WO2020204060A1

WO2020204060A1 - Bending angle prediction method, bending angle prediction device, program, and recording medium

Info

Publication number: WO2020204060A1
Application number: PCT/JP2020/014990
Authority: WO
Inventors: 孝博相藤; 繁米村
Original assignee: 日本製鉄株式会社
Priority date: 2019-04-01
Filing date: 2020-04-01
Publication date: 2020-10-08
Also published as: JP7243816B2; JPWO2020204060A1

Abstract

This bending angle prediction method includes: a first step for acquiring, on the basis of the material characteristics of a steel material, the bending angle of which is to be predicted, the maximum main strain of an outermost bending surface of the steel material; and a second step for calculating a limit VDA bending angle of the steel material by inputting the sheet thickness of the steel material and the maximum main strain of the outermost bending surface of the steel material acquired in the first step to a relational expression that is predetermined by using a finite element method and that defines the limit VDA bending angle through a function of the sheet thickness and the maximum main strain of the outermost bending surface. As a result, with respect to a steel material having intended material characteristics, a limit VDA bending angle in any sheet thickness after deformation can be easily and accurately acquired, for example, when sheet thickness has changed as a result of preliminary deformation performed in a previous step.

Description

Bending angle prediction method, bending angle prediction device, program and recording medium

The present invention relates to a bending angle prediction method, a bending angle prediction device, a program, and a recording medium.

In recent years, as a method for accurately evaluating the bending characteristics of steel plates used for, for example, the body of an automobile, which is necessary for evaluating the deformation behavior and impact energy absorption characteristics of the vehicle body at the time of a collision of an automobile, the VDA German Association of the Automotive Industry An evaluation method using a plate bending test (VDA bending test) for a metal material according to a test standard (Non-Patent Document 1) is becoming widespread. In the VDA bending test, a steel sheet is bent while pushing a punch between a pair of rolls, and the bending angle of the steel sheet at the timing when the reaction force of the punch becomes the maximum value is defined as the limit VDA bending angle of the steel sheet. According to this evaluation method, not only can the limit bending angle be determined from the continuous bending angle data, but there is an advantage that the measurer does not vary.

Japanese Unexamined Patent Publication No. 2012-11458 Japanese Patent No. 6330981 Japanese Unexamined Patent Publication No. 2011-141237

Generally, automobile members are formed by press forming a steel plate. During this press forming, tensile force and compressive force are applied to the steel sheet, and depending on the part of the steel sheet, the thickness may be reduced or increased, which is several percent of the thickness of the steel sheet before press forming. There are some parts where the plate thickness fluctuates by more than 10%.

The car body is assembled by welding the press-molded members, and when the collision deformation prediction of the car body is performed by finite element analysis on the computer, the stress introduced in the press-molding process, which is the previous process. It is known that the prediction accuracy of collision deformation is further improved by mapping the strain and plate thickness distribution to the model of collision deformation analysis and performing collision deformation analysis.

On the other hand, since fracture may occur at the bent portion at the time of collision, an attempt to predict bending fracture at the time of collision deformation analysis using, for example, the value of the limit VDA bending angle of the steel sheet is also considered in the collision deformation analysis. There is.

However, since the limit VDA bending angle obtained from the VDA bending test is a value that changes depending on the plate thickness of the steel plate, it is necessary to perform the test for each steel type and plate thickness. Therefore, for example, in the first step, when the press molding is performed as described above and a portion where the plate thickness of the steel plate is changed occurs, the value of the limit VDA bending angle is also increased according to the plate thickness distribution after molding. It will be changing. However, the fluctuation of the plate thickness in the part during molding is wide-ranging, and it is extremely difficult to prepare the test pieces of all the plate thicknesses and perform the VDA bending test. Therefore, when predicting bending fracture at the time of collision deformation of the vehicle body in the second step, it is not enough to obtain the stress, strain and plate thickness distribution in the press forming process which is the first step, and the plate thickness fluctuates. It is necessary to obtain the limit VDA bending angle for each part according to the situation, but it is extremely difficult.

The present invention has been made in view of the above problems, and the maximum principal strain of the outermost surface layer of the bent steel material is obtained by using the finite element method with the material properties and plate thickness of the steel material as input values. The limit VDA bending angle of the steel material is calculated based on the above, that is, for a steel material having arbitrary material properties, for example, when the plate thickness fluctuates due to pre-deformation in the previous step, in an arbitrary plate thickness after deformation. It is possible to easily and accurately obtain the limit VDA bending angle, and to predict the bending fracture of steel materials using the result, which contributes to a significant reduction in the cost required for product development and shortening of the development period. It is an object of the present invention to provide a bending angle prediction method, a bending angle prediction device, a program, and a recording medium capable of predicting the bending angle.

