JP7741390B2 - Fracture prediction method, device, and program - Google Patents

Description

The present invention relates to a fracture prediction method, device, and program.

Patent Document 1 discloses a method for determining fracture from shear edges where flange deformation accompanied by tensile bending deformation occurs. The method involves determining the deformation limit from hole expansion test experiments, determining the strain gradient at the shear edge from hole expansion forming analysis, determining the formable region, and, in press forming analysis, predicting tensile bending fracture using the strain amount and strain gradient on the surface with the larger strain amount if the difference in strain between the front and back surfaces of the plate is equal to or greater than a specified value.

Patent documents 2, 3, and 4 disclose methods for evaluating deformation limits, which evaluate the deformation limit using index values calculated from two surface stress distribution gradients at the evaluation position: the gradient of the surface stress distribution in the thickness direction and the gradient of the surface stress distribution in the direction away from the sheared surface, among the stress distributions generated near the sheared surface of a metal plate due to press forming.

Japanese Patent Application Laid-Open No. 2021-1754 Patent No. 6769561 Patent No. 6558515 Patent No. 6547920

In the technology described in Patent Document 1, bending deformation generally occurs in a form in which high strain occurs only on the outer bent surface of the plate. This form of deformation is different from deformation in hole expansion tests, in which the edge of the hole is stretched by tension. Therefore, it is not possible to predict fracture in tensile bending deformation using the deformation limit determined in hole expansion tests.

Furthermore, with the technologies described in Patent Documents 2, 3, and 4, in order to obtain the stress distribution gradient in an analysis using the finite element method (FEM), it is necessary to obtain information between adjacent elements, but it is difficult to obtain the stress gradient during a deformation analysis that changes sequentially.

Furthermore, in analyses using the finite element method, in areas where strain is concentrated and localized deformation occurs, the calculated strain differs depending on the mesh size used. Therefore, even if the fracture limit strain can be determined using the above method, sufficient accuracy cannot be achieved in deformation analyses using models with different mesh sizes.

The present invention was made in consideration of the above circumstances, and aims to provide a fracture prediction method, device, and program that can accurately predict bending fracture of thin metal plates while reducing the amount of work and labor required.

The fracture prediction method according to the first aspect is a fracture prediction method that uses the finite element method to predict bending fracture from the punched end of a thin plate of a metal material, and includes the steps of: obtaining a bending fracture limit bend angle αh through a bending test for each of a plurality of test pieces that are thin plates of a metal material having a specific plate thickness, each having a punched end with a different punching clearance; obtaining a hole expansion ratio λ of a punched hole corresponding to the punched end through a hole expansion test for each of test pieces that are under the same conditions as the plurality of test pieces; obtaining a bending fracture limit bend angle αb through a bending test for a base material that is a test piece of the specific plate thickness and does not have a punched end; obtaining a relationship between the ratio of the hole expansion ratio λ and the bend angle αb and the ratio of the bend angle αh and the bend angle αb based on the hole expansion ratio λ, the bend angle αh, and the bend angle αb for each of the test pieces; The method includes the steps of: obtaining a hole expansion ratio λ' of a punched hole corresponding to a punched end through a hole expansion test for a thin plate of a metal material to be predicted, the thin plate having a punched end; obtaining a bending fracture limit bending angle αb' through a bending test for a base material, which is a thin plate of the metal material to be predicted having the specific thickness and which is a thin plate of the metal material to be predicted without a punched end; obtaining a bending fracture limit bending angle αh' from the relationship between the ratio of the hole expansion ratio λ to the bending angle αb and the ratio of the bending angle αh to the bending angle αb, and the ratio of the hole expansion ratio λ' to the bending angle αb'; and predicting bending fracture of the element at the punched end by comparing the bending angle α of the element at the punched end with the bending fracture limit bending angle αh', which changes sequentially during deformation analysis using a finite element model representing the thin plate of the metal material to be predicted, the thin plate of the metal material to be predicted, having a punched end.

The fracture prediction method according to the second aspect is a fracture prediction method that uses the finite element method to predict bending fracture from the punched end of a thin sheet of metal material. The fracture prediction method includes the steps of: obtaining the bending fracture limit bending angle αh through a bending test for each of a plurality of test pieces that are thin sheets of metal material having an arbitrary thickness, each having a punched end with a different punching clearance; obtaining the hole expansion ratio λ of the punched hole corresponding to the punched end through a hole expansion test for each of a plurality of test pieces that are under the same conditions as the plurality of test pieces; and calculating the hole expansion ratio λ for each of the plurality of test pieces that are under the same conditions as the plurality of test pieces by calculating the hole expansion ratio λ of the punched hole. a step of converting the bending angle αb of the bending fracture limit by a bending test for the base material which is a test piece of the arbitrary plate thickness and which does not have a punched end; a step of converting the bending angle αb for the base material which is a test piece of the arbitrary plate thickness and which does not have a punched end into a fracture limit strain εb of the bend outer surface layer of the element at the bend crest; and a step of calculating the ratio of the fracture limit strain εb and the bending angle αh and the bending angle αh based on the fracture limit strain εt, the fracture limit strain εb, the bending angle αh, and the bending angle αh for each of the test pieces. a step of acquiring a relationship between the ratio of the bending angle αb' of the bending fracture limit and the ratio of the bending angle αb' of the bending outer surface layer of the element at the bend crest, a step of acquiring a hole expansion ratio λ' of the punched hole corresponding to the punched end by a hole expansion test for the thin plate of the metal material to be predicted having the arbitrary plate thickness and having a punched end, a step of converting the hole expansion ratio λ' into a fracture limit strain εt' of the hole edge element of the punched hole, a step of acquiring a bending angle αb' of the bending fracture limit by a bending test for the base material which is the thin plate of the metal material to be predicted having the arbitrary plate thickness and having no punched end, and a step of converting the bending angle αb' into a fracture limit strain εt' of the bending outer surface layer of the element at the bend crest, the relationship between the ratio of the fracture limit strain εt and the fracture limit strain εb and the ratio of the bending angle αh and the bending angle αb, the ratio of the fracture limit strain εt' and the fracture limit strain εb', and the bending angle αb'; and predicting bending fracture of the element at the punched end by comparing the bending angle α of the element at the punched end, which changes sequentially during deformation analysis using a finite element model representing the thin plate of the metallic material having a punched end, with the bending angle αh' of the bending fracture limit.

The fracture prediction device according to the third aspect is a fracture prediction device that uses the finite element method to predict bending fracture from the punched end of a thin plate of a metal material, and includes a first experimental result acquisition unit that acquires the bending fracture limit bend angle αh through a bending test for each of a plurality of test pieces that are thin plates of a metal material having a specific plate thickness, each having a punched end with a different punching clearance, acquires the hole expansion ratio λ of the punched hole corresponding to the punched end through a hole expansion test for each of test pieces under the same conditions as the plurality of test pieces, and acquires the bending fracture limit bend angle αb through a bending test for a base material that is a test piece of the specific plate thickness and does not have a punched end; a relationship acquisition unit that acquires the relationship between the ratio of the hole expansion ratio λ and the bending angle αb and the ratio of the bending angle αh and the bending angle αb based on the hole expansion ratio λ, the bending angle αh, and the bending angle αb for each of the test pieces; and the second experimental result acquisition unit acquires a hole expansion ratio λ' of a punched hole corresponding to the punched end through a hole expansion test for a target thin plate of a metallic material having a punched end, and acquires a bending angle αb' of the bending fracture limit through a bending test for a base material thin plate of a metallic material having the specific thickness and which is a thin plate of the metallic material that does not have a punched end; a bending fracture limit acquisition unit acquires a bending angle αh' of the bending fracture limit from the relationship between the ratio of the hole expansion ratio λ to the bending angle αb and the ratio of the bending angle αh to the bending angle αb, and the ratio of the hole expansion ratio λ' to the bending angle αb'; and a fracture prediction unit compares the bending angle α of the element at the punched end, which changes sequentially during deformation analysis using a finite element model representing the thin plate of a metallic material having a punched end, to predict bending fracture of the element at the punched end.

