Rupture prediction method and fracture prediction device, as well as fracture prediction program and recording medium.

Abstract

This invention provides a fracture prediction method that quantitatively and accurately determines the damage value of the elongated flange edge at the limit of molding height that does not cause fracture, thereby enabling flange-up molding with a large flange height while avoiding elongated flanges. [Solution] A method for predicting fracture of a member by flange-up molding, comprising: a first step of obtaining the fracture limit of the molded product obtained by a molding test; and a second step of reproducing the molding test by simulation and obtaining the limit damage value when fracture occurs in the molded product.

Description

Technical Field

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

Background Art

[0002] In recent years, in the automotive industry, the development of a vehicle body structure capable of reducing injuries to occupants during a collision has become an urgent issue. On the other hand, weight reduction of the vehicle body is also important for improving fuel efficiency. In order to solve these problems, the application of higher-strength materials, particularly high-strength steel sheets in steel materials, is being considered. However, generally, an increase in strength is said to cause deterioration of formability, and improvement of formability, particularly improvement of stretch flangeability, is important for expanding the application.

[0003] In Patent Document 1, for a thin plate as a test subject, the fracture limit hole expansion rate obtained by a hole expansion test is theoretically calculated from the relationship between stress and strain obtained by a tensile test, the fracture limit strain at the plate end is calculated based on the fracture limit hole expansion rate, and when the maximum principal strain obtained from numerical analysis by the finite element method reaches the fracture limit strain, a fracture prediction method for evaluating that the risk of fracture is high is disclosed.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, in the method of calculating the fracture limit strain at the plate end based on the fracture limit hole expansion rate, it is difficult to accurately grasp the damage value of the stretch flange edge at the forming limit height where no fracture occurs for saddle-shaped formed products.

[0006] The present invention has been made in view of the above problems, and aims to provide a fracture prediction method and apparatus, as well as a program and recording medium, that can quantitatively and accurately grasp the damage value of the stretched flange edge at the limit height at which fracture does not occur, and that can realize flange-up molding with a large flange height while avoiding stretched flanges. [Means for solving the problem]

[0007] In order to solve the above problems, after diligent study, we have come up with the following embodiments of the invention. The gist of the present invention is as follows.

[0008] [1] A method for predicting fracture of a component formed by flange-up molding, The first step is to obtain the fracture limit of the molded product obtained by the molding test, The aforementioned Based on the fracture limit of the molded product obtained in the first step, The second step involves reproducing the molding test through simulation and obtaining the limit damage value at which fracture occurs in the molded product. to have death , The process further includes a third step of comparing the limit damage value obtained in the molding analysis of the part with the limit damage value obtained in the second step to determine if the part will break. Method for predicting fracture.

[0009] [2] The molding test described above is a saddle-type molding test. The fracture prediction method described in [1].

[0010] [3] The molding test is performed using a sheared blank. The fracture prediction method described in [2].

[0011] [4] The molding test is performed using a laser-cut blank. The fracture prediction method described in [2] or [3].

[0012] [5] The first step described above is: Using the database in which the breaking limits of the molded products obtained by the molding test are accumulated, acquiring the breaking limit from the database, The fracture prediction method according to any one of [1] to [4].

[0013] [6] The second step is using the Cockcroft-Latham formula

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[0014] [7] The second step is performing finite element method analysis as the simulation, The fracture prediction method according to any one of [1] to [6].

[0015] [8] The second step is performing molding analysis on the blank to be the molded product using a solid model, The fracture prediction method according to [7].

[0017] 9 A fracture prediction device for a member by flanging-up molding, comprising an input part for inputting the breaking limit of the molded product obtained by the molding test, the Based on the fracture limit of the molded product obtained from the molding test, analysis part for reproducing the molding test by simulation and acquiring the limit damage value when fracture occurs in the molded product, having death , The system further includes a comparison unit that compares the limit damage value obtained from the molding analysis of the part with the limit damage value obtained from the analysis unit to determine if the part will break. Fracture prediction device.

