Break prediction method and break prediction device

Abstract

To accurately predict fracture of an edge part of a metal plate.SOLUTION: In the fracture prediction method, fracture of an edge part 2 of a metal plate 1 is predicted by finite element analysis. The fracture prediction method includes acquiring a strain gradient in a direction away from the edge portion 2 by analysis simulating deformation of the edge portion 2, acquiring a corrected fracture limit curve by replacing an equivalent plastic strain when a predetermined stress triaxial degree in the fracture limit curve is uniaxial tensile deformation with a fracture limit strain of an experimental value, creating an analysis model SM by applying the corrected fracture limit curve to the edge portion 2 and applying an uncorrected fracture limit curve to portions other than the edge portion, and predicting a fracture of the edge portion 2 using the analysis model SM.SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

[0002] Technologies have been developed to predict fracture from the edge of a metal plate in deformation analysis such as automobile collision deformation simulations. For example, Patent Document 1 discloses a method for predicting fracture at the edge based on the fact that strain at the edge is collected and the fracture limit changes depending on the hole expansion ratio. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2023-119935 Summary of the Invention [Problem to be solved by the invention]

[0004] In Patent Document 1, it is stated that the fracture limit is determined by the hole expansion ratio, and the influence of various strain conditions that may change depending on the processing mode of the edge portion and the end face properties of the edge portion are not taken into consideration, so there is room for improvement in the fracture prediction accuracy.

[0005] An object of the present invention is to accurately predict fracture of an edge portion of a metal plate. [Means for solving the problem]

[0006] A first aspect of the present invention is A fracture prediction method for predicting fracture of an edge portion of a metal plate by finite element analysis, comprising: obtaining a strain gradient in a direction away from the edge portion by an analysis simulating deformation of the edge portion; A modified fracture limit curve is obtained by replacing the equivalent plastic strain at a predetermined stress triaxiality in the fracture limit curve with the fracture limit strain of the experimental value at the strain gradient. creating an analytical model by applying the corrected fracture limit curve to the edge portion and applying the uncorrected fracture limit curve to portions other than the edge portion; The analytical model is used to predict the fracture of the edge portion. The present invention provides a method for predicting fracture, comprising:

[0007] According to this configuration, the strain gradient is acquired to take into account the end surface properties of the edge portion, and the fracture limit curve is corrected using the fracture limit strain experimental value at that strain gradient. Therefore, compared to when the fracture limit curve is not corrected, fracture of the edge portion of the metal plate can be predicted with higher accuracy. In the above, the corrected fracture limit curve is used only for the edge portion to take into account damage during edge processing, and the general fracture limit curve is used for parts other than the edge portion that are not damaged by edge processing.

[0008] The predetermined stress triaxiality may correspond to a stress state at the edge portion in an analysis for obtaining the strain gradient.

[0009] According to this configuration, the stress state of the edge portion is confirmed in advance, and the equivalent plastic strain of the stress triaxiality corresponding to that stress state is replaced with the experimental fracture limit strain, thereby enabling more accurate fracture predictions that are in line with reality.

[0010] The predetermined stress triaxiality may correspond to a uniaxial tensile deformation.

[0011] According to this configuration, since deformation at the edge portion is often dominated by uniaxial tensile deformation, this can be easily reflected.

[0012] GISSMO may be used as a fracture prediction model.

[0013] This configuration enables highly accurate fracture prediction that takes damage accumulation into account. Note that GISSMO (Generalized Incremental Stress State-dependent damage Model) is a well-known fracture prediction model that determines fracture based on accumulated damage (damage value) and leads to fracture (element deletion) when the accumulated damage reaches a predetermined value.

[0014] In the modified fracture limit curve, the section of the stress triaxiality from shear deformation to the predetermined stress triaxiality and the section of the stress triaxiality from the predetermined stress triaxiality to plane strain deformation may be interpolated by straight lines.

[0015] This configuration allows for easy linear interpolation to obtain a corrected fracture limit curve. Here, shear deformation indicates a stress triaxiality of approximately 0, uniaxial tensile deformation indicates a stress triaxiality of approximately one-third, and plane strain deformation indicates a stress triaxiality of approximately one-third. Note that the explanation using approximate stress triaxialities means that the details of each deformation state can be interpreted from the graph shape.

