Strain path dependent stiffness degradation of a loaded sheet

Material stiffness is an important material property especially in analyses of springback, due to its influence on a final result. Despite all that, the elastic response of the formed part associated with the forming tools removal is in the most of computational analyses still performed by Hooke’s law and with initial values of elastic constants used, though it was reported several times that material stiffness drops with the increase of plastic deformation. Another important task of science regarding stiffness degradation is to find a cause of the phenomenon, which is still an open subject for a discussion. According to great importance of the subject of stiffness degradation, this work experimentally investigates anisotropic elastic properties of a sheet metal (stainless steel 1.4301), which has been previously subjected to different loading conditions and plastically deformed to a different degree. To our knowledge, elastic anisotropy in sheet metals induced by straining has not been measured yet. Besides the direct use in springback analyses, the acquired experimental information could contribute to a better understanding of material behaviour, and could be used, consequently, as a basis for development and validation of particular constitutive models, especially in the field of continuum damage mechanics.