JP2007179385A - Apparatus and method for cae analysis - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To appropriately reflect the effect of plastic deformation (work hardening) that occurs during machining on CAE analysis. <P>SOLUTION: An apparatus for CAE analysis, which, for a subject of analysis including metallic parts manufactured from a metallic plate through machining, conducts nonlinear analysis using a finite element model of the subject of analysis on its behavior involving plastic deformation under preset analysis conditions, calculates plastic strain of the machined part of the finite element model using parameters about an angle formed between adjacent elements, the plate thickness of each element and the size of each element, as a pretreatment prior to the nonlinear analysis, for each element corresponding to at least the machined part of the finite element model. The plastic strain calculated is reflected on the initial state of the finite element model. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a CAE analysis apparatus and method for an analysis object including a metal part manufactured from a metal plate through a forming process.

Conventionally, a CAE analysis device that corrects an analysis algorithm in accordance with the consistency between an actual measurement value and an analysis value is known (see, for example, Patent Document 1).
JP 2005-182529 A

  By the way, metal parts manufactured by forming from metal plates undergo plastic deformation at the time of forming, so if you do not create an analysis model that takes into account the influence of the plastic deformation (work hardening), you can obtain highly accurate analysis results. I can't get it.

  Accordingly, an object of the present invention is to provide an apparatus and method for CAE analysis that can obtain a highly accurate analysis result in a simple and appropriate manner taking into account the influence of plastic deformation that occurs during molding.

In order to achieve the above object, the first invention provides an analysis set using a finite element model of an analysis target for an analysis target including a metal part manufactured from a metal plate through a forming process. In CAE analysis equipment that performs non-linear analysis of behavior with plastic deformation under conditions,
As pre-processing prior to the nonlinear analysis, with respect to each element corresponding to at least the molded part in the finite element model, the angle between adjacent elements, the plate thickness of the element, and the size of the element A parameter is used to calculate (estimate) the plastic strain at the machining site, and the calculated plastic strain is reflected in the initial state of the finite element model.

  A second invention is characterized in that, in the CAE analysis apparatus according to the first invention, the calculated plastic strain is applied as an initial strain of a corresponding element.

According to a third aspect of the present invention, a plastic deformation under a set load / restraint condition is applied to an analysis object including a metal part manufactured by forming from a metal plate using a finite element model of the analysis object. In the CAE analysis method for performing nonlinear analysis on behavior with
For each element corresponding to at least the molded part in the finite element model, parameters relating to the angle formed between adjacent elements, the plate thickness of the element, and the size of the element are used. Calculating a plastic strain;
Reflecting the calculated plastic strain in the finite element model;
Performing the nonlinear analysis using the finite element model in which the calculated plastic strain is reflected.

  According to the present invention, for each element corresponding to a machining site, the plastic strain at the machining site is calculated using parameters relating to the angle between adjacent elements, the plate thickness of the element, and the size of the element. Then, by reflecting the calculated plastic strain in the initial state of the finite element model, it is possible to realize a CAE analysis that easily and appropriately considers the influence of plastic deformation that occurs during the forming process.

  The best mode for carrying out the present invention will be described below with reference to the drawings.

  The CAE analysis apparatus according to the present invention is realized by a computer (including a supercomputer) in which software for realizing the functions described in detail below is incorporated. The software according to the present invention is implemented separately from the analysis software and separately as preprocessing software, but existing analysis software (for example, LS-DYNA, ABAQUS, PAM-CRASH (both are registered trademarks), etc.) Alternatively, it can be incorporated as pre-processing software into new analysis software.

  A computer terminal used directly by a user has, for example, a mouse and a keyboard as a user interface, and a display for displaying an analysis model, an analysis result, and the like. The computer terminal may be connected to a super computer that executes a calculation with a large load, a CAD terminal that supplies CAD data that is a basis of an analysis model, and the like by an in-house LAN, for example. In addition, model creation software (for example, IDEAS, Hyper-Mesh (both are registered trademarks), etc.) may be installed in the computer terminal.

  FIG. 1 is a flowchart showing an outline of the main processing flow related to the CAE analysis method according to the present invention.

