Structure analysis method, analysis device, and program

Abstract

To provide a method, an apparatus and a program for analyzing a structure capable of evaluating breakage at a nugget part with high accuracy, while suppressing a calculation load.SOLUTION: A method for analyzing a structure includes: a six force components acquisition step S1 which acquires six force components at prescribed time generated in a first node string; a state quantity calculation step S2 which calculates at least one of a load or a displacement which is a state quantity in each node of a second node string; a partial analysis step which performs partial analysis including the state quantity in each node of the second node string as a restraint condition with respect to a partial analysis model; and a nugget part breakage evaluation step which evaluates a breakage state at a nugget part, on the basis of the calculated stress and strain.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a method, an apparatus, and a program for analyzing a structure. [Background technology]

[0002] Conventionally, in the design of structures such as automobiles, the structural characteristics of the structure, such as the crash performance, are analyzed by computer simulation. For example, finite element analysis is used as a method for analyzing the structural characteristics of the structure. In finite element analysis, the structure is modeled by elements connecting a plurality of nodes, and the stress and strain occurring in each element are obtained, so that the stress and strain occurring in each part of the structure can be obtained. Incidentally, such a structure to be analyzed may be an integrated structure formed by joining a plurality of plate-like members to each other by spot welding. In such a structure, fracture evaluation at a nugget portion formed by spot welding and connecting the plate-like members is important in evaluating the structural characteristics of the structure.

[0003] For example, Patent Document 1 proposes a method for fracture analysis of the above-mentioned nugget portion by carrying out the steps of: determining a maximum allowable load value of the weld in a predetermined fracture mode based on at least one of the sheet thickness of each steel plate to be spot-welded, the tensile strength, the elongation, the chemical composition of the nugget portion, the nugget diameter of the weld, the effective width determined by the distance between the weld and an adjacent weld, edge or ridge line, and the cross-sectional height; and determining the allowable load value at each moment after the maximum allowable load value of the weld is reached according to the predetermined fracture mode, and determining the displacement or time at which the allowable load value becomes zero. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] International Publication No. 2011 / 126057 Summary of the Invention [Problem to be solved by the invention]

[0005] However, in the method of Patent Document 1, although fracture within the nugget is taken into consideration and the allowable load value of the nugget is set based on the chemical composition of the nugget, the analysis method is elastic analysis and accurate prediction is not possible, and in particular in the case of a high-strength material in which the strength difference between the base material and the HAZ-softened portion and the inside of the nugget is small, it is not possible to accurately analyze cases in which fracture occurs inside the nugget rather than in the HAZ-softened portion. Also, there is a problem that the calculation load becomes large when an elastic-plastic analysis is performed on the entire structure to evaluate fracture of the nugget.

[0006] In view of the above circumstances, the present invention aims to provide a method, an apparatus, and a program for analyzing a structure having a plurality of plate-like members stacked on top of each other in the thickness direction and a nugget portion formed by spot welding the plurality of plate-like members to each other, which is capable of evaluating fracture in the nugget portion with high accuracy and while reducing the calculation load. [Means for solving the problem]

[0007] A method for analyzing a structure according to one aspect of the present invention includes the steps of: 1. A computer-implemented method for analyzing a structure, comprising:A method for analyzing a structure having a plurality of plate-like members overlapped with each other in a thickness direction and a nugget portion formed by spot welding the plurality of plate-like members to each other, the method comprising the steps of: acquiring six-component forces at a predetermined time occurring in a first node row composed of a plurality of nodes forming a closed loop including the nugget portion when viewed in the thickness direction in the structure, for the structure which is deformed over time by an external force; acquiring six-component forces at the acquired first node row, and acquiring six-component forces at a predetermined time occurring in a first node row composed of a plurality of nodes which form a closed loop including the nugget portion when viewed in the thickness direction in the structure; the state quantity calculation step of calculating at least one of the load and the displacement, which are state quantities at each node of the second node series, based on a second node series composed of points; a partial analysis step of performing a partial analysis on a partial analysis model including each node of the second node series and a plurality of nodes in the second node series, at least a portion of which simulates the nugget portion, using the calculated state quantities at each node of the second node series as constraint conditions, and calculating the stress and strain occurring between each node of the partial analysis model; and a nugget portion fracture evaluation step of evaluating the fracture state of the nugget portion based on the calculated stress and strain.

[0008] An analysis device according to one aspect of the present invention is an analysis device for a structure having a plurality of plate-like members overlapped with each other in a thickness direction and a nugget portion formed by spot welding the plurality of plate-like members to each other, the analysis device including a six-component force acquisition unit that acquires six-component forces at a predetermined time that occur in a first node row composed of a plurality of nodes that form a closed loop including the nugget portion when viewed in the thickness direction in the structure, for the structure that deforms over time due to an external force, and acquires six-component forces at the acquired first node row, and a six-component force acquisition unit that acquires six-component forces at a predetermined time that occur in a first node row composed of a plurality of nodes that form a closed loop including the nugget portion when viewed in the thickness direction in the structure, the six-component forces at the acquired first node row, and the state quantity calculation unit calculating at least one of the load and the displacement, which are state quantities at each node of the second node series, based on a second node series composed of a plurality of nodes calculated above; a partial analysis processing unit performing a partial analysis on a partial analysis model including each node of the second node series and a plurality of nodes in the second node series, at least a portion of which simulates the nugget portion, using the calculated state quantities at each node of the second node series as constraint conditions, and calculating the stress and strain occurring between each node of the partial analysis model; and a nugget portion fracture evaluation unit evaluating the fracture state of the nugget portion based on the calculated stress and strain.

[0009] A program according to one aspect of the present invention is a program for causing a computer to function as an analysis device for a structure having a plurality of plate-like members overlapping each other in a thickness direction and a nugget portion formed by spot welding the plurality of plate-like members to each other, the program comprising: a six-component force acquisition means for acquiring, for the structure which deforms over time due to an external force, six-component forces generated at a predetermined time in a first node row composed of a plurality of nodes forming a closed loop including the nugget portion when viewed in the thickness direction in the structure; a six-component force acquisition means for acquiring six-component forces generated at a predetermined time in a first node row composed of a plurality of nodes forming a closed loop including the nugget portion when viewed in the thickness direction in the structure; The system functions as: a state quantity calculation means for calculating at least one of the load and the displacement, which are state quantities at each node of the second node series, based on a second node series composed of a plurality of nodes preset to surround a nugget portion; a partial analysis processing means for performing a partial analysis on a partial analysis model including each node of the second node series and a plurality of nodes in the second node series, at least a portion of which simulates the nugget portion, using the calculated state quantities at each node of the second node series as constraint conditions, and calculating the stress and strain occurring between each node of the partial analysis model; and a nugget portion fracture evaluation means for evaluating the fracture state of the nugget portion based on the calculated stress and strain. Effect of the Invention

[0010] According to the present invention, for a structure having a plurality of plate-shaped members stacked on top of each other in the thickness direction and a nugget portion formed by spot welding the plurality of plate-shaped members to each other, it is possible to evaluate fracture in the nugget portion with high accuracy and while reducing the calculation load. [Brief description of the drawings]

[0011] [Figure 1] FIG. 2 is a flow diagram illustrating a method for analyzing a structure according to an embodiment. [Diagram 2] 1 is a perspective view showing an example of a structure to be analyzed by a method for analyzing a structure according to an embodiment; [Diagram 3]1 is an explanatory diagram showing the periphery of a nugget portion in a structural analysis model that simulates a structure to be analyzed by a method for analyzing a structure according to an embodiment. FIG. [Figure 4] FIG. 2 is an explanatory diagram for explaining a beam model as an example of a partial analysis model simulating the periphery of a nugget portion, among the structures to be analyzed by the method for analyzing a structure according to the embodiment; [Diagram 5] FIG. 2 is an explanatory diagram for explaining a solid model as an example of a partial analysis model simulating the periphery of a nugget portion of a structure to be analyzed by the method for analyzing a structure of an embodiment. [Figure 6] FIG. 11 is an explanatory diagram for explaining a method for calculating stiffness parameters of a nugget portion in the method for analyzing a structure according to the embodiment, and is a graph showing the relationship between stress and strain. [Figure 7] FIG. 4 is a flow diagram for explaining details of a partial analysis step in the structure analysis method of the embodiment. [Figure 8] FIG. 4 is a flow diagram illustrating details of a nugget fracture evaluation step in the method for analyzing a structure according to the embodiment. [Figure 9] 2 is a block diagram showing an example of a hardware configuration of the analysis apparatus according to the embodiment; FIG. [Figure 10] 2 is a block diagram showing an example of a functional configuration of a control unit in the embodiment. FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] Hereinafter, a structure analysis device, a structure analysis method, and a program according to an embodiment will be described with reference to the drawings. First, a structure characteristic analysis method executed by the analysis device according to the embodiment will be described.