[0016] In the modified fracture limit curve, the section of the stress triaxiality from shear deformation to the predetermined stress triaxiality and the section of the stress triaxiality from the predetermined stress triaxiality to plane strain deformation may be interpolated by curves.

[0017] According to this configuration, since a fracture limit curve is generally composed of curved lines, a corrected fracture limit curve that is close to the shape of the original fracture limit curve can be obtained by curve interpolation.

[0018] and obtaining a modified necking limit curve by replacing the equivalent plastic strain at the predetermined stress triaxiality in the necking limit curve with the experimental necking limit strain at the strain gradient, In creating the analysis model, the modified necking limit curve may be applied to the edge portion, and the unmodified necking limit curve may be applied to portions other than the edge portion.

[0019] According to this configuration, by correcting not only the fracture limit curve but also the necking limit curve, fracture prediction can be performed with even higher accuracy.

[0020] The edge portion may be a stamped edge portion, a laser processed edge portion, or a machined edge portion.

[0021] These configurations enable highly accurate fracture prediction for metal plates that have undergone edge processing that causes damage to the edge, such as punching, laser processing, or cutting.

[0022] In the analytical model, the edge portion may consist of only one row of finite elements.

[0023] According to this configuration, damage caused by end face processing of the edge portion affects only the edge, so by correcting the fracture limit curve (and necking limit curve) using only one row of finite elements of the edge as the edge portion, the fracture limit curve (and necking limit curve) can be corrected just enough.

[0024] A second aspect of the present invention is A fracture prediction device that predicts fracture of an edge portion of a metal plate by finite element analysis, a strain gradient acquisition unit that acquires a strain gradient in a direction away from the edge portion by an analysis that simulates deformation of the edge portion; a fracture limit curve correction unit that obtains a corrected fracture limit curve by replacing an equivalent plastic strain at a predetermined stress triaxiality in the fracture limit curve with an experimental fracture limit strain at the strain gradient; an analytical model creation unit that creates an analytical model by applying the corrected fracture limit curve to the edge portion and applying the uncorrected fracture limit curve to portions other than the edge portion; a fracture prediction unit that predicts fracture of the edge portion using the analysis model; A fracture prediction device is provided.

[0025] The predetermined stress triaxiality may correspond to the stress state of the edge portion in an analysis for obtaining the strain gradient.

[0026] The predetermined stress triaxiality may correspond to a uniaxial tensile deformation. [Effects of the Invention]

[0027] According to the present invention, fracture of the edge portion of a metal plate can be predicted with high accuracy. [Brief explanation of the drawings]

[0028] [Figure 1] FIG. 1 is a perspective view of a metal plate including an edge portion. [Figure 2] 1 is a schematic configuration diagram of a fracture prediction device according to an embodiment of the present invention. [Figure 3] Graph showing maximum principal strain εm (fracture limit strain and necking limit strain) against strain gradient Δε. [Figure 4] Graph showing equivalent plastic strain εs versus stress triaxiality η (fracture limit curve and modified fracture limit curve). [Figure 5] Graph showing equivalent plastic strain εs (necking limit curve and modified necking limit curve) against stress triaxiality η. [Figure 6] Plan view of the analytical model. [Figure 7] 1 is a flowchart of a fracture prediction method according to an embodiment of the present invention. [Figure 8] Comparison table showing the accuracy of fracture location predictions. [Figure 9] Comparison table showing the accuracy of break stroke predictions. [Figure 10] 10 is a graph showing a breaking limit curve and a modified breaking limit curve in another modified example. [Figure 11] 10 is a graph showing a fracture limit curve and a modified fracture limit curve in yet another modified example. DETAILED DESCRIPTION OF THE INVENTION

[0029] Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings.

[0030] In this embodiment, a fracture prediction method and a fracture prediction device for predicting fracture of a metal plate including an edge portion will be described. In particular, the fracture of the edge portion of a metal plate used as an automobile part against an impact during an automobile collision can be predicted with high accuracy.

[0031] FIG. 1 is a perspective view of a metal plate 1 including an edge portion 2. As shown in FIG.

