Effect of novel triple twin variant selection on fatigue crack-tip behaivour in Ti alloy

Metals normally deform by plastic deformation mediated by the movement of dislocations. Through additive manufacturing we have developed a novel Ti alloy comprising nano-scale martensite having a unique triple-twinned substructure. Uniquely, this deforms to large strain not by plasticity, but by detwinning as one or more twin variants grow at the expense of the others. So far only the tensile response has been studied but its fatigue response is potentially of great interest. This novel strain hardening mechanism is expected to activate near a fatigue crack tip in a unique way, redistributing stress during fatigue crack propagation, providing exceptional crack propagation resistance. In this proposal we aim to:
• map the crack tip-stress field by high resolution XRD over a fatigue cycle.
• track changes in variant selection (texture) during crack opening and closing,
• quantify the size and shape of the ‘plastic’ zone .
• extract the stress intensity factor directly fro