JP2019034312A - Moldability evaluation method, program and recording medium - Google Patents

Abstract

To avoid in advance flange fracture which is one of molding problems at the time of application of a high strength steel sheet, and to achieve press molding of a component having a high strength and a light weight.SOLUTION: A method for evaluating possibility of press molding of a material includes: a first step at which a hole expansion rate, which is obtained from a test for expansion of two or more conical holes having different apical angles, is inputted; a second step at which from data concerning two or more different hole expansion rates, a fracture limit strain and a radial strain gradient of each plate end part are calculated according to a peripheral length difference of a plate thickness of a hole edge; a third step at which a fracture criteria is calculated from a relationship of two or more fracture limit strains and strain gradients; and a fourth step at which it is evaluated that fracture occurs when a maximum main strain, which is obtained from a numerical analysis by a finite-element method, and a strain gradient between adjacent elements reach said criteria. Moldability of a material is evaluated on the basis of an analysis result which is obtained by execution of the first to fourth steps as a series of processes.SELECTED DRAWING: Figure 9

Description

  The present invention relates to a formability evaluation method, a program, and a recording medium.

  In recent years, the application of high-strength steel sheets to automobile bodies has been progressing rapidly due to demands for collision safety and weight reduction. These high-strength steel plates can increase the absorbed energy and strength at the time of collision without increasing the plate thickness. However, since the reduction in ductility accompanying the increase in strength of steel sheets increases the risk of fracture during press forming, there is an increasing need for fracture prediction of materials by the finite element method and higher accuracy.

  The margin for breakage during forming is generally determined using a plate thickness reduction rate or a forming limit diagram (FLD). FLD is a diagram showing the maximum principal strain that gives the fracture limit for each minimum principal strain, and is used for fracture evaluation in molding analysis and collision analysis. The FLD measurement method by experiment is generally such that a circle or lattice pattern is drawn on the surface of a metal plate in advance by etching or the like and fractured by hydroforming or overhanging with a rigid tool, and then the deformation of the circle. The fracture limit strain is measured from the amount. The fracture limit line is obtained by proportionally loading a metal plate for various in-plane strain ratios, plotting the fracture limit strain at each strain ratio on the main strain axis, and connecting them with a line (FIG. 1).

  On the other hand, there are various FLD theoretical predictions such as the combined use of Hill's local constriction model and Swift's diffusion constriction model, the Marciniak-Kuczynski method, and the Storen-Rice model. Ductile fracture of the material occurs at the location where deformation is localized due to local constriction. When this local constriction occurs, it breaks in a very short time. Therefore, in practice, the fracture limit is often considered as the local constriction limit, and the fracture limit prediction is often handled in the framework of plastic instability. The risk of fracture is evaluated by comparing the positional relationship between the fracture limit line obtained in this way and the strain state of each part obtained from the result of numerical simulation by the finite element method. When strain is reached, it is determined that the fracture or the risk is high.

Japanese Patent Application No. 2014-137185 JP 2011-140046 A

  The FLD obtained from experiments and theoretical predictions is intended for the case where materials are separated under a uniform stress state or when local constriction occurs (FIG. 2). However, in stretch flange forming in which a crack occurs from the end of the steel plate, strain decreases from the flange end toward the inside, so that the material end is constrained on the inside and the occurrence of constriction is suppressed (FIG. 3). . That is, even if the stretch flange end portion satisfies the fracture condition in the uniform distribution, the condition has not yet been reached on the inside, so the inner support effect cannot be a plastic unstable state as a whole, and the fracture does not occur. . This is different from local necking in a uniform stress field such as uniaxial tension, overhang, or deep drawing, and when there is a strain gradient from the flange end to the inside, such as stretch flange breakage. The conditions for the occurrence of unstable neck have not been clarified yet. In addition, the fracture mechanism is complicated due to the influence of microscopic damage introduced into the end of the steel plate during shearing, and due to this and the influence of the strain gradient described above, the prediction accuracy can be ensured in the conventional fracture prediction by FLD. Can not.

