JP2007304005A - Device, method, computer program for predicting rupture of spot welding part, and computer-readable recording medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To predict rupture of, for example, a spot weld zone of an automobile member, in finite element method analysis by a computer. <P>SOLUTION: A plate thickness, a nugget diameter of the spot welding, material strength of a parent material part, a part or the whole of rupture elongation, and either or both of a welding interval of a joint and a joint length orthogonal to the welding interval are input into a computer, based on a cross type tension test and/or a shearing type tension test, in a spot welding joint. The computer calculates a rupture strain parameter of the spot welding part in the cross type tension and/or the shearing type tension from input data, stores the rupture strain parameter of each steel kind in a parameter storage means, and introduces the rupture strain parameter stored in the parameter storage means into a rupture prediction formula acquired by modeling deformation in the periphery of the spot welding by a finite element method to determine the rupture of the spot welding part. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a spot welded portion failure prediction apparatus, method, computer program, and computer-readable recording medium for predicting breakage of a spot welded portion at the time of collision deformation in spot welding of a structural member for an automobile, for example. About.

  In recent years, in the automobile industry, the development of a vehicle body structure that can reduce injury to passengers during a collision has become an urgent issue. Such a vehicle body structure excellent in collision safety can be realized by absorbing the impact energy at the time of collision by a structural member other than the passenger compartment to ensure the living space by minimizing the deformation of the passenger compartment. That is, it is important to absorb impact energy by the structural member.

  The main structural member that absorbs impact energy in automobile full-wrap collision and offset collision is the front side member. The front side member has a closed cross-section by spot welding after forming the member by press molding or the like. Normally, the impact energy is absorbed by buckling the front side member. In order to improve the absorption of impact energy, it is important to stabilize the buckling form and not to bend or break along the way.

  For spot welding of the above members, in order to stabilize buckling, if the spot welding interval, nugget diameter and welding conditions are not optimized, fracture from the weld point will occur at the time of buckling, and stable buckling mode There is a problem that the absorption of impact energy is not reduced.

  Conventionally, in order to solve this kind of problem, as described in Non-Patent Document 1, etc., a member is made by changing the spot welding interval, a buckling test is performed, and a stable seating is performed without breaking at the welding point. I was investigating the conditions to bend.

  However, this method has a problem that trial and error such as trial manufacture and test for each automobile and each member is necessary, which requires manufacturing costs and takes time for designing.

  Further, Patent Document 1 proposes a structure for preventing the peeling of a welded portion where a load is applied to the floor panel, but it is a structure only for the floor panel, and the welding point is peeled off by all impact absorbing members. The spot welding method that absorbs impact energy by preventing stable buckling has been trial and error by trial production.

  Further, Patent Document 2 proposes optimization of the spot welding interval, but the individual spot welding strength is only a simple index and is not an accurate prediction of the fracture itself, so it has high accuracy. There was a problem that design based on the prediction of spot weld fracture could not be performed.

  Typical strength indicators for spot welds are the shear tensile test and the cross-shaped tensile test defined in Non-Patent Documents 2 and 3. There are other examples of reports in various test forms that assume various load conditions. Generally, the two types of tests specified by JIS are used to determine the shear tensile test value as the shear strength of the welded part. The cross-shaped tensile test value is treated as the peel strength of the weld.

  However, since the shear strength and peel strength of spot welding obtained by the test are affected by the structure such as the width, the actual member must be corrected and estimated from various viewpoints. In recent years, the functions of computers have dramatically improved, and there are systems that perform optimal design by simulation of automobile collisions on computers, but the estimation accuracy is not sufficient.

  In addition, Patent Document 3 disclosed by the present inventor proposes a method for predicting the fracture strength of spot welding in consideration of structural effects such as width, but the actual fracture of a spot weld will be ductile fracture. However, the prediction accuracy was limited because it was not predicted with the fracture strain that was the dominant factor.

