JP2008142774A - Method, system and program for stress-strain relation simulation, and recording medium recording the program - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method, a system and a program for stress-strain relation simulation which are suitable for simulating the stress-strain relation of a material in the press forming. <P>SOLUTION: The system 100 for stress-strain relation simulation includes a parameter identification unit 11 for identifying parameters of plastic constitutive equation used for simulation based on the test result acquired by a test result acquisition unit 10, a first simulation unit 13 for simulating the stress-strain relation of a material during the press forming by using plastic constitutive equation with the result of identification being input therein, a second simulation unit 14 for simulating the stress-strain relation of the material during the spring-back by using the result of simulation of the first simulation unit 13 and plastic constitutive equation with the result of identification being input therein, and an image display unit 15 for performing the image display of the result of simulation. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a stress-strain relationship simulation method, a stress-strain relationship simulation system, a stress-strain relationship simulation program, and a recording medium on which the program is recorded. About.

In recent years, for example, high-tensile steel (high-tensile material having a tensile strength of 500 MPa or more) is frequently used for automobile parts.
Press forming of high-strength steel plates is much more difficult to form than conventional automotive steel plates (soft steel plates). In particular, high-strength steel plates that have been released from press-molding dies are spring-backed. Deformation is extremely large. In addition, cracks associated with forming tend to occur as compared with mild steel sheets. In this way, in the press molding of metal materials such as high-tensile steel plates that are difficult to form, when designing the mold for the press molding, in order to reduce the deformation due to the springback or to prevent cracking Furthermore, if the method of the era of press forming of mild steel sheets, in which a mold is prototyped and the experiment is repeated, the number of repetitions increases, and the mold prototype cost increases accordingly. Therefore, the current trend is to take measures such as predicting the spring back after release from the press mold and reflecting it in the design of the press mold.

For example, the finite element method is used as a program or software that predicts not only the springback but also the deformation of metal materials (hereinafter referred to as materials) when it is molded. (Eg: LSTC, LS-DYNA) and the like are known.
In addition, conventional finite element method programs and software use different programs and software to perform calculations to identify the values of various constant parameters that make up the plastic constitutive equation to match the experimental results. It is done using. For example, as in Patent Document 1, an identification program is prepared separately from the finite element method program and the springback amount prediction program, and the input of the experimental value to the identification program, the parameter identification by the identification program, and the identification result are reflected. There is an invention that automates a series of processes such as inputting a plastic constitutive springback amount prediction program.

  In Patent Document 1, (a) changes in stress, strain, shape, and the like of a material when the material is press-molded are based on the force to be applied to the material at the time of molding and according to the stress-strain relationship of the material. The first step is to simulate, and (b) the spring back amount of the material is predicted based on the final value of the stress, strain, shape, etc. simulated by the first step and according to the stress-strain relationship of the material. As a second step, the method of simulating the stress-strain relationship of the material is also proposed to be applied to either the first step, the second step, or both.

On the other hand, in order to simulate the stress-strain relationship of a material, it is aimed to reproduce a phenomenon called the Bauschinger effect, which is cited as a problem in Patent Document 2 described below.
Hereinafter, a part of the figures and texts will be extracted from Patent Document 2, and the Bausinger effect will be described.
“The state of springback is shown using FIG. 13 in which a stress-strain curve of a general elastic-plastic material is shown with strain on the horizontal axis and stress on the vertical axis. As shown in FIG. 13, when a tensile external force is applied to the material and a load is applied, plastic deformation occurs at the boundary of the yield point A through the elastic deformation region. Since this yield point A is the yield point when plastic deformation of the material is started for the first time, it is particularly named the initial yield point, and the stress at that time is the initial yield stress Y0. The external force is continuously applied beyond the initial yield point A, the material is plastically deformed, the processing is stopped at a point B that reaches a predetermined strain corresponding to a desired shape, and the external force is unloaded there. When the external force is unloaded from the plastically deformed material, some strain returns to the state of the balance point D where the residual stress in the material balances, and thus springback occurs.

  The springback amount is given by the difference between the strain amount at the unloading point B and the strain amount at the balance point D. After the unloading point B, the material first returns in the opposite direction according to the elastic properties. In the model called the isotropic hardening model, the point C where the stress is zero is considered to be an elastic region from the unloading point B and the target point E. Therefore, from the strain d1 on the elastic characteristic curve corresponding to the balance point D, the spring back The amount will be predicted.

In practice, however, most materials yield at point F under stress less than point E and deviate from elastic properties. This yield is distinguished from the initial yield point and is referred to as the yield point F in the unloading process. The stress-strain curve of the material after the yield point F in the unloading process has a larger slope than the stress-strain curve between the initial yield point A and the unloading point B at the first tensile plastic deformation. Thus, the phenomenon in which the yield stress decreases and the slope of the stress-strain curve increases more in the unloading process than in the loading process is called the Bauschinger effect. As described above, the simulation of the stress-strain relationship of the material is directed to the reproduction of the Bauschinger effect. However, even if the Bauschinger effect is taken into account, for example, at the balance point D, Depending on whether the strain amount is set to d2 or d3 in FIG. 13, the prediction of the springback amount differs. ]
Now, although the story changes here, the technical background will be explained a little in the following in relation to the embodiments described later.

  The relationship between stress and strain is as described in FIG. 13 above, and this can be said to schematically show the case where the material is pulled or compressed in a certain direction. The material is actually an object with a three-dimensional expanse, and it appears in the explanation partially extracted from the above-mentioned Patent Document 2 when considering the direction of pulling and compressing in a omnidirectional manner. The initial yield point A is merely one point in FIG. 13 schematically showing a case where the initial yield point A is pulled or compressed in a specific direction, but actually, as shown in FIG. It is virtually represented as an enveloped spherical yield surface S that passes through the initial yield point A, centered on a point of 0 and strain = 0 (shown two-dimensionally for convenience. Actually, Because it is necessary to think three-dimensionally, stress σ, strain Each coordinate axis indicating the, including the following figures figure, can take also the plane of the normal direction).

  If it is in the state of the initial yield point, the yield surface S is in the state shown on the inner side in FIG. 14, but the stress and strain both increase and reach a point B that reaches a predetermined strain corresponding to the desired shape. In this case, it is expressed as a yield surface S as shown on the outside in FIG. It is assumed that the yield surface S shown in FIG. 14 does not move the center O even when the state changes from the state of point A to the state of point B, and only the radius increases.

  Here, what happens when the direction of the force applied to the material is the opposite direction is the next problem, but the point B and the sign that the stress and strain both reach the predetermined strain corresponding to the desired shape are as follows. On the other hand, assuming that yielding occurs again at B 'where the same stress of the same size is applied, the above-mentioned yield surface S is changed to the assumption that the center O does not move and only the radius increases. It is not necessary to add. Thus, a calculation model that simulates the stress-strain relationship of a material by changing only the radius without moving the center of the yield surface S is called an isotropic hardening model. However, only this isotropic hardening model cannot perform a simulation capable of reproducing the Bauschinger effect.

In addition, as shown in FIG. 15, the stress of the material is assumed to be that the radius of the yield surface S does not change and only the center moves as shown in FIG. A calculation model that simulates a strain relationship is called a kinematic hardening model.
Further, although not shown, a calculation model that simulates the stress-strain relationship of the material so as to assume that the center of the yield surface S moves and the radius also changes is called a composite hardening model.

