Metal plate shearing testing method, metal plate shearing testing system, and metal plate shearing material manufacturing method

Abstract

To provide a metal plate shearing testing method, a metal plate shearing testing system, and a metal plate shearing material manufacturing method for calculating residual stress at a shearing end of a metal plate shearing material.SOLUTION: A metal plate shearing testing method according to the present invention includes: a process (P1) of reproducing a formation process of a shearing end 103 of a shearing material 101 through shearing of a test piece 121; and a process (P3) of calculating the residual stress distribution on a shearing end side face 127 of a shearing end 123 formed by shearing of the test piece 121. The metal plate shearing testing method further includes: acquiring a strain history and a spin history of the shearing end side face 127 in a deformation process of the shearing end 123 through the shearing of the test piece 121 (S10); sequentially updating and calculating stress at the shearing end side face 127 from the start of deformation to the end of deformation of the shearing end 123 (S20); and calculating the residual stress distribution on the shearing end side face 127 at the end of deformation (S30).SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a metal plate shear processing test method for calculating residual stress at a sheared end portion of a sheared material obtained by shearing a metal plate, a metal plate shear processing test system, and a metal plate shear processing method for producing a sheared material obtained by shearing a metal plate. [Background technology]

[0002] Sheared materials produced by shearing metal sheets are used as blanks for press-formed products (e.g., automotive parts), but it is known that the residual stress of the sheared materials caused by shearing affects the fatigue life and delayed fracture properties of the press-formed products. Therefore, understanding the residual stress of the sheared materials is important in order to guarantee the fatigue life, etc. of the press-formed products that use the sheared materials.

[0003] Conventionally, the residual stress of a metal plate has been measured using X-rays or ultrasonic waves, or calculated by measuring the strain during the deformation process of the metal plate. Furthermore, it has been predicted by finite element analysis of the shear processing 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 for non-destructively measuring the stress inside the sample based on information about the diffracted X-rays. Furthermore, Patent Document 2 discloses a technique for generating ultrasonic waves in a plastically deformed test object (such as a metal plate) and non-destructively measuring residual stress based on information on the measured sound velocity of the ultrasonic waves. Furthermore, Patent Document 3 discloses a technology for determining the residual stress in a deformed area by measuring the strain in the deformed area during the deformation process of plastically deforming a metal plate to obtain a strain history, and then sequentially updating the stress in the deformed area from the start to the end of deformation based on the obtained strain history.

[0004] Furthermore, prediction of residual stress by finite element analysis of the shear processing process can be performed using commonly used finite element analysis software, and in such finite element analysis, efforts are being made to improve the accuracy of material constitutive laws. For example, the material constitutive law (hereinafter referred to as the "YU model") disclosed in Non-Patent Document 1 contributes to improving the accuracy of springback analysis, which is important for predicting residual stress in press-formed products. Furthermore, Non-Patent Document 2 presents the fracture conditions that lead to fracture of ductile materials, and a model is created to simulate the behavior of the material up to the fracture. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2002-333409 A [Patent Document 2] JP 2011-196953 A [Patent Document 3] Patent No. 6981521 [Non-patent literature]

[0006] [Non-Patent Document 1] F. Yoshida and T. Uemori, International Journal of Mechanical Sciences, 45(2003), 1687-1702. [Non-Patent Document 2] FXC Andrade, M. Feucht, A. Haufe and F. Neukamm, International Journal of Fracture, 200(2016),127-150. Summary of the Invention [Problem to be solved by the invention]

[0007] However, the stress measurement using X-rays disclosed in Patent Document 1 and the residual stress measurement using ultrasonic waves disclosed in Patent Document 2 assume that the sample (metal plate, etc.) is uniform within the region where the X-rays are incident or where the ultrasonic waves are generated. Therefore, these measurement techniques have a problem in that it is difficult to accurately measure the residual stress of a metal plate having two or more phases (e.g., a dual phase (DP) steel plate, etc.). Furthermore, the techniques of Patent Documents 1 and 2 each measure the residual stress after deformation, and have the problem that they cannot measure the stress history during deformation.

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

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

[0010] In contrast to the techniques of Patent Documents 1 to 3, the method of predicting residual stress by finite element analysis makes it easy to calculate the distribution of residual stress. However, the input values ​​(shape, material properties, deformation properties, boundary conditions, etc.) given to the finite element analysis software used in the finite element analysis have a large effect on the prediction results of residual stress. Therefore, in order to accurately predict residual stress by finite element analysis, it is necessary to make more accurate various input values ​​such as boundary conditions such as the deformation properties of the tool that applies plastic deformation, the contact conditions between the metal plate and the tool, and the sliding properties, in addition to the material properties of the metal plate.

[0011] Furthermore, in order to predict the residual stress in a sheared metal plate by finite element analysis, it is necessary to incorporate the fracture conditions of the metal plate into the finite element analysis. Various fracture criteria have been proposed as fracture conditions, such as the ductile fracture criteria of Cockcroft et al. and the fracture criteria based on the stress triaxiality of GISSMO et al. disclosed in Patent Document 2. However, a judgment criterion capable of accurately predicting fracture in shear processing has not yet been established. In addition, when modeling fracture phenomena in finite element analysis, it is common to determine whether each element of the finite element analysis model satisfies the fracture condition, and to delete elements that satisfy the fracture condition from the finite element analysis model. However, deleting elements means that the mass and energy of the metal plate (sheared material) disappears, which can cause a deviation from the actual fracture phenomenon. For this reason, there was a problem that it was very difficult to predict with high accuracy the residual stress that occurs on the sheared end surface of the metal plate after shearing using finite element analysis.

[0012] The present invention has been made to solve the above-mentioned problems, and has an object to provide a method and system for testing shear processing of metal plates, which can reproduce the shear processing of metal plates and accurately and easily determine the residual stress at the shear end formed in a test piece. A further object of the present invention is to provide a method for producing a sheared metal plate material in which measures are appropriately taken to suppress the occurrence of tensile residual stress that affects fatigue life and delayed fracture properties. [Means for solving the problem]

[0013] (1) The method for testing shear processing of a metal plate according to the present invention is for calculating residual stress at a shear end of a sheared material obtained by shear processing a metal plate, The method includes a shear processing reproduction test process for reproducing the formation process of the shear end by shear processing of a test piece using the metal plate as a test material, and a residual stress distribution calculation process for calculating a residual stress distribution on the shear end side of the shear end formed on the test piece, The shear processing reproduction test process uses a shearing die having a punch, a die, and a holder, and with the test piece disposed between the die and the holder, the punch and the die are relatively moved to shear the test piece. The residual stress distribution calculation process includes a deformation history acquisition step, a sequential stress update step, and a residual stress distribution calculation step. The deformation history acquisition step sets a plurality of measurement points on the side surface of the sheared end portion of the test piece to be formed, and measures the three-dimensional coordinates of each of the plurality of measurement points in the deformation process of the sheared end portion due to the shearing of the test piece in the shear processing reproduction test process, thereby obtaining a surface deformation history of the side surface of the sheared end portion from the start of deformation to the end of deformation of the sheared end portion, which is a surface deformation history acquisition step; a strain history acquisition step of obtaining a strain history of the side surface of the sheared end portion in the deformation process of the sheared end portion from the obtained surface deformation history of the side surface of the sheared end portion; a spin history acquisition step of obtaining a spin history of the side surface of the sheared end portion in the deformation process of the sheared end portion from the obtained surface deformation history of the side surface of the sheared end portion. The sequential stress update step an acquired strain increment calculation step of calculating an acquired strain increment from the strain history of the side surface of the sheared end portion obtained in the strain history acquisition step; a hypothetical strain increment calculation step of calculating a hypothetical strain increment, which is an increment of a strain other than the strain for which the strain history was obtained in the strain history acquisition step, assuming the deformed state of the side surface of the sheared end portion; an acquired spin increment calculation step of calculating an acquired spin increment from the spin history obtained in the spin history acquisition step; a stress increment calculation step of calculating stress increments of the plurality of measurement points according to a material constitutive law using the acquired strain increment, the hypothetical strain increment, and the acquired spin increment; A sequential stress update step of sequentially updating the stress in the material coordinate system of each of the plurality of measurement points by using the stress increment calculated for each of the plurality of measurement points, from the start of deformation of the shear end portion due to the shear processing of the test piece to the end of deformation, The residual stress distribution calculation step includes: The method further comprises 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 portion, which is sequentially updated in the sequential stress update step, into a global stress value in a predetermined direction in a global coordinate system, and determining the converted global stress value of each of the plurality of measurement points as a residual stress distribution on the side surface of the shear end portion.

[0014] (2) In the above (1), The residual stress distribution calculation step further comprises 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] (3) In the above (1) or (2), The assumed strain increment calculation step is characterized in that a deformation state of the side surface of the shear end is assumed from the deformation process of the shear end due to shear processing of the test piece, and the assumed strain increment at the side surface of the shear end is calculated based on a theory of plastic mechanics in the assumed deformation state.

