Fracture toughness of Ti–15Al–8Nb alloy under mixed mode I/III loading

Fracture toughness of Ti–Al–Nb alloys under mixed mode I/III loading was studied. ► Alloys undergo stress-induced martensitic transformation (SIMT) at four grain sizes. ► Fracture toughness under mixed mode in alloys with SIMT was explored for the first time. ► Fracture toughness under mixed mode loading was higher than that under mode I loading. ► This was due to effect of stress/strain fields ahead of mixed mode crack on martensitic zone. The effect of mixed mode I/III loading on fracture toughness of Ti-15 at.% Al-8 at.% Nb alloy, which undergoes stress-induced martensitic transformation, was investigated for four different grain sizes. The fracture toughness under mixed mode I/III loading was found to be significantly higher than that under mode I loading in all cases. The results were explained on the basis of the stress and strain fields ahead of a mixed mode crack and its influence on the martensitic transformation zone.