Stretch flange crack prediction method, stretch flange crack prediction apparatus, computer program, and recording medium

Patent metadata

Field	Value
Publication number	US-10467361-B2
Application number	US-201515322409-A
Country	US
Kind code	B2
Filing date	Jul 2, 2015
Priority date	Jul 2, 2014
Publication date	Nov 5, 2019
Grant date	Nov 5, 2019

Abstract

A stretch flange crack prediction method of predicting initiation of stretch flange cracks that occurs in a flange end section during stretch flange forming of a deformable sheet, includes: a measurement value acquisition process of acquiring, for each of a plurality of sheet-shaped test pieces, a fracture strain measurement value, a normal strain gradient measurement value, and a circumferential strain gradient measurement value; a CAE analysis process of acquiring a maximum major strain maximum element having a highest maximum major strain, a normal strain gradient of the maximum major strain maximum element, and a circumferential strain gradient of the maximum major strain maximum element; a fracture determination threshold acquisition process of acquiring a fracture determination threshold by converting the fracture strain measurement value; and a prediction process of predicting that stretch flange cracks will be initiated, when the maximum major strain is equal to or higher than the fracture determination threshold.

First claim

The invention claimed is:

1. A stretch flange crack prediction method of predicting initiation of stretch flange cracks that occurs in a flange end section during stretch flange forming of a deformable sheet, comprising:
a measurement value acquisition process of acquiring, for each of a plurality of sheet-shaped test pieces, under an experimental measurement environment with a predetermined gauge length and a predetermined gradient evaluation length,
a fracture strain measurement value,
a normal strain gradient measurement value, and
a circumferential strain gradient measurement value;

performing a CAE analysis process by performing numerical analysis by a finite element method of a stretch flange forming process of the deformable sheet to obtain forming data regarding the flange end section, under a CAE analysis measurement environment with a predetermined element size and a predetermined gradient evaluation length, and acquiring, on the basis of the numerical analysis,
a maximum major strain maximum element having a highest maximum major strain,
a normal strain gradient of the maximum major strain maximum element, and
a circumferential strain gradient of the maximum major strain maximum element;

a fracture determination threshold acquisition process of acquiring a fracture determination threshold by converting the fracture strain measurement value obtained by the measurement value acquisition process within the experimental measurement environment, on the basis of, in addition to the normal strain gradient measurement value and the circumferential strain gradient measurement value,
the element size,
the gradient evaluation length,
the normal strain gradient, and
the circumferential strain gradient,

obtained in the CAE analysis process; and
a prediction process of predicting that stretch flange cracks will be initiated, when the maximum major strain is equal to or higher than the fracture determination threshold by comparing
the maximum major strain of the maximum major strain maximum element and
the fracture determination threshold

to each other.

2. The stretch flange crack prediction method according to claim 1 , further comprising:
a fracture strain function acquisition process of acquiring a fracture strain function to define a fracture strain, using the normal strain gradient and the circumferential strain gradient as variables, on the basis of
the fracture strain measurement value,
the normal strain gradient measurement value, and
the circumferential strain gradient measurement value

obtained in the measurement value acquisition process,
wherein, in the fracture determination threshold acquisition process, the fracture determination threshold is acquired by converting the fracture strain value according to the CAE analysis measurement environment on the basis of the following Expressions (1) to (4),
ε 1(CAE) * =f (ε 1(exp) * ,GL,L s(exp) ,Δε N(exp) ,Δε C(exp) ,ES,L s(CAE) ,Δε N(CAE) ,Δε C(CAE) )  Expression (1)

ε 1(exp) * =f (Δε N(exp) ,Δε C(exp) )  Expression (2)

Δε N(exp) =f ( GL,L s(exp) ,Δε C(exp) ,ε (CAE) ,ES,L s(CAE) ,Δε N(CAE) ,Δε C(CAE) )  Expression (3)

Δε C(exp) =f ( GL,L s(exp) ,Δε N(exp) ,ε (CAE) ,ES,L s(CAE) ,Δε N(CAE) ,Δε C(CAE) )  Expression (4)

here,
ε 1(CAE) * is the fracture determination threshold,
ε 1(exp) * is the fracture strain measurement value acquired in the measurement value acquisition process,
GL is the gauge length used in the measurement value acquisition process,
L S(exp) is the gradient evaluation length used in the measurement value acquisition process,
Δε N(exp) is the normal strain gradient measurement value acquired in the measurement value acquisition process,
Δε C(exp) is the circumferential strain gradient measurement value acquired in the measurement value acquisition process,
ε (CAE) is the maximum major strain of the maximum major strain maximum element,
ES is the element size used in the CAE analysis process,
L S(CAE) is the gradient evaluation length used in the CAE analysis process,
Δε N(CAE) is the normal strain gradient acquired in the CAE analysis process, and
Δε C(CAE) is the circumferential strain gradient acquired in the CAE analysis process.