Further, as one of kinematic hardening models, there is also a well-known Yoshida-Uemori model that separately assumes a limit curved surface BS that defines a region where the yield curved surface S can move as shown in FIG. In FIG. 7, α and β are component vectors at the centers of the yield surface S and the limit surface BS, respectively.
According to the kinematic hardening model, the composite hardening model, etc., a simulation capable of reproducing the Bauschinger effect can be performed.
JP 2000-275154 A JP 2003-194686 A

  However, in Patent Document 1, a method for simulating the stress-strain relationship of a material is described in (a) a first step for simulating press forming and (b) a second step for simulating spring back. Although proposed to be shared, the contents of the plastic constitutive equation used in the first step and the content of the plastic constitutive equation used in the second step are not specified. Therefore, if the content of the plastic constitutive equation (such as the type of yield function) differs between parameter identification and simulation, an inappropriate identification result is applied to the plastic constitutive equation used during simulation, and simulation is performed. There was a risk of inaccurate results.

Neither the above-mentioned patent document 1 nor the above-mentioned patent document 2 has been said to be sufficient in the function of displaying the simulation result in an easy-to-understand manner.
Furthermore, when new parameters are added to the parameters constituting the plastic constitutive equation and these parameters are identified, if all parameters are identified simultaneously using preset initial values, the convergence of the identification calculation is improved. It was newly found that the simulation results that entered the identification results were significantly different from the experimental results.

  The present invention has been made paying attention to such an unsolved problem of the prior art, and is suitable for simulating the stress-strain relationship of a material to be molded in press molding. It is an object of the present invention to provide a method, a stress-strain relationship simulation system, a stress-strain relationship simulation program, and a recording medium on which the program is recorded.

In order to achieve the above object, the stress-strain relationship simulation method according to claim 1 according to the present invention comprises:
Press forming the stress-strain relationship of the material to be molded by a plastic constitutive equation configured by combining a hardening model that models the hardening law of the material to be molded and a yield function that gives yield conditions for the material to be formed. A stress-strain relationship simulation method for simulating the stress-strain relationship of the workpiece in
A test result acquisition process for acquiring a result of a test for applying a load in the tension direction and the compression direction to the material to be molded;
A parameter identification process for identifying a parameter of the plastic constitutive equation based on the result of the test;
Using a plastic constitutive equation in which the identified parameters are input, and simulating a stress-strain relationship of the workpiece,
In the parameter identification process and the simulation process, the same plastic constitutive equation is used.

Here, as described above, the hardening model includes an isotropic hardening model, a moving hardening model, a composite hardening model, a Yoshida-Uemori model, and the like.
Furthermore, the invention according to claim 2 is the stress-strain relationship simulation method according to claim 1,
The stress-strain relationship simulating method is characterized in that at least one of a process for simulating a stress-strain relationship during press forming and a process for simulating a stress-strain relationship during spring back is performed.

Furthermore, the invention according to claim 3 is the stress-strain relationship simulating method according to claim 1 or 2,
In the parameter identification process, when identifying a plurality of the parameters, a part of the plurality of parameters is identified first, and then the remaining parameters are converted using the plastic constitutive equation to which the identification result is input. It is characterized by identifying the parameters to be included.

  Here, the parameter including the remaining parameters is, for example, a combination of the previously identified parameter and one or more of the remaining parameters when there are a plurality of remaining parameters. For example, when there are two remaining parameters and identification is performed by adding them one by one, the parameter identified previously is set as the initial value, and the remaining parameters Add parameters to identify. Specifically, when identifying all the nine parameters, if the seven parameters are identified first, then the seven identification results are set as initial values, and the seven parameters are included in the remaining two parameters. Eight parameters added with one parameter are identified. Finally, using these eight parameters as initial values, nine parameters obtained by adding the remaining one parameter to these eight parameters are identified. The number of parameters added at the same time is not limited to one, but may be two or more, but finally all parameters are identified. The same applies to the stress-strain relationship simulation system of claim 9 and the stress-strain relationship simulation program of claim 15.

Furthermore, the invention according to claim 4 is the stress-strain relationship simulation method according to claim 3,
When a new parameter is added to the plastic constitutive equation,
In the parameter identification process, parameters other than the added parameter are identified first, and then the parameter including the added new parameter is identified using a plastic constitutive equation to which the identification result is input. It is characterized by.

  Here, the parameter including the added new parameter is, for example, when there are a plurality of new parameters to be added, a combination of the parameter previously identified and one or more parameters among the added parameters. Become. For example, when there are two parameters to be added and identification is performed by adding them one by one, the parameter previously identified is used as an initial value, and a new parameter is added to the previously identified parameter. Add one parameter to identify. Specifically, when there are seven initial parameters and two new parameters are added to identify a total of nine parameters, the initial seven parameters are identified first, and then these seven parameters are identified. Using eight identification results as initial values, eight parameters obtained by adding one of the two newly added parameters to these seven parameters are identified. Finally, using these eight parameters as initial values, nine parameters obtained by adding the remaining one parameter to these eight parameters are identified. The number of parameters added at the same time is not limited to one, but may be two or more. Finally, all parameters including the new addition are identified. The same applies to the stress-strain relationship simulation system of claim 10 and the stress-strain relationship simulation program of claim 16.

Furthermore, the invention according to claim 5 is the stress-strain relationship simulation method according to any one of claims 1 to 4,
The curing model is a Yoshida-Uemori model.
Here, the Yoshida-Uemori model is an elasto-plastic constitutive model based on a two-surface model in which a yield surface moves in a limit surface, and is a model that can reproduce the Bauschinger effect.

Furthermore, the invention according to claim 6 is the stress-strain relationship simulation method according to any one of claims 1 to 5,
It includes image display processing of information relating to the result of simulation by the simulation method.
Here, the information on the simulation result corresponds to information on the simulation result, information on the test result when identifying the parameters of the plastic constitutive equation used in the simulation, information on comparison between the simulation result and the test result, and the like. In addition, image information (including animation processing) that shows the deformation state of the molding material reflecting the simulation results, stress distribution information of the molding material during press molding, a graph generated based on numerical information, and calculation based on numerical information Information generated based on numerical information obtained by simulation, such as statistical information. The same applies to the stress-strain relationship simulation system of claim 12 and the stress-strain relationship simulation program of claim 18.

On the other hand, in order to achieve the above object, the stress-strain relationship simulation system according to claim 7 comprises:
Press forming the stress-strain relationship of the material to be molded by a plastic constitutive equation configured by combining a hardening model that models the hardening law of the material to be molded and a yield function that gives yield conditions for the material to be formed. A stress-strain relationship simulation system for simulating the stress-strain relationship of the workpiece in
A test result acquisition means for acquiring a result of a test for applying a load in the tensile direction and the compression direction to the material to be molded;
Parameter identifying means for identifying the parameters of the plastic constitutive equation based on the results of the test;
Using a plastic constitutive equation in which the identified parameters are input, and a simulation means for simulating the stress-strain relationship of the molding material,
The parameter identifying means and the simulation means use the same plastic constitutive equation.

  With such a configuration, it is possible to acquire a result of a test in which a load is applied to the molding material in the tensile direction and the compression direction by the test result acquiring unit, and the parameter identification unit can acquire the test result. Based on the result, it is possible to identify the parameters of the plastic constitutive equation, and the simulation means simulates the stress-strain relationship of the workpiece using the plastic constitutive equation to which the identified parameters are input. It is possible.

Further, the parameter identification unit and the simulation unit can execute a process for identifying a parameter and a simulation process using the identification result by using the same plastic constitutive equation.
Here, this system may be realized as a single device, terminal, or other device, or may be realized as a network system in which a plurality of devices, terminals, or other devices are communicably connected. . In the latter case, each component may belong to any one of a plurality of devices and the like as long as they are connected so as to communicate with each other.

Furthermore, the invention according to claim 8 is the stress-strain relationship simulation system according to claim 7,
The stress-strain relationship simulation system includes at least one of a means for simulating a stress-strain relationship during press forming and a means for simulating a stress-strain relationship in a springback process.

