Modeling the Residual Stresses Induced in the Metastable Austenitic Stainless Steel Disc Springs manufactured by Incremental Sheet Forming by a Combined Hardening Model with Phase Transformation

Abstract A numerical model for predicting the beneficial residual stress induced in metastable austenitic stainless steel (MASS) disc springs through incremental sheet forming (ISF) is developed. An important input for the numerical model is the phase-specific flow curves of the MASS constituents, i.e., austenite γ and martensite α phase. These curves are determined by using an available CP-FEM framework. The cyclic plasticity effects introduced by the bending/unbending deformation mechanism of the ISF are modeled by using a combined non-linear isotropic/kinematic hardening model. The kinetics of the strain-induced martensite transformation is modeled by using the Olson-Cohen model, whereas the stresses in the whole material are approximated by a mixture rule. The combined non-linear isotropic/kinematic hardening along with Olson-Cohen model and the mixture rule is integrated as a user-material routine (UMAT). The model parameters are calibrated by tensile tests with online Feritscope measurements and tension-compression tests. Afterward, the incremental forming simulations of disc spring manufacturing are performed and the numerically determined residual stress values are compared to the experimental values. The comparison indicates a good match. Hence, the developed numerical strategy provides accurate residual stresses prediction and can be utilized to design the disc spring properties through adjusting residual stresses, which is possible by varying process parameters of the ISF process.