JP2023078860A - Metallic material testing method - Google Patents

Abstract

To provide a metallic material testing method capable of achieving characteristics appropriate for determining moldability of a metallic material at high precision.SOLUTION: A testing method includes a cutting-out step, a compression step, a sampling step, a tensile testing step, and a calculation step. The cutting-out step is composed of cutting out a rectangular plate-shaped sample from the metallic material. The compression step is composed of applying a compression load to the sample under a condition of a composite deformation process and introducing corresponding plastic strain of 0.20 or more to the sample. The sampling step is composed of collecting a round bar like tensile test piece from the sample. The tensile testing step is composed of applying a tensile test load to the tensile test piece in an axial direction to break the tensile test piece. The calculation step is composed of calculating mechanical characteristics associated with the corresponding plastic strain under a prescribed condition according to a result of the tensile test.SELECTED DRAWING: Figure 1

Description

The present disclosure relates to methods for testing metallic materials. More particularly, the present disclosure relates to testing methods for metallic materials that undergo compressive deformation and then ultimately tensile deformation.

Many automobile parts are formed by pressing steel plates. During press forming, the steel sheet is bent and drawn. Therefore, the steel plate is deformed in tension or compression. Conventionally, in order to grasp the characteristics of steel sheets during press forming, a tensile compression test is performed on a test piece taken from a steel sheet material (for example, Japanese Patent No. 6246074 (Patent Document 1), and Japanese Patent Application Laid-Open No. 2016-3951 Publication (Patent Document 2)). In the tension-compression test, a compressive load and a tensile load are repeatedly applied along the longitudinal direction of the test piece.

Japanese Patent No. 6246074 JP 2016-3951 A

For example, in the process of forming an automobile part such as a cup-shaped part (for example, a transmission gear), a steel plate may be partially thickened by forging. In this case, a large compressive plastic strain that reaches 0.5 in equivalent plastic strain is introduced into the steel plate. This steel plate is further pressed in a post-process. Therefore, depending on the part in the steel sheet, it is finally subjected to tensile deformation after a large compressive plastic strain is introduced. In the present specification, a series of deformation processes, such as compression deformation in which a large compressive plastic strain is introduced, and finally tensile deformation, are also referred to as a compound deformation process.

Conventionally, a ductile fracture parameter is used to determine whether or not each part in a steel plate material undergoing a compound deformation process can be formed by FEM. As the ductile fracture parameter, the damage value Df represented by the following Cockroft-Lathman formula (1) is widely used.

Therefore, the damage value Df involves only the maximum normal stress and strain occurring in the FEM analysis element in the steel plate material due to deformation. Therefore, the damage value Df does not change due to compressive deformation. On the other hand, as an actual phenomenon, cracks may occur due to subsequent tensile deformation due to a decrease in residual ductility after compressive deformation. Further, in the techniques described in Patent Documents 1 and 2, the maximum compressive plastic strain introduced into the test piece is only about 0.10. Therefore, in the conventional technique, it is difficult to determine with high accuracy whether the steel sheet material can be formed in the case of forming through a compound deformation process including compressive deformation in which a large compressive plastic strain is introduced.

The purpose of the present disclosure is to obtain characteristics suitable for accurately determining whether a metal material to be evaluated can be molded in the case of molding that undergoes a complex deformation process including compressive deformation in which a large compressive plastic strain is introduced. It is to provide a test method for metallic materials that can

A method for testing a metallic material according to the present disclosure includes a cutting step, a compression step, a sampling step, a tensile test step, and a calculation step. In the cutting step, a rectangular plate-shaped sample is cut out from the metal material. In the compression step, a compressive load is applied to the sample under predetermined conditions using a mold to introduce an equivalent plastic strain of 0.20 or more to the sample. In the sampling step, a round bar-shaped tensile test piece is sampled from the sample after the compression step. In the tensile test step, a tensile load is applied to the tensile test piece in the axial direction to break the tensile test piece. The calculation step calculates mechanical properties corresponding to the equivalent plastic strain under the above predetermined conditions from the results of the tensile test step.

According to the test method for a metallic material according to the present disclosure, in the case of molding that undergoes a complex deformation process including compressive deformation in which a large compressive plastic strain is introduced, it is possible to determine with high accuracy whether the metallic material to be evaluated can be molded. suitable properties can be obtained.