Explanation paper No. 9705JSAE SYMPOSIUM “New Body Structure Molding Technology” JIS Z3136 JIS Z3137 JP-A-6-182561 JP 2002-31627 A JP 2005-326401 A

  The present invention has been made in view of the above points, and the prediction of fracture of a spot welded part at the time of impact deformation is limited by finite element method analysis on a computer, not by trial production of a member or a collision test. Judging by the prediction model incorporated during the element method analysis, the purpose is to prevent weld fracture during impact of the member, optimize the deformation buckling mode, and improve the absorption of impact energy. is there.

The spot welded portion failure prediction apparatus according to the present invention is based on a cross-type tensile test and / or a shear-type tensile test in a spot welded joint, based on a plate thickness, a spot weld nugget diameter, a base material strength, and a fracture. Input means for inputting one or both of part or all of the elongation, the welding interval of the joint, and the joint length orthogonal to the welding interval, the plate thickness, the nugget diameter of spot welding, the base material portion Spot welds in cross-type tension and / or shear-type tension from part or all of the material strength and elongation at break and any or both of the weld interval between the joints and the joint length orthogonal to the weld interval. Computing means for calculating the fracture strain parameter of the steel, parameter storage means for storing the fracture strain parameter for each steel type, and the fracture strain stored in the parameter storage means. Only parameters, introduced in a fracture prediction formula that models the deformation around the spot welding by the finite element method, characterized in that it has a determining operation means the spot weld failure.
Another spot weld failure prediction apparatus according to the present invention is based on a cross-type tensile test and / or a shear-type tensile test in a spot weld joint, based on a plate thickness, a spot weld nugget diameter, a base material portion material strength, And input means for inputting one or both of a part or all of the breaking elongation, the welding interval of the joint, and the joint length orthogonal to the welding interval, the plate thickness, the nugget diameter of spot welding, the base material From part or all of the material strength of the part and the elongation at break and either or both of the joint weld interval and the joint length orthogonal to the weld interval, in cross-type tension and / or shear-type tension Calculation means for calculating the fracture strain parameter of the spot weld, parameter storage means for storing the fracture strain parameter for each steel type, and storage in the parameter storage means The fracture strain parameters, introduced in a deformed modeled fracture limit line around spot welding by the finite element method, characterized in that it has a determining operation means the spot weld failure.
The spot weld failure prediction apparatus according to the present invention is a spot weld joint, based on a cross-type tensile test and / or a shear-type tensile test, based on a plate thickness, a spot weld nugget diameter, a base material material strength, and an elongation at break. The fracture strain parameter of a spot weld in cross-type tension and / or shear-type tension is calculated from a part or all of the above, and the weld interval of the joint and the joint length orthogonal to the weld interval or both. A step of calculating, a step of storing the fracture strain parameter for each steel type in the parameter storage means, and a fracture prediction parameter obtained by modeling the deformation around the spot welding by the finite element method using the fracture strain parameter stored in the parameter storage means And having a step of determining spot weld fracture.
Another spot weld failure prediction method according to the present invention includes a plate weld, a spot weld nugget diameter, a base material material strength, and a spot weld joint based on a cross-type tensile test and / or a shear-type tensile test. Fracture strain of spot weld in cross-type tension and / or shear-type tension from part or all of elongation at break, joint weld interval, and / or joint length orthogonal to the weld interval A step of calculating a parameter, a step of storing a fracture strain parameter for each steel type in a parameter storage unit, and a fracture strain parameter stored in the parameter storage unit, wherein the deformation around a spot weld is modeled by a finite element method. It is characterized in that it has a step of introducing a limit line and determining spot weld fracture.
The computer program according to the present invention is a spot welding joint, based on a cross-type tensile test and / or a shear-type tensile test, based on the plate thickness, spot weld nugget diameter, material strength of the base material part, and part or all of the elongation at break. A process of calculating a fracture strain parameter of a spot weld in cross-type tension and / or shear-type tension from either or both of the weld interval of the joint and the joint length orthogonal to the weld interval; The process of storing the fracture strain parameter for each steel type in the parameter storage means, and the fracture strain parameter stored in the parameter storage means are introduced into a fracture prediction formula that models deformation around spot welding by the finite element method, The present invention is characterized in that a computer executes a process of determining spot welded portion destruction.
Another computer program according to the present invention is based on a cross weld tensile test and / or a shear tensile test in a spot welded joint, the plate thickness, the spot weld nugget diameter, the material strength of the base metal part, and a part of the elongation at break. Alternatively, a process of calculating a fracture strain parameter of a spot welded portion in cross-type tension and / or shear-type tension from all or any one or both of the weld interval of the joint and the joint length orthogonal to the weld interval. And the process of storing the fracture strain parameters for each steel type in the parameter storage means, and the fracture strain parameters stored in the parameter storage means are introduced into the fracture limit line modeling the deformation around spot welding by the finite element method. Thus, the present invention is characterized in that a computer executes a process of determining spot welded portion destruction.
The computer-readable recording medium according to the present invention is characterized in that the computer program according to the present invention is recorded.

