CLAIMS
1. A break prediction method which predicts a break of a joint portion of an ;
object to be analyzed including a pair of members joined to each other by using a finite
element method, the method comprising:
a first step of acquiring at least an element size of a base material portion, from among parameters set in an element model for the object to be analyzed;
a second step of calculating, as a break discernment standard, a break limit moment defined by a function including the element size of the base material portion as a variable; and
a third step of discerning whether the moment applied to the joint portion in a j
deformation analysis of the element model for the object to be analyzed exceeds the
break limit moment, and outputting a result of the discernment as a break prediction
result for the joint portion. j
2. The break prediction method according to claim 1,
wherein in the first step, from among the parameters set in the element model,
a tensile strength of the object to be analyzed and the element size of the base material ■
portion are acquired; and
wherein in the second step, the function used in the calculation of the break limit moment is changed depending on the tensile strength.
3. The break prediction method according to claim 2,
wherein in a case where the tensile strength is equal to or greater than 980 MPa,
in the second step, the break limit moment is calculated by using Equation (1)

as the function.
Mf - Me ■ F (Me, t, D, W, L, e) ... (1) where, Mf: break limit moment (N ■ mm) Me: modified elastic bending moment (N - mm) F (Me, t, D, W, L, e): correction terms
t: thickness of the object to be analyzed (mm)
D: nugget diameter in a case where a joint portion is a spot-welded I
portion (mm)
W: effective width that a spot-welded portion receives a load (mm)
L: arm length (mm)
e: an element size of a base material portion (mm)
4. The break prediction method according to claim 3, wherein in Equation (1), the modified elastic bending moment Me is defined by Equation (2), the correction terms F(Me, t, D, W, L, e) are defined by Equation (3). Me-(el/L)-(E-D-t3)/12... (2) where, el: total elongation of an object to be analyzed (e) E: Young's modulus of the object to be analyzed (MPa)
F(Me, t, D, W, L, e) j
= f(Me) • f(t) - f(D) ■ f(W) • f(L) - f(e) ... (3)
where, f(Me): correction term of the modified elastic bending moment Me f(t): correction term of the thickness t f(D): correction term of the nugget diameter D f(W): correction term of the effective width W f(L): correction term of the arm length L

f(e): correction term of the element size e of the base material portion
5. The break prediction method according to claim 4,
wherein f(Me), f(t), f(D), f(W), f(L), and f(e) are equations which are determined from multiple regression such that an error between a moment applied to a spot-welded portion, obtained by loading a breaking load which is confirmed by experiments to a test piece edge and the break limit moment Mf calculated using
Equation (1) is minimized, in a finite element method model generated using an L- !
shaped joint type test piece.
6. The break prediction method according to claim 2, |
wherein in a case where the tensile strength is less than 980 MPa,
in the second step, the break limit moment is calculated using Equation (4) as the function.
Mf - Mp - F(Mp, t, D, W, el, e)... (4) where, Mf: break limit moment (N * mm) Mp: total plastic bending moment (N ■ mm) F(Mp, t, D, W, el, e); correction terms
t: thickness of the object to be analyzed (mm)
D: nugget diameter in a case where a joint portion is a spot-welded portion (mm)
W: effective width that a spot-welded portion receives a load (mm)
el: total elongation of the object to be analyzed (e)
e: an element size of a base material portion (mm)

7. The break prediction method according to claim 6,
wherein in Equation (4), the total plastic bending moment Mp is defined by Equation (5), and the correction terms F(Mp, t, D, W, el, e) are defined by Equation (6). Mp-CTS-W-t2)^... (5)
where, TS: tensile strength of the object to be analyzed (MPa) F(Mp,t,D,W,el,e)
- f(Mp) - f(t) - f(D) - f(W) • f(el) • f(e)... (6) where, f(Mp): correction term of the total plastic bending moment Mp f(t): correction term of the thickness t f(D): correction term of the nugget diameter D f(W): correction term of the effective width W f(el): correction term of total elongation el f(e); correction term of the element size e of the base material portion
8. The break prediction method according to claim 7,
wherein f(Mp); f(t), f(D), f(W), f(el), and f(e) are equations which are determined from multiple regression such that an error between a moment applied to a spot-welded portion, obtained by loading a breaking load which is confirmed by experiments to a test piece edge and the break limit moment Mf calculated using Equation (4) is minimized, in a finite element method model generated using an L-shaped joint type test piece.
9. The break prediction method according to any one of claims 1 to 8,
wherein in the third step, in a case where a relationship between the moment
Ml applied to the joint portion in a deformation analysis of an element model of the