In order to solve the above problems, as a result of diligent studies, we came up with the following aspects of the invention. The gist of the present invention is as follows.

(1)
The first step of obtaining the maximum principal strain of the outermost surface layer of the steel material based on the material properties of the steel material for which the bending angle is predicted, and
The thickness of the steel material and the thickness of the steel material and the first step were obtained by the relational expression in which the limit VDA bending angle was defined by the function of the plate thickness and the maximum principal strain of the outermost surface layer of the bending, which was defined by using the finite element method. The second step of calculating the limit VDA bending angle of the steel material by inputting (substituting) the maximum principal strain of the outermost surface layer of the bending of the steel material, and
A bending angle prediction method characterized by being provided with.

(2)
The first step is to obtain the maximum principal strain of the bent outermost surface layer of the steel material corresponding to the material characteristics of the steel material based on the relationship in which the maximum principal strain of the bent outermost surface layer is uniquely determined from the material properties. The bending angle prediction method according to (1), which is a feature.

(3)
In the above relational expression, the limit VDA bending angle is θ.
θ = exp {(ε _b −b) / a}
ε _b : The bending angle prediction method according to claim 1 or 2, wherein a: the maximum principal strain of the outermost surface layer of bending a: the relational expression of the plate thickness t b: the relational expression of the plate thickness t.

(4)
The bending angle prediction method according to any one of (1) to (3), wherein the plate thickness of the steel material is a value after undergoing pre-deformation.

(5)
The bending angle prediction method according to any one of (1) to (4), wherein the steel material is a steel plate of a steel type of 980 MPa class or higher.

(6)
An acquisition unit that acquires the maximum principal strain of the outermost surface layer of the steel material based on the material properties of the steel material for which the bending angle is predicted, and the acquisition unit.
The plate thickness of the steel material and the plate thickness of the first step were obtained by the relational expression in which the limit VDA bending angle was defined by the function of the plate thickness and the maximum principal strain of the outermost surface layer of the bending, which was defined by using the finite element method. A calculation unit that calculates the limit VDA bending angle of the steel material by inputting (substituting) the maximum principal strain of the outermost surface layer of the steel material.
Bending angle prediction device characterized by being equipped with.

(7)
The acquisition unit is characterized by acquiring the maximum principal strain of the bent outermost surface layer of the steel material corresponding to the material characteristics of the steel material based on the relationship in which the maximum principal strain of the bent outermost surface layer is uniquely determined from the material characteristics. The bending angle prediction device according to (6).

(8)
In the above relational expression, the limit VDA bending angle is θ.
θ = exp {(ε _b −b) / a}
ε _b : Maximum principal strain of the outermost surface layer of bending a: Relational expression of plate thickness t b: Bending angle prediction device according to (6) or (7), which is represented by the relational expression of plate thickness t. ..

(9)
The bending angle predictor according to any one of (6) to (8), wherein the plate thickness of the steel material is a value after undergoing pre-deformation.

(10)
The bending angle predictor according to any one of (6) to (9), wherein the steel material is a steel plate of a steel type of 980 MPa class or higher.

(11)
The first step of obtaining the maximum principal strain of the outermost surface layer of the steel material based on the material properties of the steel material for which the bending angle is predicted, and
The plate thickness of the steel material and the plate thickness of the steel material and the first step were obtained by the relational expression in which the limit VDA bending angle was defined by the function of the plate thickness and the maximum principal strain of the outermost surface layer of the bending, which was defined by using the finite element method. The second step of calculating the limit VDA bending angle of the steel material by inputting (substituting) the maximum principal strain of the outermost surface layer of the bending of the steel material, and
An angle prediction program that lets your computer run.

(12)
The first step is to obtain the maximum principal strain of the bent outermost surface layer of the steel material corresponding to the material characteristics of the steel material based on the relationship in which the maximum principal strain of the bent outermost surface layer is uniquely determined from the material properties. The bending angle prediction program according to (11).

(13)
In the above relational expression, the limit VDA bending angle is θ.
θ = exp {(ε _b −b) / a}
ε _b : Maximum principal strain of the outermost surface layer of bending a: Relational expression of plate thickness t b: Bending angle prediction program according to (11) or (12), which is represented by the relational expression of plate thickness t. ..

