Al–Li系合金の破壊靭性–破壊形態–引張特性の関係

抄録

Uniaxial tensile property and plane strain fracture toughness K_IVj of Al–Li alloys 2090, 2091 and 8090 were examined as functions of aging condition and plate orientation. Each relation between K_IVj and yield strength is presented separately with respect to the short-transverse (S) direction and the longitudinal (L) direction of a plate. The superior combination of strength and toughness in the L–T orientation compared with the S–L orientation is produced by transgranular fracture (TGF) and an effect of crack-divider delamination, where T designates the long-transverse direction. The fracture surface profiles in the S–L specimens were measured with a laser focus-displacement instrument to analyze the area fractions, f_i and f_t corresponding to IGF (intergranular fracture) and TGF, respectively. The fracture toughness evaluated by relating f_i and f_t with the fracture strain energy density in the tensile test is found to be in a good correlation with the measured K_IVj. It is supported that the fracture in the Al–Li alloys occurs in terms of the characteristic distance ahead of crack, comparable with the mean spacing of coarse inclusion particles.