A Comparative Study of Forming and Crash Behavior of High Strength Steels

Advanced high strength (AHS) steel sheets of various grades have been increasingly used in the automotive industries because of their advantageous mechanical properties. High strength and great energy absorption are desired for a structural component design. On the other hand, large formability and strain hardening are necessary for achieving an effective forming process. To apply eligible steel grades, precise understanding of their forming and crash characteristics is needed. In this work, AHS steels with varying strengths, namely grades 780, 980, and 1180, were investigated. First, tensile tests were performed, and mechanical properties, including r-values, of the examined steels were obtained for different loading directions. The forming limit curves (FLCs) and respective forming limit stress curves (FLSCs) were determined bymeans of a Nakajima forming test and finite element simulation. The cyclic tension-compression tests were conducted to characterize the elastic recovery andBauschinger effect of steels. Afterward, forming processes of an automotive part were performed, and the forming and springback behaviors of steels were evaluated by using simulations coupled with Hill' 48 and Yoshida-Uemori models, determined material parameters, FLCs, and FLSCs. In addition, crashworthiness of steels was numerically studied by means of a crash rectangle profile and simplified side impact pole test. Themechanical, forming, and crash performances of all the investigated AHS steels were evaluated and discussed so that the results can be applied for part design and manufacturing.