(14)
The bending angle prediction program according to any one of (11) to (13), wherein the plate thickness of the steel material is a value after undergoing pre-deformation.

(15)
The bending angle prediction program according to any one of (11) to (14), wherein the steel material is a steel plate of a steel type of 980 MPa class or higher.

(16)
A computer-readable recording medium comprising recording the angle prediction program according to any one of (11) to (15).

According to the present invention, the limit VDA bending at an arbitrary plate thickness after deformation is performed for a steel material having arbitrary material properties by using the finite element method, for example, when the plate thickness fluctuates due to pre-deformation in the previous process. It is possible to obtain the angle easily and accurately. In addition, the presence or absence of bending fracture of the steel material can be predicted by using the obtained limit VDA bending angle. As a result, it is possible to omit the collision test on the actual automobile member or to significantly reduce the number of collision tests. In addition, since the steel material that prevents breakage during a collision can be designed on a computer, it contributes to a significant cost reduction and shortening of the development period.

FIG. 1A is a perspective view showing how the limit VDA bending angle is experimentally acquired. FIG. 1B is an enlarged front view showing how the limit VDA bending angle is obtained on a trial basis. FIG. 2 is a diagram showing the obtained limit VDA bending angle (experimental value) and the maximum principal strain of the bending outermost surface layer at the bending outer top (solid element detailed FEM analysis value) for each plate thickness. FIG. 3 is a characteristic diagram showing the relationship between the distance from the bending outer top and the maximum principal strain of the bending outer outermost layer. FIG. 4 is a characteristic diagram showing the relationship between the limit VDA bending angle and the maximum principal strain of the outermost surface layer of bending. FIG. 5 is a block diagram showing a bending angle prediction device according to the first embodiment. FIG. 6 is a flow chart showing a bending angle prediction method according to the first embodiment. FIG. 7 is a diagram showing the relationship between the steel grade (strength grade) of the steel sheet and the maximum principal strain on the bending outer side. FIG. 8 is a flow chart showing a bending fracture prediction method according to the second embodiment. FIG. 9 is a flow chart showing a bending fracture prediction method according to the third embodiment. FIG. 10 is a block diagram showing a computer function.

(Basic gist of the present invention)
First, in disclosing the embodiments of the present invention, the basic gist of the present invention will be described.

In this embodiment, as a method for evaluating the bendability of a steel sheet, a test standard called a plate bending test (VDA bending test) for a metal material by the German Association of the Automotive Industry (VDA) is used. As a result of various investigations on the relationship between the fracture of the steel sheet and the material properties of the steel sheet in the VDA bending test, the present inventor found that when the maximum principal strain of the outermost surface layer of the bending reaches the material-specific limit value, the bending fracture in the VDA bending test. Was found to occur.

The state of performing the VDA bending experiment is shown in FIGS. 1A and 1B. The steel plate 10 is placed on the pair of

rolls

21 and 22, and the punch 20 is brought into contact with the central portion (bending center) of the surface of the steel plate 10 between the pair of

rolls

21 and 22. The steel plate 10 is bent while pushing the punch 20, and the bending angle of the steel plate 10 at the timing when the pushing load of the punch is maximized (the timing when the bending break occurs) is defined as the limit VDA bending angle θ (FIG. 1B). The maximum principal strain when the limit VDA bending angle θ is reached at the point P on the back surface corresponding to the contact portion of the punch 20 on the front surface of the steel sheet 10 is defined as the maximum principal strain of the outermost surface layer of bending at the outer top of bending. ..

The obtained limit VDA bending angle (experimental value) and bending at the outer top of the bending were obtained for three types of steel sheets (plate thickness: 1.0 mm, 1.4 mm, 2.3 mm) with a tensile strength class of 1500 MPa and different plate thicknesses. The maximum principal strain of the outer outermost layer (detailed FEM analysis value using a solid element having a mesh size of 0.1 mm) is shown in FIG. Further, for the above three types of steel sheets, the relationship between the distance from the bending outer top and the maximum principal strain of the bending outer outermost layer is shown in FIG.

Generally, in FEM analysis, a detailed FEM model (solid model) using a solid element and a FEM model (shell model) using a shell element are mainly used. The solid model is modeled using a three-dimensional solid element such as a tetrahedron, a hexahedron, or a pentahedron. Generally, the analysis time is long, but the analysis accuracy is high. The shell model is modeled using shell elements that are two-dimensional surface elements such as triangles and quadrangles, and generally, the analysis target is a member composed of plates that are thinner than the length and width. It is often used in targeted analysis and has the advantage of short analysis time. Therefore, even analysis with a large-scale model, which cannot be analyzed with a solid model, can be performed by using shell elements.

