Fracture prediction method and device, program and recording medium

Abstract

To contribute to reduction in cost required for product development and considerable reduction of a development period by allowing for accurate fracture prediction according to a composite and complicated deformation state caused by simultaneous application of in-plane deformation and bending deformation (out-of-plane deformation) to a steel material, which may occur in an actual member.SOLUTION: In a member fracture prediction method using the finite element method, an in-plane deformation fracture limit line formed by a relationship between a stress triaxial degree and an equivalent plastic strain of a material used in a member is generated, and a bending fracture limit line is generated by proportionally multiplying a value of the equivalent plastic strain on the in-plane deformation fracture limit line until the value intersects a plot point obtained from values of a stress triaxial degree and an equivalent plastic strain of a bending outer surface layer at a bending fracture limit, a composite deformation degree is acquired using a strain in a plate thickness direction of the bending outer surface layer and a strain in the plate thickness direction of a bending inner surface layer, and a composite deformation fracture limit line is generated from them, and the stress triaxial degree and the equivalent plastic strain obtained by collision deformation analysis are compared with the composite deformation fracture limit line to determine whether the member is fractured or not.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a fracture prediction method and device, a program, and a recording medium. [Background technology]

[0002] In recent years, development of vehicle body structures that can reduce the impact of a collision has been progressing. One method of dealing with a vehicle collision is to use the structural components of the vehicle to absorb the collision energy and protect the passenger space. Therefore, when designing a vehicle body structure, a structural design is made with collisions in mind, and as part of this, for example, analysis of the collision deformation of the body structural components is performed using FEM (finite element method) analysis, including analysis to determine fracture. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2012-33039 [Patent Document 2] Japanese Patent Application Laid-Open No. 2024-163668 Summary of the Invention [Problem to be solved by the invention]

[0004] During collision deformation, in addition to tensile fracture due to in-plane tensile force, bending fracture due to out-of-plane bending caused by buckling or other factors can occur. Furthermore, complex deformation fracture can occur, in which fracture occurs due to the simultaneous application of in-plane tensile force and out-of-plane bending. In other words, collision-deformable components can be deformed in various ways in the in-plane direction while also being subjected to out-of-plane bending. Therefore, a fracture prediction method that can respond to these complex deformation states is required.

[0005] Patent Document 1 discloses a method for predicting tensile bending fracture. This is a method for predicting bending fracture strength from the relationship between tension and elongation for each inner bending radius, and determining fracture in tensile bending. However, Patent Document 1 is a method for predicting fracture under tensile bending deformation only, and is not applicable to cases where fracture occurs only due to bending deformation in a state where almost no tension is applied, such as pure bending.

[0006] Patent Document 2 discloses a fracture prediction method that can handle cases where tensile deformation and bending deformation are mixed. This is a method that changes the fracture limit based on the strain gradient in the plate thickness direction, but in actual components, fracture occurs while complex deformation occurs not only in the plate thickness direction but also in the plane, so this method cannot be applied to cases where fracture occurs while in-plane deformation is also combined.

[0007] The present invention has been made in consideration of the above-mentioned problems, and aims to provide a fracture prediction method and device, as well as a program and a recording medium, that enable accurate fracture prediction according to the composite and complex deformation state that occurs when steel material is simultaneously subjected to in-plane deformation and bending deformation (out-of-plane deformation), such as occurs in actual components, thereby contributing to reducing the costs required for product development and significantly shortening the development period. [Means for solving the problem]

[0008] In order to solve the above problems, the present inventors have conducted extensive research and have come up with the following aspects of the invention.

[0009] [1] A method for predicting fracture of a component using a finite element method, comprising: A first step of creating an in-plane deformation fracture limit line according to an in-plane deformation form formed by the relationship between stress triaxiality and equivalent plastic strain of a material used for the member; A second step of creating a bending fracture limit line for the material by proportionally multiplying the value of the equivalent plastic strain of the bending outer surface layer at the bending fracture limit of the material until the value of the equivalent plastic strain of the in-plane deformation fracture limit line intersects with a plot point obtained from the values ​​of the stress triaxiality and equivalent plastic strain of the bending outer surface layer at the bending fracture limit; A third step of acquiring a composite deformation degree using the thickness direction strain of the bending outer surface layer and the thickness direction strain of the bending inner surface layer of the member obtained by the collision deformation analysis; A fourth step of creating a composite deformation fracture limit line using the in-plane deformation fracture limit line, the bending fracture limit line, and the composite deformation degree; a fifth step of comparing the stress triaxiality and equivalent plastic strain generated in the member obtained by the collision deformation analysis with the composite deformation fracture limit line to determine whether or not fracture will occur in the member; A fracture prediction method comprising:

[0010] [2] In the first step, the in-plane deformation fracture limit line is corrected using a relationship between element size and tensile limit strain in a finite element method, which has been previously obtained, to obtain the in-plane deformation fracture limit line according to the element size; In the second step, the bending fracture limit line is corrected using a relationship between element size and bending limit strain in a finite element method, which has been obtained in advance, to obtain the bending fracture limit line according to the element size. [1] The fracture prediction method according to the present invention.

[0011] [3] The equivalent plastic strain of the outer surface layer at the bending fracture limit is the equivalent plastic strain of the outer surface layer at the time when the limit VDA bending angle is reached. The fracture prediction method according to [1] or [2].

[0012] [4] The combined deformation degree is b, and the strain in the thickness direction of the outer surface layer of the bent part is ε out , the strain in the thickness direction of the inner surface layer of the bending is ε in As a result, the following relationship holds: b=(ε out -ε in ) / (2*ε out ) 0≦b≦1 The fracture prediction method according to any one of [1] to [3].