  According to the present invention, in a finite element method analysis on a computer, for example, it is possible to accurately perform a fracture prediction at a portion where spot welding of an automobile member is modeled. Therefore, at the time of a collision test with an actual automobile member, Verification of spot welded portion fracture can be omitted, or the number of verification tests can be greatly reduced. In addition, it is possible to replace the design of a member that prevents spot welding fractures in large-scale experiments such as trial productions and collision tests with different spot welding conditions for automobile parts with a design that prevents spot welding fractures by computer crash analysis. It is possible to contribute to significant cost reduction and shortening of the design and development period.

Preferred embodiments of the present invention will be described below with reference to the accompanying drawings.
FIG. 1 shows an outline of a shear type tensile test. As shown in FIG. 1, the test piece is formed by stacking two steel plates that are the base material 2 having a test piece width of 4 and spot-welding to form a nugget 1. The tensile test is performed until the test piece breaks in the direction indicated by the tensile direction (arrow 3).

At this time, the displacement and load of the test piece in the tensile direction 3 are measured. A fracture occurs around the nugget 1, and at this time, the strain becomes maximum, and this is taken as a fracture strain parameter Ef (−). This fracture strain parameter is defined as in equation (1). Here, EL is a reference strain, and A is a form factor, which will be described below.
Ef = EL · A (1)

Assuming that the maximum strain has reached the fracture strain parameter Ef (−) around the nugget 1 that is the starting point of the fracture, the shape factor A of the limit strain change at the end of the nugget 1 and the base material 2 is expressed as follows: From the width W (mm) and the nugget diameter d (mm), it is defined as in equation (2).
A = (W / (a · d−b)) ^c (2)

  In a test piece with one spot welding spot, the weld interval of the joint and the joint length orthogonal to the weld interval are the test piece width W shown in FIG. When there are a plurality of spot welding hit points, the welding interval of the joint is, for example, the adjacent spot welding interval 6 in the member shown in FIG. 2, and the joint length orthogonal to the welding interval is the interval of the spot welding. It becomes the length 5 of the member which is orthogonal and overlaps the plates to be welded.

Further, the reference strain EL at this time is defined as shown in Equation (3) from the tensile strength TS (MPa) of the material, the plate thickness t (mm), and the total elongation TEL (-) in the tensile test of the material. .
EL = k · TEL · (t / e) ^f · (g / TS) ^h (3)

  Here, a, b, c, e, f, g, h, and k are materials of various tensile strengths TS and total elongation TEL, and various specimen widths W, plate thicknesses t, and nugget diameters d. When the fracture strain parameter Ef is measured and arranged, it becomes a single curve, and is a parameter for fitting the relationship of the curves with the equations (2) and (3). These parameters are: a = 0.01-100, b = 0.0001-1000, c = 0.0001-10, k = 0.001-100, e = 0.01-100, f = 0.0001 -10, g = 1 to 5000, and h = 0.0001 to 10. However, the equation for fitting the curve does not necessarily have the form of the equations (2) and (3), and may be any equation that can fit the curve relationship. Further, the shape factor A and the reference strain EL may be read directly from the curve graph without using the equations (2) and (3).