As shown in FIGS. 2 and 3, the limit VDA bending angles obtained in the experiment were 75 °, 65 °, and 55 ° for each steel sheet having a thickness of 1.0 mm, 1.4 mm, and 2.3 mm. ..

Create an FEM model that reproduces the VDA bending experiment, use solid elements with high strain reproduction accuracy, and model with a detailed mesh with a size of, for example, about 0.1 mm. Using this FEM model, in the VDA bending experiment, the punch is pushed to the bending angle at which the fracture occurred (limit VDA bending angle), the maximum principal strain on the bending outside of the steel sheet at that time is obtained, and the relationship with the limit VDA bending angle is determined. investigated. As a result, as shown in FIGS. 2 and 3, the maximum bending outer maximum principal strain at the bending outer top is 0.386, 0.396, for each steel sheet having the limit VDA bending angles of 75 °, 65 ° and 55 °. It was 0.393, showing a value that can be regarded as almost the same. That is, it was found that the maximum principal strain on the bending outer side at the bending outer top is almost the same value regardless of the plate thickness, even though the limit VDA bending angle is changed due to the difference in the plate thickness of the steel plate. It was. Hereinafter, for convenience of description, the maximum principal strain of the outermost surface layer of the bent outer surface of the bent outermost layer is simply referred to as "the maximum principal strain of the outermost surface layer of the bent outer layer".

When the FEM model consisting of detailed solid elements is used, the present inventor applies bending deformation to the limit VDA bending angle at each plate thickness even if the plate thickness is different if the steel plate is of the same steel type. Using the above findings that the maximum principal strains of the outermost surface layer of bending are almost equal, the limit VDA bending angles at various plate thicknesses were obtained from FEM analysis. Similarly, for other steel types, analysis was performed using an FEM model composed of detailed solid elements, and the limit VDA bending angle at each plate thickness was obtained. FIG. 4 shows the results of plotting the relationship between a large number of limit VDA bending angles and the maximum principal strain of the outermost surface layer of bending at various steel types and various plate thicknesses obtained in this way. In FIG. 4, the plate thickness is shown as t ₁ , t ₂ , and t ₃ .

From FIG. 4, the present inventor found that the maximum principal strain of the outermost surface layer of bending due to the solid element is represented by a function of the limit VDA bending angle and the plate thickness. The present inventor scrutinized this finding to embody it, and found that the maximum principal strain of the outermost surface layer of bending due to the lid element was formulated by the linear logarithm of the limit VDA bending angle for each plate thickness regardless of the steel type. I found out what I could do.

Bending by a solid element The maximum principal strain of the outermost surface layer is ε _b , the limit VDA bending angle is θ, and ε _b is expressed using coefficients a and b as follows.
ε _b = a · ln (θ) + b ··· (1)

The coefficient a and the coefficient b are represented by the relational expression of the plate thickness t. This relational expression is determined to fit the test result by the above equation (1), and the form of the equation is not particularly limited, but can be expressed by, for example, a polynomial of plate thickness t.

From the above equation (1), if the limit VDA bending angle θ is solved, θ is expressed as follows.
θ = exp {(ε _b − b) / a} ・・・・ (2)

In the present embodiment, the limit VDA bending angle of the steel sheet at an arbitrary steel type and an arbitrary plate thickness is calculated by using the equation (2) defined as described above. That is, in the present embodiment, the limit VDA bending angle can be obtained extremely easily, in a short time, and accurately without performing a test or simulation.

(First Embodiment)
In the first embodiment, a bending angle prediction method and a bending angle prediction device for a steel plate, which is a steel material, will be described in detail with reference to the drawings. FIG. 5 is a block diagram showing a bending angle prediction device according to the first embodiment, and FIG. 6 is a flow diagram showing a bending angle prediction method according to the first embodiment.

As shown in FIG. 5, the bending angle prediction device according to the present embodiment includes a steel grade (strength grade) determination unit 1, a maximum main strain acquisition unit 2, and an angle calculation unit 3.
When predicting the limit VDA bending angle of a steel sheet, first, the material properties of the steel sheet are input to the steel type (strength grade) determination unit 1 from the input file. Specifically, as the material property, there is a Swift coefficient obtained by fitting a tensile strength property corresponding to the material property, for example, a stress-strain curve or a stress-strain curve by a Swift equation.