FIG. 1 is a flow chart showing an example of a fracture evaluation method for metal materials using the test method of the present embodiment. FIG. 2 is a perspective view showing an example of a sample cut out in the cutting process. FIG. 3 is a plan view showing an example of conditions for the compression process. FIG. 4 is a plan view showing an example of conditions for the compression process. FIG. 5 is a plan view showing an example of conditions for the compression process. FIG. 6 is a plan view showing an example of conditions for the compression process. FIG. 7 is a plan view showing an example of a tensile test piece sampled in the sampling step. FIG. 8 is a plan view showing another example of the tensile test piece sampled in the sampling step. FIG. 9 is a diagram summarizing an example of the mechanical properties calculated in the calculation process for each condition. FIG. 10 is a flow diagram showing an example of the evaluation process.

Embodiments of the present disclosure will be described below. In the following description, the embodiments of the present disclosure will be described with examples, but the present disclosure is not limited to the examples described below. Although specific numerical values and specific materials may be exemplified in the following description, the present disclosure is not limited to those exemplifications.

A test method for a metallic material according to an embodiment of the present disclosure includes a cutting process, a compression process, a sampling process, a tensile test process, and a calculation process. In the cutting step, a rectangular plate-shaped sample is cut out from the metal material. In the compression step, a compressive load is applied to the sample under predetermined conditions using a mold to introduce an equivalent plastic strain of 0.20 or more to the sample. In the sampling step, a round bar-shaped tensile test piece is sampled from the sample after the compression step. In the tensile test step, a tensile load is applied to the tensile test piece in the axial direction to break the tensile test piece. In the calculation step, the mechanical properties corresponding to the equivalent plastic strain under the predetermined conditions are calculated from the results of the tensile test step (first configuration).

According to the test method of the first configuration, in the case of molding that undergoes a complex deformation process including compressive deformation in which a large compressive plastic strain is introduced, a metal material is used as a starting material, and in the compression process, the conditions for the complex deformation process are set. A compressive load is applied to the sample assuming compressive deformation, and a large compressive plastic strain of 0.20 or more in terms of equivalent plastic strain is introduced into the sample. In the sampling step, a tensile test piece is sampled from the sample to which the compressive plastic strain has been introduced. Furthermore, in the tensile test step, a tensile load is applied to the tensile test piece assuming tensile deformation in the compound deformation process, and the tensile test piece is broken. In short, a load is applied to the metal material assuming each deformation in a compound deformation process including compressive deformation in which a large compressive plastic strain is introduced. Then, in the calculation step, the mechanical properties corresponding to the equivalent plastic strain in the compound deformation process are calculated from the results of the tensile test step. Therefore, according to the test method of the first configuration, it is possible to appropriately acquire the mechanical properties of a metal material that undergoes a compound deformation process. This mechanical property is suitable for determining with high accuracy whether a metal material undergoing a complex deformation process can be formed.

In a typical example, the mechanical property calculated in the calculation step is the ultimate deformability. A mechanical property may be a stress-strain curve.

The test method described above preferably has the following configuration. In the compression step, the predetermined condition is either one of the following conditions (a) and (b) (second configuration).
(a) releasing deformation in the longitudinal direction and transverse direction of the sample and applying a compressive load to the sample; Release the deformation and apply a compressive load to the sample.

In the second configuration, condition (a) corresponds to uniaxial compression. Condition (b) corresponds to plane strain compression. An appropriate condition may be selected from conditions (a) and (b) according to the composite deformation process. The value of the equivalent plastic strain to be introduced into the sample may be appropriately set for each of these conditions. Multiple equivalent plastic strain values are set for each condition. The reduction amount due to the compressive load is determined according to the value of the equivalent plastic strain. The direction in which the compressive load is applied can be appropriately set according to each condition.

The above test method may comprise the following configuration. In the collection step, a tensile test piece is collected from the sample according to the following conditions (i) or (ii) (third configuration).
(i) the axial direction of the tensile test piece coincides with the rolling direction of the metallic material in the sample; and (ii) the axial direction of the tensile test piece coincides with the direction perpendicular to the rolling direction of the metallic material in the sample.

In the third configuration, the direction in which the tensile test piece is taken differs between condition (i) and condition (ii). Therefore, the properties of the metal material can be evaluated from the anisotropic point of view.

