Sheet metal shear testing methods, sheet metal shear testing systems, and manufacturing methods for sheared sheet metal materials.

Abstract

Invention details;

Description

METHOD FOR TESTING SHEAR WORK OF METAL PLATES, METAL PLATE SHEAR WORK TEST SYSTEM, AND METHOD FOR MANUFACTURING SHEAR-WORKED METAL PLATES

[0001] The present invention relates to a metal plate shearing test method for calculating residual stress at the sheared edge of a sheared material obtained by shearing a metal plate, a metal plate shearing test system, and a metal plate shearing material manufacturing method for producing a sheared material obtained by shearing a metal plate.

[0002] Sheared materials produced by shearing metal sheets are used as blanks for press-formed parts (e.g., automotive parts). However, residual stresses in sheared materials caused by shearing are known to affect the fatigue life and delayed fracture characteristics of press-formed parts. Therefore, understanding the residual stresses in sheared materials is important for ensuring the fatigue life of press-formed parts made from sheared materials.

[0003] Conventionally, residual stress in metal plates has been measured using X-rays or supersonic waves, or calculated by measuring strain during the deformation process of the metal plate. Furthermore, predictions have been made using finite element analysis of the shearing process. Patent Document 1 discloses a technique for detecting diffracted X-rays emitted from a sample when the sample is irradiated with X-rays, and nondestructively measuring the stress inside the sample based on the information from the diffracted X-rays. Patent Document 2 discloses a technique for generating ultrasonic waves in a plastically deformed test object (e.g., a metal plate) and nondestructively measuring the residual stress based on the measured ultrasonic wave speed information. Patent Document 3 also discloses a technique for measuring the strain at a deformed portion during a deformation process of a metal plate to obtain a strain history, and incrementally updating the stress at the deformed portion from the start to the end of deformation based on the obtained strain history, thereby determining the residual stress at the deformed portion.

[0004] Furthermore, prediction of residual stresses during shearing by finite element analysis can be performed using commonly used finite element analysis software, and efforts are being made to improve the accuracy of material constitutive laws in such finite element analysis. For example, the material constitutive law disclosed in Non-Patent Document 1 (hereinafter referred to as the "YU model (Yoshida-Uemori model)") contributes to improving the accuracy of springback analysis, which is important for predicting residual stresses in press-formed products. Furthermore, Non-Patent Document 2 presents fracture conditions under which ductile materials fracture, and a model has been developed to simulate the behavior of the material up to fracture.

[0005] JP 2002-333409 A JP 2011-196953 A Japanese Patent No. 6981521 A

[0006] F. Yoshida and T. Uemori, International Journal of Mechanical Sciences, 45(2003), 1687-1702.F.

[0007] However, the stress measurement using X-rays disclosed in Patent Document 1 and the residual stress measurement using ultrasound disclosed in Patent Document 2 assume that the sample (metal plate, etc.) is uniform within the region where the X-rays are incident or the ultrasound is generated. As a result, these measurement techniques have difficulty accurately measuring the residual stress of metal plates with two or more phases (e.g., dual phase (DP) steel plates, etc.). Furthermore, both the techniques of Patent Document 1 and Patent Document 2 measure residual stress after deformation, but are unable to measure the stress history during deformation.

[0008] Furthermore, the techniques of Patent Document 1 and Patent Document 2 are both techniques for determining the stress at a specific point on the sample to be measured, and in order to obtain the distribution of residual stress, it is necessary to repeatedly measure the stress at multiple points.

[0009] Furthermore, the technology of Patent Document 3 calculates the residual stress generated in a metal plate that has been subjected to plastic deformation based on a coordinate system defined at each position on the metal plate. Therefore, if the orientation of the coordinate system changes due to rotational deformation of the metal plate itself during the deformation process, the direction of the residual stress generation becomes unclear.

[0010] In contrast to the techniques described in Patent Documents 1 to 3, the method of predicting residual stress using finite element analysis (FEA) allows for easy calculation of residual stress distribution. However, the input values ​​(shape, material properties, deformation characteristics, boundary conditions, etc.) given to the FEA software used for FEA significantly affect the residual stress prediction results. Therefore, in order to accurately predict residual stress using FEA, it is necessary to set more accurate values ​​for various input values, such as not only the material properties of the metal plate but also the deformation properties of the tool that applies plastic deformation, and boundary conditions such as the contact properties and sliding characteristics between the metal plate and the tool.

[0011] Furthermore, to predict residual stress in sheared metal sheets using finite element analysis, it is necessary to incorporate the fracture conditions of the metal sheets into the finite element analysis. Various fracture criteria have been proposed, such as the ductile fracture condition of Cockcroft et al. and the fracture condition based on stress triaxiality of GISSMO et al. (Patent Document 2). However, no criterion has yet been established that can accurately predict fracture during shearing. Furthermore, when modeling fracture phenomena in finite element analysis, it is common to determine whether each element in the finite element analysis model satisfies the fracture condition, and then delete elements that satisfy the fracture condition from the finite element analysis model. However, deleting elements results in the loss of mass and energy of the metal sheet (sheared material), which can lead to discrepancies with the actual fracture phenomenon. For this reason, it is extremely difficult to accurately predict the residual stress that occurs at the sheared edge of a metal plate after shearing using finite element analysis.

[0012] The present invention has been made to solve the above-mentioned problems, and its object is to provide a shearing test method and shearing test system for metal plates that can reproduce the shearing of metal plates and accurately and easily determine the residual stress at the sheared edge formed in the test piece.Furthermore, another object of the present invention is to provide a manufacturing method for sheared metal plates in which measures are appropriately taken to suppress the generation of tensile residual stress that affects fatigue life and delayed fracture properties.

[0013] The shearing test method for metal plates according to the present invention calculates residual stress at a sheared edge of a sheared material obtained by shearing a metal plate, and includes a shearing reproduction test process for reproducing the formation process of the sheared edge by shearing a test piece using the metal plate as a test material, and a residual stress distribution calculation process for calculating a residual stress distribution at a side surface of the sheared edge formed on the test piece. The shearing reproduction test process includes a punch, a die, and a blank holder. The test piece is sheared by relatively moving the punch and the die while the test piece is disposed between the die and the holder, and the residual stress distribution calculation process includes a deformation history acquisition step, a sequential stress update step, and a residual stress distribution calculation step, and the deformation history acquisition step sets a plurality of measurement points on the side surface of the sheared end of the sheared end formed on the test piece, and measures three-dimensional coordinates of each of the plurality of measurement points during the deformation process of the sheared end due to the shearing of the test piece in the shearing process reproduction test process, thereby obtaining a surface deformation history (surface a surface deformation history acquisition step of acquiring a strain history of the shear end side surface in the deformation process of the shear end from the acquired surface deformation history of the shear end side; and a spin history acquisition step of acquiring a spin history of the shear end side surface in the deformation process of the shear end from the acquired surface deformation history of the shear end side, wherein the sequential stress update process includes an acquired strain increment calculation step of calculating an acquired strain increment from the strain history of the shear end side surface acquired in the strain history acquisition step; and an assumed strain increment calculation step of calculating an assumed incremental strain by assuming a deformation state of the shear end side surface, which is an increment of strain other than the strain whose strain history was acquired in the strain history acquisition step.the residual stress distribution calculation step includes a stress coordinate system conversion step of converting the stress in the material coordinate system of each of the plurality of measurement points at the end of deformation of the shear end due to shearing of the test piece, which is obtained by sequentially updating the stress in the material coordinate system of each of the plurality of measurement points at the end of deformation of the shear end, which is obtained by sequentially updating the stress in the material coordinate system of each of the plurality of measurement points at the end of deformation of the shear end, which is obtained by sequentially updating the stress in the material coordinate system of each of the plurality of measurement points at the end of deformation of the shear end, which is obtained by sequentially updating the stress in the material coordinate system of each of the plurality of measurement points at the end of deformation of the shear end, which is obtained by sequentially updating the stress in the material coordinate system of each of the plurality of measurement points at the end of deformation of the shear end, which is obtained by sequentially updating the stress in the material coordinate system of each of the plurality of measurement points at the end of deformation of the shear end, which is obtained by sequentially updating the stress in the material coordinate system of each of the plurality of measurement points at the end of deformation of the shear end, which is obtained by

[0014] The residual stress distribution calculation step may further include a residual stress distribution display step of displaying the residual stress distribution on the side surface of the shear end portion obtained in the stress coordinate system conversion step.

[0015] The assumed strain increment calculation step may include assuming a deformation state of the shear end side from the deformation process of the shear end due to shear processing of the test piece, and calculating the assumed strain increment at the shear end side based on the mechanics of plasticity in the assumed deformation state.

[0016] The assumed strain increment calculation step may include assuming a deformation state of the shear end side surface by finite element analysis of the deformation process of the shear end surface due to shear processing of the test piece, and calculating the assumed strain increment at the shear end side surface based on the assumed deformation state.

