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 ne utron diffraction measurements from 22.9 vol.%, 50.7 at.% Ni-Ti fiber actuated 6082-T6 aluminum matrix composite and 6082-T6 homogeneous alu minum control materials subjected to a room temperature 4% tensile elo ngation, 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 expansi on. The composite thermal contraction was clearly the result of a powe rful shape memory response in the actuating NiTi fibers. The paper fur ther presents a one-dimensional thermal strain, internal stress and fi ber phase transformation composite model. Model parameters were identi fied from tests on extracted single fibers, calculations using these p arameters quantitatively agree with experimental thermal mechanical an d neutron diffraction measurements.