JP7698209B2 - Analysis device, analysis method, manufacturing method, and program - Google Patents

Description

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

Metal parts are often used in industrial products such as automobiles. One important indicator of the high performance of such metal parts is their durability against repeated use.

JP 2009-172677 A

By the way, a phenomenon called fatigue cracking may occur in metals. Fatigue cracking is a phenomenon in which even a small deformation is repeated (fatigue load), causing the metal to break at the part where tensile stress is repeatedly generated. Therefore, in order to improve the performance of metal parts, it is necessary to suppress the occurrence of fatigue cracking. In order to suppress fatigue cracking, it is important to identify the cause of fatigue cracking. One of the causes of fatigue cracking is thought to be tensile residual stress generated by molding. This is because if tensile stress is generated in advance in the part where repeated tensile stress occurs, the residual stress is added to the stress due to fatigue load, and the tensile stress in that part becomes high. Therefore, it is required to reduce the tensile residual stress in the part where high repeated tensile stress occurs during fatigue load (part where fatigue cracking is a concern). In order to reduce the residual stress when the cross-sectional shape of the part is uniform, it is possible to deal with it by changing the processing method of the part where the residual stress is to be reduced or the part shape. However, when the cross-sectional shape of a part is non-uniform, changing the processing method or part shape of the part where you want to reduce the residual stress may not reduce the residual stress in that part. In other words, 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 inventor's reasons for this are explained using Figures 25 to 28.

First, cases where it is easy to identify the residual stress that affects fatigue cracking will be explained using Figures 25 and 26, and then cases where it is difficult to identify the residual stress that affects fatigue cracking will be explained using Figures 27 and 28. Figure 25 is a diagram explaining the stress at bottom dead center when the cross-sectional shape of the part is uniform. In the case of Figure 25, the cross-sectional shape of the part is uniform, which means that the shape is uniform in the direction perpendicular to the figure. In such a case, compressive stress occurs on the inside of the bend at bottom dead center, and tensile stress occurs on the outside of the bend. In such a case, a moment that causes springback is generated due to the stress distribution in the plate thickness direction. Because 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.

Figure 26 shows the state after the metal in the state of Figure 25 springs back. In the state of Figure 26, due to the moment described in Figure 25, compressive stress occurs on the outside of the bend due to springback, and tensile stress occurs on the inside of the bend. This stress after springback is the residual stress that affects the fatigue characteristics. When repeated tensile stress occurs inside the bend under fatigue load, the tensile residual stress occurring on the inside of the bend becomes the residual stress that reduces the fatigue characteristics. In this case, since the cross-sectional shape is uniform, this part is the cause of the residual stress occurring on the inside of the bend, and the moment caused by the stress distribution in the plate thickness direction at this part causes springback, which causes tensile residual stress on the inside of the bend. Therefore, if the cross-sectional shape is uniform, by improving the processing method of this part or the part shape, the moment of this part can be reduced, and the tensile residual stress on the inside of the bend can be reduced, resulting in improved fatigue characteristics. In other words, if the cross-sectional shape is uniform, the part where you want to reduce the residual stress and the part where you want to improve the processing method or shape are the same (so there is no problem in this invention when the cross-sectional shape of the part is uniform).

In this way, when the cross-sectional shape of a part is uniform, it is easy to identify the residual stress that affects fatigue cracking. However, when the cross-sectional shape of a part is non-uniform, it is difficult to identify the location that causes the residual stress that affects fatigue cracking. Figure 27 is a diagram explaining the stress at bottom dead center when the cross-sectional shape of a part is non-uniform. Even when the cross-sectional shape of a part is non-uniform, compressive stress occurs on the inside of the bend at bottom dead center, and tensile stress occurs on the outside of the bend. However, this stress distribution differs in the direction perpendicular to the cross section.

Figure 28 shows the state after the metal in the state of Figure 27 springs back. In the state of Figure 28, due to the moment described in Figure 27, compressive stress occurs on the outside of the bend and tensile stress occurs on the inside of the bend. However, in the case of a non-uniform cross section, the shape and stress distribution at this time are affected by the stress distribution perpendicular to the cross section, so they are different from the case of a uniform cross section. Figure 28 shows an example in which the tensile stress on the inside of the bend is larger than in the case of a uniform cross section. In this case, it is affected by the stress distribution in areas other than this cross section. Therefore, in order to reduce the tensile stress on the inside of the bend in this area, it is necessary to improve the processing method of the area other than this cross section and the part shape. In this way, when the cross-sectional shape of a part is non-uniform, stresses at positions away from the position where you want to reduce the residual stress (the position where fatigue cracking is a concern) are also factors that cause fatigue cracking, so it is not easy to identify the residual stress that affects fatigue cracking.

In view of the above, the present invention aims to provide a technology for evaluating the effects of residual stress at each part during molding.

