Fracture toughening mechanism of shape memory alloys under mixed-mode loading due to martensite transformation

This paper is devoted to the fracture toughening analysis of shape memory alloys (SMAs) with a macrocrack under mixed mode loads. The asymptotic analysis of the stress field and the derivation of the two-dimensional weight function for the semi-infinite crack in isotropic SMAs are investigated. The transformation boundaries for static crack and steady advanced crack are determined. The toughening mechanism due to martensite transformation of SMAs is also studied on the basis of the Eshelby inclusion method and weight function method. The results show that, for the mixed mode problem, the boundaries of the transformation zone is not symmetric and depend on the applied remote load field phase angle. Instead of stress intensity factors, the energy release rate and load phase angle are used for the analysis. It is found that the crack flanks may be closed owing to the martensite transformation near the crack tip when the remote load phase angle is small. The analytical results also show that the martensite transformation reduces the crack tip energy release rate and increases the toughness. The toughness of SMAs is enhanced by the transformation strain, which tends to limit or prevents crack advancing. (C) 2001 Elsevier Science Ltd. All rights reserved.