Analysis device, analysis method, manufacturing method, and program

Abstract

To provide a technique for evaluating an influence of residual stress at each part in molding.SOLUTION: One embodiment of the present invention is an analysis device comprising: a lower dead center molding analysis unit which executes molding analysis for obtaining information of an object after molding as an analysis object in a state of being restricted at a lower dead center after molding to the lower dead center is performed on the basis of information of an object before molding as an analysis object before molding to the lower dead center is performed; an area setting unit which divides a shape into a plurality of analysis object areas; and a contribution degree analysis unit which obtains strength of an influence that stress to be generated by the molding has on a fatigue crack at a fatigue analysis object part in each analysis object area by analysis for restoring elasticity based on fatigue analysis object part information showing the fatigue analysis object part as an analysis object of generation of the fatigue crack of the part of the object after molding and a fatigue object direction as a fatigue crack development direction at the fatigue analysis object part and a result of the molding analysis.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to an analysis device, an analysis method, a manufacturing method, and a program.

Background Art

[0002] Metal parts may be used in industrial products such as automobiles. As one of the important indicators indicating the high performance of such metal parts, there is an indicator indicating durability against repeated use.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] By the way, a phenomenon called fatigue cracking may occur in metals. Fatigue cracking is a phenomenon in which even a minute deformation, when repeated (fatigue loading), causes the metal to break at a site where tensile stress is repeatedly generated. Therefore, in order to improve the performance of metal parts, it is required to suppress the occurrence of fatigue cracking. To suppress fatigue cracking, it is important to identify the cause of its occurrence. As one of the causes of fatigue cracking, it is considered that the tensile residual stress generated by forming is the cause. This is because if tensile stress is pre-generated at a site where repeated tensile stress is generated, the residual stress is added to the stress due to fatigue loading, increasing the tensile stress at that site. Therefore, it is required to reduce the tensile residual stress at the site where high repeated tensile stress is generated during fatigue loading (the site where fatigue cracking is a concern). When the cross-sectional shape of the part is uniform, to reduce the residual stress, it can be addressed by changing the processing method or the part shape of the site where the residual stress is to be reduced. However, when the cross-sectional shape of the part is non-uniform, there are cases where the residual stress at the site where the residual stress is to be reduced cannot be reduced even if the processing method or the part shape of that site is changed. That is, when the cross-sectional shape is non-uniform, it may be difficult to identify which part's processing method or part shape should be changed. The reason considered by the inventor will be explained with reference to FIGS. 25 to 28.

[0005] First, the case where it is easy to identify the residual stress affecting fatigue cracking will be explained with reference to FIGS. 25 and 26, and then the case where it is difficult to identify the residual stress affecting fatigue cracking will be explained with reference to FIGS. 27 and 28. FIG. 25 is a diagram explaining the stress at the bottom dead center when the cross-sectional shape of the part is uniform. That the cross-sectional shape of the part is uniform means, in the case of FIG. 25, that the shape is uniform in the direction perpendicular to the drawing. In such a case, at the bottom dead center, compressive stress is generated on the inner side of the bend, and tensile stress is generated on the outer side of the bend. In such a case, a moment that causes springback is generated due to the stress distribution in the plate thickness direction. Since the cross-sectional shape is uniform, the stress and moment in the direction perpendicular to the cross-section are the same regardless of the position in the direction perpendicular to the cross-section.

[0006] Figure 26 shows the state after the metal in the state of Figure 25 has springback. Due to the moment described in Figure 25, in the state of Figure 26, compressive stress is generated on the bending outer side and tensile stress is generated on the bending inner side due to springback. The stress after this springback is the residual stress that affects the fatigue characteristics. When repeated tensile stress is generated inside the bend under fatigue loading, the tensile residual stress generated on the bending inner side becomes the residual stress that reduces the fatigue characteristics. In this case, since the cross-sectional shape is uniform, the cause site of the residual stress generated on the bending inner side is this site, and the moment generated by the stress distribution in the plate thickness direction at this site causes springback, thereby generating tensile residual stress on the bending inner side. Therefore, when the cross-sectional shape is uniform, by improving the processing method and part shape of this site, the moment of this site can be reduced, the tensile residual stress on the bending inner side can be reduced, and as a result, the fatigue characteristics can be improved. That is, when the cross-sectional shape is uniform, the site where the residual stress is desired to be reduced coincides with the site where the processing method and shape should be improved (therefore, there is no problem in the present invention when the cross-sectional shape of the part is uniform).

[0007] Thus, when the cross-sectional shape of the part is uniform, it is easy to identify the residual stress that affects fatigue cracking. However, when the cross-sectional shape of the part is non-uniform, it is difficult to identify the cause site of the residual stress that affects fatigue cracking. Figure 27 is a diagram for explaining the stress at the bottom dead center when the cross-sectional shape of the part is non-uniform. Even when the cross-sectional shape of the part is non-uniform, compressive stress is generated on the bending inner side and tensile stress is generated on the bending outer side at the bottom dead center. However, this stress distribution is different in the direction perpendicular to the cross-section.

[0008] FIG. 28 shows the state after the metal in the state of FIG. 27 has springback. Due to the moment described in FIG. 27, in the state of FIG. 28, compressive stress is generated on the bending outer side, and tensile stress is generated on the bending inner side. However, in the case of a non-uniform cross-section, the shape and stress distribution at this time are affected by the stress distribution in the direction perpendicular to the cross-section, so it is different from the case of a uniform cross-section. What is shown in FIG. 28 is an example where the tensile stress on the bending inner side is larger than that in the case of a uniform cross-section. In this case, it means that it is affected by the stress distribution of the parts other than this cross-section. Therefore, in order to reduce the tensile stress on the bending inner side of this part, it is necessary to improve the processing method and part shape of the parts other than this cross-section. Thus, when the cross-sectional shape of the part is non-uniform, since the stress at a position away from the position where residual stress is to be reduced (the position where fatigue cracking is a concern) is also a factor causing the occurrence of fatigue cracking, it is not easy to identify the residual stress that affects fatigue cracking.