object to be analyzed and the break limit moment Mf satisfies Equation (9), a result indicating that there is a break is output as the break prediction result. Ml/Mf>l ... (9)
10. The break prediction method according to any one of claims 1 to 9,
wherein in the third step, in a case where an axial force applied to the joint
portion in a deformation analysis of an element model of the object to be analyzed is a compressed axial force, a result indicating that there is no break is forcibly output as the break prediction result.
11. Abreak prediction device which predicts abreak of ajoint portion of an
object to be analyzed including a pair of members joined to each other by using a finite
element method, the break prediction device comprising:
a parameter acquisition unit that acquires at least an element size of a base material portion, from among parameters set in an element model for the object to be analyzed;
a storage unit that stores a break limit moment defined by a function including the element size of the base material portion as a variable;
a break discernment standard calculation unit that calculates the break limit moment as a break discernment standard, by reading the function from the storage unit and inputting the element size of the base material portion which is acquired by the parameter acquisition unit to the function; and
a break discernment unit that discerns whether the moment applied to the joint portion in a deformation analysis of the element model for the object to be analyzed exceeds the break limit moment, and outputs a result of the discernment as a break

prediction result for the joint portion.
12. The break prediction device according to claim 11,
wherein the parameter acquisition unit acquires a tensile strength of the object to be analyzed and the element size of the base material portion, from among the parameters set in the element model,
wherein the storage unit stores a plurality of functions corresponding to the tensile strength, and
wherein the break discernment standard calculation unit reads the function corresponding to the tensile strength acquired by the parameter acquisition unit from the storage unit and calculates the break limit moment.
13. The break prediction device according to claim 12,
wherein in a case where the tensile strength is equal to or greater than 980 MPa, the break discernment standard calculation unit reads the function represented by Equation (1) from the storage unit and calculates the break limit moment. Mf = Me ■ F (Me, t, D, W, L, e) ... (1) where, Mf: break limit moment (N ■ mm) Me: modified elastic bending moment (N • mm) F (Me, t, D, W, L, e): correction terms
t: thickness of the object to be analyzed (mm) D: nugget diameter in a case where a joint portion is a spot-welded portion (mm)
W: effective width that a spot-welded portion receives a load (mm) L: arm length (mm)

e: ail element size of a base material portion (mm)
14. The break prediction device according to claim 13,
wherein in Equation (1), the modified elastic bending moment Me is defined by Equation (2), the correction terms F(Me, t, D, W, L, e) are defined by Equation (3). Me = (el/L)-(E-D-t3)/12... (2)
where, el: total elongation of an object to be analyzed (e)
E: Young's modulus of the object to be analyzed (MPa)
F(Me, t, D, W, L, e)
= f(Me) • f(t) • f(D) - f(W) • f(L) • f(e) ... (3)
where, f(Me): correction term of the modified elastic bending moment Me
f(t): correction term of the thickness t
f(D): correction term of the nugget diameter D
f(W): correction term of the effective width W
f(L): correction term of the arm length L
f(e): correction term of the element size e of the base material portion
15. The break prediction device according to claim 14,
wherein f(Me), f(t), f(D), f(W), f(L), and f(e) are equations which are determined from multiple regression such that an error between a moment applied to a spot-welded portion, obtained by loading a breaking load which is confirmed by experiments to a test piece edge and the break limit moment Mf calculated using Equation (1) is minimized, in a finite element method model generated using an L-sbaped joint type test piece.