  From this, the fracture strain parameter Ef at an arbitrary tensile strength TS, total elongation TEL, sheet thickness t, width W, and nugget diameter d can be predicted from the formula (1) as a fracture prediction formula (fracture prediction formula). Further, the fracture strain parameter Ef at an arbitrary tensile strength TS, total elongation TEL, plate thickness t, width W, nugget diameter d may be read directly from the graph of the above curve.

Next, members having arbitrary shapes joined by spot welding are modeled on a computer using a finite element method. The computer sequentially calculates the deformation of the collision analysis in which the equivalent plastic strain εp of the element connecting the members, which modeled the spot welding, is reproduced by the finite element method. The means for calculating the equivalent plastic strain εp depends on a general-purpose analysis code. For example, refer to PAM-CRASH v2002 user's manual manufactured by ESI. The break determination on the computer is made when the equation (4) is established.
εp ≧ Ef (4)

  By doing so, it is possible to accurately predict spot welding fracture determination on a computer without actually creating a member and verifying it by a collision test. By using this method, the conditions under which spot welding does not break can be examined by changing the member shape, material, plate thickness, nugget diameter, and welding position on a computer, and an optimal member can be designed. .

  This method can be applied to any material, not just steel materials. In addition to spot welding, all welding such as laser welding, arc welding, seam welding, mash seam welding, etc., and all mechanical bonding such as TOX bonding, rivet bonding, friction bonding, diffusion bonding, friction diffusion bonding, adhesives It can be applied to all joints. Furthermore, the calculation method on the computer is not limited to the finite element method, but can be applied to the boundary element method, the difference method, the meshless method, the primary analysis, and any calculation method. It may be applied.

  The calculation method of the fracture strain parameter Ef by experiment is not limited to the above-described shear type tensile test, and can be calculated by any test piece shape and load application method.

  Needless to say, the above-described prediction of fracture determination can be applied not only to the collision analysis of the entire automobile and members, but also to parts other than automobiles, and can also be applied to analysis using quasi-static deformation other than collision.

  FIG. 3 is a block diagram showing an example of a computer system that can constitute a spot welded portion failure prediction apparatus. In the figure, reference numeral 1200 denotes a computer PC. The PC 1200 includes a CPU 1201, executes device control software stored in a ROM 1202 or a hard disk (HD) 1211, or supplied by a flexible disk drive (FD) 1212, and collects all devices connected to the system bus 1204. To control. Each function unit of the present embodiment is configured by a program stored in the CPU 1201, ROM 1202, or hard disk (HD) 1211 of the PC 1200.

  A RAM 1203 functions as a main memory, work area, and the like for the CPU 1201. Reference numeral 1205 denotes a keyboard controller (KBC), which controls to input a signal input from the keyboard (KB) 1209 into the system main body. Reference numeral 1206 denotes a display controller (CRTC) which performs display control on the display device (CRT) 1210. A disk controller (DKC) 1207 is a hard disk (boot program (start program: a program that starts execution (operation) of personal computer hardware and software)), a plurality of applications, editing files, user files, a network management program, and the like. HD) 1211 and flexible disk (FD) 1212 are controlled.

  Reference numeral 1208 denotes a network interface card (NIC) that exchanges data bidirectionally with a network printer, another network device, or another PC via the LAN 1220.

  The functions of the above-described embodiments can also be realized by a computer executing a computer program. Further, means for supplying a computer program to a computer, for example, a computer-readable recording medium such as a CD-ROM in which such a program is recorded, or a transmission medium such as the Internet for transmitting such a program is also applied as an embodiment of the present invention. be able to. A computer program product such as a computer-readable recording medium in which the program is recorded can also be applied as an embodiment of the present invention. The computer program, recording medium, transmission medium, and computer program product are included in the scope of the present invention. As the recording medium, for example, a flexible disk, a hard disk, an optical disk, a magneto-optical disk, a CD-ROM, a magnetic tape, a nonvolatile memory, a ROM, or the like can be used.

Example 1
Using the above fracture prediction model, a system for automatically judging fracture of spot welds during analysis of collision deformation of members was constructed as a subroutine program in the general-purpose collision analysis FEM code. The code used is PAM-CRASH v2002 manufactured by ESI, and the spot welded part is modeled using Multi-PLINK for the members modeled with shell elements.

