Forming Limits of Several High-Strength Steel Sheets under Proportional/Non-Proportional Deformation Paths

摘要

Forming limits of several high-strength steel (HSS) sheets under non-proportional deformation paths were examined experimentally and predicted analytically. Forming limit curves (FLCs) for 590MPa, 780MPa and 980MPa grade HSS sheets were obtained by performing stretch forming tests under proportional deformation and two types of non-proportional deformation. The experimental results showed strong path-dependent characteristics of FLCs of HSS sheets. Forming limits of equi-biaxially prestrained HSS sheets became markedly lower compared to the original FLCs under proportional deformation, while forming limits of uniaxially prestrained HSS sheets became partially higher than the original FLCs. It was confirmed that Marciniak-Kuczynski type analysis gave reasonably good predictions of forming limits under non-proportional deformation paths. Especially forming limit predictions of equi-biaxially-prestrained sheets showed good agreement with the corresponding experimental results.