Breaking prediction method, program, recording medium, and arithmetic processing device

1. A breaking prediction method of predicting a breaking portion of a flange crack of a component obtained by press forming a metal sheet having a tensile strength of equal to or greater than 980 MPa, the method comprising:

determining a first mesh coarseness and a second mesh coarseness on the basis of an n value indicating a work hardening property of the metal sheet, when dividing the component into a plurality of meshes;

performing forming analysis by using a finite element method in each of a case where the metal sheet is divided on the basis of the first mesh coarseness and a case where the metal sheet is divided on the basis of the second mesh coarseness which is coarser than the first mesh coarseness;

obtaining a maximum main stress for each mesh in each of the case of the first mesh coarseness and the case of the second mesh coarseness;

obtaining a difference value of the maximum main stress between the maximum main stress in the case of the first mesh coarseness and the maximum main stress in the case of the second mesh coarseness in each portion of the component, and extracting a portion in the case of the first mesh coarseness, which corresponds to a portion in which the difference value is larger than 100 MPa, as the breaking portion;

setting forming conditions based on the breaking portion that has been extracted; and

press forming the metal sheet using the forming conditions,

wherein an average mesh size of a first mesh L-fine and an average mesh size of a second mesh L-coarse satisfy the following expressions (1B) and (2B):

f ( n;k, 2.0× t 0,1.5× t 0)≤ L coarse≤ f ( n;k, 5.0,2.0× t 0)  (1B), and

f ( n;k, 2.5× t 0, t 0)≤ L fine≤ f ( n;k, 4.0× t 0,2.5× t 0)  (2B),

where t0 is a sheet thickness at an early stage, k is a parameter for adjusting a rate of variation in a mesh size with respect to the n value, a value of a function f(n; k, L, L0) is given by (L-L0)×(2/π)×tan −1 (k×n)+L0, and L and L0 are an upper limit and a lower limit of the mesh size, respectively.

2. The breaking prediction method according to claim 1 ,

wherein in a case where the breaking portion is not extracted by obtaining the difference value of the maximum stress, steps of the forming analysis, obtaining the maximum main stress for the each mesh, and obtaining the difference value of the maximum main stress, are performed again after resetting at least the first mesh coarseness, out of the first mesh coarseness and the second mesh coarseness, to a coarseness coarser than at least the first mesh coarseness or resetting 100 MPa to a smaller value, or a combination thereof.

3. The breaking prediction method according to claim 1 , wherein an adaptive mesh is used when division based on the first mesh coarseness is performed.

4. The breaking prediction method according to claim 1 , wherein the forming analysis is terminated in the middle of forming of the component.

5. The breaking prediction method according to claim 1 ,

wherein the method further includes;

obtaining a shape index value, which is at least one of a maximum main strain and a ratio of a reduction in a sheet thickness, for each mesh with respect to a case of division based on the first mesh coarseness and a case of division based on the second mesh coarseness; and

obtaining a difference value of the shape index between the shape index value in the case of the first mesh coarseness and the shape index value in the case of the second mesh coarseness in the each portion of the component,

wherein the portion in the case of the first mesh coarseness, which corresponds to a portion satisfying the difference value in the shape index value being larger than a predetermined value, or the difference value in the maximum main stress being larger than 100 MPa, or a combination thereof, is extracted as the breaking portion.

6. The breaking prediction method according to claim 1 , wherein an occurrence portion of a stretch flange crack is predicted as the breaking portion.

7. The breaking prediction method according to claim 1 , wherein the breaking portion at an end portion of the component is extracted.

8. The breaking prediction method according to claim 1 ,

wherein a ratio of the first mesh coarseness to the second mesh coarseness is equal to or greater than 1.5.