a cross joint type and an L-joint type, which were made of the same material and plate thickness as the member and had the same nugget diameter of the spot weld as the member,
The third step comprises:
The fracture prediction program according to claim 24, characterized in that axial force component values and moment component values of the first fracture value and the third fracture value are obtained by a simulation analysis that reproduces the tensile test. Tensile tests were conducted using test pieces of cross joint type and L-joint type with multiple materials, plate thicknesses, and nugget diameters of spot welds.
The fracture prediction program according to claim 24, characterized in that the first step obtains axial force component values and moment component values of the first fracture value and the third fracture value using a database that accumulates information obtained by a simulation analysis that reproduces the tensile test. The fracture prediction program according to any one of claims 24 to 26, characterized in that the third fracture value is a value obtained by projecting the L-joint fracture load value plotted on a plane with axial force and moment as two axes onto the moment axis. A computer-readable recording medium having the fracture prediction program according to any one of claims 19 to 27 recorded thereon.

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