[0032] In this embodiment, for a rectangular metal plate 1 having a processed portion 3 in the form of a semicircular notch (hole), fracture of an edge portion 2 (see the shaded area) forming the edge of the processed portion 3 is predicted. The metal plate 1 is, for example, a steel material (980 MPa-class steel plate). The processed portion 3 is formed, for example, by punching. That is, the edge portion 2 is the punched end portion. However, the shape, material, processing method, etc. of the metal plate 1 are not particularly limited. For example, laser processing or cutting may be performed instead of punching to form the processed portion 3.

[0033] A strain ε occurs in the metal plate 1 due to punching of the processed portion 3. The gradient of the strain ε in the direction away from the edge portion 2 (X direction: the radial direction of the processed portion 3) is called the strain gradient Δε. In Figure 1, the strain gradient Δε is shown as a schematic graph superimposed on the metal plate 1.

[0034] FIG. 2 shows a schematic configuration diagram of a fracture prediction device 10 according to one embodiment of the present invention.

[0035] The fracture prediction device 10 predicts fracture of the edge portion 2 of the metal plate 1 by finite element analysis. In this embodiment, GISSMO (Generalized Incremental Stress State Dependent Damage Model) is used as the fracture prediction model. GISSMO is a well-known fracture prediction model that determines fracture based on accumulated damage (damage value) and leads to fracture (element deletion) when the accumulated damage reaches a predetermined value. However, the fracture prediction model is not limited to GISSMO, and any fracture prediction model may be used, including a simple damage threshold determination model that does not consider damage accumulation.

[0036] In this embodiment, fracture and necking limits are evaluated using a fracture limit curve that indicates the equivalent plastic strain related to fracture versus stress triaxiality, and a necking limit curve that indicates the equivalent plastic strain related to necking limit versus stress triaxiality. The fracture limit curve and necking limit curve can be obtained from literature or through experiments. As will be described in detail later, in this embodiment, fracture prediction is performed by modifying known fracture limit curves and necking limit curves rather than using them as they are.

[0037] The fracture prediction device 10 has a control unit (processor) 11, an input unit 12, an output unit 13, and a memory unit 14. The control unit 11 performs calculation processing and controls the entire device. The input unit 12 generates or receives input data for the device and is composed of, for example, a keyboard, a mouse, a touch panel, etc. The output unit 13 displays processing results by the control unit 11 and is composed of, for example, a liquid crystal display, an organic EL display, a plasma display, etc. The memory unit 14 stores programs running on the control unit 11 and parameter data necessary for finite element analysis. The control unit 11, the input unit 12, and the output unit 13 are connected to each other by an appropriate bus. The fracture prediction device 10 can be composed of, for example, an information processing device such as a desktop computer, a laptop computer, a workstation, or a tablet terminal, or a printed circuit board with equivalent functions.

[0038] The fracture prediction device 10 realizes predetermined functions by reading data and programs stored in the storage unit 14 and performing various arithmetic processing. The programs executed by the fracture prediction device 10 may be provided from an external device using a communication unit that communicates in accordance with a predetermined communication standard, or may be stored in a portable recording medium.

[0039] The fracture prediction device 10 includes, as functional components, a strain gradient acquisition unit 15, a fracture limit curve correction unit 16, a necking limit curve correction unit 17, an analysis model creation unit 18, and a fracture prediction unit 19. These are realized by cooperation of hardware and software. These may also be interpreted as corresponding circuits.

[0040] The strain gradient acquisition unit 15 acquires the strain gradient Δε in the direction away from the edge portion 2 by performing an analysis that simulates the deformation of the edge portion 2. For example, an analysis for acquiring this strain gradient Δε may be performed by a collision analysis of an automobile that includes the metal plate 1 as a component, or a press-molding analysis that deforms the metal plate 1 into a predetermined shape. This analysis may be performed by any known method that can simulate the deformation of the edge portion 2, and therefore a detailed description thereof will be omitted here. Here, the following description will be given assuming that the value of the strain gradient Δε in the edge portion 2 is obtained as Δεx by an automobile collision analysis, as an example.

