Effect of plate thickness on the environmental fatigue crack growth behavior of AA7085-T7451

•Plate thickness dependent fatigue behavior of 7085-T7451 is quantified.•Crack propagation likely follows precipitate free zones formed in the thicker plate.•Growth rates are slower in thick plate materials for various loading environments.•At low R, crack closure governs changes in growth rates.•At high R, crack path tortuosity and branching governs changes in growth rates.

Fatigue crack growth rates (L–T) for 102 and 178 mm plates of 7085-T7451 are established at R = 0.1 and 0.5 for a wide-range of ΔK and environments. At R of 0.1, the 178 mm plate exhibits slower crack growth rates independent of environment. The crack growth trends correlate with changes in the fracture surface roughness and compliance-based closure indications, suggesting a dominant role of roughness induced closure. At R of 0.5 compliance-based metrics indicate that minimal closure exists, but plate thickness dependent crack growth behavior persists; grain-scale crack path tortuosity and crack branching govern this behavior. Increased crack path roughness, tortuosity, and branching in the 178 mm plate is attributed to strain localization/cracking along precipitate free zones formed in the thicker plate due to a slower quench rate.