The fracture prediction device according to the fourth aspect is a fracture prediction device that uses the finite element method to predict bending fracture from the punched end of a thin plate of a metal material. For each of a plurality of test pieces that are thin plates of a metal material having an arbitrary plate thickness and each having a punched end with a different punching clearance, the bending angle αh at the bending fracture limit is obtained by a bending test, and for each of test pieces that are under the same conditions as the plurality of test pieces, the hole expansion ratio λ of the punched hole corresponding to the punched end is obtained by a hole expansion test, and for a base material that is a test piece of the arbitrary plate thickness and does not have a punched end, the bending angle αb at the bending fracture limit is obtained by a bending test. a first conversion unit that converts the hole expansion ratio λ into a fracture limit strain εt of a hole edge element of the punched hole for each of the plurality of test pieces under the same conditions as the plurality of test pieces, and converts the bending angle αb into a fracture limit strain εb of a bent outer surface layer of an element at a bend crest for a base material that is a test piece of the arbitrary plate thickness and that does not have a punched end; and a first conversion unit that calculates a relationship between the ratio of the fracture limit strain εt and the fracture limit strain εb and the ratio of the bending angle αh and the bending angle αb based on the fracture limit strain εt, the fracture limit strain εb, the bending angle αb, and the bending angle αh for each of the test pieces. a second experimental result acquisition unit that acquires, by a hole expansion test, a hole expansion ratio λ' of a punched hole corresponding to the punched end for a thin plate of a metallic material that is a prediction target having the arbitrary plate thickness and that has a punched end, and that acquires, by a bending test, a bending angle αb' of a bending fracture limit for a base material that is a thin plate of a metallic material that is a prediction target having the arbitrary plate thickness and that does not have a punched end; and that converts the hole expansion ratio λ' into a fracture limit strain εt' of a hole edge element of the punched hole, and converts the bending angle αb' into a fracture limit strain εb' of a bending outer surface layer of an element at the bend crest. a bending fracture limit acquisition unit that acquires the bending angle αh' of the bending fracture limit from the relationship between the ratio of the fracture limit strain εt and the fracture limit strain εb and the ratio of the bending angle αh and the bending angle αb, the ratio of the fracture limit strain εt' and the fracture limit strain εb', and the bending angle αb'; and a fracture prediction unit that predicts bending fracture of the element at the punched end by comparing the bending angle α of the element at the punched end, which changes sequentially during deformation analysis using a finite element model that represents the thin plate of the metallic material having a punched end.

The fracture prediction program according to the fifth aspect is a fracture prediction program for predicting bending fracture from a punched end of a thin plate of a metallic material using the finite element method. The fracture prediction program includes: a first experimental result acquisition unit that acquires, through a bending test, a bending fracture limit bend angle αh for each of a plurality of test pieces that are thin plates of a metallic material having a specific plate thickness, each having a punched end with a different punching clearance; a hole expansion ratio λ for a punched hole corresponding to the punched end for each of test pieces under the same conditions as the plurality of test pieces, through a hole expansion test; and an experimental result acquisition unit that acquires, through a bending test, a bending fracture limit bend angle αb for a base material that is a test piece of the specific plate thickness and does not have a punched end; a relationship acquisition unit that acquires, based on the hole expansion ratio λ, the bend angle αh, and the bend angle αb for each of the test pieces, a relationship between the ratio of the hole expansion ratio λ and the bend angle αb and the ratio of the bend angle αh and the bend angle αb; and a second experimental result acquisition unit that acquires a hole expansion ratio λ' of a punched hole corresponding to a punched end through a hole expansion test for a thin plate of the metallic material having a punched end, and acquires a bending angle αb' of the bending fracture limit through a bending test for a base material that is a thin plate of the metallic material having the specific thickness and that does not have a punched end; a bending fracture limit acquisition unit that acquires a bending angle αh' of the bending fracture limit from the relationship between the ratio of the hole expansion ratio λ and the bending angle αb and the ratio of the bending angle αh and the bending angle αb, and the ratio of the hole expansion ratio λ' and the bending angle αb'; and a fracture prediction unit that compares the bending angle α of the element at the punched end, which changes sequentially during deformation analysis using a finite element model representing the thin plate of the metallic material having a punched end, to predict bending fracture of the element at the punched end.

The fracture prediction program according to the sixth aspect is a fracture prediction program for predicting bending fracture from the punched end of a thin metal plate using the finite element method. The program performs a bending test to obtain the bending fracture limit bend angle αh for each of a plurality of test pieces that are thin metal plates of arbitrary thickness, each having a punched end with a different punching clearance; performs a hole expansion test to obtain the hole expansion ratio λ of the punched hole corresponding to the punched end for each of test pieces that are identical in condition to the plurality of test pieces; and performs a bending test to obtain the bending fracture limit bend angle αh for a base material that is a test piece of arbitrary thickness and that does not have a punched end. a first conversion unit that converts the hole expansion ratio λ into a fracture limit strain εt of a hole edge element of the punched hole for each of the plurality of test pieces under the same conditions, and converts the bending angle αb into a fracture limit strain εb of a bend outer surface layer of an element at a bend crest for a base material that is a test piece of the arbitrary plate thickness and does not have a punched end; and a relationship acquisition unit that acquires a relationship between the ratio of the fracture limit strain εt and the fracture limit strain εb and the ratio of the bending angle αh and the bending angle αb based on the fracture limit strain εt, the fracture limit strain εb, the bending angle αb, and the bending angle αh for each of the test pieces. a second experimental result acquisition unit that acquires a hole expansion ratio λ' of a punched hole corresponding to the punched end by a hole expansion test for a thin plate of a metallic material that is a prediction target having the arbitrary plate thickness and that has a punched end, and acquires a bending angle αb' of a bending fracture limit by a bending test for a base material that is a thin plate of a metallic material that is a prediction target having the arbitrary plate thickness and that does not have a punched end; a second conversion unit that converts the hole expansion ratio λ' into a fracture limit strain εt' of a hole edge element of the punched hole and converts the bending angle αb' into a fracture limit strain εb' of a bending outer surface layer of an element at the bend crest; The program causes a computer to function as a bending fracture limit acquisition unit that acquires the bending fracture limit bending angle αh' from the relationship between the ratio of t and the fracture limit strain εb and the ratio of the bending angle αh and the bending angle αb, the ratio of the fracture limit strain εt' and the fracture limit strain εb', and the bending angle αb'; and a fracture prediction unit that predicts bending fracture of the element at the punched end by comparing the bending angle α of the element at the punched end, which changes sequentially during deformation analysis using a finite element model representing the thin plate of the metal material having a punched end.

The fracture prediction method, device, and program of one aspect of the present invention make it possible to accurately predict bending fracture of thin metal plates with reduced effort and man-hours.

1 is a schematic diagram showing a schematic configuration of a fracture prediction device according to a first embodiment of the present invention. FIG. 1A is a top view showing an example of a test piece, FIG. 1B is a side view for explaining a bending test, and FIG. 1C is a perspective view for explaining the bending angle at the timing when fracture occurs from the hole edge. 10 is a graph showing an example of an approximation curve representing the relationship between the ratio of the hole expansion ratio λ to the bending angle αb and the ratio of the bending angle αh to the bending angle αb. FIG. 1 is a schematic block diagram of an example of a computer that functions as a fracture prediction device. 10 is a flowchart illustrating an example of a pre-processing according to the first embodiment of the present invention. 10 is a flowchart illustrating an example of a fracture prediction process according to the first and second embodiments of the present invention. 1 is a graph showing an example of an approximation curve representing the relationship between the ratio of the fracture limit strain εt to the fracture limit strain εb and the ratio of the bending angle αh to the bending angle αb. FIG. 4 is a schematic diagram showing a schematic configuration of a fracture prediction device according to a second embodiment of the present invention. 10 is a flowchart illustrating an example of a pre-processing according to the second embodiment of the present invention. 10 is a graph showing the results of a comparison between predicted results and experimental results of the bending angle for each mesh size in the examples. FIG. 10 is a diagram showing the maximum principal strain distribution when predicting fracture for each mesh size in the examples.

The following describes a fracture prediction device according to one embodiment of the present invention, with appropriate reference to the attached drawings.

<Outline of the embodiment of the present invention>
In the automotive industry, the development of vehicle body structures that can reduce impact during collisions is an urgent issue. In this case, it is important for the structural components of an automobile to absorb collision energy. To absorb collision energy, it is important for the structural components to deform in a targeted mode during a collision. If material fracture occurs during the deformation process, the targeted deformation mode may not be achieved, and sufficient energy absorption performance may not be achieved. It is generally known that ductility decreases as the strength of steel plates increases, and the possibility of material fracture during collision deformation of an automobile body is thought to increase. In particular, it is known that steel plates known as ultra-high-tensile steels, which have a tensile strength of over 980 MPa, may experience material fracture due to bending deformation caused by buckling (hereinafter referred to as "bending fracture") in addition to fracture due to in-plane tensile force during collision deformation.

Automotive parts have holes for various purposes, typically punched holes created by a press die. The edges of these punched holes and the trim edges around the components are damaged when punched out by the die, and when these areas are subjected to bending deformation, cracks can occur at a lower strain than in other areas, leading to early fractures. Therefore, when using FEM analysis to predict material fractures that occur during deformation in a vehicle collision, prediction technology is required that also takes into account early bending fractures that occur from the edges of punched holes and trim edges.

In this embodiment, in deformation analysis such as automobile collision deformation simulation, any material and plate thickness can be predicted, and bending fracture from the edge of a hole or edge of ultra-high strength steel plate exceeding 980 MPa can be predicted with high accuracy.