  The present invention has been made in view of the above problems, and avoids stretch flange breakage, which is one of the forming problems when applying high-strength steel sheets, and realizes press forming of high-strength and lightweight parts. It is an object of the present invention to provide a moldability evaluation method, a program, and a recording medium.

  In order to solve the above-mentioned problems, the present inventors have devised various aspects of the invention shown below as a result of intensive studies. The gist of the present invention is as follows.

1. A method for evaluating whether a material can be press-molded,
A first step of inputting two or more different hole expansion rates obtained from the hole expansion test;
The two or more different fracture limit strains and the two or more different radial strain gradients are calculated from the data of the two or more different hole expansion ratios according to the circumferential length difference of the plate thickness at the hole edge. A second step;
A third step of calculating a fracture criterion from a relationship between the two or more fracture limit strains and the two or more strain gradients;
A fourth step of evaluating that the maximum principal strain obtained from the numerical analysis by the finite element method and the strain gradient between the adjacent elements have broken when reaching the fracture criteria;
A formability evaluation method characterized by evaluating formability of the material based on an analysis result obtained by executing the first step to the fourth step as a series of steps.

  2. In the first step, the respective hole expansion rates obtained from the conical hole expansion test of the two or more different apex angles are input. The formability evaluation method as described in 2.

  3. In the first step, the hole expansion rate obtained from a hole expansion test using a cone tool with a single apex angle using the material having the two or more different initial hole diameters is input. 1. The formability evaluation method as described in 2.

4). In the second step, the hole expansion ratio is λ (%), the fracture limit strain of the plate end is (ε _θ ) _{r = 0} , the strain gradient is dε _θ / dr, and the conical surface method of the conical tool is used. The angle between the line and the vertical direction is φ (deg.), The hole diameter of the base plate is d ₀ (mm), the radial coordinate indicating the position after deformation is r (mm), and the material is broken at the end of the plate. The resulting hole diameter d is obtained as (1 + λ / 100) d ₀ ,

Assuming that the initial plate thickness of the base plate is t ₀ (mm), the plate thickness t of the hole edge after molding is

  Obtained, and the distortion distributed in the plate thickness direction with the position in the plate thickness direction after deformation as x (mm),

  It is characterized by calculating as 1. ~ 4. The moldability evaluation method according to any one of the above.

5. 1. When calculating the strain gradient dε _θ / dr, the element size used for the analysis of the finite element method is set as a reference length dr. ~ 4. The moldability evaluation method according to any one of the above.

6). The fracture criterion ε ^cr = f (dε _θ / dr) is calculated from the two or more fracture limit strains and strain gradients, and dε _11, which is the strain gradient between adjacent elements, is obtained from numerical analysis by a finite element method. / dr and seek epsilon ₁₁ is the maximum main strain, said a strain gradient d? ₁₁ / dr and the maximum principal strain in which epsilon ₁₁ is ε ₁₁ / ε ^cr as an indicator of whether or not reached the breaking criterion And the result is contour-displayed. ~ 5. The moldability evaluation method according to any one of the above.

7). A program for evaluating whether or not a material can be press formed,
A first step of inputting two or more different hole expansion rates obtained from the hole expansion test;
The two or more different fracture limit strains and the two or more different radial strain gradients are calculated from the data of the two or more different hole expansion ratios according to the circumferential length difference of the plate thickness at the hole edge. A second step;
A third step of calculating a fracture criterion from a relationship between the two or more fracture limit strains and the two or more strain gradients;
And causing the computer to execute a fourth step of evaluating that the maximum principal strain obtained from the numerical analysis by the finite element method and the strain gradient between adjacent elements have broken when reaching the fracture criteria,
A formability evaluation program for evaluating formability of the material based on an analysis result obtained by executing the first step to the fourth step as a series of steps.

  8). 6. In the first step, the respective hole expansion ratios obtained from the conical hole expansion test of the two or more different apex angles are input. Formability evaluation program described in 1.

  9. In the first step, the hole expansion rate obtained from a hole expansion test using a cone tool with a single apex angle using the material having the two or more different initial hole diameters is input. 7). Formability evaluation program described in 1.