[0018] 10 ​​​​The molding test described above is a saddle-type molding test. [ 9 The fracture prediction device described in [ ].

[0019] [ 11 ] The aforementioned analysis unit, Cockcroft-Latham formula

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[0020] [ 12 ] The aforementioned analysis unit, As the aforementioned simulation, a finite element method analysis is performed. [ 9 ]~[ 11 A fracture prediction device as described in any one of the following.

[0021] [ 13 ] The aforementioned analysis unit, The blank to be molded is subjected to molding analysis using a solid model. [ 12 The fracture prediction device described in [ ].

[0023] [ 14 ] A program for predicting the fracture of a component by flange-up forming, The first step is to obtain the fracture limit of the molded product obtained by the molding test, The aforementioned Based on the fracture limit of the molded product obtained in the first step, The second step involves reproducing the molding test through simulation and obtaining the limit damage value at which fracture occurs in the molded product, A third step involves comparing the limit damage value obtained from the molding analysis of the part with the limit damage value obtained in the second step to determine if the part will break, A fracture prediction program to be executed by a computer.

[0024] [15 ] The molding test described above is a saddle-type molding test. [ 14 The fracture prediction program described in [ ].

[0025] [ 16 ] The second step is, Cockcroft-Latham formula

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[0026] [ 17 ] The second step is, As the aforementioned simulation, a finite element method analysis is performed. [ 14 ]~[ 16 A fracture prediction program described in one of the following:

[0027] [ 18 ] The blank to be molded is subjected to molding analysis using a solid model. [ 17 The fracture prediction program described in [ ].

[0029] [ 19 ] [ 14 ]~[ 18 A computer-readable recording medium containing a fracture prediction program as described in any one of the following. [Effects of the Invention]

[0030] According to the present invention, it is possible to quantitatively and accurately determine the damage value of the stretched flange edge at the limit of molding height that does not break, and to achieve flange-up molding with a large flange height while avoiding stretched flanges. [Brief explanation of the drawing]

[0031] [Figure 1] This is a perspective view showing a disassembled molding apparatus used for saddle-type molding tests. [Figure 2] This is a schematic cross-sectional view showing the arrangement of each mold in a molding apparatus. [Figure 3] This is a perspective view showing how a saddle-shaped mold is formed using a molding device, for example, by a plate thickness compression method. [Figure 4] This is a schematic diagram showing a punch viewed from above. [Figure 5] This is a block diagram showing the functional configuration of the fracture prediction device according to this embodiment. [Figure 6] This is a schematic diagram showing the critical damage value (integral value) at the flange edge of a saddle-shaped molded product obtained by FEM analysis. [Figure 7] This is a schematic diagram showing the results of an FEM analysis on a specified component, for example, the lower arm of an automobile. [Figure 8] This block diagram shows an example of the hardware configuration of the fracture prediction device according to this embodiment. [Figure 9] This flowchart shows the fracture prediction method according to this embodiment in step order. [Figure 10] This is a schematic diagram showing the lower arm that was actually prototyped as a specified part, based on the comparison results from the comparison unit. [Modes for carrying out the invention]

[0032] The following describes in detail the fracture prediction method, fracture prediction device, program, and recording medium embodiments with reference to the drawings.

[0033] [Saddle-shaped molding test] In this embodiment, first, a flange-up molding test, specifically a saddle-type molding test, is performed. Figure 1 is a perspective view showing a disassembled molding apparatus used for saddle-type molding tests. Figure 2 is a schematic cross-sectional view showing the arrangement of each mold in the molding apparatus.

[0034] The molding apparatus (press machine) used for saddle-type molding tests includes a die 11, which is a mold for molding a blank 10, which is the component to be processed, by pressing it down; a pad 12, which is a mold placed between the die 11 and the blank 10; and a punch 13, which is a mold on which a holder 14 is placed and on which the blank 10 is mounted.