The test method described above preferably has the following configuration. In the tensile test step, the pre-test cross-sectional area S0 and the post-test cross-sectional area S1 at the fracture position of the tensile test piece are measured. In the calculation step, the ultimate deformability is calculated as a mechanical property from the pre-test cross-sectional area S0 and the post-test cross-sectional area S1 (fourth configuration).

In a fourth configuration, the mechanical property calculated in the calculating step is ultimate deformability. Ultimate deformability is a ductile failure parameter. In this case, based on the ultimate deformability, it is possible to evaluate whether or not the metal material will fracture. Therefore, it is possible to determine with high accuracy whether or not the metal material to be evaluated that undergoes a complex deformation process can be molded.

A specific example of the method for testing a metal material according to the present embodiment will be described below with reference to the drawings. The same or corresponding parts in the drawings are denoted by the same reference numerals, and overlapping descriptions are omitted as appropriate. The test method of this embodiment can be used as a fracture evaluation method for metallic materials.

[Breaking evaluation method]
FIG. 1 is a flow chart showing an example of a fracture evaluation method for metal materials using the test method of the present embodiment. An object to be evaluated by the fracture evaluation method using the test method of the present embodiment is a metal material that undergoes compressive deformation and finally tensile deformation. A large compressive plastic strain of 0.20 or more in terms of equivalent plastic strain is introduced into the metal material to be evaluated by compressive deformation. That is, in the present embodiment, as an evaluation target, molding that undergoes a compound deformation process including compression deformation in which a large compressive plastic strain is introduced is assumed. Referring to FIG. 1, the fracture evaluation method includes a preliminary test process (#100), a storage process (#200), and an evaluation process (#300). The preliminary test step (#100) corresponds to the test method for the metallic material of this embodiment.

The preliminary test process (#100) includes a cutting process (#105), a compression process (#110), a collection process (#115), a tensile test process (#120), and a calculation process (#125). In the preliminary test step (#100), by going through these steps, tests are performed for each of a plurality of mutually different composite deformation processes. Then, the ultimate deformability corresponding to each compound deformation process is calculated. In the storage step (#200), each ultimate deformability calculated in the preliminary test step (#100) is stored in association with the corresponding composite deformation process. The evaluation step (#300) extracts, from among the composite deformation processes stored in the storage step (#200), those that match the deformation processes acting on the metal material to be evaluated. Then, based on the ultimate deformability associated with the extracted composite deformation process, it is evaluated whether the metal material will fracture. Hereinafter, each step will be specifically described by taking a rolled steel strip as an example of the metal material of the starting material.

[Preliminary test step (#100): test method for metal material]
As described above, the preliminary test step (#100) includes a cutting step (#105), a compression step (#110), a sampling step (#115), a tensile test step (#120), and a calculation step (#125). include.

[Cutting step (#105)]
In the cutting step (#105), a rectangular plate-shaped sample is cut out from the rolled steel strip. A rolled steel strip is, for example, a hot rolled steel strip.

FIG. 2 is a perspective view showing an example of the sample 10 cut out in the cutting step (#105). Referring to FIG. 2, a sample 10 is cut out from a hot-rolled steel plate for automobile construction (SAPH490) having a thickness of 14 mm, and has a square shape in which the vertical direction D and the horizontal direction W are the same in plan view. In the sample 10, the length LD in the longitudinal direction D is 15 mm, the length LW in the lateral direction W is 15 mm, and the length Lt in the thickness direction t is 8 mm. In this specification, the longitudinal direction D is the direction that coincides with the rolling direction C of the rolled steel strip (see the two-dot chain line in FIG. 2), and can also be called the longitudinal direction on the basis of the rolled steel strip. The transverse direction W is a direction perpendicular to the rolling direction C, and can also be called a width direction on the basis of the rolled steel strip.

[Compression step (#110)]
Returning to FIG. 1, the description continues. In the compression step (#110), a compressive load is applied to the sample 10 under predetermined conditions using a mold, and a compressive plastic strain of 0.20 or more in terms of equivalent plastic strain is introduced into the sample 10 . That is, using a press device (eg, a servo press device), the sample 10 is accommodated in a lower die having a predetermined shape, and the sample 10 is pressed down by lowering the upper punch. The predetermined condition is a condition corresponding to the compound deformation process.