[0041] The fracture limit curve correction unit 16 obtains a corrected fracture limit curve by replacing the equivalent plastic strain when the stress triaxiality in the fracture limit curve is uniaxial tensile deformation with the fracture limit strain of the experimental value at the strain gradient Δεx. The fracture limit strain of the experimental value at the strain gradient Δεx used here is obtained in advance as shown below.

[0042] Similarly, the necking limit curve correction unit 17 obtains a corrected necking limit curve by replacing the equivalent plastic strain in the necking limit curve when the stress triaxiality is uniaxial tensile deformation with the experimental necking limit strain at the strain gradient Δεx. The experimental necking limit strain at the strain gradient Δεx used here is obtained in advance as shown below.

[0043] FIG. 3 is a graph showing the maximum principal strain ε m (fracture limit strain and necking limit strain) versus the strain gradient Δε.

[0044] The fracture limit strain is shown linearly with a solid line (see line L1). Line L1 is a linear approximation of the fracture limit strain experimentally measured at various strain gradients Δε (see multiple black circles). Similarly, the necking limit strain is shown linearly with a dashed line (see line L2). Line L2 is a linear approximation of the necking limit strain experimentally measured at various strain gradients Δε (see multiple white circles). Therefore, by referring to Figure 3, the fracture limit strain and necking limit strain for any strain gradient Δε can be easily obtained. Here, it is assumed that the fracture limit strain εm1 and the necking limit strain εm2 are obtained when the strain gradient is Δεx.

[0045] Fig. 4 is a graph showing equivalent plastic strain εs (fracture limit curve C11 and modified fracture limit curve C12) versus stress triaxiality η. Fig. 5 is a graph showing equivalent plastic strain εs (necking limit curve C21 and modified necking limit curve C22) versus stress triaxiality η.

[0046] In the graphs of Figures 4 and 5, when the stress triaxiality η is approximately 0 (η = η0), it indicates shear deformation, when the stress triaxiality η is approximately one-third (η = η1), it indicates uniaxial tensile deformation, and when the stress triaxiality η is approximately one-third (η = η2), it indicates plane strain deformation. The shape of each graph can also be used to determine the state of deformation.

[0047] In this embodiment, the fracture limit curve correction unit 16 obtains a corrected fracture limit curve C12 by replacing the equivalent plastic strain (see point P1) when the stress triaxiality η in the fracture limit curve C11 is uniaxial tensile deformation (η = η1) with the experimental fracture limit strain εm1 when the strain gradient Δεx is the same. In the corrected fracture limit curve C12, the range of stress triaxiality from shear deformation to uniaxial tensile deformation (η0 < η < η1) and the range of stress triaxiality from uniaxial tensile deformation to plane strain deformation (η1 < η < η2) are interpolated with straight lines (see dashed dotted lines). In the ranges other than these (η < η0 and η2 < η), the fracture limit curve C11 and the corrected fracture limit curve C12 coincide.

[0048] In this embodiment, the necking limit curve correction unit 17 obtains a modified necking limit curve C22 by replacing the equivalent plastic strain (see point P2) when the stress triaxiality η in the necking limit curve C21 is uniaxial tensile deformation (η = η1) with the experimental necking limit strain εm2 when the strain gradient Δεx is the same. In the modified necking limit curve C22, the ranges (η<η<η1) in which the stress triaxiality η changes from shear deformation to uniaxial tensile deformation and the range (η<η<η2) in which the stress triaxiality η changes from uniaxial tensile deformation to plane strain deformation are interpolated with straight lines (see the two-dot chain line). In the ranges other than these ranges (η<η0 and η2<η), the necking limit curve C21 and the modified necking limit curve C22 coincide.

[0049] The analytical model creation unit 18 divides the CAD data of the metal plate 1 into finite elements. Furthermore, the analytical model creation unit 18 creates an analytical model by applying a corrected fracture limit curve C12 to the edge portion 2 and applying an uncorrected fracture limit curve C11 to the interior 4 other than the edge portion 2. Furthermore, the analytical model creation unit 18 applies a corrected necking limit curve C22 to the edge portion 2 and applies an uncorrected necking limit curve C21 to the interior 4 other than the edge portion 2.

