Experimental investigation on damage evolution in pre-corroded aluminum alloy 7075-T7651 under fatigue loading

This paper experimentally investigates the fatigue damage evolution in pre-corroded aluminum alloy (AA) 7075-T7651 via digital image correlation (DIC) and scanning electron microscopy (SEM). Three stages of fatigue damage evolution including damage accumulation, macro-crack initiation and propagation are identified and described via the combined analysis of damage severity curves and strain maps. The micro-cracking characteristics in the dominant fracture regions are examined by fractography analysis. The experimental results show that localized corrosion penetrated in the L-S or L-T surfaces promotes fatigue crack initiation, affecting crack nucleation location, cracking path, and is accompanied with quasi-cleavage fracture. Damage evolution and failure progression differed temporally and spatially between specimens for the same loading conditions, due to the stochastic diversity of localized corrosion. Multiple corrosion-induced cracks were observed to initiate and evolve under different loading conditions: three typical failure modes, viz. single crack fracture, multi-crack competition and multi-crack parallel growth, were observed to depend on loading condition and relative location of macro-crack initiation.