JP7243816B2 - Bending angle prediction method, bending angle prediction device, program and recording medium - Google Patents

Description

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 properties of steel sheets used for automobile bodies, for example, which is necessary when evaluating the deformation behavior and impact energy absorption characteristics of automobile bodies during collisions, the VDA German Automobile Manufacturers Association An evaluation method using a plate bending test (VDA bending test) of metal materials according to the test standard (Non-Patent Document 1) is spreading. In the VDA bending test, a steel plate is bent while pushing a punch between a pair of rolls, and the bending angle of the steel plate at the timing when the reaction force of the punch reaches its maximum value is defined as the limit VDA bending angle of the steel plate. According to this evaluation method, not only can the limit bending angle be determined from continuous bending angle data, but there is also the advantage that there is no variation depending on the operator.

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

VDA 238-100 "Plate bending test for metallic materials" Validation Rule, 01 June 2017

Automobile members are generally formed by press forming a steel plate. During this press forming, tensile and compressive forces are applied to the steel sheet, and depending on the part of the steel sheet, there are parts where the thickness of the steel sheet is reduced or increased. There is a part where the plate thickness fluctuates by ~10%.

Automobile bodies are assembled by welding press-formed members, and when prediction of collision deformation of the automobile body is performed by finite element analysis on a computer, the stress introduced in the press-forming process, which is the preceding process, It is known that the prediction accuracy of impact deformation is improved by performing impact deformation analysis by mapping the strain and plate thickness distribution to the model of impact deformation analysis.

On the other hand, since fracture may occur at the bending part during collision, attempts are being made to predict bending fracture during collision deformation analysis, for example, using the value of the limit VDA bending angle of the steel plate in collision deformation analysis. there is

However, since the limit VDA bending angle obtained from the VDA bending test is a value that varies depending on the plate thickness of the steel plate, it is necessary to test each steel type and plate thickness. Therefore, for example, in the first step, press forming is performed as described above, and if there is a portion where the plate thickness of the steel plate has changed, the value of the limit VDA bending angle is also changed according to the plate thickness distribution after forming. It is changing. However, there are a wide variety of plate thickness variations within a part during molding, and it is extremely difficult to prepare test pieces of all plate thicknesses and perform the VDA bending test. Therefore, in the case of predicting bending fracture at the time of collision deformation of the car body in the second process, it is not enough to acquire the stress, strain and plate thickness distribution in the press forming process which is the first step. Obtaining the corresponding limit VDA bend angle for each site is necessary and extremely difficult.

The present invention has been made in view of the above problems, and uses the finite element method to acquire the maximum principal strain of the outermost surface layer of the steel material using the material properties and plate thickness of the steel material as input values. Calculating the limit VDA bending angle of steel based on It is possible to obtain the limit VDA bending angle easily and accurately, and to predict the bending fracture of steel materials using the result, contributing to a significant reduction in the cost required for product development and a 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 that can predict bending angles.

In order to solve the above problems, as a result of intensive studies, the following aspects of the invention were conceived. The gist of the present invention is as follows.

(1)
A method of predicting a bend angle using a computer, comprising:
a first step of acquiring the maximum principal strain of the outermost surface layer of the steel material on the bending outer side according to the material properties of the steel material whose bending angle is to be predicted;
The relational expression that defines the limit VDA bending angle as a function of the plate thickness and the maximum principal strain of the bending outermost surface layer, which is predetermined using the finite element method, includes the plate thickness of the steel material and the obtained in the first step a second step of inputting (substituting) the maximum principal strain of the bending outermost surface layer of the steel material to calculate the limit VDA bending angle of the steel material;
A bending angle prediction method comprising:

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

(3)
Assuming the limit VDA bending angle as θ, the relational expression is:
θ=exp {( _εb −b)/a}
ε _b : Maximum principal strain of the outermost surface layer on the bending outer side a: Relational expression of plate thickness t b: Relational expression of plate thickness t The bending angle prediction method according to claim 1 or 2, characterized by the following.

