Multiaxial fatigue of extruded AZ31B magnesium alloy

Multiaxial fatigue behavior of extruded AZ31B magnesium alloy was experimentally studied in ambient air under strain-controlled axial-torsion loading using tubular specimens. Four fully reversed loading paths were employed: tension–compression, pure torsion, proportional axial-torsion, and 90° out-of-phase nonproportional axial-torsion. Tension–compression asymmetry in cyclic plastic deformation was observed for tension–compression and combined axial-torsion loading. For the same equivalent strain amplitude, the 90° out-of-phase nonproportional loading path resulted in the shortest fatigue life and the proportional loading path produced the longest fatigue life. Two critical plane multiaxial fatigue models, namely, the modified Smith–Watson–Topper (SWT) model and the Jiang multiaxial fatigue criterion, were evaluated based on the experimentally obtained fatigue results. Both models were found to be able to correlate the fatigue experiments reasonably well.