[0017] The shearing test system for metal plates according to the present invention calculates the residual stress at the sheared end of a sheared material obtained by shearing a metal plate, and includes a shearing reproduction test device that reproduces the formation process of the sheared end by shearing a test piece using the metal plate as a test material, and a residual stress distribution calculation device that calculates the residual stress distribution at the sheared end side of the sheared end formed on the test piece. The shearing reproduction test device includes a shearing mold having a punch, a die, and a holder, and performs a shearing test on the sheared end side of the sheared end formed on the test piece with the test piece placed between the die and the holder. The punch and the die are moved relative to each other to shear the test piece, and the residual stress distribution calculation device has a deformation history acquisition unit, a sequential stress update unit, and a residual stress distribution calculation unit, and the deformation history acquisition unit measures three-dimensional coordinates of a plurality of measurement points set on the side surface of the sheared end of the sheared end formed on the test piece during the deformation process of the sheared end due to the shearing of the test piece using the shearing process reproduction test device, and acquires a surface deformation history of the side surface of the sheared end from the start of deformation of the sheared end to the end of deformation of the sheared end. The sequential stress update unit includes a deformation history acquisition unit, a strain history acquisition unit that acquires a strain history of the shear end side surface in the deformation process of the shear end from the acquired surface deformation history of the shear end side, and a spin history acquisition unit that acquires a spin history of the shear end side surface in the deformation process of the shear end from the acquired surface deformation history of the shear end side, and the sequential stress update unit includes an acquired strain increment calculation unit that calculates an acquired strain increment from the strain history of the shear end side surface acquired by the strain history acquisition unit, and a spin history acquisition unit that calculates an acquired strain increment from the strain history of the shear end side surface acquired by the strain history acquisition unit. an assumed strain increment calculation unit that calculates an assumed strain increment by assuming a deformation state of the shear end side surface, which is an increment of strain other than the acquired strain; an acquired spin increment calculation unit that calculates an acquired spin increment from the spin history acquired by the spin history acquisition unit; a stress increment calculation unit that calculates a stress increment for each of the plurality of measurement points in accordance with a material constitutive law using the acquired strain increment, the assumed strain increment, and the acquired spin increment; and a stress increment calculation unit that calculates a stress in a material coordinate system for each of the plurality of measurement points using the stress increment calculated for each of the plurality of measurement points.and a sequential stress update unit that sequentially updates the stress in the material coordinate system of each of the plurality of measurement points at the end of deformation of the shear end due to shearing of the test piece from the start to the end of deformation, and the residual stress distribution calculation unit has a stress coordinate system conversion unit that converts the stress in the material coordinate system of each of the plurality of measurement points at the end of deformation of the shear end, which is obtained by sequential updating by the sequential stress update unit, into a global stress value in a predetermined direction in a global coordinate system, and obtains the converted global stress value of each of the plurality of measurement points as the residual stress distribution on the side surface of the shear end.

[0018] The residual stress distribution calculation unit may further include a residual stress distribution display unit that displays the residual stress distribution on the side surface of the shear end portion calculated by the stress coordinate system conversion unit.

[0019] The assumed strain increment calculation unit may assume a deformation state of the shear end side from the deformation process of the shear end due to shear processing of the test piece, and calculate the assumed strain increment at the shear end side based on plastic mechanics theory in the assumed deformation state.

[0020] The assumed strain increment calculation unit may assume a deformation state of the shear end side by finite element analysis of the deformation process of the shear end due to shear processing of the test piece, and calculate the assumed strain increment at the shear end side based on the assumed deformation state.

[0021] The method for manufacturing a sheared material of a metal plate according to the present invention is a method for manufacturing a sheared material by shearing a metal plate, and includes a temporary shear condition setting step for setting temporary shear conditions for shearing the metal plate, a shear processing reproduction test step for reproducing the formation process of the sheared end of the metal plate by shearing the test piece under the temporary shear conditions using the metal plate shear processing test method according to the present invention, and calculating the residual stress distribution at the sheared end side surface based on the surface deformation history of the sheared end side surface of the sheared end formed on the test piece, and a tensile residual stress test step for determining whether the tensile residual stress at the sheared end side surface is within a predetermined range. The method includes a residual stress amount determination step, a tentative shear condition changing step for changing the tentative shear conditions if it is determined that the tensile residual stress is outside a predetermined range, a repeating step for repeatedly executing the tentative shear condition changing step, the shear processing reproduction test step, and the tensile residual stress amount determination step until it is determined that the tensile residual stress is within the predetermined range, a shear condition determination step for determining the tentative shear conditions as shear conditions if it is determined that the tensile residual stress is within the predetermined range in the tensile residual stress amount determination step, and a shear processing step for shearing the metal plate under the determined shear conditions.

[0022] In the present invention, the process of forming a sheared edge in a sheared material obtained by shearing a metal plate is reproduced by shearing a test piece using a metal plate as a test material, and the surface deformation history of the side of the sheared edge during the deformation process of the sheared edge formed in the test piece is obtained. Then, based on the obtained surface deformation history of the side of the sheared edge, the stress on the side of the sheared edge from the start to the end of deformation of the sheared edge is sequentially updated and calculated. This makes it possible to align the stress direction and easily calculate the residual stress distribution on the side of the sheared edge with high accuracy, even if the orientation of the material coordinate system changes for each measurement point on the side of the sheared edge due to shearing of the test piece.

[0023] Furthermore, according to the present invention, by evaluating the maximum residual stress (maximum tensile residual stress) from the residual stress distribution obtained on the side surface of the sheared end of the test piece, it is possible to determine whether or not there is a site on the sheared end surface generated by shearing that could become the initiation point of cracks due to delayed fracture or fatigue fracture.

[0024] Furthermore, according to the present invention, it is possible to obtain a highly accurate history of stress distribution even during deformation of the sheared edge due to shearing of the test piece.Moreover, it is possible to accurately and easily calculate the residual stress distribution generated at the sheared edge even in shear deformation accompanied by fracture of a metal plate, which is difficult to predict using finite element analysis.

[0025] Furthermore, in the present invention, by determining the residual stress distribution on the sheared end side of a sheared metal plate, it is possible to produce a sheared metal plate material in which appropriate measures have been taken to suppress the generation of tensile residual stress that affects fatigue life and delayed fracture characteristics.

[0026] FIG. 1 is a flow chart showing the processing flow in the metal plate shearing test method according to the first embodiment of the present invention ((a) overall, (b) residual stress distribution calculation process). FIG. 2 is a diagram illustrating the sheared material targeted by the present invention. FIG. 3 is a graph showing the correlation between the residual stress at the sheared end face of the sheared material and the maximum residual stress at the sheared end side face ((a) graph showing the position of the sheared end face and the sheared end side face, (b) graph showing the correlation between residual stress). FIG. 4 is a diagram illustrating the change in the orientation of the material coordinate system and the global coordinate system before and after shearing of the metal plate ((a) before shearing, (b) after shearing). FIG. 5 is a diagram illustrating the configuration of the metal plate shearing test system according to the first embodiment of the present invention. FIG. 6 is a diagram illustrating the surface deformation history of each measurement point and the strain and spin occurring in the area consisting of three measurement points, based on the three-dimensional coordinates measured before and after deformation due to shearing at three measurement points set on the side of the sheared end of a test piece in the metal plate shearing test method according to the first embodiment ((a) before deformation due to shearing, (b) after deformation due to shearing). FIG. 7 is a flow diagram illustrating the process flow in the manufacturing method for sheared metal plate material according to the second embodiment of the present invention. FIG. 8 is a diagram illustrating the shape of the shearing test device used to determine the residual stress on the side of the sheared end during the deformation process of the sheared end of the test piece due to shearing, and the shape of the test piece in Example 1 ((a) side view of the shearing test device, (b) front view of the shearing test device, (c) test piece). FIG. 9 is a contour diagram illustrating the residual stress distribution at the sheared end of the sheared test piece in Example 1. Fig. 10 is a graph showing the relationship between the distance from the sheared end surface at the sheared end of the test piece and the residual stress in the thickness direction at the center of the sheared end in Example 1. Fig. 11 is a contour diagram showing the residual stress distribution at the sheared end side of the test piece formed under hypothetical shear conditions and under shear conditions determined so that the residual stress at the sheared end side falls within a predetermined range in Example 2 ((a) hypothetical shear conditions, (b) shear conditions determined so that the residual stress falls within a predetermined range).

[0027] Before describing the embodiments of the present invention, the background to the invention will be described.

[0028] 2 , when a metal plate 100 is sheared using a shearing blade 110, it is cut into a sheared material 101 to be used in a product and a scrap material 111 to be discarded, and a sheared edge 103 is formed in the sheared material 101 due to plastic deformation caused by the shearing. The sheared edge 103 has a sheared edge face 105, which is a surface newly generated by the shearing, and a sheared edge side face 107, which is part of a plate side face 109 of the metal plate 100 and is deformed by the formation of the sheared edge 103. The sheared edge 103 is within a range of less than 1 mm from the sheared edge face 105.

[0029] It is known that fatigue failure and delayed fracture cracks during use of parts (e.g., press-formed products) made from sheared material 101 initiate from the sheared end surface 105 and originate from areas with high residual stress.

[0030] Therefore, in order to suppress the occurrence of fatigue fracture or delayed fracture in the sheared material 101, it is important to understand the residual stress at the sheared end surface 105 of the sheared material 101 and to manufacture the sheared material 101 so that the residual stress is low. However, as mentioned above, it has been difficult to determine the residual stress at the sheared end surface 105. Therefore, the inventors have intensively studied a method for understanding the residual stress at the sheared end surface 105, which is the crack initiation point of fatigue fracture or delayed fracture.

[0031] In this study, we considered that the residual stress at the sheared edge 105 generated by shearing might be related to the residual stress at the side of the sheared edge that is deformed by the formation of the sheared edge. Therefore, as shown in Figure 3(a), the residual stress at the center in the plate thickness direction of the sheared edge 105 of the sheared material 101 obtained by shearing a metal plate 100 was measured by X-ray diffraction (XRD), and the relationship with the residual stress at the side of the sheared edge 107 was investigated.

[0032] As a result, as shown in Figure 3(b), it was found that the residual stress at the center of the sheared end surface 105 in the thickness direction correlates with the maximum tensile residual stress (hereinafter referred to as "maximum residual stress") at the sheared end side surface 107.

[0033] Based on this, the inventors thought that if it were possible to determine the maximum residual stress from the residual stress distribution at the shear end side surface 107, it might be possible to determine whether or not there are any locations at the shear end surface 105 that could serve as the starting point for cracks in fatigue fracture or delayed fracture.

[0034] Next, the inventors investigated a method for determining the residual stress distribution on the sheared edge side surface 107. According to the method disclosed in the aforementioned Patent Document 3, the residual stress distribution on the deformed portion can be determined by acquiring the strain history on the plate side surface of the deformed portion of a metal plate undergoing plastic deformation and sequentially updating the stress on the plate side surface from the start to the end of deformation. However, this method calculates the residual stress generated in the deformed portion of a metal plate subjected to plastic deformation based on a coordinate system defined by the positions of each measurement point where strain is measured. Therefore, if the orientation of the coordinate system changes due to rotational deformation of the metal plate itself during the deformation process, the direction of generation of the residual stress becomes unclear.