One aspect of the present invention is an analysis device that includes a bottom dead center forming analysis unit that performs a forming analysis to obtain information on a post-formed object that is an analysis object that is in a state of being restrained at the bottom dead center after forming to the bottom dead center based on information on a pre-formed object that is an analysis object before forming to the bottom dead center is performed; a region setting unit that divides the shape of the post-formed object into a plurality of analysis object regions; fatigue analysis object portion information indicating fatigue analysis object portions that are analysis objects for fatigue crack occurrence among the portions of the post-formed object and fatigue object directions that are fatigue crack propagation directions in the fatigue analysis object portions; and a contribution analysis unit that obtains the strength of the effect that the stress generated by the forming in each of the analysis object regions has on fatigue cracks in the fatigue analysis object portions by performing an analysis of elastic recovery based on the results of the forming analysis.

One aspect of the present invention is the above-mentioned analysis device, in which the contribution analysis unit performs an analysis of elastic recovery for each of the analysis target regions under contribution analysis conditions including a contribution analysis shape condition that the shape of the analysis target is the shape at bottom dead center, and a contribution analysis stress distribution condition that the stress of some of the multiple analysis target regions is the stress indicated by the stress distribution at bottom dead center and the stress of the other analysis target regions is zero, which is the stress distribution in the initial state of the analysis target.

One aspect of the present invention is the above analysis device, in which the contribution analysis unit obtains an average stress, which is an in-plane stress, as the strength of the influence.

In one aspect of the present invention, the analysis device described above, the contribution analysis unit obtains the deviatoric stress, which is the stress in the plate thickness direction, as the strength of the influence.

In one aspect of the present invention, the analysis device described above, the contribution analysis unit obtains surface stress, which is the stress on the surface layer, as the strength of the influence.

In one aspect of the present invention, in the above analysis device, the distance between the boundary of the analysis target area that includes the fatigue analysis target portion and the fatigue analysis target portion is substantially the same regardless of the position of the boundary.

One aspect of the present invention is an analysis method having a bottom dead center forming analysis step of performing a forming analysis to obtain information on a post-formed object that is an analysis object that is in a state of being restrained at the bottom dead center after forming to the bottom dead center based on information on a pre-formed object that is an analysis object before forming to the bottom dead center is performed; a region setting step of dividing the shape of the post-formed object into a plurality of analysis object regions; and fatigue analysis object portion information indicating fatigue analysis object portions that are analysis objects for fatigue crack occurrence among the portions of the post-formed object and fatigue object directions that are fatigue crack propagation directions in the fatigue analysis object portions, and the results of the forming analysis, to obtain the strength of the effect that the stress generated by the forming in each of the analysis object regions has on the fatigue crack in the fatigue analysis object portion by an analysis of elastic recovery based on the results of the forming analysis.

One aspect of the present invention is a manufacturing method having a bottom dead center forming analysis step of performing a forming analysis to obtain information on a post-formed object that is an analysis object that is in a state of being restrained at the bottom dead center after forming to the bottom dead center based on information on a pre-formed object that is an analysis object before forming to the bottom dead center is performed; a region setting step of dividing the shape of the post-formed object into a plurality of analysis object regions; fatigue analysis object portion information indicating fatigue analysis object portions that are analysis objects for fatigue crack occurrence among the portions of the post-formed object and fatigue object directions that are fatigue crack propagation directions in the fatigue analysis object portions, and the results of the forming analysis, to obtain the strength of the effect of the stress generated by the forming in each of the analysis object regions on the fatigue crack in the fatigue analysis object portion by an analysis of elastic recovery based on the results of the forming analysis; and a processing step of performing processing to reduce the stress in the analysis object region where the strength obtained by the contribution analysis step satisfies a predetermined condition.

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

This invention makes it possible to evaluate the effects of residual stress at each location during molding.

FIG. 1 is an explanatory diagram for explaining an analysis device according to an embodiment. 6A to 6C are diagrams showing examples of results of bottom dead center forming analysis processing in the embodiment. 6A to 6C are diagrams showing examples of results of area setting processing in the embodiment. FIG. 11 is a diagram showing an example of a result of contribution analysis in the embodiment. FIG. 1 is a first explanatory diagram for explaining an evaluation experiment in an embodiment. FIG. 2 is a second explanatory diagram for explaining an evaluation experiment in the embodiment. FIG. 11 is a third explanatory diagram for explaining an evaluation experiment in the embodiment. FIG. 4 is a fourth explanatory diagram for explaining an evaluation experiment in the embodiment. FIG. 2 is a diagram illustrating an example of a hardware configuration of an analysis apparatus according to an embodiment. FIG. 2 is a diagram showing an example of the configuration of a control unit in the embodiment. 4 is a flowchart showing an example of a flow of a process executed by an analysis device in an embodiment. FIG. 11 is a first explanatory diagram illustrating a first reduction processing example in the modified example. FIG. 11 is a second explanatory diagram illustrating the first reduction processing example in the modified example. FIG. 11 is a first explanatory diagram illustrating a second reduction processing example in the modified example. FIG. 2 is a second explanatory diagram illustrating a second reduction processing example in the modified example. FIG. 13 is an explanatory diagram illustrating an example of a process for providing a bead according to a modified example. FIG. 13 is an explanatory diagram illustrating a coining method according to a modified example. 10 is a flowchart illustrating an example of a manufacturing method according to a modified example. FIG. 11 is a first explanatory diagram illustrating the relationship between average stress, deviation adaptive force, springback, and contribution analysis processing in the modified example. FIG. 2 is a second explanatory diagram illustrating the relationship between the average stress, the deviation accommodation force, the springback, and the contribution analysis process in the modified example. FIG. 3 is a third explanatory diagram illustrating the relationship between the average stress, the deviation adaptive force, the springback, and the contribution analysis process in the modified example. FIG. 4 is a fourth explanatory diagram illustrating the relationship between the average stress, the deviation adaptive force, the springback, and the contribution analysis process in the modified example. FIG. 5 is a fifth explanatory diagram illustrating the relationship between average stress, deviation adaptive force, springback, and contribution analysis processing in the modified example. 10A to 10C are explanatory diagrams illustrating a region setting process in a modified example. FIG. 1 is a first explanatory diagram illustrating the difficulty of identifying residual stress that affects fatigue cracking. FIG. 2 is a second explanatory diagram illustrating the difficulty of identifying residual stress that affects fatigue cracking. FIG. 3 is a third explanatory diagram illustrating the difficulty of identifying residual stress that affects fatigue cracking. FIG. 4 is a fourth explanatory diagram illustrating the difficulty of identifying residual stress that affects fatigue cracking.