  The accuracy verification of the fracture prediction model is best because the comparison between the analysis and the experiment modeling the shear type tensile test and the cross type tensile test itself can be made strictly. Therefore, a shear type tensile test piece and a cross-type tensile test piece according to JIS standards 3136 and 3137 were made of a steel plate of 590 MPa thickness t = 1.8 mm. The spot weld nugget diameter is 5√t. The test was carried out using an Instron type testing machine, and the load and displacement until the spot weld fracture was measured.

  At the same time, a shear type tensile test and a cross type tensile test of the same shape as the test are modeled on a computer, the tensile test is analyzed with the FEM code in which the above subroutine program is installed, and the spot welded portion is automatically determined for breakage. The load and displacement up to the fracture of spot welding as in the experiment were calculated.

  The input initial parameters are tensile strength TS = 642 (MPa), sheet thickness t = 1.8 (mm), nugget diameter d = 6.7 (mm), total elongation TEL = 0.315 (−). . The weld interval between the joints and the joint length perpendicular to the weld interval is the test piece width W in the case of spot welding at one point. Therefore, the test piece width W = 40 (mm) in the shear type tensile test, and the cross shape In the tensile test, the test piece width W is 50 (mm).

  Next, the test is performed by changing the test piece width W of the shear-type tensile test to 20 to 50 mm and simultaneously changing the nugget diameter d to 4 to 7 mm, and the fracture strain parameter Ef is tested at the maximum load. Measured as the strain around the nugget of the piece, or as the strain of the welded joint element in the finite element analysis under the same conditions as the maximum load of the test. From this result, the fracture limit line by the fracture strain parameter shown in FIG. 4 can be obtained. Under the conditions of the initial parameters, the fracture strain parameter Ef = 0.40 can be read from the fracture limit line, as indicated by the circles in FIG. Similarly, the cross-shaped tensile test can be read as the fracture strain parameter Ef = 0.42 as indicated by the □ marks in FIG.

  As another method, by fitting the curve in FIG. 4 with the equations (2) and (3), EL = 0.37, A = 1.08 in the shear type tensile test, EL = 0.37 and A = 1.135. From these values, Ef = 0.42 in the shear type tensile test and Ef = 0.40 in the cross type tensile test using the formula (1), and the same value as described above can be obtained from the fracture prediction formula.

  This fracture strain parameter Ef was introduced into the equation (4) of the fracture determination condition in which the deformation around the spot weld was modeled by the finite element method to determine the spot weld fracture. In consideration of the fact that the test model can be applied to collision analysis of actual members, the test model is created with shell elements having rough collision analysis levels of actual vehicles, and the boundary conditions are simplified.

  FIGS. 5 and 6 are verification examples of this system. Although the fracture mode is different in each of the shear type tensile test and the cross type tensile test, the fracture load on the load-stroke curve of the experiment and the FEM analysis agrees. You can see that

  In the shear type tensile test, the shape of the load-displacement curve up to the breaking load appears to be different between the experiment and the analysis. This is because the test piece chuck is connected to the crosshead via the universal joint in the experiment, so the chuck part is rotating at the time of load rise, and the analysis does not take this rotation into account in the simplification of the model. It just looks like. Since this only changes the behavior of the initial stroke change, it is essentially unaffected by the load at the time of fracture.

  Even in the cross-type tensile test, the behavior of the load-displacement curve is a little different between the experiment and analysis, and it is a problem of the chuck of the experiment as well as the slightly different one.

  Of course, if the model including the chuck part is modeled in the analysis, the behavior of this part also agrees with the experiment, but here it is omitted because it is not an essential problem. Rather, the FEM analysis, which is a simple model of this test, can accurately predict the rupture load of the actual test, so that the details can be simplified in a large-scale collision analysis of the entire model or partial model of the actual vehicle. It is shown that spot breakage can be accurately predicted even in a practical level analysis.