[0035] As an example of how the orientation of the material coordinate system of a metal plate that has undergone plastic deformation changes, consider a metal plate 100 that is being sheared, as shown in Figure 4. In Figure 4, (a) shows the metal plate 100 before shearing, and (b) shows the metal plate 100 (seared material 101 and scrap material 111) after shearing. The coordinate system defined at each position on the metal plate 100 is called the material coordinate system. In contrast, the coordinate system when the metal plate 100 that is deformed by shearing is viewed from the outside is called the global coordinate system.

[0036] 4(a), in the metal plate 100 before shearing, the orientation of the material coordinate system is constant regardless of the position on the metal plate 100 and coincides with the orientation of the global coordinate system. In contrast, in the sheared material 101 after deformation by shearing, the orientation of the material coordinate system differs depending on the position on the sheared material 101, as shown in FIG. 4(b), and deviates from the orientation of the global coordinate system.

[0037] That is, the orientation of the material coordinate system changes according to the deformation occurring in the sheared material 101, and furthermore, the orientation differs depending on the position in the sheared material 101. In contrast, unlike the material coordinate system, the orientation of the global coordinate system does not change according to the deformation of the sheared material 101 due to shearing, and remains the same regardless of the position of the sheared material 101.

[0038] Furthermore, in order to calculate the distribution of residual stress in a sheared material deformed by shearing, it is necessary to calculate the residual stress at multiple positions in the sheared material 101. However, the residual stress calculated by the method disclosed in Patent Document 3 is based on the material coordinate system of the position where the stress is calculated. Therefore, when calculating the residual stress at multiple positions, the direction of the residual stress differs depending on the position, which may cause variations and inconsistencies.

[0039] To align the direction of residual stress, it is considered necessary to align the direction of residual stress based on the orientation of the material coordinate system for each measurement point where residual stress is calculated. However, in the method disclosed in Patent Document 3, stress during the deformation process is calculated sequentially using only the strain history. Therefore, it is not possible to know how the orientation of the sheared material 101 changes during the deformation process, and it is not possible to obtain information regarding the orientation of the material coordinate system for each measurement point where stress is calculated.

[0040] The inventors conducted extensive research to solve this problem. As a result, they came up with the idea of ​​acquiring not only the strain history during the deformation process of a metal plate due to shearing, but also the history of the rotation (hereinafter referred to as "spin") of the material coordinate system at each measurement point where the strain history is acquired. The spin history at each measurement point is acquired as information about the orientation of the material coordinate system relative to the global coordinate system, which is updated sequentially during the deformation process of the metal plate. Furthermore, they discovered that by converting the residual stress calculated according to the material coordinate system at each measurement point of the metal plate into a stress in a predetermined direction in the global coordinate system based on the spin history, it is possible to align the residual stress orientations at multiple measurement points and obtain their distribution.

[0041] The present invention was made based on the results of the above investigation, and will be specifically described below.

[0042] [Embodiment 1] <Metal Plate Shearing Test Method> A metal plate shearing test method according to embodiment 1 of the present invention calculates residual stress at a sheared end of a sheared metal plate, and includes a shearing reproduction test process P1 and a residual stress distribution calculation process P3, as shown in FIG. 1( a). The residual stress distribution calculation process P3 includes a deformation history acquisition process S10, a sequential stress update process S20, and a residual stress distribution calculation process S30, as shown in FIG. 1( b). Below, the above-mentioned processes and steps will be described for the case of calculating the residual stress distribution at a sheared end side surface 127 of a sheared end 123, which is a deformed portion of a sheared test piece 121, as shown in FIG. 2.

[0043] [Shearing Reproduction Test Process] The shearing reproduction test process P1 is a process for reproducing the process of forming the sheared end 103 of the sheared material 101 obtained by shearing a metal plate 100 by shearing a test piece 121 made of a metal plate (see Figure 2).

[0044] In the shearing reproduction test process P1, a test piece 121 can be sheared using shearing tools 11 having a punch 13, a die 15, and a holder 17, as shown in Fig. 5, for example. In the shearing process using the shearing tools 11, the test piece 121 is placed between the die 15 and the holder 17, and the punch 13 and the die 15 are moved relative to each other while the die 15 and the holder 17 are fixed with bolts to prevent the test piece 121 from lifting up from the die 15 during the shearing process. The method of preventing the test piece 121 from lifting up from the die 15 is not limited to fixing with bolts, and may also be to apply a constant load to the holder 17 using a power source such as hydraulics.

[0045] [Residual Stress Distribution Calculation Process] The residual stress distribution calculation process P3 is a process for calculating the residual stress distribution at the sheared end side surface 127 (see FIG. 2) of the sheared end 123 formed in the test piece 121 in the shearing process reproduction test process P1.

[0046] As shown in FIG. 1B, the residual stress distribution calculation process P3 includes a deformation history acquisition step S10, a sequential stress update step S20, and a residual stress distribution calculation step S30.

[0047] <<Deformation History Acquisition Process>> The deformation history acquisition process S10 is a process for acquiring the deformation history of the shear end side surface 127 during the deformation process of the shear end portion 123 due to shear processing of the test piece 121, and as shown in FIG. 1(b), includes a surface deformation history acquisition step S11, a strain history acquisition step S13, and a spin history acquisition step S15.

[0048] (Surface Deformation History Acquisition Step) The surface deformation history acquisition step S11 is a step in which a plurality of measurement points are set on the sheared end side surface 127 of the test piece 121, and the three-dimensional coordinates of each measurement point are measured during the shearing of the test piece 121 in the shearing reproduction test process P1, thereby acquiring the surface deformation history of the sheared end side surface 127 from the start to the end of deformation of the sheared end 123. In the first embodiment, as shown in FIG. 5 , two cameras 29 are installed at positions where they can photograph the sheared end side surface 127 of the test piece 121. Then, the three-dimensional coordinates of each measurement point are measured using a digital image correlation method (hereinafter referred to as "DIC").

[0049] In DIC, two cameras 29 are used to capture images of the sheared edge 127 at predetermined time intervals during the deformation process of the sheared edge 123 of the test specimen 121 due to shearing. The images captured at each time step (hereinafter referred to as "DIC images") are then analyzed. This allows the three-dimensional coordinates of each measurement point at each time step from the start to the end of deformation of the sheared edge 123 to be measured. As shown in Figure 2, the imaging range of the two cameras 29 should be determined so that the plate side surface 129a, including the sheared edge 127 of the test specimen 121, does not fall outside the imaging range from the start to the end of deformation. Furthermore, it is sufficient to capture the plate side surface 129a, including the sheared edge 127 of the test specimen 121; it is not necessary to capture the entire plate side surface 129.

[0050] (Strain history acquisition step) The strain history acquisition step S13 is a step of acquiring the strain history of the shear end side surface 127 during shear processing of the test piece 121 from the surface deformation history of the shear end side surface 127 acquired in the surface deformation history acquisition step S11.

[0051] (Spin History Acquisition Step) The spin history acquisition step S15 is a step of acquiring the spin history of the shear end side surface 127 during the deformation process of the shear end portion 123 from the surface deformation history of the shear end portion side surface 127 acquired in the surface deformation history acquisition step S11.

[0052] The specific processing in the deformation history acquisition step S10 will be described using an example in which three measurement points are set on the shear end side surface 127 as shown in FIG.

[0053] First, as shown in FIG. 6, a plurality of measurement points are set on the shear end side surface 127, and the three-dimensional coordinates of each measurement point are measured at predetermined time intervals during the deformation process of the shear end surface 123 due to shearing of the test piece.

[0054] In FIG. 6, the coordinates of each measurement point at a certain time step in the deformation process are defined as the coordinates Xi before deformation, and the coordinates of each measurement point at a time step after a predetermined time interval has elapsed from that time step are defined as the coordinates x after deformation. i (i=0,1,2).

[0055] Then, if an area a1 consisting of three measurement points in the time step before deformation is transformed into an area a2 in the time step after deformation, the strain and spin resulting from the deformation of the area consisting of the three measurement points can be calculated as follows:

[0056] The measurement points of the area a1 before deformation and the area a2 after deformation are set as the reference points, respectively, at coordinates X0 and x0. i , x i The relative positions of the measurement points (i = 1, 2) from the reference point (X0 or x0) are respectively dX i =X i -X0 (i=1, 2), dx i =x i -x0 (i=1, 2). At this time, dx i =FdX i F that satisfies is called the deformation gradient tensor.

[0057] In general, deformation of an area consisting of a plurality of measurement points does not need to be calculated from the displacements of the three measurement points described above, but can be expressed by the following equation (1).

[0058]

[0059] Solving equation (1) for the deformation gradient tensor F gives equation (2).

[0060]

[0061] Furthermore, using the deformation gradient tensor F, the right Caushy-Green deformation tensor C and the right stretch tensor U are expressed by equations (3) and (4), respectively.

[0062]

[0063] Using these, the logarithmic strain tensor (Hencky strain tensor E) and the spin tensor R are defined by equations (5) and (6), respectively.

[0064]

[0065] In equation (5), the Hencky strain tensor E is the strain at each time step from the start to the end of the deformation, and in equation (6), the spin tensor R is the spin at each time step from the start to the end of the deformation.

[0066] As described above, in acquiring the deformation history using DIC, first, images of the shear end side surface 127 of the test piece 121 during the deformation process are taken at predetermined time intervals. Next, the DIC images taken at each time step are analyzed to measure the three-dimensional coordinates (Xi, xi) of each measurement point set on the shear end side surface 127. Next, the Hencky strain tensor E and spin tensor R at a predetermined position on the shear end side surface 127 are calculated from the three-dimensional coordinates of each measurement point (Equations (1) to (6)).

[0067] Then, the Hencky strain tensor E calculated at each time step from the start to the end of deformation is acquired as a strain history (S13). Similarly, the spin tensor R calculated at each time step from the start to the end of deformation is acquired as a spin history (S15).