[0016] (4) In the above (1) or (2), The assumed strain increment calculation step is characterized in that a deformation state of the shear end side is assumed by finite element analysis of the deformation process of the shear end due to shear processing of the test piece, and the assumed strain increment at the shear end side is calculated based on the assumed deformation state.

[0017] (5) The metal plate shear processing test system according to the present invention calculates residual stress at a shear end of a sheared material obtained by shearing a metal plate, The present invention includes a shear processing reproduction test device that reproduces the formation process of the sheared end by shear processing a test piece using the metal plate as a test material, and a residual stress distribution calculation device that calculates a residual stress distribution on the sheared end side of the sheared end formed on the test piece, The shear processing reproduction test device includes a shear mold having a punch, a die, and a holder, and in a state in which the test piece is disposed between the die and the holder, the punch and the die are moved relative to each other to shear the test piece, The residual stress distribution calculation device includes a deformation history acquisition unit, a sequential stress update unit, and a residual stress distribution calculation unit, The deformation history acquisition unit includes: a surface deformation history acquisition unit that measures three-dimensional coordinates during a deformation process of the sheared end portion of the sheared end portion formed on the test piece by the shearing process of the test piece using the shearing process reproduction test device for a plurality of measurement points set on the sheared end portion side surface of the sheared end portion formed on the test piece, and acquires a surface deformation history of the sheared end portion side surface from the start of deformation of the sheared end portion to the end of deformation; A strain history acquisition unit that acquires a strain history of the side surface of the shear end portion during a deformation process of the shear end portion from the acquired surface deformation history of the side surface of the shear end portion; A spin history acquisition unit that acquires a spin history of the shear end side surface during a deformation process of the shear end portion from the acquired surface deformation history of the shear end side surface, The incremental stress update unit comprises: an acquired strain increment calculation unit that calculates an acquired strain increment from the strain history of the shear end side 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, which is an increment of strain other than the strain whose strain history is acquired by the strain history acquisition unit; 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 at each of the plurality of measurement points according to a material constitutive law using the acquired strain increment, the assumed strain increment, and the acquired spin increment; A sequential stress update unit sequentially updates the stress in the material coordinate system of each of the plurality of measurement points by using the stress increment calculated for each of the plurality of measurement points, from the start of deformation of the shear end portion due to the shear processing of the test piece to the end of deformation, The residual stress distribution calculation unit is The present invention is characterized in that it has a stress coordinate system conversion unit that converts the stress in the material coordinate system of each of the multiple measurement points at the end of deformation of the shear end portion, which is sequentially updated 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 multiple measurement points as a residual stress distribution on the side surface of the shear end portion.

[0018] (6) In the above (5), The residual stress distribution calculation unit is characterized by further comprising 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] (7) In the above (5) or (6), The assumed strain increment calculation unit assumes 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 calculates the assumed strain increment at the shear end side based on a plastic mechanics theory in the assumed deformation state.

[0020] (8) In the above (5) or (6), The assumed strain increment calculation unit assumes 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 calculates the assumed strain increment at the shear end side based on the assumed deformation state.

[0021] (9) The manufacturing method of 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, A temporary shear condition setting process for setting temporary shear conditions for shearing the metal plate; A shear processing reproduction test process in which the formation process of the shear end of the metal plate is reproduced by shearing the test piece under the hypothetical shear conditions by the metal plate shear processing test method described in any one of (1) to (4) above, and a residual stress distribution on the shear end side is calculated based on the surface deformation history of the shear end side of the shear end formed on the test piece; a tensile residual stress amount determination step of determining whether the tensile residual stress at the shear end side surface is within a predetermined range; a tentative shear condition changing step of changing the tentative shear condition when it is determined that the tensile residual stress is outside a predetermined range; a repeating step of repeatedly executing the provisional shearing condition changing step, the shearing process reproduction test step, and the tensile residual stress amount determining step until the tensile residual stress is determined to be within a predetermined range; a shear condition determination step of determining, when the tensile residual stress is determined to be within a predetermined range in the tensile residual stress amount determination step, the tentative shear condition in that case as a shear condition; and a shearing process step of shearing the metal plate under the determined shearing conditions. Effect of the Invention

[0022] In the present invention, the formation process of the sheared end of 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 end during the deformation process of the sheared end formed in the test piece is obtained. Then, based on the obtained surface deformation history of the side of the sheared end, the stress of the side of the sheared end from the start of deformation of the sheared end to the end of deformation is sequentially updated and obtained. As a result, even if the orientation of the material coordinate system changes for each position of the measurement point on the side of the sheared end due to shearing of the test piece, the direction of the stress can be aligned and the residual stress distribution on the side of the sheared end can be obtained with high accuracy and ease.

[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 shear processing 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 history of highly accurate stress distribution even during deformation of the sheared end due to shear processing of the test piece.Moreover, it is possible to accurately and easily calculate the residual stress distribution generated at the sheared end even in the case of shear deformation accompanied by destruction of a metal plate, which is difficult to predict by finite element analysis.

[0025] Furthermore, in the present invention, by determining the residual stress distribution on the side surface of the sheared end 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 occurrence of tensile residual stress that affects fatigue life and delayed fracture characteristics. [Brief description of the drawings]

[0026] [Figure 1] FIG. 2 is a flow chart showing a process flow in the metal plate shear processing test method according to the first embodiment of the present invention ((a) overall, (b) residual stress distribution calculation process). [Diagram 2] FIG. 2 is a diagram illustrating a sheared material that is the subject of the present invention. [Diagram 3] A graph showing the correlation between the residual stress on the sheared end face of the sheared workpiece and the maximum residual stress on the side face of the sheared end ((a) positions of the sheared end face and the side face of the sheared end, (b) graph showing the correlation of residual stress). [Figure 4] A diagram explaining the changes in the directions of the material coordinate system and the global coordinate system before and after shearing of a metal plate ((a) before shearing, (b) after shearing). [Diagram 5] A diagram explaining the configuration of a shearing test system for a metal plate according to Embodiment 1 of the present invention. [Figure 6] In the shearing test method for a metal plate according to Embodiment 1 of the present invention, from the three-dimensional coordinates before and after deformation by shearing measured at three measurement points set on the side face of the sheared end of the test piece, the surface deformation history of each measurement point, and the strain and spin generated in the region composed of the three measurement points are explained ((a) before deformation by shearing, (b) after deformation by shearing). [Figure 7] A flowchart showing the process flow in the manufacturing method of a sheared workpiece of a metal plate according to Embodiment 2 of the present invention. [Figure 8] In Example 1, a shearing test apparatus for obtaining the residual stress on the side face of the sheared end in the deformation process of the sheared end of a test piece by shearing, and a diagram explaining the shape of the test piece ((a) side view of the shearing test apparatus, (b) front view of the shearing test apparatus, (c) test piece). [Figure 9] In Example 1, a contour diagram showing the residual stress distribution at the sheared end of the sheared test piece. [Figure 10] In Example 1, a graph showing the relationship between the distance from the sheared end face at the sheared end of the test piece and the residual stress in the plate thickness direction at the center of the plate thickness. [Figure 11] In Example 2, a contour diagram showing the residual stress distribution on the side face of the sheared end of a test piece formed under a provisional shearing condition and a shearing condition determined such that the residual stress on the side face of the sheared end is within a predetermined range ((a) provisional shearing condition, (b) shearing condition determined such that the residual stress is within a predetermined range). DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0027] Before describing the embodiments of the present invention, the background to the invention will be described. <How the present invention was arrived at> As shown in Fig. 2, when a metal plate 100 is sheared using a shear 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 end 103 that has been plastically deformed by the shearing is formed in the sheared material 101. The sheared end 103 has a sheared end face 105, which is a surface newly generated by the shearing, and a sheared end side face 107, which is a part of a plate side face 109 of the metal plate 100 and is deformed by the formation of the sheared end 103. The sheared end 103 is in a range of less than 1 mm from the sheared end face 105.

[0028] It is known that fatigue fracture or delayed fracture cracks during use of a part (eg, a press-molded product) using the sheared material 101 initiate from the sheared end surface 105, and originate from a portion with high residual stress.

[0029] Therefore, in order to suppress the occurrence of fatigue failure or delayed failure of 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 described above, it is difficult to obtain the residual stress at the sheared edge 105. Therefore, the inventors have earnestly studied a method for grasping the residual stress at the sheared edge 105, which is the starting point of cracks in fatigue fracture and delayed fracture.

[0030] In this study, we considered that the residual stress at the sheared end surface 105 generated by shearing might be related to the residual stress at the side surface of the sheared end that is deformed by the formation of the sheared end. Therefore, as shown in Fig. 3(a), the residual stress at the center in the plate thickness direction of the sheared end surface 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 surface 107 of the sheared end was investigated.