[First embodiment]
<Configuration of fracture prediction device>
Fig. 1 is a schematic diagram showing the overall configuration of a fracture prediction device according to a first embodiment of the present invention. As shown in Fig. 1, the fracture prediction device 100 according to this embodiment is a device that predicts bending fracture from the edge of a punched hole in a thin plate of a metal material using the finite element method, and includes a first experiment result acquisition unit 10, a relationship acquisition unit 12, a second experiment result acquisition unit 14, a bending fracture limit acquisition unit 16, a deformation analysis unit 18, and a fracture prediction unit 20.

The fracture prediction device 100 according to this embodiment receives input of the bending angle αh at the bending fracture limit obtained through bending tests for each of a plurality of test pieces of various steel grades with specific plate thicknesses, each having punched ends with different punching clearances.

For example, when a hole expansion test is performed by varying the punching clearance of the die to create a punched hole, it is known that the hole expansion ratio λ changes depending on the punching clearance. Therefore, as shown in Figure 2(A), a 10 mm diameter punched hole 32 is made in the center of a 30 mm wide x 60 mm long test piece 30, with the punching clearance varied between 8 and 22%. The test piece 30 is then set so that the burrs generated by punching are on the outside of the bend, and a bending test is performed as shown in Figure 2(B). The bending angle of the test piece 30 is measured at the moment when fracture occurs from the hole edge, as shown in Figure 2(C).

The fracture prediction device 100 also receives input of the hole expansion ratio λ of the punched hole obtained through the hole expansion test for each of the above-mentioned multiple test pieces for various steel types and test pieces under the same conditions.

For example, as in the bending test described above, a 10 mm diameter hole is punched in the center of the test piece with the punching clearance varied between 8 and 22%, and a tensile test is carried out until fracture occurs from the edge of the hole. The gauge length elongation at the time fracture occurs is measured, and the relationship with the hole expansion ratio λ is obtained.

The fracture prediction device 100 also receives input of the bending angle αb at the bending fracture limit obtained through bending tests on base materials of various steel types, which are test pieces of a specific plate thickness and do not have punched holes.

For example, a bending test is performed on a base material that is a test piece with the same specific plate thickness as the test piece in the bending test above but without a punched hole, and the bending angle at the moment when fracture occurs at the bend peak is measured, and this is taken as the bending fracture limit bending angle αb.

The fracture prediction device 100 also receives as input the material to be predicted (SS curve), plate thickness, hole expansion ratio λ' (%), and bending angle αb' at the bending fracture limit for the base material. In this embodiment, steel plates with a strength class of 980 MPa or higher are primarily used as thin metal plates to be predicted.

For example, for a material to be predicted that has a punched hole and is of the same specific thickness as the test piece for the bending test described above, a hole expansion test is performed to measure the hole expansion ratio λ of the punched hole.

In addition, a bending test is conducted on the base material, which is the material to be predicted and has a specific plate thickness and no punched holes, and the bending angle αb' at the time when fracture occurs at the bend peak is measured, and this is taken as the bending angle at the bending fracture limit.

The first experimental result acquisition unit 10 acquires the bending angle αh at the bending fracture limit obtained through a bending test for each of the input test pieces having a specific plate thickness and each having a punched hole with a different punching clearance.

The first experimental result acquisition unit 10 acquires the hole expansion ratio λ of the punched hole obtained by the hole expansion test for each of the input test pieces and test pieces under the same conditions.

The first experimental result acquisition unit 10 also acquires the bending angle αb at the bending fracture limit obtained through a bending test for the input base material, which is a test piece having a specific plate thickness and no punched holes.

The relationship acquisition unit 12 acquires the relationship between the ratio of the hole expansion ratio λ to the bending angle αb and the ratio of the bending angle αh to the bending angle αb based on the hole expansion ratio λ, bending angle αb, and bending angle αh for each test piece acquired by the experimental result acquisition unit 10.

The inventors have found that, as shown in Figure 3, a certain correlation can be obtained by plotting the ratio of the hole expansion ratio λ to the bending angle αb and the ratio of the bending angle αh to the bending angle αb as indicators on the horizontal and vertical axes.

In this embodiment, an approximation curve is derived that represents the relationship between the ratio of the hole expansion ratio λ to the bending angle αb and the ratio of the bending angle αh to the bending angle αb. In Figure 3, the solid curve represents the approximation curve, and the white circles represent points plotted using the ratio of the hole expansion ratio λ to the bending angle αb and the ratio of the bending angle αh to the bending angle αb as indicators on the horizontal and vertical axes.

The second experimental result acquisition unit 14 acquires the hole expansion ratio λ' of the punched hole obtained by a hole expansion test for the input thin metal plate of the prediction target metal material having a specific plate thickness and having a punched hole.

The second experimental result acquisition unit 14 also acquires the bending angle αb' at the bending fracture limit obtained by a bending test for the input base material, which is a thin plate of the metal material to be predicted that has a specific plate thickness and does not have a punched hole.

The bending fracture limit acquisition unit 16 acquires the bending angle αh' at the bending fracture limit from the relationship between the ratio of the hole expansion ratio λ to the bending angle αb and the ratio of the bending angle αh to the bending angle αb, and the ratio of the hole expansion ratio λ' to the bending angle αb'.

Specifically, the ratio of bending angles αh and αb corresponding to the ratio of hole expansion ratio λ' and bending angle αb' is determined from an approximation curve that represents the relationship between the ratio of hole expansion ratio λ and bending angle αb and the ratio of bending angle αh and bending angle αb. Then, the bending angle αh' at the bending fracture limit is determined from the determined ratio of bending angles αh and αb and bending angle αb'.

The deformation analysis unit 18 performs deformation analysis using a finite element model that represents a thin metal plate having a punched hole, which is the target of prediction. For example, the deformation analysis unit 18 performs bending deformation analysis, such as a collision deformation simulation, using a finite element model that represents a target material having a punched hole.

The fracture prediction unit 20 compares the bending angle α of the hole edge element of the punched hole, which changes sequentially during deformation analysis by the deformation analysis unit 18, with the bending angle αh' of the bending fracture limit acquired by the bending fracture limit acquisition unit 16, and predicts bending fracture of the hole edge element.

Specifically, the ratio α/αh of the bending angle α of the hole edge element of the punched hole to the bending angle αh' of the bending fracture limit acquired by the bending fracture limit acquisition unit 16 is calculated sequentially, and when α/αh = 1, the element is determined to have fractured due to bending. In this case, if a bending fracture is determined, the element may be deleted.

In addition, to improve analysis efficiency in finite element models, it is possible to extract only the hole edge elements in advance, and then predict bending fracture of the hole edge elements by comparing the bending angle α with the bending angle αh' at the bending fracture limit obtained for the hole edge elements, focusing only on the extracted hole edge elements, which change sequentially during deformation analysis.

The fracture prediction device 100 is realized, for example, by a computer 64 shown in FIG. 4. The computer 64 includes a CPU 66, memory 68, a storage unit 70 that stores a fracture prediction program 76, a display unit 26 including a monitor, and an input unit 28 that includes a keyboard and mouse. The CPU 66, memory 68, storage unit 70, display unit 26, and input unit 28 are connected to each other via a bus 74.

The memory unit 70 is realized by a HDD, SSD, flash memory, etc. The memory unit 70 stores a fracture prediction program 76 that causes the computer 64 to function as the fracture prediction device 100. The CPU 66 reads the fracture prediction program 76 from the memory unit 70, expands it into the memory 68, and executes the fracture prediction program 76.

<Function of the fracture prediction device>
Next, the operation of this embodiment will be described with reference to Figures 5 and 6. First, an operator performs a bending test on each of a plurality of test pieces of various steel grades having a specific plate thickness and each having a punched hole with a different punching clearance, and measures the bending angle αh at the bending fracture limit.

The operator also performs hole expansion tests on each of the above multiple test pieces for various steel types and test pieces under the same conditions, and measures the hole expansion ratio λ of the punched holes.

The operator also performs bending tests on base material specimens of various steel grades with a specific plate thickness and no punched holes, and measures the bending angle αb at the bending fracture limit.

Then, the operator inputs the bending fracture limit bending angle αh for each test piece, the hole expansion ratio λ of the punched holes, and the bending fracture limit bending angle αb for the base material, which is a test piece without punched holes, into the fracture prediction device 100.

The operator also performs a hole expansion test on the material to be predicted, which has the same specific plate thickness as the test piece used in the bending test and has a punched hole, and measures the hole expansion ratio λ' of the punched hole.

The operator also conducts a bending test on the base material, which is the material to be predicted and has a specific plate thickness and no punched holes, and measures the bending angle αb' at the moment when fracture occurs at the bend peak, which is the bending angle at the bending fracture limit.