[0068] <Sequential Stress Update Process> The sequential stress update process S20 is a process of sequentially updating the stress in the material coordinate system of each measurement point set on the shear end side surface 127 of the test piece 121 (hereinafter also referred to as "local stress") from the start of deformation to the end of deformation in the deformation process of the shear end portion 123. As shown in FIG. 1(b), the sequential stress update process S20 includes an acquired strain increment calculation step S21, an assumed strain increment calculation step S23, an acquired spin increment calculation step S25, a stress increment calculation step S27, and a sequential stress update step S29.

[0069] (Acquired Strain Increment Calculation Step) First, in the acquired strain increment calculation step S21, an acquired strain increment is calculated from the strain history of the shear end side surface 127 acquired in the strain history acquisition step S13. The acquired strain increment is the strain increment for each time step of the strain whose strain history is acquired in the strain history acquisition step S13. When the three-dimensional coordinates of each measurement point set on the shear end side surface 127 during the deformation process are acquired as the surface deformation history in the surface deformation history acquisition step S11, the strain history acquired in the strain history acquisition step S13 is the strain increment in two in-plane directions and the in-plane shear strain. Therefore, the acquired strain increment calculated in the acquired strain increment calculation step S21 is the strain increment in each of the strain increment in two in-plane directions and the in-plane shear strain.

[0070] The acquired strain increment is calculated for each time step at which the strain history is acquired. The acquired strain increment at each time step can be calculated, for example, from the strain at that time step and the strain at the time steps before and after that time step.

[0071] (Assumed strain increment calculation step) Next, in the assumed strain increment calculation step S23, an assumed strain increment is calculated. The assumed strain increment is the increment of strain for each time step other than the strain whose strain history is acquired in the strain history acquisition step S13. The strain other than the strain whose strain history is acquired can be calculated by assuming the deformation state of the shear end side surface 127 from the deformation process of the shear end 123 due to shearing of the test piece 121, and based on the theory of plastic mechanics for the assumed deformation state.

[0072] As described above, in the strain history acquisition step S13, the strain ε in each of the two in-plane directions (x direction and y direction) of the shear end side surface 127 is x and ε y and the in-plane (xy plane) shear strain ε xy The strain of the three components,

[0073] However, the shear end side surface 127 of the test piece 121 is subjected to six strain components (ε x , ε y , ε z , ε xy , ε yz , ε zx ) is occurring.

[0074] Generally, the surface of the test piece 121 is a free surface during the deformation process due to shearing, so no stress occurs in the direction perpendicular to the surface of the test piece 121. In other words, it can be assumed that the deformation state of the sheared end side surface 127 of the test piece 121 is under plane stress conditions.

[0075] Then, based on the theory of plasticity in the assumed deformation state, the strain (ε x , ε y and ε xy ) and the strain (ε z , ε yz , ε zx ) gives the stress increment in the out-of-plane direction.

[0076] If we assume that the deformation state of the shear end side surface 127 is a plane stress state, the stress increment in the out-of-plane direction is 0. Therefore, using the equation for strain and stress increment based on the theory of plastic mechanics, we can calculate the strain in the out-of-plane direction (ε z ) can be calculated uniquely.

[0077] That is, the deformation state of the shear end side surface 127 is assumed from the deformation process of the shear end 123 due to shearing of the test piece 121. Then, based on the theory of plastic mechanics in the assumed deformation state, strains other than the strains whose strain history has been acquired in the strain history acquisition step S13 can be obtained.

[0078] In this way, in the assumed strain increment calculation step S23, strains other than the strains for which the strain history is acquired at each time step in the deformation process of the shear end 123 are calculated by assuming the deformation state of the shear end side surface 127. Then, similar to the acquired strain increment described above, the assumed strain increment is calculated from the strain (assumed strain) calculated by assuming the deformation state of the shear end side surface 127 at each time step in the deformation process of the shear end 123. Similar to the acquired strain increment described above, the assumed strain increment at each time step can be calculated from the strains obtained at the time step and the time steps before and after it.

[0079] (Acquired Spin Increment Calculation Step) Subsequently, in acquired spin increment calculation step S25, an acquired spin increment is calculated from the spin history acquired in spin history acquisition step S15. The acquired spin increment is the increment of spin for each time step of the sheared end side surface 127 acquired at a predetermined time interval. The acquired spin increment at each time step can be calculated, for example, from the spin at the time step and the spins at the time steps before and after that.

[0080] (Stress Increment Calculation Step) Subsequently, in the stress increment calculation step S27, the stress increment of the shear end side surface 127 in the deformation process is calculated using the acquired strain increment, the assumed strain increment, and the acquired spin increment.

[0081] The stress increment can be calculated using a material constitutive law based on elasto-plastic dynamics. In this case, the stress increment in the material coordinate system is expressed by the relationship shown in Equation (7) using the strain increment (obtained strain increment and assumed strain increment) and the spin increment.

[0082]

[0083] In equation (7), the strain increment tensor D is the increment of the strain tensor E per unit time step, and the spin increment tensor W is the increment of the spin tensor R per unit time step.

[0084] Furthermore, the elastic-plastic coefficient tensor C in Eq. (7) ep can be given by equation (8).

[0085]

[0086] In this first embodiment, as an example of a material constitutive law, a stress increment is calculated from a strain increment (obtained strain increment, assumed strain increment) based on the YU model disclosed in Non-Patent Document 1, which is capable of reproducing the Bauschinger effect with high accuracy.

[0087] The YU model can be classified as a two-surface model in which the yield surface moves within the bounding surface. The evolution of the bounding surface (center β, radius R) and the yield surface (center α, radius Y) is defined by the strain increment as follows:

[0088]

[0089] In this case, equation (8) is expressed as equation (10).

[0090]

[0091] In this way, once the strain increment and spin increment are determined, the stress increment can be obtained according to the material constitutive law.

[0092] The material constitutive law is not limited to the YU model described above, and the elastic-plastic modulus tensor may be calculated according to any material constitutive law. For example, if a material constitutive law assuming isotropic hardening is used instead of the YU model, the elastic-plastic modulus tensor C ep is expressed by equation (11).

[0093]

[0094] Also, the elastic-plastic coefficient tensor C ep The yield function f used to obtain σ is not limited to the isotropic von Mises yield function, but can also be any yield function such as Hill'48 or Yld2000-2d, which can accurately represent the anisotropy of the material (metal plate).

[0095] (Sequential Stress Update Step) Subsequently, in the sequential stress update step S29, the stress in the material coordinate system of each measurement point is sequentially updated from the start of deformation of the shear end to the end of deformation using the stress increment calculated for each measurement point.

[0096] In the sequential stress update step S29, first, the local stress is updated using the stress increment calculated for each measurement point at a certain time step in the deformation process (S29a), and then it is determined whether the stress update for all measurement points has been completed (S29b).

[0097] If it is determined that stress updating has not been completed for all measurement points (S29b), as shown in Figure 1(b), the aforementioned processes of S21, S23, S25, S27 and S29 are performed for the measurement points for which stress updating has not been completed, and the local stress is updated (S29a).

[0098] If it is determined that stress updating has been completed for all measurement points (S29b), it is determined whether the deformation of the shear end has ended, i.e., whether there is a next time step until the deformation of the shear end has ended (S29c).

[0099] If it is determined that the deformation has not ended, the process proceeds to the next time step in the deformation process. Then, for all measurement points, the following steps are performed: calculation of the acquired strain increment (S21), calculation of the assumed strain increment (S23), calculation of the acquired spin increment (S25), calculation of the stress increment (S27), sequential update of the local stress (S29a), and determination of the stress update (S29b). In this way, in the sequential stress update step S29, by performing the processes of S29a to S29c, the local stresses of all measurement points are sequentially updated from the start of deformation to the end of deformation.

[0100] <<Residual Stress Distribution Calculation Step>> The residual stress distribution calculation step S30 is a step of converting the local stress at each measurement point at the end of deformation of the sheared end 123 into a global stress value in a global coordinate system, and calculating the residual stress distribution on the sheared end side surface 127. In the first embodiment, the residual stress distribution calculation step S30 includes a stress coordinate system conversion step S31 and a residual stress distribution display step S33.

[0101] (Stress coordinate system conversion step) First, in the stress coordinate system conversion step S31, among the local stresses at each measurement point sequentially updated from the start to the end of deformation of the shear end 123 in the sequential stress update process S20, the local stress at the end of deformation is converted into a stress value in a predetermined direction in a global coordinate system (global stress value). Then, in the stress coordinate system conversion step S31, the converted global stress value at each measurement point is obtained as the residual stress distribution of the shear end side surface 127.

[0102] If the local stress obtained at each measurement point is σ and the vector in a given direction in the global coordinate system is n, then the global stress value in the global coordinate system is σ g can be calculated by equation (12).

[0103]

[0104] The predetermined direction in the global coordinate system is not particularly limited as long as it is a direction expressed in the global coordinate system, and the direction to be calculated may be set appropriately by aligning the direction of stress.

[0105] (Residual Stress Distribution Display Step) Subsequently, in the residual stress distribution display step S33, the residual stress distribution of the shear end side surface 127 obtained in the stress coordinate system conversion step S31 is displayed.

[0106] To display the residual stress distribution, for example, the coordinates of each measurement point at which the global stress value is determined may be converted into coordinates on the DIC image of the sheared end side surface 127 .

[0107] To convert the coordinates of the shear end side surface 127 onto the DIC image, the coordinates (X, Y, Z) of each measurement point in the global coordinate system can be converted into coordinates (u, v) on a two-dimensional plane on the DIC image using equation (13).

[0108] In the first embodiment, the residual stress distribution calculation step S30 is performed after the completion of the sequential stress update step S20. However, in order to display the strain distribution of the shear end side surface 127 during the deformation process of the shear end 123, the residual stress distribution calculation step S30 may be performed for each time step after the completion of stress update for all measurement points for each time step in the sequential stress update step S29 (S29b).

