Impact of alternating corrosion and fatigue on the fatigue life of a 7475-T7351 aluminum alloy in an aircraft beam structure

This study compares the fatigue life of a 7475-T7351 aluminum alloy lower wall plate in an aircraft beam structure under alternating corrosion and fatigue conditions to universal fatigue life. It incorporates a corrosive environment and variable amplitude fatigue loads. The current study uses the "beach marking" technique and visual inspection to monitor crack propagation and evaluate the corrosive environment's impact on fatigue life and damage tolerance. The experimental results indicate that during the fatigue crack initiation and penetration stages, the corrosion environment does not significantly impact the fatigue life of the beam structure because of the protection from uniform oxide films, epoxy primer, and sealants at joints. In the crack propagation stage, the corrosive environment speeds up crack growth compared to universal fatigue tests. Additionally, a "hysteresis effect" in alternating corrosion and fatigue tests shows the fatigue crack growth rate changing discontinuously, caused mainly by corrosion dissolving slip bands at the crack tip. Altogether, this study provides new insights into the influence of alternating corrosion and variable amplitude load on an aircraft beam structure's fatigue life and damage tolerance.