With such a configuration, the plastic configuration used for parameter identification by the parameter identification means for at least one of the simulation of the stress-strain relationship during press molding and the simulation of the stress-strain relationship during springback It is possible to use the same plastic constitutive equation as the equation.
Furthermore, the invention according to claim 9 is the stress-strain relationship simulation system according to claim 7 or claim 8,
The parameter identification means first identifies a part of the plurality of parameters when identifying the plurality of parameters, and then uses the plastic constitutive equation to which the identification result is input to determine the remaining parameters. It is characterized by identifying the parameters to be included.

In such a configuration, when the parameter identification unit identifies a plurality of the parameters, the parameter identification unit first identifies a part of the plurality of parameters, and then inputs the identification result of the plastic constitutive equation. Can be used to identify parameters including the remaining parameters.
The invention according to claim 10 is the stress-strain relationship simulation system according to claim 9,
When a new parameter is added to the plastic constitutive equation,
The parameter identification means first identifies a parameter other than the added parameter, and then identifies a parameter including the added new parameter using a plastic constitutive equation to which the identification result is input. It is characterized by.

With such a configuration, when a new parameter is added to the plastic constitutive equation,
In the parameter identification means, it is possible to first identify parameters other than the added parameter, and then identify a parameter including the added parameter using a plastic constitutive equation to which the identification result is input. It is.
Further, an invention according to claim 11 is the stress-strain relationship simulation system according to any one of claims 7 to 10,
The curing model is a Yoshida-Uemori model.

With such a configuration, the parameter identification unit and the simulation unit perform each processing using a plastic constitutive equation in which the combination content of the Yoshida-Uemori model and the predetermined yield function is the same for both. Is possible.
Furthermore, an invention according to claim 12 is the stress-strain relationship simulation system according to any one of claims 7 to 11,
An image display means for displaying information related to the result of the simulation by the simulation system is provided.

With such a configuration, it is possible to display information on the result of the simulation by the image display means.
In order to achieve the above object, a stress-strain relationship simulation program according to claim 13 comprises:
Press forming the stress-strain relationship of the material to be molded by a plastic constitutive equation configured by combining a hardening model that models the hardening law of the material to be molded and a yield function that gives yield conditions for the material to be formed. A stress-strain relationship simulation program for simulating the stress-strain relationship of the material to be molded in
A test result acquisition process for acquiring a result of a test for applying a load in the tension direction and the compression direction to the material to be molded;
A parameter identification process for identifying a parameter of the plastic constitutive equation based on the result of the test;
A program for causing a computer to execute a process consisting of a simulation process for simulating a stress-strain relationship of the material to be molded, using a plastic constitutive equation in which the identified parameters are input;
In the parameter identification process and the simulation process, the same plastic constitutive equation is used.

Furthermore, the invention according to claim 14 is the stress-strain relationship simulation program according to claim 13,
The stress-strain relationship simulation program includes at least one of a process for simulating a stress-strain relationship during press forming and a process for simulating a stress-strain relationship during spring back.

Furthermore, the invention according to claim 15 is the stress-strain relationship simulation program according to claim 13 or 14,
In the parameter identification process, when identifying a plurality of the parameters, a part of the plurality of parameters is identified first, and then the remaining parameters are input using the plastic constitutive equation to which the identification result is input. It is characterized in that the parameter including is identified.

Furthermore, the invention according to claim 16 is the stress-strain relationship simulation program according to claim 15,
When a new parameter is added to the plastic constitutive equation,
In the parameter identification process, parameters other than the added parameter are identified first, and then a parameter including the added new parameter is identified using a plastic constitutive equation to which the identification result is input. It is characterized by.

Furthermore, the invention according to claim 17 is the stress-strain relationship simulation program according to any one of claims 13 to 16,
The curing model is a Yoshida-Uemori model.
Furthermore, the invention according to claim 18 is the stress-strain relationship simulation program according to any one of claims 13 to 17,
A program for causing a computer to execute an image display process of information related to a simulation result by the simulation program is included.

  In order to achieve the above object, a computer-readable recording medium according to claim 19 is read by a computer recording the stress-strain relationship simulation program according to any one of claims 13 to 18. It is a possible recording medium.

  According to the stress-strain relationship simulation method of the present invention according to claim 1, in the test result acquisition process, a result of a test in which a load is applied to the material to be molded in the tensile direction and the compression direction is acquired, and parameter identification process is performed. In the simulation process, the parameters constituting the plastic constitutive equation are identified, and in the simulation process, using the plastic constitutive equation in which the identified parameters are input, the stress-strain of the workpiece in press forming is determined. Since the relationship is simulated and the same plastic constitutive equation is used in the parameter identification process and the simulation process, the stress-strain relationship of the workpiece can be accurately simulated. .

  According to the stress-strain relationship simulation method of the present invention according to claim 2, in the simulation process, the stress-strain relationship during press forming and the stress-strain relationship during spring back are simulated. Since the same plastic constitutive equation as the plastic constitutive equation used in the parameter identification process can be used, at least one of the stress-strain relationship during press forming and the stress-strain relationship during spring back can be used. Can be accurately simulated.

  According to the stress-strain relationship simulation method of the present invention according to claim 3, when identifying a plurality of the parameters in the parameter identification process, a part of the plurality of parameters is identified first, After that, the parameters including the remaining parameters are identified using the plastic constitutive equation to which the identification result is input. Therefore, all the parameters are identified simultaneously using the preset initial values of the parameters. Compared to the case, the convergence of the identification calculation can be improved and the accuracy of the simulation can be improved.

  According to the stress-strain relationship simulation method of the present invention according to claim 4, when a new parameter is added to the plastic constitutive equation, in the parameter identification process, parameters other than the added parameter are identified. First, using the plastic constitutive equation to which the identification result is input, the parameter including the added parameter is identified, so the initial value of the preset parameter is used to Compared to the case where all parameters including the parameter added to are identified at the same time, the convergence of the identification calculation can be made faster, the convergence can be improved, and the accuracy of the simulation can be improved.

Moreover, according to the stress-strain relationship simulation method of the present invention according to claim 5, since the hardening model is the Yoshida-Uemori model, a simulation capable of reproducing the Bauschinger effect can be performed.
Further, according to the stress-strain relationship simulation method of the present invention according to claim 6, since the information regarding the result of the simulation is displayed in the image display process, the result of the simulation can be easily understood. it can.

Further, according to the stress-strain relationship simulation system of the present invention according to claims 7 to 12, since means corresponding to each process is provided according to claims 1 to 7, respectively, The same effect as that of the seventh aspect can be obtained.
Further, according to the stress-strain relationship simulation program of the present invention according to claims 13 to 18, when the program is read by the computer and the computer executes processing in accordance with the read program, the claims 1 to 1, respectively. The same effect as that of Item 7 is obtained.

  According to the computer-readable recording medium of the present invention according to claim 19, the stress-strain relationship simulation program of the present invention according to any one of claims 13 to 18 is recorded. When the program is read from the storage medium by the computer and the computer executes processing according to the read program, the same effects as the effects of claims 1 to 7 are obtained.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. 1 to 12 are diagrams showing embodiments of a stress-strain relationship simulation method, a stress-strain relationship simulation system, a stress-strain relationship simulation program, and a recording medium on which the program is recorded according to the present invention. .
First, the configuration of a stress-strain relationship simulation system according to the present invention will be described with reference to FIG. FIG. 1 is a block diagram showing a functional configuration of a stress-strain relationship simulation system 100 according to the present invention.