16. The break prediction device according to claim 12,
wherein in a case where the tensile strength is less than 980 MPa,the break discernment standard calculation unit reads the function represented by Equation (4) from the storage unit and calculates the break limit moment. Mf - Mp • F(Mp, t, D, W, el, e) ... (4) where, Mf: break limit moment (N • mm) Mp: total plastic bending moment (N • mm) F(Mp, t, D, W, el, e): correction terms
t: thickness of the object to be analyzed (mm) D: nugget diameter in a case where a joint portion is a spot-welded portion (mm)
W: effective width that a spot-welded portion receives a load (mm) el: total elongation of the object to be analyzed (s) e: an element size of a base material portion (mm)
17. The break prediction device according to claim 16,
wherein in Equation (4), the total plastic bending moment Mp is defined by Equation (5), and the correction terms F(Mp, t, D, W, el, e) are defined by Equation (6). Mp-(TS-W-t2)/4... (5)
where, TS: tensile strength of the object to be analyzed (MPa)
F(Mp, t, D, W, el, e)
= f(Mp) • f(t) • f(D) • f(W) - f(el) • f(e)... (6)
where, f(Mp): correction term of the total plastic bending moment Mp
f(t): correction term of the thickness t
f(D): correction term of the nugget diameter D

f(W): correction term of the effective width W
f(el): correction term of total elongation el
f(e): correction term of the element size e of the base material portion
18. The break prediction device according to claim 17,
wherein f(Mp), f(t), f(D), f(W), f(el), and f(e) are equations which are determined from multiple regression such that an error between a moment applied to a spot-welded portion, obtained by loading a breaking load which is confirmed by experiments to a test piece edge and the break limit moment Mf calculated using Equation (4) is minimized, in a finite element method model generated using an L-shaped joint type test piece.
19. The break prediction device according to any one of claims 11 to 18,
wherein in a case where a relationship between the moment Ml applied to the
joint portion in a deformation analysis of an element model of the object to be analyzed and the break limit moment Mf satisfies Equation (9), the break discernment unit outputs a result indicating that there is a break as the break prediction result. Ml/Mf>l ... (9)
20. The break prediction device according to any one of claims 11 to 19,
wherein in a case where an axial force applied to the joint portion in a
deformation analysis of an element model of the object to be analyzed is a compressed axial force, the break discernment unit forcibly outputs a result indicating that there is no break as the break prediction result.

21. A program causing a computer to execute a process of predicting a break
of a joint portion of an object to be analyzed including a pair of members joined to
each other by using a finite element method, the process comprising:
a first process of acquiring at least an element size of a base material portion, from among parameters set in an element model for the object to be analyzed;
a second process of calculating, as a break discernment standard, a break limit moment defined by a function including the element size of the base material portion as a variable; and
a third process of discerning whether the moment applied to the joint portion in a deformation analysis of the element model for the object to be analyzed exceeds the break limit moment, and outputting a result of the discernment as a break prediction result for the joint portion.
22. The program according to claim 21,
wherein in the first process, the computer is caused to execute a process of acquiring a tensile strength of the object to be analyzed and the element size of the base material portion from among the parameters set in the element model, and
wherein in the second process, the computer is caused to execute a process of changing the function used in the calculation of the break limit moment depending on the tensile strength.
23. The program according to claim 22,
wherein in a case where the tensile strength is equal to or greater than 980 MPa,
in the second process, the computer is caused to execute a process of

