Fatigue Crack Propagation in Magnesium Alloy AZ31 Rolled Plate
Keiro TOKAJI, Mitsutoshi KAMAKURA, Norihiko HASEGAWA and Yasuki TSUBOI
Abstract:his paper describes the fatigue crack propagation (FCP) characteristics in magnesium alloy AZ31 rolled plate. FCP ex-periments have been performed at stress ratios, R, of 0.05 and 0.7 in laboratory air at ambient temperature using CT specimens with two different orientations of L-T and T-L. The effects of orientation and stress ratio and fracture mechanism were dis-cussed on the basis of crack closure measurement and fracture surface analysis. Regardless of orientation, the relationship be-tween FCP rate and stress intensity factor at R=0.05 consisted of two parts with different slops, which became much more re-markable when FCP rates were characterized in terms of the effective stress intensity factor. This was attributed to fracture mechanism transition because the fracture mechanisms operated were different above and below a stress intensity factor where the slops changed. After allowing for crack closure, a slight difference in FCP behaviour between both orientations and a clear stress ratio dependence of FCP rate were still seen, but these could be due to some problems in measuring crack closure, be-cause fracture mechanism was not affected by orientation and stress ratio. The intrinsic FCP resistance of the present Mg alloy was found to be inferior to that of other materials such as aluminium alloys and pure titanium. Key Words:Fatigue crack propagation, Magnesium alloy, Orientation, Stress ratio, Fracture mechanism