Then, the operator inputs the material (S-S curve) to be predicted, the plate thickness, the hole expansion ratio λ' (%), and the bending angle αb' at the bending fracture limit for the base material into the fracture prediction device 100. Next, we will explain the pre-processing that is executed by the fracture prediction device 100 when an operation such as issuing a command to start the pre-processing is performed.

In step S102 of the pre-processing shown in Figure 5, the first experimental result acquisition unit 10 acquires the bending angle αh at the bending fracture limit obtained by bending tests for each of the input test pieces having a specific plate thickness and each having a punched end with a different punching clearance.

In step S104, the first experimental result acquisition unit 10 acquires the hole expansion ratio λ of the punched hole obtained by the hole expansion test for each of the input test pieces under the same conditions as the multiple test pieces.

In step S106, the first experimental result acquisition unit 10 acquires the bending angle αb at the bending fracture limit obtained by a bending test for the input base material, which is a test piece with a specific plate thickness and no punched holes.

In step S108, the relationship acquisition unit 12 derives an approximation curve representing the relationship between the ratio of the hole expansion ratio λ to the bending angle αb and the ratio of the bending angle αh to the bending angle αb, based on the hole expansion ratio λ, bending angle αb, and bending angle αh for each test piece acquired by the experimental result acquisition unit 10.

In step S112, the second experiment result acquisition unit 14 acquires the hole expansion ratio λ' of the punched hole obtained by a hole expansion test for the input thin metal plate of the prediction target metal material having a specific plate thickness and having a punched hole.

In step S114, the second experimental result acquisition unit 14 acquires the bending angle αb' at the bending fracture limit obtained by a bending test for the input base material, which is a thin plate of the metal material to be predicted that has a specific plate thickness and does not have a punched hole.

In step S116, the bending fracture limit acquisition unit 16 acquires the bending fracture limit bending angle αh' from the relationship between the ratio of the hole expansion ratio λ to the bending angle αb and the ratio of the bending angle αh to the bending angle αb, as well as the ratio of the hole expansion ratio λ' to the bending angle αb', and ends the pre-processing.

The following describes the fracture prediction process executed by the fracture prediction device 100 when an operation such as an instruction to start the fracture prediction process is performed.

In step S120 of the fracture prediction process shown in Figure 6, the deformation analysis unit 18 begins deformation analysis using a finite element model representing the thin metal plate to be predicted, which is a thin metal plate having a punched hole.

In step S122, the fracture prediction unit 20 obtains the bending angle α of the hole edge element of the punched hole at the current time during deformation analysis by the deformation analysis unit 18.

In step S124, the fracture prediction unit 20 compares the bending angle α of the hole edge element of the punched hole obtained in step S122 with the bending angle αh' of the bending fracture limit obtained by the bending fracture limit acquisition unit 16, and predicts bending fracture of the hole edge element.

In step S126, the deformation analysis unit 18 determines whether to end the deformation analysis. For example, if an input instructing the end of the deformation analysis is received, or if a predetermined end condition is met, it determines that the deformation analysis should be ended, and ends the fracture prediction process. On the other hand, if it determines that the deformation analysis should not be ended, the process returns to step S122 and repeats the processes from step S122 onwards for the next time.

As described above, the fracture prediction device 100 according to this embodiment obtains the relationship between the ratio of the hole expansion ratio λ and the bending angle αb and the ratio of the bending angle αh and the bending angle αb based on the hole expansion ratio λ, the bending fracture limit bending angle αh, and the bending fracture limit bending angle αb of the base material for each of a plurality of test pieces having a specific thickness. The bending fracture limit bending angle αh' is obtained from the ratio of the hole expansion ratio λ' for a target thin plate of metal material having a specific thickness and having a punched hole to the bending fracture limit bending angle αb' for the base material. The bending fracture limit bending angle αh' is then compared with the bending angle α of the hole edge element of the punched hole, which changes sequentially during deformation analysis using a finite element model representing the target thin plate of metal material, to predict the bending fracture of the hole edge element of the punched hole. This reduces the amount of work and man-hours required and enables accurate prediction of bending fracture of thin plate of metal material.

Furthermore, for example, when predicting collision deformation of automobile components on a computer, it is possible to predict with high accuracy material fractures occurring at areas including punched hole edges. As a result, it is possible to omit crash tests on actual automobile components, or significantly reduce the number of crash tests required. Furthermore, component designs that prevent fractures during a collision can be accurately performed on a computer, contributing to significant cost reductions and shortened development times.

Second Embodiment
Next, a fracture prediction device according to a second embodiment will be described. Note that parts having the same configuration as those in the first embodiment will be given the same reference numerals and descriptions thereof will be omitted.

<Overview>
By conducting hole expansion tests and bending tests for various steel types, plate thicknesses, and punched holes and measuring the strain at the fracture site when fracture occurs, it is possible to obtain the fracture limit strain εt of the hole edge element of the punched hole and the fracture limit strain εb of the base material. This can also be obtained by calculating the maximum principal strain of the element at the position where fracture occurred when the same punch stroke as in the experiment is applied through analysis using a finite element model that reproduces the bending experiment.

Figure 7 is a graph in which the values on the vertical axis are the same as those in Figure 3 above, but the hole expansion ratio λ on the horizontal axis is replaced with the fracture limit strain εt, and the bending angle αb at the bending fracture limit of the base material is replaced with the fracture limit strain εb. The inventors have found that, as shown in Figure 7, there is a certain correlation between the indicators on the vertical and horizontal axes.

It is also known that the hole expansion ratio λ and its conversion into fracture limit strain εt vary little with plate thickness. On the other hand, the bending angle αb at the bending fracture limit of the base material is known to vary greatly with plate thickness, even for the same steel type. However, since it is known that bending fracture occurs when the outer surface layer of the bend reaches the material's inherent fracture limit strain, an investigation into the strain εb of the outer surface layer of the bend at the bend apex when the bending fracture limit bending angle αb is reached revealed that, although the bending angle αb differs depending on the plate thickness, the strain εb of the outer surface layer of the bend at the bend apex shows approximately the same value regardless of the plate thickness.

Therefore, by using the approximate curve that shows the relationship between the indicators on the vertical and horizontal axes in Figure 7, it is possible to obtain the bending fracture limit bending angle αh of a punched hole from only the hole expansion ratio and the bending fracture limit bending angle of the base material for any steel type and any plate thickness used in the deformation analysis. Bending fracture can then be predicted based on whether the bending angle of the punched hole element during deformation analysis reaches αh.

<Configuration of fracture prediction device>
Fig. 8 is a schematic diagram showing the overall configuration of a fracture prediction device according to a second embodiment of the present invention. As shown in Fig. 8, the fracture prediction device 200 according to this embodiment is a device that predicts bending fracture from the edge of a punched hole in a thin plate of a metal material using the finite element method, and includes a first experiment result acquisition unit 210, a first conversion unit 212, a relationship acquisition unit 214, a second experiment result acquisition unit 216, a second conversion unit 218, a bending fracture limit acquisition unit 220, a deformation analysis unit 222, and a fracture prediction unit 224.

The fracture prediction device 200 according to this embodiment receives input of the bending angle αh at the bending fracture limit obtained through bending tests for each of a plurality of test pieces of various steel types and of arbitrary plate thickness, each having a punched end with a different punching clearance.

In addition, the fracture prediction device 200 receives input of the hole expansion ratio λ of the punched hole obtained through the hole expansion test for each of the above-mentioned multiple test pieces for various steel types and test pieces under the same conditions.

The fracture prediction device 200 also receives input of the bending angle αb at the bending fracture limit obtained through bending tests on base material, which is a test piece of any thickness for various steel types and does not have a punched hole.

The fracture prediction device 200 also receives as input the material to be predicted (SS curve), plate thickness, hole expansion ratio λ' (%), and bending angle αb' at the bending fracture limit for the base material. In this embodiment, steel plates with a strength class of 980 MPa or higher are primarily used as thin sheets of metallic material to be predicted.

The first experimental result acquisition unit 210 acquires the bending angle αh at the bending fracture limit obtained through a bending test for each of the input test pieces of any thickness, each having a punched end with a different punching clearance.

The first experimental result acquisition unit 210 acquires the hole expansion ratio λ of the punched hole obtained by the hole expansion test for each of the input test pieces and test pieces with the same conditions.

The first experimental result acquisition unit 210 also acquires the bending angle αb at the bending fracture limit obtained by a bending test for the input base material, which is a test piece of any thickness and does not have a punched hole.

The first conversion unit 212 converts the hole expansion ratio λ into the fracture limit strain εt of the hole edge element of the punched hole for each of the multiple test specimens and test specimens under the same conditions.

Specifically, the hole expansion ratio λ is converted to the fracture limit strain εt of the hole edge element of the punched hole using the following equation 1, which expresses the relationship between the hole expansion ratio λ and the fracture limit strain εt of the hole edge element of the punched hole.