[0050] FIG. 6 shows a plan view of the analytical model SM. In the analytical model SM, the rectangular metal plate 1 having the semicircular processed portion 3 of FIG. 1 is divided into finite elements. In the illustrated example, the edge portion 2 consists of only one row of finite elements (see the shaded area). In other words, two or more finite elements are not arranged in the direction away from the edge portion 2 (the radial direction of the processed portion 3) as elements constituting the edge portion 2. Note that the number of finite elements constituting the edge portion 2 or the interior 4 may be adjusted as necessary. For example, the edge portion 2 may consist of two or more rows of finite elements depending on the mesh size (the size of each finite element).

[0051] The fracture prediction unit 19 performs deformation analysis by the finite element method using the analytical model SM created by the analytical model creation unit 18, and predicts fracture of the edge portion 2. The deformation analysis can be performed by any known method, so a detailed description thereof will be omitted here. For example, if the metal plate 1 is an automobile part, a deformation analysis simulating an automobile collision may be performed.

[0052] The fracture prediction method in this embodiment will be described with reference to FIG.

[0053] FIG. 7 is a flowchart of a fracture prediction method according to one embodiment of the present invention.

[0054] First, as a preliminary step, the fracture limit strain and the necking limit strain with respect to the strain gradient Δε are experimentally obtained as shown in FIG. 3 (step S1). Next, the strain gradient Δεx in the direction away from the edge portion 2 is obtained by an analysis simulating deformation of the edge portion 2 (for example, a collision analysis of an automobile including the metal plate 1 as a component) (step S2). The strain gradient Δεx can be obtained by the strain gradient obtaining unit 15. Next, the fracture limit curve and the necking limit curve are corrected as described above based on the strain gradient Δεx (step S3). That is, the corrected fracture limit curve C12 and the corrected necking limit curve C22 are obtained. The corrected fracture limit curve C12 can be obtained by the fracture limit curve correcting unit 16. The corrected necking limit curve C22 can be obtained by the necking limit curve correcting unit 17. Next, an analytical model SM is created by applying the modified fracture limit curve C12 and the modified necking limit curve C22 only to the edge portion 2, and applying the fracture limit curve C11 and the necking limit curve C21 to the interior portion 4 (step S4). The analytical model SM can be created by the analytical model creation unit 18. Next, a deformation analysis is performed by the finite element method using the analytical model SM, and fracture prediction is performed for the edge portion 2 (step S5). The fracture prediction can be performed by the fracture prediction unit 19. Finally, the fracture prediction result is output (step S6). The result can be output to the output unit 13.

[0055] In a modified example of this embodiment, the part related to obtaining the corrected necking limit curve C22 may be omitted. In other words, the necking limit curve correcting unit 17 may be omitted from the fracture prediction device 10 shown in Fig. 2, and only the fracture limit curve may be corrected in the fracture limit curve and necking limit curve correcting step (step S3) shown in Fig. 7. In this case, the uncorrected necking limit curve C21 is applied to both the edge portion 2 and the interior portion 4.

[0056] The fracture prediction accuracy of the fracture prediction device 10 and fracture prediction method of this embodiment will be described with reference to FIGS.

[0057] Figure 8 is a comparison table showing the accuracy of fracture location prediction.

[0058] To confirm the fracture prediction accuracy, hole expansion tests were conducted for four cases. Specifically, in case 1, a circular hole with an initial diameter of 10 mm was expanded with a conical punch; in case 2, a circular hole with an initial diameter of 15 mm was expanded with a conical punch; in case 3, a circular hole with an initial diameter of 7.5 mm was expanded with a cylindrical punch; and in case 4, a circular hole with an initial diameter of 15 mm was expanded with a cylindrical punch. The fracture location (edge ​​2 or interior 4) was confirmed for these four cases.

[0059] In the experiment, the edge portion 2 cracked in all cases, whereas a conventional general method, which does not modify the fracture limit curve or necking limit curve, unlike the present embodiment, predicted that the edge portion 2 would crack only in the first case and that the inner portion 4 would crack in the second to fourth cases. In other words, the experimental results and the predicted results differ, indicating that the prediction accuracy of conventional general methods, which differ from the present embodiment, is low. In contrast, in the present embodiment, in which both the fracture limit curve and the necking limit curve are modified as described above, the edge portion 2 was predicted to crack in all cases. In other words, the actual experimental results and the predicted results matched, indicating the high prediction accuracy of the present embodiment. Furthermore, even when only the fracture limit curve was modified as described above, the actual experimental results and the predicted results matched, confirming the high prediction accuracy of the modified embodiment of the present embodiment.