10. In the second step, the hole expansion ratio is λ (%), the fracture limit strain of the plate end is (ε _θ ) _{r = 0} , the strain gradient is dε _θ / dr, and the conical surface method of the conical tool is used. If the angle between the line and the vertical direction is φ (deg.), The hole diameter of the base plate is d ₀ (mm), and the radius coordinate indicating the position after deformation is r (mm),
The hole diameter d when fracture occurs at the end of the plate of the material is obtained as (1 + λ / 100) d ₀ ,

Assuming that the initial plate thickness of the base plate is t ₀ (mm), the plate thickness t of the hole edge after molding is

Obtained, and the distortion distributed in the plate thickness direction with the position in the plate thickness direction after deformation as x (mm),

  It is characterized by calculating as 7. ~ 9. The moldability evaluation program according to any one of the above.

11. 6. When calculating the strain gradient dε _θ / dr, the element size used for the analysis of the finite element method is set as the reference length dr. -10. The moldability evaluation program according to any one of the above.

12 The fracture criterion ε ^cr = f (dε _θ / dr) is calculated from the two or more fracture limit strains and strain gradients, and dε _11, which is the strain gradient between adjacent elements, is obtained from numerical analysis by a finite element method. / dr and seek epsilon ₁₁ is the maximum main strain, said a strain gradient d? ₁₁ / dr and the maximum principal strain in which epsilon ₁₁ is ε ₁₁ / ε ^cr as an indicator of whether or not reached the breaking criterion And the result is contour-displayed. ~ 11. The moldability evaluation program according to any one of the above.

  13.7. -12. A computer-readable recording medium in which the formability evaluation program according to any one of the above is recorded.

  According to the present invention, it is possible to estimate the stretch flange fracture criteria in consideration of the influence of the strain gradient from the plate edge, the punched state, and the thickness direction strain distribution after molding, and this is applied to the molding simulation. Thus, the risk of stretch flange breakage can be quantitatively evaluated. As a result, it is possible to avoid stretch flange breakage, which is one of the forming problems when applying high-strength steel sheets, and to realize press forming of high-strength and lightweight parts.

It is a characteristic view which shows a shaping | molding limit diagram (FLD) used for description of a prior art. It is a characteristic view for demonstrating the local constriction in a uniform stress state. It is a characteristic view for demonstrating the distortion gradient toward the inner side from the board edge part of the stretch flange part. It is a schematic diagram for demonstrating a hole expansion test. It is a schematic diagram for calculating | requiring the distortion and distortion gradient of a hole edge in a hole expansion test by correct | amending the circumferential length difference of a hole edge according to board thickness. The results of comparing the distortion and strain gradient of the hole edge in the hole expansion test with the value calculated by correcting the difference in the peripheral length of the hole edge according to the plate thickness and the value calculated without correction are shown. FIG. It is a characteristic view for demonstrating the relationship between the strain gradient which is a fracture criteria, and a fracture limit strain. It is one of the embodiments, and is a characteristic diagram explaining the fracture criteria using the result of calculating the distortion and strain gradient of the hole edge from the hole expansion rate when materials with different hole diameters are tested with a conical tool. is there. It is a flowchart which shows the fracture | rupture prediction method of this embodiment. It is a schematic diagram which shows the result of having evaluated fracture | rupture risk by this embodiment. It is a schematic diagram which shows the internal structure of a personal user terminal device.

  Hereinafter, this embodiment will be described in detail with reference to the drawings.

(Basic outline of fracture prediction method)
In stretch flange forming in which a crack is generated from the end of the steel plate, strain is reduced from the flange end toward the inside, so that the material end is constrained on the inside and the occurrence of constriction is suppressed. Moreover, the fracture mechanism is complicated due to the influence of microscopic damage introduced into the end of the steel plate during shearing, and prediction accuracy cannot be ensured by conventional fracture prediction by FLD. In view of this, an extension flange fracture prediction technique has been devised that utilizes the results of a hole expansion test that takes into account the strain gradient from the end of the plate, the punched state of the end, and the thickness direction strain distribution after forming.