[0031] As a result, it was found that the residual stress at the center in the sheet thickness direction of the sheared end surface 105 correlates with the maximum tensile residual stress (hereinafter referred to as "maximum residual stress") at the sheared end side surface 107, as shown in FIG. 3(b).

[0032] Based on this, the inventors thought that if the maximum residual stress could be obtained from the residual stress distribution at the shear end side 107, it might be possible to determine whether or not there is a location at the shear end face 105 that could serve as the starting point for cracks causing fatigue failure or delayed fracture.

[0033] Next, the inventors investigated a method for determining the residual stress distribution on the shear end side surface 107. According to the method disclosed in the above-mentioned Patent Document 3, the strain history on the plate side of the deformed part of a metal plate undergoing plastic deformation is acquired, and the stress on the plate side is successively updated from the start to the end of deformation, thereby obtaining the residual stress distribution in the deformed part. However, this method has a problem that the residual stress generated in the deformed part of the metal plate subjected to plastic deformation is calculated based on a coordinate system defined by the positions of each measurement point for measuring the strain, and therefore, if the orientation of the coordinate system changes due to the rotational deformation of the metal plate itself during the deformation process, the direction in which the residual stress is generated becomes unclear.

[0034] As an example of the change in the orientation of the material coordinate system of a metal plate that has been subjected to plastic deformation, consider a metal plate 100 that is sheared, as shown in Fig. 4. In Fig. 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. Here, the coordinate system defined at each position of 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.

[0035] In the metal plate 100 before shearing, as shown in FIG. 4(a), 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 being deformed by shearing, as shown in FIG. 4(b), the orientation of the material coordinate system differs depending on the position in the sheared material 101, and deviates from the orientation of the global coordinate system.

[0036] That is, the orientation of the material coordinate system changes according to the deformation occurring in the sheared material 101, and further, the orientation differs depending on the position in the sheared material 101. In contrast, the global coordinate system is different from the material coordinate system in that its orientation does not change with the deformation of the sheared material 101 due to shearing, and is the same regardless of the position of the sheared material 101.

[0037] Furthermore, in order to calculate the distribution of residual stress in the 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, there is a possibility that the direction of the residual stress differs depending on the position, resulting in variation and inconsistency.

[0038] In order to align the directions of the residual stresses, it is considered that the direction of the residual stresses should be aligned based on the orientation of the material coordinate system for each position of the measurement point where the residual stresses are calculated. However, in the method disclosed in Patent Document 3, the stresses in the deformation process are calculated sequentially using only the strain history. Therefore, it is not possible to know how the orientation of the sheared material 101 changes in the deformation process, and it is not possible to obtain information regarding the orientation of the material coordinate system for each position of the measurement point where the stress is calculated.

[0039] The inventors have conducted extensive research to solve this problem, and have come up with the idea of ​​acquiring not only the strain history during the deformation process of a metal plate caused by shear processing, 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 obtained as information on 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, the residual stress calculated according to the material coordinate system at each measurement point of the metal plate is converted into a stress in a predetermined direction in the global coordinate system based on the spin history, and it has been found that the residual stress distribution can be obtained by aligning the orientations of the residual stresses at multiple measurement points.

[0040] The present invention has been made based on the results of the above investigation, and will be specifically described below.

[0041] [Embodiment 1] <Metal plate shear processing test method> The metal plate shear processing test method according to the first embodiment of the present invention calculates the residual stress at the sheared end of the sheared metal plate, and includes a shear processing 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). Hereinafter, the above-mentioned processes and steps will be described for the case of calculating the residual stress distribution of the sheared end side surface 127 of the sheared end 123, which is a deformed portion of the sheared test piece 121, as shown in FIG.

[0042] [Shear processing reproduction test process] The shearing reproduction test process P1 is a process for reproducing the formation process of 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 as a test material (see FIG. 2).

[0043] 5, the shear processing reproduction test process P1 can shear a test piece 121 using a shear mold 11 having a punch 13, a die 15, and a holder 17. In the shear processing using the shear mold 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 relatively to each other while the die 15 and the holder 17 are fixed with bolts to prevent the test piece 121 from floating up from the die 15 during the shear processing. The method of preventing the test piece 121 from floating up from the die 15 is not limited to fixing with bolts, but may be to apply a constant load to the holder 17 using a power source such as hydraulic pressure.

[0044] [Residual stress distribution calculation process] The residual stress distribution calculation process P3 is a process for calculating the residual stress distribution at the shear end side surface 127 (see FIG. 2) of the shear end 123 formed in the test piece 121 in the shear processing reproduction test process P1.

[0045] As shown in FIG. 1(b), 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.

[0046] <Deformation history acquisition process> The deformation history acquisition process S10 is a process for acquiring the deformation history of the shear end side 127 during the deformation process of the shear end 123 due to shear processing of the test piece 121, and includes a surface deformation history acquisition step S11, a strain history acquisition step S13, and a spin history acquisition step S15, as shown in Figure 1(b).

[0047] (Surface deformation history acquisition step) The surface deformation history acquisition step S11 is a step of acquiring the surface deformation history of the shear end side 127 of the shear end 123 from the start of deformation to the end of deformation by setting multiple measurement points on the shear end side 127 of the test piece 121 and measuring the three-dimensional coordinates of each measurement point during the process of shearing the test piece 121 in the shear processing reproduction test process P1. 5, in the present embodiment 1, two cameras 29 are installed at positions where they can capture an image of the shear end side surface 127 of the test piece 121. Then, the three-dimensional coordinates of each measurement point are measured by digital image correlation (hereinafter referred to as "DIC").

[0048] In DIC, two cameras 29 are used to capture images of the shear end side surface 127 during the deformation process of the shear end 123 due to shear processing of the test piece 121 at predetermined time intervals, and the images captured at each time step (hereinafter referred to as "DIC images") are analyzed. This makes it possible to measure 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. The photographing range of the two cameras 29 may be determined so that the plate side surface 129a including the shear end side surface 127 of the test piece 121 does not go outside the photographing range at any time from the start to the end of deformation, as shown in Fig. 2. Also, it is sufficient to photograph the plate side surface 129a including the shear end side surface 127 of the test piece 121, and it is not necessary to photograph the entire plate side surface 129.

[0049] (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 the shearing 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.

[0050] (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 surface 123 from the surface deformation history of the shear end side surface 127 acquired in the surface deformation history acquisition step S11.

[0051] A specific process 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.

[0052] 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 a predetermined time interval during the deformation process of the shear end portion 123 due to shear processing of the test piece.

[0053] In FIG. 6, the coordinates of each measurement point at a certain time step in the deformation process are defined as the coordinates before deformation Xi, and the coordinates of each measurement point at a time step after a certain time interval has elapsed from the time step are defined as the coordinates after deformation x i (i=0,1,2).

[0054] 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 caused by the deformation of the area consisting of the three measurement points can be calculated as follows:

[0055] For each of the area a1 before deformation and the area a2 after deformation, the coordinates X 0 and x 0 The measurement point of is used as the reference. And the coordinate X i , x i The reference point (X 0 or x 0The relative positions from i =X i -X 0 (i = 1, 2), dx i =x i -x 0 (i = 1, 2) are represented as follows. At this time, dx i =FdX i The F that satisfies this is called the deformation gradient tensor.

[0056] Generally, the deformation of a region composed of multiple measurement points does not necessarily need to be obtained from the displacements of the aforementioned three measurement points, and can be represented by the following formula (1).

Equation

[0057] Solving formula (1) for the deformation gradient tensor F results in formula (2).

Equation

[0058] Furthermore, using the deformation gradient tensor F, the right Cauchy–Green deformation tensor C and the right stretch tensor U are represented by formulas (3) and (4), respectively.

Equation

[0059] Using these, the logarithmic strain tensor (Hencky strain tensor E) and the spin tensor R are defined by formulas (5) and (6), respectively.

Equation

[0060] In formula (5), the Hencky strain tensor E is the strain at each time step from the start of deformation to the end of deformation. Also, in formula (6), the spin tensor R is the spin at each time step from the start of deformation to the end of deformation.

[0061] As described above, in acquiring the deformation history by 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 captured at each time step are subjected to image analysis, and the three-dimensional coordinates (Xi, xi) of each measurement point set on the shear end side surface 127 are measured. Next, the Hencky strain tensor E and the spin tensor R at a predetermined position on the shear end side surface 127 are calculated from the three-dimensional coordinates of each measured point (Equations (1) to (6)).

[0062] Then, the Hencky strain tensor E calculated at each time step from the start to the end of the deformation is obtained as a strain history (S13). Similarly, the spin tensor R calculated at each time step from the start to the end of the deformation is obtained as a spin history (S15).

[0063] <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 127 of the test piece 121 (hereinafter also referred to as "local stress") from the start of deformation to the end of deformation during the deformation process of the shear end 123. 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, as shown in FIG. 1(b).