(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 being pre-deformed.

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

(6)
an acquisition unit that acquires the maximum principal strain of the outermost surface layer of the steel material for which the bending angle is to be predicted, based on the material properties of the steel material;
The relational expression that defines the limit VDA bending angle as a function of the plate thickness and the maximum principal strain of the outermost surface layer of the bending outermost layer, which is predetermined using the finite element method, includes the plate thickness of the steel material and the obtained in the obtaining unit a calculation unit that inputs (substitutes) the maximum principal strain of the outermost surface layer of the steel material to calculate the limit VDA bending angle of the steel material;
A bending angle prediction device comprising:

(7)
The acquisition unit acquires the maximum principal strain of the outermost surface layer on the bending outer side of the steel material corresponding to the material properties of the steel material based on a relationship that uniquely determines the maximum principal strain on the outermost surface layer on the outermost bending side from the material properties. The bending angle prediction device according to (6).

(8)
Assuming the limit VDA bending angle as θ, the relational expression is:
θ=exp {( _εb −b)/a}
ε _b : Maximum principal strain of the outermost surface layer on the bending outer side a: Relational expression of plate thickness t b: Relational expression of plate thickness t The bending angle prediction device according to (6) or (7) characterized by being represented by .

(9)
The bending angle prediction device according to any one of (6) to (8), wherein the plate thickness of the steel material is a value after being pre-deformed.

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

(11)
a first step of acquiring the maximum principal strain of the outermost surface layer of the steel material on the bending outer side according to the material properties of the steel material whose bending angle is to be predicted;
The relational expression that defines the limit VDA bending angle as a function of the plate thickness and the maximum principal strain of the bending outermost surface layer, which is predetermined using the finite element method, includes the plate thickness of the steel material and the obtained in the first step a second step of inputting (substituting) the maximum principal strain of the bending outermost surface layer of the steel material to calculate the limit VDA bending angle of the steel material;
An angle prediction program that causes a computer to execute

(12)
The first step includes acquiring the maximum principal strain of the outermost surface layer on the bending outer side of the steel material corresponding to the material properties of the steel material, based on the relationship in which the maximum principal strain of the outermost outer layer on the bending outermost layer is uniquely determined from the material properties. The bending angle prediction program according to (11) characterized by the following.

(13)
Assuming the limit VDA bending angle as θ, the relational expression is:
θ=exp {( _εb −b)/a}
ε _b : Maximum principal strain of the outermost surface layer on the bending outer side a: Relational expression of plate thickness t b: Relational expression of plate thickness t The bending angle prediction program according to (11) or (12), characterized by being represented by .

(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 being pre-deformed.

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

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

According to the present invention, using the finite element method, for a steel material having arbitrary material properties, for example, when the plate thickness fluctuates due to pre-deformation in the previous process, the limit VDA bending at an arbitrary plate thickness after deformation It becomes possible to obtain the angle easily and accurately. In addition, it is possible to predict the presence or absence of bending fracture of the steel material using the obtained limit VDA bending angle. As a result, it is possible to omit the collision test for actual automobile members, or to greatly reduce the number of collision tests. In addition, since it is possible to design the steel materials that prevent breakage in the event of a collision on a computer, it is possible to significantly reduce costs and shorten the development period.

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

(Basic gist of the present invention)
First, in disclosing 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 plate, a test standard called a plate bending test for metal materials (VDA bending test) by the German Automobile Manufacturers Association (VDA) is used. As a result of various investigations of 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 on the bending outer side reaches the material-specific limit value, bending fracture occurs in the VDA bending test. was found to occur.

1A and 1B show how the VDA bending experiment is performed. A steel plate 10 is placed on a pair of rolls 21 and 22 , and a 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 becomes maximum (timing when bending fracture 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 surface of the steel plate 10 is defined as the maximum principal strain of the outermost surface layer of the bending outer side at the top of the bending outer side. .