Since the edge forming limit occurs when the circumferential elongation strain at the flange end reaches the limit value, the circumferential elongation strain at the flange end can be considered as an index indicating the degree of molding difficulty. The hole expansion rate λ obtained by the test is evaluated. In the hole expansion test, generally, a circular hole with a diameter of 10 mm, for example, is drilled in a material, the diameter of the hole is expanded by, for example, a conical punch with an apex angle of 60 °, and a fracture occurs when a crack occurs at the edge of the hole Limit. It is obtained by calculating the hole expansion ratio {(d−d ₀ ) / d ₀ } × 100 from the diameter d and the initial diameter d ₀ at that time (FIG. 4). The hole at this time is generally sheared by setting the clearance between the punch and the die to be, for example, 12% of the plate thickness. For this reason, microscopic damage such as dimples, cracks and voids is observed on the fracture surface of the flange end. Therefore, the hole expansion test is also a test method in consideration of microscopic damage introduced at the time of shearing.

  It is known that the hole expansion rate varies greatly depending on test dimensions such as a hole diameter and a punch diameter and a punch bottom shape. This is because the stretch flange forming limit is strongly influenced by a strain gradient that decreases inward from the flange end. Therefore, it is necessary to evaluate the fracture limit by an evaluation test that combines the strain state (strain gradient from the plate end portion to the inside) introduced in the stretch flange molding of the actual part and the strain gradient in the hole expansion test. However, in the stretch flange fracture, which is a problem in actual parts, the strain distribution often varies greatly depending on the part shape and the blank shape. When evaluating breakage using the hole expansion rate obtained from the experiment, it is necessary to prepare a breakage limit by changing innumerably the hole diameter and punch diameter according to the strain gradient.

  On the other hand, the side bend test method is proposed as a method for examining the relationship between the strain state (strain gradient from the plate edge to the inside, strain gradient along the edge) and the fracture limit introduced in the stretch flange molding of actual parts. (For example, see Patent Documents 1 and 2). The feature is that an image processing system is introduced to measure distortion and a camera for observing the behavior of crack generation at the end face is provided. A method has been proposed in which a fracture limit curved surface is defined from the relationship between the fracture limit strain obtained from this method and the strain distribution and used for prediction of stretch flange fracture.

  However, in order to obtain a radial strain gradient from the edge by this method, a circle or lattice pattern is drawn in advance on the surface of the material by etching or the like, and the strain gradient is measured from the deformation amount of the circle after deformation. There is a need to. In addition, there is a method of obtaining the fracture limit of various strain gradients by numerical simulation, but it is complicated to obtain the fracture limit for an infinite number of test piece shapes corresponding to the strain distribution which is a problem in actual parts, Practically difficult.

  In the present embodiment, a hole according to the plate thickness after forming the fracture limit strain and radial strain gradient at the end of the plate from the hole expansion test, specifically, the test value of the hole expansion rate obtained from the conical hole expansion test. Consider a method that can be easily obtained by correcting the peripheral length difference of the edge. FIG. 5 shows a schematic diagram for obtaining an outline of a hole expanding test using a conical punch and a distortion and distortion gradient of the hole edge by correcting the peripheral length difference according to the plate thickness. Here, the normal to the conical surface of the conical tool and the vertical direction (the angle formed with the z-axis is φ (the half apex angle of the conical tool is 90 ° −φ). The balance equation for the elements of is given by

Here, r is a radial coordinate indicating the position of the element after deformation, t is a thickness after deformation, σ _θ and σ _φ are stresses in the circumferential direction and radial direction, and μ is a friction coefficient.

Subsequently, the circumferential strain ε _φ and the radial strain ε _θ are respectively given as follows.

  Here, s represents a radius coordinate before deformation of the plate element. From these, the following conditional expression for distortion is obtained.

  Further, it is assumed that the deformation is based on the total strain theory, and the work hardening characteristics of the material are approximated by the n-th power hardening law.