(Embodiment)
1 is an explanatory diagram illustrating an analysis device 1 according to an embodiment. The analysis device 1 executes a fatigue analysis target portion 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 portion 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 following order: fatigue analysis target portion information acquisition process, bottom dead center forming analysis process, the region setting process, the contribution analysis process, and the analysis result analysis process.

The fatigue analysis target part information acquisition process is a process for acquiring information on the fatigue analysis target part. The fatigue analysis target part information is information indicating the part of the post-forming target that is to be analyzed for fatigue crack occurrence (hereinafter referred to as the "fatigue analysis target part") and the fatigue crack propagation direction in the fatigue analysis target part (hereinafter referred to as the "fatigue target direction"). The post-forming target is the analysis target material that is in a restrained state at the bottom dead center after being formed up to the bottom dead center. The analysis target material is the metal part that is to be analyzed by the analysis device 1. The fatigue target direction is information required to identify the direction of the stress that causes the fatigue crack.

In the process of acquiring information on parts to be subjected to fatigue analysis, the information on parts to be subjected to fatigue analysis may be obtained by experiment or by performing a simulation. In the case of an experiment, a fatigue test is performed on the target part to identify the parts that will experience fatigue cracks and the direction in which the fatigue cracks will progress. A 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 parts on the surface of the part where the maximum principal stress is high and the direction of the maximum principal stress in those parts.

Bottom dead point forming analysis processing is processing that executes forming analysis to obtain information on the post-forming target based on information on the analysis target material before forming to the bottom dead point (hereinafter referred to as the "pre-forming target"). Note that physical property information is also used in forming analysis, and the physical property information is information including each physical property value at the bottom dead point of the analysis target material. Including physical property values means including at least Young's modulus, Poisson's ratio, strain distribution, stress distribution, and plate thickness. Bottom dead point forming analysis is processing that performs forming analysis on the analysis target material in a mold, for example. In such a case, the execution of bottom dead point forming analysis processing outputs the bottom dead point shape and bottom dead point stress distribution of the analysis target material. The bottom dead point shape is the shape of the post-forming target. The bottom dead point stress distribution is the stress distribution in the post-forming target.

The region setting process is a process in which the shape obtained by the bottom dead center forming analysis process (i.e., the bottom dead center shape) is divided into multiple regions (hereinafter referred to as "analysis target regions"), and information indicating each analysis target region after division is recorded in a specified storage device. The analysis target regions may be the same as or different from the mesh in the bottom dead center forming analysis.

The contribution analysis process is a process that obtains the strength of the influence on the occurrence of fatigue cracks in the fatigue analysis target area (hereinafter referred to as "contribution") for each area of the analysis target area based on fatigue analysis target area information, physical property information, and the results of the bottom dead point forming analysis process. The results of the bottom dead point forming analysis process are specifically the bottom dead point shape, plate thickness distribution, strain distribution, and bottom dead point stress distribution output by executing the bottom dead point forming analysis process. The contribution analysis process may be any process that can obtain the contribution based on the physical property information and the results of the bottom dead point forming analysis process. The contribution analysis process obtains the contribution by, for example, executing an analysis that causes elastic recovery. The analysis that causes elastic recovery is also called springback analysis.

The contribution analysis process is, for example, a process that executes an analysis for elastic recovery under contribution analysis conditions for each analysis target region (hereinafter referred to as "conditional elastic analysis process"). Hereinafter, the analysis target region that is the target of the analysis for elastic recovery in the conditional elastic analysis process is referred to as the target region. In other words, the conditional elastic analysis process is a process that executes an analysis for elastic recovery under contribution analysis conditions for each target region. The contribution analysis conditions are conditions that are satisfied in the conditional elastic analysis process, and include at least physical property conditions, contribution analysis shape conditions, and contribution analysis stress distribution conditions.

The contribution analysis shape condition is a condition that the shape of the material to be analyzed is a bottom dead center shape. The contribution analysis stress distribution condition is a condition that the stress distribution in the initial state of the material to be analyzed satisfies a non-uniform distribution condition. Therefore, the contribution analysis stress distribution condition may be any condition as long as the stress distribution that satisfies 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 a condition in which the stress in some of the multiple analysis target regions is the stress indicated by the bottom dead center stress distribution, and the stress in the other analysis target regions is zero.