[0060] Figure 9 is a comparison table showing the prediction accuracy of the break stroke.

[0061] When the fracture location matched between the experiment and the prediction, the fracture stroke (the punch plunge amount at fracture) was confirmed. Specifically, as in the case of predicting the fracture location described above, the agreement rate of the fracture stroke was compared for the actual experimental results when using the conventional method, when only the fracture limit curve was corrected (a modified version of this embodiment), and when both the fracture limit curve and the necking limit curve were corrected (this embodiment). The comparison results showed that when using the conventional method, the agreement was 83% with the experiment, when only the fracture limit curve was corrected (a modified version of this embodiment), the agreement was 90.8%, and when both the fracture limit curve and the necking limit curve were corrected (this embodiment), the agreement was 90.9%. Therefore, the high effectiveness of this embodiment and its modified versions was confirmed.

[0062] According to this embodiment, the following advantageous effects are achieved.

[0063] The strain gradient Δεx is acquired to take into account the end surface properties of the edge portion 2, and the fracture limit curve is corrected using the fracture limit strain εm1 experimentally obtained at that strain gradient Δεx. Therefore, compared to when the fracture limit curve is not corrected, fracture of the edge portion 2 of the metal sheet 1 can be predicted with higher accuracy. In particular, in the above embodiment, the corrected fracture limit curve C12 is used only for the edge portion 2 to take into account damage during end surface processing, and the general fracture limit curve C11 is used for the interior 4 other than the edge portion 2 that has not been damaged by end surface processing.

[0064] In addition, the equivalent plastic strain when the stress triaxiality is uniaxial tensile deformation is replaced with the experimental value, which can easily reflect the fact that uniaxial tensile deformation is often dominant in deformation at the edge portion 2.

[0065] In addition, because GISSMO is used as the fracture prediction model, highly accurate fracture prediction is possible, taking into account the accumulation of damage.

[0066] In addition, the stress triaxiality is interpolated by straight lines in the range from shear deformation to uniaxial tensile deformation (η0<η<η1) and in the range from uniaxial tensile deformation to plane strain deformation (η1<η<η2), so the corrected fracture limit curve C12 can be easily obtained.

[0067] Furthermore, in this embodiment, by correcting not only the fracture limit curve C11 but also the necking limit curve C21, fracture prediction can be performed with even higher accuracy.

[0068] Furthermore, it is possible to predict with high accuracy the fracture of a metal plate 1 that has undergone edge processing such as punching, which causes damage to the edge portion 2.

[0069] Furthermore, since damage caused by end face processing of the edge portion 2 affects only the edge, by correcting the fracture limit curve and necking limit curve using only one row of finite elements of the edge as the edge portion 2, the fracture limit curve and necking limit curve can be corrected without excess or deficiency.

[0070] Although specific embodiments of the present invention have been described above, the present invention is not limited to the above embodiments and can be implemented with various modifications within the scope of the present invention.

[0071] FIG. 10 is a graph showing a fracture limit curve C11 and a modified fracture limit curve C12 in another modified example.

[0072] When obtaining the modified fracture limit curve C12, the section where the stress triaxiality η changes from shear deformation to uniaxial tensile deformation (η0<η<η1) and the section where the stress triaxiality η changes from uniaxial tensile deformation to plane strain deformation (η1<η<η2) may be interpolated with curves, respectively.

[0073] Specifically, the method for interpolating the curve is based on the following equation (1). In equation (1), α, β, γ, and δ are constants called fitting parameters, which can be adjusted arbitrarily to match the desired shape of the graph. Furthermore, τmax is the maximum shear stress, and σs is the equivalent stress. However, the following equation (1) is only an example of curve interpolation, and other equations may also be used.

[0074]

number

[0075] FIG. 11 is a graph showing a fracture limit curve C11 and a modified fracture limit curve C12 in yet another modified example.

