Experimental and numerical analysis of cyclic deformation and fatigue behavior of a Mg-RE alloy

TL;DR

This study combines experimental and numerical methods to analyze the cyclic deformation and fatigue behavior of a Mg-RE alloy, revealing the roles of twinning and detwinning in fatigue life prediction.

Contribution

It introduces a comprehensive crystal plasticity model that includes twinning/detwinning and uses simulation to predict fatigue life of Mg alloys.

Findings

Limited tension-compression anisotropy due to texture.

Cyclic hardening under compression and softening under tension observed.

Twin volume fraction varies with failure mode, indicating ongoing twinning-detwinning during fatigue.

Abstract

Strain-controlled fatigue of Mg-1Mn-0.5Nd (wt.\%) alloy were studied by experiment and simulation. The microstructure was made up of a dispersion of strongly texture grains (13\%) embedded in a matrix of grains with a random texture. The cyclic stress-strain curves showed limited tension-compression anisotropy because of the limited texture. Cyclic hardening under compression and cyclic softening under tension occurred due to the presence of twinning. Moreover, the twin volume fraction of the broken samples depended on whether the sample was broken in tension or compression, indicating that twining-detwinning occurs during the whole fatigue life. The mechanical response of the polycrystalline alloy was simulated by means of computational homogenization. The behavior of the Mg grains was modelled using a phenomenological crystal plasticity model that accounted for basal, prismatic and pyramidal slip (including isotropic and kinematic hardening) as well as twining and detwinning. The model parameters were calibrated from the cyclic stress-strain curves at different cyclic strain amplitudes. Numerical simulations were used to understand the dominant deformation mechanisms and to predict the fatigue life by means of a fatigue indicator parameter based on the accumulated plastic shear strain in each fatigue cycle.