[0013] [5] In the third step, the composite deformation degree that changes during the collision deformation analysis is sequentially acquired. The fracture prediction method according to any one of [1] to [4].

[0014] [6] A fracture prediction device that predicts fracture of a component using a finite element method, an in-plane deformation fracture limit line creation unit that creates an in-plane deformation fracture limit line according to an in-plane deformation form formed by the relationship between stress triaxiality and equivalent plastic strain of a material used for the member; A bending fracture limit line creation unit that creates a bending fracture limit line for the material by proportionally multiplying the value of the equivalent plastic strain of the bending outer surface layer at the bending fracture limit of the material until the value of the equivalent plastic strain of the in-plane deformation fracture limit line intersects with a plot point obtained from the stress triaxiality and the value of the equivalent plastic strain of the bending outer surface layer at the bending fracture limit; a composite deformation degree acquisition unit that acquires a composite deformation degree using the thickness direction strain of the bending outer surface layer and the thickness direction strain of the bending inner surface layer of the member obtained by the collision deformation analysis; A composite deformation fracture limit line creation unit that creates a composite deformation fracture limit line using the in-plane deformation fracture limit line, the bending fracture limit line, and the composite deformation degree; a fracture determination unit that compares the stress triaxiality and equivalent plastic strain generated in the member obtained by the collision deformation analysis with the composite deformation fracture limit line to determine whether or not fracture will occur in the member; A fracture prediction device having the above structure.

[0015] [7] a first correction unit that corrects the in-plane deformation fracture limit line using a previously determined relationship between element size and tensile limit strain in a finite element method, and acquires the in-plane deformation fracture limit line according to the element size; a second correction unit that corrects the bending fracture limit line using a relationship between an element size and a bending limit strain in a finite element method that has been obtained in advance, and acquires the bending fracture limit line according to the element size; Further comprising: [6] The fracture prediction device described in [6].

[0016] [8] The equivalent plastic strain of the outer surface layer at the bending fracture limit is the equivalent plastic strain of the outer surface layer at the time when the limit VDA bending angle is reached. [6] or [7], the fracture prediction device.

[0017] [9] The combined deformation degree is b, and the strain in the thickness direction of the outer surface layer of the bent part is ε out , the strain in the thickness direction of the inner surface layer of the bending is ε in As a result, the following relationship holds: b=(ε out -ε in ) / (2*ε out ) 0≦b≦1 The fracture prediction device according to any one of [6] to [8].

[0018]

[10] The composite deformation degree acquisition unit sequentially acquires the composite deformation degree that changes during collision deformation analysis. The fracture prediction device according to any one of [6] to [9].

[0019]

[11] A method for predicting fracture of a component using a finite element method, comprising: A first step of creating an in-plane deformation fracture limit line according to an in-plane deformation form formed by the relationship between stress triaxiality and equivalent plastic strain of a material used for the member; A second step of creating a bending fracture limit line for the material by proportionally multiplying the value of the equivalent plastic strain of the bending outer surface layer at the bending fracture limit of the material until the value of the equivalent plastic strain of the in-plane deformation fracture limit line intersects with a plot point obtained from the values ​​of the stress triaxiality and equivalent plastic strain of the bending outer surface layer at the bending fracture limit; A third step of acquiring a composite deformation degree using the thickness direction strain of the bending outer surface layer and the thickness direction strain of the bending inner surface layer of the member obtained by the collision deformation analysis; A fourth step of creating a composite deformation fracture limit line using the in-plane deformation fracture limit line, the bending fracture limit line, and the composite deformation degree; a fifth step of comparing the stress triaxiality and equivalent plastic strain generated in the member obtained by the collision deformation analysis with the composite deformation fracture limit line to determine whether or not fracture will occur in the member; A program for causing a computer to execute the fracture prediction method, comprising:

[0020]

[12] In the first step, the in-plane deformation fracture limit line is corrected using a relationship between element size and tensile limit strain in a finite element method, which has been previously obtained, to obtain the in-plane deformation fracture limit line according to the element size; In the second step, the bending fracture limit line is corrected using a relationship between element size and bending limit strain in a finite element method, which has been obtained in advance, to obtain the bending fracture limit line according to the element size.

[11] The program described in.

[0021]

[13] The equivalent plastic strain of the outer surface layer at the bending fracture limit is the equivalent plastic strain of the outer surface layer at the time when the limit VDA bending angle is reached.

[11] or

[12] .

[0022]

[14] The combined deformation degree is b, and the strain in the thickness direction of the outer surface layer of the bent part is ε out , the strain in the thickness direction of the inner surface layer of the bending is ε inAs a result, the following relationship holds: b=(ε out -ε in ) / (2*ε out ) 0≦b≦1 The program according to any one of

[11] to

[13] .

[0023]

[15] In the third step, the composite deformation degree that changes during the collision deformation analysis is sequentially acquired. The program according to any one of

[11] to

[14] .