The non-uniform distribution condition may be, for example, a condition in which the stress in the target region is the stress indicated by the bottom dead center stress distribution, and the stress in the other analysis target regions is zero. The non-uniform distribution condition may be, for example, a condition in which the stress in the target region is zero, and the stress in the other analysis target regions is the stress indicated by the bottom dead center stress distribution. The non-uniform distribution condition may be, for example, a condition in which the stress distribution in multiple analysis target regions including the target region is the stress indicated by the bottom dead center stress distribution, and the stress in the other analysis target regions is zero. The non-uniform distribution condition may be, for example, a condition in which the stress in multiple analysis target regions including the target region is zero, and the stress in the other analysis target regions is the stress indicated by the bottom dead center stress distribution.

In this way, the analysis of elastic recovery in the conditional elastic analysis process is an analysis of elastic recovery that includes the initial condition that the shape is at the bottom dead center and the stress distribution that satisfies the non-uniform distribution condition.

By executing the conditional elasticity analysis process, 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, is obtained for each target region. An index or amount indicating the stress generated in the fatigue analysis target part is an example of the degree of contribution.

In this way, the degree of contribution is, for example, an index or amount indicating the stress generated in the part subject to fatigue analysis. The index or amount indicating the stress generated in the part subject to fatigue analysis may be any index or amount that indicates the stress generated in the part subject to fatigue analysis. The degree of contribution is, for example, the maximum principal stress generated in the part subject to fatigue analysis. A desirable degree of contribution is a stress in a direction perpendicular to the direction of propagation of a fatigue crack generated in the part subject to fatigue analysis. This is because stress in a direction perpendicular to the fatigue crack causes the fatigue crack.

The maximum principal stress occurring in the fatigue analysis target part is the stress with the largest magnitude among multiple stresses occurring in different directions in the fatigue analysis target part. The contribution degree may be, for example, the angle between the direction of the maximum principal stress occurring in the fatigue analysis target part and the crack direction vector. The crack direction vector is a vector that faces in a direction perpendicular to the fatigue target direction. The contribution degree may be, for example, a value obtained by multiplying the angle between the direction of the maximum principal stress occurring in the fatigue analysis target part and the direction of the fatigue crack by a predetermined weight.

In this way, the conditional elasticity analysis process is a process that obtains the contribution degree for each region of the analysis target region by performing an analysis of elastic recovery under the contribution analysis conditions for each target region. Therefore, the contribution degree analysis process is a process that obtains the contribution degree for each region of the analysis target region.

In other words, the contribution analysis process is a process that obtains the strength of the effect that the stress generated by molding in each analysis target area has on fatigue cracks in the fatigue analysis target area based on the fatigue analysis target area information and the results of the bottom dead center molding analysis process.

The analysis result analysis process is a process for determining the analysis target area whose contribution level satisfies a predetermined condition regarding the contribution level (hereinafter referred to as the "contribution level condition") based on the result of the contribution level analysis process. The result of the contribution level analysis is specifically the contribution level of each area of the analysis target area. The contribution level condition is, for example, a condition that the contribution level is the highest. The contribution level condition may be, for example, a condition that the contribution level is higher than a predetermined rank in the permutation of the contribution level. The contribution level condition may be, for example, a condition that the contribution level is higher than a predetermined rank.

Figure 2 shows an example of the results of bottom dead center forming analysis processing in an embodiment. As an example, Figure 2 shows the stress distribution that occurs on the surface of a molded product when a lower arm of an automobile part is pressed and molded. The area surrounded by a dotted line and displayed in gray in Figure 2 is the area where the stress on the surface of the lower surface of the vehicle exceeds 1000 MPa, and other areas are areas where the stress is 1000 MPa or less. Point P1 in Figure 2 indicates the part that is the subject of fatigue analysis. Figure 2 shows that the stress at point P1 is 1431 MPa. Note that P1 is the position on the lower surface of the vehicle.

Figure 3 is a diagram showing an example of the results of the region setting process in the embodiment. Figure 3 shows that the material to be analyzed has been divided into multiple simply connected regions to be analyzed. Note that the regions to be analyzed do not necessarily have to be simply connected. The numbers shown as an example in Figure 3 are identifiers that identify each region to be analyzed. In the example of Figure 3, the number of regions to be analyzed into which the material to be analyzed is divided is 200.

Figure 4 is a diagram showing an example of the results of a contribution analysis in an embodiment. In Figure 4, the horizontal axis indicates the identifier of the analysis target area, and the vertical axis indicates the contribution. Specifically, the contribution in the example of Figure 4 is the stress in the fatigue target direction in the fatigue analysis target area. The vertical axis of Figure 4 is in units of MPa. Figure 4 shows the contribution of each of the top 30 analysis target areas with the highest contribution, in order of highest contribution. For example, the contribution of the analysis target area with identifier 025 is 63 MPa. For example, the contribution of the analysis target area with identifier 163 is 11 MPa.

