Stretch Flange Crack Evaluation Using Strain Gradient Reference Data
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Solution Overview
Problem
Current methods for predicting stretch flange cracking at the sheared end face of high strength steel sheets in press forming are time-consuming and impractical due to the need for frequent forming analyses and specialized equipment, especially when metal sheet warping occurs during conical hole expansion forming.
Innovation Solution
A method involving hole expansion forming analyses on a randomly selected metal sheet to establish a relationship between strain at the hole edge and strain gradient, which can be used as analytical data for evaluating stretch flange cracking, independent of material conditions, allowing for quick prediction of stretch flange cracking without performing forming analyses for each different material.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If forming analysis is performed for each metal sheet to evaluate stretch flange cracking limit, then prediction accuracy is improved, but evaluation time increases significantly
Solution Approach 1:
The patent performs forming analysis in advance on a reference metal sheet to establish the relationship between strain at hole edge and strain gradient. This preliminary analysis creates a universal evaluation model that can be applied to any metal sheet without requiring separate forming analyses, thus resolving the contradiction between prediction accuracy and evaluation time.
Solution Approach 2:
The patent uses a reference metal sheet to create a model that can be copied and applied to evaluate other metal sheets. Instead of performing unique forming analyses for each metal sheet, the strain-strain gradient relationship obtained from the reference sheet serves as a template for evaluating different materials, maintaining accuracy while reducing time consumption.
2Measurement precision
If conical hole expansion forming is used to measure strain gradient, then measurement capability is improved, but metal sheet warping occurs making measurement difficult
Solution Approach 1:
The patent introduces an intermediary approach by using finite element analysis to calculate strain gradients based on forming conditions and material properties, rather than relying solely on direct physical measurement. This computational intermediary allows strain gradient determination without the warping issues that plague direct measurement methods during conical hole expansion forming.
3Measurement precision
If specialized measurement devices are used for direct strain gradient calculation, then measurement accuracy is improved, but device complexity and cost increase
Solution Approach 1:
The patent replaces complex mechanical measurement devices with computational methods. Instead of using specialized physical equipment to directly measure strain gradients, the invention uses finite element analysis and mathematical calculations based on forming conditions and material properties to determine strain gradients, thereby eliminating the need for complex measurement hardware.
Data Source
AI summary
A method includes two or more reference strain gradient information being a relationship between the strain at the hole edge and a strain gradient along a radial direction. Hole expansion forming is performed on the evaluation metal sheet under the same forming conditions as respective forming conditions corresponding to at least two pieces of the reference strain gradient information to obtain at least two limit hole expansion ratios at a hole expansion limit of the evaluation metal sheet. A formable region of the evaluation metal sheet is obtained from the at least two pieces of the reference strain gradient information and the obtained at least two limit hole expansion ratios at the hole expansion limit. Stretch flange cracking at the sheared end face of the evaluation metal sheet is evaluated by the obtained formable region.