Abstract:The fracture behavior and micro-mechanism of aluminum alloy were investigated experimentally under different mixed mode loadings in different processes of heat-treatment (quenching(LY12-CZ) and annealing (LY12-M)) materials. Under modeⅠloading, the fracture behavior and micro-mechanism of the above two materials coincided with those of typical ductile fracture. Under modeⅡloading or near modeⅡ loading, the differences between fracture behavior and micro-mechanism of the two materials were outstanding. The fracture of the material LY12-CZ was initiated and propagated under the control of maximum tensile stress, and that of the material LY12-M was also initiated under the control of maximum tensile stress, but propagated under the control of maximum shear stress. In all mechanical parameters of ductile material, the strain hardening indexnis the main factor controlling the transformation of fracture mechanism with the loading condition varied from modeⅠto modeⅡ.

Key words: mixed mode fracture　fracture mechanism　shearing yield　strain hardening index