Multiaxial fatigue of extruded AZ61A magnesium alloy

Strain-controlled multiaxial fatigue experiments were conducted on extruded AZ61A magnesium alloy using thin-walled tubular specimens in ambient air. The experiments included fully reversed tension–compression, cyclic torsion, proportional axial-torsion, and 90° out-of-phase axial-torsion. For the same equivalent strain amplitude, fatigue life under proportional loading was the highest and the nonproportional loading resulted in the shortest fatigue life. Detectable kinks were identified in the strain–life curves for all the loading paths. Fatigue experiments subjected to fully reversed strain-controlled torsion with a static axial load were also conducted. A positive static axial stress reduced the fatigue life and a compressive static axial stress was found to significantly enhance the fatigue life. Two critical plane multiaxial fatigue criteria were evaluated in terms of fatigue life predictions based on the experimental results. The Fatemi–Socie criterion correlated well with the fatigue life in the low-cycle fatigue regime which was characterized by shear cracking. The fatigue life predictions made by the Fatemi–Socie criterion did not agree well with the experimental results in the high-cycle fatigue regime. A modified Smith–Watson–Topper (SWT) criterion was found to be able to predict fatigue lives well for all the loading paths conducted in the current investigation.