[0009] In view of the above circumstances, an object of the present invention is to provide a technique for evaluating the influence of residual stress at each part during forming.

Means for Solving the Problems

[0010] One aspect of the present invention is a bottom dead center forming analysis unit that executes a forming analysis to obtain information on a post-forming object that is the object of analysis and is in a state constrained at the bottom dead center after forming is performed up to the bottom dead center based on information on a pre-forming object that is the object of analysis before forming up to the bottom dead center, a region setting unit that divides the shape of the post-forming object into a plurality of analysis target regions, fatigue analysis target part information indicating a fatigue analysis target part that is the object of analysis for fatigue crack generation and a fatigue target direction that is the fatigue crack propagation direction in the fatigue analysis target part among the parts of the post-forming object, and a contribution degree analysis unit that obtains the strength of the influence of the stress generated by the forming on the fatigue crack in the fatigue analysis target part in each of the analysis target regions by an analysis of elastic recovery based on the result of the forming analysis.

[0011] One aspect of the present invention is the above-described analysis device, wherein the contribution degree analysis unit executes an analysis for elastically recovering each of the analysis target regions under contribution degree analysis conditions including a contribution degree analysis shape condition that the shape of the analysis target is the shape at the bottom dead center, and a contribution degree analysis stress distribution condition that the stress distribution of a part of the plurality of analysis target regions is the stress indicated by the stress distribution at the bottom dead center and the stress of the other analysis target regions is zero, and that this stress distribution is the stress distribution of the initial state of the analysis target.

[0012] One aspect of the present invention is the above-described analysis device, wherein the contribution degree analysis unit obtains an average stress, which is a stress in the in-plane direction, as the strength of the influence.

[0013] One aspect of the present invention is the above-described analysis device, wherein the contribution degree analysis unit obtains a deviational stress, which is a stress in the plate thickness direction, as the strength of the influence.

[0014] One aspect of the present invention is the above-described analysis device, wherein the contribution degree analysis unit obtains a surface stress, which is a stress on the surface layer, as the strength of the influence.

[0015] One aspect of the present invention is the above-described analysis device, wherein the distance between the boundary of the analysis target region including the fatigue analysis target site and the fatigue analysis target site is substantially the same regardless of the position of the boundary.

[0016] One aspect of the present invention is a forming analysis step of performing a forming analysis to obtain information on a post-forming object that is the object of analysis and is in a constrained state at the bottom dead center after forming up to the bottom dead center based on information on a pre-forming object that is the object of analysis before forming up to the bottom dead center, a region setting step of dividing the shape of the post-forming object into a plurality of analysis target regions, fatigue analysis target part information indicating a fatigue analysis target part that is the object of analysis for fatigue crack generation among the parts of the post-forming object and a fatigue target direction that is the fatigue crack propagation direction in the fatigue analysis target part, and a contribution degree analysis step of obtaining the strength of the influence of the stress generated by the forming on the fatigue crack in the fatigue analysis target part in each of the analysis target regions by an analysis of elastic recovery based on the fatigue analysis target part information and the result of the forming analysis.

[0017] One aspect of the present invention is a forming analysis step of performing a forming analysis to obtain information on a post-forming object that is the object of analysis and is in a constrained state at the bottom dead center after forming up to the bottom dead center based on information on a pre-forming object that is the object of analysis before forming up to the bottom dead center, a region setting step of dividing the shape of the post-forming object into a plurality of analysis target regions, fatigue analysis target part information indicating a fatigue analysis target part that is the object of analysis for fatigue crack generation among the parts of the post-forming object and a fatigue target direction that is the fatigue crack propagation direction in the fatigue analysis target part, and a contribution degree analysis step of obtaining the strength of the influence of the stress generated by the forming on the fatigue crack in the fatigue analysis target part in each of the analysis target regions by an analysis of elastic recovery based on the fatigue analysis target part information and the result of the forming analysis, and a processing step of performing processing to reduce the stress in the analysis target region where the strength obtained by the contribution degree analysis step satisfies a predetermined condition.

[0018] One aspect of the present invention is a program for causing a computer to function as the above-described analysis device.

Effect of the Invention

[0019] According to the present invention, it becomes possible to evaluate the influence of residual stress at each part during forming.

Brief Description of the Drawings

[0020]

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Mode for Carrying Out the Invention

[0021] (Embodiment) FIG. 1 is an explanatory diagram for explaining the analysis device 1 of the embodiment. The analysis device 1 executes a fatigue analysis target part information acquisition process, a bottom dead center forming analysis process, a region setting process, a contribution analysis process, and an analysis result analysis process. More specifically, the analysis device 1 executes the fatigue analysis target part information acquisition process, the bottom dead center forming analysis process, the region setting process, the contribution analysis process, and the analysis result analysis process in the order of the fatigue analysis target part information acquisition process, the bottom dead center forming analysis process, the region setting process, the contribution analysis process, and the analysis result analysis process.

[0022] The fatigue analysis target part information acquisition process is a process for acquiring fatigue analysis target part information. The fatigue analysis target part information is information indicating the part to be analyzed for fatigue crack generation (hereinafter referred to as the "fatigue analysis target part") among the target parts after forming and the fatigue crack propagation direction in the fatigue analysis target part (hereinafter referred to as the "fatigue target direction"). The target after forming is the analysis target material that is in a constrained state at the bottom dead center after forming up to the bottom dead center. The analysis target material is the metal part to be analyzed by the analysis device 1. Note that the fatigue target direction is information necessary for specifying the direction of the stress that causes fatigue cracks.