[0064] (Step to calculate the increment of strain) First, in an 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 increment of strain for each time step whose strain history is acquired in the strain history acquisition step S13. When the three-dimensional coordinates in the deformation process of each measurement point set on the shear end side surface 127 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 in two in-plane directions and the in-plane shear strain. Therefore, the acquired strain increments calculated in the acquired strain increment calculation step S21 are the strain increments of the strain in two in-plane directions and the in-plane shear strain.

[0065] The acquired strain increment is calculated for each time step in which the strain history is acquired. The acquired strain increment at each time step can be calculated, for example, from the strain at the time step and the strains at the time steps before and after the time step.

[0066] (Step to calculate assumed strain increment) Next, in an assumed strain increment calculation step S23, an assumed strain increment is calculated. The assumed strain increment is an 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 obtained by assuming the deformation state of the shear end side surface 127 from the deformation process of the shear end 123 due to the shearing of the test piece 121, and based on the theory of plastic mechanics in the assumed deformation state.

[0067] As described above, in the strain history acquisition step S13, the strain ε x and ε y and the in-plane (xy plane) shear strain ε xy The strain of the three components, , and , are calculated.

[0068] 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 , εzx ) is occurring.

[0069] In general, the surface of the test piece 121 during the deformation process due to shear processing is a free surface, so no stress is generated in the direction perpendicular to the surface of the test piece 121. In other words, the deformation state of the shear end side surface 127 of the test piece 121 can be assumed to be a plane stress state.

[0070] 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.

[0071] Here, if we assume that the deformation state of the shear end side 127 is a plane stress state, the stress increment in the out-of-plane direction is 0. Therefore, the strain in the out-of-plane direction (ε z ) can be calculated uniquely.

[0072] 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 the shearing of the test piece 121. Then, based on the theory of plastic mechanics in the assumed deformation state, it is possible to obtain strains other than the strains whose strain history has been acquired in the strain history acquisition step S13.

[0073] In this way, in the assumed strain increment calculation step S23, the strain other than the strain whose strain history is acquired at each time step in the deformation process of the shear end 123 is 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. 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, similar to the acquired strain increment described above.

[0074] (Acquisition spin increment calculation step) Next, in an acquired spin increment calculation step S25, an acquired spin increment is calculated from the spin history acquired in the spin history acquisition step S15. Here, the acquired spin increment is an increment of the spin for each time step of the shear end side surface 127 acquired at a predetermined time interval. The acquisition spin increment at each time step can be calculated, for example, from the spin at that time step and the spins at the time steps before and after that time step.

[0075] (Stress increment calculation step) Subsequently, in a 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.

[0076] The stress increment can be calculated using the material constitutive law based on elastic-plastic mechanics. 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.

number

[0077] 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.

[0078] Furthermore, the elastic-plastic coefficient tensor C in Eq. ep can be given by equation (8).

number

[0079] In this embodiment 1, as an example of a material constitutive law, the stress increment is calculated from the 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.

[0080] The YU model can be classified as a two-surface model in which the yield surface moves within the limit surface, and the evolution of the limit surface (center β, radius R) and the yield surface (center α, radius Y) is defined by the following equation (9) depending on the strain increment.

[0081]

number

[0082] In this case, equation (8) is expressed as equation (10).

number

[0083] In this way, once the strain increment and spin increment are known, the stress increment can be obtained according to the material constitutive law.

[0084] The material constitutive law is not limited to the above-mentioned YU model, and the elastic-plastic coefficient 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 coefficient tensor C epis expressed by equation (11).

number

[0085] In addition, the elastic-plastic coefficient tensor C ep The yield function f used to give is not limited to the isotropic von Mises yield function, but can be any yield function such as Hill'48 or Yld2000-2d, which can express the anisotropy of the material (metal plate) with high accuracy.

[0086] (Sequential stress update step) Next, in a 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.

[0087] In the sequential stress update step S29, first, at a certain time step in the deformation process, the local stress is updated using the stress increment calculated for each measurement point (S29a). Then, it is determined whether or not the stress update for all measurement points has been completed (S29b).

[0088] 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 S21, S23, S25, S27 and S29 are executed for the measurement points for which stress updating has not been completed, and the local stress is updated (S29a).

[0089] 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).

[0090] If it is determined that the deformation has not ended, the process proceeds to the next time step of the deformation process. Then, for all measurement points, 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) are performed. In this manner, in the sequential stress update step S29, the processes of S29a to S29c are performed to sequentially update the local stresses at all measurement points from the start of deformation to the end of deformation.

[0091] <Residual stress distribution calculation process> The residual stress distribution calculation step S30 is a step of converting the local stresses at each measurement point at the end of deformation of the sheared end 123 into global stress values ​​in a global coordinate system, and calculating the residual stress distribution of the sheared end side surface 127. In the present embodiment 1, the residual stress distribution calculation step S30 includes a stress coordinate system conversion step S31 and a residual stress distribution display step S33.

[0092] (Stress coordinate system transformation 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 the deformation of the shear end 123 in the sequential stress update step S20, the local stress at the end of the deformation is converted into a stress value in a predetermined direction in the 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.

[0093] 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, the global stress value in the global coordinate system is σ g can be calculated using equation (12).

number

[0094] 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 appropriately set by aligning the stress direction.

[0095] (Residual stress distribution display step) Subsequently, in a 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.

[0096] In order to display the residual stress distribution, for example, the coordinates of each measurement point at which the global stress value was obtained may be converted into coordinates on a DIC image of the sheared end side surface 127 .

[0097] To convert to coordinates on the DIC image of the shear end side 127, the coordinates (X, Y, Z) of each measurement point in the global coordinate system can be converted to coordinates (u, v) in a two-dimensional plane on the DIC image using equation (13).

number

[0098] In the first embodiment, the residual stress distribution calculation step S30 is performed after the sequential stress update step S20 is completed. 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 stress update for all measurement points for each time step is completed (S29b) in the sequential stress update step S29.

[0099] As described above, in the metal plate shear processing test method according to the first embodiment, the formation process of the sheared end 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 end side 127 in the deformation process of the sheared end 123 formed by shearing the test piece 121 is obtained. Furthermore, based on the surface deformation history of the sheared end side 127, the stress of the sheared end side 127 from the start of deformation of the sheared end 123 to the end of deformation is sequentially updated and obtained. As a result, even if the orientation of the material coordinate system changes for each position of the measurement point on the sheared end side 127 due to the shearing of the test piece 121, the residual stress distribution on the sheared end side 127 can be obtained with high accuracy by aligning the stress direction.

[0100] 3(b), the maximum residual stress at the sheared end side 127 correlates with the residual stress at the sheared end surface 125. Therefore, according to the metal plate shear processing test method according to the first embodiment, it is possible to judge the presence or absence of a site that may be the starting point of a crack due to delayed fracture or fatigue fracture at the sheared end surface 125 generated by shear processing by evaluating the maximum residual stress from the residual stress distribution obtained for the sheared end side 127 of the test piece 121. Note that this judgment can be made, for example, by checking whether the maximum residual stress at the sheared end side 127 exceeds a predetermined value.

[0101] 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 portion 123 due to shear processing of the test piece 121. Furthermore, even for shear deformation accompanied by destruction of the metal plate, which is difficult to predict by 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.

[0102] In addition, in the metal plate shear processing test method according to the present embodiment 1, the assumed strain increment calculation step S23 assumes a deformation state of the shear end side 127 from the deformation process of the shear end 123 in the test piece 121, and calculates an assumed strain increment based on the theory of plastic mechanics in the assumed deformation state. However, in the present invention, the hypothetical strain increment calculation step may also involve 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, assuming the deformation state (e.g., strain ratio) of the shear end side 127 from the results, and calculating the hypothetical strain increment at the shear end side 127.

[0103] When calculating an 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 perform finite element analysis by modeling only the shear end portion 123 and its vicinity. 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.

[0104] In particular, finite element analysis using solid elements, which can calculate stress in the plate thickness direction with high accuracy, is rarely used for general shear processing of metal plates because it significantly increases the calculation time. However, if the analysis target is a part of a metal plate including a shear end that is plastically deformed by shear processing, the deformation state of the shear end side can be predicted with high accuracy in a short time even if finite element analysis is performed using solid elements. 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 shear end side 127 during the deformation process of the shear end, it becomes possible to calculate the residual stress distribution on the shear end side with even higher accuracy.

[0105] [Embodiment 2] <Shear processing test system for metal plates> A metal plate shear processing test system according to a second embodiment of the present invention (hereinafter referred to as "shear processing test system") calculates the distribution of residual stress occurring at the sheared end of a sheared metal plate material. Hereinafter, each component of the shear processing test system 1 will be described for the case where a test piece 121 is sheared and the distribution of residual stress generated on a shear end side surface 127 is calculated as shown in FIG.

[0106] As an example, as shown in FIG. 5, 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 at the shear end side 127 (see FIG. 2) of the shear end 123 formed in the test piece 121 by shear processing.

