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The issue of improving car crash energy management and maintaining cost and weight reduction are the driving forces behind the growing use of advanced high strength steels, particularly in Europe and Japan. Recent developments in the manufacture of high strength steel (HSS) sheets in North America, in particular Dual Phase (DP) steels, offers an attractive option to the automotive designer for weight reduction and improved safety performance. For example, the use of dual phase steels, as opposed to more conventional steel products such as high strength low alloys (HSLA), in some cases may result in up to 40% part weight reduction at similar vehicle crash performance. In this paper the formability of commercially produced hot-dipped dual phase steels of various gages and grades is assessed. Forming Limit Curves (FLCs) are determined for commercial DP590 and DP780 grades. These FLCs were compared to the conventional ASM FLCs calculated from n-value and sheet thickness.

An experimental study of springback was conducted for a hat channel section with varying cross sections and controlled gap between punch and die. The channel section was formed in a single step forming process with upper pressure pad. DP590 steel was compared to a group of high strength steels (HSS), e.g. HSLA270, 340 and 420. In addition, sidewall curl phenomenon was studied utilizing bending under tension test. This paper describes methodology of experiment and discusses springback related results. It also offers recommendations that can be applied to die-punch gap control or material substitution situations. The results of this investigation can be used to verify accuracy of springback predictions in finite element analysis (FEA).

Continuing pressure to reduce mass and cost of vehicles is driving the development of new high strength steel products with improved combinations of strength and formability. Galvanized, cold rolled dual phase steel products are new alternatives to conventional high strength low alloy (HSLA) steel for strength limited applications in vehicles. These steels have higher tensile strengths than HSLA products with nearly equivalent formability. This paper compares the performance of HSLA and dual phase sheet steel products in a series of drop tower tests. Samples were prepared by stamping the steel sheets into typical rail-type parts using a production-intent die process. The parts were sectioned, and subsequently fabricated into hat-shaped assemblies that were then dynamically crushed by a drop weight. The experiments were designed such that the entire energy input by the drop weight was absorbed by the samples.