[0023] In the fatigue analysis target part information acquisition process, the fatigue analysis target part information may be obtained by experiments or by executing simulations. In the case of experiments, a fatigue test of the target part is carried out to identify the part where fatigue cracks occur and the propagation direction of the fatigue cracks. The simulation is, for example, a fatigue analysis in which the residual stress is set to zero. In this case, a fatigue analysis is performed under the same conditions as the fatigue test to identify the part with the highest maximum principal stress on the surface layer of the part and the direction of the maximum principal stress at that part.

[0024] The bottom dead center forming analysis process is a process for executing a forming analysis to obtain information on the target after forming based on information on the analysis target material (hereinafter referred to as the "target before forming") before forming up to the bottom dead center. Note that in the forming analysis, material property information is also used, and the material property information is information including each material property value of the analysis target material at the bottom dead center. Including material property values means including at least Young's modulus, Poisson's ratio, strain distribution, stress distribution, and plate thickness. The forming analysis at the bottom dead center is, for example, a process for performing a forming analysis on the analysis target material in the mold. In such a case, by executing the bottom dead center forming analysis process, the bottom dead center shape and the bottom dead center stress distribution of the analysis target material are output. The bottom dead center shape is the shape of the target after forming. The bottom dead center stress distribution is the stress distribution in the target after forming.

[0025] The area setting process is a process of dividing the shape obtained by the bottom dead center forming analysis process (i.e., the bottom dead center shape) into a plurality of areas (hereinafter referred to as "analysis target areas") and recording information indicating each of the divided analysis target areas in a predetermined storage device. The analysis target areas may be the same as or different from the meshes in the bottom dead center forming analysis.

[0026] The contribution degree analysis process is a process of obtaining, for each area of the analysis target area, the strength of the influence on the occurrence of fatigue cracks in the fatigue analysis target part (hereinafter referred to as "contribution degree") based on the fatigue analysis target part information, the material property information, and the result of the bottom dead center forming analysis process. Specifically, the result of the bottom dead center forming analysis process is the bottom dead center shape, the plate thickness distribution, the strain distribution, and the bottom dead center stress distribution output by executing the bottom dead center forming analysis process. The contribution degree analysis process may be any process as long as it can obtain the contribution degree based on the material property information and the result of the bottom dead center forming analysis process. For example, the contribution degree analysis process obtains the contribution degree by executing an analysis of elastic recovery. Note that the analysis of elastic recovery is also called springback analysis.

[0027] The contribution degree analysis process is, for example, a process of executing an analysis of elastic recovery under the contribution degree analysis conditions for each analysis target area (hereinafter referred to as "elastic analysis process under conditions"). Hereinafter, the analysis target area of the analysis of elastic recovery in the elastic analysis process under conditions is referred to as the target area. That is, the elastic analysis process under conditions is a process of executing an analysis of elastic recovery under the contribution degree analysis conditions for each target area. The contribution degree analysis conditions are the conditions satisfied in the elastic analysis process under conditions, and are conditions including at least material property conditions, contribution degree analysis shape conditions, and contribution degree analysis stress distribution conditions.

[0028] The contribution analysis shape condition is the condition that the shape of the material to be analyzed is the bottom dead center shape. The contribution analysis stress distribution condition is the condition that the stress distribution in the initial state of the material to be analyzed satisfies the non-uniform distribution condition. Therefore, the contribution analysis stress distribution condition can be any condition as long as the stress distribution satisfying the non-uniform distribution condition is the stress distribution in the initial state of the material to be analyzed. The non-uniform distribution condition is the condition that the stress in some of the plurality of analysis target regions is the stress indicated by the bottom dead center stress distribution and the stress in other analysis target regions is zero.

[0029] The non-uniform distribution condition is, for example, the condition that the stress in the target region is the stress indicated by the bottom dead center stress distribution and the stress in other analysis target regions is zero. The non-uniform distribution condition may also be, for example, the condition that the stress in the target region is zero and the stress in other analysis target regions is the stress indicated by the bottom dead center stress distribution. The non-uniform distribution condition may also be, for example, the condition that the stress distribution in a plurality of analysis target regions including the target region is the stress indicated by the bottom dead center stress distribution and the stress in other analysis target regions is zero. The non-uniform distribution condition may also be, for example, the condition that the stress in a plurality of analysis target regions including the target region is zero and the stress in other analysis target regions is the stress indicated by the bottom dead center stress distribution.

[0030] Thus, the elastic recovery analysis in the conditional elastic analysis process is an elastic recovery analysis including the condition that the shape is the bottom dead center shape as the initial condition and the condition that the stress distribution is a stress distribution satisfying the non-uniform distribution condition.

[0031] By executing the conditional elastic analysis process, for each target region, the stress generated in the fatigue analysis target part of the analysis target material whose initial state shape is the bottom dead center shape and whose stress distribution in the initial state satisfies the non-uniform distribution condition can be obtained. An index or quantity indicating the stress generated in the fatigue analysis target part is an example of the contribution degree.

[0032] Thus, the contribution degree is, for example, an index or quantity indicating the stress generated in the fatigue analysis target part. The index or quantity indicating the stress generated in the fatigue analysis target part may be any index or quantity as long as it can indicate the stress generated in the fatigue analysis target part. The contribution degree is, for example, the maximum principal stress generated in the fatigue analysis target part. As the contribution degree, the stress in the direction perpendicular to the propagation direction of the fatigue crack generated in the fatigue analysis target part is desirable. This is because the stress in the direction perpendicular to the fatigue crack causes the fatigue crack.