[0013] (Overview of structure analysis methods) The method of analyzing a structure in this embodiment is a method of analyzing a structure that deforms over time due to an external force. The method of analyzing a structure in this embodiment is used, for example, in vehicle body analysis in which all or a part of the body of an automobile is the structure. The method of analyzing a structure includes, for example, a crash performance analysis that analyzes crash performance. The method of analyzing a structure includes a strength analysis that analyzes the strength of the entire structure as a structural characteristic, and a fatigue analysis that analyzes fatigue characteristics as a structural characteristic. In the present embodiment, the crash performance analysis that analyzes crash performance will be described below as an example. The analysis target is a structure having a plurality of plate-shaped members overlapped in the thickness direction and a nugget portion formed by spot welding the plurality of plate-shaped members to each other. The structure is, for example, an automobile. The analysis target of the crash performance analysis method does not necessarily have to be the automobile itself, and may be only a part that constitutes the automobile.

[0014] FIG. 1 is a flowchart showing an example of a process flow in the analysis method of the structure 100 of the embodiment. As shown in FIG. 1, the analysis method of the structure 100 of the embodiment includes a structural analysis step S1, a six-component force acquisition step S2, a state quantity calculation step S3, a partial analysis step S4, a nugget fracture evaluation step S5, and an update step S6. In the analysis method of the structure 100 of the embodiment, the structural analysis step S1, the six-component force acquisition step S2, the state quantity calculation step S3, the partial analysis step S4, and the nugget fracture evaluation step S5 are repeatedly performed for each unit time, and the structural analysis model M1 simulating the structure 100, which will be described in detail below, is updated in the update step S6 as necessary based on the evaluation result of the nugget fracture evaluation step S5, and the structural analysis step S1 at the next time is performed. Each step and the detailed steps performed in each step will be described below.

[0015] First, in the structural analysis step S1, structural analysis is performed using a structural analysis model M1 that models the structure 100 to be analyzed. As described above, the structure 100 to be analyzed has a plurality of plate-shaped members 101 that are at least partially overlapped with each other in the thickness direction, and a nugget portion 102 formed by spot welding the plurality of plate-shaped members 101 to each other. As shown in FIG. 2, the structure 100 of this embodiment, as an example, is a first plate-shaped member 101A and a second plate-shaped member 101B that are plate-shaped members 101 that are overlapped with each other in the thickness direction and are spot-welded and joined. In the nugget portion 102, the base materials of the first plate-shaped member 101A and the second plate-shaped member 101B are melted together and integrated. In this embodiment, the structure 100 has a plurality of nugget portions 102. The plurality of nugget portions 102 are arranged in a row with intervals between them. Then, as shown in FIG. 3, the structural analysis model M1 models each of the plate-shaped members 101 as a shell element, for example. 2 and 3, the axial direction of the nugget portion 102, i.e., the thickness direction of the first plate-like member 101A and the second plate-like member 101B, is defined as the X direction, and the axis extending in the X direction is defined as the X axis. The direction in which the nugget portions 102 are arranged is defined as the Y direction, and the axis extending in the Y direction is defined as the Y axis. Furthermore, the direction perpendicular to the X direction and the Y direction is defined as the Z direction, and the axis extending in the Z direction is defined as the Z axis. Furthermore, the X-axis, Y-axis, and Z-axis components of each parameter will be described below with lowercase x, y, and z added.

[0016] In the structural analysis step S1 of this embodiment, a crash analysis is performed using the finite element method. The structural analysis method is not limited to the finite element method, and other analysis methods may be used. The type of structural analysis is not limited to the crash analysis, and may be, for example, strength analysis or fatigue analysis as described above. The structural analysis model M1 used in the structural analysis step S1 of this embodiment may be a model composed of a plurality of general meshes used in the finite element method. For the nugget portion 102, a simple combination of meshes that can simulate the outer periphery of the nugget portion 102 may also be used.

[0017] In the structural analysis step S1 of this embodiment, six components of forces at each node of each mesh are calculated based on a preset boundary condition. The six components of forces here are the X-axis component, the Y-axis component, and the Z-axis component of the applied force, and the moment around the X-axis, the moment around the Y-axis, and the moment around the Z-axis. Specifically, the structural analysis step S1 of this embodiment is performed using, for example, an incremental method, and the six components of forces at each time for each unit time are calculated at each node. In this embodiment, after the structural analysis step S1 is performed for a predetermined time, each subsequent step is executed, and the structural analysis step S1 is repeated by setting a time unit time after the predetermined time as the predetermined time based on the result.

[0018] That is, after the structural analysis step S1 is performed at a predetermined time, in the six-component force acquisition step S2, six-component forces occurring at each of the first node row N1 composed of a plurality of nodes at a predetermined time are extracted from the calculation results in the structural analysis step S1. The predetermined time here refers to any of the times that are unit time intervals at which the structural analysis step S1 is performed. As shown in FIG. 3, the first node row N1 forms a closed loop L including the nugget portion 102 inside when viewed in the X direction. It is preferable that the first node row N1 is set so as to include the heat-affected zone (HAZ portion) occurring in the base material of the plate-like member 101 when forming the nugget portion 102 when viewed in the thickness direction. Note that the upper limit of the diameter dimension is not particularly limited, but it is preferable that it is not too large in terms of accuracy and calculation load in the partial analysis step S4 described later. In addition, the shape of the closed loop L formed by the first node row N1 is also not particularly limited, but it is more preferable that it is a polygonal shape that is approximately similar to the outer circumferential shape of the nugget portion 102 in terms of accuracy. In the structure 100 of this embodiment, since it has a plurality of nugget portions 102, a first nodal row N1 is set in each nugget portion 102, and six component forces are extracted in each first nodal row N1.

[0019] Next, in a state quantity calculation step S3, a load or a displacement is calculated as a state quantity in the first node row N1. Specifically, as shown in FIG. 4, in the state quantity calculation step S3, a second node row N2 composed of a plurality of nodes included in the first node row N1 as viewed in the X direction is set in advance. The second node row N2 is set so as to surround the nugget portion 102 as viewed in the X direction. The second node row N2 may be set so as to substantially coincide with the outer periphery of the nugget portion 102, or may be located outside the outer periphery of the nugget portion 102. The second node row N2 may be set so as to coincide with the first node row N1. The second node row N2 is preferably set so as to include a heat-affected zone in the nugget portion 102. It is preferable that the second node row N2 has a polygonal shape that is substantially similar to the outer periphery shape of the nugget portion 102 in terms of accuracy.