In step S1, the steel type (strength grade) determination unit 1 determines the steel type (strength grade) of the steel sheet based on the input material properties of the steel sheet.
In the present embodiment, as the steel type of the steel sheet, it is particularly preferable to target a steel sheet of 980 MPa class or higher. Since the steel sheet in which bending fracture is a problem is mainly a high-strength material, in the present embodiment, a steel sheet of 980 MPa class or higher is applied to the fracture prediction as a specific index of the high-strength material.

In the maximum principal strain acquisition section 2, the relationship is such that the maximum principal strain of the outermost surface layer of the bent steel sheet is uniquely determined from the steel sheet grade (strength grade) of the steel sheet, for example, as shown in FIG. A table showing the relationship with the main strain is stored. In the table, the maximum principal strain on the outside of the bend is almost the same value regardless of the plate thickness according to the steel type (strength grade), and the plate thickness is arbitrary for each steel type (strength grade). The maximum principal strain on the outside of the obtained bend is listed. In step S2, the maximum principal strain acquisition unit 2 acquires the maximum principal strain on the bending outer side from the above table based on the steel grade (strength grade) of the steel sheet determined in step S1.

In the angle calculation unit 3, a predetermined plate thickness of the steel plate for each element from the input file, here, the plate thickness after pre-deformation and the maximum principal strain of the outermost surface layer of bending acquired by the maximum principal strain acquisition unit 2 are obtained. Entered. In step S3, the angle calculation unit 3 uses the above equation (2) to preliminarily predict the steel sheet based on the plate thickness after pre-deformation of the steel sheet and the maximum principal strain of the outermost surface layer of bending, which are input for each element. The limit VDA bending angle after deformation is calculated.

As described above, according to the present embodiment, when the plate thickness of a steel material having arbitrary material properties fluctuates due to pre-deformation in the previous process, for example, any arbitrary material after deformation is used by FEM analysis. The limit VDA bending angle in the plate thickness can be easily and accurately obtained.

(Second Embodiment)
In the second embodiment, a bending fracture prediction method for a steel sheet using the bending angle prediction method according to the first embodiment will be described in detail with reference to the drawings. In this embodiment, a method for predicting bending fracture of a steel sheet when the thickness of the steel sheet fluctuates due to pre-deformation in a plurality of forming steps in the press forming analysis is illustrated. FIG. 8 is a flow chart showing a bending fracture prediction method according to the second embodiment.

Automobile parts are generally formed by press forming a steel plate. Usually, press molding involves forming a steel sheet into a final shape through a plurality of steps such as a draw forming step, a bending forming step, a trim forming step, and a wrist-like forming step. If it is a soft steel sheet, fracture rarely occurs during bending and forming, but for example, when a high-strength steel sheet exceeding 980 MPa is press-formed, fracture may occur at the bent portion. In this embodiment, the draw forming step and the bending forming step are illustrated, and the drawing forming step is described as the first forming analysis step S10, and the bending forming step is described as the second forming analysis step S20.

In the draw forming process, when draw forming is performed on a steel sheet, for example, the shoulder portion is subjected to tensile deformation due to the pushing of a punch, and the plate thickness is reduced. On the other hand, when the material flows in due to the pushing of the punch, the peripheral portion (die flange portion) of the component is deformed by compression due to the reduction of the peripheral length, and the plate thickness increases.

In the present embodiment, first, in step S11, FEM analysis is performed on the draw forming step of the first forming analysis step S10.
Subsequently, in step S12, the plate thickness and strain component of the steel sheet after drawing and forming are acquired for each element (mesh) of the FEM model in the first forming analysis step S10.

Subsequently, in step S21, the plate thickness and strain component of the steel plate acquired in step S12 are taken over and mapped to each element of the FEM model of the bending forming step which is the second forming analysis step S20.

Subsequently, in step S22, steps S1 to S3 of the bending angle prediction method according to the first embodiment shown in FIG. 6 are executed, and the limit VDA bending angle in the plate thickness after pre-deformation of the steel plate is calculated.

Subsequently, in step S23, FEM analysis is performed on the bending molding step of the second molding analysis step S20.
Then, in step S24, it is determined whether or not bending breakage occurs for each element of the FEM model in the second molding analysis step S20, and the element determined to cause breakage is deleted.
As described above, the bending fracture of the steel sheet can be accurately predicted by FEM analysis.

