FRACTURE-TOUGHNESS OF QUATERNARY AL-LI-CU-MG ALLOY UNDER MODE-I, MODE-II, AND MODE-III LOADING CONDITIONS

The fracture toughness under mode I, mode II, and mode III loading con ditions was evaluated for a quaternary 8090 Al-Li-Cu-Mg alloy in under aged and peak-aged conditions. The effect of aging was found to be sig nificantly different for different loading conditions. The alloy in th e underaged (T3) condition exhibited minimum fracture toughness under mode II loading, whereas mode I fracture toughness was the lowest in t he case of the peak-aged (T8E51)condition. Significant anisotropy in t he fracture resistance is observed only in case of the peakaged alloy under mode I loading, whereas in all other cases, the fracture resista nce is found to be isotropic. The fracture mode was transgranular shea r in all three modes of loading in the underaged condition as well as under mode II and mode III loading in the peak-aged condition. The all oy exhibited ductile intergranular fracture under mode I loading in th e peak-aged condition. The results obtained are explained on the basis of these dominant fracture mechanisms prevalent under different loadi ng conditions.