[0107] <Shear processing simulation test device> The shearing process reproduction test device 10 is a device that reproduces the formation process of the sheared end of a sheared metal plate by shearing a test piece 121 made of a metal plate as a test material. As illustrated in Fig. 5, the shearing process reproduction test device 10 is equipped with a shearing die 11 having a punch (upper blade) 13, a die (lower blade) 15, and a holder 17, and shears the test piece 121 by moving the punch 13 and the die 15 relatively with the test piece 121 placed between the die 15 and the holder 17.

[0108] <Residual stress distribution calculation device> The residual stress distribution calculation device 20 is a device that calculates the residual stress distribution at the shear end side surface 127 of the shear end 123 formed in the test piece 121 by the shear processing reproduction test device 10.

[0109] In the second embodiment, the residual stress distribution calculation device 20 includes 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 / arithmetic processing unit 31, as shown in FIG.

[0110] In the residual stress distribution calculation device 20, the display device 21, the input device 23, the main storage device 25, the auxiliary storage device 27, and the measurement control / calculation processing unit 31 may be configured with a PC (personal computer) or the like. In this case, the display device 21, the input device 23, the main storage device 25, the auxiliary storage device 27, and the cameras 29, 29 are connected to the measurement control / calculation processing unit 31, and each function is executed by a command from the measurement control / calculation processing unit 31.

[0111] The display device 21 is used to display images of the shear end side 127 at the shear end 123 of the test piece 121 captured by the two cameras 29, and the calculated residual stress distribution at the shear end side 127, and is composed of an LCD monitor or the like.

[0112] The input device 23 is used for displaying and instructing the image of the shear end side surface 127 and the residual stress distribution, and for inputting conditions by the operator, and is composed of a keyboard, a mouse, and the like.

[0113] The main memory device 25 is used for storing various files such as images of the shear end side surface 127 captured by the two cameras 29 and programs for calculating the residual stress distribution, and is composed of a hard disk or the like.

[0114] The auxiliary storage device 27 is used for temporary storage of data used in the measurement control / calculation processing unit 31 and for calculations, and is composed of a RAM (Random Access Memory) or the like.

[0115] The cameras 29, 29 are used to stereophotograph the shear end side surface 127 during the process of deformation of the shear end 123 due to the shearing process of the test piece 121.

[0116] The measurement control / calculation processing unit 31 has a measurement control unit 33 that controls the measurement of the surface deformation history of the shear end side 127, and a calculation processing unit 35 that performs calculation processing to calculate the residual stress distribution based on the measured surface deformation history.

[0117] 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 by the two cameras 29 during the deformation process of the shear end portion 123 due to the shearing process of the test piece 121. The three-dimensional coordinate calculation means 33b calculates three-dimensional coordinates of a plurality of measurement points set on the shear end side surface 127 during the deformation process by performing image analysis on the captured image of the shear end side surface 127.

[0118] In this embodiment 2, the three-dimensional coordinate calculation means 33b processes images of the shear end side 127 of the test piece 121 stereoscopically photographed by the two cameras 29 using DIC, and calculates the three-dimensional coordinates of multiple measurement points set on the shear end side 127.

[0119] In DIC, the shear end side surface 127 of the test piece 121 is imaged at a predetermined time interval during the deformation process of the shear end 123, and the images taken at each time step (hereinafter referred to as "DIC images") are subjected to image analysis. This makes it possible to measure 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. <Transformation History Acquisition Unit> The deformation history acquisition unit 37 acquires the surface deformation history of the shear end side 127 during the deformation process of the shear end 123 due to shear processing of the test piece 121, and acquires the strain history and spin history occurring on the shear end side 127 from the acquired surface deformation history. As shown in FIG. 5, the deformation history acquisition unit 37 includes a surface deformation history acquisition section 37a, a strain history acquisition section 37b, and a spin history acquisition section 37c.

[0120] The surface deformation history acquisition unit 37a measures three-dimensional coordinates during the deformation process of the sheared end 123 due to shear processing of the test piece 121 using the shear processing reproduction test device 10 for multiple measurement points set on the sheared end side 127 of the sheared end 123 formed on the test piece 121, and acquires this as the surface deformation history of the sheared end side 127 from the start of deformation of the sheared end 123 to the end of deformation.

[0121] 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 side surface 127 acquired by the surface deformation history acquisition unit 37a.

[0122] 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 side surface 127 acquired by the surface deformation history acquisition unit 37a.

[0123] <Sequential stress update unit> The sequential stress update unit 39 sequentially updates and determines the stress in the material coordinate system at each measurement point set on the shear end side 127 of the test piece 121 from the start of deformation to the end of deformation during the deformation process of the shear end 123. As shown in FIG. 5, the sequential stress update unit 39 has an acquired strain increment calculator 39a, an assumed strain increment calculator 39b, an acquired spin increment calculator 39c, a stress increment calculator 39d, and a sequential stress updater 39e.

[0124] (Calculation of strain increment) The acquired strain increment calculation unit 39a calculates an acquired strain increment from the strain history of the shear end side surface 127 acquired by the strain history acquisition unit 37b.

[0125] The acquired strain increment is an increment of strain for each time step whose strain history is acquired by the strain history acquisition unit 37b. For example, when the three-dimensional coordinates in the deformation process of each measurement point set on the shear end side surface 127 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 of each of the strain in two in-plane directions and the in-plane shear strain.

[0126] The acquired strain increment is calculated for each time step at which the strain history of the shear end side 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 the time step.

[0127] (Assumed strain increment calculation section) The assumed strain increment calculation section 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 based on the theory of plastic mechanics in the assumed deformation state by assuming the deformation state of the shear end side surface 127 from the deformation process of the shear end.

[0128] 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 in the metal sheet shear processing test method according to the first embodiment described above. 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 from 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.

[0129] Here, if we assume that the deformation state of the shear end side 127 is a plane stress state, the stress increment in the out-of-plane direction is 0, so the strain in the out-of-plane direction can be calculated uniquely by using the equation for strain and stress increment based on the theory of plastic mechanics.

[0130] In this way, the assumed strain increment calculation unit 39b calculates strains other than the strains whose strain history is acquired at each time step in the deformation process of the shear end 123 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 strains 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.

[0131] (Acquired spin increment calculation part) The acquired spin increment calculation unit 39c calculates an acquired spin increment from the spin history acquired by the spin history acquisition unit 37c. Here, the acquired spin increment is an increment of the spin of the shear end side surface 127 obtained at a predetermined time interval. The acquisition spin increment at each time step can be calculated, for example, from the spin at that time step and the spins at the time steps before and after that time step.

[0132] (Stress increment calculation section) The stress increment calculation unit 39d calculates the stress increment of the shear end side surface 127 during the deformation process of the shear end 123 by using the acquired strain increment, the assumed strain increment, and the acquired spin increment. The calculation of the stress increment by the stress increment calculation unit 39d may be performed in a similar procedure to the stress increment calculation step S27 in the above-described method for testing a metal plate in shear processing according to the first embodiment.

[0133] In the calculation of the stress increment by the stress increment calculation unit 39d, as described above, the YU model (Non-Patent Document 1), which is capable of reproducing the Bauschinger effect with high accuracy, can be suitably applied as the material constitutive law. However, the stress increment calculation unit 39d is not limited to the one that applies 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 f is not limited to the isotropic von Mises yield function, but may be any yield function such as Hill'48 or Yld2000-2d that can express the anisotropy of the material (metal plate) with high accuracy.

[0134] (Sequential stress update section) The sequential stress update unit 39e sequentially updates 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, using the stress increment calculated for each measurement point by the stress increment calculation unit 39d.

[0135] 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.

[0136] Next, the sequential stress update unit 39e judges whether the update of the local stress is completed for all the measurement points. If it is judged that the update of the local stress is not completed for all the measurement points, the acquired strain increment calculation unit 39a, the assumed strain increment calculation unit 39b, the acquired spin increment calculation unit 39c, and the stress increment calculation unit 39d perform processing for the measurement points for which the local stress is not updated. Then, the sequential stress update unit 39e updates the local stress of the measurement points for which the local stress is not updated.

[0137] When it is determined that the local stresses have 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.

[0138] If it is determined that the deformation is not complete, 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 calculator 39a, the assumed strain increment calculator 39b, the acquired spin increment calculator 39c, and the stress increment calculator 39d. Then, the local stresses for all measurement points are updated. When it is determined that the transformation has ended, the processing by the sequential stress update unit 39e ends.

[0139] In this manner, 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.

[0140] <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 part 41a and a residual stress distribution display part 41b.

[0141] (Stress coordinate system conversion part) The stress coordinate system conversion unit 41a converts the stress at the end of the deformation of the shear end 123 into a value of stress in a predetermined direction in a global coordinate system (global stress value) among the stresses in the material coordinate system of each measurement point obtained by sequentially updating from the start to the end of the deformation of the shear end 123 by the sequential stress update unit 39. Then, the stress coordinate system conversion unit 41a obtains the converted global stress values ​​of each measurement point as the residual stress distribution of the shear end side surface 127.