<Effects of non-uniform distribution conditions>
Here, the effect of the non-uniform distribution condition will be explained. When the non-uniform distribution condition is satisfied, a situation in which residual stress exists only in a part of the material to be analyzed is analyzed. Here, if a situation in which residual stress exists only in a part is analyzed, a doubt arises that the analysis result will be significantly different from the analysis result when the stress distribution is a bottom dead center stress distribution. However, in general, physical phenomena are governed by superposition or linear sum. Therefore, it is presumed that the stress occurring in the part to be analyzed by fatigue is approximated by the linear sum of each stress caused by the residual stress occurring in each part other than the part to be analyzed by fatigue.

Therefore, it is inferred that the analysis of the contribution of the part to be analyzed can be performed, for example, under conditions where residual stress exists only in the part to be analyzed. Furthermore, since the stress occurring in the part to be analyzed is a linear sum of the stresses caused by the residual stresses occurring in each part other than the part to be analyzed, it is inferred that the analysis of the contribution of the part to be analyzed can be performed under conditions where there is no residual stress only in the part to be analyzed. In this way, since the stress occurring in the part to be analyzed is a linear sum of the stresses caused by the residual stresses occurring in each part other than the part to be analyzed, it is inferred that the analysis of the contribution of the part to be analyzed can be performed under a stress distribution that satisfies the non-uniform distribution condition. The accuracy of this inference has been demonstrated by experiment. An example of the experimental results will be described later.

In addition, the amount of calculation required to calculate data containing many zeros is generally less than the amount of calculation required to calculate data containing a small number of zeros. Therefore, the amount of calculation required to analyze a situation in which stress occurs only in a part of the material being analyzed is less than the amount of calculation required to analyze a situation in which stress occurs in all of the material being analyzed. Therefore, when the non-uniform distribution condition is satisfied, the amount of calculation required to execute the contribution analysis process is reduced compared to when the non-uniform distribution condition is not satisfied.

<Experimental Results>
Here, an example of the results of an experiment to evaluate the accuracy of analysis by the analysis device 1 (hereinafter referred to as the "evaluation experiment") is shown. In the evaluation experiment, processing (hereinafter referred to as the "reduction processing") was performed to reduce the stress in the analysis target area that was determined by the analysis device 1 to satisfy the contribution height condition, and an experiment was conducted to measure the residual stress in the fatigue target direction of the fatigue analysis target area before and after processing. The contribution height condition in the evaluation experiment was the highest contribution level. Specifically, the contribution level in the evaluation experiment was compressive stress. The residual stress measured in the evaluation experiment was the surface stress measured by X-rays.

Figure 5 is a first explanatory diagram for explaining an evaluation experiment in an embodiment. Figure 5 shows a perspective view of the molded product used in the evaluation experiment. The Z direction in Figure 5 is the upward direction of the vehicle. Figure 5 shows that the molded product used in the evaluation experiment has a non-uniform cross-sectional shape. In other words, Figure 5 shows that the molded product used in the evaluation experiment is a part in which it is not easy to identify 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, for example, in the following Figure 6.

Figure 6 is a second explanatory diagram for explaining the evaluation experiment in the embodiment. Figure 6 shows a cross section at cross section A-A' in Figure 5. Figure 6 shows that the shape of cross section A-A' is a bimodal shape. As such, the molded product used in the evaluation experiment is an example of a molded product in which it is not easy to identify the residual stress that affects fatigue cracking because the cross section is non-uniform. The evaluation experiment showed that the analysis device 1 can identify the residual stress that affects fatigue cracking with high accuracy even for such a molded product. This will be explained in more detail using Figures 7 and 8.

Figure 7 is a third explanatory diagram illustrating an evaluation experiment in an embodiment. Figure 7 shows region D1. Region D1 is an analysis target region of the metal material used in the evaluation experiment that is determined by analysis device 1 to satisfy the contribution height condition. Cross section A-A' is a cross section that includes a portion of region D1.

Figure 8 is a fourth explanatory diagram for explaining the evaluation experiment in the embodiment. More specifically, Figure 8 is an explanatory diagram for explaining the reduction processing in the evaluation experiment. The target of the reduction processing in the evaluation experiment was the analysis target area that was determined to satisfy the contribution height condition. The reduction processing in the evaluation experiment was a process in which the recess in the analysis target area of the processing target was shallowly formed in the previous process, and then formed into the product shape in the subsequent process. Forming shallowly means forming with a large R. More specifically, the reduction processing in the evaluation experiment was a process in which, for a product shape R of 5 mm, the recess was formed with R15 mm in the previous process, and then formed into the product shape in the subsequent process. More specifically, the subsequent process was a process in which the recess was formed with a small R.

In the evaluation experiment, the result of measuring the stress on the surface layer of the molded product using X-rays showed that the residual stress in the fatigue target direction of the fatigue analysis target area was reduced from 400 MPa to 200 MPa by reduction processing. In this way, the evaluation experiment shows that the residual stress in the fatigue target direction of the fatigue analysis target area was reduced by performing reduction processing on the analysis target area determined by the analysis device 1 to satisfy the contribution height condition. In this way, the evaluation experiment showed that the analysis device 1 is capable of identifying residual stresses that affect fatigue cracking.

