Patent ID: 11971390
Assignee: JFE STEEL CORPORATION
Field: Measurement (Instruments)
Classification: CPC G  B | IPC B  G

Claim 9:
10. A stretch flange cracking evaluation method for evaluating stretch flange cracking of an evaluation metal sheet formed by a metal sheet with a sheared end face, the stretch flange cracking evaluation method comprising:
including a storage unit configured to store reference strain gradient information acquired by performing, under set forming conditions, a forming analysis of a hole expansion test on a second metal sheet being a metal sheet selected regardless of the evaluation metal sheet and having randomly selected sheet conditions and converting a hole expansion ratio to a strain at a hole edge composed of true strain, the reference strain gradient information being represented by a relationship between the strain at the hole edge and a strain gradient along a radial direction from the hole edge and being linked to the forming conditions and stored in the storage unit, in which the storage unit stores two or more pieces of the reference strain gradient information with the forming conditions being different, and comprising as steps of evaluating stretch flange cracking of the evaluation metal sheet:
an actual test step of performing hole expansion forming on the evaluation metal sheet under the same forming conditions as forming conditions corresponding to first reference strain gradient information selected from the plurality of pieces of the reference strain gradient information stored in the storage unit to obtain a limit hole expansion ratio at a hole expansion limit of the evaluation metal sheet;
a limit strain gradient calculation step of, on a basis of the first reference strain gradient information and a limit strain being a strain at the hole edge at the hole expansion limit corresponding to the limit hole expansion ratio obtained in the actual test step, calculating a strain gradient along the radial direction from the hole edge corresponding to the limit strain; and
a possible region setting step of obtaining a formable region from two or more sets of data (the limit strain and the strain gradient) obtained by performing the actual test step and the limit strain gradient calculation step twice or more times by changing the reference strain gradient information, wherein the stretch flange cracking at the sheared end face of the evaluation metal sheet is evaluated by the formable region obtained by the possible region setting step.