3 to 6 are plan views showing an example of the conditions of the compression step (#110). FIG. 3 shows the situation in the case of uniaxial compression. 4 and 5 show the situation in the case of plane strain compression. FIG. 6 shows the situation in the case of plane strain compression and in the case of a plane including the plate thickness direction. These figures show how the sample 10 accommodated in the lower die before the compression process is viewed from above. In these figures, the dotted line indicates the inner wall of the lower die. Of the surfaces of the sample 10, the surface away from the inner wall of the lower die is free from the mold, meaning that the sample 10 is free from deformation in the direction perpendicular to that surface. On the other hand, of the surfaces of the sample 10, the surface that is in contact with the inner wall of the lower die is not free from the mold, meaning that the sample 10 is restrained from deformation in the direction perpendicular to that surface. do. In these figures, a compressive load is applied to the sample 10 in a direction perpendicular to the plane of the drawing.

The conditions shown in FIGS. 4 and 6 are plane strain compression, and the constraint conditions by the die in the rolling direction are also the same. However, the direction of compression under the conditions shown in FIG. 4 is the plate thickness direction t, and the direction of compression under the conditions shown in FIG. 6 is the lateral direction W, which is different from the conditions shown in FIG. Hot-rolled steel strip generally has different material properties in the in-plane and through-thickness directions, ie, anisotropy. Therefore, by considering the above anisotropy in the ultimate deformability used for fracture determination, it is possible to more precisely determine whether or not the metal material can be molded.

In the case of the conditions shown in FIG. 3 , a compressive load is applied to the sample 10 in the plate thickness direction t while the sample 10 is freed from deformation in the longitudinal direction D and the lateral direction W. In this case, the sample 10 is compressed and deformed in the plate thickness direction t and spreads in both the longitudinal direction D and the transverse direction W. Hereinafter, this condition may be referred to as condition (A). Note that this condition (A) corresponds to the condition (a) described above.

In the case of the conditions shown in FIG. 4 , a compressive load is applied to the sample 10 in the plate thickness direction t in a state in which deformation in the lateral direction W of the sample 10 is restrained and deformation in the longitudinal direction D is released. In this case, the sample 10 is compressed and deformed in the plate thickness direction t, and spreads in the longitudinal direction D while the deformation in the lateral direction W is suppressed. Hereinafter, this condition may be referred to as condition (B).

In the case of the conditions shown in FIG. 5 , a compression load is applied to the sample 10 in the plate thickness direction t in a state in which deformation in the longitudinal direction D of the sample 10 is restrained and deformation in the lateral direction W is released. In this case, the sample 10 is compressed and deformed in the plate thickness direction t, and expands in the lateral direction W while the deformation in the longitudinal direction D is suppressed. Hereinafter, this condition may be referred to as condition (C). These conditions (B) and (C) correspond to the condition (b) described above.

In the case of the conditions shown in FIG. 6, a compressive load is applied in the lateral direction W of the sample 10 in a state in which deformation in the plate thickness direction t of the sample 10 is restrained and deformation in the longitudinal direction D is released. In this case, the sample 10 is compressed and deformed in the lateral direction W, and expands in the longitudinal direction D while being restrained from being deformed in the plate thickness direction t. Hereinafter, this condition may be referred to as condition (D). Note that this condition (D) corresponds to the condition (b) described above. Alternatively, a compressive load may be applied in the longitudinal direction D of the sample 10 in a state in which deformation in the plate thickness direction t of the sample 10 is restrained and deformation in the lateral direction W is released.

For each of these conditions (A) to (D), the value of the equivalent plastic strain introduced into the sample 10 by applying a compressive load is set. For example, two values of 0.25 and 0.50 are set as equivalent plastic strain values. Such a set of values is the same for conditions (A)-(D). However, the number of values to be set is not limited to two, and may be three or more. Depending on the value of the equivalent plastic strain, the amount of reduction due to the compressive load under conditions (A) to (D) is determined.

A compression step (#110) is performed for each of the conditions (A) to (D). As a result, Sample 10 introduced with an equivalent plastic strain of 0.25 and Sample 10 introduced with an equivalent plastic strain of 0.50 are obtained for each of the conditions (A) to (D). In order to suppress friction between the mold and the sample 10, the mold is coated with a lubricant.

[Collecting step (#115)]
Returning to FIG. 1, the description continues. In the collecting step (#115), a round bar-shaped tensile test piece is collected from the sample 10 obtained under each condition after the compression step (#110).

