Large Deformation Thermal-Plasticity in a Shape Active Aluminum Metal Matrix Composite

The present work reports macroscopic thermal mechanical and in-situ neutron diffraction measurements from a 14.4 volume percent, 50.7 at% Ni-Ti fiber actuated 6082-T4 aluminum matrix composite and 6082-T4 homogeneous aluminum control material subjected to a room temperature 5% tensile elongation, and subsequent room temperature to 120 deg. C unconstrained heating process. During the unconstrained room temperature to 120 deg. C heating process, the composite exhibited a 2.2%, nonlinear thermal contraction, while the homogeneous control exhibited the expected linear thermal expansion. The composite thermal compression was clearly the result of a powerful shape memory response in the actuating NiTi fibers. During a subsequent temperature hold at 120 deg. C the composite exhibited an external stress free compressive creep response. The compressive creep behavior was the result of matrix creep under the large compressive stresses imposed by the shape memory active NiTi fibers. In summary, the experimental composite has demonstrated a new form of large deformation self thermal-plastic response which may be used in thermally controlled adaptive machine parts and structures.