  Then, the circumferential and radial strain distributions are respectively given by the following equations.

  Here, the first derivative (distortion gradient) and the second derivative are given by the following equations, respectively.

Here, for example, when the base plate having the initial hole diameter d ₀ becomes the diameter d by the hole expansion test, the distortion of the end portion is obtained by the following equation:

This and Equation (6), (9) can be calculated radial strain distribution epsilon _theta From (13).

Further, assuming that the initial plate thickness of the base plate is t ₀ (mm), the plate thickness t of the hole edge after molding is obtained by the following equation.

  Further, the distortion of the end portion distributed in the plate thickness direction with the position in the plate thickness direction after deformation as x (mm) is obtained by the following equation.

From the equations (6) and (9) to (15), the radial strain distribution ε _θ ^* in consideration of the circumferential length difference corresponding to the plate thickness can be calculated.

In the following, a method of calculating the fracture limit criteria will be described using a 1.4 mm thick high strength steel sheet of 980 MPa as an example.
First, a conical hole expansion test with different apex angles is performed off-line. Here, as an example, punches of 30 ° cone and 60 ° cone were used. The clearance between the die and the punch at this time was set to 12% of the plate thickness, and a hole with a diameter of 10 mm was punched in the center of the base plate. The base plate is subjected to a hole expansion test, and when the crack penetrates the plate thickness at the edge of the hole, the fracture limit is set, and the hole expansion rate {(d−d ₀ ) / d from the diameter d and the initial diameter d ₀ at that time. ₀ } × 100 was calculated. As a result, the hole expansion ratios of the 30 ° cone and the 60 ° cone were 20% and 14%, respectively.

From this result and the equations (6) and (9) to (15), the radial strain distribution ε _θ ^* corresponding to the circumferential length difference of the plate thickness of the hole edge after forming when each conical punch is used is Can be calculated. FIG. 6 shows the result of comparing the presence / absence of correction of the difference in the circumferential length corresponding to the thickness of the sheet after forming from Expression (13) and Expression (15). The experimental value was obtained from the amount of deformation of the circle after the test by etching a grid-like scribed circle with a distance of 0.5 mm between the grades on the material. As a result, it was confirmed that the calculation result of the radial strain distribution corrected in consideration of the circumferential length difference of the plate thickness after forming reproduced the experiment with good accuracy compared to the result without correction. . That is, in both the 30 ° cone and the 60 ° cone, the maximum value of the circumferential strain ε _θ is observed at the hole edge, and it can be seen that it decreases monotonously from the hole edge toward the inside in the radial direction. Furthermore, in the plate thickness direction of the hole edge, the maximum value is observed on the outside of the hole edge due to the difference in the circumferential length corresponding to the plate thickness, and it can be seen that it decreases toward the inside of the plate thickness direction.

Subsequently, the circumferential rupture strain corresponding to the strain gradient is calculated from the above calculation result. Since the circumferential strain distribution is gradually reduced as it moves away from the hole edge, the strain gradient changes depending on the reference size dr. Therefore, when calculating the strain gradient dε _θ / dr, the accuracy of fracture prediction is improved by setting the element size used for the analysis of the finite element method to the reference length dr. If evaluation with such high accuracy is not necessary, the first derivative of equation (9) may be used.

From the relationship between the two or more strain gradients | dε / dr | obtained in this way and the fracture limit strain ε ^cr = (ε _θ ) _{r = 0} at the hole edge, linear approximation or multi-line data connecting them Is the fracture criterion ε ^cr = f (dε _θ / dr) (FIG. 7).

Subsequently, the forming analysis of the part to be evaluated for formability is performed by numerical analysis by the finite element method, and the strain gradient dε ₁₁ / dr and the maximum principal strain ε ₁₁ between adjacent elements are obtained from the resulting strain distribution. If it reaches the fracture criteria, it is judged that the risk of fracture is high. Further, ε ₁₁ / ε ^cr is calculated as an index for quantitatively evaluating the risk of fracture (corresponding to the size of OR / OA in FIG. 7), and the result is displayed in a contour.