[0033] Note that the maximum principal stress generated in the fatigue analysis target part is the stress with the maximum magnitude among a plurality of stresses with different directions generated in the fatigue analysis target part. The contribution degree may be, for example, the angle formed by the direction of the maximum principal stress generated in the fatigue analysis target part and the crack direction vector. Note that the crack direction vector is a vector pointing in the direction perpendicular to the fatigue target direction. The contribution degree may be, for example, a value obtained by multiplying the angle formed by the direction of the maximum principal stress generated in the fatigue analysis target part and the direction of the fatigue crack by a predetermined weight.

[0034] Thus, the conditional elastic analysis process is a process of obtaining the contribution degree for each region of the analysis target region by performing an analysis of elastic recovery under the contribution degree analysis conditions for each target region. Therefore, the contribution degree analysis process is a process of obtaining the contribution degree for each region of the analysis target region.

[0035] That is, the contribution degree analysis process is a process of obtaining the strength of the influence of the stress generated by forming in each analysis target region on the fatigue crack in the fatigue analysis target part based on the fatigue analysis target part information and the result of the bottom dead center forming analysis process.

[0036] The analysis result analysis process is a process of determining an analysis target area whose contribution degree meets a predetermined condition (hereinafter referred to as the "high contribution degree condition") regarding the height of the contribution degree based on the result of the contribution degree analysis process. Specifically, the result of the contribution degree analysis is the contribution degree of each area of the analysis target area. The high contribution degree condition is, for example, the condition that the contribution degree is the highest. The high contribution degree condition may be, for example, the condition that the contribution degree is at a rank higher than a predetermined rank in the permutation of the contribution degrees. The high contribution degree condition may be, for example, the condition that the contribution degree is higher than a predetermined height.

[0037] FIG. 2 is a diagram showing an example of the result of the bottom dead center forming analysis process in the embodiment. FIG. 2 shows, as an example, the stress distribution generated on the surface layer of the molded product when pressing and molding the lower arm of an automotive part. The area surrounded by the dotted line and shown in gray in FIG. 2 is an area where the stress on the surface layer of the lower surface of the vehicle exceeds 1000 MPa, and the other areas are areas where the stress is 1000 MPa or less. Point P1 in FIG. 2 indicates the fatigue analysis target site. FIG. 2 shows that the stress at point P1 is 1431 MPa. Note that P1 is the position of the lower surface of the vehicle.

[0038] FIG. 3 is a diagram showing an example of the result of the area setting process in the embodiment. FIG. 3 shows that the analysis target material is divided into a plurality of simply connected analysis target areas. Note that the analysis target area does not necessarily have to be simply connected. The numbers described as an example in FIG. 3 are identifiers for identifying each analysis target area. In the example of FIG. 3, the number of analysis target areas for dividing the analysis target material is 200.

[0039] FIG. 4 is a diagram showing an example of the result of the contribution degree analysis in the embodiment. In FIG. 4, the horizontal axis indicates the identifier of the analysis target area, and the vertical axis indicates the contribution degree. Specifically, the contribution degree in the example of FIG. 4 is the stress in the fatigue target direction at the fatigue analysis target site. The unit of the vertical axis in FIG. 4 is MPa. FIG. 4 shows the contribution degrees of the top 30 analysis target areas with high contribution degrees in the order of high contribution degrees. For example, the contribution degree of the analysis target area with the identifier 025 is 63 MPa. For example, the contribution degree of the analysis target area with the identifier 163 is 11 MPa.

[0040] <Effect of non-uniform distribution condition> Here, the effect of the non-uniform distribution condition will be described. When the non-uniform distribution condition is satisfied, a situation where residual stress exists only in a part of the material to be analyzed is analyzed. Here, assuming that a situation where residual stress exists only in a part is analyzed, there may arise a doubt that the analysis result will be significantly different from the analysis result when the stress distribution is the bottom dead center stress distribution. However, generally, physical phenomena satisfy superposition or linear summation. Therefore, it is presumed that the stress generated in the fatigue analysis target part is approximated by the linear sum of the stresses caused by the residual stresses generated in each part other than the fatigue analysis target part.

[0041] Therefore, it is presumed that for the analysis of the contribution degree of the part to be analyzed, for example, the analysis may be performed in a situation where residual stress exists only for the part to be analyzed. Also, since the stress generated in the fatigue analysis target part is the linear sum of the stresses caused by the residual stresses generated in each part other than the fatigue analysis target part, it is presumed that for the analysis of the contribution degree of the part to be analyzed, the situation where there is no residual stress only in the part to be analyzed may also be analyzed. Thus, since the stress generated in the fatigue analysis target part is the linear sum of the stresses caused by the residual stresses generated in each part other than the fatigue analysis target part, it is presumed that for the analysis of the contribution degree of the part to be analyzed, the analysis may be performed under the stress distribution that satisfies the non-uniform distribution condition. That this presumption is correct has been shown by experiments. An example of the experimental results will be described later.

[0042] Also, generally, the amount of calculation required for the calculation of data containing many zeros is less than the amount of calculation required for the calculation of data containing fewer zeros. Therefore, the amount of calculation when analyzing a situation where stress is generated only in a part of the material to be analyzed is less than the amount of calculation when analyzing a situation where stress is generated in all of the material to be analyzed. Therefore, when the non-uniform distribution condition is satisfied, the amount of calculation required for executing the contribution degree analysis process is reduced compared to when the non-uniform distribution condition is not satisfied.

[0043] <Experimental Results> Here, an example of the results of an experiment (hereinafter referred to as the "evaluation experiment") for evaluating the accuracy of the analysis by the analyzer 1 is shown. In the evaluation experiment, a process of reducing the stress of the analysis target region determined to satisfy the high contribution condition by the analyzer 1 (hereinafter referred to as the "reduction process") was performed, and an experiment was conducted to measure the residual stress in the fatigue target direction of the fatigue analysis target part before and after the process. The high contribution condition in the evaluation experiment was the condition that the contribution was the highest. Specifically, the contribution in the evaluation experiment was compressive stress. The residual stress measured in the evaluation experiment was the surface stress measured by X-rays.