The limit VDA bending angle (experimental value) obtained for steel plates of three different thicknesses (plate thickness: 1.0 mm, 1.4 mm, 2.3 mm) with a tensile strength class of 1500 MPa class and bending at the top of the bending outside FIG. 2 shows the maximum principal strain of the outermost surface layer (detailed FEM analysis value using solid elements with a mesh size of 0.1 mm). Further, FIG. 3 shows the relationship between the distance from the top portion on the outer side of the bend and the maximum principal strain of the outermost surface layer on the outer side of the bend for the above three types of steel plates.

Generally, in FEM analysis, a detailed FEM model using solid elements (solid model) and an FEM model using shell elements (shell model) are mainly used. A solid model is modeled using three-dimensional solid elements such as a tetrahedron, a hexahedron, or a pentahedron, and generally has a long analysis time but high analysis accuracy. Shell models are modeled using shell elements, which are two-dimensional surface elements such as triangles and squares. It is often used in target analysis and has the advantage of short analysis time. Therefore, even analysis of large-scale models, which would be impossible with solid models, can be performed by using shell elements.

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

An FEM model that reproduces the VDA bending experiment is created, and solid elements with high strain reproduction accuracy are used, and the model is modeled with a detailed mesh having a size of, for example, about 0.1 mm. Using this FEM model, in a VDA bending experiment, the punch is pushed to the bending angle at which fracture occurs (limit VDA bending angle), the maximum principal strain on the outside of the bending of the steel plate at that time is obtained, and the relationship with the limiting VDA bending angle is calculated. investigated. As a result, as shown in FIGS. 2 and 3, the maximum principal strains on the outer side of the bend at the top of the outer side of the bend are 0.386, 0.396, 0.393, which can be regarded as almost the same value. That is, it was found that the maximum principal strain on the outer side of the bend at the top of the outer side of the bend is almost the same regardless of the plate thickness, even though the critical VDA bending angle changes as the thickness of the steel plate differs. rice field. Hereinafter, for convenience of description, the maximum principal strain of the bending outermost surface layer of the bending outer top portion is simply referred to as "the maximum principal strain of the bending outermost surface layer".

When using an FEM model consisting of detailed solid elements, the present inventor found that if the steel plate is the same steel grade, even if the plate thickness is different, when bending deformation is applied to the limit VDA bending angle for each plate thickness, , Using the above knowledge that the maximum principal strain of the bending outermost surface layer is almost equal, the limit VDA bending angle at various plate thicknesses was obtained from FEM analysis. Similarly, analysis using FEM models consisting of detailed solid elements was performed for other steel types, and the limit VDA bending angle for each plate thickness was obtained. FIG. 4 shows the results of plotting the relationship between the maximum principal strain of the bending outermost surface layer and the many limit VDA bending angles obtained in this way for various steel types and various plate thicknesses. In FIG. 4, plate thicknesses are indicated as t ₁ , t ₂ and t ₃ .

The present inventor found from FIG. 4 that the maximum principal strain of the bending outermost surface layer due to the solid element is expressed as a function of the limit VDA bending angle and plate thickness. As a result of detailed investigation to embody this knowledge, the present inventors found that the maximum principal strain of the outermost surface layer of bending by a solid element is a linear expression of the natural logarithm of the limit VDA bending angle for each plate thickness, regardless of the steel type. I found that it can be made

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

Coefficient a and coefficient b are represented by a relational expression of plate thickness t. This relational expression is determined in order to fit the test results with the above equation (1), and although the form of the equation is not particularly limited, it can be represented by, for example, a polynomial of the plate thickness t.