[0024]

[16] A computer-readable recording medium having the program according to any one of

[11] to

[15] recorded thereon. [Effects of the Invention]

[0025] The present invention makes it possible to accurately predict fractures in response to complex deformation conditions that occur when steel materials are subjected to simultaneous in-plane and bending (out-of-plane) deformation, as occurs in actual components. This can contribute to reducing the costs and time required for product development. [Brief explanation of the drawings]

[0026] [Figure 1] 1 is a block diagram showing a fracture prediction device according to a first embodiment. [Figure 2] FIG. 2 is a block diagram showing the main configuration of a control unit of the fracture prediction device according to the first embodiment. [Figure 3] 3 is a flowchart showing a fracture prediction method according to the first embodiment. [Figure 4] FIG. 2 is a characteristic diagram showing an in-plane deformation fracture limit line L1. [Figure 5] FIG. 10 is a characteristic diagram showing how a bending fracture limit line L2 is created. [Figure 6] FIG. 1 is a schematic diagram generally showing the positions of outer surface layers and inner surface layers of a bent steel material. [Figure 7] FIG. 10 is a characteristic diagram showing how a combined deformation fracture limit line L3 is created. [Figure 8] FIG. 10 is a block diagram showing the main configuration of a control unit of a fracture prediction device according to a second embodiment. [Figure 9] 10 is a flowchart showing a fracture prediction method according to a second embodiment. [Figure 10] FIG. 10 is a characteristic diagram for explaining correction of an in-plane deformation fracture limit line. [Figure 11] FIG. 10 is a characteristic diagram for explaining correction of a bending fracture limit line. [Figure 12] FIG. 2 is a characteristic diagram showing various breaking limit lines used in Examples 1 and 2 and a comparative example. [Figure 13] This is a schematic diagram showing an FEM analysis that reproduces an experiment in which a square tube breaks. [Figure 14] FIG. 1 is a characteristic diagram showing fracture prediction results in Examples 1 and 2 and a comparative example. DETAILED DESCRIPTION OF THE INVENTION

[0027] Hereinafter, various embodiments will be described in detail with reference to the drawings.

[0028] -First embodiment- A first embodiment will be described below. Fig. 1 is a block diagram showing a fracture prediction device according to this embodiment. Fig. 2 is a block diagram showing the main configuration of a control unit of the fracture prediction device according to this embodiment. Fig. 3 is a flowchart showing a fracture prediction method according to this embodiment.

[0029] [Fracture prediction device] As shown in FIG. 1, the fracture prediction device 10 according to this embodiment is configured to include a CPU 1, a ROM 2, a RAM 3, a secondary storage device 4, an input device 5, and a display device 6. These components are connected to each other via a connection bus 7. The CPU (Central Processing Unit) 1 is responsible for overall control of the fracture prediction device 10. The CPU 1 executes a control program stored in the ROM 2 or the like to perform the processing of each flowchart described below. Note that a GPU (Graphics Processing Unit) may be used instead of or together with the CPU.

[0030] ROM 2 is a non-volatile memory that stores control programs and various parameter data. RAM 3 is a volatile memory that temporarily stores images, control programs, and their execution results. Secondary storage device 4 is a rewritable storage device such as a hard disk or flash memory, and stores various data used in each flowchart described below. For example, it stores input data and processing results. This information is output to RAM 3 and used by CPU 1 to execute the control program. Input device 5 is a keyboard, mouse, touch panel device, etc., and is used to input various user instructions. Display device 6 is a monitor that displays processing results, images, etc.

[0031] In this embodiment, the processes described below are implemented by software using the CPU 1, but some or all of the processes described below may be implemented by hardware. Examples of hardware that can be used include dedicated circuits (ASICs) and processors (reconfigurable processors, DSPs). The fracture prediction device 10 also includes a communication unit for communicating with an external device. The device may acquire input data, control programs, learning datasets, and the like from the external device via the communication unit, and may output processing results and the like to the external device via the communication unit.

[0032] The CPU 1 is a control unit that comprehensively controls and sets various components of the fracture prediction device 10. As shown in Fig. 2, the CPU 1 includes an in-plane deformation fracture limit line creation unit 11, a bending fracture limit line creation unit 12, a composite deformation degree acquisition unit 13, a composite deformation fracture limit line creation unit 14, and a fracture determination unit 15.

[0033] The in-plane deformation fracture limit line creation unit 11 creates an in-plane deformation fracture limit line according to the in-plane deformation form formed by the relationship between stress triaxiality and equivalent plastic strain of the material used in the member (steel material) that is the object of deformation analysis.

[0034] The bending fracture limit line creation unit 12 uses the value of the equivalent plastic strain of the bending outer surface layer at the bending fracture limit of the material to proportionally multiply the value of the equivalent plastic strain of the in-plane deformation fracture limit line until it intersects with the plotted point obtained from the values ​​of the stress triaxiality and equivalent plastic strain of the bending outer surface layer at the bending fracture limit, thereby creating the bending fracture limit line.

[0035] The composite deformation degree acquisition unit 13 acquires the composite deformation degree using the strain in the thickness direction of the outer surface layer of the bent part and the strain in the thickness direction of the inner surface layer of the bent part, which are obtained by the collision deformation analysis. The composite deformation degree acquisition unit 13 sequentially acquires the composite deformation degree that changes during the collision deformation analysis.

[0036] The combined deformation fracture limit line creating unit 14 creates a combined deformation fracture limit line using the in-plane deformation fracture limit line created by the in-plane deformation fracture limit line creating unit 11, the bending fracture limit line created by the bending fracture limit line creating unit 12, and the combined deformation degree acquired by the combined deformation degree acquiring unit 13. Because the combined deformation degree changes during the collision deformation analysis, the combined deformation fracture limit line creating unit 13 sequentially creates combined deformation fracture limit lines that change during the collision deformation analysis.

[0037] The fracture determination unit 15 compares the stress triaxiality and equivalent plastic strain generated in the member, obtained by the collision deformation analysis, with the combined deformation fracture limit line, and determines whether or not fracture will occur in the member.

[0038] [Fracture prediction method] In the fracture prediction method according to this embodiment, steps S1 to S6 are executed in sequence as shown in FIG.