[0076] When obtaining the modified fracture limit curve C12, the fracture limit curve C11 may be offset to obtain the modified fracture limit curve C12. The offset amount should be such that the modified fracture limit curve C12 passes through the fracture limit strain εm1 when the stress triaxiality η is uniaxial tensile deformation (η=η1).

[0077] According to the above and further other modified examples, since the fracture limit curve C11 in GISSMO is generally composed of a curve, a corrected fracture limit curve C12 that is close to the shape of the original fracture limit curve C11 can be obtained by curve interpolation.

[0078] In the above embodiment, the equivalent plastic strain when the stress triaxiality is uniaxial tensile deformation (η = η1) is replaced with the experimental value, but the stress triaxiality to be replaced is not limited to uniaxial tensile deformation. For example, in an analysis to obtain the strain gradient Δε, the stress state of the edge portion 2 may be confirmed to obtain the stress triaxiality (e.g., η3), and the equivalent plastic strain when the stress triaxiality is η3 may be replaced with the experimental value. This enables more accurate fracture prediction based on actual conditions.

[0079] The present disclosure may include the following aspects. (Aspect 1) A fracture prediction method for predicting fracture of an edge portion of a metal plate by finite element analysis, comprising: obtaining a strain gradient in a direction away from the edge portion by an analysis simulating deformation of the edge portion; A modified fracture limit curve is obtained by replacing the equivalent plastic strain at a predetermined stress triaxiality in the fracture limit curve with the fracture limit strain of the experimental value at the strain gradient. creating an analytical model by applying the corrected fracture limit curve to the edge portion and applying the uncorrected fracture limit curve to portions other than the edge portion; The analytical model is used to predict the fracture of the edge portion. A fracture prediction method comprising: (Aspect 2) 2. The fracture prediction method according to claim 1, wherein the predetermined stress triaxiality corresponds to the stress state of the edge portion in the analysis for obtaining the strain gradient. (Aspect 3) 2. The fracture prediction method of claim 1, wherein the predetermined stress triaxiality corresponds to a uniaxial tensile deformation. (Aspect 4) 4. The fracture prediction method according to any one of aspects 1 to 3, wherein GISSMO is used as the fracture prediction model. (Aspect 5) 5. The fracture prediction method according to any one of aspects 1 to 4, wherein, in the modified fracture limit curve, a section of the stress triaxiality from shear deformation to the predetermined stress triaxiality and a section of the stress triaxiality from the predetermined stress triaxiality to plane strain deformation are each interpolated with a straight line. (Aspect 6) 5. The fracture prediction method according to any one of aspects 1 to 4, wherein, in the modified fracture limit curve, a section of the stress triaxiality from shear deformation to the predetermined stress triaxiality and a section of the stress triaxiality from the predetermined stress triaxiality to plane strain deformation are each interpolated with a curve. (Aspect 7) and obtaining a modified necking limit curve by replacing the equivalent plastic strain at the predetermined stress triaxiality in the necking limit curve with the experimental necking limit strain at the strain gradient, A fracture prediction method according to any one of aspects 1 to 6, wherein in creating the analysis model, the modified necking limit curve is applied to the edge portion, and the unmodified necking limit curve is applied to portions other than the edge portion. (Aspect 8) Aspect 8. The fracture prediction method according to any one of aspects 1 to 7, wherein the edge portion is a punched end portion. (Aspect 9) Aspect 8. The fracture prediction method according to any one of aspects 1 to 7, wherein the edge portion is a laser-processed end portion. (Aspect 10) Aspect 8. The fracture prediction method according to any one of aspects 1 to 7, wherein the edge portion is a machined end portion. (Aspect 11) 11. The fracture prediction method according to any one of aspects 1 to 10, wherein in the analysis model, the edge portion is composed of only one row of finite elements. (Aspect 12) A fracture prediction device that predicts fracture of an edge portion of a metal plate by finite element analysis, a strain gradient acquisition unit that acquires a strain gradient in a direction away from the edge portion by an analysis that simulates deformation of the edge portion; a fracture limit curve correction unit that obtains a corrected fracture limit curve by replacing an equivalent plastic strain at a predetermined stress triaxiality in the fracture limit curve with an experimental fracture limit strain at the strain gradient; an analytical model creation unit that creates an analytical model by applying the corrected fracture limit curve to the edge portion and applying the uncorrected fracture limit curve to portions other than the edge portion; a fracture prediction unit that predicts fracture of the edge portion using the analysis model; A fracture prediction device comprising: (Aspect 13) A fracture prediction device according to aspect 12, wherein the predetermined stress triaxiality corresponds to the stress state of the edge portion in the analysis for obtaining the strain gradient. (Aspect 14) 13. The fracture prediction apparatus of claim 12, wherein the predetermined stress triaxiality corresponds to a uniaxial tensile deformation. [Explanation of symbols]