[0044] FIG. 5 is a first explanatory diagram for explaining the evaluation experiment in the embodiment. FIG. 5 shows a perspective view of the molded product used in the evaluation experiment. The Z direction in FIG. 5 is the upward direction of the vehicle. FIG. 5 shows that the cross-sectional shape of the molded product used in the evaluation experiment is non-uniform. That is, FIG. 5 shows that the molded product used in the evaluation experiment is a part in which it is not easy to specify the residual stress that affects fatigue cracking. The non-uniformity of the cross-section of the molded product used in the evaluation experiment is clearly shown in, for example, FIG. 6 below.

[0045] FIG. 6 is a second explanatory diagram for explaining the evaluation experiment in the embodiment. FIG. 6 shows the cross-section at cross-section A-A' of FIG. 5. FIG. 6 shows that the shape of cross-section A-A' is a bimodal shape. Thus, since the molded product used in the evaluation experiment has a non-uniform cross-section, it is an example of a molded product in which it is not easy to specify the residual stress that affects fatigue cracking. In the evaluation experiment, it was shown that the analyzer 1 can specify the residual stress that affects fatigue cracking with high accuracy even for such a molded product. This will be described in more detail with reference to FIGS. 7 and 8.

[0046] FIG. 7 is a third explanatory diagram for explaining the evaluation experiment in the embodiment. FIG. 7 shows region D1. Region D1 is the analysis target region among the analysis target regions of the metal material used in the evaluation experiment that was determined to satisfy the high contribution condition by the analyzer 1. Cross-section A-A' is a cross-section including a part of region D1.

[0047] FIG. 8 is a fourth explanatory diagram for explaining the evaluation experiment in the embodiment. More specifically, FIG. 8 is an explanatory diagram for explaining the reduction process in the evaluation experiment. The object of the reduction process in the evaluation experiment was the analysis target area determined to satisfy the high contribution degree condition. The reduction process in the evaluation experiment was a process of shallowly forming the concave portion in the analysis target area of the processing target in the previous process and forming it into the product shape in the subsequent process. Note that shallowly forming means forming with a large R. More specifically, the reduction process in the evaluation experiment was a process of forming with R15 mm in the previous process and forming it into the product shape in the subsequent process with respect to the product shape of R5 mm. The subsequent process was, more specifically, a process of forming with a small R.

[0048] In the evaluation experiment, the result that the residual stress in the fatigue target direction of the fatigue analysis target part was reduced from 400 MPa to 200 MPa by the reduction process was obtained by measuring the stress on the surface layer of the molded product by X-ray. Thus, the evaluation experiment shows that by performing the reduction process on the analysis target area determined to satisfy the high contribution degree condition by the analysis device 1, the reduction of the residual stress in the fatigue target direction of the fatigue analysis target part occurred. Thus, it was shown that the analysis device 1 can specify the residual stress that affects fatigue cracking by the evaluation experiment.

[0049] FIG. 9 is a diagram showing an example of the hardware configuration of the analysis device 1 of the embodiment. The analysis device 1 includes a control unit 11 including a processor 91 such as a CPU (Central Processing Unit) connected by a bus and a memory 92, and executes a program. The analysis device 1 functions as a device including a control unit 11, an input unit 12, a communication unit 13, a storage unit 14, and an output unit 15 by executing a program.

[0050] More specifically, the processor 91 reads out the program stored in the storage unit 14 and stores the read program in the memory 92. By the processor 91 executing the program stored in the memory 92, the analysis device 1 functions as a device including a control unit 11, an input unit 12, a communication unit 13, a storage unit 14, and an output unit 15.

[0051] The control unit 11 controls the operations of various functional units provided in the analysis device 1. The control unit 11 executes, for example, a fatigue analysis target part information acquisition process. The control unit 11 executes, for example, a bottom dead center forming analysis process. The control unit 11 executes, for example, a region setting process. The control unit 11 executes, for example, a contribution degree analysis process. The control unit 11 executes, for example, an analysis result analysis process.

[0052] The control unit 11 controls the operation of the output unit 15, for example. The control unit 11 records various information generated by executing the fatigue analysis target part information acquisition process in the storage unit 14, for example. The control unit 11 records various information generated by executing the bottom dead center forming analysis process in the storage unit 14, for example. The control unit 11 records various information generated by executing the region setting process in the storage unit 14, for example. The control unit 11 records various information generated by executing the contribution degree analysis process in the storage unit 14, for example. The control unit 11 records various information generated by executing the analysis result analysis process in the storage unit 14, for example.

[0053] The input unit 12 is configured to include input devices such as a mouse, a keyboard, and a touch panel. The input unit 12 may be configured as an interface for connecting these input devices to the analysis device 1. The input unit 12 receives the input of various information to the analysis device 1. For example, fatigue analysis target part information is input to the input unit 12. For example, physical property information and the restraint conditions during forming for forming the analysis target material are input to the input unit 12.

[0054] Note that the physical property information and the restraint conditions during forming for forming the analysis target material may be input via the communication unit 13. Note that the physical property information and the restraint conditions during forming for forming the analysis target material do not necessarily have to be input via the input unit 12 or the communication unit 13, and may have been stored in the storage unit 14 in advance. Hereinafter, for the sake of simplicity of explanation, the analysis device 1 will be described by taking as an example the case where the physical property information and the restraint conditions during forming for forming the analysis target material have been stored in the storage unit 14 in advance.