[0039] (Step S1) In step S1, an in-plane deformation fracture limit line L1 is created. The in-plane deformation fracture limit line creation unit 11 creates an in-plane deformation fracture limit line L1 according to the in-plane deformation form formed by the relationship between stress triaxiality and equivalent plastic strain of the material used in the component (steel material) that is the object of deformation analysis.

[0040] First, to change the in-plane deformation mode of the component, experiments are conducted in which several different deformation modes (for example, uniaxial tensile deformation, shear deformation, plane strain deformation, and equibiaxial deformation) are created, and the timing at which fracture occurs in the component is obtained. Then, the in-plane deformation fracture limit line creation unit 11 performs an analysis using the finite element method (FEM analysis) that reproduces the above experiment, and obtains the stress triaxiality and equivalent plastic strain of the element at the fracture occurrence location at the timing of fracture occurrence in the experiment, for each in-plane deformation mode.

[0041] The stress triaxiality is defined by the following equations (1) to (3): The stress triaxiality is a value that changes depending on the deformation mode. η=σ m / σ eq ···(1) σ m =(σ1+σ2+σ3) / 3 (2) σ eq =[(1 / 2){(σ1-σ2) 2 +(σ2-σ3) 2 +(σ3-σ1) 2}] 1 / 2 ···(3) where: η: Stress triaxiality σ1, σ2, σ3: Principal stresses σ m : Hydrostatic stress σ eq : Equivalent stress is.

[0042] The in-plane deformation fracture limit line creation unit 11 fits the thus obtained stress triaxiality and equivalent plastic strain of the element at the fracture occurrence site at the experimental fracture occurrence timing for each in-plane deformation mode, for example, using the modified Mohr Coulomb equation, thereby obtaining a limit surface.

[0043] Fig. 4 is a characteristic diagram showing the in-plane deformation fracture limit line L1, in which the horizontal axis represents stress triaxiality and the vertical axis represents fracture strain (equivalent plastic strain). The in-plane deformation fracture limit line creation unit 11 creates a fracture limit line (in-plane deformation fracture limit line L1) according to the in-plane deformation form, which is obtained by assuming a plane stress state for the limit surface obtained by the above fitting.

[0044] (Step S2) In step S2, the equivalent plastic strain of the outer surface layer of the bent part when the critical VDA bending angle is reached is obtained.

[0045] The bending fracture limit line creation unit 12 calculates the equivalent plastic strain of the outer surface layer of the bent member when the member reaches the limit VDA bending angle, using the limit VDA bending angle of the member and the plate thickness of the member obtained by the FEM model that reproduces the VDA bending test. Here, the VDA bending test is one of the methods for evaluating the bendability of steel plate, and is a bending test of metallic materials in accordance with the test standard of the German Association of the Automotive Industry (VDA).

[0046] Equivalent plastic strain ε of the outer surface layer of a bent object using shell elements when the critical VDA bending angle is reached VDA can be expressed by the following approximate formula, for example: Maximum principal strain ε at outer surface of bending c teeth, ε c =a*M b +c It is expressed as: M: Element size (Use the same value as the element size of the FEM model used to reproduce the experiment, which was used to obtain the in-plane deformation fracture limit line.) a, b, c: Plate thickness t and maximum principal strain ε of outer surface layer using solid elements based on detailed FEM model s The relation At this time, ε s =d*ln(α)+e holds true. α: Limit VDA bending angle d, e: Relational formula for plate thickness t ε VDA is ε c Using ε VDA =ε c *2 / √3 It can be expressed as:

[0047] (Step S3) In step S3, a bending fracture limit line L2 is created. The bending fracture limit line creation unit 12 calculates the equivalent plastic strain ε of the outer surface layer of the bending when the limit VDA bending angle obtained in step S2 is reached. VDA The bending fracture limit line L2 is created using ε VDA is the equivalent plastic strain at the fracture limit during pure bending, and the stress triaxiality is known to be 0.57.

[0048] Fig. 5 is a characteristic diagram showing how the bending fracture limit line L2 is created. In Fig. 5, the horizontal axis represents stress triaxiality, and the vertical axis represents fracture strain (equivalent plastic strain). As shown in Figure 5, ε VDA The plotted ε can be plotted. VDA The vertical axis value (value of equivalent plastic strain) of the in-plane deformation fracture limit line L1 created in step S1 is multiplied proportionally until it intersects with the line L2. This creates the bending fracture limit line L2.

[0049] (Step S4) In step S4, the composite deformation degree of the member that is the object of deformation analysis is obtained. First, the composite deformation degree acquisition unit 13 acquires the strain in the thickness direction of the outer surface layer of the bent part and the strain in the thickness direction of the inner surface layer of the bent part of the member that is the object of deformation analysis in the collision deformation analysis by FEM.

[0050] Fig. 6 is a schematic diagram showing the positions of the outer surface layer and the inner surface layer of a typical steel material. Generally, in a tensile bending deformation load analysis, when a steel material 20 is bent while being pulled, an outer position 20a of the part of the steel material 20 where bending has occurred, as shown enlarged in Fig. 6, is defined as the position of the outer surface layer of the bend, and an inner position 20b is defined as the position of the inner surface layer of the bend.

[0051] The composite deformation degree acquisition unit 13 then acquires the composite deformation degree using the thickness direction strain of the bent outer surface layer and the thickness direction strain of the bent inner surface layer of the component obtained in the collision deformation analysis. Since the thickness direction strain of the bent outer surface layer and the thickness direction strain of the bent inner surface layer change during the collision deformation analysis, the composite deformation degree also changes in the same way. The composite deformation degree acquisition unit 13 sequentially acquires the composite deformation degree that changes during the collision deformation analysis.

