An analysis of fatigue crack features at various crack lengths through mating fracture surface pairs.

This paper presents a novel high‐resolution direct analysis of mating AA7050‐T7451 fracture surfaces at crack lengths from 0.1 to 1.3 mm (Kmax of 4.51 to 16.39 MPa√m) for the purpose of analyzing the fatigue growth mechanisms. The various fractographic features observed at these crack lengths were then compared to the known accelerative effects of an applied loading sequence that contained underloads at regular intervals. A correlation was found between some of the observed features and the local fatigue crack growth rate. This study provides new insight into the prominent mechanisms that dictate crack growth rate and ultimately should assist with developing crack growth prediction methods that more accurately represent the physics of the fatigue crack growth mechanisms. Highlights: Mating fatigue surfaces are compared at high resolution in AA7050‐T7451.Striation features are shown to significantly differ on mating surfaces.Fissuring from underloads is found to occur at all investigated crack lengths.This fissuring may be mechanistically linked to underload acceleration effects. [ABSTRACT FROM AUTHOR]