[0055] The communication unit 13 is configured to include a communication interface for connecting the analysis device 1 to an external device. The communication unit 13 communicates with the external device via wired or wireless means. The external device is, for example, a device that is the source of the input of the fatigue analysis target site information. In such a case, the communication unit 13 acquires the fatigue analysis target site information through communication with the device that is the source of the input of the fatigue analysis target site information.

[0056] The storage unit 14 is configured using a computer-readable storage medium device such as a magnetic hard disk device or a semiconductor storage device. The storage unit 14 stores various types of information related to the analysis device 1. The storage unit 14 stores information input, for example, via the input unit 12 or the communication unit 13. The storage unit 14 stores various types of information generated, for example, by executing the fatigue analysis target site information acquisition process. The storage unit 14 stores various types of information generated, for example, by executing the bottom dead center forming analysis process. The storage unit 14 stores various types of information generated, for example, by executing the region setting process. The storage unit 14 stores various types of information generated, for example, by executing the contribution degree analysis process. The storage unit 14 stores various types of information generated, for example, by executing the analysis result analysis process. The storage unit 14 stores in advance the contribution degree height condition. Note that the content of the contribution degree height condition stored in the storage unit 14 may be changeable by the user via the input unit 12 or the communication unit 13. The storage unit 14 stores, for example, material property information. The storage unit 14 stores the restraint conditions during forming for forming the analysis target material.

[0057] The output unit 15 outputs various types of information. The output unit 15 is configured to include a display device such as a CRT (Cathode Ray Tube) display, a liquid crystal display, an organic EL (Electro-Luminescence) display, etc. The output unit 15 may be configured as an interface for connecting these display devices to the analysis device 1. The output unit 15 outputs, for example, the information input to the input unit 12. The output unit 15 may display, for example, the execution result of the fatigue analysis target part information acquisition process. The execution result of the fatigue analysis target part information acquisition process is, for example, the fatigue analysis target part information. The output unit 15 may display, for example, the execution result of the bottom dead center forming analysis process. The output unit 15 may display, for example, the execution result of the region setting process. The output unit 15 may display, for example, the execution result of the contribution degree analysis process. The execution result of the contribution degree analysis process is, for example, the graph in FIG. 4. The output unit 15 may display, for example, the execution result of the analysis result analysis process.

[0058] FIG. 10 is a diagram showing an example of the configuration of the control unit 11 in the embodiment. The control unit 11 includes a fatigue analysis target part information acquisition unit 110, a bottom dead center forming analysis unit 120, a region setting unit 130, a contribution degree analysis unit 140, an analysis result analysis unit 150, a memory control unit 160, a communication control unit 170, and an output control unit 180.

[0059] The fatigue analysis target part information acquisition unit 110 executes the fatigue analysis target part information acquisition process. The bottom dead center forming analysis unit 120 executes the bottom dead center forming analysis process. The region setting unit 130 executes the region setting process. The contribution degree analysis unit 140 executes the contribution degree analysis process. The analysis result analysis unit 150 executes the analysis result analysis process.

[0060] The memory control unit 160 records various types of information in the memory unit 14. The communication control unit 170 controls the operation of the communication unit 13. The output control unit 180 controls the operation of the output unit 15.

[0061] FIG. 11 is a flowchart showing an example of the flow of processing executed by the analysis apparatus 1 in the embodiment. The fatigue analysis target part information acquisition unit 110 executes a fatigue analysis target part information acquisition process. By executing the fatigue analysis target part information acquisition process, the fatigue analysis target part information acquisition unit 110 acquires fatigue analysis target part information (step S101). Next, the bottom dead center forming analysis unit 120 executes a bottom dead center forming analysis process. By executing the bottom dead center forming analysis process, the bottom dead center forming analysis unit 120 obtains the bottom dead center shape and the bottom dead center stress component of the material to be analyzed (step S102).

[0062] Next, the region setting unit 130 executes a region setting process. By executing the region setting process, the shape obtained by the bottom dead center forming analysis process is divided into a plurality of analysis target regions, and information indicating each analysis target region after division is recorded in the storage unit 14 (step S103). Next, the contribution degree analysis unit 140 executes a contribution degree analysis process. By executing the contribution degree analysis process, the contribution degree analysis unit 140 obtains the contribution degree for each region of the analysis target region (step S104). Next, the analysis result analysis unit 150 executes an analysis result analysis process. By executing the analysis result analysis process, the analysis result analysis unit 150 determines an analysis target region that satisfies the high contribution degree condition (step S105). Note that the process of step S101 may be executed at any timing as long as it is executed before the execution of the process of step S104.

[0063] The analysis apparatus 1 configured as described above can obtain a part that has a strong influence on the occurrence of fatigue cracks among the respective parts of the analysis target. Therefore, the analysis apparatus 1 can evaluate the influence of the residual stress at each part during molding.

[0064] (Modification example) As described in the explanation of the evaluation experiment, it is possible to mold a molded product with a reduced frequency of fatigue crack occurrence by performing reduction processing using the results of the analysis apparatus 1. The reduction processing method is, for example, a step crushing method. The reduction processing may be, for example, a bending R change method. The reduction processing method may be, for example, a coining method.

[0065] Here, an example of reduction processing (hereinafter referred to as "the first reduction processing example") in the case where the reduction processing method is the step crushing method will be described with reference to FIGS. 12 and 13. Next, an example of reduction processing (hereinafter referred to as "the second reduction processing example") in the case where the reduction processing method is the bending R change method will be described with reference to FIGS. 14 and 15.

[0066] FIG. 12 is a first explanatory diagram for explaining the first reduction processing example in the modified example. FIG. 13 is a second explanatory diagram for explaining the first reduction processing example in the modified example. Point P1 in FIG. 12 indicates the fatigue analysis target part. FIG. 12 shows the analysis target area satisfying the contribution degree height condition as area D2. As shown in FIG. 12, area D2 is located inside rather than at the peripheral part of the analyzed molded product. In the first reduction processing example, the contribution degree is the average stress. Therefore, in the first reduction processing example, the average stress in area D2 is the cause of fatigue cracking. Note that the average stress is the in-plane stress.