[0052] The composite deformation degree will be explained below. If the in-plane strain is ε1 and ε2 and the thickness direction strain is ε3, the volume of the member is constant, so ε3=-(ε1+ε2) It is defined as follows.

[0053] The strain in the thickness direction at the strain measurement point on the outer surface of the bent plate and the strain measurement point on the inner surface of the bent plate are respectively defined as ε out and ε in Then, the bending deformation state ratio b can be defined as follows: b=(ε out -ε in ) / (2*ε out )

[0054] When the member is in pure bending, i.e., undergoing pure out-of-plane deformation, e.g., ε out If is 1, the inverted value (-1) is ε in Therefore, the bending deformation state ratio b is 1. On the other hand, when deformation occurs in the plane, ε out and ε inare the same value, so the bending deformation state ratio b is 0. In this way, in a combined deformation state where out-of-plane deformation and in-plane deformation are combined, the bending deformation state ratio b indicates a value between 0 and 1 (0≦b≦1). In other words, by calculating the deformation state ratio b, it is possible to recognize the degree of combined deformation of each part during deformation analysis. Hereinafter, the bending deformation state ratio b will be referred to as the combined deformation degree b.

[0055] (Step S5) In step S5, a combined deformation fracture limit line L3 is created. The combined deformation fracture limit line creation unit 14 creates a combined deformation fracture limit line L3 using the in-plane deformation fracture limit line L1 created in step S1, the bending fracture limit line L2 created in step S3, and the combined deformation degree b acquired in step S4. Since the combined deformation degree b changes during the collision deformation analysis, the combined deformation fracture limit line L3 also changes. The combined deformation fracture limit line creation unit 13 sequentially creates the combined deformation fracture limit line L3 that changes during the collision deformation analysis.

[0056] Fig. 7 is a characteristic diagram showing how the combined deformation fracture limit line L3 is created. In Fig. 7, the in-plane deformation fracture limit line L1 created in step S1 can be said to be the fracture limit line when the combined deformation degree b = 0, and the bending fracture limit line L2 created in step S3 can be said to be the fracture limit line when the combined deformation degree b = 1. Therefore, in the combined deformation state, the combined deformation fracture limit line L3 is created by multiplying these two fracture limit lines proportionally by the ratio of the value of the combined deformation degree b.

[0057] (Step S6) In step S6, it is determined whether or not the member will break. The fracture determination unit 15 compares the stress triaxiality and equivalent plastic strain generated in the component obtained by the collision deformation analysis with the successively changing combined deformation fracture limit line L3 to determine whether or not fracture will occur in the component. When the value of the equivalent plastic strain generated in the component exceeds the combined deformation fracture limit line L3, it is determined that fracture has occurred in the component.

[0058] As described above, this embodiment makes it possible to accurately predict fractures in response to complex deformation conditions that occur when steel is subjected to in-plane deformation and bending deformation (out-of-plane deformation) simultaneously, as occurs in actual components. This can contribute to reducing the costs and time required for product development.

[0059] -Second embodiment- The second embodiment will be described below. This embodiment discloses a fracture prediction device and a fracture prediction method similar to the first embodiment, but differs from the first embodiment in that the element size used in FEM analysis is appropriately taken into consideration. FIG. 8 is a block diagram showing the main configuration of the control unit of the fracture prediction device according to this embodiment. FIG. 9 is a flowchart showing the fracture prediction method according to this embodiment. Note that the components of the fracture prediction device 10 described in the first embodiment will be denoted by dynamic symbols and detailed explanations will be omitted.

[0060] [Fracture prediction device] In this embodiment, as shown in Figure 8, the CPU 1 has, in addition to the in-plane deformation fracture limit line creation unit 11, bending fracture limit line creation unit 12, composite deformation degree acquisition unit 13, composite deformation fracture limit line creation unit 14, and fracture determination unit 15 similar to those in Figure 2 of the first embodiment, a first scale factor acquisition unit 21 and a first correction unit 22, and a second scale factor acquisition unit 23 and a second correction unit 24.

[0061] The first scale factor acquisition unit 21 acquires a scale factor corresponding to the element size in the in-plane deformation, which indicates the relationship between the tensile limit strain and the element size in the FEM analysis of the in-plane deformation.

[0062] The first correction unit 22 corrects the value of the vertical axis (value of fracture strain (equivalent plastic strain)) of the in-plane deformation fracture limit line created by the in-plane deformation fracture limit line creation unit 11 by multiplying the scale factor of the element size of the FEM model used in the collision deformation analysis. In this way, the corrected in-plane deformation fracture limit line is obtained.

[0063] The second scale factor acquisition unit 23 acquires a scale factor for each bending element size. The second correction unit 24 corrects the value of the vertical axis (value of fracture strain (equivalent plastic strain)) of the bending fracture limit line created by the bending fracture limit line creation unit 12 by multiplying the scale factor in the element size of the FEM model used in the collision deformation analysis. In this way, a corrected bending fracture limit line is obtained.

[0064] [Fracture prediction method] In the fracture prediction method according to this embodiment, as shown in Fig. 9, in addition to steps S1 to S6 similar to those in Fig. 3 of the first embodiment, steps S11 to S14 are appropriately executed. Fig. 10 is a characteristic diagram for explaining the correction of the in-plane deformation fracture limit line, where (a) shows how the corrected in-plane deformation fracture limit line is obtained, and (b) shows the scale factor corresponding to the element size. Fig. 11 is a characteristic diagram for explaining the correction of the bending fracture limit line, where (a) shows how the corrected bending fracture limit line is obtained, and (b) shows the scale factor corresponding to the element size.

