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 a lloys (SMAs) with a macrocrack under mixed mode loads. The asymptotic analy sis of the stress field and the derivation of the two-dimensional weight fu nction for the semi-infinite crack in isotropic SMAs are investigated. The transformation boundaries for static crack and steady advanced crack are de termined. The toughening mechanism due to martensite transformation of SMAs is also studied on the basis of the Eshelby inclusion method and weight fu nction method. The results show that, for the mixed mode problem, the bound aries of the transformation zone is not symmetric and depend on the applied remote load field phase angle. Instead of stress intensity factors, the en ergy release rate and load phase angle are used for the analysis. It is fou nd that the crack flanks may be closed owing to the martensite transformati on near the crack tip when the remote load phase angle is small. The analyt ical 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.