[0035] In this embodiment, since the fracture of the flange edge portion formed on the blank 10 is the target of the determination, it is preferable to use a blank 10 in which the flange edge portion has been processed by saddle-type shearing, which provides excellent processing accuracy. In saddle-type shearing, the effect of punching clearance is taken into account. Here, the punching clearance may be set to any value. Instead of saddle-type shearing, laser processing, which provides excellent processing accuracy, may be used, and a laser-cut blank 10 may be used.

[0036] In this embodiment, the saddle-shaped forming test is performed using one of the following methods: stamping, pad bending, deep drawing, and plate thickness compression. Here, plate thickness compression is a type of deep drawing in which the target area of ​​deep drawing is limited to the vicinity of the area where curvature is formed in the blank, and a hydrostatic pressure effect can be obtained in the plate thickness direction.

[0037] As shown in Figure 2, in stamping, die 11 and punch 13 are used as molds. In pad bending, die 11, pad 12, and punch 13 are used as molds. In deep drawing and sheet thickness compression methods, die 11, pad 12, punch 13, and holder 14 are used as molds. Saddle molding is performed either as single-sided molding, where a flange is formed on only one side of the blank 10, or as double-sided molding, where flanges are formed on both sides of the blank 10. Single-sided molding is acceptable considering ease of molding, while double-sided molding is acceptable considering avoiding uneven load on the press machine.

[0038] Figure 3 is a perspective view showing how a saddle-shaped mold is formed, for example, by a plate thickness compression method, using the molding apparatus configured as described above, with (a) showing the state before molding and (b) showing the state after molding. As shown in Figure 3(a), a blank 10 is placed on a punch 13 in which a holder 14 is positioned, and a die 11 is placed on top of it via a pad 12. Then, as shown in Figure 3(b), the die 11 presses the pad 12 and the blank 10 downwards. As a result, the blank 10 is compressed to match the shape of the punch 13 in Figure 3, and a saddle-shaped molded product with the desired flange is obtained.

[0039] Figure 4 is a schematic diagram showing a top view of the punch 13. For example, the punch 13 may have a radius of curvature R of 5 mm or more and 500 mm or less, and a clamping angle θ of 30° or more and 270° or less.

[0040] In this embodiment, the fracture limit of the blank 10 is determined by the saddle molding test described above. Specifically, the saddle molding test is performed by changing the width L of the blank 10 shown in Figure 1 to various values, and the limit width L at which no defects (such as constriction or fracture) occur in the flange edge portion (flange edge) of the resulting saddle molded product is obtained.

[0041] [Functional Configuration of the Rupture Prediction Device] Figure 5 is a block diagram showing the functional configuration of the fracture prediction device according to this embodiment. This fracture prediction device comprises an input unit 21 for inputting fracture limit values, an analysis unit 22 that performs saddle-shaped molding analysis using CAE (Computer-Aided Engineering) simulation, an output unit 23 that outputs the analysis results from the analysis unit 22, and a comparison unit 24 that compares the analysis results obtained by molding a predetermined part having a flange with the analysis results from the analysis unit 22.

[0042] The input unit 21 receives parameters such as the material, thickness, and tensile strength of the blank 10, as well as the fracture limit value identified in the saddle molding test described above (for example, the width L that is the limit at which defects (such as necking or fracture) do not occur in the saddle molded product). Instead of actually performing a saddle molding test each time the present invention is implemented, the fracture limit value may be obtained from a database containing data on fracture limit values ​​acquired by changing various parameters such as the material and thickness of the blank 10, and tensile strength.

[0043] The analysis unit 22 reproduces the saddle molding test described above using CAE, in this case the finite element method (FEM), to obtain the critical damage value (damage value of the flange edge at the molding limit height where no fracture occurs) when fracture occurs in the saddle molded product. Here, the size of the blank 10 is changed for each molding limit height to obtain the critical damage value. The output unit 23 outputs the critical damage value obtained by the analysis unit 22.

[0044] In this embodiment, the mesh size for FEM analysis is preferably 5 mm or less, and more preferably 3 mm or less, or 2 mm or less.

