FRACTURE-BEHAVIOR OF QUATERNARY AL-LI-CU-MG ALLOY UNDER MIXED-MODE I III LOADING/

The fracture toughness under mixed-mode I/III loading conditions was e valuated for a quaternary 8090 Al-Li-Cu-Mg alloy in underaged and peak -aged conditions. The mixed-mode fracture behavior was found to be sig nificantly different for the two aging conditions. Super-imposed mode III component lowered the fracture resistance of the alloy in underage d condition, whereas it had no significant effect in peak-aged conditi on. The results obtained have been discussed in the light of the preva lent fracture processes, namely, transgranular shear and ductile inter granular fracture mechanisms. Further, these results are analyzed in t erms of different fracture criteria and they were found to deviate sig nificantly from those predicted by the energy release rate criterion.