[0020] In this embodiment, the second node row N2 is configured in a hexagonal shape with eight nodes along the periphery of the heat-affected zone so as to include the heat-affected zone. A group of nodes is configured by a plurality of nodes including each node of the first node row N1 and the second node row N2. The group of nodes may include nodes between the first node row N1 and the second node row N2, and also nodes in the second node row N2. Note that the area near the outer periphery of the nugget has a large influence on evaluating the fracture state by performing the partial analysis step S4 and the nugget fracture evaluation step S5 described later. For this reason, it is preferable to set the inter-node distance to a small mesh near the outer periphery of the nugget and set a relatively coarse mesh for the part inside the second node row far from the periphery, from the viewpoint of improving the analysis accuracy and reducing the calculation load. In this embodiment, within the second node row N2, a node row consisting of eight nodes along the outer periphery of the nugget portion, eight nodes that are similar in shape to the node row and located inside the node row, and one node located at the center of the nugget portion 102 are set as nodes that constitute the node group.

[0021] Then, based on this node group and the load or displacement at each node of the first node group N1 acquired in the six-component force acquisition step S2, the load or displacement at each node of the second node group N2 is calculated. The load at each node of the second node group N2 is expressed, for example, using a linear combination of shape functions of multiple meshes formed by the node group. Each coefficient in the linear combination can be found by matrix calculation such as the least squares method. This makes it possible to calculate the load or displacement around the weld (each node of the second node group N2) at a specified time. Note that although the above refers to the load or displacement, it is also possible to find both the load and the displacement.

[0022] Next, in the partial analysis step S4, a partial structural analysis is performed limited to a portion including the nugget portion, using the state quantities (stress, strain) at each node of the second node row N2 calculated in the state quantity calculation step S3 as constraint conditions. The partial structural analysis is performed by a preset partial analytical model M2. Specifically, as shown in Figs. 4 and 5, the partial analytical model M2 is composed of the second node row N2 and each node set in the second node row N2, and includes shell elements E1 set in each of the first plate-like member 101A and the second plate-like member 101B. A beam model M2A or a solid model M2B is applied to the partial analytical model M2. As shown in Fig. 4, the beam model M2A is composed of the above-mentioned shell elements E1 set in each plate-like member 101 and a beam element E2 connecting the central nodes of each shell element E1. The shell element E1 is not particularly limited, but may be, for example, a spider mesh. The spider mesh is a quadrilateral finite element in which nodes are arranged in a spider web shape. In particular, the spider mesh divides the approximately circular region into two, an inner region and an outer region, by an approximately circular region concentric with the outermost contour shape. The inner region is composed of elements mainly made of quadrilateral elements, and has a concentric center as a node as necessary. The outer region is further divided into approximately concentric circular regions in the radial direction as necessary, and the divided approximately circular regions are counted in order from the inner region, such as 1st layer, 2nd layer, 3rd layer, etc., and each layer is composed of elements mainly made of quadrilateral elements. The beam element E2 is composed of one or more nodes arranged in the X direction, and includes at least a node set at the center position of the nugget portion 102 in the X direction. The center position of the nugget portion 102 in the X direction is a point included in the opposing surfaces of the adjacent plate-like members 101 to be joined to each other, or a point included in a surface located in the middle of the opposing surfaces in the X direction, and usually corresponds to a point through which the annular portion of the nugget portion 102 with the maximum diameter passes.

[0023] As shown in Fig. 5(a), the solid model M2B is composed of the above-mentioned shell element E1 and a solid element E3 that penetrates the shell element E1 and is disposed in a portion corresponding to the nugget portion 102. As shown in Fig. 5(b), the solid element E3 is composed of a plurality of meshes formed by arranging a node row simulating the outer periphery of the nugget portion 102 in the shell element E1 and a plurality of nodes corresponding to the nodes located inside the node row along the X direction and connecting these plurality of nodes. Note that the above-mentioned models are merely examples, but from the viewpoint of calculation load, the above-mentioned beam model M2A and solid model M2B are preferable, and in particular, the beam model M2A is more preferable.

[0024] In the partial analysis step S4, a partial structural analysis is performed on the partial analysis model M2 thus preset, using the calculated state quantities at each node of the second node row N2 as constraint conditions, and the stress and strain occurring between each node of the partial analysis model M2 are calculated. First, the elastic-plastic constitutive equation used in the partial analysis step S4 of this embodiment will be described. In this embodiment, the analysis target is a structure 100 in which plate-like members 101 are joined to each other in the X direction, which is the thickness direction. Therefore, if the normal stress components of the Y axis and Z axis perpendicular to the X axis are assumed to be 0, and the shear stress component in the YZ plane is assumed to be 0, the elastic-plastic constitutive equation can be expressed from the general formula based on the nine-directional stress components as shown in the following formula (1).

[0025]

number

[0026] However, in the above formula (1), S0 is expressed by the following formula (2).

[0027]

number

[0028] In addition, in formulas (1) and (2), each symbol is defined as follows.

number

[0029] In this embodiment, the analysis target is the structure 100 in which the plate-like members 101 are joined to each other in the thickness direction, that is, the X direction, as described above. That is, since the influence of components other than the diagonal components is small, the elastoplastic constitutive equation can be expressed as the following equation (3) by omitting components other than the diagonal components.

[0030]

number

[0031] Furthermore, considering that the influence of the shear component is small, the elastic-plastic constitutive equation can be expressed as the following equation (4) by omitting all components except for the normal stress component generated in the cross section perpendicular to the X direction.

[0032]

number

[0033] By adopting any one of these equations (1), (3), or (4), it is possible to reduce the calculation load and improve the calculation speed while ensuring the calculation accuracy in the calculation of stress and strain in the partial analysis step S4 shown in the following procedure.

[0034] Next, an example of the handling of the stress-strain characteristic in the nugget portion 102 will be described. The stress-strain characteristic (correlation data of stress-strain) of the nugget portion 102 is influenced by the mutual stress-strain characteristic and plate thickness of the plate-like members 101 to be joined. That is, the stress-strain characteristic of the nugget portion 102 can be determined by the melt volume fraction of the stress-strain characteristic of the multiple plate-like members 101 to be joined, that is, the weighted sum of the plate thickness. The stress-strain characteristic of the multiple plate-like members 101 to be joined can be obtained by previously acquiring the stress-strain characteristic of the material forming each plate-like member 101. FIG. 6 shows an example in which two plate-like members 101 having different stress-strain characteristics are joined by spot welding. As shown in FIG. 6, the stress-strain line Q3 showing the stress-strain characteristic of the nugget portion 102 formed by spot welding is located between the stress-strain line Q1 showing the stress-strain characteristic of the first plate-like member 101A and the stress-strain line Q2 showing the stress-strain characteristic of the second plate-like member 101B. The stress-strain line Q3 can be determined to pass through a position (a position away from the stress-strain line Q1 by T2 / (T1+T2) toward the stress-strain line Q2) that is proportionally determined based on the plate thickness T1 of the first plate-shaped member 101A and the plate thickness T2 of the second plate-shaped member 101B. Note that this example merely shows one example of how to handle the stress-strain characteristic of the nugget portion 102, and an average value may be obtained without considering the thickness, or a sample of the nugget portion 102 in which the first plate-shaped member 101A and the second plate-shaped member 101B are spot-welded may be prepared, and the stress-strain characteristic of the nugget portion 102 may be obtained from the strength test results of the sample.

[0035] Next, an example of more detailed steps of the partial structural analysis performed in the partial analysis step S4 will be described. The partial structural analysis, which is an example, is not limited to a particular analytical model, but may be, for example, an analytical method based on the subloading surface model disclosed in Reference 1 (Hashiguchi Koichi, "Latest Elastoplasticity", Asakura Publishing Co., Ltd., May 20, 1990, pp. 95-139, 146-161, 176-186). Specifically, as shown in FIG. 7, the partial analysis step S4 includes a material condition setting step S411, a constraint condition setting step S412, a stress / strain rate setting step S413, a stress rate parameter calculation step S421, an elastic constitutive matrix calculation step S422, a plastic strain rate parameter calculation step S423, an elastic-plastic constitutive matrix calculation step S424, a stress / strain rate calculation step S425, an unloading / loading determination step S426, a stress / strain calculation step S431, a plasticity parameter calculation step S432, and a hardening / softening parameter calculation step S433.