[0067] In the first reduction processing example, reduction processing is performed on area D2. As shown in FIG. 13, in the first step, processing for imparting a step is performed, and in the second step, processing for crushing the step is performed. By crushing the step, compressive stress is imparted.

[0068] FIG. 14 is a first explanatory diagram for explaining the second reduction processing example in the modified example. FIG. 15 is a second explanatory diagram for explaining the second reduction processing example in the modified example. Point P1 in FIG. 14 indicates the fatigue analysis target part. FIG. 14 shows the analysis target area satisfying the contribution degree height condition as area D3. As shown in FIG. 14, area D3 is located at the peripheral part rather than inside the analyzed metal material. In the second reduction processing example, the contribution degree is the deviation adaptive stress. Therefore, in the second reduction processing example, the deviation stress in area D3 is the cause of fatigue cracking. Note that the deviation stress is the stress in the plate thickness direction.

[0069] In the second reduction process example, a reduction process is performed on region D3. As shown in FIG. 15, in the first step, a process of forming a small R is performed, and in the second step, a process of reforming into a large R is performed. In short, by changing the bending R in the previous and subsequent steps at the site with a high contribution degree, a process of changing the deviation stress is performed to reduce the stress at the fatigue analysis target site.

[0070] In addition, in the reduction process, a process of reducing the occurrence frequency of fatigue cracks may be performed by imparting irregularities such as beads to the designed shape. FIG. 16 is an explanatory diagram for explaining an example of a process of imparting beads in a modified example. FIG. 16 shows a bimodal shape as an example of the result of the reduction process. By performing such a process on a site with a high contribution degree, the stress at the site with a high contribution degree is changed to reduce the stress at the fatigue analysis target site.

[0071] FIG. 17 is an explanatory diagram for explaining the coining method in a modified example. As described above, the reduction process method may be the coining method. FIG. 17 is a diagram showing an example of the reduction process using the coining method. Region D4 in FIG. 17 indicates an analysis target region that satisfies the high contribution degree condition. FIG. 17 shows that region D4 is coined by the coining method to change the surface stress. By coining, region D4 is compressed in the plate thickness direction. As a result, in region D4, a conversion from tensile stress to compressive stress is performed. Since the moment is mostly affected by the surface stress, by changing the surface stress of the site with a high contribution degree by coining, the stress at the fatigue analysis target site can be reduced. Note that the surface stress is generally referred to as the surface stress. The definition of the surface layer is a region within 100 μm from the surface.

[0072] FIG. 18 is a flowchart for explaining an example of the manufacturing method in a modified example. Hereinafter, the same processes as those described in FIG. 11 will be denoted by the same reference numerals as in FIG. 11, and the description will be omitted. After the execution of the processes in steps S101 to S105, a reduction process is performed on the analysis target region that satisfies the high contribution degree condition obtained in the process of step S105 (step S106).

[0073] In the contribution analysis process, the contribution may be obtained by dividing it into average stress and deviational stress, or it may be obtained by dividing it into average stress, deviational stress, and surface stress. That is, in the contribution analysis process, the contribution may be obtained for the average stress, the contribution may be obtained for the deviational stress, or the contribution may be obtained for the surface stress.

[0074] <Relationship between average stress, deviational stress, springback, and contribution analysis process> Springback affects fatigue cracking. And springback is mainly affected by average stress and deviational stress. Therefore, in order to help understand the influence of average stress and deviational stress on fatigue cracking, the relationship between average stress, deviational stress, springback, and contribution analysis process will be described using FIGS. 19 to 23. Furthermore, the relationship with the contribution analysis process will also be described.

[0075] FIG. 19 is a first explanatory diagram for explaining the relationship between average stress, deviational stress, springback, and contribution analysis process in a modified example. FIG. 19 shows an example of the distribution of average stress and deviational stress at the bottom dead center.

[0076] FIG. 20 is a second explanatory diagram for explaining the relationship between average stress, deviational stress, springback, and contribution analysis process in a modified example. FIG. 20 shows that springback occurs due to the distribution of average stress, which is in-plane stress, and the plate is deformed or twisted. The plate is a molded product to be analyzed by the analysis device 1.

[0077] FIG. 21 is a third explanatory diagram for explaining the relationship between average stress, deviational stress, springback, and contribution analysis process in a modified example. When performing the contribution analysis process for analyzing the influence of average stress on fatigue cracking, for the stress in the plate thickness direction, the average value of the stress in the plate thickness direction is used.

[0078] FIG. 22 is a fourth explanatory diagram for explaining the relationship between the average stress, the deviation stress, the springback, and the contribution analysis process in the modified example. FIG. 22 shows that springback occurs due to the distribution of the deviation stress, which is the stress in the plate thickness direction, and the plate is bent.

[0079] FIG. 23 is a fifth explanatory diagram for explaining the relationship between the average stress, the deviation stress, the springback, and the contribution analysis process in the modified example. When performing the contribution analysis process for analyzing the influence of the stress distribution in the plate thickness direction on fatigue cracking, the contribution is obtained using only the difference from the minimum value in the stress distribution in the plate thickness direction.

[0080] Note that when performing the contribution analysis process for analyzing the influence of the surface stress on fatigue cracking, the contribution is obtained in a state where the stress other than the surface stress is set to zero, for example. When performing the contribution analysis process for analyzing the influence of the surface stress on fatigue cracking, for example, the contribution may be obtained in a state where a coefficient is multiplied by the surface stress and the value of the surface stress is larger than the magnitudes of other stresses.