εt=a*LN(1+λ/100) ^b +c...(Formula 1)

where a, b, and c are fitting coefficients determined based on multiple pairs of pre-prepared hole expansion ratios λ and tensile fracture limit strains εt of the hole edge elements of the punched hole.

The first conversion unit 212 also converts the bending angle αb into the fracture limit strain εb of the outer surface layer of the bend at the bend crest for a base material that is a test piece of any thickness and does not have a punched hole.

Specifically, the bending angle αb and the mesh size S of the finite element model are converted to the fracture limit strain εb using the following equation 2 to calculate the fracture limit strain εb of the outer surface layer of the bend at the top of the bend.

εb = d*S ^e +f (Formula 2)

where S is the mesh size of the finite element model, and d, e, and f are values determined according to the plate thickness t and εs, based on multiple combinations of pre-prepared plate thickness t, bending angle αb, finite element model mesh size S, and fracture limit strain εb of the outer surface layer at the bend crest. εs is expressed as εs = g ln(αb) + h, and g and h are values determined according to the plate thickness t.

The relationship acquisition unit 214 acquires the relationship between the ratio of the fracture limit strain εt to the fracture limit strain εb and the ratio of the bending angle αh to the bending angle αb based on the fracture limit strain εt and the fracture limit strain εb for each test piece obtained by the first conversion unit 212 and the bending angle αb and the bending angle αh for each test piece obtained by the first experiment result acquisition unit 210.

In this embodiment, an approximate curve is obtained that represents the relationship between the ratio of the fracture limit strain εt to the fracture limit strain εb and the ratio of the bending angle αh to the bending angle αb, as shown in Figure 7 above. Specifically, the approximate formula shown in Equation (3) below is derived.

y1=m*LN(n+x2) ^p ...(Formula 3)

where y1 is αh/αb, x2 is εt/εb, and m, n, and p are fitting coefficients. If y1≧1, then y1=1.

The second experimental result acquisition unit 216 acquires the hole expansion ratio λ' of the punched hole obtained by a hole expansion test for the input thin plate of the metallic material to be predicted, which has an arbitrary thickness and has a punched hole. The second experimental result acquisition unit 216 also acquires the bending angle αb' at the bending fracture limit obtained by a bending test for the input thin plate of the metallic material to be predicted, which has an arbitrary thickness and is a base material, which is a thin plate of the metallic material without a punched hole.

The second conversion unit 218 converts the input hole expansion ratio λ' into the fracture limit strain εt' of the hole edge element of the punched hole.

Specifically, using the above equation 1, the hole expansion ratio λ' is converted into the fracture limit strain εt' of the hole edge element of the punched hole.

The second conversion unit 218 also converts the input bending angle αb' into the fracture limit strain εb' of the outer surface layer of the bending crest element.

Specifically, using Equation 2 above, the bending angle αb' is converted into the fracture limit strain εb' of the outer surface layer of the bent part of the element at the bend crest.

The bending fracture limit acquisition unit 220 acquires the bending angle αh' at the bending fracture limit from the relationship between the ratio of the hole expansion ratio λ to the bending angle αb and the ratio of the bending angle αh to the bending angle αb, and the ratio of the hole expansion ratio λ' to the bending angle αb'.

Specifically, the ratio of the hole expansion ratio λ' and the bending angle αb' is calculated as the horizontal axis value x2, and substituted into the above equation 3. From the obtained value of y1 and the bending angle αb', the bending angle αh' at the bending fracture limit for the material being predicted is calculated.

The deformation analysis unit 222 performs bending deformation analysis using a finite element model that represents a thin metal plate having a punched hole, which is the target of prediction. For example, the deformation analysis unit 222 performs bending deformation analysis such as a collision deformation simulation using a finite element model that represents a target material having a punched hole.

The fracture prediction unit 224 compares the bending angle α of the hole edge element of the punched hole, which changes sequentially during bending deformation analysis by the deformation analysis unit 222, with the bending angle αh' of the bending fracture limit acquired by the bending fracture limit acquisition unit 220, and predicts bending fracture of the hole edge element.

In addition, in the finite element model, only the hole edge elements can be extracted, and bending fracture of the hole edge elements can be predicted by comparing the bending angle α of the hole edge elements, which changes sequentially during deformation analysis, with the bending angle αh' at the bending fracture limit obtained for the hole edge elements.

The fracture prediction device 200 is realized, for example, by the computer 64 shown in Figure 4 above. The computer 64 includes a CPU 66, memory 68, a storage unit 70 that stores a fracture prediction program 76, a display unit 26 including a monitor, and an input unit 28 that includes a keyboard and mouse. The CPU 66, memory 68, storage unit 70, display unit 26, and input unit 28 are connected to each other via a bus 74.

The memory unit 70 is realized by a HDD, SSD, flash memory, etc. The memory unit 70 stores a fracture prediction program 76 that causes the computer 64 to function as the fracture prediction device 200. The CPU 66 reads the fracture prediction program 76 from the memory unit 70, expands it into the memory 68, and executes the fracture prediction program 76.

<Function of the fracture prediction device>
Next, the operation of this embodiment will be described with reference to Figures 6 and 9. First, an operator performs a bending test on each of a plurality of test pieces of various steel types and of arbitrary plate thicknesses, each having a punched hole with a different punching clearance, and measures the bending angle αh at the bending fracture limit.

The operator also performs hole expansion tests on each of the above multiple test pieces for various steel types and test pieces under the same conditions, and measures the hole expansion ratio λ of the punched holes.

The operator also performs bending tests on base materials, which are test pieces of various steel types with any thickness and no punched holes, and measures the bending angle αb at the bending fracture limit.

Then, the operator inputs the bending fracture limit bending angle αh for each test piece, the hole expansion ratio λ of the punched holes, and the bending fracture limit bending angle αb for the base material, which is a test piece without punched holes, into the fracture prediction device 100.

The operator also performs a hole expansion test on the material to be predicted, which has the same arbitrary plate thickness as the test piece for the bending test described above and has a punched hole, and measures the hole expansion ratio λ of the punched hole.

The operator also conducts a bending test on the base material, which is the material to be predicted and has an arbitrary thickness and no punched holes, and measures the bending angle αb' at the moment when fracture occurs at the top of the bend.

Then, the operator inputs the material (S-S curve), plate thickness, hole expansion ratio λ' (%), and bending angle αb' at the bending fracture limit for the base material to the fracture prediction device 200. Next, we will explain the pre-processing that is executed by the fracture prediction device 200 when an operation such as issuing a command to start the pre-processing is performed.

In step S202 of the pre-processing shown in Figure 9, the first experiment result acquisition unit 210 acquires the bending angle αh at the bending fracture limit obtained by bending tests for each of the input test pieces of arbitrary plate thickness, each having punched holes with different punching clearances.

In step S204, the first experiment result acquisition unit 210 acquires the hole expansion ratio λ of the punched hole obtained by the hole expansion test for each of the input test pieces under the same conditions as the multiple test pieces.

In step S206, the first conversion unit 212 converts the hole expansion ratio λ into the fracture limit strain εt of the hole edge element of the punched hole for each of the multiple test specimens and test specimens under the same conditions.

In step S208, the first experimental result acquisition unit 10 acquires the bending angle αb at the bending fracture limit obtained by a bending test for the input base material, which is a test piece of any thickness and does not have a punched hole.

In step S210, the first conversion unit 212 converts the bending fracture limit bending angle αb into the fracture limit strain εb of the outer surface layer of the bend at the bend crest for a base material that is a test piece of arbitrary thickness and does not have a punched hole.

In step S212, the relationship acquisition unit 214 derives an approximation of Equation 3 above, which expresses the relationship between the ratio of the fracture limit strain εt to the fracture limit strain εb and the ratio of the bending angle αh to the bending angle αb, based on the fracture limit strain εt and the fracture limit strain εb for each test specimen obtained by the first conversion unit 212 and the bending angle αb and the bending angle αh for each test specimen obtained by the first experiment result acquisition unit 210.

In step S216, the second experiment result acquisition unit 216 acquires the hole expansion ratio λ' of the punched hole obtained by a hole expansion test for the input thin metal plate of the target metal material having an arbitrary thickness and having a punched hole.

In step S218, the second conversion unit 218 converts the input hole expansion ratio λ' into the fracture limit strain εt' of the hole edge element of the punched hole.

In step S220, the second experiment result acquisition unit 216 acquires the bending angle αb' at the bending fracture limit obtained by a bending test for the input base material, which is a thin plate of the metal material to be predicted, having an arbitrary plate thickness and which does not have a punched hole.

In step S222, the second conversion unit 218 converts the bending angle αb' at the bending fracture limit into the fracture limit strain εb' of the outer bending surface layer of the element at the bend crest.

In step S224, the bending fracture limit acquisition unit 220 acquires the bending fracture limit bending angle αh' from the relationship between the ratio of the hole expansion ratio λ to the bending angle αb and the ratio of the bending angle αh to the bending angle αb, as well as the ratio of the hole expansion ratio λ' to the bending angle αb', and ends the pre-processing.