(Other examples of fracture prediction methods)
As a hole expansion test for determining fracture criteria, in addition to conical hole expansion of two or more different apex angles, a hole expansion test is performed in which materials of different hole diameters are expanded by a single-shaped conical punch. Also good. In the case of different hole diameters, the initial hole diameters d ₀ in equations (13) and (15) may be used as the respective hole diameters.

[1] Hole expansion test using a conical punch As an example of a hole expansion test using a conical punch, a material obtained by punching a 10 mm diameter hole and a 50 mm diameter hole in the center of a base plate using a 60 ° conical punch. It used for the hole expansion test. As a result, the hole expansion rates using the 10 mm diameter hole and the 50 mm diameter material were 42% and 18%, respectively. From this result and the equations (6) and (9) to (15), the radial strain distribution when the respective initial hole diameters are used can be calculated. The result is shown in FIG. The experimental value was obtained from the amount of deformation of the test circle by etching a concentric scribed circle having a distance between the gauge points of 0.5 mm. As a result, it was confirmed that the calculated value can reproduce the experiment with good accuracy. FIG. 8B shows the fracture criteria determined from the relationship between the two or more strain gradients obtained here and the fracture limit strain at the hole edge.

(Specific configuration of this embodiment)
A specific configuration of the present embodiment will be described as an example of evaluating the moldability of an automobile part with reference to FIG.

  In evaluating the formability of automobile parts, first, the structure of the automobile is set (step S1), then the shape of the automobile part is set using CAD (step S2), and the three-dimensional part shape is recorded on the computer. (Step S3). Here, in order to evaluate whether or not press working can be performed using a mold, the mold is designed with a mold CAD (step S4), and software is selected according to the purpose and recorded on the computer. Next, the moldability is evaluated by molding analysis (step S8). For this purpose, first, the material parameters, plate thickness, and molding conditions of the parts used for the moldability evaluation are set (step S5).

  Then, the result of the conical hole expansion test of two or more different apex angles tested offline is input (step S6). When performing a hole expansion test with a single-shaped apex angle conical tool using two or more different initial hole diameter materials instead of two or more different apex angle conical hole expansion tests In step S6, the hole expansion rate obtained from the test is input. When performing a hole expansion test with a single-shaped apex angle conical tool using two or more different initial hole diameter materials instead of two or more different apex angle conical hole expansion tests, The hole expansion rate obtained from the test is input in step S6.

Subsequently, the fracture criterion ε ^cr = f (dε _θ / dr) is calculated by the method described above using the two or more hole expansion ratio values (step S7). Furthermore, the evaluation of the fracture is evaluated by comparing the positional relationship between the fracture criteria obtained in this way and the maximum principal strain of each element and the adjacent strain gradient obtained from the result of the finite element simulation of the deformation process. To do. When this strain reaches the fracture criteria, it is determined that the fracture or the risk thereof is high (steps S8 to S10). Specifically, in the relationship between the strain gradient and the fracture limit strain shown in FIG. 7, the strain state of the element obtained by the finite element method is R, and the intersection of the straight line connecting the straight lines connecting the states O and R of the strain 0 with the criteria. When A is assumed, the risk of breakage can be quantified as OR / OA.

  Finally, the fracture risk rate is contour-displayed (step S11), and whether or not molding is possible is determined. As a specific implementation, the risk of fracture when a bowl-shaped part having a flange height H = 30 mm, a corner R = 30 mm, and an opening angle of 120 ° was formed from a 1.4 mm-thick 980 MPa class high-strength steel sheet was evaluated. The results are shown in FIG.

  As described above, according to the present embodiment, it is possible to estimate the stretch flange fracture criteria in consideration of the influence of the strain gradient from the plate end, the punched state, and the strain distribution in the plate thickness direction, and this can be estimated as a molding simulation. By applying to, the risk of stretch flange breakage can be quantitatively evaluated. As a result, it is possible to avoid stretch flange breakage, which is one of the forming problems when applying high-strength steel sheets, and to realize press forming of high-strength and lightweight parts.

