Fracture toughness and SCC behavior of 7075 aluminum alloy under mixed-mode I-II loading
Ohsaki Shuhei; Utsue Masaki; Yokofujita Hisashi; Iino Makio
Abstract:Under mode I, II and mixed-mode I-II loading, the fracture toughness and SCC response of aluminum alloy 7075-T6 plate have been studied in the S-L and L-S orientations. The fracture toughness in S-L under mixed-mode loading coincides with K1C for K2/K1 less than l and K2C for K2/K1 greater than 1, where K1C and K2C are the fracture toughness under mode I and mode II respectively, and K2/K1 is the stress intensity ratio. The former fracture occurs due to a preferential intergranular delamination controlled by a normal stress component on grain boundaries, while the latter fracture proceeds in a transgranular shear mode. The SCC growth rate under the mixed-mode loading decreases with an increase of K2 component, and under the pure mode II loading SCC growth becomes more difficult. Based on the experimental results and discussions of stress-induced hydrogen accumulation at crack tip the intergranular SCC of 7075-T6 can assumed principally controlled by hydrogen embrittlement, and an anodic dissolution reaction involved in the mode II SCC process plays an assisting role in lamellar crack joining in transgranular fracture. Key Words:mixed-mode I-II, aluminum alloy, 7075, fracture toughness, SCC, hydrogen embrittlement