[0142] If the local stress in the material coordinate system obtained for each measurement point is σ and a specific direction in the global coordinate system is vector n, the global stress value σ in the global coordinate system is calculated by the above-mentioned formula (12). g can be calculated.

[0143] (Residual stress distribution display section) The residual stress distribution display section 41b displays the residual stress distribution of the shear end side surface 127 obtained by the stress coordinate system conversion section 41a. In order to display the residual stress distribution using the residual stress distribution display unit 41b, the coordinates of each measurement point from which the global stress value was determined may be converted into coordinates on the DIC image of the shear end side 127, similar to the residual stress distribution display step S33 described above. To convert to coordinates on the DIC image of the shear end side 127, the coordinates (X, Y, Z) of each measurement point in the global coordinate system can be converted to coordinates (u, v) on a two-dimensional plane on the DIC image using the above-mentioned equation (13).

[0144] As described above, in the shear processing test system 1 according to the second embodiment, the formation process of the sheared end 103 of the sheared material 101 obtained by shearing the metal plate 100 is reproduced by shear processing the test piece 121 using the metal plate 100 as a test material. Then, the surface deformation history of the sheared end side 127 in the deformation process of the sheared end 123 formed by shear processing of the test piece 121 is obtained. Furthermore, based on the surface deformation history of the sheared end side 127, the stress of the sheared end side 127 from the start of deformation of the sheared end 123 to the end of deformation is sequentially updated and obtained. As a result, even if the orientation of the material coordinate system changes for each position of the sheared end side 127 of the sheared end 123 during the shear processing of the test piece 121, the residual stress distribution at the sheared end side 127 of the sheared end 123 can be obtained with high accuracy by aligning the stress direction.

[0145] In addition, 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 127 of the test piece 121, it is also possible to determine whether or not there is a location on the shear end face 125 generated by the shear processing that could become the starting point of a crack due to delayed fracture or fatigue fracture.

[0146] Furthermore, in the metal plate shear processing 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 shear processing of the test piece. Furthermore, even for shear deformation accompanied by destruction of the metal plate, which is difficult to predict by finite element analysis, it is possible to accurately and easily calculate the residual stress distribution generated in the metal plate.

[0147] In the metal plate shear processing 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 of each measurement point into a stress value in a predetermined direction in the global coordinate system. However, the present invention is not limited to having the residual stress distribution display section 41b.

[0148] In the shear 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 deformation state of the shear end side surface 127 assumed from the deformation process of the shear end portion 123 in the test piece 121. However, in the present invention, the assumed strain increment calculation unit may perform a finite element analysis of the process in which the metal plate undergoes plastic deformation, and assume the deformation state (e.g., strain ratio) of the shear end side surface 127 from the results of the analysis.

[0149] When assuming the deformation state of the shear end side 127 by finite element analysis of the deformation process due to shearing of a metal plate (test piece) and calculating the assumed strain increment, as described above, it is not necessary to analyze the entire metal plate, and it is sufficient to model only the shear end 123 and its vicinity and perform the finite element analysis. This makes it possible to assume the deformation state of the shear end side 127 in a shorter time than in finite element analysis that analyzes the entire metal plate. Furthermore, it also becomes possible to use solid elements that can calculate the stress in the plate thickness direction with high accuracy in the finite element analysis, and the residual stress distribution can be calculated with higher accuracy.

[0150] The metal plate shear processing test method and metal plate shear processing test system of the present invention are not limited to measuring the three-dimensional coordinates of each measurement point by DIC, but may be 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. In addition, the present invention may obtain, as a surface deformation history, the three-dimensional coordinates of each measurement point measured at a predetermined time interval from the start of deformation of the sheared end portion due to shear processing of the test piece to the end of deformation. As described above, the metal plate shear processing test method and metal plate shear processing 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 shear end side of the test piece. Therefore, it is possible to accurately calculate the residual stress distribution even for non-uniform metal plates having two or more types of phases, which was a problem in the measurement of residual stress using X-rays or ultrasonic waves as in the conventional technology.

[0151] Furthermore, as mentioned above, in order to predict the residual stress distribution with high accuracy in finite element analysis, a significant amount of calculation time is required, and analysis is difficult when fracture such as cracking or shearing is involved. In particular, metal plates that have been plastically deformed by shear processing often fracture from their ends. Therefore, it is important to accurately determine the residual stress distribution at the end faces of the metal plates in order to understand the fatigue life and delayed fracture characteristics. In contrast, according to the metal plate shear processing test method and metal plate shear processing test system of the present invention, the strain history and spin history of the shear end side during the deformation process in which the shear end is plastically deformed by shear processing of the test piece can be easily measured, and the residual stress distribution on the shear end side can be accurately calculated.

[0152] The above explanation was about the case where stress increment is calculated using the YU model. However, in the YU model, the stress-strain relationship is defined in a velocity system, so in the case of nonlinear deformation, if the strain increment is not made small enough, an error will occur in the stress increment. Therefore, when calculating stress increment using the YU model, it is recommended to set the strain increment to 10-6 It is preferable to adjust the time interval for acquiring the three-dimensional coordinates of each measurement point as the surface deformation history so as to satisfy the following: In addition, the surface deformation history acquired in the present invention is considered to include measurement noise, and there is concern that the strain history and spin history acquired from the surface deformation history including such measurement noise will also include noise.

[0153] Therefore, when the stress increment is calculated using the minute strain increment (obtained strain increment) calculated from the strain history, the noise in the strain history has a large effect on the stress increment, and the accuracy of the successively calculated stress may be reduced. In such a case, it is preferable to smooth the strain history using a low-pass filter or the like to remove noise, so that the residual stress distribution can be calculated with high accuracy.

[0154] Furthermore, according to the present invention, it is possible to know not only the residual stress after the end of deformation as in the conventional technology, but also the stress during deformation at the shear end of the sheared material, so that it is possible to calculate the maximum stress generated in the deformed body.

[0155] [Implementation form 3] The manufacturing method of the sheared metal plate material according to one aspect of the third embodiment of the present invention is to shear the metal plate to manufacture the sheared material. The manufacturing method of the sheared metal plate material according to the third embodiment includes a tentative shear condition setting step S41, a shear reproduction test step S43, a tensile residual stress amount determination step S45, a tentative shear condition changing step S47, a repeating step S49, a shear condition determination step S51, and a shearing step S53, as shown in Fig. 7. Each of these steps will be described below.

[0156] <Temporary shear condition setting process> The provisional shearing condition setting step S41 is a step of setting provisional shearing conditions for the sheared material. As tentative shearing conditions, for example, when using the shearing die 11 shown in Figure 5, 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 shearing speed (the relative moving speed between the punch 13 and the die 15), the radii of curvature of the cutting edge 13a of the punch 13 and the cutting edge 15a of the die 15, the cutting allowance, etc. may be set.

[0157] <Shear processing reproduction test process> 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-mentioned embodiment 1. Then, based on the surface deformation history of the sheared end side surface 127 formed in the test piece 121, the residual stress distribution in the sheared end side surface 127 is calculated.

[0158] In the shear processing reproduction test process S43, as shown in FIG. 6, the shear end side 127 during the deformation process of the shear end 123 due to the shear processing of the test piece 121 is stereo-photographed by two cameras 29, and the three-dimensional coordinates of each measurement point set on the shear end side 127 are measured by DIC.

[0159] <<Tensile residual stress determination process>> The tensile residual stress amount determination step S45 is a step of determining whether the tensile residual stress at the shear end side surface 127 of the test piece 121 calculated in the shear processing reproduction test step S43 is within a predetermined range. In the tensile residual stress amount 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 range of tensile residual stress in which good hydrogen embrittlement resistance can be obtained when a test piece to which a tensile residual stress has been imparted is placed in a hydrogen penetration environment (for example, immersed in a pH of 4.0 and a McIlvaine buffer solution with a concentration of 0.1%) for 30 hours.

[0160] <Temporary shear condition change process> The tentative shear condition changing step S47 is a step of changing the tentative shear conditions in a direction to relieve 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 the predetermined range. Examples of changing the tentative shear conditions include narrowing the clearance between the punch 13 and the die 15, increasing the shear rate, and the like.

[0161] <Repetitive process> The repetitive process S49 is a process of repeatedly executing the provisional shear condition change process S47, the shear processing reproduction test process S43, and the tensile residual stress determination process S45 until the tensile residual stress at the shear end side 127 is determined to be within a predetermined range.

[0162] <Shearing condition determination process> The shear condition determination process S51 is a process for determining the provisional shear conditions as the shear conditions when the tensile residual stress at the shear end side 127 of the test piece 121 is determined to be within a predetermined range in the tensile residual stress amount determination process S45.