In FEM molding analysis of automobile parts, it is a large-scale model, so it is generally difficult to model with detailed solid elements because the calculation load is too high. Therefore, it is often modeled with a shell element having a small calculation load and a relatively coarse element size of, for example, about 1 mm to 5 mm. When modeled with a shell element, the strain is averaged within the element at a site where strain is locally concentrated, such as the bent top of a steel plate, so it is calculated according to the element size used. It is known that the strain values are different. In the present embodiment, after capturing the change in strain for each element size of the shell element, in step S24, the limit strain on the bending outside of the shell element at the limit VDA bending angle is obtained, and the shell element under molding analysis is being analyzed. Fracture can also be predicted by whether or not the maximum principal strain of the outermost surface layer of the bend reaches the limit strain on the outer side of the bend.

The strain applied by the pre-deformation in the first molding step is naturally inherited in the second molding step. Therefore, also in the FEM analysis, the strain component is acquired together with the plate thickness after the first molding analysis step S10 and mapped to each element of the FEM model in the second molding analysis step S20. As a result, it is possible to further improve the accuracy when predicting fracture based on whether or not the strain on the bending outer side of the shell element reaches the limit strain.

In step S24, the presence or absence of fracture is determined based on whether or not the bending angle of the steel sheet reaches the limit VDA bending angle in the FEM analysis without converting the limit VDA bending angle into the limit strain on the outside of the bending of the shell element. You can also do it.

As described above, according to the present embodiment, the presence or absence of bending fracture of the steel material is accurately predicted by using the limit VDA bending angle obtained by using the bending angle prediction method according to the first embodiment. As a result, the steel sheet that prevents bending fracture can be designed on the computer, which contributes to a significant cost reduction and shortening of the development period.

(Third Embodiment)
In the third embodiment, a bending fracture prediction method for a steel sheet using the bending angle prediction method according to the first embodiment will be described in detail with reference to the drawings. In this embodiment, in the press forming analysis and the subsequent collision analysis, a method for predicting bending fracture of a steel sheet when the sheet thickness fluctuates due to pre-deformation is illustrated. FIG. 9 is a flow chart showing a bending fracture prediction method according to the third embodiment.

Automobile parts are generally formed by press forming a steel plate, and then an automobile body is formed through an assembly process such as welding. From the viewpoint of collision safety, automobile bodies are required to absorb energy while generating the target reaction force at the time of a collision, but if the steel plate breaks at the time of a collision, the target reaction force may not be obtained. .. Therefore, it is required to perform FEM analysis of collision and predict rupture in advance.

At the time of a collision, each steel material of the automobile body undergoes various deformations, and the steel plate undergoes bending deformation at the part where it is compressed and buckled by the collision input. If it is a soft steel sheet, fracture rarely occurs during bending deformation, but if it is a high-strength steel sheet exceeding 980 MPa, for example, fracture may occur during bending deformation.

In the process of press forming a steel sheet, for example, the shoulder portion is subjected to tensile deformation due to pushing of a punch, and the plate thickness is reduced. On the other hand, when the material flows in due to the pushing of the punch, the peripheral portion (die flange portion) of the component is subjected to compression deformation due to the contraction of the peripheral length, and the plate thickness increases.

In the present embodiment, first, in step S31, FEM analysis is performed in the steel sheet forming analysis step S30.
Subsequently, in step S32, the plate thickness and strain component of the molded steel sheet are acquired for each element (mesh) of the FEM model in the molding analysis step S30.

Subsequently, in step S41, the plate thickness and strain component of the steel plate acquired in step S32 are taken over and mapped to each element of the FEM model in the collision analysis step S40.

Subsequently, in step S42, steps S1 to S3 of the bending angle prediction method according to the first embodiment shown in FIG. 2 are executed, and the limit VDA bending angle in the plate thickness after pre-deformation of the steel plate is calculated.

Subsequently, in step S43, FEM analysis is performed in the collision analysis step S40.
Then, in step S44, it is determined whether or not bending breakage occurs for each element of the FEM model in the collision analysis step S40, and the element determined to cause breakage is deleted.
From the above, it is possible to accurately predict bending fracture at the time of a collision of an automobile body on FEM analysis.

Also in the present embodiment, as in the second embodiment, after capturing the change in strain for each element size of the shell element, in step S44, the limit strain on the bending outside of the shell element at the limit VDA bending angle is determined. Fracture is predicted by determining whether or not the maximum principal strain of the outermost bending outer layer of the shell element during the molding analysis reaches the limit strain on the outer bending side.