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

More specifically, the processor 91 reads out a program stored in the storage unit 14 and stores the read out program in the memory 92. The processor 91 executes the program stored in the memory 92, whereby 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.

The control unit 11 controls the operation of the various functional units of 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 analysis process. The control unit 11 executes, for example, an analysis result analysis process.

The control unit 11 controls the operation of the output unit 15, for example. The control unit 11 records in the memory unit 14 various information generated, for example, by the execution of a fatigue analysis target part information acquisition process. The control unit 11 records in the memory unit 14 various information generated, for example, by the execution of a bottom dead center forming analysis process. The control unit 11 records in the memory unit 14 various information generated, for example, by the execution of a region setting process. The control unit 11 records in the memory unit 14 various information generated, for example, by the execution of a contribution analysis process. The control unit 11 records in the memory unit 14 various information generated, for example, by the execution of an analysis result analysis process.

The input unit 12 includes input devices such as a mouse, keyboard, and touch panel. The input unit 12 may be configured as an interface that connects these input devices to the analysis device 1. The input unit 12 accepts input of various information to the analysis device 1. For example, information on the part to be subjected to fatigue analysis is input to the input unit 12. For example, physical property information and constraint conditions during molding of the material to be analyzed are input to the input unit 12.

The physical property information and the constraint conditions during molding of the analysis target material may be input via the communication unit 13. The physical property information and the constraint conditions during molding of the analysis target material do not necessarily need to be input via the input unit 12 or the communication unit 13, and may be stored in advance in the storage unit 14. For ease of explanation, the analysis device 1 will be described below using as an example a case in which the physical property information and the constraint conditions during molding of the analysis target material are stored in advance in the storage unit 14.

The communication unit 13 includes a communication interface for connecting the analysis device 1 to an external device. The communication unit 13 communicates with the external device via a wired or wireless connection. The external device is, for example, a device that inputs fatigue analysis target part information. In such a case, the communication unit 13 acquires fatigue analysis target part information by communicating with the device that inputs the fatigue analysis target part information.

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 information related to the analysis device 1. The storage unit 14 stores information inputted, for example, via the input unit 12 or the communication unit 13. The storage unit 14 stores various information generated, for example, by the execution of a fatigue analysis target part information acquisition process. The storage unit 14 stores various information generated, for example, by the execution of a bottom dead center forming analysis process. The storage unit 14 stores various information generated, for example, by the execution of a region setting process. The storage unit 14 stores various information generated, for example, by the execution of a contribution analysis process. The storage unit 14 stores various information generated, for example, by the execution of an analysis result analysis process. The storage unit 14 stores the contribution height condition in advance. The content of the contribution 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, physical property information. The memory unit 14 stores the constraint conditions during molding of the material to be analyzed.

The output unit 15 outputs various information. The output unit 15 includes a display device such as a CRT (Cathode Ray Tube) display, a liquid crystal display, or an organic EL (Electro-Luminescence) display. The output unit 15 may be configured as an interface that connects these display devices to the analysis device 1. The output unit 15 outputs information input to the input unit 12, for example. 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, 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 analysis process. The execution result of the contribution analysis process is, for example, the graph of FIG. 4. The output unit 15 may display, for example, the execution result of the analysis result analysis process.

Figure 10 is a diagram showing an example of the configuration of the control unit 11 in an embodiment. The control unit 11 includes a fatigue analysis target part information acquisition unit 110, a bottom dead center forming analysis unit 120, an area setting unit 130, a contribution 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.

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

The memory control unit 160 records various 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.

Figure 11 is a flowchart showing an example of the flow of processing executed by the analysis device 1 in the embodiment. The fatigue analysis target part information acquisition unit 110 executes the 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 the 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 bottom dead center stress of the analysis target material (step S102).

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 multiple analysis target regions, and information indicating each analysis target region after division is recorded in the storage unit 14 (step S103). Next, the contribution analysis unit 140 executes a contribution analysis process. By executing the contribution analysis process, the contribution analysis unit 140 obtains the contribution 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 the analysis target region that satisfies the contribution height condition (step S105). Note that the process of step S101 may be executed at any timing as long as it is executed before the process of step S104 is executed.

The analysis device 1 configured in this manner can obtain the parts of the analysis target that have the greatest influence on the occurrence of fatigue cracks. Therefore, the analysis device 1 can evaluate the influence of residual stress at each part during molding.

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

Here, an example of reduction processing in the case where the reduction processing method is the step-busting method (hereinafter referred to as the "first reduction processing example") will be described using Figures 12 and 13. Next, an example of reduction processing in the case where the reduction processing method is the bend R change method (hereinafter referred to as the "second reduction processing example") will be described using Figures 14 and 15.

Figure 12 is a first explanatory diagram for explaining a first reduction processing example in the modified example. Figure 13 is a second explanatory diagram for explaining a first reduction processing example in the modified example. Point P1 in Figure 12 indicates the fatigue analysis target portion. Figure 12 shows the analysis target region that satisfies the contribution degree height condition as region D2. As shown in Figure 12, region D2 is located inside, not on the periphery, of the molded product to be analyzed. In the first reduction processing example, the contribution degree is average stress. Therefore, in the first reduction processing example, the average stress in region D2 is the cause of fatigue cracking. The average stress is a stress in the in-plane direction.