[0065] In this embodiment, similarly to the first embodiment, first, in step S1, an in-plane deformation fracture limit line L1 is created.

[0066] (Step S11) In step S11, in the FEM analysis of in-plane deformation, a scale factor corresponding to the element size in the in-plane deformation, which indicates the relationship between the tensile limit strain and the element size, is acquired.

[0067] For example, in an FEM collision deformation analysis that reproduces a uniaxial tensile test, the first scale factor acquisition unit 21 acquires the average equivalent plastic strain value for each strain reading range from the equivalent plastic strain distribution at the fracture occurrence site at the timing of experimental fracture occurrence. As a result, a scale factor for each element size in in-plane deformation can be obtained, as shown in Figure 10(b).

[0068] (Step S12) In step S12, the in-plane deformation fracture limit line L1 is corrected. The first correction unit 22 multiplies the vertical axis value (value of fracture strain (equivalent plastic strain)) of the in-plane deformation fracture limit line L1 created in step S1 by a scale factor in the element size of the FEM model used in the collision deformation analysis. As a result, a corrected in-plane deformation fracture limit line L1' corrected by the scale factor is obtained, as shown in Fig. 10(a).

[0069] In this embodiment, similarly to the first embodiment, the bending fracture limit line L2 is created in steps S2 and S3.

[0070] (Step S13) In step S13, in the bending FEM analysis, a scale factor corresponding to the element size in bending deformation is acquired, which indicates the relationship between the bending limit strain and the element size.

[0071] The second scale factor acquisition unit 23 calculates the equivalent plastic strain ε of the outer surface layer of the bent part using the shell element when the limit VDA bending angle is reached. VDA In the following equation, ε' is obtained by substituting an arbitrary value for the element size. VDA The ratio of the values ​​of , for example, as shown in Fig. 11(b), obtains the scale factor for each bending element size. Maximum principal strain ε' on outer surface of bending c teeth, ε' c =a*M b +c It is expressed as: M: Element size (use any element size value) a, b, c: Plate thickness t and maximum principal strain ε of outer surface layer using solid elements based on detailed FEM model s The relation At this time, ε s =d*ln(α)+e This becomes: α: Limit VDA bending angle d, e: Relational formula for plate thickness t ε' VDA is ε'c Using ε' VDA =ε' c *2 / √3 It can be expressed as:

[0072] (Step S14) In step S14, the bending fracture limit line L2 is corrected. The second correction unit 24 multiplies the vertical axis value (value of fracture strain (equivalent plastic strain)) of the bending fracture limit line L2 created in step S2 by a scale factor in the element size of the FEM model used in the collision deformation analysis. As a result, a corrected bending fracture limit line L2' corrected by the scale factor is obtained, as shown in Fig. 11(a).

[0073] In this embodiment, similarly to the first embodiment, the composite deformation degree of the member that is the deformation analysis target is acquired in step S4.

[0074] (Step S5) In step S5, a corrected combined deformation fracture limit line L3' is created. The combined deformation fracture limit line creating unit 14 creates a combined deformation fracture limit line L3' using the corrected in-plane deformation fracture limit line L1' created in step S12, the corrected bending fracture limit line L2' created in step S14, and the combined deformation degree b acquired in step S4. Since the combined deformation degree b changes during the collision deformation analysis, the corrected combined deformation fracture limit line L3' also changes. The combined deformation fracture limit line creating unit 13 sequentially creates the corrected combined deformation fracture limit line L3' that changes during the collision deformation analysis.

[0075] (Step S6) In step S6, it is determined whether or not the member will break. The fracture determination unit 15 compares the stress triaxiality and equivalent plastic strain generated in the component obtained by the collision deformation analysis with the corrected combined deformation fracture limit line L3', which changes sequentially, to determine whether or not fracture will occur in the component. When the value of the equivalent plastic strain generated in the component exceeds the corrected combined deformation fracture limit line L3', it is determined that fracture has occurred in the component.

[0076] As described above, this embodiment makes it possible to accurately predict fracture in response to the composite and complex deformation state that occurs when steel is subjected to in-plane deformation and bending deformation (out-of-plane deformation) simultaneously, as occurs in actual components. In this embodiment, fracture prediction can be performed with even higher accuracy by correcting the fracture limit line using the element size of FEM analysis. This can contribute to reducing the costs required for product development and significantly shortening the development period.

[0077] -Other embodiments- In the above-described embodiments, a storage medium such as ROM 2 stores a computer program for controlling the fracture prediction device 10. This computer program is a control program for implementing various functions of the CPU 1 (such as the in-plane deformation fracture limit line creation unit 11, the bending fracture limit line creation unit 12, the combined deformation degree acquisition unit 13, the combined deformation fracture limit line creation unit 14, the fracture determination unit 15, the first and second scale factor acquisition units 21 and 23, and the first and second correction units 22 and 24). Specifically, the program corresponds to steps shown in FIGS. 3 and 9 . Steps S1 to S6 correspond to steps S1 to S6 and S11 to S14 correspond to steps S1 to S6 and S11 to S14 in FIG. 9 . The CPU 1, as a computer, reads and executes the computer program from a computer-readable storage medium such as ROM 2. The various embodiments can also be implemented by providing the computer program to a system or device via a network or storage medium, and having one or more processors in the computer of the system or device read and execute the program. It can also be realized by a circuit (for example, an ASIC) that realizes one or more functions. The program code itself read from the recording medium realizes the functions of the above-mentioned embodiments, and the recording medium on which the program code is recorded constitutes the present disclosure.