  As shown in FIG. 1, the stress-strain relationship simulation system 100 includes a test result acquisition unit 10 that acquires a result of a test performed on a metal material (hereinafter referred to as a material) that is a molding material, The parameter identification unit 11 for identifying the parameters of the plastic constitutive equation used for the simulation of the stress-strain relationship based on the acquired test result and the plastic constitutive equation information acquired via the plastic constitutive equation information storage unit 12 described later; Using the plastic constitutive equation information storage unit 12 for storing information on the plastic constitutive equation and the plastic constitutive equation to which the identification result is input, the stress-strain relationship of the material during press forming is simulated by the finite element method. Using the first simulation unit 13, the simulation result by the first simulation unit 13, and the plastic constitutive equation to which the identification result is input Stress of the material during springback - has strain relationship with a second simulating unit 14 for simulating, and the identification result and the simulation result including an image display unit 15 for displaying images, etc. configuration.

The test result acquisition unit 10 is, for example, a tensile test for measuring a stress-strain relationship when a force is applied to a material in the tensile direction, and a force in a direction opposite to the tensile direction (compression direction). It has a function of acquiring results of tests such as a compression test for measuring a stress-strain relationship when added, a tensile test and a tensile-compression test combining the compression test.
The parameter identification unit 11 performs parameters of the plastic constitutive equation used in the simulation of each stress-strain relationship executed by the first simulation unit 13 and the second simulation unit 14 in the test acquired by the test result acquisition unit 10. Based on the result, it has a function of identifying using a known identification algorithm such as Multi Point Approximation Method.

Here, the parameters constituting the plastic constitutive equation are constants according to the characteristics of the material.
The plastic constitutive equation includes a hardening model that models a hardening rule that defines a change in yield surface during plastic deformation of the material to be simulated, a flow law for defining plastic deformation of the material, It is configured in combination with a yield function that gives a yield condition for defining the start of plastic deformation of the material.

  The curing model is an isotropic curing model, kinematic curing model, composite curing model, or Yoshida-Uemori model, which is one of kinematic curing models (reference: Yoshida, F., Uemori, T., A model). There are various models such as large-strain cyclic plasticity describing the Bauschinger effect and workhardening stagnation. Int. J. Plasticity 18, 661-686).

  In addition, as the yield function, the maximum shear stress acting on the material, which was assumed to be isotropic, reached a certain value determined by the type and condition of the material. Sometimes, it is assumed that plastic deformation begins. Others, such as those proposed by von Mises, assume that the material yields when it reaches a certain material constant value (scalarized multidimensional stress).

  In addition, for example, (1) Hill (Reference 1: Hill, R .: Proc. Roy. Soc., A193 (1948), 281., Reference 2: Hill, R .: J. Mech. Phys. Solids, 38-3 (1990), 405.), (2) Logan-Hosford (reference: Logan RW, Hosford WF: Int. J. Mech. Sci., 19 (1977) ), 505.), (3) Gotoh (reference: Gotoh, M .: Int. J. Mech. Sci., 19 (1977), 505.), (4) Barlat (reference: Barlat, F. et al: Yield function proposed by Int. J. Plasticity, 19 (2003), 1297).

In addition, when a new parameter is added to the plastic constitutive equation, the parameter identification unit 11 first identifies parameters other than the added parameters using the plastic constitutive equation before adding the parameter. Next, the parameters including the remaining parameters are identified using the plastic constitutive equation to which the identification result is input.
The plastic constitutive equation information storage unit 12 stores information on a plastic constitutive equation used in each simulation of the first simulating unit 13 and the second simulating unit 14 (hereinafter referred to as plastic constitutive equation information) in a storage device 70 described later. And a function of reading and providing plastic constitutive equation information stored in the storage device 70 in response to requests from the parameter identification unit 11, the first simulation unit 13, and the second simulation unit 14. Have.

  Here, the plastic constitutive equation information includes the information of the constitutive equation itself, such as the hardening model, the yield function, and the parameter type, which constitutes the plastic constitutive equation, as well as the parameters associated with each material type and its characteristics. Information related to the identification result, and information related to a subroutine program (hereinafter referred to as subroutine) that calculates and outputs the corresponding strain or stress when the stress or strain is input using the plastic constitutive equation to which the identification result is input Including. This subroutine is shared by the parameter identification unit 11, the first simulation unit 13, and the second simulation unit 14.

  The first simulation unit 13 acquires finite element analysis data including various data such as mesh data, stress conditions, boundary conditions, and the identification result of the parameter identification unit 11 via the plastic constitutive equation information storage unit 12. Is obtained, and a function of simulating the stress-strain relationship of the material at the time of press forming is obtained using a finite element method.

  The second simulating unit 14 acquires from the first simulating unit 13 the result of the simulation of the stress-strain relationship of the material at the time of press forming, and the parameter identifying unit 11 via the plastic constitutive equation information storage unit 12. The function of simulating the stress-strain relationship of the springback process using the acquired simulation result and the acquired subroutine is obtained. .

  The image display unit 15 acquires information on the identification result by the parameter identification unit 11 (test value, identified parameter value, simulation result using the identification result, etc.), and based on the acquired information, the actual test It has a function of displaying, for example, comparison information between the results and the simulation results. Furthermore, the image display unit 15 acquires simulation results by the first simulation unit 13 and the second simulation unit 14, and based on the acquired information, results of simulation of a stress-strain relationship during press molding, and It has the function of displaying information based on the result of simulation of the stress-strain relationship in the springback process.

  Here, the stress-strain relationship simulation system 100 includes various controls for simulation, the test result acquisition unit 10, the parameter identification unit 11, the plastic constitutive equation information storage unit 12, the first simulation unit 13, and the second simulation. 2 is a computer system for realizing the functions of the unit 14 and the image display unit 15 on computer software, that is, by executing a computer-readable simulation program, and the hardware configuration thereof is as shown in FIG. A central processing unit (CPU) 60 that is a central processing unit responsible for various controls and arithmetic processing, a RAM (Random Access Memory) 62 that constitutes a main storage device (Main Storage), and a read-only storage device A ROM (Read Only Memory) 64 is connected with various internal / external buses 68 such as a peripheral component interconnect (PCI) bus, and the HDD 68 (input / output interface (I / F) 66) is connected to the bus 68. An external storage device (Secondary Storage) 70 such as a Hard Disk Drive, an output device 72 such as an LCD monitor, and an input device 74 such as an operation panel are connected.

  When the power is turned on, a system program such as BIOS stored in the ROM 64 or the like, various dedicated computer programs stored in the ROM 64 in advance, a CD-ROM, a DVD-ROM, a flexible disk (FD), or the like The various dedicated computer programs installed in the storage device 70 are loaded into the RAM 62 via the recording medium or the communication network L such as the Internet, and the instructions described in the program loaded in the RAM 62 are loaded. Accordingly, the functions of the respective units as described above can be realized on the software by the CPU 60 performing various controls and arithmetic processing for actually performing the simulation using various resources.

Next, based on FIG. 3, the flow of processing by the above-described stress-strain relationship simulation system 100 will be described. Here, FIG. 3 is a flowchart showing a flow of processing by the stress-strain relationship simulation system 100.
When execution of the dedicated computer program is started by the CPU 60, as shown in FIG. 3, first, the process proceeds to step S100, and the test result acquisition unit 10 has received an instruction to start parameter identification processing (identification start instruction). If it is determined that there is a start instruction (Yes), the process proceeds to step S102, and if not (No), the process proceeds to step S108.

  When the process proceeds to step S102, the test result acquisition unit 10 acquires the test result of the material to be simulated, and inputs the acquired test result to the parameter identification unit 11, and the process proceeds to step S104. To do. Here, the result of the test of the target material is obtained by reading out the result of the test performed in advance and stored in the storage device 70 in advance.

In step S104, the parameter identification unit 11 executes parameter identification processing for identifying the parameters of the plastic constitutive equation used in the simulation using the test result acquired in step S102, identifies the parameters, and proceeds to step S106. .
In step S106, the image display unit 15 displays an image of information based on the identification result in step S104, ends the series of processes, and proceeds to step S100.