FIG. 7 is a plan view showing an example of the tensile test piece 11 sampled in the sampling step (#115). Referring to FIG. 7, a tensile test piece 11 is taken along the rolling direction C (see FIGS. 3 to 6) of the sample 10 after the compression step (#110). In this case, the axial direction of the tensile test piece 11 coincides with the rolling direction C of the sample 10 . Hereinafter, this condition may be referred to as condition (i).

However, the tensile test piece 11 may be taken along the direction perpendicular to the rolling direction C. In this case, the axial direction of the tensile test piece 11 coincides with the direction perpendicular to the rolling direction C in the sample 10 . Hereinafter, this condition may be referred to as condition (ii). However, the tensile test piece 11 may be sampled along a direction inclined from the rolling direction C.

Referring to FIG. 7, in tensile test piece 11, diameter φa of parallel portion 11a is 1.0 mm. The axial length of the parallel portion 11a is 2.0 mm.

However, the shape of the tensile test piece 11 is not limited to the shape shown in FIG. FIG. 8 is a plan view showing another example of the tensile test piece 11. FIG. Referring to FIG. 8, in tensile test piece 11, parallel portion 11a may be provided with constricted portion 11b. In this case, the diameter φb of the constricted portion 11b is 0.80 mm. A curvature radius Rb of the longitudinal section of the constricted portion 11b is, for example, 2.0 mm, 1.0 mm, or 0.50 mm.

Tensile test piece 11 with an equivalent plastic strain of 0.25 introduced and tensile test piece with an equivalent plastic strain of 0.50 introduced for each of the conditions (A) to (D) by the sampling step (#115) 11 is obtained.

[Tensile test step (#120)]
Returning to FIG. 1, the description continues. In the tensile test step (#120), a tensile load is applied to the tensile test piece 11 in the axial direction, and the tensile test piece 11 is broken. In the tensile test step (#120), the tensile load and elongation of the tensile test piece 11 are measured. In the tensile test step (#120), the breaking position of the tensile test piece 11 is determined, and the pre-test cross-sectional area S0 and the post-test cross-sectional area S1 at the breaking position are measured. In the case of the tensile test piece 11 shown in FIG. 7, the fracture position appears in the parallel portion 11a. In the case of the tensile test piece 11 shown in FIG. 8, the fracture position appears at the constricted portion 11b.

The post-test cross-sectional area S1 means the area of the fracture surface. Therefore, the post-test cross-sectional area S1 can be calculated from the diameter of the fracture surface. The fracture surface is not limited to a strictly circular shape, and may be elliptical in some cases. Therefore, the post-test cross-sectional area S1 can be calculated by measuring the diameter of the fracture surface from two directions perpendicular to each other. The fracture surface may be photographed with a camera, and the post-test cross-sectional area S1 may be calculated from the image data. On the other hand, the pre-test cross-sectional area S0 can be calculated from the dimensions of the tensile test piece 11 before the test. In the case of the tensile test piece 11 shown in FIG. 7, the pre-test cross-sectional area S0 can be calculated from the diameter φa of the parallel portion 11a. In the case of the tensile test piece 11 shown in FIG. 8, the pre-test cross-sectional area S0 can be calculated from the diameter φb of the constricted portion 11b.

In short, in the above-described compression step (#110) and tensile test step (#120), a load is applied to the steel sheet material assuming each deformation in the compound deformation process including compression deformation in which a large compressive plastic strain is introduced. . That is, for each of conditions (A) to (D), using a tensile test piece 11 with an equivalent plastic strain of 0.25 and a tensile test piece 11 with an equivalent plastic strain of 0.50, tensile A test step (#120) is performed.

For reference, the tensile test step (#120) is performed using the tensile test piece 11 that has not been subjected to the compression step (#110). In this case, the tensile test piece 11 may be taken directly from the rolled steel strip. Therefore, no equivalent plastic strain was introduced into the tensile test piece 11 . Hereinafter, the condition in which the compression step (#110) is not performed may be referred to as condition (N). Condition (N) is a condition that does not undergo a complex deformation process.