Then, when an operation such as issuing a command to start the fracture prediction process is performed, the fracture prediction device 200 executes processing similar to the fracture prediction process shown in Figure 6 above.

As described above, the fracture prediction device 200 according to this embodiment obtains the relationship between the ratio of the fracture limit strain εt to the fracture limit strain εb and the ratio of the bending angle αh to the bending angle αb based on the fracture limit strain εt, bending fracture limit bend angle αh, fracture limit strain εb for the base material, and bending fracture limit bend angle αb for each of multiple test specimens of an arbitrary thickness. The bending fracture limit bend angle αh' is obtained from the ratio of the fracture limit strain εt' to the fracture limit strain εb' and the bending angle αb' for a target thin plate of metal material of an arbitrary thickness that has a punched hole. This is then compared with the bending angle α of the hole edge element of the punched hole, which changes sequentially during deformation analysis using a finite element model representing the target thin plate of metal material, to predict the bending fracture of the hole edge element of the punched hole. This reduces the amount of time and effort required and enables accurate prediction of bending fracture of thin plates of metal material.

[Third embodiment]
Next, a fracture prediction device according to a third embodiment will be described. Since the fracture prediction device according to the third embodiment has the same configuration as that of the second embodiment, the same reference numerals are used and the description thereof will be omitted.

<Configuration of fracture prediction device>
The bending fracture limit acquisition unit 220 of the fracture prediction device according to the third embodiment acquires the relationship between the ratio of the fracture limit strain εt and the fracture limit strain εb and the ratio of the bending angle αh and the bending angle αb based on the fracture limit strain εt, the bending angle αh of the bending fracture limit, the fracture limit strain εb for the base material, and the bending angle αb of the bending fracture limit for each of a plurality of test pieces of an arbitrary plate thickness, and acquires the bending angle αh' of the bending fracture limit from the ratio of the fracture limit strain εt' and the fracture limit strain εb' and the bending angle αb' for a thin plate of a metal material to be predicted of an arbitrary plate thickness and having a punched hole.

The bending fracture limit acquisition unit 220 then substitutes the bending angle αh' at the bending fracture limit and the mesh size used in the deformation analysis into the following equation 4 to determine the fracture limit strain εc of the outer surface layer of the bend for an arbitrary mesh size.

εc=q*M ^r +s (Formula 4)

where M is the mesh size of the finite element model used in the deformation analysis, q, r, and s are values determined according to the plate thickness t and εs, where εs is εs = t ln(αh) + u, and t and u are values determined according to the plate thickness t.

The fracture prediction unit 224 compares the maximum principal strain ε of the outer bending surface layer of the hole edge element of the punched hole, which changes sequentially during bending deformation analysis by the deformation analysis unit 222, with the fracture limit strain εc acquired by the bending fracture limit acquisition unit 220, and predicts bending fracture of the hole edge element.

Specifically, the ratio ε/εc of the maximum principal strain ε of the outer bending surface layer of the hole edge element of the punched hole to the fracture limit strain εc acquired by the bending fracture limit acquisition unit 220 is calculated sequentially, and when ε/εc = 1, the element is determined to have fractured in bending. In this case, if a bending fracture is determined, the element may be deleted.

In addition, to improve analysis efficiency, it is also possible to extract only the hole edge elements from the finite element model, and predict bending fracture of the hole edge elements by comparing the maximum principal strain ε of the outer bending surface layer of the hole edge elements, which changes sequentially during deformation analysis, with the fracture limit strain εc obtained for the hole edge elements.

The other configurations and operations of the fracture prediction device according to the third embodiment are the same as those of the second embodiment, so a description thereof will be omitted.

<Example>
An example of the fracture prediction device according to the third embodiment will now be described. The test specimen was 30 mm wide x 60 mm long, with a 10 mm diameter punched hole in the center. The steel type was 980 MPa-class steel plate, the plate thickness was 1.4 mm, and three types of finite element models were created with mesh sizes of 0.7 mm, 1.0 mm, and 1.4 mm. Bending deformation analysis was performed on this test specimen as the prediction target, and the fracture limit maximum principal strain εc of the outer surface layer of the hole edge element of the punched hole was calculated using the method described in the third embodiment, and used as the criteria. Table 1 shows the fracture limit maximum principal strain of the outer surface layer of the hole edge element of the punched hole for each mesh size.

The bending angle at which the maximum principal strain ε of the outer surface layer of the hole edge element at the top of the bend reached the fracture limit maximum principal strain εc was determined and compared with the bending angle at the fracture limit measured in the experiment.

As a result, as shown in Figure 10, for all mesh sizes, fracture could be predicted at bending angles roughly equivalent to the bending angle at which fracture was confirmed experimentally. Figure 10 shows the ratio of the bending angle at which fracture was predicted from the hole edge element (criterion reached) to the bending angle at which fracture occurred experimentally, for each mesh size.

Figure 11 also shows contour plots of the maximum principal strain in the outer surface layer of bending when the criteria are reached for finite element models of each mesh size. As the mesh size becomes coarser, the calculated strain is smoothed, resulting in smaller values. However, by being able to derive the corresponding criteria (Table 1), it can be seen that the bending angle at the bending fracture limit for detecting fracture is approximately the same value for finite element models of all mesh sizes.

[Modification]
Although the above description is based on an example in which the metal sheet or test piece to be predicted has a punched hole, the present invention is not limited to this. The metal sheet or test piece to be predicted may have a punched edge formed by punching with a die. For example, the shape of the punched edge may be linear. By punching with a die, punching damage is applied to the edge surface compared to laser or cutting processing, and fracture prediction can be performed in the same manner as in the above embodiment. In this case, bending fracture of the punched edge of the metal sheet is predicted.

For example, as in the first embodiment described above, the first experimental results acquisition unit 10 performs a bending test to acquire the bending fracture limit bending angle αh for each of a plurality of test pieces of a specific plate thickness, each having a punched end with a different punching clearance, performs a hole expansion test to acquire the hole expansion ratio λ of the punched hole corresponding to the punched end for each of the plurality of test pieces under the same conditions as the test pieces, and performs a bending test to acquire the bending fracture limit bending angle αb for a base material that is a test piece of a specific plate thickness and does not have a punched end. The relationship acquisition unit 12 acquires the relationship between the ratio of the hole expansion ratio λ to the bending angle αb and the ratio of the bending angle αh to the bending angle αb based on the hole expansion ratio λ, bending angle αh, and bending angle αb for each of the test pieces. The second experimental result acquisition unit 14 acquires a hole expansion ratio λ' of the punched hole corresponding to the punched end through a hole expansion test for a target metal sheet having a specific thickness and a punched end, and acquires a bending angle αb' of the bending fracture limit through a bending test for a target metal sheet having a specific thickness and no punched hole. The bending fracture limit acquisition unit 16 acquires a bending angle αh' of the bending fracture limit from the relationship between the ratio of the hole expansion ratio λ and the bending angle αb and the ratio of the bending angle αh and the bending angle αb, as well as the ratio of the hole expansion ratio λ' and the bending angle αb'. The deformation analysis unit 18 performs deformation analysis using a finite element model representing the target metal sheet having a punched end. The fracture prediction unit 20 predicts bending fracture of the punched end element by comparing the bending angle α of the punched end element with the bending angle αh' of the bending fracture limit, which changes sequentially during the deformation analysis. The hole expansion test is performed on a test piece with a punched hole. The hole expansion ratio to be entered should be the hole expansion ratio determined for a thin plate of the same metal material that has a punched hole that is the same as the clearance at the punched end of the thin plate of the metal material to be predicted.