  In the model creation stage (step 100), a finite element model (CAE analysis model) of a structure to be analyzed is created using model creation software. The structure to be analyzed is arbitrary, for example, a body structure of the entire vehicle or a door alone. A finite element model is generally created based on CAD data of these structures.

  In general, a sheet metal member formed of a thin plate (steel plate or the like) such as a door or a floor is modeled by a shell element. For example, a thick cast part such as a cylinder block of an engine is solid. Modeled with elements. Note that the mesh size and the like are appropriately determined in consideration of the purpose of analysis and calculation load. Each element is given plate thickness information and material characteristics (elastic coefficients E, G, Poisson's ratio ν, elastic region, etc.) of the corresponding member. The stress-strain characteristics of each element during the analysis are determined by the material characteristics.

  In the constraint condition setting stage (step 110), the constraint conditions used in the analysis stage are modeled (set). For example, an appropriate restraint condition is given to the connection part between each part according to the freedom degree which it accept | permits. Further, a contact condition may be defined for a portion where the plates overlap. The spot welded portion may be modeled by a beam element, a spring element, or the like that models spot welding.

  In the load condition setting stage (step 120), constraint conditions used in the analysis stage are set. For example, when analyzing a case where a load is applied to a certain part of a certain member, a load condition is set in which the load is applied to a node of a shell element of the part. In the case of the collision analysis, the collision speed may be included in the load condition, and the fracture condition between the elements (connection portions) in the deformation process may be further defined as the constraint condition.

  In the initial strain setting stage (step 130), the initial strain is set so that the influence of work hardening in the processed portion is reflected on the finite element model used in the analysis stage. Details of this process will be described later.

  When the above steps 100 to 130 are completed, an analysis model including a finite element model and various analysis conditions is completed, and the preprocessing for analysis is completed.

  In the analysis stage (step 140), the behavior of the structure to be analyzed is analyzed under the analysis conditions set as described above. In this analysis, an analysis algorithm corresponding to the analysis purpose is appropriately selected. In this embodiment, not a linear analysis but a nonlinear analysis (nonlinear static analysis, dynamic structural analysis / nonlinear structural transient analysis) capable of analyzing the behavior accompanied by plastic deformation of a structure to be analyzed is executed. The behavior of the structure to be analyzed depends on the purpose of the analysis.For example, the load-deformation mode of the entire structure, the load-deformation mode of each part, the stress generation mode of each part, and whether or not each part is broken Etc. The analysis result is output to a predetermined file and displayed on a display, for example, and a stress generation mode is presented by contour lines having different colors.

  Next, details of the processing in the initial distortion setting stage (step 130) will be described with reference to FIG.

  FIG. 2 is a perspective view showing a finite element model of a certain part generated in the model creation stage. The component shown in FIG. 2 is a sheet metal member manufactured by a thin plate, and is modeled by a shell element. Generally, a sheet metal member such as a door or a floor of a vehicle is formed by cutting a flat base plate (raw material) into a predetermined shape and performing bending or drawing with a press machine or the like. In FIG. 2, a part of such a processing site is representatively indicated by a circle X. In such a processed part, since it is formed into a desired bent shape or the like, plastic deformation inevitably occurs.

  FIG. 3A is a diagram showing stress-strain characteristics in analysis of an element having no plastic strain (initial strain). The element exhibits a behavior in an elastic region and a plastic region as shown in FIG. 3A in accordance with the set material properties. In other words, the stress increases linearly with respect to the increase in strain with an inclination (elastic coefficient E) until the point A (elastic limit) in FIG. When the point A is exceeded (when shifting to the plastic region), the stress increases nonlinearly as shown in FIG.

FIG. 3B is a diagram illustrating an example of a process of occurrence of work hardening. For example, when the material exceeds the elastic limit A and reaches a plastic region such as point B in FIG. 3B during processing, work hardening occurs, and after processing, as indicated by point C in FIG. 3B. A plastic strain ε _wh is generated.

FIG. 3C is a diagram showing stress-strain characteristics of an element having a plastic strain _εwh . When a plastic strain ε _wh is applied to an element, the elastic region (elastic limit) of the element changes, and the element passes through the plastic region after exceeding the point B of the elastic limit as shown in FIG. Will show non-linear behavior.