[Calculation step (#125)]
Returning to FIG. 1, the description continues. In the calculation step (#125), the mechanical properties corresponding to the equivalent plastic strains (0.25 and 0.50) under conditions (A) to (D) are calculated from the results of the tensile test step (#120). do. Also, the mechanical properties corresponding to the condition (N) are calculated. In the calculation step (#125), the ultimate deformability Dcr is calculated as the mechanical property. The ultimate deformability Dcr is defined by the following formula (2).
Dcr=ln(S0/S1) (2)
In formula (2), S0 indicates the pre-test cross-sectional area of the tensile test piece 11 at the fracture position, and S1 indicates the post-test cross-sectional area of the tensile test piece 11 at the fracture position.

However, the mechanical property calculated in the calculation step (#125) is not limited to the ultimate deformability Dcr, and may be a stress-strain curve.

FIG. 9 is a diagram summarizing an example of the mechanical properties calculated in the calculation step (#125) for each condition. FIG. 9 shows the ultimate deformability Dcr as a mechanical property. The results shown in FIG. 9 reveal the following.

Comparing the condition (N) with each of the other conditions, the ultimate deformability is lowered through the complex deformation process. The degree of reduction in ultimate deformability according to the equivalent plastic strain differs between conditions of compressive deformation in the compound deformation process. For example, the degree of decrease in ultimate deformability under the plane strain compression conditions (B) ((B0.25) and (B0.50)) is the same as the uniaxial compression conditions (A) ((A0.25) and (A0. 50)). In addition, conditions (B) ((B0.25) and (B0.50)) and conditions (C) ((C0.25) and (C0.50)) are both plane strain compression conditions, and this There is no significant difference between the two steel types.

Thus, by going through each step of the preliminary test step (#100), it is possible to appropriately acquire the mechanical properties of the steel plate material that has undergone the compound deformation process. This mechanical property is suitable for determining with high accuracy whether or not each FEM analysis element in a steel plate material undergoing a complex deformation process can be formed.

Further, in the above embodiment, the condition (i) is adopted in the sampling step (#115), and the tensile test piece 11 is sampled from the sample 10 along the rolling direction C. Furthermore, by adopting the condition (ii) and taking a tensile test piece 11 along the direction perpendicular to the rolling direction C of the sample 10, the properties of the steel sheet material can be evaluated from the anisotropic point of view. be able to.

[Storage step (#200)]
Returning to FIG. 1, the description continues. In the storage step (#200), each ultimate deformability calculated in the preliminary test step (#100) is stored in association with the corresponding conditions of the combined deformation process and the value of the equivalent plastic strain. More specifically, the ultimate deformability calculated in the preliminary test step (#100) was subjected to the corresponding conditions (N), (A0.25), (A0.50), (B0.25), (B0. 50), (C0.25), (C0.50), (D0.25) and (D0.50). These data are stored in the computer's memory. This can be used to determine whether molding is possible by FEM.

Here, if there are new conditions different from the stored conditions, a new preliminary test step (#100) may be performed under the new conditions. In other words, the ultimate deformability is calculated under new conditions, and this ultimate deformability is stored in association with the new conditions.

However, if there are new conditions different from the stored conditions, they may be set by calculation without executing the preliminary test step (#100). For example, linear interpolation can be used. Specific examples are shown below.

If there is a new equivalent plastic strain condition of 0.10 in the condition (A), the value of this equivalent plastic strain is between 0 and 0.25. The condition in this case can be represented by condition (A0.10). In this case, the ultimate deformability of condition (A0.10) lies between the ultimate deformability of condition (N) and the ultimate deformability of condition (A0.25). Then, from the value of the equivalent plastic strain under condition (N), condition (A0.10), and condition (A0.25), if the ultimate deformability under condition (N) and condition (A0.25) is linearly interpolated, , the ultimate deformability of condition (A0.10) can be calculated. This ultimate deformability is stored in association with the condition (A0.10).

Moreover, when there is a new condition of equivalent plastic strain of 0.40 in condition (A), the value of this equivalent plastic strain is between 0.25 and 0.50. The condition in this case can be represented by condition (A0.40). In this case, the ultimate deformability of condition (A0.40) lies between the ultimate deformability of condition (A0.25) and the ultimate deformability of condition (A0.50). Then, from the equivalent plastic strain values of conditions (A0.25), conditions (A0.40) and conditions (A0.50), the ultimate deformability of conditions (A0.25) and conditions (A0.50) By linear interpolation, the ultimate deformability of the condition (A0.40) can be calculated. This ultimate deformability is stored in association with the condition (A0.40).

