Metal Sheet Necking Limit Strain Identification by Strain Gradient
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional methods for predicting fracture in press forming fail to accurately identify necking before it occurs, leading to potential fractures in mass-produced products due to variations in deformation behavior.
Innovation Solution
A method to identify necking limit strain by measuring strain distribution, increment ratio, and gradient in notched sheet specimens, using image correlation and finite element analysis to predict necking and prevent fractures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional fracture prediction methods using strain or strain gradient at fracture occurrence are used, then fracture limit can be predicted, but necking cannot be predicted before fracture occurs
Solution Approach 1:
The patent performs preliminary identification of the necking limit strain through tensile tests on notched sheet specimens before mass production. By establishing the relationship between necking limit strain and strain gradient in advance, the method enables prediction of necking occurrence in the stretch flanging process before actual production begins, allowing preventive measures to be taken
2Measurement precision
If hole expansion test and FEM analysis are used to identify stretch flanging limit strain, then fracture limit can be predicted, but the method is complex and requires multiple tests and analyses
Solution Approach 1:
The patent extracts and focuses specifically on the identification of necking limit strain through tensile tests on notched sheet specimens, separating this critical parameter identification from the complex hole expansion test and FEM analysis workflow. By concentrating on this essential element, the method simplifies the overall process while maintaining prediction accuracy
Solution Approach 2:
The patent changes the approach from performing complex hole expansion tests and FEM analyses to conducting simpler tensile tests on notched specimens. By changing the test parameters and methodology to focus on identifying necking limit strain directly, the process becomes less complex while still enabling accurate prediction of stretch flanging behavior
3Measurement precision
If side bending test with arcuate shape is performed to identify fracture strain, then fracture strain at flange portion can be identified, but necking limit strain cannot be determined
Solution Approach 1:
Instead of using side bending tests that measure fracture strain after deformation, the patent inverts the approach by using tensile tests on notched specimens to directly identify the necking limit strain before fracture occurs. This inverted methodology captures the critical necking information that would otherwise be lost
Data Source
Figure 1
Figure 2
Figure 3(a)~3(b)
AI summary
A method for identifying a necking limit strain of a metal sheet according to the present invention includes a step (S1) of measuring the distribution of strain in a tensile orthogonal direction in a tensile deformation process of a notch root 5a for two or more types of sheet specimens 1 having a notch geometry 5 in a portion of a sheet edge 3; a step (S3) of obtaining a strain increment ratio of the notch root 5a in the tensile deformation process and a strain gradient in the tensile orthogonal direction; a step (S5) of obtaining necking limit strain at which necking occurs in the notch root 5a based on the strain increment ratio in the tensile deformation process; and a step (S7) of identifying the necking limit strain as a function of the strain gradient from the relation between the necking limit strain obtained for the two or more types of sheet specimens 1 and the strain gradient at that time.