[0045] In the FEM analysis of this embodiment, a shell model can be used, but when a plate thickness compression method is used in saddle-type forming, it is desirable to form the blank 10 as a solid model. In the plate thickness compression method, stress acts in the plate thickness direction, and since the shell model does not reflect stress in the plate thickness direction, it is necessary to use a solid model. However, in order to shorten the calculation time, for example, only the part of the flange edge of the blank 10 with the smallest radius of curvature (the part where the largest stress occurs) may be formed as a solid model, and the rest of the blank 10 may be formed as a shell model.

[0046] In this embodiment, the Cockcroft-Latham ductile fracture criterion is applied to flange-up forming in FEM analysis to calculate the damage value (damage accumulation value) at the limit width L in which no defects (such as necking or fracture) occur, particularly at the flange edge of the blank 10. The Cockcroft-Latham formula is expressed as follows: Here, I is the limit damage value, σ max The maximum principal stress is ε - This is considerable strain, ε - f is the equivalent strain at which fracture occurs, and C1 is a material constant representing the limit of ductile damage, obtained from reaming hole expansion.

[0047]

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[0048] In equation (1), the Cockcroft-Latham ductile fracture criterion formula typically determines that the damage value has reached the fracture criterion when the integral value I becomes 1. In contrast, in this embodiment, since the fracture of the flange edge, which is the tip portion, rather than the in-plane fracture of the blank, is the target of the determination, the fracture criterion is determined to have been reached when the integral value I becomes a predetermined value less than 1 (e.g., 0.5) rather than 1, due to the influence of the flange edge (including the influence of the punching clearance during saddle-type shearing). In other words, in this embodiment, it is possible to quantitatively evaluate the fracture of the flange edge, which incorporates the influence of the punching clearance, etc. In this respect as well, it differs from the conventional usage of the Cockcroft-Latham ductile fracture criterion formula. Note that in this embodiment, C1 is not necessarily required, and the critical damage value can be obtained using only the integral part of equation (1).

[0049]

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[0050] Figure 6 is a schematic diagram showing the critical damage value (integral value) at the flange edge of a saddle-shaped molded product obtained by FEM analysis. The critical damage value may be evaluated within the plane of the saddle-shaped molded product, or it may be evaluated only at the flange edge. Furthermore, the critical damage value may be the average value in the thickness direction of the saddle-shaped molded product, the maximum value in the thickness direction, the value at the center of the thickness, the FEM element, or the value at a node.

[0051] The comparison unit 24 compares the limit damage value of the flange edge obtained by performing a molding analysis of an actual predetermined part having a flange using FEM or the like, in the same manner as described above, with the limit damage value of the flange edge obtained by the analysis unit 22. The output unit 23 outputs the comparison results from the comparison unit 24 as appropriate.

[0052] Figure 7 is a schematic diagram showing the results of an FEM analysis on a predetermined component, for example, the lower arm of an automobile. In this embodiment, the limit damage value of the flange edge in the lower arm, indicated by the arrow, is compared with the limit damage value of the flange edge obtained by the analysis unit 22 to determine if fracture is occurring. The lower arm is then designed so that its limit damage value is smaller than the limit damage value obtained by the analysis unit 22. This makes it possible to obtain a predetermined part that will not fracture or break.

[0053] [Hardware configuration of fracture prediction device] Figure 8 is a block diagram showing an example of the hardware configuration of a fracture prediction device according to this embodiment. The fracture prediction device comprises a CPU 31, ROM 32, RAM 33, secondary storage device 34, input device 35, and display unit 36. These components are interconnected via a connection bus 37. The CPU (Central Processing Unit) 31 controls the entire fracture prediction device. The CPU 31 performs functions such as the analysis unit 22 and comparison unit 24 of the fracture prediction device, and executes the flowchart processing described later by executing the control program stored in the ROM 32, etc. Note that a GPU (Graphics Processing Unit) may be used instead of the CPU, or together with the CPU.