Conceptually speaking, these specific examples are as follows. The two stored composite deformation processes include a first composite deformation process and a second composite deformation process. That is, for example, the first composite deformation process is condition (A0.25), and the second composite deformation process is condition (A0.50). The equivalent plastic strain of the first composite deformation process is referred to as the first equivalent plastic strain, and the equivalent plastic strain of the second composite deformation process is referred to as the second equivalent plastic strain. That is, the first equivalent plastic strain is 0.25 and the second equivalent plastic strain is 0.50. The first composite deformation process and the second composite deformation process differ only in the value of the first equivalent plastic strain and the value of the second equivalent plastic strain. In other words, for example, the first composite deformation process and the second composite deformation process are common under condition (A). The ultimate deformability corresponding to the first equivalent plastic strain is referred to as the first ultimate deformability, and the ultimate deformability corresponding to the second equivalent plastic strain is referred to as the second ultimate deformability.

In this case, for the third equivalent plastic strain (plastic strain of condition (A0.40)) set between the first equivalent plastic strain and the second equivalent plastic strain, the first limit A third ultimate deformability (the ultimate deformability of the condition (A0.40)) set between the deformability and the second ultimate deformability can be calculated. The calculated third ultimate deformability is stored in association with the third composite deformation process (condition (A0.40)) that depends on the corresponding third equivalent plastic strain.

In this way, the value of the ultimate deformability obtained in the preliminary test step (#100), that is, the values of the first ultimate deformability and the second ultimate deformability are used to determine the third ultimate deformability. can be calculated. That is, it is possible to estimate the third ultimate deformability corresponding to the third equivalent plastic strain in the third compound deformation process without actually conducting the test in the preliminary test step (#100). This is efficient. Therefore, it is possible to efficiently evaluate whether or not each element in the steel plate material will eventually break.

[Evaluation step (#300)]
In the evaluation step (#300), from the composite deformation processes stored in the storage step (#200), a deformation process that matches each element in the steel sheet material to be evaluated is extracted. Based on the ultimate deformability associated with the extracted compound deformation process, it is evaluated whether fracture occurs in each element in the steel plate material. This evaluation is performed, for example, by a computer.

FIG. 10 is a flow chart showing an example of the evaluation process (#300). The evaluation step (#300) is performed by FEM using a computer. First, an analysis model of the steel sheet material to be evaluated is created, and forming analysis by FEM is started (step #305). Referring to FIG. 10, at step #310, the i-th forming step is executed. The first stage is the first molding step.

Next, at step #315, the stress state is calculated for each element of the analysis model at that time. Next, at step #320, for each element of the analysis model at that time, a ductile fracture parameter in the stress state of the element is extracted. Here, from the data stored in the memory, the composite deformation process that matches the composite deformation process expected for the element is extracted, and the ultimate deformability associated with the extracted composite deformation process is extracted. The extracted ultimate transformability is stored in the storage.

Next, in step #325, for each element of the analysis model at that time, the ductile fracture parameter in the i-th forming step is added to the total ductile fracture parameter up to the (i-1)-th forming step. to add. Here, the ultimate deformability in the i-th forming step is added to the total ultimate deformability up to the (i−1)th forming step stored in the storage. The total ultimate deformability of the sum is stored in the storage.

Then, at step #330, it is determined whether or not the predetermined molding step has been reached. If the scheduled molding step has not been reached, the process returns to step #310 to execute the next molding step. Steps #310-#330 are repeated until the predetermined molding step is reached.

When the predetermined forming step is reached, the forming analysis is terminated at step #335, and the fracture determination is started at step #340. Then, at step #345, each element of the analysis model is determined to be fractured from the ductile fracture parameter. Here, the total ultimate deformability stored in storage is used to evaluate whether or not rupture occurs. After the evaluation, at step #350, the fracture judgment is terminated.

Therefore, it is possible to determine with high accuracy whether or not the steel sheet material to be evaluated that undergoes the compound deformation process can be formed.

[Modification]
In the above embodiment, the case where there is one compressive deformation condition in the compound deformation process has been described. In this case, the compound deformation process is a combination of compressive deformation of one of condition (A), condition (B), condition (C) and condition (D) and tensile deformation.