[0036] First, a material condition setting step S411 is performed. In the material condition setting step S411, material constants in the partial analysis model M2 are set. The material constants include, for example, stiffness parameters such as a longitudinal elastic modulus and a shear elastic modulus, and stress and strain occurring in each element of the partial analysis model M2 at the previous time. The stiffness parameters such as a longitudinal elastic modulus and a shear elastic modulus can be calculated based on the stress-strain characteristics (stress-strain correlation data) and plate thickness of each plate-like member 101 joined by the nugget portion 102 targeted by the partial analysis model M2, for example, as described above, based on the idea based on FIG. 6. These material constants may be calculated in this step, or the results of calculations may be stored in advance. In addition, these material constants may be set to the same value throughout the partial analysis model M2, or may be set for each element constituting the partial analysis model M2. The stress and strain occurring in each element of the partial analysis model M2 at the previous time are obtained by storing the calculation results of the stress and strain of each element of the partial analysis model M2 obtained by performing the partial analysis step S4 at the previous time in the storage unit 7, and referring to the stress and strain stored in the storage unit 7. Note that the material condition setting step S411 is performed at each time corresponding to the results of the structural analysis step S1 at each time, but if the same material constants are used, it may be performed in advance or the first time and then omitted, or it may be performed for each partial analysis step S4 performed at each time.

[0037] Next, a constraint condition setting step S412 is performed. In the constraint condition setting step S412, a constraint condition for the partial analytical model M2 to be analyzed is set. The constraint condition is the load or displacement at each node of the second node series N2 obtained in the state quantity calculation step S3.

[0038] Next, a stress / strain rate setting step S413 is performed. In the stress / strain rate setting step S413, the initial values ​​of the stress rate and strain rate used in the calculations in the following steps are set. The initial values ​​of the stress rate and strain rate are given to each element constituting the partial analysis model M2. For example, the initial values ​​of the stress rate and strain rate are set to each corresponding element by the stress rate and strain rate obtained for each element in the previous partial analysis step S4, that is, the unit time before the time of the partial analysis step S4 in which the stress / strain rate setting step S413 is performed. The stress rate and strain rate obtained for each element in the previous partial analysis step S4 are stored in the storage unit 7 when the partial analysis step S4 is performed, and can be obtained by referring to the stress rate and strain rate stored in the storage unit 7. The calculation results in the previous partial analysis step S4 may be used as they are, or preprocessing such as multiplying by a certain coefficient may be performed. The initial values ​​of the stress rate and strain rate may be fixed values ​​set in advance without using the calculation results in the previous partial analysis step S4.

[0039] Next, a stress rate parameter calculation step S421 is performed. In the stress rate parameter calculation step S421, parameters related to the stress rate used in the subsequent elastic constitutive matrix calculation step S422, plastic strain rate parameter calculation step S423, elastic-plastic constitutive matrix calculation step S424, and stress-strain rate calculation step S425 are calculated. Such parameters include an isotropic hardening variable, a normal yield back stress and a lower yield back stress, mean stresses and deviator stresses for the normal yield back stress and the lower yield back stress, and a ratio of the size of the lower loading surface to the size of the normal yield surface.

[0040] Next, an elastic constitutive matrix calculation step S422 is performed. In the elastic constitutive matrix calculation step S422, each component of a predefined elastic constitutive matrix is ​​calculated based on the material constants set in the material condition setting step S411. Furthermore, in the elastic constitutive matrix calculation step S422, each component of a predefined elastic constitutive inverse matrix is ​​calculated based on the material constants set in the material condition setting step S411. The elastic constitutive matrix and the elastic constitutive inverse matrix are defined based on the elastic terms in the mathematical expressions shown in the above formulas (1), (3) or (4), for example, and are stored in the storage unit 7 in advance.

[0041] Next, a plastic strain rate parameter calculation step S423 is performed. In the plastic strain rate parameter calculation step S423, a parameter related to the plastic strain rate is calculated based on the calculation result obtained in the stress rate parameter calculation step S421. Such a parameter includes a function U of the ratio of the size of the subloading surface to the size of the normal yield surface, a plastic coefficient, etc.

[0042] Next, an elastic-plastic constitutive matrix calculation step S424 is performed. In the elastic-plastic constitutive matrix calculation step S424, each component of the elastic-plastic coefficient matrix is ​​calculated based on the calculation results of the elastic constitutive matrix calculation step S422 and the plastic strain rate parameter calculation step S423. The elastic-plastic coefficient matrix is ​​defined based on the plastic terms in the formula shown in the above formula (1), (3) or (4), for example, and is stored in the storage unit 7 in advance.

[0043] Next, a stress / strain rate calculation step S425 is performed. In the stress / strain rate calculation step S425, the stress rate and strain rate of each element in the partial analysis model M2 are calculated based on the elastic constitutive matrix calculated in the elastic constitutive matrix calculation step S422, the elasto-plastic coefficient matrix calculated in the elasto-plastic constitutive matrix calculation step S424, and the elasto-plastic constitutive equation shown in the above equation (1), (3) or (4).

[0044] Next, the unloading / loading judgment step S426 is performed. In the unloading / loading judgment step S426, it is judged whether each element of the partial analysis model M2 is in an unloaded state or a loaded state based on the calculation result of the stress / strain rate calculation step S425. To judge whether the state is unloaded or loaded, the stress-strain line Q3 in the target nugget part 102 is used. Here, the stress-strain line Q3 is expressed as a broken line with a straight line indicating the elastic range and a straight line indicating the plastic range, so that the calculation load related to the judgment can be reduced. If any element is in an unloaded state (YES), recalculation of the stress / strain rate calculation step S425 is performed. On the other hand, if all elements are in a loaded state (NO), the process proceeds to the next stress / strain calculation step S431. That is, the stress / strain rate calculation step S425 is repeatedly performed until it is judged that all elements are in a loaded state in the unloading / loading judgment step S426.

[0045] In the stress-strain calculation step S431, the stress and strain in each element of the partial analytical model M2 are calculated. The stress and strain in each element of the partial analytical model M2 are calculated based on the stress rate and strain rate of each element of the partial analytical model M2 obtained in the stress-strain rate calculation step S425 and the stress and strain set in the constraint condition setting step S412. Then, in the stress-strain calculation step S431, the stress and strain in each element of the partial analytical model M2 stored in the storage unit 7 are updated to the stress and strain calculated in this step. At this time, the stress rate and strain rate in each element of the partial analytical model M2 stored in the storage unit 7 may also be updated to the result of the stress-strain rate calculation step S425.

[0046] Next, a plasticity parameter calculation step S432 is performed. In the plasticity parameter calculation step S432, the plastic strain rate and the normal and tangential components of the plastic strain rate are calculated. The plastic strain rate is obtained based on the calculation result of the stress / strain calculation step S431. Finally, in the hardening / softening parameter calculation step S433, parameters related to hardening / softening are calculated. The parameters related to hardening / softening include an isotropic hardening variable, a normal yield stress, a lower yield stress, and a plastic history parameter. Then, in the plasticity parameter calculation step S432 and the hardening / softening parameter calculation step S433, the plastic strain rate, the normal and tangential components of the plastic strain rate, and the parameters related to hardening / softening calculated at the previous time stored in the storage unit 7 are updated to the results calculated in these steps. With the above, the partial analysis step S4 is completed.

[0047] Next, a nugget portion fracture evaluation step S5 is performed. In the nugget portion fracture evaluation step S5, a fracture state in the nugget portion 102 is evaluated based on the stress and strain calculated in the partial analysis step S4. As shown in FIG. 8, the nugget portion fracture evaluation step S5 of this embodiment has a fracture determination step S51 and a fracture direction determination step S52. In the fracture determination step S51, it is determined whether or not a fracture has occurred. Furthermore, in the fracture direction determination step S52, the direction of the fracture is determined when it is determined in the fracture determination step S51 that a fracture has occurred. Each step will be described in detail below.