[0109] As described above, in the metal plate shearing test method according to the first embodiment, the process of forming the sheared edge 103 of the sheared material 101 obtained by shearing the metal plate 100 is reproduced by shearing the test piece 121 using the metal plate 100 as a test material. Then, the surface deformation history of the sheared edge side surface 127 during the deformation process of the sheared edge 123 formed by shearing the test piece 121 is acquired. Furthermore, based on the surface deformation history of the sheared edge side surface 127, the stress of the sheared edge side surface 127 from the start to the end of deformation of the sheared edge 123 is sequentially updated and calculated. This allows the residual stress distribution at the sheared edge side surface 127 to be calculated with high accuracy, even if the orientation of the material coordinate system changes for each measurement point on the sheared edge side surface 127 due to the shearing of the test piece 121.

[0110] 3B, the maximum residual stress at the sheared end side surface 127 correlates with the residual stress at the sheared end surface 125. Therefore, according to the metal plate shearing test method of the first embodiment, by evaluating the maximum residual stress from the residual stress distribution obtained for the sheared end side surface 127 of the test piece 121, it is possible to determine whether or not there is a site at the sheared end surface 125 generated by shearing that could be the starting point of a crack due to delayed fracture or fatigue fracture. Note that this determination can be made, for example, by determining whether or not the maximum residual stress at the sheared end side surface 127 exceeds a predetermined value.

[0111] Furthermore, in the metal plate shear processing test method according to the first embodiment, it is possible to calculate with high accuracy the history of stress distribution on the shear end side surface 127 even during deformation of the shear end 123 due to shear processing of the test piece 121. Furthermore, even for shear deformation accompanied by fracture of the metal plate, which is difficult to predict using finite element analysis, it is possible to accurately and easily calculate the residual stress distribution generated on the shear end side surface of the metal plate.

[0112] In the metal plate shear processing test method according to the first embodiment, the assumed strain increment calculation step S23 assumes a deformation state of the shear end side surface 127 from the deformation process of the shear end 123 of the test piece 121, and calculates the assumed strain increment based on the theory of plastic mechanics in the assumed deformation state. However, in the present invention, the assumed strain increment calculation step may also be performed by performing a finite element analysis of the process in which the shear end 123 is plastically deformed by shear processing of the test piece 121, and assuming a deformation state (e.g., strain ratio) of the shear end side surface 127 from the results, and calculating the assumed strain increment at the shear end side surface 127.

[0113] When calculating the assumed strain increment by assuming the deformation state of the shear end side surface 127 through finite element analysis of the deformation process of the shear end portion 123, it is not necessary to analyze the entire test piece 121, and it is sufficient to model only the shear end portion 123 and its vicinity and perform finite element analysis. This makes it possible to assume the deformation state of the shear end side surface 127 in a shorter time than in finite element analysis that analyzes the entire test piece 121.

[0114] In particular, finite element analysis using solid elements, which can calculate stress in the thickness direction with high accuracy, is rarely used for general shearing of metal plates because it significantly increases calculation time. However, if the analysis target is a portion of a metal plate including a sheared edge that undergoes plastic deformation due to shearing, finite element analysis using solid elements can predict the deformation state of the sheared edge side surface with high accuracy in a short time. Therefore, in the present invention, by assuming the deformation state predicted by finite element analysis using solid elements and combining it with the acquisition of the strain history and spin history of the sheared edge side surface 127 during the deformation process of the sheared edge, it is possible to calculate the residual stress distribution on the sheared edge side surface with even higher accuracy.

[0115] [Embodiment 2] <Shearing test system for metal plates> A shearing test system for metal plates (hereinafter referred to as "shearing test system") according to embodiment 2 of the present invention calculates the distribution of residual stress occurring at the sheared end of a sheared metal plate. Below, each component of the shearing test system 1 will be described for the case where a test piece 121 is sheared and the distribution of residual stress occurring at a side surface 127 of the sheared end is calculated, as shown in Figure 5.

[0116] As shown in FIG. 5 as an example, the shear processing test system 1 includes a shear processing reproduction test device 10 that shears a test piece 121, and a residual stress distribution calculation device 20 that calculates the residual stress distribution on the shear end side surface 127 (see FIG. 2) of the shear end 123 formed on the test piece 121 by shear processing.

[0117] <<Shearing Reproduction Test Apparatus>> The shearing reproduction test apparatus 10 is an apparatus that reproduces the process of forming a sheared end of a sheared metal plate by shearing a metal plate as a test material, a test piece 121. As illustrated in Fig. 5 , the shearing reproduction test apparatus 10 is equipped with a shearing mold 11 having a punch (upper blade) 13, a die (lower blade) 15, and a holder 17, and with the test piece 121 positioned between the die 15 and the holder 17, the punch 13 and the die 15 are moved relative to each other to shear the test piece 121.

[0118] <<Residual Stress Distribution Calculation Device>> The residual stress distribution calculation device 20 is a device that calculates the residual stress distribution at the sheared end side surface 127 of the sheared end 123 formed in the test piece 121 by the shearing process reproduction test device 10.

[0119] In the second embodiment, the residual stress distribution calculation device 20 is configured to include a display device 21, an input device 23, a main memory device 25, an auxiliary memory device 27, cameras 29, 29, and a measurement control and calculation processing unit 31, as shown in FIG.

[0120] In the residual stress distribution calculation device 20, the display device 21, input device 23, main storage device 25, auxiliary storage device 27, and measurement control / arithmetic processing unit 31 may be configured as a PC (personal computer) or the like. In this case, the display device 21, input device 23, main storage device 25, auxiliary storage device 27, and cameras 29, 29 are connected to the measurement control / arithmetic processing unit 31, and each function is executed in response to a command from the measurement control / arithmetic processing unit 31.

[0121] The display device 21 is used to display images of the shear end side surface 127 at the shear end surface 123 of the test piece 121 captured by the two cameras 29, and the calculated residual stress distribution at the shear end surface 127, and is composed of an LCD monitor or the like.

[0122] The input device 23 is used for displaying an image of the shear end side surface 127 and residual stress distribution, and for inputting conditions by the operator, and is composed of a keyboard, a mouse, and the like.

[0123] The main memory device 25 is used to store various files such as images of the sheared end side surface 127 captured by the two cameras 29 and programs for calculating residual stress distribution, and is composed of a hard disk or the like.

[0124] The auxiliary storage device 27 is used for temporary storage of data used in the measurement control and calculation processing unit 31 and for calculations, and is composed of RAM (Random Access Memory) and the like.

[0125] The cameras 29, 29 are used to take stereo photographs of the sheared end side surface 127 during the deformation process of the sheared end 123 due to shearing of the test piece 121.

[0126] The measurement control / arithmetic processing unit 31 has a measurement control unit 33 that controls the measurement of the surface deformation history of the shear end side surface 127, and an arithmetic processing unit 35 that performs arithmetic processing to calculate the residual stress distribution based on the measured surface deformation history.

[0127] The measurement control unit 33 has an image capturing means 33a and a three-dimensional coordinate calculation means 33b. The image capturing means 33a controls the capturing of images of the shear end side surface 127 at predetermined time intervals using two cameras 29 during the deformation process of the shear end 123 due to shearing of the test piece 121. The three-dimensional coordinate calculation means 33b calculates three-dimensional coordinates during the deformation process for multiple measurement points set on the shear end side surface 127 by image analysis of the captured images of the shear end side surface 127.

[0128] In this embodiment 2, the three-dimensional coordinate calculation means 33b processes images of the shear end side surface 127 of the test piece 121 taken stereoscopically by two cameras 29 using DIC, and calculates the three-dimensional coordinates of multiple measurement points set on the shear end side surface 127.

[0129] In DIC, the shear end side surface 127 of the shear end 123 of the test piece 121 is imaged at predetermined time intervals during the deformation process of the shear end 123, and the images taken at each time step (hereinafter referred to as "DIC images") are analyzed. This allows measurement of the three-dimensional coordinates of each measurement point at each time step from the start to the end of deformation of the shear end 123.

[0130] <<Deformation History Acquisition Unit>> The deformation history acquisition unit 37 acquires the surface deformation history of the sheared end side surface 127 during the deformation process of the sheared end portion 123 due to shearing of the test piece 121, and acquires, from the acquired surface deformation history, the strain history and spin history occurring on the sheared end side surface 127. As shown in Fig. 5 , the deformation history acquisition unit 37 has a surface deformation history acquisition unit 37a, a strain history acquisition unit 37b, and a spin history acquisition unit 37c.

[0131] The surface deformation history acquisition unit 37a measures the three-dimensional coordinates of multiple measurement points set on the shear end side 127 of the shear end 123 formed on the test piece 121 during the deformation process of the shear end 123 due to shear processing of the test piece 121 using the shear processing reproduction test device 10, and acquires this as the surface deformation history of the shear end side 127 from the start of deformation of the shear end 123 to the end of deformation.

[0132] The strain history acquisition unit 37b acquires the strain history of the shear end side surface 127 in the deformation process of the shear end portion 123 from the surface deformation history of the shear end portion side surface 127 acquired by the surface deformation history acquisition unit 37a.

[0133] The spin history acquisition unit 37c acquires the spin history of the sheared end side surface 127 during the deformation process of the sheared end portion 123 from the surface deformation history of the sheared end portion side surface 127 acquired by the surface deformation history acquisition unit 37a.

[0134] <Sequential Stress Update Unit> The sequential stress update unit 39 sequentially updates and obtains the stress in the material coordinate system at each measurement point set on the shear end side surface 127 of the test piece 121 from the start of deformation to the end of deformation during the deformation process of the shear end portion 123. As shown in Figure 5, the sequential stress update unit 39 has an acquired strain increment calculation unit 39a, an assumed strain increment calculation unit 39b, an acquired spin increment calculation unit 39c, a stress increment calculation unit 39d, and a sequential stress update unit 39e.

[0135] (Obtained Strain Increment Calculation Unit) The obtained strain increment calculation unit 39a calculates an obtained strain increment from the strain history of the shear end side surface 127 acquired by the strain history acquisition unit 37b.