However, there may be two conditions for compressive deformation in the compound deformation process. In this case, the compound deformation process is a combination of compressive deformation and tensile deformation under conditions (A), (B), (C), and (D). More specifically, the compound deformation process is, for example, a combination of uniaxial compression of condition (A), plane strain compression of condition (B), and tensile deformation. Of course, there may be two or more compression deformation conditions in the composite deformation process.

When the compound deformation process is a combination of uniaxial compression of condition (A), plane strain compression of condition (B), and tensile deformation, method 1 and method 2 below can be adopted.

In Method 1, a preliminary test step (#100) is specially performed. Specifically, in the preliminary test step (#100), first, the compression step (#110) is performed under the condition (A). Subsequently, the compression step (#110) is performed under the condition (B) on the sample 10 to which the compressive plastic strain has been introduced under the condition (A). After that, the collection step (#115), the tensile test step (#120), and the calculation step (#125) are performed in order. In this case, the mechanical properties can be obtained by faithfully considering the order of each deformation in the compound deformation process.

In method 2, the preliminary test step (#100) is not specially performed. Specifically, the mechanical properties obtained by the preliminary test step (#100) performed only under the condition (A) and the mechanical properties obtained by the preliminary test step (#100) performed only under the condition (B) Add the characteristics and . In this case, although the order of each deformation in the compound deformation process is not considered, the mechanical properties can be obtained easily.

Also, two conditions for tensile deformation in the compound deformation process may be used. In this case, the compound deformation process is a combination of compressive deformation in one of condition (A), condition (B), condition (C) and condition (D) and two tensile deformations. More specifically, the compound deformation process is, for example, a combination of tensile deformation, uniaxial compression of condition (A), and tensile deformation. However, two or more conditions for tensile deformation may be included in the composite deformation process.

When the compound deformation process is a combination of tensile deformation, uniaxial compression of condition (A), and tensile deformation, the following method can be adopted. A tension step is added before the preliminary test step (#100). This pulling process cuts an intermediate sample, one size larger than sample 10, from the rolled steel strip. Next, a tensile load is applied to the intermediate sample so that the intermediate sample stretches uniformly along the rolling direction, for example. This introduces a uniform elongation of, for example, 10%, 20%, etc. into the intermediate sample. After the tensioning step, a preliminary test step (#100) is performed. In this case, in the cutting step (#105), the sample 10 is cut out from the intermediate sample.

The embodiments of the present disclosure have been described above. However, the above-described embodiments are merely examples for implementing the present disclosure. Therefore, the present disclosure is not limited to the above-described embodiments, and the above-described embodiments can be modified as appropriate without departing from the scope of the present disclosure.

10: Sample 11: Tensile test piece

Claims (4)

A cutting step of cutting out a rectangular plate-shaped sample from a metal material;
A compression step of applying a compressive load under predetermined conditions to the sample using a mold and introducing an equivalent plastic strain of 0.20 or more to the sample;
A collection step of collecting a round bar-shaped tensile test piece from the sample after the compression step;
A tensile test step of applying a tensile load to the tensile test piece in the axial direction to break the tensile test piece;
and a calculation step of calculating mechanical properties corresponding to the equivalent plastic strain under the predetermined conditions from the result of the tensile test step. A method for testing a metallic material according to claim 1,
In the compression step, the predetermined condition is either one of the following conditions (a) and (b).
(a) releasing the longitudinal and lateral deformation of the sample and applying a compressive load to the sample; and (b) constraining the longitudinal and lateral deformation of the sample. or release the deformation in the other direction and apply a compressive load to the sample. A method for testing a metal material according to claim 1 or 2,
A method for testing a metallic material, wherein in the collecting step, the tensile test piece is collected from the sample according to the following conditions (i) or (ii).
(i) the axial direction of the tensile test piece coincides with the rolling direction of the metallic material in the sample; and (ii) the axial direction of the tensile test piece is in the rolling direction of the metallic material in the sample. Match the vertical direction. A method for testing a metal material according to any one of claims 1 to 3,
In the tensile test step, the pre-test cross-sectional area S0 and the post-test cross-sectional area S1 at the breaking position of the tensile test piece are measured,
A method for testing a metal material, wherein in the calculation step, the ultimate deformability as the mechanical property is calculated from the pre-test cross-sectional area S0 and the post-test cross-sectional area S1.

Images