By solving the limit VDA bending angle θ from the above equation (1), θ is expressed as follows.
θ=exp{(εb− _b )/a} (2)

In this embodiment, the limit VDA bending angle of a steel plate of any steel type and any plate thickness is calculated using the formula (2) defined as described above. That is, in this embodiment, the critical VDA bending angle can be obtained very easily, in a short time, and accurately without testing 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 the bending angle prediction device according to the first embodiment, and FIG. 6 is a flow chart showing the bending angle prediction method according to the first embodiment.

The bending angle prediction device according to this embodiment includes a steel type (strength grade) determination unit 1, a maximum principal strain acquisition unit 2, and an angle calculation unit 3, as shown in FIG.
When predicting the limit VDA bending angle of a steel plate, first, the steel type (strength grade) determining unit 1 receives the material properties of the steel plate from an input file. Specifically, material properties include tensile strength properties corresponding to the material properties, for example, a Swift coefficient obtained by fitting a stress-strain curve or a stress-strain curve using the Swift equation.

In step S1, the steel type (strength grade) determining 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, it is preferable to target a steel plate of 980 MPa class or higher, in particular, as the steel type of the steel plate. Since the steel sheets that pose a problem of bending fracture are mainly high-strength materials, in the present embodiment, steel sheets of 980 MPa class or higher are targeted for fracture prediction as a specific indicator of high-strength materials.

In the maximum principal strain acquisition unit 2, there is a relationship in which the maximum principal strain of the outermost surface layer of the bending side is uniquely determined from the steel type (strength grade) of the steel plate. A table showing the relationship with the principal strain is stored. In this table, using the fact that the maximum principal strain on the outside of bending is almost the same regardless of the plate thickness, corresponding to the steel type (strength grade), The maximum principal strains outside the bending obtained are listed. In step S2, the maximum principal strain acquiring unit 2 acquires the maximum principal strain on the outer side of bending from the above table based on the steel type (strength grade) of the steel plate determined in step S1.

In the angle calculation unit 3, the 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 on the bending outer side acquired by the maximum principal strain acquisition unit 2 is entered. In step S3, the angle calculation unit 3 calculates the pre-deformation of the steel plate using the above equation (2) based on the pre-deformed plate thickness and the maximum principal strain of the bending outermost surface layer of the steel plate input for each element. Calculate the critical VDA bend angle after deformation.

As described above, according to the present embodiment, using FEM analysis, for steel materials having arbitrary material properties, for example, when the plate thickness fluctuates due to pre-deformation in the previous process, arbitrary post-deformation It is possible to easily and accurately obtain the critical VDA bending angle in the plate thickness.

(Second embodiment)
In the second embodiment, a bending fracture prediction method for a steel plate using the bending angle prediction method according to the first embodiment will be described in detail with reference to the drawings. In the present embodiment, a bending fracture prediction method of a steel sheet in a case where thickness variation occurs in the steel sheet due to pre-deformation in a plurality of forming steps in press forming analysis will be exemplified. FIG. 8 is a flow diagram showing a bending fracture prediction method according to the second embodiment.

Automobile parts are generally formed by press forming steel plates. Generally, in press forming, a steel plate is formed into a final shape through a plurality of processes such as a drawing process, a bending process, a trim forming process, and a restrike forming process. If it is a soft steel sheet, breakage hardly occurs during bending, but if a high-strength steel sheet exceeding 980 MPa is press-formed, there is a possibility that breakage will occur at the bent portion. In this embodiment, the drawing process and the bending process are illustrated, and the drawing process is described as the first forming analysis process S10, and the bending process as the second forming analysis process S20.

In the draw forming process, when the steel sheet is drawn, for example, the shoulder portion is subjected to tensile deformation due to the pressing of a punch, and the thickness of the steel sheet is reduced. On the other hand, due to the inflow of material due to the pressing of the punch, the peripheral portion (die flange portion) of the part receives compression deformation due to the shrinkage of the peripheral length, and the plate thickness increases.

