Low-Cycle Fatigue Deformation Behavior and Evaluation of Fatigue Life on Extruded Magnesium Alloys

Abstract

Extruded magnesium alloy shows a strong anisotropy of mechanical properties, which is caused by both of a crystallographic nature in hexagonal close packed lattice structure and a fiber texture with basal plane aligned parallel to the extruded direction by mechanical processing. To evaluate fatigue deformation behavior and fatigue life of extruded magnesium alloys, total strain-controlled and stress-controlled low-cycle fatigue test of three extruded magnesium alloys, AZ31, AZ61 and AZ80, were performed in ambient atmosphere at room temperature using smooth round bar specimen. Mean tensile stress during the total strain-controlled fatigue process and mean compressive strain during the stress-controlled fatigue process appeared due to the difference between tensile yield stress and compressive one, which resulted in mechanical twinning in the compressive phase. Fatigue criteria proposed previously considering the mean stress effect were evaluated in terms of fatigue life predictions based on the experimental results. Also, an energy-based model taken into account of plastic and elastic energy density was discussed to predict the fatigue lives obtained from the total strain-and the stress-controlled fatigue experiments.

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

“…They attributed the variation of stress and strain amplitudes to the anisotropy and asymmetry of AZ31B and concluded that energy is a suitable fatigue parameter. Shiozawa et al [9] performed stress-and strain-controlled tests on AZ31B. Similarly to Park et al [8], they showed that an energybased fatigue parameter shows a very good correlation with the experimental results.…”

A phenomenological stress–strain model for wrought magnesium alloys under elastoplastic strain-controlled variable amplitude loading

“…(10)), also called total strain energy density, was used [20,22,26,29,30]. The combined strain energy density DW comb(t) (Eq.…”

“…A comprehensive summary of fatigue investigations on wrought magnesium alloys is given in [30]. Accordingly, most low-cycle fatigue investigations [9,[14][15][16][17][18][19][20][21][22][23] were done using completely reversed strain-controlled conditions, and in [24][25][26][27][28][29][30] the influence of the strain ratio was considered. The Manson-Coffin-Basquin approach [31][32][33] was found to show an adequate correlation with the experiments for completely reversed strain-controlled conditions (e.g.…”

“…[9,[15][16][17][18][19]23]). In addition, energy based fatigue models were shown to give good correlation in cases of variable strain or stress ratios [20,22,26,29,30]. http Zenner and Renner [34] analyzed the shape of hysteresis loops at variable amplitude loading and showed that different magnesium alloys exhibit material memory.…”

“…In most previous studies, the experimentally determined hysteresis loops were used to obtain the necessary values (e.g. [14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30]), which is not practicable in an engineering fatigue analysis. Therefore, the shape of stress-strain hysteresis loops must be described with an efficient model.…”