(Other embodiments)
Each step (steps S1 to S11 in FIG. 9 and the like) of the formability prediction evaluation method according to the present embodiment described above can be realized by operating a program recorded in a RAM or ROM of a computer. This program and a computer-readable recording medium on which the program is recorded are included in this embodiment.

  Specifically, the above program is recorded on a recording medium such as a CD-ROM, or provided to a computer via various transmission media. As a recording medium for recording the program, a flexible disk, a hard disk, a magnetic tape, a magneto-optical disk, a nonvolatile memory card, and the like can be used in addition to the CD-ROM. On the other hand, a communication medium in a computer network system for propagating and supplying program information as a carrier wave can be used as the program transmission medium. Here, the computer network is a WAN such as a LAN or the Internet, a wireless communication network, or the like, and the communication medium is a wired line such as an optical fiber or a wireless line.

  Further, the program included in the present embodiment is not limited to the one in which the functions of the present embodiment are realized by the computer executing the supplied program. For example, when the function of the present embodiment is realized in cooperation with an OS (operating system) running on a computer or other application software, the program is included in the present embodiment. Further, when all or part of the processing of the supplied program is performed by a function expansion board or a function expansion unit of the computer and the functions of the present embodiment are realized, the program is included in the present embodiment.

  For example, FIG. 11 is a schematic diagram illustrating an internal configuration of a personal user terminal device. In FIG. 11, reference numeral 1200 denotes a personal computer (PC) having a CPU 1201. The PC 1200 executes device control software stored in the ROM 1202 or the hard disk (HD) 1211 or supplied from the flexible disk drive (FD) 1212. The PC 1200 generally controls each device connected to the system bus 1204.

  By the program stored in the CPU 1201, the ROM 1202, or the hard disk (HD) 1211 of the PC 1200, the procedure of steps S1 to S11 in FIG.

  Reference numeral 1203 denotes a RAM which functions as a main memory, work area, and the like for the CPU 1201. A keyboard controller (KBC) 1205 controls instruction input from a keyboard (KB) 1209, a device (not shown), or the like.

  Reference numeral 1206 denotes a CRT controller (CRTC), which controls display on a CRT display (CRT) 1210. Reference numeral 1207 denotes a disk controller (DKC). The DKC 1207 controls access to a hard disk (HD) 1211 and a flexible disk (FD) 1212 that store a boot program, a plurality of applications, an edit file, a user file, a network management program, and the like. Here, the boot program is a startup program that starts execution (operation) of hardware and software of a personal computer.

Reference numeral 1208 denotes a network interface card (NIC) which performs bidirectional data exchange with a network printer, another network device, or another PC via the LAN 1220.
Instead of using the personal user terminal device, a predetermined computer specialized for the formability prediction evaluation method may be used.

Claims (13)

A method for evaluating whether a material can be press-molded,
A first step of inputting two or more different hole expansion rates obtained from the hole expansion test;
The two or more different fracture limit strains and the two or more different radial strain gradients are calculated from the data of the two or more different hole expansion ratios according to the circumferential length difference of the plate thickness at the hole edge. A second step;
A third step of calculating a fracture criterion from a relationship between the two or more fracture limit strains and the two or more strain gradients;
A fourth step of evaluating that the maximum principal strain obtained from the numerical analysis by the finite element method and the strain gradient between the adjacent elements have broken when reaching the fracture criteria;
A formability evaluation method characterized by evaluating formability of the material based on an analysis result obtained by executing the first step to the fourth step as a series of steps.   2. The formability evaluation method according to claim 1, wherein in the first step, each of the hole expansion ratios obtained from the conical hole expansion test of the two or more different apex angles is input.   In the first step, the hole expansion rate obtained from a hole expansion test using a cone tool with a single apex angle using the material having the two or more different initial hole diameters is input. The moldability evaluation method according to claim 1. In the second step, the hole expansion ratio is λ (%), the fracture limit strain of the plate end is (ε _θ ) _{r = 0} , the strain gradient is dε _θ / dr, and the conical surface method of the conical tool is used. If the angle between the line and the vertical direction is φ (deg.), The hole diameter of the base plate is d ₀ (mm), and the radius coordinate indicating the position after deformation is r (mm),
The hole diameter d when fracture occurs at the end of the plate of the material is obtained as (1 + λ / 100) d ₀ ,