Furthermore, as in the second embodiment described above, the first experimental result acquisition unit performs a bending test to acquire the bending fracture limit bending angle αh for each of a plurality of test pieces, which are thin plates of a metal material of arbitrary thickness and each have punched holes with different punching clearances. For each of the plurality of test pieces with the same conditions as the plurality of test pieces, the unit performs a hole expansion test to acquire the hole expansion ratio λ of the punched hole corresponding to the punched end. For each of the plurality of test pieces with the same conditions as the plurality of test pieces, the unit performs a bending test to acquire the bending fracture limit bending angle αb for the base material, which is a test piece of arbitrary thickness and without a punched end. The first conversion unit 212 converts the hole expansion ratio λ for each of the plurality of test pieces with the same conditions as the plurality of test pieces into the fracture limit strain εt of the hole edge element of the punched hole, and for the base material, which is a test piece of arbitrary thickness and without a punched end, the unit converts the bending angle αb into the fracture limit strain εb of the outer surface layer of the bend crest element. The relationship acquisition unit 214 acquires the relationship between the ratio of the fracture limit strain ε to the fracture limit strain ε and the ratio of the bending angle α to the bending angle α based on the fracture limit strain ε, the fracture limit strain ε, the bending angle α, and the bending angle α for each test piece. The second experimental result acquisition unit 216 acquires the hole expansion ratio λ' of the punched hole corresponding to the punched end by a hole expansion test for a thin sheet of metal material to be predicted having an arbitrary thickness and a punched end, and acquires the bending angle α' of the bending fracture limit by a bending test for a thin sheet of metal material to be predicted having an arbitrary thickness and a base material that is a thin sheet of metal material to be predicted having no punched end. The second conversion unit 218 converts the hole expansion ratio λ' into the fracture limit strain ε of the hole edge element of the punched hole and converts the bending angle α to the fracture limit strain ε of the outer surface layer of the bend crest element. The bending fracture limit acquisition unit 220 acquires the bending fracture limit bending angle αh' from the relationship between the ratio of the fracture limit strain εt and the fracture limit strain εb and the ratio of the bending angle αh and the bending angle αb, the ratio of the fracture limit strain εt' and the fracture limit strain εb', and the bending angle αb'. The deformation analysis unit 222 performs deformation analysis using a finite element model representing the metal sheet to be predicted, which is a thin metal sheet having a punched end. The fracture prediction unit 224 predicts bending fracture of the punched end element by comparing the bending angle α of the punched end element, which changes sequentially during deformation analysis, with the bending fracture limit bending angle αh'.

10, 210 First experiment result acquisition unit 12, 214 Relationship acquisition unit 14, 216 Second experiment result acquisition unit 16, 220 Bending fracture limit acquisition unit 18, 222 Deformation analysis unit 20, 224 Fracture prediction unit 26 Display unit 28 Input unit 30 Test piece 32 Punched hole 64 Computer 66 CPU
68 Memory 70 Storage unit 76 Fracture prediction program 100, 200 Fracture prediction device 212 First conversion unit 218 Second conversion unit

Claims (11)