On the other hand, if there is no identification start instruction in step S100 and the process proceeds to step S108, the first simulating unit 13 determines whether there is a simulation start instruction, and if it is determined that there is a start instruction (Yes ) Goes to step S110, otherwise (No) goes to step S100.
When the process proceeds to step S110, the first simulating unit 13 uses the plastic constitutive equation information (subroutine) to which the identification result of step S104 is input to simulate the stress-strain relationship during the press forming (first process). The simulation process is executed, and the process proceeds to step S112.

In step S112, the second simulating unit 14 uses the plastic constitutive equation information (subroutine) to which the identification result in step S104 is input to simulate the stress-strain relationship during spring back (second simulating process). And the process proceeds to step S114.
In step S114, information based on the result of the simulation is displayed on the image display unit 15, and a series of processing ends, and the process proceeds to step S100.

Furthermore, the flow of the parameter identification process in step S104 will be described based on FIG. Here, FIG. 4 is a flowchart showing the flow of parameter identification processing in the parameter identification unit 11.
As shown in FIG. 4, the parameter identification process first proceeds to step S <b> 200, and whether or not the parameter identification unit 11 has acquired the test result instructed by the identification start instruction from the test result acquisition unit 10. If it is determined that it has been acquired (Yes), the process proceeds to step S202. If not (No), the process is repeated until it is determined that it has been acquired.

When the process proceeds to step S202, the parameter identification unit 11 acquires the plastic constitutive equation information having the content instructed by the identification start instruction from the storage device 70 via the plastic constitutive equation information storage unit 12, and step S204. Migrate to The plastic constitutive equation information here includes information on the type of hardening model, the type of flow law, the type of yield function, the type of parameter, and the like.
In step S204, the parameter identification unit 11 determines whether or not a new parameter is added to a parameter that is commonly used in the plastic constitutive equation. If it is determined that there is an addition (Yes), step S206 is performed. If not (No), the process proceeds to step S212.

When the process proceeds to step S206, the parameter identification unit 11 first identifies parameters other than the added parameter based on the test result acquired in step S200 and the plastic constitutive equation information acquired in step S202. The process proceeds to S208.
Here, the identification process is performed using, for example, a multi-point approximation method that is one of known identification methods. In addition, a random value or an initial value of a constant such as 0 is given in advance as a parameter. Using the test result as original data, the original data and the simulation result when the identified parameter is input Evaluate the difference. That is, the calculation process (learning calculation) for correcting the parameter value is repeated so that the difference is minimized (local solution), and the parameter value when the difference is minimized is output as the identification result of the parameter. At the same time, the identification process is completed.

  In step S208, the parameter identification unit 11 sets the value of the parameter other than the newly added part (ordinary parameter) identified in step S206 as the initial value of the parameter other than the added part, and includes the parameter including the added part (only the added part). , Or all including additional parts), and the process proceeds to step S210. In this identification process, a new test result may be acquired and used as original data, or the same test result as in the identification process in step S206 may be used. In step S208, the identification process as described above is performed until the identification of all the parameters including the added part is completed.

In step S210, the parameter identification unit 11 outputs the identification result of step S208 to the plastic constitutive equation information storage unit 12 and stores it in the storage device 70 via the plastic constitutive equation information storage unit 12. The identification result in step S208 is output to the image display unit 15, the series of processes is terminated, and the process proceeds to step S106.
On the other hand, when there is no additional parameter in step S204 and the process proceeds to step S212, the parameter identification unit 11 uses the test result acquired in step S200 and the plastic constitutive equation information acquired in step S202. All parameters are identified simultaneously, and the process proceeds to step S210. That is, if there are only ordinary parameters, all parameters are identified simultaneously.

Further, the flow of the first simulation process in step S110 will be described with reference to FIG. Here, FIG. 5 is a flowchart showing the flow of the first simulation process in the first simulator 13.
As shown in FIG. 5, in the first simulation process, first, the process proceeds to step S300, and the finite element analysis data input or designated by the first simulation unit 13 via the input device 74 is used. Acquire and move to step S302.

In step S302, in the first simulation unit 13, the parameter identification result corresponding to the target material and the plastic constitutive equation information (subroutine) stored in the storage device 70 via the plastic constitutive equation information storage unit 12 are stored. ) And the process proceeds to step S304.
In step S304, the first simulating unit 13 simulates the stress-strain relationship of the material during press forming using the plastic constitutive equation information (subroutine) in which the parameter identification result obtained in step S302 is input. The process proceeds to step S306.

In step S306, the first simulation unit 13 outputs the result of the simulation in step S304 to the second simulation unit 14, ends the series of processes, and proceeds to step S112.
Furthermore, the flow of the second simulation process in step S112 will be described with reference to FIG. Here, FIG. 6 is a flowchart showing the flow of the second simulation process in the second simulator 14.

In the second simulation process, as shown in FIG. 6, first, the process proceeds to step S <b> 400, and it is determined whether or not the second simulation unit 14 has obtained the result of the simulation by the first simulation unit 13. If it is determined that acquisition is possible (Yes), the process proceeds to step S402. If not (No), the process is repeated until it is determined that acquisition is possible.
When the process proceeds to step S402, the second simulation unit 14 identifies the same parameters as those stored in the storage device 70 via the plastic constitutive equation information storage unit 12 and used in the first simulation process. The result and plastic constitutive information (subroutine) are acquired, and the process proceeds to step S404.

In step S404, the second simulating unit 14 uses the plastic constitutive equation information (subroutine) in which the simulation result acquired in step S400 and the parameter identification result acquired in step S402 are input. The stress-strain relationship of the material is simulated, and the process proceeds to step S406.
In step S406, the second simulation unit 14 outputs the simulation results of the first simulation process and the second simulation process to the image display unit 15, ends the series of processes, and proceeds to step S114.

Next, based on FIGS. 7-12, the flow of a process of the stress-strain relationship simulation system 100 of this Embodiment is demonstrated more concretely.
Here, FIG. 7 is a diagram schematically illustrating the Yoshida-Uemori model, and FIGS. 8A and 8B are diagrams illustrating an example of a Non-IH (Isotropic Hardening) region. FIGS. 9A and 9B are diagrams showing the relationship between the limit curved surface BS and the Non-IH region. FIG. 10 is a diagram illustrating an image display example when the process of first identifying parameters other than the added amount is performed, and FIG. 11 is an image display example when the process of simultaneously identifying all parameters is performed. FIG. Moreover, FIG. 12 is a figure which shows an example of the result of the simulation of the stress-strain relationship at the time of press molding. In addition to the images shown in FIGS. 11 and 12, images such as those shown in FIGS. 14 and 15 may be displayed. Not only the stationary state but also the moving state with a change in stress may be displayed as an animation.

  Hereinafter, in explaining the processing flow of the stress-strain relationship simulation system 100, a plastic constitutive equation combining the Yoshida-Uemori model and the yield function proposed by Hill will be used. Hill's yield function (1948) is expressed by the following equation (1).

In the above formula (1), σ ′ ₁₁ , σ ′ ₂₂ , σ ′ ₃₃ (or normal stress), σ ′ ₁₂ , σ ′ ₂₃ and σ ′ ₃₁ (or shear stress) are stresses in each direction in the material. Deviation component (however, the normal stress is obtained by subtracting the hydrostatic pressure stress), and F, G, H, L, M, and N are parameters for defining the anisotropy of the material.

As shown in FIG. 7, the Yoshida-Uemori model is an elasto-plastic model based on a two-surface model in which the yield surface S moves in the limit surface BS, and is a model that can reproduce the Bausinger effect.
An elastoplastic model (plastic constitutive equation) combining the Yoshida-Uemori model and the Hill yield function will be described below.
Assuming that the yield function is φ (σ _ij ), the initial yield surface S ₀ can be defined by the following equation (2).