calculating the break limit moment by using Equation (1) as the function. Mf = Me • F (Me, t, D, W, L, e) ... (1) where, Mf: break limit moment (N • mm) Me: modified elastic bending moment (N - mm) F (Me, t, D, W, L, e): correction terms
t: thickness of the object to be analyzed (mm)
D: nugget diameter m a case where a joint portion is a spot-welded portion (mm)
W: effective width that a spot-welded portion receives a load (mm)
L: arm length (mm)
e: an element size of a base material portion (mm)
24. The program according to claim 23,
wherein in Equation (1), the modified elastic bending moment Me is defined by Equation (2), the correction terms F(Me, t, D, W, L, e) are defined by Equation (3). Me-(el/L)-(E-D-t3)/12... (2) where, el: total elongation of an object to be analyzed (e) E: Young's modulus of the object to be analyzed (MPa) F(Me,t,D,W,L,e)
- f(Me) - f(t) • f(D) • f(W) • f(L) • f(e)... (3)
where, f(Me): correction term of the modified elastic bending moment Me f(t): correction term of the thickness t f(D): correction term of the nugget diameter D f(W): correction term of the effective width W f(L): correction term of the arm length L

f(e): correction term of the element size e of the base material portion
25. The program according to claim 24,
wherein f(Me), f(t), f(D), f(W), f(L), and f(e) are equations which are determined from multiple regression such that an error between a moment applied to a spot-welded portion, obtained by loading a breaking load which is confirmed by experiments to a test piece edge and the break limit moment Mf calculated using Equation (1) is minimized, in a finite element method model generated using an L-shaped joint type test piece.
26. The program according to claim 22,
wherein in a case where the tensile strength is less than 980 MPa,
in the second process, the computer is caused to execute a process of calculating the break limit moment by using Equation (4) as the function.
Mf - Mp ■ F(Mp, t, D, W, el, e) ... (4)
where, Mf: break limit moment (N • mm)
Mp: total plastic bending moment (N ■ mm)
F(Mp, t, D, W, el, e): correction terms
t: thickness of the object to be analyzed (mm) D: nugget diameter in a case where a joint portion is a spot-welded portion (mm)
W: effective width that a spot-welded portion receives a load (mm) el: total elongation of the object to be analyzed (s) e: an element size of a base material portion (mm)

27. The program according to claim 26,
wherein in Equation (4), the total plastic bending moment Mp is defined by Equation (5), and the correction terms F(Mp, t, D, W, el, e) are defined by Equation (6). Mp = (TS-W-t2)/4... (5)
where, TS: tensile strength of the object to be analyzed (MPa) F(Mp,t,D,W,el,e)
= f(Mp) • f(t) • f(D) • f(W) - f(el) • f(e)... (6) where, f(Mp): correction term of the total plastic bending moment Mp f(t): correction term of the thickness t f(D): correction term of the nugget diameter D f(W): correction term of the effective width W f(el): correction term of total elongation el f(e): correction term of the element size e of the base material portion
28. The program according to claim 27,
wherein f(Mp), f(t), f(D), f(W), f(el), and f(e) are equations which are determined from multiple regression such that an error between a moment applied to a spot-welded portion, obtained by loading a breaking load which is confirmed by experiments to a test piece edge and the break limit moment Mf calculated using Equation (4) is minimized, in a finite element method model generated using an L-shaped joint type test piece.
29. The program according to any one of claims 21 to 28,
wherein in the third process, in a case where a relationship between the
moment Ml applied to the joint portion in a deformation analysis of an element model

of the object to be analyzed and the break limit moment Mf satisfies Equation (9), the computer is caused to execute a process of outputting a result indicating that mere is a break as the break prediction result.
Ml/Mf>l ... (9)
30. The program according to any one of claims 21 to 29,
wherein in the third process, in a case where an axial force applied to the joint portion in a deformation analysis of an element model of the object to be analyzed is a compressed axial force, the computer is caused to execute a process of forcibly outputting a result indicating that there is no break as the break prediction result.
31. A computer-readable recording medium having the program according to any one of claims 21 to 30 recorded therein.
32. A break discernment standard calculation method which calculates a break discernment standard used when predicting a break of a joint portion of an object to be analyzed including a pair of members joined to each other by using a finite element method, the method comprising:
a first step of acquiring at least an element size of a base material portion, from among parameters set in an element model for the object to be analyzed; and
a second step of calculating, as a break discernment standard, a break limit moment defined by a function including the element size of the base material portion as a variable.