[0078] -Example- Examples of the first and second embodiments will be described below together with comparative examples. Here, Example 1 corresponds to the first embodiment, and Example 2 corresponds to the second embodiment. In the comparative example, fracture prediction of the member was performed using only the in-plane deformation fracture limit line creating unit 11.

[0079] Fig. 12 is a characteristic diagram showing various fracture limit lines used in Examples 1 and 2 and the Comparative Example. Fig. 13 is a schematic diagram showing an FEM analysis reproducing an experiment in which fracture occurred in a square tube. Fig. 14 is a characteristic diagram showing fracture prediction results in Examples 1 and 2 and the Comparative Example.

[0080] A square tube with a cross section of 50 x 50 mm and a length of 200 mm was created using 980 MPa-grade steel plate (thickness: 1.4 mm, limit VDA bending angle: 70°), and an impactor was used to impact the tube from the axial direction at a speed of 20 km / hr. As a result, fracture occurred at the bent portion that had been folded due to buckling at an impactor stroke of 15.5 mm.

[0081] Next, in Example 1, the fracture judgment flow of the first embodiment shown in Fig. 3 was followed, and in Example 2, the fracture judgment flow of the second embodiment shown in Fig. 9 was followed, to obtain the in-plane deformation fracture limit line L1 for a 980 MPa-class steel plate with a plate thickness of 1.4 mm. At the same time, the bending fracture limit line L2 was obtained from the limit VDA bending angle and plate thickness, and plotted in Fig. 12.

[0082] In Example 2, a correction coefficient of 0.88 was obtained for the element size of 1 mm used in this FEM analysis from the separately obtained relationship between the element size scale factors for in-plane deformation. Then, the vertical axis of the in-plane deformation fracture limit line l1 was multiplied by 0.88 to obtain a corrected in-plane deformation fracture limit line L1', which was plotted in Fig. 12. Similarly, in Example 2, a correction coefficient of 0.76 was obtained for an element size of 1 mm from the separately obtained relationship between the element size scale factors for bending, and the vertical axis of the bending fracture limit line L2 was multiplied by 0.76 to obtain a corrected bending fracture limit line L2', which was plotted in Fig. 12.

[0083] Furthermore, an FEM analysis model that reproduced the above-mentioned experiment was created, and an FEM crash analysis was performed using the crash analysis software LS-DYNA. Focusing on the elements at the location where fracture occurred in the experiment, the history of stress triaxiality and equivalent plastic strain was obtained.

[0084] In the comparative example, the in-plane deformation fracture limit line L1 was used, and the timing at which the in-plane deformation fracture limit line L1 was crossed was considered to be the fracture, and the impactor stroke at that time was obtained. The impactor stroke value was 11 mm, as shown in Figure 14. This value was a significantly earlier prediction than the 15.5 mm obtained in the experiment.

[0085] In Example 1, the bending deformation state ratio b of the element at the fracture occurrence site, obtained using the method of the first embodiment, was 0.91. A composite deformation limit line L3 was obtained, located between the in-plane deformation fracture limit line L1 and the bending fracture limit line L2, where the ratio was 0.91. The timing at which the composite deformation limit line L3 was crossed was considered to be fracture, and the impactor stroke at that time was obtained. The impactor stroke value was 17 mm, as shown in Figure 14. Although this value was slightly delayed compared to the 15.5 mm obtained in the experiment, it was possible to predict a fracture stroke close to that obtained in the experiment.

[0086] In Example 2, which considered the effect of element size in the FEM analysis, the value of the combined deformation index b, which is the bending deformation state ratio of the element at the fracture occurrence site, was 0.91. Using this combined deformation index b, a corrected combined deformation limit line L3' was obtained, located at a ratio of 0.91 between the corrected in-plane deformation fracture limit line L1' and the corrected bending fracture limit line L2'. The timing at which the corrected combined deformation limit line L3' was crossed was considered to be fracture, and the impactor stroke at that time was obtained. The impactor stroke value was 15.3 mm, as shown in Figure 14. This value was very close to the 15.5 mm obtained in the experiment, and the fracture stroke could be predicted with high accuracy. [Explanation of symbols]

[0087] 1:CPU 2:ROM 3: RAM 4: Secondary storage 5: Input device 6:Display device 11: In-plane deformation fracture limit line creation section 12: Bending fracture limit line creation section 13: Composite deformation degree acquisition unit 14: Complex deformation fracture limit line creation section 15: Breakage judgment section 21: First scale factor acquisition unit 22: First correction unit 23: Second scale factor acquisition unit 24: Second correction unit

Claims

1. A method for predicting fracture of a component using a finite element method, A first step of creating an in-plane deformation fracture limit line according to an in-plane deformation form formed by the relationship between stress triaxiality and equivalent plastic strain of a material used for the member; A second step of creating a bending fracture limit line for the material by proportionally multiplying the value of the equivalent plastic strain of the bending outer surface layer at the bending fracture limit of the material until the value of the equivalent plastic strain of the in-plane deformation fracture limit line intersects with a plot point obtained from the values ​​of the stress triaxiality and equivalent plastic strain of the bending outer surface layer at the bending fracture limit; A third step of acquiring a composite deformation degree using the thickness direction strain of the bending outer surface layer and the thickness direction strain of the bending inner surface layer of the member obtained by the collision deformation analysis; A fourth step of creating a composite deformation fracture limit line using the in-plane deformation fracture limit line, the bending fracture limit line, and the composite deformation degree; a fifth step of comparing the stress triaxiality and equivalent plastic strain generated in the member obtained by the collision deformation analysis with the composite deformation fracture limit line to determine whether or not fracture will occur in the member; A fracture prediction method comprising:

2. In the first step, the in-plane deformation fracture limit line is corrected using a relationship between element size and tensile limit strain in a finite element method, which has been previously obtained, to obtain the in-plane deformation fracture limit line according to the element size; In the second step, the bending fracture limit line is corrected using a relationship between an element size and a bending limit strain in a finite element method, which has been obtained in advance, to obtain the bending fracture limit line according to the element size. The fracture prediction method according to claim 1 .