3. The stretch flange crack prediction method according to claim 1 , further comprising:
a fracture strain function acquisition process of acquiring a fracture strain function to define a fracture strain, using the normal strain gradient and the circumferential strain gradient as variables, on the basis of
the fracture strain measurement value,
the normal strain gradient measurement value, and
the circumferential strain gradient measurement value

obtained in the measurement value acquisition process,
wherein, in the fracture determination threshold acquisition process, the fracture determination threshold is acquired by converting the fracture strain value according to the CAE analysis measurement environment on the basis of the following Expressions (5) to (8),
ε 1(CAE) * =f (ε 1(exp) * ,GL,L s(exp) ,Δε N(exp) ,Δε C(exp) ,ES,L s(CAE) ,Δε N(CAE) ,Δε C(CAE) )  Expression (5)

ε 1(exp) * =f (Δε N(exp) ,Δε C(exp) ,Cl (exp) ,Cl (CAE) )  Expression (6)

Δε N(exp) =f ( GL,L s(exp) ,Δε C(exp) ,ε (CAE) ,ES,L s(CAE) ,Δε N(CAE) ,Δε C(CAE) )  Expression (7)

Δε C(exp) =f ( GL,L s(exp) ,Δε N(exp) ,ε (CAE) ,ES,L s(CAE) ,Δε N(CAE) ,Δε C(CAE) )  Expression (8)

here,
ε 1(CAE) * is the fracture determination threshold,
ε 1(exp) * is the fracture strain measurement value acquired in the measurement value acquisition process,
GL is the gauge length used in the measurement value acquisition process,
L S(exp) is the gradient evaluation length used in the measurement value acquisition process,
Cl (exp) is a processing condition when the sheet-shaped test pieces are obtained,
Δε N(exp) is the normal strain gradient measurement value acquired in the measurement value acquisition process,
Δε C(exp) is the circumferential strain gradient measurement value acquired in the measurement value acquisition process,
ε (CAE) is the maximum major strain of the maximum major strain maximum element,
ES is the element size used in the CAE analysis process,
L S(CAE) is the gradient evaluation length used in the CAE analysis process,
Cl (CAE) is a processing condition when the deformable sheet is obtained,
Δε N(CAE) is the normal strain gradient acquired in the CAE analysis process, and
Δε C(CAE) is the circumferential strain gradient acquired in the CAE analysis process.

4. The stretch flange crack prediction method according to claim 1 , further comprising:
a strain distribution data acquisition process of acquiring, for each of the plurality of sheet-shaped test pieces, strain distribution data representing a correlation among
the fracture strain measurement value,
the normal strain gradient measurement value, and
the circumferential strain gradient measurement value

obtained in the measurement value acquisition process,
wherein, in the fracture determination threshold acquisition process,
the strain distribution data is processed based on the CAE analysis process,
a fracture determination curved surface is generated by using the processed strain distribution data, and
the fracture determination threshold is acquired from the fracture determination curved surface.

5. The stretch flange crack prediction method according to claim 4 ,
wherein, in the fracture determination threshold acquisition process, a strain distribution function of the following Expression (9) is used to determine the strain distribution data,
ε= f ( B N ,C N ,B C ,C C ,ε 0 )  Expression (9)

here,
ε is the strain distr

Assignees

• Nippon Steel & Sumitomo Metal Corp
• Nippon Steel Corp

Inventors

• Shirakami Satoshi
• Yoshida Hiroshi
• Miyagi Takashi
• Nitta Jun
• Yoshida Tohru

Classifications

• B21D22/00

  Shaping without cutting, by stamping, spinning, or deep-drawing (otherwise than using rigid devices or tools or yieldable or resilient pads B21D26/00) · CPC title

• G06F2113/24

  Sheet material · CPC title

• G06F30/00 Primary

  Computer-aided design [CAD] · CPC title

• G06F30/23 Primary

  using finite element methods [FEM] or finite difference methods [FDM] · CPC title

• G06F2111/10

  Numerical modelling · CPC title