Material characterization of local strain-induced α’-martensitic reinforcements

The reinforcement of metastable austenitic steels during deep drawing to utilize the α’-martensitic phase transformation in combination with the work-hardening effect is one concept of lightweight construction. One aim concerning this contribution is the material characterization of those local strain-induced reinforcements in sheet metal. After a short introduction in the field of enhancing stiffness during forming processes, crash tests and Nakajima tests are analyzed regarding their applicability for the modified material. The successful determination of the reaction of flexure and the energy absorption was realized by crash tests, including the comparison of reinforced and original material. To adapt well established methods for the material characterization for this special case, new approaches for this challenge were developed to evaluate the material behavior for different states of stress according to Nakajima tests. Thus, the developed Forming Curves (FC) enable the determination of varied failure areas and the material behavior of reinforced and original steel including bulge height. The FCs allow a comparison of different reinforced steel grades considering the deformation of reinforcements during the Nakajima test.