Plastic anisotropy evolution of SS316L and modeling for novel cruciform specimen

In this paper, the evolution of the plastic anisotropy of stainless steel 316L samples is investigated under proportional loading paths using a customized cruciform specimen. The determination of a novel cruciform specimen by a design of experiments approach integrated with finite element simulations is described. The mechanical properties of the material are characterized under uniaxial tension applied in every 15 from the rolling direction and equibiaxial tension from hydraulic bulge experiments. The results reveal that the plastic anisotropy shown in stress and strain significantly evolves with respect to the plastic work. Based on the experiments, the material behavior is modeled using a non-quadratic anisotropic yield function, Yld2004-18p, with parameters modeled as a function of the equivalent plastic strain, assuming plastic work equivalence, and with constant parameters for comparison. The Hockett-Sherby model is also used for the strain hardening behavior to extrapolate the results to higher strain values. The models are implemented into a user material subroutine for finite element simulations. To validate the model, in-plane biaxial tension experiments are performed, using a customized specimen, to achieve greater deformation than previous designs by introducing double-sided pockets for thickness reduction and notches in the corner areas. The results are compared with finite element simulations implemented with the plasticity models.