In the first reduction processing example, reduction processing is performed on region D2. As shown in FIG. 13, reduction processing involves a first process that creates a step, and a second process that removes the step. By removing the step, compressive stress is applied.

Figure 14 is a first explanatory diagram for explaining a second reduction processing example in the modified example. Figure 15 is a second explanatory diagram for explaining a second reduction processing example in the modified example. Point P1 in Figure 14 indicates the fatigue analysis target portion. Figure 14 shows the analysis target region that satisfies the contribution degree height condition as region D3. As shown in Figure 14, region D3 is located not inside the metal material to be analyzed but on the periphery. In the second reduction processing example, the contribution degree is the deviation adaptability. Therefore, in the second reduction processing example, the deviation stress in region D3 is the cause of the fatigue crack. The deviation stress is the stress in the plate thickness direction.

In the second reduction processing example, reduction processing is performed on region D3. As shown in FIG. 15, reduction processing involves forming the area with a small radius in the first process, and then reforming it to a large radius in the second process. In short, in areas with high contribution, the bending radius is changed between the previous and next processes to change the deviatoric stress, thereby reducing the stress in the area subject to fatigue analysis.

In addition, in the reduction process, unevenness such as beads may be added to the designed shape to reduce the frequency of fatigue cracks. FIG. 16 is an explanatory diagram illustrating an example of a process for adding beads in a modified example. FIG. 16 shows a bimodal shape as an example of the result of reduction process. By performing such a process on the area with a high contribution, the stress in the area with a high contribution is changed, thereby reducing the stress in the area subject to fatigue analysis.

Figure 17 is an explanatory diagram for explaining the coining method in a modified example. As described above, the method of reduction processing may be the coining method. Figure 17 is a diagram showing an example of reduction processing using the coining method. Region D4 in Figure 17 shows an analysis target region that satisfies the contribution height condition. Figure 17 shows coining region D4 using the coining method to change the stress in the surface layer. 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 occurs. Since the moment is largely influenced by the stress in the surface layer, the stress in the surface layer of the part with high contribution can be changed by coining, thereby reducing the stress in the fatigue analysis target part. The stress in the surface layer is generally called the surface stress. The definition of the surface layer is the region 100 μm or less from the surface.

Figure 18 is a flow chart explaining an example of a manufacturing method in a modified example. Hereinafter, processes similar to those described in Figure 11 are given the same reference numerals as in Figure 11 and will not be explained again. After steps S101 to S105 are performed, reduction processing is performed on the analysis target area that satisfies the contribution height condition obtained in step S105 (step S106).

In the contribution analysis process, the contribution may be obtained by dividing the stress into average stress and deviatoric stress, or by dividing the stress into average stress, deviatoric stress, and surface stress. That is, the contribution analysis process may obtain the contribution for average stress, the contribution for deviatoric stress, or the contribution for surface stress.

<Relationship between average stress, deviation accommodation force, springback, and contribution analysis process>
Springback has an effect on fatigue cracking. Springback is mainly affected by mean stress and deviatoric stress. In order to help understand the effects of mean stress and deviatoric stress on fatigue cracking, the relationship between mean stress, deviatoric stress, and springback will be explained using Figures 19 to 23. Furthermore, the relationship with the contribution analysis process will also be explained.

Figure 19 is a first explanatory diagram illustrating the relationship between the average stress, deviation adaptability, springback, and contribution analysis processing in a modified example. Figure 19 shows an example of the distribution of the average stress and deviation adaptability at the bottom dead center.

Figure 20 is a second explanatory diagram that explains the relationship between the average stress, deviatoric stress, springback, and contribution analysis processing in the modified example. Figure 20 shows that springback occurs due to the distribution of average stress, which is an in-plane stress, and the plate is distorted or twisted. The plate is the molded product that is the analysis target of the analysis device 1.

Figure 21 is a third explanatory diagram illustrating the relationship between the average stress, deviatoric stress, springback, and contribution analysis processing in the modified example. When performing the contribution analysis processing to analyze the effect of the average stress on fatigue cracking, the average value of the stress in the plate thickness direction is used for the stress in the plate thickness direction.

Figure 22 is a fourth explanatory diagram that explains the relationship between the average stress, the deviation adaptive force, the springback, and the contribution analysis process in the modified example. Figure 22 shows that the distribution of the deviation adaptive force, which is the stress in the plate thickness direction, causes springback and bends the plate.

Figure 23 is a fifth explanatory diagram that explains the relationship between the average stress, deviation adaptability, springback, and contribution analysis processing in the modified example. When performing the contribution analysis processing to analyze the effect of 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.

When performing a contribution analysis process to analyze the effect of surface stress on fatigue cracking, the contribution is obtained with stresses other than surface stress set to zero, for example. When performing a contribution analysis process to analyze the effect of surface stress on fatigue cracking, the contribution may be obtained with the surface stress multiplied by a coefficient, for example, so that the surface stress has a larger value than the magnitude of the other stresses.

