ABSTRACT
Recently, the idea of using composite fibers or particles of shape memory alloy (SMA) to arrest crack propagation in brittle materials or to repair cracks in metals has gained widespread attention. The concept of an intelligent material that uses shape memory and the super elastic properties of SMA activated in response to thermo-elastic transformation is analogous to the concept of reactive adaptivity in a biological system. The desired functions could be manifested through two mechanisms. One promotes the induced transformation of these fibers or particles of SMA in the stress field generated near the tip of a crack that propagates in a material. This mechanism exploits the stress release effects due to the volumetric change at the point of transformation.The other mechanism uses the compressive residual stress produced at the interface of the fibers or particles and matrix during preliminary shape memory processing to reduce the stress field near the crack tip. The former mechanism of arresting crack propagation of using the volumetric changes of dispersed particles by the phase transformation has already been realized in partially stabilized Zr02 and Zr02 reinforced ceramics. [l]-[3] Due to the unique characteristics of SMA, it is possible to create materials with new functions: -The transformation temperature can be tightly controlled by varying the composition. -The effects of residual stress can be controlled by memory processing using a small to large pre-strain.