S ₀ = φ (σ _ij ) −Y = 0 (2)

Here, in the above equation (2), σ _ij is a stress tensor amount. Y is the initial yield stress and is one of the parameters to be identified.

Further, the subsequent yield surface S following the initial yield surface S ₀ is defined by the following equation (3).

S = φ (σ _ij −α _ij ) −Y = 0 (3)

Here, α in the above equation (3) is the back stress, and α _ij is the tensor amount.

In view of the fact that the re-yield at the time of stress reversal starts from a relatively early stage due to the Bauschinger effect, isotropic hardening is not considered, and the above expression (3) is an expression that incorporates only kinematic hardening.
In addition, as with a general elasto-plastic model, the combined flow law shown in the following equation (4) was adopted as the flow law.

Here, D ^p _ij in the above equation (4) is a strain rate, and is the product of ∂S / ∂σ _ij indicating the direction of plastic deformation and dλ / dt indicating the temporal change in plastic deformation. Defined.
The limit curved surface BS is expressed by the following formula (5).

BS = φ (σ _ij −β _ij ) − (B + R) = 0 (5)

In the above equation (5), β is the center of the limit curved surface and is the tensor amount (β _ij ). In the above equation (5), B is a constant corresponding to the material characteristics, and is the initial size (radius) of the limit curved surface. B is also one of identification target parameters. In the above equation (5), R is an increment (variable) due to isotropic hardening of the limit curved surface. The initial value of R is “0”.

Accordingly, in the above equation (5), the center position and radius of the limit curved surface BS change. That is, for the limit curved surface BS, both isotropic hardening and kinematic hardening are considered.
Further, the following equations (6) to (10) were adopted as the evolution equations for the back stress of the yield surface. Note that the evolution equation of α _* shown in the following equations (6) and (7) is a modification of the Armstrong-Frederick equation.

Here, in the above formulas (6) and (7), α _* is the center of the yield surface viewed from the limit surface and is the tensor amount (α _{* ij} ). In the above equation (7), C is a material parameter relating to kinematic hardening of the yield surface, and defines the speed of kinematic hardening. C is also one of parameters to be identified. Further, dp / dt in the above equation (7) is a temporal change in the equivalent plastic strain, and is represented by the above equation (8).

  Further, the following equations (11) and (12) were adopted as the evolution equations for the back stress of the limit curved surface. The Chaboche-Rousselier equation was used as the R evolution equation, and the Armstrong-Frederick rule was adopted as the β evolution equation.

In the above equation (11), dR / dt is the time variation of the radius of the limit curved surface, and R _sat is the limit value of R. Note that R _sat is also one of parameters to be identified. In the above equation (12), β ′ _ij is a deviation stress component at the center of the limit curved surface, and is obtained by subtracting the hydrostatic stress excluding the shear stress from the center β of the limit curve. Further, in the above equation (12), b is a parameter that defines a movable region of kinematic hardening of the limit curved surface, and is one of identification target parameters.

  In the Yoshida-Uemori model, another curved surface is defined in order to express the Non-IH region (hereinafter referred to as the anisotropic hardening region) shown in FIGS. 8A and 8B. In addition, a restriction is added to the development formula of R shown in the above formula (11). This curved surface is called a Non-IH surface and is defined by the following equations (13) to (17). Hereinafter, this Non-IH surface is referred to as an anisotropically hardened curved surface.

  Here, in the above formulas (15) and (17), h is a material parameter for controlling the non-cured region, and is one of identification target parameters. In the above formula (14), r is the size (radius) of the non-cured curved surface, and dr / dt is the time change of the radius r of the non-cured curved surface.

That is, according to the above formulas (13) to (17), as shown in FIGS. 9A and 9B, when the center β of the limit curved surface BS exists inside the anisotropic hardening curved surface, the R is enlarged. In this way, the anisotropic hardening region is expressed.
It is also possible to add a new parameter to the elastic-plastic model (plastic constitutive equation) defined by the above equations (1) to (17).

For example, it is possible to add r _initial which is a parameter indicating the initial size of r, which is the size (radius) of the non-cured curved surface, in the above equation (14).
In addition, C, which is a material parameter related to kinematic hardening of the yield surface, is expressed by the following formulas (18) and (19): the initial C value C1 and the subsequent C value C2. It can be divided into two parameters.

Furthermore, it is also possible to add material parameters E ₀ , E _a , ξ relating to the apparent Young's modulus. In this case, the relationship of the following formula (20) is established.

E = E ₀ − (E ₀ −E _a ) (1−exp (−ξp)) (20)

Here, in the above formula (20), p is the equivalent plastic strain.

Next, the operation of the stress-strain relationship simulation system 100 of the present invention will be described on the assumption that the plastic constitutive equation information including the plastic constitutive equation is stored in the storage device 70.
When an identification start instruction is input from the user via the input device 74 ("Yes" branch in step S100), the test result acquisition unit 10 acquires the test result stored in the storage device 70 ( Step S102). This identification start instruction includes the type of test results (type of material, test content, etc.), the type of plastic constitutive equation (type of hardening model, flow law, yield function, etc.) used in the identification process, and the plastic configuration This includes the type of parameter corresponding to the expression.

  Here, in order to make the material type a high-tensile steel plate and accurately reproduce the Bauschinger effect, a tensile-compression test is specified as the test result type, and the result of the test is acquired. The details of the tensile-compression test were as follows. After applying a tensile force to the high-tensile steel plate to be simulated, the tensile force was gradually reduced and unloaded. A process of applying a force in a direction opposite to the pulling direction (compression direction) is performed.

  When acquiring the result of the tensile-compression test, the parameter identification unit 11 executes a parameter identification process (step S104). When the parameter identification process is executed (the result of the test is acquired) (the branch of “Yes” in step S200), the parameter identification unit 11 firstly stores the storage device 70 via the plastic constitutive equation information storage unit 12. The plastic constitutive equation information designated by the identification start instruction is acquired from the plastic constitutive equation information stored in (Step S202). Here, it is assumed that plastic constitutive equation information composed of a combination of the Yoshida-Uemori model and the Hill yield function is specified, and the plastic constitutive equation information is acquired.

Once the plastic constitutive equation information is acquired, it is next determined whether or not a new parameter has been added based on the identification start instruction (step S204). Here, it is assumed that, in the start instruction, the above-described r _initial addition instruction is given for the parameters commonly used in the Yoshida-Uemori model (“Yes” branch in step S204).
That is, the parameter identification unit 11 in the Yoshida-Uemori model has an initial yield stress Y, an initial size B of the limit curved surface, a work hardening limit value R _{sat of} the limit curved surface, a material parameter C relating to kinematic hardening of the yield surface, A total of eight parameters: a material parameter k relating to isotropic hardening of a curved surface, a parameter b defining a moving region of kinematic hardening of a limit curved surface, a material parameter h controlling a non-curing region, and an _initial size r _initial of the non-curing surface Will be identified.

First, the parameter identification unit 11 first performs identification processing of seven common parameters constituting the plastic constitutive equation before the addition of the parameter r _initial (step S206). As described above, the parameters are identified by iterative calculation using a known multipoint approximation method using the obtained test results as original data. As a result, seven parameters Y, B, R _sat , C, k, b, and h are identified first.

When the identification of these seven parameters is completed, next, eight parameters obtained by adding r _initial to these seven parameters are identified (step S208). At this time, the identification results of the previously identified seven parameters are used as initial values for the remaining seven parameters excluding r _initial .
The parameter identification process can be performed using only the results of one test, but the results of a plurality of tests can also be used. In that case, it is possible to include the results of a pull-only or compression-only test.