In the region setting process, it is desirable to divide the region to be analyzed (hereinafter referred to as the "fatigue region") that includes the part to be analyzed for fatigue analysis so that the boundaries of the region to be analyzed are approximately the same and equidistant from the part to be analyzed for fatigue analysis. In other words, it is desirable that the distance between the boundary of the fatigue region and the part to be analyzed for fatigue analysis is approximately the same regardless of the position of the boundary of the fatigue region. The reason for this will be explained using FIG. 24.

Figure 24 is an explanatory diagram illustrating the region setting process in a modified example. Figure 24 shows the result of a region setting process in which the distance between the boundary of the fatigue region and the fatigue analysis target part (hereinafter referred to as "fatigue distance") is not equal. If the fatigue distance is not equal regardless of direction, the contribution of other analysis target areas adjacent to the fatigue region may change depending on the division method. For example, even if the fatigue distance is equal, the contribution of other analysis target areas adjacent to the fatigue region will be the same, but because the fatigue distance is not equal, a phenomenon occurs in which an analysis target area with a close distance between its boundary and the fatigue analysis target part has a high contribution.

Note that the explanation has been given using metal materials as examples, but examples of metal materials include iron, aluminum, stainless steel, titanium and magnesium.

The analysis device 1 may be implemented using multiple information processing devices that are communicatively connected to each other via a network. In this case, each functional unit of the analysis device 1 may be distributed and implemented in multiple information processing devices.

All or part of the functions 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. Examples of computer-readable recording media include portable media such as flexible disks, optical magnetic disks, ROMs, and CD-ROMs, and storage devices such as hard disks built into computer systems. The program may be transmitted via a telecommunications line.

The above describes an embodiment of the present invention in detail with reference to the drawings, but the specific configuration is not limited to this embodiment, and includes designs that do not deviate from the gist of the present invention.

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

Claims (7)

a bottom dead center forming analysis unit that executes forming analysis to obtain information on a post-forming object that is an analysis object that is in a state of being restrained at the bottom dead center after forming to the bottom dead center is performed, based on information on a pre-forming object that is an analysis object before forming to the bottom dead center is performed;
A region setting unit that divides the shape of the molded object into a plurality of analysis target regions;
a contribution analysis unit that obtains the strength of the effect that the stress generated by the molding in each of the analysis target regions has on the fatigue crack in the fatigue analysis target portion by performing an analysis of elastic recovery based on fatigue analysis target portion information indicating a fatigue analysis target portion that is an analysis target for fatigue crack occurrence among the portions of the target after molding and a fatigue target direction that is a fatigue crack propagation direction in the fatigue analysis target portion, and a result of the molding analysis;
An analysis device comprising: the contribution analysis unit executes an analysis for elastic recovery for each of the analysis target regions under contribution analysis conditions including a contribution analysis shape condition that the shape of the analysis target is the shape at the bottom dead center, and a contribution analysis stress distribution condition that the stress distribution in a part of the analysis target regions is the stress indicated by the stress distribution at the bottom dead center and the stress in the other analysis target regions is zero, which is the stress distribution in the initial state of the analysis target;
The analysis device according to claim 1 . The contribution analysis unit obtains an average stress, which is a stress in an in-plane direction, as the strength of the influence.
The analysis device according to claim 1 or 2. The contribution analysis unit obtains a deviatoric stress, which is a stress in the plate thickness direction, as the strength of the influence.
The analysis device according to claim 1 . The contribution analysis unit obtains a surface stress, which is a stress of a surface layer, as the strength of the influence.
The analysis device according to claim 1 . a bottom dead center forming analysis step of executing a forming analysis to obtain information on a post-forming object which is an analysis object that is in a state of being restrained at the bottom dead center after forming up to the bottom dead center is performed, based on information on a pre-forming object which is an analysis object before forming up to the bottom dead center is performed;
A region setting step of dividing the shape of the molded object into a plurality of analysis target regions;
a contribution analysis step of obtaining the strength of the effect that the stress generated by the molding in each of the analysis target regions has on the fatigue crack in the fatigue analysis target portion by performing an analysis of elastic recovery based on fatigue analysis target portion information indicating a fatigue analysis target portion that is an analysis target for fatigue crack occurrence among the portions of the target after molding and a fatigue target direction that is a fatigue crack propagation direction in the fatigue analysis target portion, and the results of the molding analysis;
The analysis method has the following features: a bottom dead center forming analysis step of executing a forming analysis to obtain information on a post-forming object which is an analysis object that is in a state of being restrained at the bottom dead center after forming up to the bottom dead center is performed, based on information on a pre-forming object which is an analysis object before forming up to the bottom dead center is performed;
A region setting step of dividing the shape of the molded object into a plurality of analysis target regions;
a contribution analysis step of obtaining the strength of the effect that the stress generated by the molding in each of the analysis target regions has on the fatigue crack in the fatigue analysis target portion by performing an analysis of elastic recovery based on fatigue analysis target portion information indicating a fatigue analysis target portion that is an analysis target for fatigue crack occurrence among the portions of the target after molding and a fatigue target direction that is a fatigue crack propagation direction in the fatigue analysis target portion, and the results of the molding analysis;
a processing step of performing processing to reduce stress in the analysis target region in which the strength obtained by the contribution degree analysis step satisfies a predetermined condition;
The manufacturing method according to claim 1,

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