Correlation of slip behavior, strain evolution and fatigue crack growth retardation

To evaluate the intrinsic mechanisms underlying fatigue crack growth retardation behavior, crack initiation and early growth behavior at the notch were monitored using in-situ SEM in a magnesium alloy. The evolution of crack-tip plastic strain and the associated microstructural damage were quantitatively characterized by EBSD and DIC. Results demonstrate that the crack growth rate followed a V-shaped pattern of decreasing before increasing, which could be correlated with strain field and slip activation. The strain decreasing zone was found originated from dynamic transfer of compressive strain near the crack-tip, while the strain appeared a positive correlation with fatigue crack growth rate in both retardation and recovery regimes. Both the retardation and recovery processes were grain orientation dependent, and the transition to recovery was assisted by the enhanced basal slip transfer. The findings offer a novel perspective on transient cracking behavior, guiding the fatigue-resistant design of magnesium alloys.