[0048] The fracture determination step S51 of this embodiment determines the presence or absence of fracture based on at least one of the ratio of the yield area and the strain energy in the YZ cross section perpendicular to the X direction, which are calculated from the strain of the nugget portion 102 at a predetermined time calculated in the partial analysis step S4. More specifically, the fracture determination step S51 of this embodiment has a first determination step S511 and a second determination step S512. In the first determination step S511, at least one of the ratio of the yield area and the strain energy in the YZ cross section perpendicular to the X direction is calculated from the strain of the nugget portion 102 at a predetermined time calculated in the partial analysis step S4 (step S511a). Then, it is determined whether or not the calculation result exceeds a first threshold value (S511b). That is, when the ratio of the yield area is adopted, the ratio of the yield area in the YZ plane is obtained, and it is determined whether or not it exceeds a first threshold value related to the yield area that is set in advance. Also, when the strain energy is adopted, the strain energy in the YZ plane is obtained, and it is determined whether or not it exceeds a first threshold value related to the strain energy that is set in advance. When both the yield region ratio and the strain energy are used, the determination may be made based on whether one of them exceeds the corresponding first threshold value, or whether both exceed the corresponding first threshold value. In either case, if it is determined that the first threshold value is not exceeded, it is determined that no fracture has occurred in the nugget portion 102, and the process proceeds to the update step S6. On the other hand, if it is determined in the first determination step S511 that the first threshold value is exceeded, the second determination step S512 is performed.

[0049] That is, in the second judgment step S512, at least one of the equivalent stress and the equivalent strain in the nugget portion 102 is obtained (step S512a). Then, it is judged whether or not the calculation result exceeds the second threshold value (S512b). Note that, if the equivalent stress and the equivalent strain have already been obtained in the partial analysis step S4, the result of the partial analysis step S4 may be used. Then, when the equivalent stress is adopted, it is judged whether or not the equivalent stress in the nugget portion 102 exceeds the second threshold value related to the equivalent stress that is set in advance and stored in the storage unit 7. Also, when the equivalent strain is adopted, it is judged whether or not the equivalent strain in the nugget portion 102 exceeds the second threshold value related to the equivalent strain that is set in advance and stored in the storage unit 7. When both the equivalent stress and the equivalent strain are adopted, it may be judged based on whether or not one of them exceeds the corresponding second threshold value, or it may be judged based on whether or not both of them exceed the corresponding second threshold value. In either case, when it is judged that the second threshold value is not exceeded, it is judged that no fracture has occurred in the nugget portion 102, and the process proceeds to the update step S6. On the other hand, if it is determined in the second determination step S512 that the second threshold value is exceeded, it is determined that a fracture has occurred in the nugget portion 102, and the fracture direction determination step S52 is performed.

[0050] In the fracture direction determination step S52, the fracture direction is determined. Specifically, based on the result of the partial analysis step S4, the X-direction component, the Y-direction component, and the Z-direction component of each parameter related to stress and strain are compared to determine which of the X-direction, Y-direction, and Z-direction has a higher contribution of stress and strain, and the fracture direction is determined based on this. For example, the parameters of each directional component are compared and the direction with the highest parameter is determined as the fracture direction. The degree of contribution may be determined in a composite manner using, for example, the principal direction or triaxial stress intensity. For example, the normal stress, shear stress, and strain energy in each of the X-direction, Y-direction, and Z-direction are compared as parameters related to stress and strain. Then, as a result of the comparison, it is determined that the fracture will occur in the direction with the higher contribution.

[0051] Next, an update step S6 is performed to update the structural analysis model M1. That is, in the update step S6, when it is determined that the target nugget portion 102 is fractured based on the result of the nugget portion fracture evaluation step S5, the structural analysis model M1 is updated to a structural analysis model M1 in which elements corresponding to the target nugget portion 102 in the structural analysis model M1 are deleted. In addition, the determination result of the fracture direction in the fracture direction determination step S52 may be reflected in the element deletion method, such as by reflecting it as a relaxation time in the calculation parameters for element deletion in the structural analysis step S1 performed after the update step S6, or by deleting many elements along the fracture direction. Note that, when no fracture is recognized in any of the nuggets 102 in the nugget portion fracture evaluation step S5, the deletion process of the elements in the structural analysis model M1 is not performed. Then, after performing the above series of steps at a predetermined time, the next time that is advanced by a unit time from the predetermined time is set as the predetermined time, and the same steps are sequentially performed. This is performed for each unit time.

[0052] Next, an example of an analysis device in which the structure analysis method in the embodiment is executed will be described. FIG. 9 is a diagram showing an example of a hardware configuration of the analysis device in the embodiment. As shown in FIG. 9, the analysis device 1 includes a control unit 4 including a processor 2 such as a CPU (Central Processing Unit) and a memory 3 connected by a bus, and executes a program. The analysis device 1 functions as a device including the control unit 4, an input unit 6, a storage unit 7, and an output unit 8 by executing the program. More specifically, the processor 2 reads out the program stored in the storage unit 7, and stores the read program in the memory 3. The processor 2 executes the program stored in the memory 3, and the analysis device 1 functions as a device including the control unit 4, the input unit 6, the storage unit 7, and the output unit 8.

[0053] The input unit 6 includes input devices such as a mouse, a keyboard, and a touch panel. The input unit 6 may be configured as an interface that connects these input devices to the device itself. The input unit 6 accepts input of various information for the device itself. The various information includes, for example, molding analysis information. The input unit 6 outputs the input information to the control unit 4.

[0054] The storage unit 7 is configured using a non-transitory computer-readable storage medium such as a magnetic hard disk device or a semiconductor storage device. The storage unit 7 stores various information related to the analysis device 1. The storage unit 7 stores, for example, forming analysis information input to the input unit 6. The storage unit 7 stores, for example, work hardening related information in advance. The storage unit 7 stores, for example, bake hardening related information in advance.

[0055] The output unit 8 outputs various information. For example, the output unit 8 outputs information indicating the crash performance of the analysis result. The output unit 8 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 8 may be configured as an interface that connects these display devices to the output unit 8 itself.

[0056] FIG. 10 is a diagram showing an example of the functional configuration of the control unit 4 in the embodiment. As shown in FIG. 10, the control unit 4 of the analysis device 1 in this embodiment includes an overall structure analysis unit 10 and a substructure analysis unit 20. The overall structure analysis unit 10 and the substructure analysis unit 20 may be executed as separate programs, or may be executed as an integrated program. Details of the processing executed by each functional component will be described below, but the details of the processing executed by each functional component are the same as those of the analysis method of the structure 100 in this embodiment. For this reason, the processing executed by each functional component is indicated by the name of each step of the analysis method of the corresponding structure 100, and the details are as described in each step of the analysis method of the structure 100.

[0057] The overall structure analysis unit 10 performs an overall structural analysis of the structure 100 based on the structural analysis model M1 stored in the storage unit 7. That is, the overall structure analysis unit 10 executes the structural analysis step S1 of the analysis method of the structure 100 of this embodiment. In the overall structure analysis unit 10 of this embodiment, as described above, for example, the incremental method is used to calculate the six component forces at each time for each unit time at each node. The overall structure analysis unit 10 outputs the six component forces calculated at each time to the substructure analysis unit 20. After outputting the calculated six component forces to the substructure analysis unit 20, the overall structure analysis unit 10 is in a standby state without proceeding to the calculation of the next time until it acquires a calculation command from the substructure analysis unit 20 as described later. Then, when the overall structure analysis unit 10 receives a calculation command output from the update unit 70, it proceeds to the calculation of the next time that has progressed by the unit time.

