An asymmetric elastic-plastic analysis of the load-controlled rotating bending test and its application in the fatigue life estimation of wrought magnesium AZ31B

Abstract

Due to different deformation mechanisms arising from limited slip systems in HCP wrought magnesium alloys, their yield and hardening in tension and compression are different. Consequently, the cyclic behavior of these alloys is asymmetric showing a non-Masing hysteresis. An elastic-plastic method of analysis is proposed in this paper to handle the pronounced asymmetry inherited by Mg wrought alloys. Samples machined from an extrusion piece of AZ31B were tested on a standard rotating bending machine at bending moment amplitudes ranging from 3.3 to 6.3 N m. Tests were conducted under two conditions: as-extruded and stress-relived. As-extruded samples showed a higher fatigue limit due to beneficial residual stresses induced by the extrusion process. The proposed elastic-plastic model was then applied to obtain the stress distribution in the tested specimens. Cyclic hystereses obtained from this analysis were used to estimate the elastic and plastic strain energy densities per cycle. An energy-life model for AZ31B was then employed in conjunction with the calculated hysteresis energies to predict fatigue life of AZ31B in rotating bending. The proposed model prediction results were in good agreement with the experimental results.