The strain applied by the pre-deformation in the molding process is naturally inherited in the collision process. Therefore, also in the FEM analysis, the strain component is acquired together with the plate thickness after the molding analysis step S30 and mapped to each element of the FEM model in the collision analysis step S40. As a result, it is possible to further improve the accuracy when predicting fracture based on whether or not the strain on the bending outer side of the shell element reaches the limit strain.

In step S44, the presence or absence of fracture is determined by whether or not the bending angle of the steel sheet reaches the limit VDA bending angle in the FEM analysis without converting the limit VDA bending angle into the limit strain outside the bending of the shell element. You can also do it.

As described above, according to the present embodiment, the presence or absence of bending fracture of the steel material is accurately predicted by using the limit VDA bending angle obtained by using the bending angle prediction method according to the first embodiment. As a result, it is possible to omit the collision test on the actual automobile member or to significantly reduce the number of collision tests. In addition, since the steel material that prevents breakage during a collision can be designed on a computer, it contributes to a significant cost reduction and shortening of the development period.

(Fourth Embodiment)
The steel grade (strength grade) determination unit 1, the maximum principal strain acquisition unit 2, and the angle calculation unit 3 shown in FIG. 5, which are the components of the bending angle prediction device according to the first embodiment described above, are dedicated hardware. It may be realized by. In addition, each of the above components is composed of a memory and a CPU (Central Processing Unit), and the functions are realized by loading and executing a program for realizing various functions of each component in the memory. There may be.

Further, a program for realizing various functions of each of the above components (steps S1 to S3 of the angle prediction method of FIG. 6, steps S10 (S11 to S12) and S20 (S21 to S24) of the bending break prediction method of FIG. ), Steps S30 (S31 to S32) and S40 (S41 to S44) of the bending break prediction method of FIG. 9 are recorded on a computer-readable recording medium, and the program recorded on the recording medium is read into the computer system. , The processing of each of the above-mentioned components may be executed by executing the above. Note that the "computer system" here includes hardware such as an OS and peripheral devices.

Further, the "computer system" may include a homepage providing environment (or display environment) as long as the WWW system is used.
Further, the "computer-readable recording medium" refers to a portable medium such as a flexible disk, a magneto-optical disk, a ROM, or a CD-ROM, or a storage device such as a hard disk built in a computer system. Further, a "computer-readable recording medium" is a communication line for transmitting a program via a network such as the Internet or a communication line such as a telephone line, and dynamically holds the program for a short period of time. It may also include a program that holds a program for a certain period of time, such as a volatile memory inside a computer system that serves as a server or a client in that case. Further, the above program may be for realizing a part of the above-mentioned functions, and may be further realized for realizing the above-mentioned functions in combination with a program already recorded in the computer system. ..

As a specific example, the bending angle prediction device and the bending angle prediction method shown in the first to third embodiments, and the bending fracture prediction method are carried out by the computer function 100 as shown in FIG.
The computer function 100 includes a CPU 101, a ROM 102, and a RAM 103. Further, the controller (CONSC) 105 of the operation unit (CONS) 109 and the display controller (DISPC) 106 of the display (DISP) 110 as a display unit such as a CRT or an LCD are provided. Further, it includes a hard disk (HD) 111, a controller (DCONT) 107 of a storage device (STD) 112 such as a flexible disk, and a network interface card (NIC) 108. The

functional units

101, 102, 103, 105, 106, 107, and 108 are connected to each other via the system bus 104 so as to be able to communicate with each other.

The CPU 101 comprehensively controls each component connected to the system bus 104 by executing the software stored in the ROM 102 or the HD 111 or the software supplied from the STD 112. That is, the CPU 101 controls to realize the operation in the present embodiment by reading and executing the processing program (structure design support program) for performing the above-described operation from the ROM 102, HD111, or STD112. I do. The RAM 103 functions as a main memory or a work area of the CPU 101.

The CONSC 105 controls the instruction input from the CONS 109. The DISPC 105 controls the display of the DISP 110. The DCONT 107 controls access to HD111 and STD112 that store boot programs, various applications, user files, network management programs, and the above processing programs in this embodiment. The NIC 108 exchanges data bidirectionally with other devices on the network 113.
Instead of using a normal computer terminal device, a predetermined computer or the like specialized for the bending angle prediction device may be used.