  Then, when the identification of the eight parameters including the newly added portion is completed, the parameter identification unit 11 outputs the identification result to the plastic constitutive equation information storage unit 12 and via the plastic constitutive equation information storage unit 12 The identification result is stored in the storage device 70 in association with the type and characteristics of the material, the plastic constitutive information used for identifying the parameters, and the like. Further, the parameter identification unit 11 outputs the identification result, the result of the simulation using the identification result (the calculation result by the subroutine), and the result of the acquired tensile-compression test to the image display unit 15 ( Step S210).

  On the other hand, when the image display unit 15 acquires the identification result, the simulation result, and the tensile-compression test result from the parameter identification unit 11, the horizontal axis is based on the simulation result and the tensile-compression test result. Is a strain and a vertical axis is stress, and a graph of a stress-strain relationship is generated. Then, as shown in FIG. 10, this graph is displayed as an image together with a graph indicating the result of the tension-compression test (step S106).

As shown in FIG. 10, the result of the simulation is considerably close to the result of the test with respect to the actual test result, and it can be said that a good identification result was obtained.
On the other hand, the graph of the stress-strain relationship shown in FIG. 11 is obtained when eight parameters including a newly added portion are simultaneously identified by one identification process. Compared with the simulation result shown in FIG. 10, it can be seen that the simulation result shown in FIG. 11 has a very large deviation from the test result. This can be said to be an inappropriate identification result.

That is, when a parameter is newly added, seven parameters other than the added portion are identified first, and a parameter including the eighth parameter that is the added portion is identified using the identification result. The method is more effective.
In addition, when identifying a total of nine parameters, in which C1 and C2 are added instead of C in the eight parameters, for example, after identifying the eight parameters, the identification result of C among these is excluded. The seven identification results are set as initial values, and C1 and C2 are added instead of C to identify a total of nine parameters. That is, when adding a plurality of new parameters, one method is conceivable in which the previous identification result is set as the initial value, one new parameter is identified, and then one is identified again. . Alternatively, a method of identifying a plurality of new parameters at once can be considered.

It should be noted that the common parameter may be identified first, and the identification result may be identified by using the identification result as an initial value and identifying a parameter including one or a plurality of new parameters or all parameters. .
Furthermore, in the state where the identification result is stored, when a simulation start instruction using the identification result and plastic constitutive equation information corresponding thereto is input to the stress-strain relationship simulation system 100 (in step S108). First, the first simulation unit 13 executes a stress-strain relationship simulation process (first simulation process) at the time of press forming (step S110). Here, the simulation start instruction includes information such as the type of plastic constitutive equation, the type of parameter, the Young's modulus, the Poisson's ratio, the Lankford value, and the like used for the simulation, information on the data for finite element analysis, and the like. The start instruction may be configured to be instructed by the user via the input device 70, or may be configured to automatically input a start instruction for the identification result after the identification processing.

As described above, since the first simulation unit 13 performs a simulation using the finite element method, when a start instruction is given, first, finite element analysis data is acquired (step S300). The data for finite element analysis includes mesh data for dividing the material into meshes, data defining the stress conditions and boundary conditions of each mesh (finite element), and the like.
When the finite element analysis data is acquired, the first simulation unit 13 then stores the identification result specified by the start instruction and the plastic constitutive equation information (subroutine) via the plastic constitutive equation information storage unit 12. Obtained from the device 70 (step S302). Here, the plastic constitutive equation information having the same contents as the plastic constitutive equation used in the identification process is acquired.

  When the identification result and plastic constitutive equation information (subroutine) are acquired, the stress-strain relationship at the time of press forming is simulated using the plastic constitutive equation information to which the identification result is input (step S304). Here, the behavior when a uniaxial tension / compression deformation is applied to a high-tensile steel plate as a target material is simulated. Specifically, the stress-strain relationship with respect to the forced displacement and reaction force is simulated.

When the simulation process of the stress-strain relationship during press forming is completed, the first simulation unit 13 outputs the result of this simulation to the second simulation unit 14 (step S306).
On the other hand, when the second simulation unit 14 acquires the result of the simulation by the first simulation unit 13 (the branch of “Yes” in step S400), the same type of parameter identification as that used in the first simulation unit 13 is obtained. The result and the same plastic constitutive equation information (subroutine) used in the parameter identification unit 11 and the first simulating unit 13 are acquired from the storage device 70 via the plastic constitutive equation information storage unit 12 (step S402). . These pieces of information may be received directly from the first simulation unit 13 without using the plastic constitutive equation information storage unit 12.

  When the identification result and the plastic constitutive equation information (subroutine) are acquired, the second simulating unit 14 simulates the stress-strain relationship at the time of springback using the plastic constitutive equation information to which the identification result is input (step). S404). Specifically, the spring back amount of the material to be formed that occurs after press forming is calculated based on the result of the simulation by the first simulating unit 13.

When the simulation process of the stress-strain relationship in the springback process is completed, the second simulation unit 14 uses the simulation result (hereinafter referred to as the second simulation result) as a result of the simulation by the first simulation unit 13. (Hereinafter referred to as a first simulation result) and output to the image display unit 15 (step S406).
When the image display unit 15 acquires the first simulation result and the second simulation result from the second simulation unit 14, the stress at the time of press forming is obtained from the first simulation result with the horizontal axis as strain and the vertical axis as stress. -As shown in FIG. 12, the graph of a strain relation is displayed as an image (step S114).

As shown in FIG. 12, in the process of compressive deformation after tensile deformation, re-yielding has begun at an early stage, and it can be seen that the Bauschinger effect can be reproduced.
Further, the image display unit 15 generates a graph of the amount of springback from the second simulation result, and displays this graph as an image (step S114).
As described above, according to the stress-strain relationship simulation system 100 of the present embodiment, when the parameter identification unit 11 adds a parameter to the ordinary parameter in the plastic constitutive equation, the identification of the ordinary parameter is first performed. And using this identification result as an initial value, it is possible to identify parameters including additional components. Thereby, compared with the case where all the parameters including an additional part are identified simultaneously, the result of a favorable simulation can be obtained.

  Further, in the parameter identification unit 11, the first simulation unit 13, and the second simulation unit 14, it is possible to perform identification processing and various simulation processing using the same plastic constitutive equation information (subroutine). is there. As a result, the contents of the plastic constitutive equation (including the calculation algorithm) such as the hardening model, flow law, yield function, parameter type, etc. are common to the respective parts, and it is possible to obtain more accurate simulation results. Become.

Further, the image display unit 15 can display information based on the identification result and information based on various simulation results. As a result, the identification result and the simulation result can be visually and easily understood.
In the above embodiment, the test result acquisition unit 10 corresponds to the test result acquisition unit described in claim 7, and the first simulation unit 13 and the second simulation unit 14 include the simulation unit described in claim 7. The parameter identification unit 11 corresponds to the parameter identification unit according to any one of claims 7, 9 and 10, and the image display unit 15 corresponds to the image display unit according to claim 12.

  Moreover, in the said embodiment, step S102 respond | corresponds to the test result acquisition process of Claim 1 or 13, and step S104 corresponds to any one of Claim 1, 3, 4, 13, 15, and 16. Corresponding to the described parameter identification processing, Step S110 and Step S112 correspond to the simulation processing according to Claim 1 or 13, and Step S114 corresponds to the image display processing according to Claim 6 or 18.

  In the above embodiment, the processing flow of the stress-strain relationship simulation system 100 will be described using a plastic constitutive equation combining the Yoshida-Uemori model and the Hill yield function (1948) as an example. However, the present invention is not limited to this, and the present invention is also applicable to a plastic constitutive equation with a different yield function combined with the Yoshida-Uemori model and other plastic constitutive equations not using the Yoshida-Uemori model. Is possible.