[0136] The acquired strain increment is the strain increment for each time step of the strain whose strain history is acquired by the strain history acquisition unit 37b. For example, when the three-dimensional coordinates of each measurement point set on the shear end side surface 127 during the deformation process are acquired as the surface deformation history, the strain history acquired by the strain history acquisition unit 37b is the strain in two in-plane directions and the in-plane shear strain. In this case, the acquired strain increment calculated by the acquired strain increment calculation unit 39a is the strain increment for each of the strain in two in-plane directions and the in-plane shear strain.

[0137] The acquired strain increment is calculated for each time step at which the strain history of the shear end side surface 127 is acquired. The acquired strain increment at each time step can be calculated, for example, from the strain at the time step and the strain at the time steps before and after that time step.

[0138] (Assumed strain increment calculation unit) The assumed strain increment calculation unit 39b calculates an assumed strain increment. The assumed strain increment is a strain increment for each time step of a strain other than the strain whose strain history is acquired by the strain history acquisition unit 37b. The strain other than the strain whose strain history is acquired can be calculated by assuming a deformation state of the shear end side surface 127 from the deformation process of the shear end and based on plastic mechanics theory for the assumed deformation state.

[0139] The calculation of the assumed strain increment by the assumed strain increment calculation unit 39b may be performed in the same procedure as the assumed strain increment calculation step S23 of the metal plate shear processing test method according to the first embodiment. That is, first, the deformation state of the shear end side surface 127 of the test piece 121 is assumed to be a plane stress state. Then, based on the theory of plastic mechanics in the assumed deformation state, an equation that gives the stress increment in the out-of-plane direction is obtained using the strain in two in-plane directions and the in-plane shear strain acquired by the strain history acquisition unit 37b, and the strain including the unknown out-of-plane direction.

[0140] If we assume that the deformation state of the shear end side surface 127 is a plane stress state, the stress increment in the out-of-plane direction will be 0, so by using the equation for strain and stress increment based on plastic mechanics theory, the strain in the out-of-plane direction can be calculated unambiguously.

[0141] In this way, the assumed strain increment calculation unit 39b calculates strain other than the strain for which the strain history is acquired at each time step in the deformation process of the shear end 123, assuming the deformation state of the shear end side surface 127. Then, similar to the acquired strain increment described above, the assumed strain increment is calculated from the strain calculated at each time step in the deformation process of the shear end 123, assuming the deformation state of the shear end side surface 127. Similar to the acquired strain increment described above, the assumed strain increment at each time step can be calculated from the strain obtained at the time step and the time steps before and after it.

[0142] (Acquired Spin Increment Calculation Unit) The acquired spin increment calculation unit 39c calculates an acquired spin increment from the spin history acquired by the spin history acquisition unit 37c. The acquired spin increment is an increment of the spin of the sheared end side surface 127 obtained at a predetermined time interval. The acquired spin increment at each time step can be calculated, for example, from the spin at the time step and the spins at the time steps before and after that time step.

[0143] (Stress increment calculation unit) The stress increment calculation unit 39d uses the acquired strain increment, the assumed strain increment, and the acquired spin increment to calculate the stress increment of the sheared end side surface 127 in the deformation process of the sheared end 123. The calculation of the stress increment by the stress increment calculation unit 39d can be performed in a procedure similar to that of the stress increment calculation step S27 in the metal plate shear processing test method according to the first embodiment described above.

[0144] In calculating the stress increment by the stress increment calculation unit 39d, the YU model (Non-Patent Document 1), which can reproduce the Bauschinger effect with high accuracy, can be suitably applied as the material constitutive law, as described above. However, the stress increment calculation unit 39d is not limited to applying the YU model as the material constitutive law, and may apply any material constitutive law. In addition, the elastic-plastic coefficient tensor C ep The yield function f used to obtain σ is not limited to the isotropic von Mises yield function, but any yield function such as Hill'48 or Yld2000-2d, which can accurately express the anisotropy of the material (metal plate), may be used.

[0145] (Sequential stress update unit) The sequential stress update unit 39e uses the stress increment calculated for each measurement point by the stress increment calculation unit 39d to sequentially update the stress (local stress) in the material coordinate system of each measurement point from the start of deformation of the shear end 123 to the end of deformation.

[0146] The sequential stress update unit 39e first updates the local stress using the stress increment calculated for each measurement point at a certain time step in the deformation process.

[0147] Next, the sequential stress update unit 39e determines whether the local stress update has been completed for all measurement points. If it determines that the local stress update has not been completed for all measurement points, the acquired strain increment calculation unit 39a, assumed strain increment calculation unit 39b, acquired spin increment calculation unit 39c, and stress increment calculation unit 39d perform processing for the measurement points for which the local stress has not been updated. Then, the sequential stress update unit 39e updates the local stress for the measurement points for which the local stress has not been updated.

[0148] If it is determined that the local stress has been updated for all measurement points, the sequential stress update unit 39e determines whether the deformation of the shear end 123 has ended, i.e., whether there is a next time step until the deformation of the shear end 123 has ended.

[0149] If it is determined that the deformation has not ended, the process proceeds to the next time step in the deformation process, and processing is performed for all measurement points by the acquired strain increment calculation unit 39a, assumed strain increment calculation unit 39b, acquired spin increment calculation unit 39c, and stress increment calculation unit 39d. Then, local stresses are updated for all measurement points. If it is determined that the deformation has ended, processing by the sequential stress update unit 39e ends.

[0150] In this way, the sequential stress update unit 39 sequentially updates the stress in the material coordinate system at all measurement points from the start of deformation of the shear end 123 to the end of deformation.

[0151] <<Residual Stress Distribution Calculation Unit>> The residual stress distribution calculation unit 41 converts the stress in the material coordinate system at each measurement point at the end of deformation into stress in the global coordinate system, and calculates the residual stress distribution on the shear end side surface 127. In the second embodiment, the residual stress distribution calculation unit 41 has a stress coordinate system conversion unit 41 a and a residual stress distribution display unit 41 b.

[0152] (Stress Coordinate System Conversion Unit) The stress coordinate system conversion unit 41a converts the stress at the end of deformation of the sheared end 123 into a stress value in a predetermined direction in a global coordinate system (global stress value), out of the stresses in the material coordinate system at each measurement point obtained by sequentially updating the stress from the start to the end of deformation of the sheared end 123 by the sequential stress update unit 39. Then, the stress coordinate system conversion unit 41a obtains the converted global stress values ​​at each measurement point as the residual stress distribution on the sheared end side surface 127.

[0153] If the local stress in the material coordinate system obtained for each measurement point is σ and a predetermined direction in the global coordinate system is a vector n, the global stress value σ in the global coordinate system can be calculated using the above-mentioned equation (12). g can be calculated.

[0154] (Residual Stress Distribution Display Unit) The residual stress distribution display unit 41b displays the residual stress distribution of the sheared end side surface 127 obtained by the stress coordinate system conversion unit 41a. To display the residual stress distribution using the residual stress distribution display unit 41b, similar to the above-described residual stress distribution display step S33, it is advisable to convert the coordinates of each measurement point at which the global stress value was obtained into coordinates on the DIC image of the sheared end side surface 127. To convert into coordinates on the DIC image of the sheared end side surface 127, the coordinates (X, Y, Z) of each measurement point in the global coordinate system can be converted into coordinates (u, v) on a two-dimensional plane on the DIC image using the above-described equation (13).

[0155] As described above, in the metal plate shearing test system 1 according to the second embodiment, the process of forming the sheared edge 103 of the sheared material 101 obtained by shearing the metal plate 100 is reproduced by shearing the test piece 121 using the metal plate 100 as a test material. Then, the surface deformation history of the sheared edge side surface 127 during the deformation process of the sheared edge 123 formed by shearing the test piece 121 is acquired. Furthermore, based on the surface deformation history of the sheared edge side surface 127, the stress of the sheared edge side surface 127 from the start to the end of deformation of the sheared edge 123 is sequentially updated and calculated. This allows the residual stress distribution at the sheared edge side surface 127 of the sheared edge 123 to be calculated with high accuracy, even if the orientation of the material coordinate system changes for each position of the sheared edge side surface 127 of the sheared edge 123 during shearing of the test piece 121.

[0156] Furthermore, according to the metal plate shear processing test system 1 of this embodiment 2, by evaluating the maximum residual stress from the residual stress distribution obtained for the shear end side surface 127 of the test piece 121, it is also possible to determine whether or not there is a location on the shear end surface 125 generated by shear processing that could be the starting point for cracks due to delayed fracture or fatigue fracture.

[0157] Furthermore, in the metal plate shearing test system 1 according to the second embodiment, it is possible to obtain a history of highly accurate stress distribution even during deformation of the sheared end portion due to shearing of the test piece. Furthermore, it is possible to accurately and easily calculate the residual stress distribution generated in the metal plate even in the case of shear deformation accompanied by fracture of the metal plate, which is difficult to predict using finite element analysis.

[0158] In the metal plate shearing test system 1 according to the second embodiment, the residual stress distribution calculation unit 41 has a residual stress distribution display section 41b that displays a global stress value obtained by converting the local stress in the material coordinate system at each measurement point into a stress value in a predetermined direction in the global coordinate system. However, the present invention is not limited to the system having the residual stress distribution display section 41b.

[0159] In the metal plate shearing processing test system 1 according to the second embodiment, the assumed strain increment calculation unit 39b calculates the assumed strain increment based on the theory of plastic mechanics in the deformed state of the shear end side surface 127 assumed from the deformation process of the shear end 123 in the test piece 121. However, in the present invention, the assumed strain increment calculation unit may also perform a finite element analysis of the process of plastic deformation of the metal plate and assume the deformation state (e.g., strain ratio) of the shear end side surface 127 from the results of the analysis.