[0163] <Shearing process> The shearing process S53 is a process for shearing the metal plate under the shearing conditions determined in the shearing condition determination process S51 to produce a sheared material.

[0164] 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 in which measures are appropriately taken to suppress the occurrence of tensile residual stress that affects fatigue life and delayed fracture characteristics. EXAMPLES

[0165] An experiment was carried out to verify the effects of the present invention, which will now be described. In Example 1, the strain of the test piece 121 from the start of shearing to fracture was measured by DIC using the metal plate shear processing test method according to the above-mentioned embodiment 1, and the distribution of residual stress in the plate thickness direction at the shear end side surface 127 of the shear end 123 formed by the shear processing of the test piece 121 was obtained. Furthermore, at the center position in the plate thickness direction of the sheared test piece 121, X-ray stress measurement was performed from the shear end surface 125 in the longitudinal direction of the test piece 121 (direction perpendicular to the shear end surface) (Comparative Example), and the result was compared with the residual stress at the shear end side surface 127 calculated by the method according to the present invention.

[0166] 8(a) and (b) show the shear processing reproduction test device 10 used in Example 1. In Fig. 8, the X-axis direction is a direction perpendicular to the shear end face, the Y-axis direction is a plate thickness direction of the test piece 121, and the Z-axis direction is a direction perpendicular to the shear end side surface 127.

[0167] The shearing device was equipped with 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 capable of photographing a sheared end side surface 127 of a sheared end 123 formed by shearing a test piece 121. Then, a plurality of measurement points were set on the sheared end side surface 127, and the three-dimensional coordinates of each measurement point were measured by DIC.

[0168] 8(c) shows a top view of the test piece 121. The test piece 121 was made from a high-strength steel plate having a tensile strength of 1470 MPa and a plate thickness of 1.4 mm.

[0169] The shear conditions of 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 of the test piece 121 (relative speed between the punch 13 and the die 15) 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 (tip 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 to the punch 13 side in FIG. 8(a)) was 15 mm.

[0170] 9 shows the distribution of residual stress in the plate thickness direction at the shear end side surface 127 of the shear end 123 after the test piece 121 was sheared and broken. Compressive (negative, black) residual stress in the plate thickness direction was confirmed about several tens of μm inward from the shear end surface 125. In addition, tensile (positive, white) residual stress in the plate thickness direction was generated from the inner side toward the upper surface of the test piece 121. Fig. 10 shows a comparison between the residual stress (example) calculated from the residual stress distribution on the shear end side surface 127 calculated by the method according to the first embodiment described above and the residual stress (comparative example) measured by X-ray diffraction (XRD). In the graph shown in Fig. 10, the horizontal axis represents the distance from the shear end surface 125 in the direction perpendicular to the shear end surface, and the vertical axis represents the thickness direction residual stress at the center in the thickness direction.

[0171] The inventive example and the comparative example are relatively consistent in the range of 0.1 to 0.4 mm from the sheared edge 125. This confirmed that the residual stress in the vicinity of the sheared edge, which is problematic in delayed fracture, can be predicted by this method. The deviation between the inventive example and the comparative example is a maximum of about 200 MPa at a distance of about 0.8 mm from the sheared edge. This is presumably due to the fact that the X-ray diffraction method (XRD) in the comparative example measures compressive stress derived from the martensite phase of the 1470 MPa class steel plate. EXAMPLES

[0172] Next, in Example 2, a manufacturing method for shear-processed metal plate material according to embodiment 3 of the present invention was used to determine shear conditions capable of suppressing the tensile residual stress that affects delayed fracture properties within a predetermined range, and a shear-processed metal plate material was manufactured.

[0173] In Example 2, the shearing device (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 surface 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, that is, 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.

[0174] In addition, the specified range of tensile residual stress used as the criterion for judging the residual stress on the side of the shear end in the tensile residual stress amount judgment process was determined to be 1000 MPa or less, which was determined as the tensile stress range in which delayed fracture does not occur in a hydrogen intrusion environment (e.g., immersion in hydrochloric acid with a concentration of 3.0% at pH = 4.0 for 96 hours) when tensile stress (load stress) is applied to the four-point bending test specimen using a bending jig and four-point bending test specimen used in a four-point bending delayed fracture test (see, for example, Figures 3 and 4 of JP 2014-0927 A).

[0175] 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 cut margin 131 for shearing, and a hole 133 through which a bolt for fixing the test piece 121 to the die 15 and the holder 17 was passed.

[0176] Table 1 shows the plate thickness and tensile strength of the steel plate used for the test piece 121 in Example 2, the shear conditions of the test piece 121, and the like.

[0177] [Table 1]

[0178] The tentative shear conditions for the test piece 121 were the conditions of 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 of the test piece 121 of 15 mm (temporary shear condition setting process S41).

[0179] The test piece 121 was sheared under hypothetical shear conditions to reproduce the formation process of the sheared end, and the surface deformation history of the sheared end side 127 was measured by taking DIC images of the sheared end side 127 using two cameras 29 (FIG. 8). Then, based on the measured surface deformation history of the sheared end side 127, the residual stress distribution in the plate thickness direction at the sheared end side 127 was calculated. At this time, the maximum residual stress at the sheared end side 127 was 1755 MPa (shear processing reproduction test step S43). FIG. 11(a) shows the residual stress distribution on the shear end side surface 127 of a test piece 121 sheared under hypothetical shear conditions (the arrow in the figure indicates the location of the maximum residual stress).

[0180] 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, which was determined in advance by a four-point bending delayed fracture test, and was determined to be outside the range (tensile residual stress determination step S45).

[0181] Therefore, the tentative shear conditions were changed from Test No. 1 to Test No. 2 in Table 1 so as to alleviate the tensile residual stress at the shear end side surface 127 of the test piece 121 (temporary shear condition changing step S47). Then, under the changed tentative shear conditions, the shear processing reproduction test step S43 and the tensile residual stress amount determination step S45 were performed. The maximum residual stress at the shear end side surface of the test piece sheared under the tentative shear condition of Test No. 2 was 1548 MPa, which was outside the predetermined range in which delayed fracture would not occur.

[0182] Therefore, the tentative shear conditions (clearance, shear angle, punch cutting edge, die cutting edge) were changed as shown in Test No. 3 to Test No. 6 in Table 1, and the shear processing reproduction test process S43 and the tensile residual stress determination process S45 were repeatedly performed (repetition process S49) until the maximum residual stress at the shear end side 127 was determined to be within a predetermined range (1000 MPa or less) where delayed fracture would not occur as determined by a four-point bending delayed fracture test.

[0183] Under the tentative shear conditions of Test No. 6, the maximum residual stress of the shear 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 shear conditions of Test No. 6 were determined as the shear conditions when shearing the metal plate (shear condition determination step S51).

[0184] FIG. 11(b) shows the residual stress distribution on the shear end side surface 127 of the test piece 121 sheared under the determined shear conditions (the arrow in the figure indicates the maximum residual stress).

[0185] Compared with the case where shear processing was performed under the hypothetical shear conditions of Test No. 1 described above (Fig. 11(a)), it can be seen that the shear end side 127 deformed by shear processing under the shear conditions of Test No. 6 has no areas where the tensile residual stress is 1000 MPa or more (white areas in the contour diagram). As a result, according to the shear conditions of Test No. 6, it is possible to manufacture a shear processed material so that the maximum residual stress at the shear end side 127 satisfies a specified range, making it possible to suppress delayed fracture.

[0186] In Test No. 6, the shear angle θ was changed from the shear conditions of Test No. 5, but by changing other shear conditions as shown in Test Nos. 7 to 11 in Table 1, it was investigated whether the maximum residual stress at the shear end side 107 would be within a specified range. Here, Test No. 7 and Test 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 Test No. 11 were changed in cutting allowance (from 15 mm to 5 mm or 25 mm).

[0187] Table 1 shows the shear conditions in Test No. 7 to Test No. 11 and the maximum residual stress obtained from the residual stress distribution at the shear end side 127. It can be seen that in all of Test No. 7 to Test No. 11, the maximum residual stress at the shear end side 127 is within a predetermined range (1000 MPa or less) in which delayed fracture does not occur, as determined in advance by a four-point bending delayed fracture test. This shows that even if the 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 127 falls within the predetermined range.

[0188] 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 127 was within a specified range. Here, in test No. 12, the steel plate had a thickness of 1.2 mm, in test No. 13, the steel plate had a thickness of 2.0 mm and a tensile strength of 780 MPa, and in test No. 14, the steel plate had a thickness of 1.2 mm and a tensile strength of 590 MPa.

[0189] Table 1 shows the maximum residual stress obtained from the residual stress distribution at the shear end side 127 for each of Test No. 12 to Test No. 14. It can be seen that even when the tensile strength and plate thickness of the steel plate are different, the maximum residual stress at the shear end side 127 is within a predetermined range where delayed fracture does not occur. From this, it can be seen that the shear conditions can be determined so that the maximum residual stress at the shear end side is within a predetermined range, regardless of the tensile strength and plate thickness of the steel plate.