[0054] ROM32 is a non-volatile memory that stores control programs and various parameter data. RAM33 is a volatile memory that temporarily stores images, control programs, and their execution results. Secondary storage device 34 is a rewritable secondary storage device such as a hard disk or flash memory that stores various data used in the flowchart described later. For example, it stores input data and processing results. This information is output to RAM33 and used by CPU31 to execute the control program. Input device 35 is a keyboard, mouse, touch panel device, etc., which inputs various user instructions. Display unit 36 ​​is a monitor that displays processing results, images, etc.

[0055] In this embodiment, the processing described later is implemented in software using the CPU 31, but some or all of the processing described later may be implemented in hardware. Dedicated circuits (ASICs) or processors (reconfigurable processors, DSPs, etc.) can be used as hardware. The fracture prediction device also has a communication unit for communicating with an external device, and may acquire input data, control programs, training datasets, etc. from an external device via the communication unit, and may output processing results etc. to an external device via the communication unit.

[0056] [Method for predicting fracture] Figure 9 is a flowchart showing the fracture prediction method according to this embodiment in step order.

[0057] In step S1, the fracture limit of the molded product obtained by performing a saddle-type molding test is acquired. For example, the user uses a molding device (press machine) to perform saddle-type molding on the blank 10 and determine the fracture limit of the blank 10. Specifically, the user performs a saddle-type molding test by changing the width L of the blank 10 to various values ​​and acquires the limit width L at which no fracture occurs, especially at the flange edge of the resulting saddle-type molded product. Instead of acquiring the fracture limit by performing a saddle-type molding test, the fracture limit may be acquired from a database that stores data on fracture limit values ​​obtained by changing various parameters such as the material and tensile strength of the blank 10.

[0058] In step S2, the user inputs various parameters that specify the material and shape of the blank 10, as well as the specified fracture limit value (for example, the width L that is the limit at which defects (such as constriction or fracture) do not occur in the saddle-shaped molded product) into the input unit 21.

[0059] In step S3, the analysis unit 22 reproduces the saddle molding test described above using CAE, in this case FEM, to obtain the critical damage value (damage value of the elongated flange edge at the molding limit height at which fracture does not occur) when fracture occurs in the saddle molded product. The critical damage value is calculated using the Cockcroft-Latham ductile fracture criterion formula described above.

[0060] In step S3, the output unit 23 outputs the limit damage value obtained by the analysis unit 22 and displays it appropriately on a predetermined display monitor or the like.

[0061] In step S4, the comparison unit 24 compares the limit damage value of the flange edge obtained by performing a molding analysis of an actual predetermined part having a flange using FEM or the like, as described above, with the limit damage value of the flange edge obtained by the analysis unit 22.

[0062] In step S5, the output unit 23 outputs the comparison result from the comparison unit 24 and displays it appropriately on a predetermined display monitor or the like.

[0063] Figure 10 is a schematic diagram showing a lower arm prototyped as a predetermined part based on the comparison results from the comparison unit 24. This prototype lower arm was designed and manufactured so that the limit damage value of the lower arm is smaller than the limit damage value obtained from the analysis unit 22. It has a tensile stress of 980 MPa class, a plate thickness of 2.9 mm, and a high hole expansion ratio. As shown in the enlarged view on the right side of Figure 10, the target height of the flange was achieved without fracture or other damage to the flange edge.

[0064] As described above, according to this embodiment, it is possible to quantitatively and accurately determine the damage value of the stretched flange edge at the limit height at which fracture does not occur, and to achieve saddle-type molding with a large flange height while avoiding stretched flanges.

[0065] -Other Embodiments- In the embodiments described above, a computer program for controlling the fracture prediction device is stored in a storage medium such as ROM 32. This computer program is a fracture prediction program for realizing the various functions of the CPU 31 of the fracture prediction device. Specifically, each step corresponds to the program as shown in Figure 9, S2 to S6, etc. The CPU 31, as a computer, reads the computer program from the storage medium such as ROM 32 and executes it. The embodiments can also be realized by supplying this computer program to a system or device via a network or storage medium, and by having one or more processors in the computer of that system or device read and execute the program. It can also be realized by a circuit (e.g., ASIC) that realizes one or more functions. The program code read from the recording medium itself realizes the functions of the embodiments described above, and the recording medium on which the program code is recorded constitutes the present invention.