[0160] When assuming the deformation state of the sheared end side surface 127 and calculating the assumed strain increment by finite element analysis of the deformation process due to shearing of a metal plate (test piece), as described above, it is not necessary to analyze the entire metal plate; instead, it is sufficient to model only the sheared end 123 and its vicinity and perform finite element analysis. This makes it possible to assume the deformation state of the sheared end side surface 127 in a shorter time than in finite element analysis that analyzes the entire metal plate. Furthermore, it becomes possible to use solid elements in the finite element analysis, which can calculate stress in the plate thickness direction with high accuracy, and it is possible to calculate the residual stress distribution with higher accuracy.

[0161] The metal plate shearing test method and shearing test system according to the present invention are not limited to measuring the three-dimensional coordinates of each measurement point using DIC, but may be any method capable of measuring the three-dimensional coordinates of each measurement point at a predetermined time interval from the start of deformation to the end of deformation. Furthermore, the present invention may also acquire the three-dimensional coordinates of each measurement point measured at a predetermined time interval from the start of deformation of the sheared end of the test piece due to shearing as the surface deformation history. As described above, the metal plate shearing test method and metal plate shearing test system according to the present invention calculate the residual stress distribution by acquiring the strain history and spin history based on the surface deformation history of the sheared end side of the test piece. Therefore, the residual stress distribution can be accurately calculated even for inhomogeneous metal plates with two or more phases, which was a problem in the prior art when measuring residual stress using X-rays or ultrasound.

[0162] Furthermore, as mentioned above, highly accurate prediction of residual stress distribution in finite element analysis requires a significant amount of calculation time, and analysis is difficult when fractures such as cracks or shearing occur. In particular, metal plates subjected to plastic deformation due to shearing often fracture from their edge surfaces. Therefore, it is important to accurately determine the residual stress distribution at the edge surfaces of the metal plates in order to understand fatigue life and delayed fracture characteristics. In contrast, the metal plate shearing test method and metal plate shearing test system according to the present invention can easily measure the strain history and spin history of the sheared edge side surface during the deformation process in which the sheared edge is plastically deformed by shearing the test specimen, thereby enabling accurate calculation of the residual stress distribution at the sheared edge side surface.

[0163] The above explanation was about calculating stress increments using the YU model. However, in the YU model, the stress-strain curve is defined in a velocity system, so in the case of nonlinear deformation, an error will occur in the stress increment unless the strain increment is made small enough. Therefore, when calculating stress increments using the YU model, it is necessary to make the strain increment small enough. -6It is preferable to adjust the time interval for acquiring the three-dimensional coordinates of each measurement point as the surface deformation history so that it becomes as follows: Furthermore, the surface deformation history acquired in the present invention is considered to contain measurement noise, and there is a concern that the strain history and spin history acquired from the surface deformation history containing such measurement noise will also contain noise.

[0164] Therefore, if stress increments are calculated using minute strain increments (obtained strain increments) calculated from the strain history, noise in the strain history may have a large effect on the stress increments, resulting in a decrease in the accuracy of the successively calculated stresses. In such cases, smoothing the strain history using a low-pass filter or the like to remove noise is preferable, as it allows for highly accurate calculation of the residual stress distribution.

[0165] Furthermore, according to the present invention, it is possible to know not only the residual stress after deformation as in the prior art, but also the stress at the sheared end of the sheared material during deformation, thereby making it possible to calculate the maximum stress generated in the deformed body.

[0166] [Embodiment 3] A manufacturing method of a sheared metal plate according to embodiment 3 of the present invention shears a metal plate to produce a sheared material. As shown in Fig. 7 , the manufacturing method of a sheared metal plate according to embodiment 3 includes a tentative shearing condition setting step S41, a shearing reproduction test step S43, a tensile residual stress determination step S45, a tentative shearing condition changing step S47, a repeating step S49, a shearing condition determination step S51, and a shearing step S53. Each of these steps will be described below.

[0167] Temporary Shearing Condition Setting Step S41 is a step of setting temporary shearing conditions for the sheared material. For example, when using the shearing die 11 shown in Fig. 5, the temporary shearing conditions may be set to include the clearance d between the punch 13 and the die 15, the opening angle (shear angle) between the punch 13 and the die 15, the shear rate (the relative movement speed between the punch 13 and the die 15), the radii of curvature of the cutting edges 13a of the punch 13 and the cutting edges 15a of the die 15, the cutting allowance, etc.

[0168] <<Shearing Reproduction Test Step>> In the shearing reproduction test step S43, the formation process of the sheared end of the metal plate is reproduced by shearing the test piece 121 under the tentative shearing conditions set in the tentative shearing condition setting step S41 by the metal plate shearing test method according to the above-described embodiment 1. Then, the residual stress distribution on the sheared end side surface 127 formed on the test piece 121 is calculated based on the surface deformation history of the sheared end side surface 127.

[0169] In the shear processing reproduction test process S43, as shown in FIG. 6, the shear end side surface 127 during the deformation process of the shear end 123 due to shear processing of the test piece 121 is stereo photographed using two cameras 29, and the three-dimensional coordinates of each measurement point set on the shear end side surface 127 are measured using DIC.

[0170] <<Tensile Residual Stress Determination Step>> The tensile residual stress determination step S45 is a step of determining whether the tensile residual stress at the sheared end side surface 127 of the test piece 121 calculated in the shearing process reproduction test step S43 is within a predetermined range. In the tensile residual stress determination step S45, the tensile residual stress at the sheared end side surface 127 may be, for example, the maximum tensile residual stress (maximum residual stress) in the residual stress distribution at the sheared end side surface 127. The predetermined range refers to a tensile residual stress range in which good hydrogen embrittlement resistance is obtained when a test piece to which tensile residual stress has been applied is placed in a hydrogen-intrusion environment (e.g., immersed in a McIlvaine buffer solution with a pH of 4.0 and a concentration of 0.1% ammonium thiocyanate for 30 hours).

[0171] <<Temporary Shear Condition Changing Step>> The temporary shear condition changing step S47 is a step of changing the temporary shear conditions in a direction that alleviates the tensile residual stress when it is determined in the tensile residual stress amount determining step S45 that the tensile residual stress at the shear end side surface 127 of the test piece 121 is outside a predetermined range. Examples of changing the temporary shear conditions include narrowing the clearance between the punch 13 and the die 15, increasing the shear rate, etc.

[0172] <<Repetition Process>> The repetition process S49 is a process of repeatedly executing the provisional shearing condition changing process S47, the shearing processing reproduction test process S43, and the tensile residual stress amount determining process S45 until it is determined that the tensile residual stress at the shear end side surface 127 is within a predetermined range.

[0173] <<Shear condition determination process>> The shear condition determination process S51 is a process for determining the tentative shear conditions as shear conditions when the tensile residual stress at the shear end side surface 127 of the test piece 121 is determined to be within a predetermined range in the tensile residual stress determination process S45.

[0174] <Shearing Step> The shearing step S53 is a step of shearing the metal plate under the shearing conditions determined in the shearing condition determination step S51 to produce a sheared material.

[0175] In this way, according to the manufacturing method of sheared metal plate material of this embodiment 3, by determining the residual stress distribution on the sheared end side of the sheared end formed by shearing, it is possible to manufacture sheared metal plate material with appropriate measures taken to suppress the occurrence of tensile residual stress that affects fatigue life and delayed fracture characteristics.

[0176] Experiments were conducted to verify the effects of the present invention, which are described below. In Example 1, the strain of a test piece 121 from the start of shearing to fracture was measured by DIC using the metal plate shearing test method according to the first embodiment described above, and the distribution of residual stress in the thickness direction at the sheared edge side surface 127 of the sheared edge 123 formed by shearing the test piece 121 was determined. Furthermore, X-ray stress measurement (X-ray stress measurement) was performed (comparative example) at the center position in the thickness direction of the sheared test piece 121 from the sheared edge surface 125 in the longitudinal direction of the test piece 121 (the direction perpendicular to the sheared edge surface), and the result was compared with the residual stress at the sheared edge side surface 127 calculated by the method according to the present invention.

[0177] 8(a) and (b) show the shearing process reproduction test device 10 used in Example 1. In Fig. 8, the X-axis direction is the direction perpendicular to the sheared end face, the Y-axis direction is the thickness direction of the test piece 121, and the Z-axis direction is the direction perpendicular to the sheared end side surface 127.

[0178] The shearing device includes a shearing die 11 having a punch 13, a die 15, and a holder 17. Furthermore, as shown in Figures 8(a) and 8(b), two cameras 29, 29 were installed at positions where they could photograph a sheared end side surface 127 of a sheared end 123 formed by shearing the test piece 121. Then, multiple measurement points were set on the sheared end side surface 127, and the three-dimensional coordinates of each measurement point were measured by DIC.

[0179] 8(c) shows a top view of the test piece 121. The test piece 121 was made from a high-strength steel sheet having a tensile strength of 1470 MPa and a thickness of 1.4 mm.

[0180] The shear conditions for the test piece 121 were as follows: the clearance d (see FIG. 8(a)) between the punch 13 and the die 15 was 20% of the plate thickness (=1.4 mm) of the test piece 121. The shear rate (relative speed between the punch 13 and the die 15) of the test piece 121 was 30 mm / min, the shear angle θ (see FIG. 8(b)) which is the opening angle between the punch 13 and the die 15 was 0°, the radii of curvature (cutting edge R) of the cutting edge 13a of the punch 13 and the cutting edge 15a of the die 15 were both 0.05 mm, and the cutting allowance of the test piece 121 (the length of the part of the test piece 121 protruding from above the die 15 toward the punch 13 in FIG. 8(a)) was 15 mm.

[0181] FIG. 9 shows the distribution of thickness-direction residual stress at the sheared edge 123 side surface 127 after shearing and fracture of the test specimen 121. Compressive (negative, black) residual stress is observed in the thickness direction approximately several tens of micrometers inward from the sheared edge 125. Furthermore, tensile (positive, white) residual stress is observed in the thickness direction from the inside toward the top surface of the test specimen 121. FIG. 10 compares the residual stress (example) calculated from the residual stress distribution at the sheared edge side surface 127 calculated using the method according to the first embodiment with the residual stress (comparison example) measured using X-ray diffraction (XRD). In the graph shown in FIG. 10, the horizontal axis represents the distance from the sheared edge 125 in the direction perpendicular to the sheared edge, and the vertical axis represents the thickness-direction residual stress at the center of the thickness direction.