Further, in the above-described embodiment, when a new parameter is added to a normal parameter, the example in which the parameter identification process is performed in a plurality of times has been described. However, the present invention is not limited to this. A part may be identified first, and parameters including the remaining parameters may be identified using the identification result.
Moreover, in the said embodiment, although the stress-strain relationship simulation system 100 was comprised as one apparatus, it is not restricted to this, The stress-strain relationship simulation system 100 is isolate | separated into a some component and each separated. It is good also as a structure which connected between several apparatuses which comprise a component so that data communication was possible.

  For example, the apparatus V includes the test result acquisition unit 10 and the parameter identification unit 11, the apparatus W includes the first simulation unit 13 and the second simulation unit 14, and includes the plastic constitutive equation information storage unit 12. A device Z composed of the device X and the image display unit 15 is configured, and the devices V, W, X, and Z are connected via a network or the like so that they can communicate with each other. .

It is a block diagram which shows the structure of the function of the stress-strain relationship simulation system 100 which concerns on this invention. It is a figure which shows the hardware constitutions of the stress-strain relationship simulation system 100 which concerns on this invention. 3 is a flowchart showing a processing flow of a stress-strain relationship simulation system 100. 3 is a flowchart showing a flow of parameter identification processing in a parameter identification unit 11. 4 is a flowchart showing a flow of first simulation processing in a first simulation unit 13. 6 is a flowchart showing a flow of a second simulation process in the second simulation unit 14. It is a figure which shows a Yoshida-Uemori model typically. (A) And (b) is a figure which shows an example of a Non-IH (Isotropic Hardening: isotropic hardening) area | region. (A) And (b) is a figure which shows the relationship between the limit curved surface BS and a Non-IH area | region. It is a figure which shows the example of an image display at the time of performing the process which identifies parameters other than an additional part previously. It is a figure which shows the example of an image display at the time of performing the process which identifies all the parameters simultaneously. It is a figure which shows an example of the result of the simulation of the stress-strain relationship at the time of press molding. It is a figure which shows the mode of a springback phenomenon, taking a distortion on a horizontal axis and taking a stress on a vertical axis | shaft. (A) And (b) is a figure which shows the mode of the change of the yield surface S in an isotropic hardening model. (A) And (b) is a figure which shows the mode of the change of the yield surface S in a kinematic hardening model.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Test result acquisition part 11 Parameter identification part 12 Plastic constitutive equation information storage part 13 1st simulation part 14 2nd simulation part 15 Image display part 100 Stress-strain relation simulation system

Claims (19)

Press forming the stress-strain relationship of the material to be molded by a plastic constitutive equation configured by combining a hardening model that models the hardening law of the material to be molded and a yield function that gives yield conditions for the material to be formed. A stress-strain relationship simulation method for simulating the stress-strain relationship of the workpiece in
A test result acquisition process for acquiring a result of a test for applying a load in the tension direction and the compression direction to the material to be molded;
A parameter identification process for identifying a parameter of the plastic constitutive equation based on the result of the test;
Using a plastic constitutive equation in which the identified parameters are input, and simulating a stress-strain relationship of the workpiece,
A stress-strain relationship simulation method using the same plastic constitutive equation in the parameter identification process and the simulation process.   The method for simulating the stress-strain relationship includes performing at least one of a process for simulating a stress-strain relationship during press forming and a process for simulating a stress-strain relationship during spring back. Item 2. The stress-strain relationship simulation method according to Item 1.   In the parameter identification process, when identifying a plurality of the parameters, a part of the plurality of parameters is identified first, and then the remaining parameters are converted using the plastic constitutive equation to which the identification result is input. 3. The stress-strain relationship simulation method according to claim 1, wherein identification of parameters including the identification is performed. When a new parameter is added to the plastic constitutive equation,
In the parameter identification process, parameters other than the added parameter are identified first, and then a parameter including the added new parameter is identified using a plastic constitutive equation to which the identification result is input. The stress-strain relationship simulation method according to claim 3.   The stress-strain relationship simulation method according to claim 1, wherein the hardening model is a Yoshida-Uemori model.   The stress-strain relationship simulation method according to claim 1, further comprising an image display process of information related to a simulation result by the simulation method. Press forming the stress-strain relationship of the material to be molded by a plastic constitutive equation configured by combining a hardening model that models the hardening law of the material to be molded and a yield function that gives yield conditions for the material to be formed. A stress-strain relationship simulation system for simulating the stress-strain relationship of the workpiece in
A test result acquisition means for acquiring a result of a test for applying a load in the tensile direction and the compression direction to the material to be molded;
Parameter identifying means for identifying the parameters of the plastic constitutive equation based on the results of the test;
Using a plastic constitutive equation in which the identified parameters are input, and a simulation means for simulating the stress-strain relationship of the molding material,
The parameter identification means and the simulation means use the same plastic constitutive equation, and the stress-strain relationship simulation system.   The stress-strain relationship simulation system includes at least one of means for simulating a stress-strain relationship during press forming and means for simulating a stress-strain relationship during a springback process. Item 8. The stress-strain relationship simulation system according to Item 7.   The parameter identification means first identifies a part of the plurality of parameters when identifying the plurality of parameters, and then uses the plastic constitutive equation to which the identification result is input to determine the remaining parameters. 9. The stress-strain relationship simulation system according to claim 7, wherein identification of parameters including the identification is performed. When a new parameter is added to the plastic constitutive equation,
The parameter identification unit first identifies a parameter other than the added parameter, and then identifies a parameter including the added new parameter using a plastic constitutive equation to which the identification result is input. The stress-strain relationship simulation system according to claim 9.   The stress-strain relationship simulation system according to any one of claims 7 to 10, wherein the hardening model is a Yoshida-Uemori model.   The stress-strain relationship simulation system according to any one of claims 7 to 11, further comprising image display means for displaying information related to a simulation result by the simulation system. Press forming the stress-strain relationship of the material to be molded by a plastic constitutive equation configured by combining a hardening model that models the hardening law of the material to be molded and a yield function that gives yield conditions for the material to be formed. A stress-strain relationship simulation program for simulating the stress-strain relationship of the material to be molded in
A test result acquisition process for acquiring a result of a test for applying a load in the tension direction and the compression direction to the material to be molded;
A parameter identification process for identifying a parameter of the plastic constitutive equation based on the result of the test;
A program for causing a computer to execute a process consisting of a simulation process for simulating a stress-strain relationship of the material to be molded, using a plastic constitutive equation in which the identified parameters are input;
A stress-strain relationship simulation program using the same plastic constitutive equation in the parameter identification process and the simulation process.   The stress-strain relation simulation program includes at least one of a process for simulating a stress-strain relation during press forming and a process for simulating a stress-strain relation during spring back. 13. The stress-strain relationship simulation program according to 13.   In the parameter identification process, when identifying a plurality of the parameters, a part of the plurality of parameters is identified first, and then the remaining parameters are input using the plastic constitutive equation to which the identification result is input. 15. The stress-strain relationship simulation program according to claim 13, wherein parameters including When a new parameter is added to the plastic constitutive equation,
In the parameter identification process, parameters other than the added parameter are identified first, and then a parameter including the added new parameter is identified using a plastic constitutive equation to which the identification result is input. The stress-strain relationship simulation program according to claim 15.   The stress-strain relationship simulation program according to any one of claims 13 to 16, wherein the hardening model is a Yoshida-Uemori model.   The stress-strain relationship simulation program according to any one of claims 13 to 17, further comprising a program for causing a computer to execute an image display process of information relating to a simulation result by the simulation program.   A computer-readable recording medium on which the stress-strain relationship simulation program according to any one of claims 13 to 18 is recorded.

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