Development of Methodology with Excellent Reproducibility for Evaluating Stretch-Flangeability Using a Sheared-Edge Tensile Test
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Stretch-flangeability is an important formability factor for advanced high-strength steels (AHSS) when manufacturing automotive parts. However, the reproducibility of the hole expansion test (HET), a standard testing method established by the international organization for standardization, is quite poor compared with other mechanical testing methods. In this study, we propose a new method, the sheared-edge tensile test (SETT), for evaluating stretch-flangeability with excellent reproducibility. SETT takes into account the deformation behavior during the HET and the critical extrinsic factors influencing the hole expansion ratio (HER). The correlation between the sheared-edge surface characteristics, the tensile properties of the SETT specimen, and stretch-flangeability were investigated to gain in-depth understanding of the proposed evaluation method. Although the correlation between HER and the post-uniform elongation of the SETT specimen with an HER >80% was ambiguous, the SETT results exhibited good reproducibility, and the stretch-flangeability indicated by HER tended to increase linearly with increases in the post-uniform elongation of the SETT specimen. Furthermore, the roughness of the sheared-edge surface had a significant effect on the local deformation behavior of the materials. The proposed method requires only a small amount of specimen, as compared with the HET and can evaluate stretch-flangeability with good reproducibility.
KeywordsHole expansion ratio Sheared-edge tension Edge fracture sensitivity Tensile test Digital image correlation
This work was supported by the National Research Foundation of Korea (NRF) grant funded by the Korea government (MSIP) (No. 2014R1A2A1A10051322) and POSCO (2016Y029).
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