Experimental Investigation of Modes II and III Fatigue Crack Growth in Unalloyed Titanium

The study is focused on finding and describing microscopic paths of modes II and III cracks in commercially pure alpha-titanium (hcp structure). Experiments were done on cylindrical bars with a circumferential cracked notch loaded in shear (modes II, III and II + III) and torsion (mode III). Fractography analysis showed that the crack growth was crystallography-controlled and the deflection and twisting angles of crack propagation direction (with respect to the shear plane) were relatively high. This behavior is a mixture of previously observed morphology in ARMCO iron (bcc) and austenitic steel (fcc). It can be understood in terms of a number of available slip systems in bcc, fcc and hcp lattices.