[0058] The partial structure analysis unit 20 of this embodiment includes a six-component force acquisition unit 30, a state quantity calculation unit 40, a partial analysis processing unit 50, a nugget fracture evaluation unit 60, and an update unit 70. The six-component force acquisition unit 30 executes a six-component force acquisition step S2 of the analysis method for the structure 100 of this embodiment. That is, the six-component force acquisition unit 30 acquires the six-component forces at a predetermined time output from the overall structure analysis unit 10.

[0059] The state quantity calculation unit 40 also executes the state quantity calculation step S3 of the analysis method for the structure 100 of this embodiment. That is, the state quantity calculation unit 40 calculates the load or displacement at each node of the second node series N2 as a state quantity in the first node series N1 of the structural analysis model M1, and outputs the load or displacement to the partial analysis processing unit 50.

[0060] Further, the partial analysis processing unit 50 executes a partial structural analysis based on the partial analysis model M2 stored in the storage unit 7, using the state quantities (stress, strain) at each node of the second node series N2 calculated by the state quantity calculation unit 40 as constraint conditions. That is, the partial analysis processing unit 50 executes the partial analysis step S4 of the analysis method for the structure 100 of this embodiment. The partial analysis processing unit 50 of this embodiment includes a material condition setting unit 511, a constraint condition setting unit 512, a stress / strain rate setting unit 513, a stress rate parameter calculation unit 521, an elastic constitutive matrix calculation unit 522, a plastic strain rate parameter calculation unit 523, an elastic-plastic constitutive matrix calculation unit 524, a stress / strain rate calculation unit 525, an unloading / loading determination unit 526, a stress / strain calculation unit 531, a plasticity parameter calculation unit 532, and a hardening / softening parameter calculation unit 533.

[0061] The material condition setting unit 511 executes the material condition setting step S411 of the analysis method of the structure 100 of this embodiment. That is, the material condition setting unit 511 reads out the material constants in the partial analysis model M2 stored in the storage unit 7, and sets them as the material constants. Furthermore, the constraint condition setting unit 512 executes the constraint condition setting step S412 of the analysis method of the structure 100 of this embodiment. That is, the constraint condition setting unit 512 acquires the load or displacement at each node of the second node series N2 calculated by the state quantity calculation unit 40 at the relevant time, and sets them as the load or displacement at the corresponding node. Furthermore, the constraint condition setting unit 512 acquires the stress and strain occurring in each element of the partial analysis model M2 calculated by the partial analysis processing unit 50 at the previous time stored in the storage unit 7, and sets them as the stress and strain of each element of the partial analysis model M2.

[0062] The stress / strain rate setting unit 513 executes the stress / strain rate setting step S413 of the analysis method of the structure 100 of this embodiment. That is, the stress / strain rate setting unit 513 sets initial values ​​of the stress rate and strain rate used in the calculations in the subsequent processes. In this embodiment, the stress rate and strain rate occurring in each element of the partial analysis model M2 calculated by the partial analysis processing unit 50 are acquired, and are set as the stress rate and strain rate of each element of the partial analysis model M2.

[0063] The stress rate parameter calculation unit 521 executes the stress rate parameter calculation step S421 of the analysis method of the structure 100 of this embodiment, and calculates parameters related to the stress rate. Moreover, the elastic constitutive matrix calculation unit 522 executes the elastic constitutive matrix calculation step S422 of the analysis method of the structure 100 of this embodiment. That is, the elastic constitutive matrix calculation unit 522 calculates each component of a predefined elastic constitutive matrix and an elastic constitutive inverse matrix.

[0064] The plastic strain rate parameter calculation unit 523 executes the plastic strain rate parameter calculation step S423 of the analysis method of the structure 100 of this embodiment, and calculates parameters related to the plastic strain rate. Moreover, the elasto-plastic constitutive matrix calculation unit 524 executes the elasto-plastic constitutive matrix calculation step S424 of the analysis method of the structure 100 of this embodiment, and calculates each component of the elasto-plastic coefficient matrix.

[0065] The stress / strain rate calculation unit 525 executes the stress / strain rate calculation step S425 of the analysis method of the structure 100 of this embodiment, and obtains the stress rate and strain rate of each element in the partial analytical model M2. Furthermore, when the stress / strain rate calculation unit 525 receives a recalculation command from the unloading / loading determination unit 526, it calculates the stress rate and strain rate again.

[0066] The unloading / load determining unit 526 executes the unloading / load determining step S426 of the analysis method of the structure 100 of this embodiment. That is, the unloading / load determining unit 526 determines whether each element of the partial analytical model M2 is in an unloaded state or in a loaded state based on the stress rate and strain rate calculated by the stress / strain rate calculating unit 525. When any element is in an unloaded state, the unloading / load determining unit 526 outputs a recalculation command to the stress / strain rate calculating unit 525. On the other hand, when all elements are in a loaded state, the unloading / load determining unit 526 outputs a stress / strain calculation command to the stress / strain calculating unit 531.

[0067] The stress / strain calculation unit 531 executes the stress / strain calculation step S431 of the analysis method of the structure 100 of this embodiment. That is, the stress / strain calculation unit 531 calculates the stress and strain in each element of the partial analytical model M2. Then, the stress / strain calculation unit 531 updates the stress and strain in each element of the partial analytical model M2 stored in the storage unit 7 to the stress and strain as a result of the current calculation.

[0068] The plasticity parameter calculation unit 532 executes the plasticity parameter calculation step S432 of the analysis method of the structure 100 of this embodiment. The plasticity parameter calculation unit 532 calculates the plastic strain rate and the normal and tangential components of the plastic strain rate. Furthermore, the plasticity parameter calculation unit 532 updates the plastic strain rate stored in the storage unit 7 to the calculated plastic strain rate. Furthermore, the hardening / softening parameter calculation unit 533 executes the hardening / softening parameter calculation step S433 of the analysis method of the structure 100 of this embodiment. That is, the hardening / softening parameter calculation unit 533 calculates parameters related to hardening / softening. The hardening / softening parameter calculation unit 533 updates the parameters related to hardening / softening stored in the storage unit 7 to the calculated parameters related to hardening / softening.

[0069] The nugget fracture evaluation unit 60 executes the nugget fracture evaluation step S5 of the analysis method for the structure 100 of this embodiment. The nugget fracture evaluation unit 60 of this embodiment has a fracture determination unit 611 and a fracture direction determination unit 612. The fracture determination unit 611 determines at least one of the ratio of the yield region and the strain energy in the YZ cross section perpendicular to the X direction from the strain of the nugget 102 at a predetermined time calculated by the partial analysis processing unit 50. Then, the fracture determination unit 611 determines the presence or absence of fracture based on at least one of the ratio of the yield region and the strain energy.

[0070] The fracture determination unit 611 of this embodiment has a first determination unit 611a and a second determination unit 611b. The first determination unit 611a obtains the ratio of the yield region or the strain energy in the YZ cross section perpendicular to the X direction from the strain of the nugget portion 102 calculated by the partial analysis processing unit 50. The first determination unit 611a then refers to a first threshold value corresponding to the calculated value that is the ratio of the yield region or the strain energy in the YZ cross section and stored in the storage unit 7, and determines whether or not the calculated value exceeds the first threshold value. If the calculated value does not exceed the first threshold value, the first determination unit 611a determines that no fracture has occurred in the nugget portion 102, and outputs an update command to the update unit 70. On the other hand, if the first determination unit 611a determines that the calculated value exceeds the first threshold value, it outputs a second determination command to the second determination unit 611b. In the above, the judgment is based on the ratio of yield areas in the YZ cross section or the strain energy, but it may also be based on both, as described in the first judgment step S511 of the analysis method for the structure 100 of this embodiment.