A fracture prediction method for predicting bending fracture from a punched edge of a thin plate of a metal material using a finite element method, comprising:
A step of obtaining a bending angle αh of a bending fracture limit by a bending test for each of a plurality of test pieces which are thin plates of a metal material having a specific plate thickness and each of which has a punched end with a different punching clearance;
A step of obtaining a hole expansion ratio λ of a punched hole corresponding to the punched end by a hole expansion test for each of the plurality of test pieces under the same conditions as those of the plurality of test pieces;
A step of obtaining a bending angle αb of the bending fracture limit by a bending test on a base material that is a test piece having the specific plate thickness and that does not have a punched end;
A step of acquiring a relationship between a ratio of the hole expansion ratio λ to the bending angle αb and a ratio of the bending angle αh to the bending angle αb based on the hole expansion ratio λ, the bending angle αh, and the bending angle αb for each of the test pieces;
A step of obtaining a hole expansion ratio λ' of a punched hole corresponding to the punched end by a hole expansion test for a thin plate of a metal material to be predicted, the thin plate of the metal material having the specific plate thickness and a punched end;
a step of obtaining a bending angle αb' of a bending fracture limit by a bending test for a base material that is a thin plate of a metal material to be predicted and has a specific plate thickness and does not have a punched end;
A step of obtaining a bending angle αh' at the bending fracture limit from the relationship between the ratio of the hole expansion ratio λ and the bending angle αb and the ratio of the bending angle αh and the bending angle αb, and the ratio of the hole expansion ratio λ' and the bending angle αb';
A process of predicting bending fracture of the element at the punched end by comparing the bending angle α of the element at the punched end, which changes sequentially during deformation analysis using a finite element model representing the thin plate of the metal material having a punched end, with the bending angle αh' of the bending fracture limit;
A fracture prediction method comprising: A fracture prediction method for predicting bending fracture from a punched edge of a thin plate of a metal material using a finite element method, comprising:
A step of obtaining a bending angle αh of a bending fracture limit by a bending test for each of a plurality of test pieces which are thin plates of a metal material having an arbitrary plate thickness and each of which has a punched end with a different punching clearance;
A step of obtaining a hole expansion ratio λ of a punched hole corresponding to the punched end by a hole expansion test for each of the plurality of test pieces under the same conditions as those of the plurality of test pieces;
For each of the test pieces under the same conditions as the plurality of test pieces, converting the hole expansion ratio λ into a fracture limit strain εt of a hole edge element of the punched hole;
A step of obtaining a bending angle αb of the bending fracture limit by a bending test for a base material that is a test piece having any plate thickness and that does not have a punched end;
A step of converting the bending angle αb into a fracture limit strain εb of the outer surface layer of the bend of the element at the bend top for a base material that is a test piece having the arbitrary plate thickness and that does not have a punched end;
A step of acquiring a relationship between the ratio of the fracture limit strain ε to the fracture limit strain ε and the ratio of the bending angle α to the bending angle α based on the fracture limit strain ε, the fracture limit strain ε, the bending angle α, and the bending angle α for each of the test pieces;
A step of obtaining a hole expansion ratio λ ′ of a punched hole corresponding to the punched end by a hole expansion test for a thin plate of a metal material having the arbitrary plate thickness and having a punched end;
converting the hole expansion ratio λ ' into a fracture limit strain ε t ' of a hole edge element of the punched hole;
A step of obtaining a bending angle αb' of a bending fracture limit by a bending test for a base material that is a thin plate of the metal material to be predicted having the arbitrary plate thickness and that does not have a punched end;
converting the bending angle α′ into a fracture limit strain ε′ of the outer surface of the bent portion of the element at the bend tip;
A step of obtaining a bending angle αh' of the bending fracture limit from the relationship between the ratio of the fracture limit strain εt and the fracture limit strain εb and the ratio of the bending angle αh and the bending angle αb, the ratio of the fracture limit strain εt' and the fracture limit strain εb', and the bending angle αb';
A process of predicting bending fracture of the element at the punched end by comparing the bending angle α of the element at the punched end, which changes sequentially during deformation analysis using a finite element model representing the thin plate of the metal material having a punched end, with the bending angle αh' of the bending fracture limit;
A fracture prediction method comprising: In the step of converting the hole expansion ratio λ into a fracture limit strain εt of a hole edge element of the punched hole,
Using the following equation 1 which represents the relationship between the hole expansion ratio λ and the tensile fracture limit strain ε of the hole edge element of the punched hole, the hole expansion ratio λ is converted into the fracture limit strain ε of the hole edge element of the punched hole,
In the step of converting the bending angle αb into the fracture limit strain εb of the outer surface layer of the bent element at the bend crest,
The bending angle αb and the mesh size of the finite element model are converted into the fracture limit strain εb using the following Equation 2 for calculating the fracture limit strain εb of the outer surface layer of the bend at the bend top,
In the step of converting the hole expansion ratio λ ′ into a fracture limit strain ε t ′ of a hole edge element of the punched hole,
Using the following equation 1, the hole expansion ratio λ ′ is converted into a fracture limit strain ε t ′ of the hole edge element of the punched hole,
In the step of converting the bending angle αb' into a fracture limit strain εb' of the outer surface layer of the bent portion of the element at the bend crest,
3. The fracture prediction method according to claim 2, wherein the bending angle αb' is converted into a fracture limit strain εb' of the outer surface layer of the bent portion of the element at the bend crest using the following equation 2:
εt=a*LN(1+λ/100) ^b +c...(Formula 1)
εb = d*S ^e +f (Formula 2)
where a, b, and c are fitting coefficients, S is the mesh size of the finite element model, d, e, and f are values determined according to the plate thickness t and εs, where εs is εs = g ln(αb) + h, and g and h are values determined according to the plate thickness t. In the step of obtaining the bending angle αh′ of the bending fracture limit,
The fracture limit strain εt and the fracture limit strain εb are expressed as a relationship between the ratio of the fracture limit strain εt and the ratio of the bending angle αh and the bending angle αb. The fracture prediction method according to any one of claims 1 to 3, wherein the bending angle αh' of the bending fracture limit is obtained from the ratio of the fracture limit strain εt ' and the fracture limit strain εb' and the bending angle αb' using the following equation 3:
y1=m*LN(n+x2) ^p ...(Formula 3)
Here, m, n, and p are fitting coefficients, and if y1≧1, then y1=1. The step of predicting bending fracture of the punched edge element comprises:
The bending angle αh′ at the bending fracture limit and the mesh size of the finite element model used in the deformation analysis are substituted into the following equation 4 to determine the fracture limit strain εc of the bending outer surface layer:
The fracture prediction method according to any one of claims 1 to 4, wherein the bending fracture of the element at the punched end is predicted by comparing the maximum principal strain ε of the bending outer surface layer of the element at the punched end, which changes sequentially during the deformation analysis, with the fracture limit strain εc.
εc=q*M ^r +s (Formula 4)
Here, M is the mesh size of the finite element model used in the deformation analysis, q, r, and s are values determined according to the plate thickness t and εs, where εs is εs = t ln(αh) + u, and t and u are values determined according to the plate thickness t. A fracture prediction method according to any one of claims 1 to 5, wherein the thin metal material sheet is a steel plate with a strength class of 980 MPa or higher. A fracture prediction method according to any one of claims 1 to 6, wherein the punched end of the thin metal plate is formed by punching with a die. A fracture prediction device that predicts bending fracture from a punched edge of a thin plate of a metal material using a finite element method,
A bending test is performed to obtain a bending angle αh at the bending fracture limit for each of a plurality of test pieces, each of which is a thin plate of a metal material having a specific plate thickness and has a punched end with a different punching clearance;
For each of the test pieces under the same conditions as the plurality of test pieces, a hole expansion ratio λ of the punched hole corresponding to the punched end is obtained by a hole expansion test;
a first experimental result acquisition unit that acquires a bending angle αb of a bending fracture limit by a bending test for a base material that is a test piece having the specific plate thickness and that does not have a punched end;
a relationship acquisition unit that acquires a relationship between a ratio of the hole expansion ratio λ to the bending angle αb and a ratio of the bending angle αh to the bending angle αb based on the hole expansion ratio λ, the bending angle αh, and the bending angle αb for each of the test pieces;
For a thin plate of a metal material to be predicted having the specific plate thickness and having a punched end, a hole expansion ratio λ' of a punched hole corresponding to the punched end is obtained by a hole expansion test;
a second experimental result acquisition unit that acquires a bending angle αb′ of a bending fracture limit by a bending test for a base material that is a thin plate of the metal material having the specific plate thickness and that does not have a punched end;
A bending fracture limit acquisition unit that acquires a bending angle αh' of a bending fracture limit from the relationship between the ratio of the hole expansion ratio λ and the bending angle αb and the ratio of the bending angle αh and the bending angle αb, and the ratio of the hole expansion ratio λ' and the bending angle αb';
a fracture prediction unit that predicts bending fracture of the element at the punched end by comparing the bending angle α of the element at the punched end, which changes sequentially during deformation analysis using a finite element model that represents the thin plate of the metal material having a punched end, with the bending angle αh' of the bending fracture limit;
A fracture prediction device comprising: A fracture prediction device that predicts bending fracture from a punched edge of a thin plate of a metal material using a finite element method,
A bending test is performed to obtain a bending angle αh at the bending fracture limit for each of a plurality of test pieces which are thin plates of a metal material having an arbitrary plate thickness and each of which has a punched end with a different punching clearance;
For each of the test pieces under the same conditions as the plurality of test pieces, a hole expansion ratio λ of the punched hole corresponding to the punched end is obtained by a hole expansion test;
a first experimental result acquisition unit that acquires a bending angle αb of a bending fracture limit by a bending test for a base material that is a test piece having any plate thickness and that does not have a punched end;
For each of the plurality of test pieces and test pieces under the same conditions, the hole expansion ratio λ is converted into a fracture limit strain εt of a hole edge element of the punched hole,
A first conversion unit converts the bending angle αb into a fracture limit strain εb of the outer surface layer of the bend of the element at the bend top for a base material that is a test piece having the arbitrary plate thickness and that does not have a punched end;
a relationship acquiring unit that acquires a relationship between a ratio of the fracture limit strain ε to the fracture limit strain ε and a ratio of the bending angle α to the bending angle α based on the fracture limit strain ε, the fracture limit strain ε, the bending angle α, and the bending angle α for each of the test pieces;
For a thin plate of a metal material to be predicted having the arbitrary plate thickness and having a punched end, a hole expansion ratio λ' of a punched hole corresponding to the punched end is obtained by a hole expansion test;
a second experimental result acquisition unit that acquires a bending angle αb′ of a bending fracture limit by a bending test for a base material that is a thin plate of the metal material having the arbitrary plate thickness and that does not have a punched end;
The hole expansion ratio λ ′ is converted into a fracture limit strain ε t ′ of a hole edge element of the punched hole,
a second conversion unit that converts the bending angle α′ into a fracture limit strain ε′ of the bending outer surface layer of the element at the bend crest;
a bending fracture limit acquisition unit that acquires a bending angle αh' of the bending fracture limit from the relationship between the ratio of the fracture limit strain εt and the fracture limit strain εb and the ratio of the bending angle αh and the bending angle αb, the ratio of the fracture limit strain εt' and the fracture limit strain εb', and the bending angle αb';
a fracture prediction unit that predicts bending fracture of the element at the punched end by comparing the bending angle α of the element at the punched end, which changes sequentially during deformation analysis using a finite element model that represents the thin plate of the metal material having a punched end, with the bending angle αh' of the bending fracture limit;
A fracture prediction device comprising: A fracture prediction program for predicting bending fracture from a punched edge of a thin plate of a metal material using the finite element method,
A bending test is performed to obtain a bending angle αh at the bending fracture limit for each of a plurality of test pieces, each of which is a thin plate of a metal material having a specific plate thickness and has a punched end with a different punching clearance;
For each of the test pieces under the same conditions as the plurality of test pieces, a hole expansion ratio λ of the punched hole corresponding to the punched end is obtained by a hole expansion test;
a first experimental result acquisition unit that acquires a bending angle αb of a bending fracture limit by a bending test for a base material that is a test piece having the specific plate thickness and that does not have a punched end;
a relationship acquisition unit that acquires a relationship between a ratio of the hole expansion ratio λ to the bending angle αb and a ratio of the bending angle αh to the bending angle αb based on the hole expansion ratio λ, the bending angle αh, and the bending angle αb for each of the test pieces;
For a thin plate of a metal material to be predicted having the specific plate thickness and having a punched end, a hole expansion ratio λ' of a punched hole corresponding to the punched end is obtained by a hole expansion test;
a second experiment result acquisition unit that acquires a bending angle αb′ of a bending fracture limit by a bending test for a base material that is a thin plate of the metal material having the specific plate thickness and that does not have a punched end;
a bending fracture limit acquisition unit that acquires the bending angle αh' of the bending fracture limit from the relationship between the ratio of the hole expansion ratio λ and the bending angle αb and the ratio of the bending angle αh and the bending angle αb, and the ratio of the hole expansion ratio λ' and the bending angle αb'; and a fracture prediction unit that predicts bending fracture of the element at the punched end by comparing the bending angle α of the element at the punched end, which changes sequentially during deformation analysis using a finite element model that represents the thin plate of the metallic material having a punched end. A fracture prediction program for predicting bending fracture from a punched edge of a thin plate of a metal material using the finite element method,
A bending test is performed to obtain a bending angle αh at the bending fracture limit for each of a plurality of test pieces which are thin plates of a metal material having an arbitrary plate thickness and each of which has a punched end with a different punching clearance;
For each of the test pieces under the same conditions as the plurality of test pieces, a hole expansion ratio λ of the punched hole corresponding to the punched end is obtained by a hole expansion test;
a first experimental result acquisition unit that acquires a bending angle αb of a bending fracture limit by a bending test for a base material that is a test piece having the arbitrary plate thickness and that does not have a punched end;
For each of the plurality of test pieces and test pieces under the same conditions, the hole expansion ratio λ is converted into a fracture limit strain εt of a hole edge element of the punched hole,
a first conversion unit for converting the bending angle αb into a fracture limit strain εb of the outer surface layer of the bend of the element at the bend top for a base material that is a test piece having the arbitrary plate thickness and that does not have a punched end;
a relationship acquiring unit that acquires a relationship between a ratio of the fracture limit strain ε to the fracture limit strain ε and a ratio of the bending angle α to the bending angle α based on the fracture limit strain ε, the fracture limit strain ε, the bending angle α, and the bending angle α for each of the test pieces;
For a thin plate of a metal material to be predicted having the arbitrary plate thickness and having a punched end, a hole expansion ratio λ' of a punched hole corresponding to the punched end is obtained by a hole expansion test;
a second experiment result acquisition unit that acquires a bending angle αb′ of a bending fracture limit by a bending test for a base material that is a thin plate of the metal material having the arbitrary plate thickness and that does not have a punched end;
The hole expansion ratio λ ′ is converted into a fracture limit strain ε t ′ of a hole edge element of the punched hole,
a second conversion unit that converts the bending angle α′ into a fracture limit strain ε′ of the bending outer surface layer of the element at the bend crest;
a bending fracture limit acquisition unit that acquires a bending fracture limit bending angle αh' from the relationship between the ratio of the fracture limit strain εt and the fracture limit strain εb and the ratio of the bending angle αh and the bending angle αb, the ratio of the fracture limit strain εt' and the fracture limit strain εb', and the bending angle αb'; and a fracture prediction unit that predicts bending fracture of an element at the punched end by comparing the bending angle α of the element at the punched end, which changes sequentially during deformation analysis using a finite element model that represents a thin plate of a metallic material having a punched end.