Influence of Cold Expansion and Aggressive Environment on Crack Growth in AA2024-T3

This research aims to establish the effect of hole cold expansion on fatigue life of precracked material under aggressive environments. A relationship between crack propagation and secondary crack initiation was established for AA2024-T3 cold-worked holes subjected to cyclic loads to determine the impact on fatigue life of joints in the presence of saline solution. Galvanic corrosion of a steel fastener/aluminum plate assembly was investigated assuming the presence of cracks in the aluminum plates, whose growth will be monitored in situ with a digital microscope throughout the fatigue process. The cold expansion treatment improved the fatigue life fourfold under a corrosive environment, and 11.3 times in a clean environment when compared to a plain hole. Corrosion revealed the possibility of a location shift in critical stress intensity factor, causing growth of the critical crack to happen outside of the region where the benefits of cold expansion can be achieved. The benefits of cold work expansion could be applied for precracked materials for an improved inspection interval but also calls for reevaluation of the inspection area to prevent secondary crack initiation that could lead to the ultimate failure of the structural component.