[0066] Although preferred embodiments of the present invention have been described above, the present invention is not limited to these embodiments, and various modifications and changes are possible within the scope of its gist. [Explanation of Symbols]

[0067] 10 Blank 11 Dies 12 pads 13 punches 14 holders 21 Input section 22 Analysis Department 23 Output section 24 Comparison Section

Claims

1. A method for predicting fracture of a component formed by flange-up molding, The first step is to obtain the fracture limit of the molded product obtained by the molding test, A second step involves reproducing the molding test in a simulation based on the fracture limit of the molded product obtained in the first step, and obtaining the limit damage value at which fracture occurs in the molded product. It has, The method further includes a third step of comparing the limit damage value obtained in the molding analysis of the part with the limit damage value obtained in the second step to determine if the part will break. Method for predicting fracture.

2. The molding test described above is a saddle-type molding test. The fracture prediction method according to claim 1.

3. The molding test is performed using a sheared blank. The fracture prediction method according to claim 2.

4. The molding test is performed using a laser-cut blank. The fracture prediction method according to claim 2.

5. The first step is, Using a database in which the fracture limits of the molded product obtained from the molding test are accumulated, The fracture limit is obtained from the aforementioned database. The fracture prediction method according to claim 1.

6. The second step described above is: Cockcroft-Latham formula [Math 1] Using this method, the limit damage value in the flange-up molding is calculated. The fracture prediction method according to claim 1.

7. The second step described above is: As the aforementioned simulation, a finite element method analysis is performed. The fracture prediction method according to claim 1.

8. The second step described above is: The blank to be molded is subjected to molding analysis using a solid model. The fracture prediction method according to claim 7.

9. A device for predicting the fracture of a component formed by flange-up molding, An input section into which the fracture limit of the molded product obtained from the molding test is input, Based on the fracture limit of the molded product obtained from the molding test, an analysis unit reproduces the molding test through simulation and obtains the limit damage value when fracture occurs in the molded product. It has, The system further includes a comparison unit that compares the limit damage value obtained from the molding analysis of the part with the limit damage value obtained from the analysis unit to determine if the part will break. Fracture prediction device.

10. The molding test described above is a saddle-type molding test. The fracture prediction device according to claim 9.

11. The aforementioned analysis unit, Cockcroft-Latham formula 【Number 1】 Using this method, the limit damage value in the flange-up molding is calculated. The fracture prediction device according to claim 9.

12. The aforementioned analysis unit, As the aforementioned simulation, a finite element method analysis is performed. The fracture prediction device according to claim 9.

13. The aforementioned analysis unit, The blank to be molded is subjected to molding analysis using a solid model. The fracture prediction device according to claim 12.

14. A program for predicting the fracture of a component by flange-up forming, The first step is to obtain the fracture limit of the molded product obtained by the molding test, A second step involves reproducing the molding test in a simulation based on the fracture limit of the molded product obtained in the first step, and obtaining the limit damage value at which fracture occurs in the molded product. A third step involves comparing the limit damage value obtained from the molding analysis of the part with the limit damage value obtained in the second step to determine if the part will break, A fracture prediction program to be executed by a computer.

15. The molding test described above is a saddle-type molding test. The fracture prediction program according to claim 14.

16. The second procedure described above is, Cockcroft-Latham formula [Math 1] Using this method, the limit damage value in the flange-up molding is calculated. The fracture prediction program according to claim 14.

17. The second procedure described above is, As the aforementioned simulation, a finite element method analysis is performed. The fracture prediction program according to claim 14.

18. The second procedure described above is, The blank to be molded is subjected to molding analysis using a solid model. The fracture prediction program according to claim 17.

19. A computer-readable recording medium that records a fracture prediction program according to any one of claims 14 to 18.

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