On the fracture toughness enhancement due to stress-induced phase transformation in shape memory alloys

A finite element analysis is carried out to model quasi-static stable crack growth in shape memory alloys under plane strain, mode I loading. The small scale transformation assumption is employed in the calculations using displacement boundary conditions on a circular region that encloses the stress-induced phase transformation zone. The crack is assumed to propagate in the region of elastically-deformed, fully-transformed martensitic zone ahead of the crack tip with the crack-tip energy release rate maintained at a critical value and the analysis is accomplished using the virtual crack closure technique. Results pertaining to the influence of stress-induced phase transformation on the near-tip mechanical fields and the ratio of the far-field energy release rate to the crack-tip energy release rate are presented, showing fracture toughness enhancement in accordance with experimental observations. Moreover, the effect of plastic dissipation on the fracture resistance of SMAs is discussed.