Large self-thermal-plastic deformation in a NiTi shape-memory alloy fiber-actuated aluminum metal-matrix composite

The present work reports macroscopic thermal-mechanical and in-situ neutron diffraction measurements from a NiTi fiber-actuated aluminum-matrix composite and homogeneous aluminum control materials. Test specimens were subjected to an initial room-temperature, 5 pct tensile elongation and a subsequent room-temperature-to-393 K unconstrained (external-stress-free) heating process. During the unconstrained heating process, the composite material exhibited a very large (2.2 pct), nonlinear, apparent thermal contraction, while the homogeneous control sample exhibited the expected linear thermal expansion. The large-deformation, self-thermal-plastic behavior of the composite material was clearly the result of a powerful shape-memory response in the NiTi composite fiber actuators.