In this embodiment, first, in step S11, FEM analysis is performed for the draw forming process of the first forming analysis process S10.
Subsequently, in step S12, the sheet thickness and strain component of the steel sheet after drawing are obtained 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 sheet acquired in step S12 are inherited and mapped to each element of the FEM model of the bending forming process, which is the second forming analysis process 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 to calculate the limit VDA bending angle at the plate thickness after pre-deformation of the steel plate.

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

In the FEM molding analysis of automobile members, a large-scale model is used, and modeling with detailed solid elements is generally difficult due to the excessive calculation load. Therefore, it is often modeled using shell elements with a small computational load and relatively coarse element sizes of, for example, about 1 mm to 5 mm. When modeled with shell elements, the strain is averaged within the element in areas where strain is concentrated locally, such as the bending top of a steel plate, so it is calculated according to the element size used. Different strain values are known. In this embodiment, after grasping the change in strain for each element size of this shell element, in step S24, the critical strain of the shell element bending outer side at the critical VDA bending angle is obtained, and the shell element under forming analysis Fracture can also be predicted based on whether or not the maximum principal strain of the outermost surface layer on the outer side of the bend reaches the critical strain on the outer side of the bend.

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

In step S24, it is determined whether or not the bending angle of the steel plate reaches the critical VDA bending angle in the FEM analysis without converting the critical VDA bending angle into the critical strain on the outer side of the shell element. You can also

As described above, according to the present embodiment, the critical VDA bend angle obtained by using the bend angle prediction method according to the first embodiment is used to accurately predict the presence or absence of bending fracture of the steel material. As a result, steel sheets that prevent bending breakage can be designed on a computer, contributing to significant cost reductions and shorter development periods.

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

Automobile parts are generally formed by press-molding a steel plate, and then undergoing an assembly process such as welding to form an automobile body. From the perspective of collision safety, automobile bodies are required to absorb energy while generating the desired reaction force in the event of a collision. . Therefore, it is required to perform FEM analysis of collision and predict fracture in advance.

Each steel material of an automobile body undergoes various deformations at the time of a collision, and the steel plate undergoes bending deformation at a portion that is compressed and buckled by the impact force. A soft steel plate hardly breaks during bending deformation, but a high-strength steel plate exceeding 980 MPa, for example, may break during bending deformation.

In the process of press-forming a steel plate, for example, the shoulder portion is subjected to tensile deformation due to the pressing of a punch, and the thickness of the steel plate is reduced. On the other hand, due to the inflow of the material due to the pressing of the punch, the peripheral portion (die flange portion) of the part undergoes compression deformation due to the shrinkage of the peripheral length, and the plate thickness increases.

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

Subsequently, in step S41, the plate thickness and strain component of the steel plate acquired in step S32 are inherited 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 to calculate the limit VDA bending angle at the plate thickness after pre-deformation of the steel plate.

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 fracture occurs for each element of the FEM model in the collision analysis step S40, and the element determined to have fracture is deleted.
As described above, it is possible to accurately predict the bending fracture of the automobile body at the time of collision on the FEM analysis.

In this embodiment, as in the second embodiment, after grasping changes in strain for each element size of the shell elements, in step S44, the limit strain on the outside of the bending of the shell elements at the limit VDA bending angle is calculated. Fracture is predicted based on whether or not the maximum principal strain of the outermost surface layer of the outermost layer of the shell element during the forming analysis reaches this critical strain of the outer side of the bending.

The strain applied by the pre-deformation in the forming process is of course inherited in the collision process. Therefore, also in the FEM analysis, along with the plate thickness after the forming analysis step S30, the strain component is acquired 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 in predicting fracture based on whether or not the strain on the outer side of the bending of the shell element reaches the limit strain.