[0190] As described above, it has been shown that the manufacturing method of shear-processed metal plate material according to embodiment 3 of the present invention makes it possible to manufacture shear-processed metal plate material in which measures are appropriately taken to suppress the occurrence of tensile residual stress that affects delayed fracture properties. [Explanation of symbols]

[0191] 1. Shear processing test system 10. Shear processing reproduction test device 11 Shearing mold 13 Punch 13a Cutting edge 15 Die 15a cutting edge 17 Holder 20 Residual stress distribution calculation device 21 Display device 23 Input Devices 25 Main memory 27 Auxiliary storage 29 Camera 31 Measurement control / calculation processing section 33 Measurement control section 33a Image capture means 33b Three-dimensional coordinate calculation means 35 Processing unit 37 Deformation History Acquisition Unit 37a Surface deformation history acquisition section 37b Strain history acquisition section 37c Spin History Acquisition Section 39 Sequential Stress Update Unit 39a Calculation of strain increment 39b Calculation of assumed strain increment 39c Acquisition spin increment calculation unit 39d Stress increment calculation section 39e Sequential stress update section 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 Shear end 105 Sheared end face 107 Shear end side 109 Plate side 110 Shear blade 111 Scrap materials 121 Test Piece 123 Shear End 125 Sheared end face 127 Shear end side 129 Plate side 129a Plate side (measurement area by DIC) 131 Cutting allowance 133 Hole

Claims

1. A metal plate shear processing test method for calculating residual stress at a shear end of a sheared material obtained by shearing a metal plate, comprising: The method includes a shear processing reproduction test process for reproducing the formation process of the shear end by shear processing of a test piece using the metal plate as a test material, and a residual stress distribution calculation process for calculating a residual stress distribution on the shear end side of the shear end formed on the test piece, The shear processing reproduction test process uses a shear mold having a punch, a die, and a holder, and in a state in which the test piece is disposed between the die and the holder, the punch and the die are moved relative to each other to shear the test piece, The residual stress distribution calculation process includes a deformation history acquisition process, a sequential stress update process, and a residual stress distribution calculation process, The deformation history acquisition step includes: a surface deformation history acquisition step of acquiring a surface deformation history of the side surface of the shear end portion from the start of deformation of the shear end portion to the end of deformation of the shear end portion by setting a plurality of measurement points on the side surface of the shear end portion of the shear end portion formed on the test piece and measuring the three-dimensional coordinates of each of the plurality of measurement points during the deformation process of the shear end portion due to the shear processing of the test piece in the shear processing reproduction test process; A strain history acquisition step of acquiring a strain history of the side surface of the shear end in a deformation process of the shear end from the acquired surface deformation history of the side surface of the shear end; A spin history acquisition step of acquiring a spin history of the side surface of the shear end in a deformation process of the shear end from the acquired surface deformation history of the side surface of the shear end, The step of sequentially updating stress includes: an acquired strain increment calculation step of calculating an acquired strain increment from the strain history of the shear end side acquired in the strain history acquisition step; An assumed strain increment calculation step of calculating an assumed strain increment by assuming a deformation state of the shear end side surface, which is an increment of strain other than the strain whose strain history is acquired in the strain history acquisition step; an acquired spin increment calculation step of calculating an acquired spin increment from the spin history acquired in the spin history acquisition step; a stress increment calculation step of calculating stress increments at the plurality of measurement points in accordance with a material constitutive law using the acquired strain increments, the assumed strain increments, and the acquired spin increments; A sequential stress update step of sequentially updating the stress in the material coordinate system of each of the plurality of measurement points by using the stress increment calculated for each of the plurality of measurement points, from the start of deformation of the shear end portion due to the shear processing of the test piece to the end of deformation, 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 portion, which is sequentially updated in the sequential stress update step, into a global stress value in a predetermined direction in a global coordinate system, and determining the converted global stress value of each of the plurality of measurement points as a residual stress distribution on a side surface of the shear end portion.

2. 2. The method for testing shear processing of a metal plate according to claim 1, wherein the residual stress distribution calculation step further includes a residual stress distribution display step of displaying the residual stress distribution of the shear end side surface obtained in the stress coordinate system conversion step.

3. 3. The method for testing a metal plate in shear processing according to claim 1, wherein the assumed strain increment calculation step assumes a deformation state of the side surface of the shear end from a deformation process of the shear end due to the shear processing of the test piece, and calculates the assumed strain increment at the side surface of the shear end based on a theory of plastic mechanics in the assumed deformation state.

4. 3. The metal plate shear processing test method according to claim 1, characterized in that the assumed strain increment calculation step assumes a deformation state of the shear end side by finite element analysis of a deformation process of the shear end due to shear processing of the test piece, and calculates the assumed strain increment at the shear end side based on the assumed deformation state.

5. A metal plate shear processing test system for calculating residual stress at a sheared end of a sheared material obtained by shearing a metal plate, The present invention includes a shear processing reproduction test device that reproduces the formation process of the sheared end by shear processing a test piece using the metal plate as a test material, and a residual stress distribution calculation device that calculates a residual stress distribution on the sheared end side of the sheared end formed on the test piece, The shear processing reproduction test device includes a shear mold having a punch, a die, and a holder, and in a state in which the test piece is disposed between the die and the holder, the punch and the die are moved relative to each other to shear the test piece, The residual stress distribution calculation device includes a deformation history acquisition unit, a sequential stress update unit, and a residual stress distribution calculation unit, The deformation history acquisition unit includes: a surface deformation history acquisition unit that measures three-dimensional coordinates during a deformation process of the sheared end portion of the sheared end portion formed on the test piece by the shearing process of the test piece using the shearing process reproduction test device for a plurality of measurement points set on the sheared end portion side surface of the sheared end portion formed on the test piece, and acquires a surface deformation history of the sheared end portion side surface from the start of deformation of the sheared end portion to the end of deformation; A strain history acquisition unit that acquires a strain history of the side surface of the shear end portion during a deformation process of the shear end portion from the acquired surface deformation history of the side surface of the shear end portion; A spin history acquisition unit that acquires a spin history of the shear end side surface during a deformation process of the shear end portion from the acquired surface deformation history of the shear end side surface, The incremental stress update unit comprises: an acquired strain increment calculation unit that calculates an acquired strain increment from the strain history of the shear end side 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, which is an increment of strain other than the strain whose strain history is acquired by the strain history acquisition unit; 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 at each of the plurality of measurement points according to a material constitutive law using the acquired strain increment, the assumed strain increment, and the acquired spin increment; A sequential stress update unit sequentially updates the stress in the material coordinate system of each of the plurality of measurement points by using the stress increment calculated for each of the plurality of measurement points, from the start of deformation of the shear end portion due to the shear processing of the test piece to the end of deformation, The residual stress distribution calculation unit is 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 portion, which is sequentially updated 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 a residual stress distribution on a side surface of the shear end portion.

6. 6. The metal plate shear processing test system according to claim 5, wherein the residual stress distribution calculation unit further comprises a residual stress distribution display unit that displays the residual stress distribution of the shear end side surface calculated by the stress coordinate system conversion unit.

7. 7. The metal plate shear processing test system according to claim 5, wherein the assumed strain increment calculation unit assumes a deformation state of the shear end side from a deformation process of the shear end due to the shear processing of the test piece, and calculates the assumed strain increment at the shear end side based on a plastic mechanics theory in the assumed deformation state.

8. 7. The metal plate shear processing test system according to claim 5, wherein the assumed strain increment calculation unit assumes a deformation state of the shear end side by finite element analysis of a deformation process of the shear end due to shear processing of the test piece, and calculates the assumed strain increment at the shear end side based on the assumed deformation state.

9. A method for producing a sheared material from a metal plate, comprising the steps of: shearing a metal plate to produce a sheared material; A temporary shear condition setting process for setting temporary shear conditions for shearing the metal plate; A shearing process reproduction test process in which the formation process of the sheared end of the metal plate is reproduced by shearing the test piece under the hypothetical shearing conditions by the metal plate shearing process test method according to claim 1 or 2, and a residual stress distribution on the sheared end side is calculated based on the surface deformation history of the sheared end side of the sheared end formed on the test piece; a tensile residual stress amount determination step of determining whether the tensile residual stress at the shear end side surface is within a predetermined range; a tentative shear condition changing step of changing the tentative shear condition when it is determined that the tensile residual stress is outside a predetermined range; a repeating step of repeatedly executing the provisional shearing condition changing step, the shearing process reproduction test step, and the tensile residual stress amount determining step until the tensile residual stress is determined to be within a predetermined range; a shear condition determination step of determining, when the tensile residual stress is determined to be within a predetermined range in the tensile residual stress amount determination step, the tentative shear condition in that case as a shear condition; and a shear processing step of shearing the metal plate under the determined shear conditions.

Images