PR-256-035 - 2008 Intl. Conf. on New Developments in AHSS

AHSS Edge Formability in Sheared-Edge Tension

J. Wang, T. Link, M. Merwin

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Abstract:
Limited local formability is a primary issue for advanced high strength steels (AHSS) in automotive applications, as evidenced by unpredicted failure in stretch bending and edge stretching. Currently, the hole expansion test is used to evaluate edge formability, but it has been criticized for poor repeatability and reproducibility of the test results. We recently explored a simple method of evaluating edge formability by the sheared edge tension (SET) test. Six AHSS materials (DP590, DP780, PM780, two variants of TRIP780, and DP980) were investigated with machined and sheared edges. The AHSS show limited necking prior to failure in the SET test with adequate gauge length to width ratio, and the stress strain response until failure is similar to that in the standard uniaxial tension test. It was further discovered that the sheared edge limit strain (SELS), as defined by the limit strain just adjacent to failure, was less sensitive to testing conditions, except shear clearance. The SET test can discriminate materials with different strengths, and the same strength but subtle microstructural differences. The SELS value is accordingly proposed as a measure of the sheared edge formability. This method can be used in both laboratory research for product development and production testing for quality assurance.


Keywords: AHSS, edge formability, stretch flangeability, uniaxial tension, sheared-edge tension, sheared-edge strain limit