In step S44, it is determined whether or not the bending angle of the steel sheet reaches the critical VDA bending angle in the FEM analysis without converting the critical VDA bending angle into the critical strain on the outer side of the shell element. You can also

As described above, according to the present embodiment, the critical VDA bend angle obtained by using the bend angle prediction method according to the first embodiment is used to accurately predict the presence or absence of bending fracture of the steel material. As a result, it is possible to omit the collision test for actual automobile members, or to greatly reduce the number of collision tests. In addition, since it is possible to design the steel materials that prevent breakage in the event of a collision on a computer, it is possible to significantly reduce costs and shorten the development period.

(Fourth embodiment)
The steel type (strength grade) determination unit 1, the maximum principal strain acquisition unit 2, and the angle calculation unit 3 shown in FIG. It may be realized by In addition, each component described above is composed of a memory and a CPU (Central Processing Unit), and the function is realized by loading and executing a program for realizing various functions of each component into the memory. It can be.

In addition, a program for realizing various functions of the above components (steps S1 to S3 of the angle prediction method in FIG. 6, steps S10 (S11 to S12) and S20 (S21 to S24 of the bending fracture prediction method in FIG. 8 ), steps S30 (S31 to S32) and S40 (S41 to S44) of the bending fracture prediction method in FIG. , the processing of each of the components described above may be executed by executing the "computer system" as used herein includes hardware such as an OS and peripheral devices.

The "computer system" may also include the home page providing environment (or display environment) if the WWW system is used.
The term "computer-readable recording medium" refers to portable media such as flexible discs, magneto-optical discs, ROMs and CD-ROMs, and storage devices such as hard discs incorporated in computer systems. In addition, "computer-readable recording medium" means dynamically storing a program for a short period of time, like a communication line when transmitting a program via a network such as the Internet or a communication line such as a telephone line. It may also include a memory that holds the program for a certain period of time, such as a volatile memory inside a computer system that serves as a server or client in that case. Further, the above program may be for realizing part of the functions described above, or may be capable of realizing the functions described above in combination with a program already recorded in the computer system. .

As a specific example, the bending angle prediction device, the bending angle prediction method, and the bending fracture prediction method shown in the first to third embodiments are implemented by a computer function 100 as shown in FIG.
The computer function 100 has a CPU 101 , a ROM 102 and a RAM 103 . It also has a controller (CONSC) 105 for an operation unit (CONS) 109 and a display controller (DISPC) 106 for a display (DISP) 110 as a display unit such as a CRT or LCD. Further, a controller (DCONT) 107 for a hard disk (HD) 111 and a storage device (STD) 112 such as a flexible disk, and a network interface card (NIC) 108 are provided. These functional units 101 , 102 , 103 , 105 , 106 , 107 and 108 are connected to each other via a system bus 104 so as to be able to communicate with each other.

The CPU 101 executes software stored in the ROM 102 or HD 111 , or software supplied from the STD 112 to collectively control each component connected to the system bus 104 . That is, the CPU 101 reads and executes a processing program (structural design support program) for performing the above-described operations from the ROM 102, HD 111, or STD 112, thereby performing control for realizing the operations in this embodiment. I do. The RAM 103 functions as a main memory, work area, or the like for the CPU 101 .

CONSC 105 controls instruction input from CONS 109 . DISPC 105 controls the display of DISP 110 . The DCONT 107 controls access to the HD 111 and STD 112 that store boot programs, various applications, user files, network management programs, and the processing programs described above in this embodiment. NIC 108 exchanges data bi-directionally with other devices on network 113 .
It should be noted that, instead of using a normal computer terminal device, a predetermined computer or the like specialized for the bending angle prediction device may be used.

INDUSTRIAL APPLICABILITY The present invention can be used, for example, in industries related to steel plates for automobile parts.