(Example 2)
The prediction model was verified by the axial crush test of a simple member. The member has the shape shown in FIG. 7, the cross section is formed by spot welding of a hat type and a patch plate, the top of the hat and the vertical wall are 50 mm each, the flange is 20 mm, and the length in the crushing direction Is 300 mm. The material used for the member is a steel material of 980 MPa class, and the nugget diameter of spot welding is 4√t (mm).

  The input initial parameters are tensile strength TS = 983 (MPa), plate thickness t = 1.4 (mm), nugget diameter d = 4.7 (mm), total elongation TEL = 0.18 (−). It was. Since the value corresponding to the test piece width W is axial crushing, the joint length 5 is orthogonal to the welding interval in FIG. 2 and is the same as the flange length 20 (mm) of the member 9 in FIG. 20 (mm).

  The fracture strain parameter Ef can be read as Ef = 0.27 as indicated by the Δ mark in FIG. Further, similarly to the first embodiment, EL = 0.21 and A = 1.29 are determined by fitting the equations (2) and (3) of the data in FIG. From these values, using Equation (1), the same value as described above can be obtained from the fracture prediction equation with Ef = 0.27.

  This fracture strain parameter Ef was introduced into the equation (4) of the fracture determination condition in which the deformation around the spot weld was modeled by the finite element method to determine the spot weld fracture. In consideration of the fact that the test model can be applied to collision analysis of actual members, the test model is created with shell elements having rough collision analysis levels of actual vehicles, and the boundary conditions are simplified.

  A dynamic crushing test was performed with a weight of falling weight of 500 kg and an initial speed at crushing of 6 m / s, and FEM analysis was performed under the same conditions. Comparing the FEM analysis results in Fig. 8 (a) and the test results in Fig. 8 (b) with the member shape after crushing, the buckling shape is the same. The form in which the board is detached matches. This shows that spot breakage can be accurately predicted even in a practical level analysis in which the detailed part is simplified in a large-scale collision analysis of an entire model or a partial model of an actual vehicle.

  In this way, it was possible to verify that the analysis method can predict spot welding fracture with high accuracy by a basic test. In addition, the prediction of spot weld fracture at the time of collision deformation at the part level is verified from both experimental and analytical aspects, and it is confirmed that the fracture prediction in the analysis is consistent with the experiment. From the above, it was confirmed that the system can control and design the deformation mode and absorbed energy of the member depending on whether or not the spot welded portion can be broken.

  This method can be applied not only to general-purpose solvers PAM-CRASH but also to general-purpose solvers such as LSTC LS-DYNA3D and MECALOG RADIOSS, and individually developed solvers. The spot weld model can be applied not only to contact types such as Multi-PLINK, but also to beam elements, shell elements, solid elements, and the like.

It is a schematic diagram which shows the outline | summary of a shear type tensile test. It is a perspective view which shows the example of the member in which multiple spot welding hit points exist. It is a block diagram which shows an example of the computer system which can comprise the destruction prediction apparatus of a spot weld part. It is a figure which shows the fracture strain parameter curve (break limit line) of various conditions. It is the characteristic view which compared the relationship between the load at the time of a fracture | rupture of the shear type | mold test in Example 1, and a displacement by experiment and simulation (FEM). It is the figure which compared the relationship between the load at the time of the fracture | rupture of the cross-shaped test in Example 1, and a displacement by experiment and simulation (FEM). It is a figure which shows the member used for Example 2. FIG. It is a figure for demonstrating the mode of a fracture | rupture of the spot welding part at the time of the dynamic crushing test of the member in Example 2, (a) is a figure which shows a FEM analysis result, (b) is a figure which shows the photograph of a test result. It is.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Nugget 2 Base material 3 Tensile direction of test piece both ends 4 Test piece width (W)
5 Joint length orthogonal to welding interval 6 Welding interval of joint

Claims (7)