[0182] The inventive example and comparative example show a relatively high degree of agreement in the range of 0.1 to 0.4 mm from the sheared edge 125. This confirms that this method can be used to estimate residual stress near the sheared edge, which can cause delayed fracture and other problems. The maximum deviation between the inventive example and comparative example is approximately 200 MPa at a distance of approximately 0.8 mm from the sheared edge. This is presumably due to the fact that the X-ray diffraction (XRD) method used in the comparative example measures compressive stress derived from the martensite phase of the 1470 MPa-class steel plate.

[0183] Next, in Example 2, shearing conditions capable of suppressing the tensile residual stress that affects delayed fracture properties within a predetermined range were determined using a manufacturing method for sheared metal plate material according to embodiment 3 of the present invention, and sheared metal plate material was manufactured.

[0184] In Example 2, the shearing apparatus (FIG. 8) used in Example 1 described above was used to measure the residual stress distribution at the sheared end side surface 127 of the sheared end 123 formed by shearing the test piece 121. Then, the shearing conditions were determined so that the residual stress distribution at the sheared end side surface 127 was equal to or less than a predetermined tensile residual stress, i.e., the maximum tensile residual stress (maximum residual stress) at the sheared end side surface 127 was equal to or less than the predetermined tensile residual stress, and a sheared material was manufactured.

[0185] The predetermined range of tensile residual stress used as the criterion for determining the residual stress on the side surface of the shear end in the tensile residual stress amount determination step was 1000 MPa or less, which was determined as the tensile stress range in which delayed fracture does not occur in a hydrogen penetration environment (for example, immersion in a 3.0% hydrochloric acid solution with a pH of 4.0 for 96 hours) when a tensile stress (load stress) is applied to the four-point bending test piece using a bending jig and a four-point bending test piece used in a four-point bending delayed fracture test (see, for example, Figures 3 and 4 of JP 2014-0927 A).

[0186] Then, a test piece 121 shown in Fig. 8(c) was prepared from a steel plate having a tensile strength of 1470 MPa and a thickness of 1.4 mm, which was the same as the metal plate (blank) to be actually sheared. The test piece 121 had a cutout 131 for shearing and holes 133 through which bolts for fixing the test piece 121 to the die 15 and holder 17 were passed.

[0187] Table 1 shows the thickness and tensile strength of the steel plate used for the test piece 121 in Example 2, the shear conditions for the test piece 121, etc.

[0188]

[0189] The provisional shear conditions for the test piece 121 were the conditions for test No. 1 in Table 1, with a shear rate of 30 mm / min, a clearance d between the punch 13 and the die 15 of 20% of the plate thickness, a shear angle θ of 0°, the cutting edge R of the punch 13 and the cutting edge R of the die 15 both of 0.05 mm, and a cutting allowance 131 for the test piece 121 of 15 mm (provisional shear condition setting step S41).

[0190] The test piece 121 was sheared under hypothetical shear conditions to reproduce the sheared edge formation process, and the surface deformation history of the sheared edge side surface 127 was measured by taking DIC images of the sheared edge side surface 127 using two cameras 29 (FIG. 8). Then, based on the measured surface deformation history of the sheared edge side surface 127, the residual stress distribution in the plate thickness direction at the sheared edge side surface 127 was calculated. The maximum residual stress at the sheared edge side surface 127 at this time was 1755 MPa (shearing process reproduction test step S43).

[0191] FIG. 11(a) shows the residual stress distribution on the sheared end side surface 127 of the test piece 121 sheared under the assumed shearing conditions (in the figure, the arrow indicates the location of the maximum residual stress).

[0192] The maximum residual stress of 1755 MPa on the side of the shear end of the test piece was compared with a predetermined range (1000 MPa or less) in which delayed fracture would not occur, as determined by a four-point bending delayed fracture test, and was determined to be outside the range (tensile residual stress determination step S45).

[0193] Therefore, the tentative shearing conditions were changed from Test No. 1 to Test No. 2 in Table 1 so as to alleviate the tensile residual stress at the sheared end side surface 127 of the test piece 121 (temporary shearing condition changing step S47). Then, under the changed tentative shearing conditions, the shearing process reproduction test step S43 and the tensile residual stress determination step S45 were performed. The maximum residual stress at the sheared end side surface of the test piece sheared under the tentative shearing conditions of Test No. 2 was 1548 MPa, which was outside the predetermined range within which delayed fracture would not occur.

[0194] Therefore, the shearing process reproduction test step S43 and the tensile residual stress determination step S45 were repeatedly performed by changing the tentative shearing conditions (clearance, shear angle, punch cutting edge, die cutting edge) as shown in Test Nos. 3 to 6 in Table 1 until the maximum residual stress at the shear end side surface 127 was determined to be within a predetermined range (1000 MPa or less) in which delayed fracture would not occur in a four-point bending delayed fracture test (repeated step S49).

[0195] Under the tentative shearing conditions of Test No. 6, the maximum residual stress of the sheared end side surface 127 of the test piece 121 was 835 MPa, which was within the predetermined range (1000 MPa or less). Therefore, the tentative shearing conditions of Test No. 6 were determined as the shearing conditions when shearing the metal plate (shearing condition determination step S51).

[0196] FIG. 11(b) shows the residual stress distribution on the sheared end side surface 127 of the test piece 121 sheared under the determined shearing conditions (in the figure, the arrow indicates the location where the maximum residual stress is present).

[0197] Compared with the case where shearing was performed under the hypothetical shearing conditions of Test No. 1 described above (FIG. 11(a)), it can be seen that the sheared end side surface 127 deformed by shearing under the shearing conditions of Test No. 6 does not have any areas where the tensile residual stress is 1000 MPa or more (white areas in the contour diagram). This shows that, under the shearing conditions of Test No. 6, it is possible to produce a sheared material so that the maximum residual stress at the sheared end side surface 127 satisfies a predetermined range, making it possible to suppress delayed fracture.

[0198] Test No. 6 was a test in which the shear angle θ was changed from the shear conditions of Test No. 5, but as shown in Tests No. 7 to No. 11 in Table 1, an investigation was conducted to see whether the maximum residual stress at the shear end side surface 107 would fall within the specified range by changing other shear conditions. Tests No. 7 and No. 8 were changed in shear rate (from 30 mm / min to 60 mm / min or 1 mm / min), Test No. 9 was changed in clearance (from 10% to 5%), and Test No. 10 and No. 11 were changed in cutting allowance (from 15 mm to 5 mm or 25 mm).

[0199] Table 1 shows the shear conditions for Test Nos. 7 to 11 and the maximum residual stress obtained from the residual stress distribution at the shear end side surface 127. In all of Test Nos. 7 to 11, it can be seen that the maximum residual stress at the shear end side surface 127 was within a predetermined range (1000 MPa or less) that did not cause delayed fracture, as determined by a four-point bending delayed fracture test. This shows that even when shear conditions other than the shear angle are changed, the shear conditions can be determined so that the maximum residual stress at the shear end side surface 127 falls within the predetermined range.

[0200] Furthermore, as shown in Tests No. 12 to No. 14 in Table 1, even when the tensile strength and thickness of the steel plate were changed from Tests No. 1 to No. 11, the shear conditions were determined so that the maximum residual stress at the shear end side surface 127 would be within a predetermined range. Test No. 12 had a steel plate thickness of 1.2 mm, Test No. 13 had a steel plate thickness of 2.0 mm and a tensile strength of 780 MPa, and Test No. 14 had a steel plate thickness of 1.2 mm and a tensile strength of 590 MPa.

[0201] Table 1 shows the maximum residual stress obtained from the residual stress distribution at the shear end side surface 127 for each of Test Nos. 12 to 14. It can be seen that even when the tensile strength and thickness of the steel plate are different, the maximum residual stress at the shear end side surface 127 is within a predetermined range where delayed fracture does not occur. This shows that the shear conditions can be determined so that the maximum residual stress at the shear end side surface falls within a predetermined range, regardless of the tensile strength and thickness of the steel plate.

[0202] As described above, it has been shown that the manufacturing method of sheared metal plate material according to embodiment 3 of the present invention makes it possible to manufacture sheared metal plate material with appropriate measures taken to suppress the occurrence of tensile residual stress that affects delayed fracture properties.

[0203] According to the present invention, it is possible to provide a shearing test method and a shearing test system for metal plates, which can reproduce the shearing of metal plates and accurately and easily determine the residual stress at the sheared end of the test piece.Furthermore, according to the present invention, it is possible to provide a manufacturing method for sheared metal plates, in which measures are appropriately taken to suppress the generation of tensile residual stress that affects fatigue life and delayed fracture properties.

[0204] 1 Shearing processing test system 10 Shearing processing reproduction test device 11 Shearing die 13 Punch 13a Cutting edge 15 Die 15a Cutting edge 17 Holder 20 Residual stress distribution calculation device 21 Display device 23 Input device 25 Main memory device 27 Auxiliary memory device 29 Camera 31 Measurement control / arithmetic processing unit 33 Measurement control unit 33a Image capturing means 33b Three-dimensional coordinate calculation means 35 Arithmetic processing unit 37 Deformation history acquisition unit 37a Surface deformation history acquisition unit 37b Strain history acquisition unit 37c Spin history acquisition unit 39 Sequential stress update unit 39a Acquired strain increment calculation unit 39b Assumed strain increment calculation unit 39c Acquired spin increment calculation unit 39d Stress increment calculation unit 39e Sequential stress update unit 41 Residual stress distribution calculation unit 41a Stress coordinate system conversion section 41b Residual stress distribution display section 100 Metal plate 101 Sheared material 103 Sheared end 105 Sheared end face 107 Sheared end side face 109 Plate side face 110 Shear blade 111 Scrap material 121 Test piece 123 Sheared end 125 Sheared end face 127 Sheared end side face 129 Plate side face 129a Plate side face (measurement range by DIC) 131 Cutting allowance 133 Hole

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