  As described above, the element in the processed part exhibits a behavior different from the element in the other part (the part not subjected to processing) due to the effect of work hardening. Therefore, in order to increase the accuracy of analysis, it is necessary to appropriately consider the influence of plastic strain (work hardening effect) that occurs during processing.

On the other hand, the mold (press mold) for forming is similarly modeled with a finite element, and the plastic strain generated during the forming process is calculated by analysis based on the finite element method. It is also conceivable to give the element in advance. According to this method, since the initial strain epsilon _wh is given to the elements in the processing unit, as shown in FIG. 3 (C), it is possible to analyze the effect of work hardening is reflected. However, in this method, it is necessary to create a finite element model of a mold and set a load condition or the like for simulating a molding process using the mold, and therefore the number of work steps becomes enormous.

  Therefore, in this embodiment, as will be described in detail below, it is possible to appropriately reflect the influence of plastic strain (the influence of work hardening) generated during processing by a simple method in the analysis.

  FIG. 4 is a diagram showing two elements in the bent portion of the circle X in FIG. As described above, in the finite element model, the bending portion is modeled by two elements having an angle corresponding to the bending.

In this embodiment, when the state before the processing shown in FIG. 5A is flat and the bending state after processing shown in FIG. 5B is reached, the angle θ is processed between adjacent elements. The plastic strain ε _wh generated by the processing is calculated by a predetermined calculation formula f (function f) using the parameters L1, L2, and t together with the parameter θ. That is, ε _wh = f (L1, L2, θ, t).

  Here, when the adjacent element is a plane, the angle θ corresponds to the outer angle formed by the normal vectors. In addition, since the case where an adjacent element is not a plane (for example, when there is a geometric distortion) is also conceivable, in this case, the angle θ is appropriately approximated and derived. For example, it may be approximately calculated as an angle formed by planes formed by three representative nodes, or may be an average value by a plurality of combinations of three nodes. The parameters L1 and L2 are the lengths of the adjacent elements, and are the lengths of the direction components forming the angle θ as shown in FIG. Actually, since the element is often not an accurate rectangle, in such a case, the parameters L1 and L2 are derived by approximation as appropriate. The parameters L1 and L2 may be, for example, average values of distances calculated at a plurality of discrete points along each side. The parameter t is the plate thickness of the element. Basically, the same member is the same for any part, and for example, a design value may be used.

Actually, as shown in FIG. 6, there are four adjacent elements for each element in a regularly meshed portion. For example, when focusing on the element S1, four elements S2 to S5 are adjacent to the element S1. Accordingly, in this case, the plastic strain ε _wh related to the element S1 is the lengths L11 and L12 of the element S1, the length L22 of the element S2, the length L32 of the element S3, the length L41 of the element S4, and the length of the element S5. L51, an angle θ12 formed by the elements S1 and S2 (see FIG. 5B), an angle θ13 formed by the elements S1 and S3 (not shown), and an angle θ14 formed by the elements S1 and S4 (not shown). 1), the angle θ15 formed by the element S1 and the element S5 (not shown), and the parameter consisting of the plate thickness t of each element (all the same in this example). That is, the plastic strain ε _wh = f (L11, L12, L22, L32, L41, L51, θ12, θ13, θ14, θ15, t) related to the element S1 is calculated. The calculation formula f may be created based on a theoretical formula or the like and experimentally adapted.

Alternatively, the adjacent elements may be considered as eight. That is, as shown in FIG. 6, when attention is paid to the element S1, for example, eight elements S2 to S9 are adjacent to the element S1. Therefore, in this case, the plastic strain ε _wh related to the element S1 is similarly calculated in relation to these eight elements S2-S9. In this case, in the relationship with the elements S6 to S9 adjacent to the element S1 at the diagonal position, the parameter L regarding the length of each element S is the length of the diagonal line (the length between the nodes at the diagonal position). ) May be used.

The plastic strain ε _wh may be comprehensively calculated for all elements of the finite element model. Or you may calculate only with respect to the element around a process part.

The plastic strain ε _wh of each element calculated in this way is preliminarily applied to the element as an initial strain in the above-described initial strain setting stage (step 130). Specifically, the initial strain (default value is zero) of each element is replaced with the value of the plastic strain ε _wh calculated as described above.