The present invention can be used, for example, in an industry related to steel sheets that are public for automobile parts.

Claims

The first step of obtaining the maximum principal strain of the outermost surface layer of the steel material based on the material properties of the steel material for which the bending angle is predicted, and
The thickness of the steel material and the thickness of the steel material and the first step were obtained by the relational expression in which the limit VDA bending angle was defined by the function of the plate thickness and the maximum principal strain of the outermost surface layer of the bending, which was defined by using the finite element method. The second step of calculating the limit VDA bending angle of the steel material by inputting the maximum principal strain of the outermost surface layer of the bending of the steel material, and
A bending angle prediction method characterized by being provided with.
The first step is to obtain the maximum principal strain of the bent outermost surface layer of the steel material corresponding to the material characteristics of the steel material based on the relationship in which the maximum principal strain of the bent outermost surface layer is uniquely determined from the material properties. The bending angle prediction method according to claim 1, wherein the bending angle is predicted.
In the above relational expression, the limit VDA bending angle is θ.
θ = exp {(ε b −b) / a}
ε b : The bending angle prediction method according to claim 1 or 2, wherein a: the maximum principal strain of the outermost surface layer of bending a: the relational expression of the plate thickness t b: the relational expression of the plate thickness t.
The bending angle prediction method according to any one of claims 1 to 3, wherein the plate thickness of the steel material is a value after undergoing pre-deformation.
The bending angle prediction method according to any one of claims 1 to 4, wherein the steel material is a steel plate of a steel type of 980 MPa class or higher.
An acquisition unit that acquires the maximum principal strain of the outermost surface layer of the steel material based on the material properties of the steel material for which the bending angle is predicted, and the acquisition unit.
The plate thickness of the steel material and the plate thickness of the first step were obtained by the relational expression in which the limit VDA bending angle was defined by the function of the plate thickness and the maximum principal strain of the outermost surface layer of the bending, which was defined by using the finite element method. A calculation unit that inputs the maximum principal strain of the outermost surface layer of the steel material and calculates the limit VDA bending angle of the steel material.
Bending angle prediction device characterized by being equipped with.
The acquisition unit is characterized by acquiring the maximum principal strain of the bent outermost surface layer of the steel material corresponding to the material characteristics of the steel material based on the relationship in which the maximum principal strain of the bent outermost surface layer is uniquely determined from the material characteristics. The bending angle prediction device according to claim 6.
In the above relational expression, the limit VDA bending angle is θ.
θ = exp {(ε b −b) / a}
ε b : The bending angle predicting apparatus according to claim 6 or 7, wherein the maximum principal strain of the outermost surface layer of bending a: the relational expression of the plate thickness t b: the relational expression of the plate thickness t.
The bending angle predictor according to any one of claims 6 to 8, wherein the plate thickness of the steel material is a value after undergoing pre-deformation.
The bending angle predictor according to any one of claims 6 to 9, wherein the steel material is a steel plate of a steel type of 980 MPa class or higher.
The first step of obtaining the maximum principal strain of the outermost surface layer of the steel material based on the material properties of the steel material for which the bending angle is predicted, and
The thickness of the steel material and the thickness of the steel material and the first step were obtained by the relational expression in which the limit VDA bending angle was defined by the function of the plate thickness and the maximum principal strain of the outermost surface layer of the bending, which was defined by using the finite element method. The second step of calculating the limit VDA bending angle of the steel material by inputting the maximum principal strain of the outermost surface layer of the bending of the steel material, and
An angle prediction program that lets your computer run.
The first step is to obtain the maximum principal strain of the bent outermost surface layer of the steel material corresponding to the material characteristics of the steel material based on the relationship in which the maximum principal strain of the bent outermost surface layer is uniquely determined from the material properties. The bending angle prediction program according to claim 11.
In the above relational expression, the limit VDA bending angle is θ.
θ = exp {(ε b −b) / a}
ε b : The bending angle prediction program according to claim 11 or 12, wherein a: the maximum principal strain of the outermost surface layer of bending a: the relational expression of the plate thickness t b: the relational expression of the plate thickness t.
The bending angle prediction program according to any one of claims 11 to 13, wherein the plate thickness of the steel material is a value after undergoing pre-deformation.
The bending angle prediction program according to any one of claims 11 to 14, wherein the steel material is a steel plate of a steel type of 980 MPa class or higher.
A computer-readable recording medium comprising recording the angle prediction program according to any one of claims 11 to 15.