Claims (16)

A method of predicting a bend angle using a computer, comprising:
a first step of acquiring the maximum principal strain of the outermost surface layer of the steel material on the bending outer side according to the material properties of the steel material whose bending angle is to be predicted;
The relational expression that defines the limit VDA bending angle as a function of the plate thickness and the maximum principal strain of the bending outermost surface layer, which is predetermined using the finite element method, includes the plate thickness of the steel material and the obtained in the first step a second step of inputting the maximum principal strain of the bending outermost surface layer of the steel material and calculating the limit VDA bending angle of the steel material;
A bending angle prediction method comprising: The first step includes acquiring the maximum principal strain of the outermost surface layer on the bending outer side of the steel material corresponding to the material properties of the steel material, based on the relationship in which the maximum principal strain of the outermost outer layer on the bending outermost layer is uniquely determined from the material properties. The bending angle prediction method according to claim 1. Assuming the limit VDA bending angle as θ, the relational expression is:
θ=exp {( _εb −b)/a}
ε _b : Maximum principal strain of the outermost surface layer on the bending outer side a: Relational expression of plate thickness t b: Relational expression of plate thickness t The bending angle prediction method according to claim 1 or 2, characterized by the following. 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 being pre-deformed. The bending angle prediction method according to any one of claims 1 to 4, wherein the steel material is a steel plate of a grade of 980 MPa or higher.
an acquisition unit that acquires the maximum principal strain of the outermost surface layer of the steel material for which the bending angle is to be predicted, based on the material properties of the steel material;
The relational expression that defines the limit VDA bending angle as a function of the plate thickness and the maximum principal strain of the outermost surface layer of the bending outermost layer, which is predetermined using the finite element method, includes the plate thickness of the steel material and the obtained in the obtaining unit a calculation unit that inputs the maximum principal strain of the outermost surface layer of the steel material to calculate the limit VDA bending angle of the steel material;
A bending angle prediction device comprising: The acquisition unit acquires the maximum principal strain of the outermost surface layer on the bending outer side of the steel material corresponding to the material properties of the steel material based on a relationship that uniquely determines the maximum principal strain on the outermost surface layer on the outermost bending side from the material properties. The bending angle prediction device according to claim 6. Assuming the limit VDA bending angle as θ, the relational expression is:
θ=exp {( _εb −b)/a}
_8. The bending angle predicting device according to claim 6 or 7, characterized in that ε b : maximum principal strain of outermost surface layer on the bending outer side, a: relational expression of plate thickness t, and b: relational expression of plate thickness t. The bending angle prediction device according to any one of claims 6 to 8, wherein the plate thickness of the steel material is a value after being pre-deformed. The bending angle prediction device according to any one of claims 6 to 9, wherein the steel material is a steel plate of a grade of 980 MPa or higher. a first step of acquiring the maximum principal strain of the outermost surface layer of the steel material on the bending outer side according to the material properties of the steel material whose bending angle is to be predicted;
The relational expression that defines the limit VDA bending angle as a function of the plate thickness and the maximum principal strain of the bending outermost surface layer, which is predetermined using the finite element method, includes the plate thickness of the steel material and the obtained in the first step a second step of inputting the maximum principal strain of the bending outermost surface layer of the steel material and calculating the limit VDA bending angle of the steel material;
A bending angle prediction program that causes a computer to execute. The first step includes acquiring the maximum principal strain of the outermost surface layer on the bending outer side of the steel material corresponding to the material properties of the steel material, based on the relationship in which the maximum principal strain of the outermost outer layer on the bending outermost layer is uniquely determined from the material properties. The bending angle prediction program according to claim 11. Assuming the limit VDA bending angle as θ, the relational expression is:
θ=exp {( _εb −b)/a}
ε _b : Maximum principal strain of the outermost surface layer on the bending outer side a: Relational expression of plate thickness t b: Relational expression of plate thickness t The bending angle prediction program according to claim 11 or 12, characterized by the following. 14. 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 being pre-deformed. The bending angle prediction program according to any one of claims 11 to 14, wherein the steel material is a steel plate of a grade of 980 MPa or higher. A computer-readable recording medium recording the bending angle prediction program according to any one of claims 11 to 15.

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