Formability Assessment of Different Materials for Automotive Sheets Based on DIC Technology

Room temperature tensile tests were conducted on a variety of materials for automotive sheets, including advanced high strength steel with different strength levels, traditional high strength steel and aluminum alloy sheet, by using a universal material testing machine. The full-field strain of the materials during tension was obtained by digital image correlation (DIC) technology. The formability of different sheets was compared, and the evaluation method of material formability was discussed. The results show that the fracture strains of the materials for automotive sheets were much larger than the percentage total extension at fracture in general. Compared with the percentage total extension at fracture, the fracture strain was more negatively correlated with the strength. The percentage total extension at maximum force reflected the ability of hardening and strain homogenization of materials, and was not the direct index of plasticity. The fracture strain represented the true plasticity of materials. The formability index took into account both the hardening ability and the true plasticity, and could evaluate the formability of the material better than the single elongation.