[0071] When the second judgment unit 611b receives the second judgment command, it determines the equivalent stress or equivalent strain in the nugget portion 102. In addition, if the equivalent stress or equivalent strain has already been determined in the process by the partial analysis processing unit 50, the processing result by the partial analysis processing unit 50 may be used. Then, the second judgment unit 611b refers to a second threshold value corresponding to the calculated value that is equivalent stress or equivalent strain and stored in the storage unit 7, and determines whether or not the calculated value exceeds the second threshold value. If it is determined that the calculated value does not exceed the second threshold value, the second judgment unit 611b determines that no fracture has occurred in the nugget portion 102, and outputs an update command to the update unit 70. On the other hand, if the second judgment unit 611b determines that the calculated value exceeds the second threshold value, it determines that a fracture has occurred in the nugget portion 102, and outputs a direction judgment command to the fracture direction judgment unit 612 and outputs the evaluation result to the update unit 70.

[0072] The fracture direction determination unit 612 receives a direction determination command when the fracture determination unit 611 determines that a fracture has occurred and outputs a direction determination command. When the fracture direction determination unit 612 receives the direction determination command, it executes the fracture direction determination step S52 of the analysis method for the structure 100 of this embodiment and determines the fracture direction. Specifically, the fracture direction determination unit 612 acquires the X-direction component, the Y-direction component, and the Z-direction component of each parameter related to stress and strain from the calculation result of the partial analysis processing unit 50. Then, the fracture direction determination unit 612 compares the X-direction component, the Y-direction component, and the Z-direction component of each parameter to determine in which of the X-direction, the Y-direction, and the Z-direction the contribution of the stress and strain is high, and determines the fracture direction based on this and outputs an update command to the update unit 70.

[0073] The update unit 70 receives an update command and also receives the evaluation result by the nugget fracture evaluation unit 60. When the update unit 70 receives the update command and determines that the target nugget 102 has fractured based on the received evaluation result, the update unit 70 updates the structural analysis model M1 stored in the storage unit 7 to a structural analysis model M1 in which elements corresponding to the target nugget 102 have been deleted. Then, after updating the structural analysis model M1, the update unit 70 outputs a calculation command to the overall structure analysis unit 10.

[0074] As described above, according to the analysis method of the structure 100, the analysis device, and the program for making the analysis device execute the analysis method of the present embodiment, in order to perform a structural analysis of the structure 100 having a plurality of plate-like members 101 overlapped with each other in the thickness direction (X direction) and a nugget portion 102 formed by spot welding the plurality of plate-like members 101 to each other, a structural analysis step S1 for performing a structural analysis of the entire structure 100 and a partial analysis step S4 for obtaining the stress and strain of the nugget portion 102 are separately performed. In the present embodiment, the fracture state of the nugget portion 102 is evaluated based on the stress and strain obtained by the partial analysis step S4. Therefore, the partial analysis step S4 is performed using a detailed partial analysis model M2 according to the shape of the nugget portion 102, and the fracture state of the nugget portion 102 can be evaluated with high accuracy by obtaining the stress and strain of the nugget portion 102. On the other hand, by performing an overall structural analysis using the structural analysis model M1 including the nugget portion 102, it is possible to perform an overall structural analysis of the structure 100 with a low calculation load regardless of the shape of the nugget portion 102. That is, in the analysis of the structure 100 including the nugget portion 102, it is possible to accurately evaluate the effect of fracture of the nugget portion 102 while suppressing the calculation load.

[0075] Furthermore, by separating the structural analysis model M1 of the entire structure 100 from the partial analysis model M2 that analyzes the nugget portion 102, the partial analysis model M2 can be a model suited to the shape of the nugget portion 102, making it possible to improve accuracy and reduce the calculation load at the same time. For example, for the partial analysis model M2 that models the portion including the nugget portion 102, the portion included in the plate-like member 101 can be made into shell elements E1 having a spider-like mesh configuration suited to the shape of the nugget portion 102, and the portions connecting the plate-like members 101 to each other can be made into beam elements E2, solid elements, or the like, making it possible to improve accuracy and reduce the calculation load at the same time.

[0076] Then, by repeating the structural analysis step S1 and the partial analysis step S4 for each unit time, the stress and strain occurring in the nugget portion 102 analyzed in the partial analysis step S4 can be obtained with high accuracy and with a reduced calculation load, and the obtained results can be reflected in the calculation results in the structural analysis step S1. In particular, the accuracy can be further improved by performing the nugget portion fracture evaluation step S5 based on the calculation results in the partial analysis step S4 and reflecting the state of the nugget portion 102 evaluated as fractured as a result in the calculation results in the structural analysis step S1.

[0077] Moreover, by adopting the formula (1) in which the stress components occurring in the cross section perpendicular to the thickness direction are omitted as the elastoplastic constitutive equation used in the partial analysis step S4, taking into consideration that the analysis is a structural analysis of the nugget portion 102 that joins the plate-like members 101 together, it is possible to reduce the calculation load while ensuring the calculation accuracy. Moreover, by adopting the following formula (3) in which components other than the diagonal components are further omitted from formula (1) as the elastoplastic constitutive equation, it is possible to further reduce the calculation load while ensuring the calculation accuracy. Moreover, by adopting the following formula (4) in which components other than the normal stress components occurring in the cross section perpendicular to the thickness direction are further omitted from formula (3) as the elastoplastic constitutive equation, it is possible to further reduce the calculation load while ensuring the calculation accuracy.

[0078] Furthermore, in this embodiment, among the material constants used in the partial analysis step S4, stiffness parameters such as the longitudinal elastic modulus and the shear elastic modulus are obtained based on stress-strain correlation data previously acquired for the material of each of the plurality of plate-like members 101 joined by the nugget portion 102 and the thickness ratio between the plurality of plate-like members 101. In this manner, the stiffness parameters of the nugget portion 102 can be obtained based on the material and thickness of the plurality of plate-like members 101 that affect the strength of the nugget portion 102, and the stiffness parameters of the nugget portion 102 can be set with high accuracy.

[0079] In addition, in the nugget fracture evaluation step S5, the presence or absence of fracture is determined based on at least one of the yield region ratio or strain energy in a cross section perpendicular to the thickness direction, which is obtained from the strain of the nugget portion 102 at a predetermined time calculated. Therefore, the fracture can be evaluated by accurately reflecting the degree of plastic deformation. Furthermore, in the nugget fracture evaluation step S5, in the fracture determination step S51, a first determination step is performed to determine whether or not at least one of the yield region ratio and strain energy exceeds a corresponding first threshold value set in advance, and if at least one of the yield region ratio and strain energy exceeds the first threshold value, it is determined whether or not at least one of the equivalent stress and equivalent strain in the nugget portion 102 exceeds a corresponding second threshold value set in advance, and if it exceeds the second threshold value, it is determined that a fracture has occurred. In this way, by evaluating the fracture in two stages, the fracture can be evaluated more accurately.

[0080] Furthermore, in the nugget fracture evaluation step S5, when it is determined that a fracture has occurred, a fracture direction determination step S52 is performed to determine the fracture direction based on the stress and strain energy of each component. Therefore, when it is determined that a fracture has occurred, it is possible to evaluate in which direction the fracture will affect and how much of an effect it will have on the entire structure 100 based on the fracture direction.

[0081] 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, magneto-optical disks, ROMs, and CD-ROMs, and storage devices such as hard disks built into computer systems. The program may be transmitted via an electric communication line.

[0082] The analysis device 1 may be implemented using a plurality of information processing devices communicably connected via a network. In this case, each functional unit of the analysis device 1 may be distributed and implemented in a plurality of information processing devices. For example, the overall structure analysis unit 10 and the partial structure analysis unit 20 may be implemented in different information processing devices.