As a result, in the analysis phase initial state (step 140) (i.e., the absence is load applied), each element is in a state of already having respective plastic strain epsilon _wh as the initial strain. Therefore, when the analysis is executed in the analysis stage (step 140), each element has a value of the initial strain _εwh given thereto as shown in FIG. 3C according to the applied load. From the corresponding point C to the elastic limit point B (the position of the point B differs depending on the value of the initial strain ε _wh ), the behavior in the elastic region is shown with an inclination corresponding to the elastic modulus E, After exceeding the limit point B, the behavior in the plastic region is shown.

As described above, in this embodiment, the plastic strain ε _wh (initial strain) is calculated by a simple calculation method focusing on only the change in the angle between the elements that occurs substantially during processing, so that the calculation load and the work man-hour are increased. Therefore, it is possible to appropriately consider the influence of plastic strain (effect of work hardening) that occurs during processing. In particular, in this embodiment, the plastic strain ε _wh (initial strain) is calculated taking into account only up to eight adjacent elements with respect to the element of _{interest, and} therefore coupled with molding analysis such as bending and drawing. Compared with a technique (a technique in which molding analysis is performed as preprocessing and the result is incorporated into a model for analysis), the calculation load can be reduced and the number of work steps can be reduced.

In this embodiment, as described above, instead of changing the material characteristics of the element itself, the initial strain corresponding to the calculated plastic strain ε _wh is set, so that the work hardening is applied to the finite element model used in the analysis. Although the influence is reflected, it is also possible to obtain an equivalent effect by correcting the material property itself of the element according to the calculated plastic strain _εwh . However, the former method is effective because only the default value of the initial strain needs to be changed, and it is not necessary to rewrite the material characteristics of each element.

  The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited to the above-described embodiments, and various modifications and substitutions can be made to the above-described embodiments without departing from the scope of the present invention. Can be added.

  For example, in the above-described embodiment, each parameter is derived based on the geometric data of the finite element model. For example, a parameter such as the angle θ is a value of the CAD model from which the finite element model is created. It may be derived based on the data. Also, the length L may be simply derived according to the average mesh size at the time of mesh creation (for example, the mesh size at the time of automatic mesh division).

It is a flowchart which shows the outline | summary of the flow of the process relevant to the analysis method by this invention. It is a perspective view which shows the general appearance of an example of a finite element model. It is a stress-strain characteristic figure which shows the change of the material characteristic by the influence of work hardening. It is a figure which shows two elements in the bending process part of the circle | round | yen X in FIG. It is explanatory drawing of the method of calculating the plastic distortion _| strain (epsilon) _wh (initial strain) based on the angle change of the process part by this invention. It is explanatory drawing of an adjacent element.

Explanation of symbols

  S1 to S9 elements (shell elements)

Claims (4)

Non-linear analysis is performed on the analysis object including the metal parts manufactured from the metal plate by using the finite element model of the analysis object with the plastic deformation under the set analysis conditions. In CAE analysis equipment,
As pre-processing prior to the nonlinear analysis, with respect to each element corresponding to at least the molded part in the finite element model, the angle between adjacent elements, the plate thickness of the element, and the size of the element An apparatus for CAE analysis, characterized in that a plastic strain at the processing site is calculated using a parameter, and the calculated plastic strain is reflected in an initial state of the finite element model.   The CAE analysis apparatus according to claim 1, wherein the calculated plastic strain is applied as an initial strain of a corresponding element.   A computer-readable program for realizing a CAE analysis apparatus according to claim 1 or 2 by a computer. Non-linear analysis of behavior with plastic deformation under a set load / constraint condition using a finite element model of the analysis object for an analysis object including a metal part manufactured from a metal plate through a forming process In the CAE analysis method
For each element corresponding to at least the molded part in the finite element model, parameters relating to the angle formed between adjacent elements, the plate thickness of the element, and the size of the element are used. Calculating a plastic strain;
Reflecting the calculated plastic strain in the finite element model;
And performing the nonlinear analysis using the finite element model in which the calculated plastic strain is reflected.

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