For spot welded joints, based on cross-type tensile test and / or shear-type tensile test, plate thickness, spot weld nugget diameter, material strength of base metal part, and part or all of elongation at break, and welding interval of joint And input means for inputting one or both of the joint lengths orthogonal to the welding interval;
From the plate thickness, the nugget diameter of spot welding, the material strength of the base material part, and a part or all of the elongation at break, and the weld interval of the joint, either or both of the joint length orthogonal to the weld interval, A calculation means for calculating a fracture strain parameter of a spot weld in cross-type tension and / or shear-type tension;
Parameter storage means for storing fracture strain parameters for each steel type;
It has calculation means for introducing a fracture strain parameter stored in the parameter storage means into a fracture prediction formula that models deformation around a spot weld by a finite element method, and determining spot weld fracture. Spot weld failure prediction device. For spot welded joints, based on cross-type tensile test and / or shear-type tensile test, plate thickness, spot weld nugget diameter, material strength of base metal part, and part or all of elongation at break, and welding interval of joint And input means for inputting one or both of the joint lengths orthogonal to the welding interval;
From the plate thickness, the nugget diameter of spot welding, the material strength of the base material part, and part or all of the elongation at break, the welding interval of the joint, and the joint length orthogonal to the welding interval, or both Calculating means for calculating a fracture strain parameter of a spot weld in cross-type tension and / or shear-type tension;
Parameter storage means for storing fracture strain parameters for each steel type;
It has calculation means for introducing a fracture strain parameter stored in the parameter storage means to a fracture limit line modeling deformation around a spot weld by a finite element method, and determining spot weld fracture. Spot weld failure prediction device. In the spot welded joint, based on the cross-type tensile test and / or the shear-type tensile test, the plate thickness, the spot weld nugget diameter, the material strength of the base metal part, and part or all of the elongation at break, and the welding interval of the joint, Calculating a fracture strain parameter of a spot weld in cross-type tension and / or shear-type tension from either or both of the joint lengths orthogonal to the welding interval;
Storing a fracture strain parameter for each steel type in a parameter storage means;
A step of introducing a fracture strain parameter stored in the parameter storage means into a failure prediction formula that models deformation around a spot weld by a finite element method and determining spot weld failure. Fracture prediction method for welds. In the spot welded joint, based on the cross-type tensile test and / or the shear-type tensile test, the plate thickness, the spot weld nugget diameter, the material strength of the base metal part, and part or all of the elongation at break, and the welding interval of the joint, Calculating a fracture strain parameter of a spot weld in cross-type tension and / or shear-type tension from either or both of the joint lengths orthogonal to the welding interval;
Storing a fracture strain parameter for each steel type in a parameter storage means;
A step of introducing a fracture strain parameter stored in the parameter storage means into a fracture limit line modeling deformation around a spot weld by a finite element method, and determining spot weld fracture. Fracture prediction method for welds. In the spot welded joint, based on the cross-type tensile test and / or the shear-type tensile test, the plate thickness, the spot weld nugget diameter, the material strength of the base metal part, and part or all of the elongation at break, and the welding interval of the joint, And a process of calculating a fracture strain parameter of a spot weld in cross-type tension and / or shear-type tension from either or both of the joint lengths orthogonal to the welding interval;
Processing for storing the fracture strain parameter for each steel type in a parameter storage means;
Introducing the fracture strain parameter stored in the parameter storage means into a fracture prediction formula that models deformation around a spot weld by a finite element method, and causing a computer to execute a process of determining spot weld fracture. A computer program for predicting fracture of spot welds. In the spot welded joint, based on the cross-type tensile test and / or the shear-type tensile test, the plate thickness, the spot weld nugget diameter, the material strength of the base metal part, and part or all of the elongation at break, and the welding interval of the joint, And a process of calculating a fracture strain parameter of a spot weld in cross-type tension and / or shear-type tension from either or both of the joint lengths orthogonal to the welding interval;
Processing for storing the fracture strain parameter for each steel type in a parameter storage means;
Introducing the fracture strain parameter stored in the parameter storage means to a fracture limit line modeling deformation around a spot weld by a finite element method, and causing a computer to execute a process of determining spot weld fracture. A computer program for predicting fracture of spot welds.   A computer-readable recording medium on which the computer program according to claim 5 or 6 is recorded.