Ratcheting of Stainless Steel 304 Under Multiaxial Nonproportional Loading

Abstract

Multiaxial ratcheting is often simulated by use of nonlinear kinematic hardening models, while in reality materials show cyclic hardening/softening and additional hardening under nonproportional loading. The effect of isotropic hardening on ratcheting needs to be addressed in simulation. In this study, ratcheting tests are conducted on stainless steel 304 under uniaxial, torsional, and combined axial-torsional loading. The ratcheting strain is predicted based on the constitutive theory that incorporates a modified Ohno-Wang kinematic hardening rule and Tanaka's isotropic hardening model. The results show that the main features of the stress-strain response can be simulated with the constitutive model. Ratcheting strain under axial mean stress depends highly on the loading path and load level, and the degree of cyclic changes in shear stress under torsional strain control is not as influential. The torsional ratcheting strain under mean shear stress with (or without) fully reversed axial strain cycling is found close to the axial ratcheting strain under equivalent mean stress with (or without) torsional strain cycling. In all, the experimental and predicted ratcheting strains for nonproportional paths are found in decent correlation. However, overprediction still prevails for some loading paths, and ratcheting rates deviate considerably from experimental values.