A review on cyclic hardening and softening behavior of alloys

Abstract

Cyclic hardening and softening are vital aspects of the cyclic plastic deformation behaviour in alloys, and accurately predicting these responses is crucial for stress analysis in engineering components via finite element analysis. Cyclic hardening can enhance stress-bearing capacity but reduce ductility, while cyclic softening can lower stress-bearing capacity but may enhance ductility. This paper provides a comprehensive review of the mechanisms underlying cyclic hardening and softening in alloys. Mechanisms for cyclic hardening include dislocation accumulation, deformation-induced phase transformations, deformation twins, and dynamic strain aging (DSA), while cyclic softening may occur due to dislocation annihilation and rearrangement, phase instability, precipitate coarsening and shearing, grain coarsening and shear band formation in ultra-fine grained alloys. The review also explores factors influencing cyclic hardening and softening, such as material composition, microstructure, loading conditions (mean and amplitude), loading rate (frequency and waveform), loading non-proportionality, pre-strain, temperature, and environmental factors. The effects of cyclic hardening and softening on alloy mechanical properties, including strength, stiffness, ductility, fatigue resistance, and wear resistance, are also discussed. The study outlines how to analytically represent cyclic hardening and softening in both stress- and strain-controlled modes and addresses modelling these behaviours in finite element analysis. Accurate modelling requires capturing both changes in stress amplitude over cycles and stress-strain hysteresis loops across cycles. Investigations into SA333 C-Mn steel and 304LN stainless steel indicate that for small to moderate cyclic hardening, as seen in SA333 C-Mn steel, cyclic hardening can be effectively modelled by adjusting the cyclic yield stress using isotropic hardening in a combined hardening model. However, for high cyclic hardening, as in 304LN stainless steel, modifications to both isotropic and kinematic hardening parameters are necessary to simulate stress-strain hysteresis loops across cycles accurately.