[0083] Although an embodiment of the present invention has been described in detail above with reference to the drawings, the specific configuration is not limited to this embodiment, and designs that do not deviate from the gist of the present invention are also included. [Explanation of symbols]

[0084] 1 Analysis device 30 6-component force acquisition part 40 State quantity calculation section 50 Partial analysis processing unit 60 Nugget fracture evaluation section 100 structures 101 Plate-shaped member 102 Nugget Section 531 Stress / Strain Calculation Unit L Closed Loop M1 structural analysis model M2 Partial Analysis Model N1 First node sequence N2 Second node sequence S1 6-component force calculation step (structural analysis step) S2 6-component force acquisition step S3 State calculation step S4 Partial analysis step S5 Nugget fracture evaluation step S6 Update Steps S51 Break Judgment Step S52 Fracture direction judgment step S411 Material condition setting step S412 Constraint condition setting step S425 Stress-strain rate calculation step S431 Stress-strain calculation step S511 First judgment step S512 Second judgment step

Claims

1. 1. A computer-implemented method for analyzing a structure, comprising: A method for analyzing a structure having a plurality of plate-like members overlapping each other in a thickness direction and a nugget portion formed by spot welding the plurality of plate-like members to each other, comprising the steps of: a six-component force acquiring step of acquiring, for the structure that is deformed over time by an external force, six-component forces generated at a predetermined time in a first node row that is composed of a plurality of nodes that form a closed loop that includes the nugget portion when viewed in the thickness direction in the structure; a state quantity calculation step of calculating at least one of a load and a displacement, which is a state quantity at each node of the second node string, based on the six-component force in the first node string obtained and a second node string including a plurality of nodes that are included in the first node string when viewed in the thickness direction and that are preset to surround the nugget portion; a partial analysis step of performing a partial analysis on a partial analysis model including each node of the second node series and a plurality of nodes in the second node series, at least a portion of which simulates the nugget portion, by using the calculated state quantities at each node of the second node series as constraint conditions, and calculating stress and strain occurring between each node of the partial analysis model; and a nugget fracture evaluation step of evaluating a fracture state in the nugget portion based on the calculated stress and strain.

2. The partial analysis step includes a material condition setting step of setting material constants including stiffness parameters of the partial analysis model; a constraint condition setting step of setting constraint conditions for the partial analysis model; a stress / strain rate calculation step for determining a stress rate and a strain rate in the partial analysis model based on an elastic-plastic constitutive equation of the structure, the material constants, and the constraint conditions; and a stress-strain calculation step of calculating stress and strain in the partial analytical model based on the calculated stress rate and strain rate, The six-component force acquisition step is performed for each unit time; 2. The method for analyzing a structure as described in claim 1, wherein each time for each unit time is set as the specified time, the stress rate, the strain rate, the stress, and the strain in the nugget portion calculated by the stress / strain rate calculation step and the stress-strain calculation step at the previous time unit time before each of the times are obtained, and the partial analysis step is performed to calculate the stress and strain in the nugget portion at the specified time.

3. 3. The method for analyzing a structure according to claim 2, wherein in the partial analysis step, the stress and strain occurring in the nugget portion are calculated based on equation (1), which is a basic equation expressed based on nine-directional stress components, and in which stress components other than the stress components occurring in a cross section perpendicular to the thickness direction are omitted, as the elastic-plastic constitutive equation. [0010] however, [0025] [0030]

4. 4. The method for analyzing a structure according to claim 3, wherein in the partial analysis step, the stress and strain generated in the nugget portion are calculated based on the following formula (3) obtained by further omitting components except for diagonal components from formula (1) as the elastic-plastic constitutive equation: [0045]

5. 5. The method for analyzing a structure according to claim 4, wherein in the partial analysis step, the stress and strain generated in the nugget portion are calculated based on the following equation (4), which is obtained by further omitting components of the equation (3) except for a normal stress component generated in a cross section perpendicular to the thickness direction, as the elastic-plastic constitutive equation: [0050]

6. At least two of the plate-like members adjacent to each other in the thickness direction are formed of different materials, the stress-strain correlation data of the nugget portion is obtained based on stress-strain correlation data previously acquired for each material of the plurality of plate-like members and a thickness ratio between the plurality of plate-like members; The method for analyzing a structure according to claim 2 , wherein the stiffness parameter is determined based on correlation data of stress and strain of the nugget portion.

7. 7. The method for analyzing a structure according to claim 1, wherein the nugget portion fracture evaluation step includes a fracture determination step of determining the presence or absence of fracture based on at least one of a ratio of a yield area in a cross section perpendicular to the thickness direction and strain energy, which is obtained from the calculated strain of the nugget portion at the specified time.

8. The fracture determination step includes a first determination step of determining whether or not at least one of the ratio of the yield region and the strain energy exceeds a corresponding first threshold value set in advance; The method for analyzing a structure as described in claim 7, further comprising a second judgment step of determining whether or not at least one of the equivalent stress and equivalent strain in the nugget portion exceeds a corresponding predetermined second threshold value when at least one of the ratio of the yield area or the strain energy exceeds the first threshold value, and determining that a fracture has occurred when the equivalent stress and equivalent strain in the nugget portion exceed the second threshold value.

9. 9. The method for analyzing a structure according to claim 7 or 8, wherein the nugget portion fracture evaluation step includes a fracture direction determination step of determining a fracture direction based on stress and strain energy of each component when it is determined that fracture has occurred.

10. a six-component force calculation step of calculating six-component forces generated in the first node row in the structure at the predetermined time based on a predetermined structural analysis model of the structure; and updating the structural analysis model based on an evaluation result of a fracture state in the nugget portion. In the updating step, the structural analysis model is sequentially updated based on an evaluation result of a fracture state in the nugget portion obtained per unit time, 10. The method for analyzing a structure according to claim 1, wherein in the six-component force calculation step, the six-component forces are calculated based on the structural analysis model updated before the unit time.

11. An apparatus for analyzing a structure having a plurality of plate-like members overlapping each other in a thickness direction and a nugget portion formed by spot welding the plurality of plate-like members to each other, a six-component force acquisition unit that acquires six-component forces at a predetermined time that are generated in a first node row that is composed of a plurality of nodes that form a closed loop that includes the nugget portion when viewed in the thickness direction in the structure, the first node row being configured with respect to the structure that is deformed over time by an external force; a state quantity calculation unit that calculates at least one of a load and a displacement, which is a state quantity, at each node of the second node string based on the six-component force in the first node string that has been acquired and a second node string that is configured from a plurality of nodes that are included in the first node string when viewed in the thickness direction and that are preset to surround the nugget portion; a partial analysis processing unit that performs a partial analysis on a partial analysis model including each node of the second node series and a plurality of nodes in the second node series, at least a portion of which simulates the nugget portion, by using the calculated state quantities at each node of the second node series as constraint conditions, and calculates stress and strain occurring between each node of the partial analysis model; and a nugget fracture evaluation unit that evaluates the fracture state in the nugget based on the calculated stress and strain.

12. A program for causing a computer to function as an analysis device for a structure having a plurality of plate-like members overlapping each other in a thickness direction and a nugget portion formed by spot welding the plurality of plate-like members to each other, the program comprising: The computer, a six-component force acquisition means for acquiring, for the structure which is deformed over time by an external force, six-component forces generated at a predetermined time in a first node row which is composed of a plurality of nodes forming a closed loop including the nugget portion when viewed in the thickness direction in the structure; a state quantity calculation means for calculating at least one of a load and a displacement, which is a state quantity at each node of the second node string, based on the six-component force in the first node string obtained and a second node string including a plurality of nodes that are included in the first node string when viewed in the thickness direction and that are preset to surround the nugget portion; a partial analysis processing means for performing a partial analysis on a partial analysis model including each node of the second node series and a plurality of nodes in the second node series, at least a portion of which simulates the nugget portion, by using the calculated state quantities at each node of the second node series as constraint conditions, and calculating stress and strain occurring between each node of the partial analysis model; and A program that functions as a nugget fracture evaluation means for evaluating the fracture state in the nugget based on the calculated stress and strain.

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