Crystallographic Fatigue Crack Growth in Aluminum Single Crystals

摘要

Single crystals of aluminum were fatigued in cantilever bending to produce many Stage I (crystallographic) fatigue cracks along parallel (111) slip planes. The average rate of crack growth was measured as a function of the strain-intensity factor in both vacuum and humid air (81% RH). Three-dimensional replicas of Stage I cracks were examined by SEM and found to be very complex in morphology with many small secondary cracks branching from the primary cracks produced in air but not from those produced in vacuum. Environmentally assisted cleavage along these secondary cracking planes is thought to account for their formation in air. The secondary cracks subsequently 'blunt' the stress-intensity at the tip of the primary crack and retard its growth. (Author)