Assuming that the initial plate thickness of the base plate is t ₀ (mm), the plate thickness t of the hole edge after molding is

Obtained, and the distortion distributed in the plate thickness direction with the position in the plate thickness direction after deformation as x (mm),

The formability evaluation method according to claim 1, wherein the moldability is calculated as follows. 5. The molding according to claim 1, wherein when calculating the strain gradient dε _θ / dr, an element size used for analysis of the finite element method is set as a reference length dr. Sex assessment method. The fracture criterion ε ^cr = f (dε _θ / dr) is calculated from the two or more fracture limit strains and strain gradients, and dε _11, which is the strain gradient between adjacent elements, is obtained from numerical analysis by a finite element method. / dr and seek epsilon ₁₁ is the maximum main strain, said a strain gradient d? ₁₁ / dr and the maximum principal strain in which epsilon ₁₁ is ε ₁₁ / ε ^cr as an indicator of whether or not reached the breaking criterion The formability evaluation method according to any one of claims 1 to 5, wherein the result is contour-displayed. A program for evaluating whether or not a material can be press formed,
A first step of inputting two or more different hole expansion rates obtained from the hole expansion test;
The two or more different fracture limit strains and the two or more different radial strain gradients are calculated from the data of the two or more different hole expansion ratios according to the circumferential length difference of the plate thickness at the hole edge. A second step;
A third step of calculating a fracture criterion from a relationship between the two or more fracture limit strains and the two or more strain gradients;
And causing the computer to execute a fourth step of evaluating that the maximum principal strain obtained from the numerical analysis by the finite element method and the strain gradient between adjacent elements have broken when reaching the fracture criteria,
A formability evaluation program for evaluating formability of the material based on an analysis result obtained by executing the first step to the fourth step as a series of steps.   The formability evaluation program according to claim 7, wherein in the first step, the hole expansion ratios obtained from the conical hole expansion test of the two or more different apex angles are input.   In the first step, the hole expansion rate obtained from a hole expansion test using a cone tool with a single apex angle using the material having the two or more different initial hole diameters is input. The moldability evaluation program according to claim 7. In the second step, the hole expansion ratio is λ (%), the fracture limit strain of the plate end is (ε _θ ) _{r = 0} , the strain gradient is dε _θ / dr, and the conical surface method of the conical tool is used. If the angle between the line and the vertical direction is φ (deg.), The hole diameter of the base plate is d ₀ (mm), and the radius coordinate indicating the position after deformation is r (mm),
The hole diameter d when fracture occurs at the end of the plate of the material is obtained as (1 + λ / 100) d ₀ ,

Assuming that the initial plate thickness of the base plate is t ₀ (mm), the plate thickness t of the hole edge after molding is

Obtained, and the distortion distributed in the plate thickness direction with the position in the plate thickness direction after deformation as x (mm),

The formability evaluation program according to claim 7, wherein the moldability evaluation program is calculated as follows. 11. The molding according to claim 7, wherein when calculating the strain gradient dε _θ / dr, an element size used for analysis of the finite element method is set as a reference length dr. Sex assessment program. The fracture criterion ε ^cr = f (dε _θ / dr) is calculated from the two or more fracture limit strains and strain gradients, and dε _11, which is the strain gradient between adjacent elements, is obtained from numerical analysis by a finite element method. / dr and seek epsilon ₁₁ is the maximum main strain, said a strain gradient d? ₁₁ / dr and the maximum principal strain in which epsilon ₁₁ is ε ₁₁ / ε ^cr as an indicator of whether or not reached the breaking criterion The formability evaluation program according to any one of claims 7 to 11, wherein the result is calculated and contoured.   A computer-readable recording medium in which the formability evaluation program according to any one of claims 7 to 12 is recorded.

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