[0081] In the region setting process, it is desirable that the division of the analysis target region is performed such that the boundaries of the analysis target region (hereinafter referred to as the "fatigue region") including the fatigue analysis target site are substantially the same and equidistant from the fatigue analysis target site. That is, it is desirable that the distance between the boundary of the fatigue region and the fatigue analysis target site is substantially the same regardless of the position of the boundary of the fatigue region. The reason will be explained with reference to FIG. 24.

[0082] FIG. 24 is an explanatory diagram for explaining the region setting process in the modified example. FIG. 24 shows the result of the region setting process in which the distance (hereinafter referred to as the "fatigue distance") between the boundary of the fatigue region and the fatigue analysis target site is not equidistant. When the fatigue distance is not equidistant regardless of the direction, the contribution of another analysis target region adjacent to the fatigue region may change depending on the division method. For example, although the contributions of other analysis target regions adjacent to the fatigue region are the same if the fatigue distance is uniform, a phenomenon may occur in which the contribution of the analysis target region with a shorter distance between the boundary and the fatigue analysis target site is higher because the fatigue distance is not uniform.

[0083] Although the description has been given by taking a metal material as an example, examples of metal materials include iron, aluminum, stainless steel, titanium, and magnesium.

[0084] Note that the analysis device 1 may be implemented using a plurality of information processing devices that are communicably connected via a network. In this case, each functional unit included in the analysis device 1 may be implemented in a distributed manner among the plurality of information processing devices.

[0085] Note that all or part of each function of the analysis device 1 may be realized using hardware such as an ASIC (Application Specific Integrated Circuit), a PLD (Programmable Logic Device), or an FPGA (Field Programmable Gate Array). The program may be recorded on a computer-readable recording medium. A computer-readable recording medium is, for example, a portable medium such as a flexible disk, a magneto-optical disk, a ROM, a CD-ROM, or the like, or a storage device such as a hard disk incorporated in a computer system. The program may be transmitted via an electric communication line.

[0086] As described above, the embodiments of the present invention have been described in detail with reference to the drawings. However, the specific configuration is not limited to this embodiment, and designs and the like within the scope not departing from the gist of the present invention are also included.

Description of Reference Numerals

[0087] 1... Analysis device, 11... Control unit, 12... Input unit, 13... Communication unit, 14... Storage unit, 15... Output unit, 91... Processor, 92... Memory

Claims

1. A bottom dead center forming analysis unit that executes a forming analysis to obtain information on a post-forming object that is the object of analysis and is in a state constrained at the bottom dead center after forming up to the bottom dead center based on information on a pre-forming object that is the object of analysis before forming up to the bottom dead center; A region setting unit that divides the shape of the post-forming object into a plurality of analysis target regions; Based on fatigue analysis target part information indicating a fatigue analysis target part that is an analysis target for fatigue crack generation among parts of the post-forming object and a fatigue target direction that is a fatigue crack propagation direction in the fatigue analysis target part, and the result of the forming analysis, a contribution degree analysis unit that obtains the strength of the influence of the stress generated by the forming on the fatigue crack in the fatigue analysis target part in each of the analysis target regions by an analysis of elastic recovery; An analysis device comprising the above.

2. The contribution degree analysis unit executes an analysis of elastic recovery for each of the analysis target regions under contribution degree analysis conditions including a contribution degree analysis shape condition that the shape of the analysis target is the shape at the bottom dead center, and a contribution degree analysis stress distribution condition that the stress distribution is the stress distribution in the initial state of the analysis target, where the stress in some of the plurality of analysis target regions is the stress indicated by the stress distribution at the bottom dead center and the stress in other analysis target regions is zero. The analysis device according to Claim 1.

3. The contribution degree analysis unit obtains an average stress that is a stress in the in-plane direction as the strength of the influence. The analysis device according to Claim 1 or 2.

4. The contribution degree analysis unit obtains a deviational stress that is a stress in the plate thickness direction as the strength of the influence. The analysis device according to any one of Claims 1 to 3.

5. The contribution degree analysis unit obtains a surface stress that is a stress on the surface layer as the strength of the influence. The analysis device according to any one of Claims 1 to 4.

6. A bottom dead center forming analysis step of executing a forming analysis to obtain information on a post-forming object that is the object of analysis and is in a state constrained at the bottom dead center after forming up to the bottom dead center based on information on a pre-forming object that is the object of analysis before forming up to the bottom dead center; A region setting step of dividing the shape of the post-forming object into a plurality of analysis target regions; A contribution analysis step of obtaining the strength of the influence of the stress generated by the forming on the fatigue crack in the fatigue analysis target part in each of the analysis target regions by an analysis of elastic recovery based on fatigue analysis target part information indicating a fatigue analysis target part that is an analysis target for fatigue crack generation among the parts of the formed target and a fatigue target direction that is a fatigue crack propagation direction in the fatigue analysis target part, and the result of the forming analysis; An analysis method having the above.

7. A bottom dead center forming analysis step of executing a forming analysis to obtain information on a formed target that is the analysis target and is in a state of being constrained at the bottom dead center after forming up to the bottom dead center based on information on a pre-forming target that is the analysis target before forming up to the bottom dead center; A region setting step of dividing the shape of the formed target into a plurality of analysis target regions; A contribution analysis step of obtaining the strength of the influence of the stress generated by the forming on the fatigue crack in the fatigue analysis target part in each of the analysis target regions by an analysis of elastic recovery based on fatigue analysis target part information indicating a fatigue analysis target part that is an analysis target for fatigue crack generation among the parts of the formed target and a fatigue target direction that is a fatigue crack propagation direction in the fatigue analysis target part, and the result of the forming analysis; A processing step of performing processing to reduce the stress in the analysis target region where the strength obtained by the contribution analysis step satisfies a predetermined condition; A manufacturing method having the above.

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