Incorporating Dislocation Mechanisms into a Phenomenological Cyclic Plasticity Model for Structural Alloys

Abstract

This article presents an approach to incorporating dislocation mechanisms into a phenomenological cyclic plasticity model that describes the cyclic hardening and softening response of structural alloys in the low cumulative plastic strain (microplastic) and high cumulative plastic strain (macroplastic) regimes. The cyclic constitutive model extends an existing microstructure-based Ramberg–Osgood type model, called MicroROM, for representing the stress-strain curves of Ni-based superalloys subjected to monotonic loading to cyclic loading by considerations of pertinent dislocation mechanisms in face-centered cubic (fcc) alloys and metals. The dislocation mechanisms considered include multipole trapping of dislocation pileups on parallel slip planes and its breakdown by cross slip, leading to the formation of low-energy dislocation structures by multiple slip. These considerations of the various dislocation mechanisms lead to a Ramberg–Osgood type constitutive model that describes the strain hardening response associated with single slip in the low cumulative plastic strain regime (before macroscopic yielding at 0.2 pct plastic strain offset), the strain hardening response during multiple slip in the high cumulative plastic strain regime (beyond macroscopic yielding at greater than 0.2 pct plastic strain offset), and the evolution of cyclic hardening to cyclic softening induced by the onset of shear localization. Applications of the extended cyclic plasticity model to several fcc metals and Ni-based superalloys are presented.