3. The equivalent plastic strain of the outer surface layer at the bending fracture limit is the equivalent plastic strain of the outer surface layer at the time when the limit VDA bending angle is reached. The fracture prediction method according to claim 1 .

4. The composite deformation degree is b, and the strain in the thickness direction of the outer surface layer of the bent part is ε out , the strain in the thickness direction of the inner surface layer of the bending is ε in As a result, the following relationship holds: b=(e) out -e in ) / (2*e out ) 0≦b≦1 The fracture prediction method according to claim 1 .

5. In the third step, the composite deformation degree that changes during the collision deformation analysis is sequentially acquired. The fracture prediction method according to claim 1 .

6. A fracture prediction device that predicts fracture of a component using a finite element method, an in-plane deformation fracture limit line creation unit that creates an in-plane deformation fracture limit line according to an in-plane deformation form formed by the relationship between stress triaxiality and equivalent plastic strain of a material used for the member; A bending fracture limit line creation unit that uses the value of the equivalent plastic strain of the bending outer surface layer at the bending fracture limit of the material to proportionally multiply the value of the equivalent plastic strain of the in-plane deformation fracture limit line until it intersects with a plot point obtained from the stress triaxiality and the value of the equivalent plastic strain of the bending outer surface layer at the bending fracture limit, thereby creating a bending fracture limit line of the material; a composite deformation degree acquisition unit that acquires a composite deformation degree using the thickness direction strain of the bending outer surface layer and the thickness direction strain of the bending inner surface layer of the member obtained by the collision deformation analysis; A composite deformation fracture limit line creation unit that creates a composite deformation fracture limit line using the in-plane deformation fracture limit line, the bending fracture limit line, and the composite deformation degree; a fracture determination unit that compares the stress triaxiality and equivalent plastic strain generated in the member obtained by the collision deformation analysis with the composite deformation fracture limit line to determine whether or not fracture will occur in the member; A fracture prediction device having the above structure.

7. a first correction unit that corrects the in-plane deformation fracture limit line using a relationship between an element size and a tensile limit strain in a finite element method that has been obtained in advance, and acquires the in-plane deformation fracture limit line according to the element size; a second correction unit that corrects the bending fracture limit line using a relationship between an element size and a bending limit strain in a finite element method that has been obtained in advance, and acquires the bending fracture limit line according to the element size; Further comprising: The fracture prediction device according to claim 6.

8. The equivalent plastic strain of the outer surface layer at the bending fracture limit is the equivalent plastic strain of the outer surface layer at the time when the limit VDA bending angle is reached. The fracture prediction device according to claim 6.

9. The composite deformation degree is b, and the strain in the thickness direction of the outer surface layer of the bent part is ε out , the strain in the thickness direction of the inner surface layer of the bending is ε in As a result, the following relationship holds: b=(e) out -e in ) / (2*e out ) 0≦b≦1 The fracture prediction device according to claim 6.

10. The composite deformation degree acquisition unit sequentially acquires the composite deformation degree that changes during collision deformation analysis. The fracture prediction device according to claim 6.

11. A method for predicting fracture of a component using a finite element method, A first step of creating an in-plane deformation fracture limit line according to an in-plane deformation form formed by the relationship between stress triaxiality and equivalent plastic strain of a material used for the member; A second step of creating a bending fracture limit line for the material by proportionally multiplying the value of the equivalent plastic strain of the bending outer surface layer at the bending fracture limit of the material until the value of the equivalent plastic strain of the in-plane deformation fracture limit line intersects with a plot point obtained from the values ​​of the stress triaxiality and equivalent plastic strain of the bending outer surface layer at the bending fracture limit; A third step of acquiring a composite deformation degree using the thickness direction strain of the bending outer surface layer and the thickness direction strain of the bending inner surface layer of the member obtained by the collision deformation analysis; A fourth step of creating a composite deformation fracture limit line using the in-plane deformation fracture limit line, the bending fracture limit line, and the composite deformation degree; a fifth step of comparing the stress triaxiality and equivalent plastic strain generated in the member obtained by the collision deformation analysis with the composite deformation fracture limit line to determine whether or not fracture will occur in the member; A program for causing a computer to execute the fracture prediction method, comprising:

12. In the first step, the in-plane deformation fracture limit line is corrected using a relationship between element size and tensile limit strain in a finite element method, which has been previously obtained, to obtain the in-plane deformation fracture limit line according to the element size; In the second step, the bending fracture limit line is corrected using a relationship between an element size and a bending limit strain in a finite element method, which has been obtained in advance, to obtain the bending fracture limit line according to the element size. The program according to claim 11.

13. The equivalent plastic strain of the outer surface layer at the bending fracture limit is the equivalent plastic strain of the outer surface layer at the time when the limit VDA bending angle is reached. The program according to claim 11.

14. The composite deformation degree is b, and the strain in the thickness direction of the outer surface layer of the bent part is ε out , the strain in the thickness direction of the inner surface layer of the bending is ε in As a result, the following relationship holds: b=(e) out -e in ) / (2*e out ) 0≦b≦1 The program according to claim 11.

15. In the third step, the composite deformation degree that changes during the collision deformation analysis is sequentially acquired. The program according to claim 11.

16. A computer-readable recording medium having the program according to any one of claims 11 to 15 recorded thereon.

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