Deformation behavior of NiTi/polymer shape memory alloy composites - Experimental verifications

Composites containing NiTi shape memory alloy (SMA) long-fiber, short-fibers or Ti long-fiber in a Polycarbonate (PC) matrix have been fabricated by the injection molding technique. Also, prestrained SMA long-fiber/Epoxy matrix composites have been fabricated. The fracture behavior and thermo-mechanical deformation behavior are examined; (1) Fracture behavior - uniaxial tensile tests up to fracture for SMA long-fiber and short-fiber composite (SMAC). (2) Thermo-mechanical deformation behavior - tensile loading-unloading tests for Pseudoelastic (PE) long-fiber/PC matrix composites. Several thermo-mechanical loading tests for Shape Memory Effect (SME) long-fiber/PC matrix and SME long-fiber/Epoxy matrix composites were used. The obtained results are as follows: (1) The stress-strain relation up to the final fracture of the Shape Memory Alloy Composites (SMACs) showed the repeated up-and-down of the stress which corresponds to the necking of the specimen, fiber fracture, and matrix fracture. The strain for the initiation of necking and the strain for the fiber or matrix fracture in the SMACs were higher than those in the Ti composite. This is attributed to the unique stress-strain relations accompanied by the stress-induced martensitic transformation of the SMA fibers. (2) The SMAC containing PE fiber and PC exhibited the pseudoelastic-like deformation under tensile loading-unloading. (3) The SMAC containing SME fiber and PC exhibited the large contraction by heating after tensile loading-unloading, but the compressive residual stress in the matrix expected in this process was not remarkable. However, compressive residual stress in the matrix may become greater by embedding prestrained fiber in the matrix.