[0080] 1 metal plate 2 Edge 3 Processing section 4 Inside 10. Fracture prediction device 11 Control section 12 Input section 13 Output section 14 Storage section 15 Strain gradient acquisition unit 16 Breaking limit curve correction section 17. Neck limit curve correction section 18 Analysis Model Creation Department 19 Breakage prediction section SM analysis model

Claims

1. A fracture prediction method for predicting fracture of an edge portion of a metal plate by finite element analysis, comprising: obtaining a strain gradient in a direction away from the edge portion by an analysis simulating deformation of the edge portion; A modified fracture limit curve is obtained by replacing the equivalent plastic strain at a predetermined stress triaxiality in the fracture limit curve with the fracture limit strain of the experimental value at the strain gradient. creating an analytical model by applying the corrected fracture limit curve to the edge portion and applying the uncorrected fracture limit curve to portions other than the edge portion; The analytical model is used to predict the fracture of the edge portion. A fracture prediction method comprising:

2. The fracture prediction method according to claim 1 , wherein the predetermined stress triaxiality corresponds to the stress state of the edge portion in an analysis for obtaining the strain gradient.

3. The fracture prediction method of claim 1 , wherein the predetermined stress triaxiality corresponds to uniaxial tensile deformation.

4. The fracture prediction method according to claim 1 , wherein GISSMO is used as the fracture prediction model.

5. 4. The fracture prediction method according to claim 1, wherein, in the modified fracture limit curve, a section of the stress triaxiality from shear deformation to the predetermined stress triaxiality and a section of the stress triaxiality from the predetermined stress triaxiality to plane strain deformation are each interpolated with a straight line.

6. 4. The fracture prediction method according to claim 1, wherein, in the modified fracture limit curve, a section of the stress triaxiality from shear deformation to the predetermined stress triaxiality and a section of the stress triaxiality from the predetermined stress triaxiality to plane strain deformation are each interpolated with a curve.

7. and obtaining a modified necking limit curve by replacing the equivalent plastic strain at the predetermined stress triaxiality in the necking limit curve with the experimental necking limit strain at the strain gradient, 4. The fracture prediction method according to claim 1, wherein in creating the analysis model, the modified necking limit curve is applied to the edge portion and the unmodified necking limit curve is applied to portions other than the edge portion.

8. The fracture prediction method according to claim 1 , wherein the edge portion is a stamped end portion.

9. The fracture prediction method according to claim 1 , wherein the edge portion is a laser-processed end portion.

10. The fracture prediction method according to claim 1 , wherein the edge portion is a machined end portion.

11. The fracture prediction method according to claim 1 , wherein in the analytical model, the edge portion is composed of only one row of finite elements.

12. A fracture prediction device that predicts fracture of an edge portion of a metal plate by finite element analysis, a strain gradient acquisition unit that acquires a strain gradient in a direction away from the edge portion by an analysis that simulates deformation of the edge portion; a fracture limit curve correction unit that obtains a corrected fracture limit curve by replacing an equivalent plastic strain at a predetermined stress triaxiality in the fracture limit curve with an experimental fracture limit strain at the strain gradient; an analytical model creation unit that creates an analytical model by applying the corrected fracture limit curve to the edge portion and applying the uncorrected fracture limit curve to portions other than the edge portion; a fracture prediction unit that predicts fracture of the edge portion using the analysis model; A fracture prediction device comprising:

13. The fracture prediction device according to claim 12 , wherein the predetermined stress triaxiality corresponds to a stress state of the edge portion in an analysis for obtaining the strain gradient.

14. The fracture prediction device of claim 12 , wherein the predetermined stress triaxiality corresponds to uniaxial tensile deformation.

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