An experimental and modeling investigation of the external strain, internal stress and fiber phase transformation behavior of a NiTi actuated aluminum metal matrix composite

The present work reports macroscopic thermal mechanical and in-situ neutron diffraction measurements from 22.9 vol.%, 50.7 at.% Ni-Ti fiber actuated 6082-T6 aluminum matrix composite and 6082-T6 homogeneous aluminum control materials subjected to a room temperature 4% tensile elongation, a subsequent room temperature to 120 degrees C unconstrained heating process, and a final 120 degrees C tensile process. During the unconstrained room temperature to 120 degrees C heating process, the composite exhibited a pronounced, nonlinear thermal contraction, while the homogeneous control exhibited the expected linear thermal expansion. The composite thermal contraction was clearly the result of a powerful shape memory response in the actuating NiTi fibers. The paper further presents a one-dimensional thermal strain, internal stress and fiber phase transformation composite model. Model parameters were identified from tests on extracted single fibers, calculations using these parameters quantitatively agree with experimental thermal mechanical and neutron diffraction measurements.