In situ displacement measurements and numerical predictions of embedded SMA transformation

The transformation behavior of an embedded shape memory alloy (SMA) ribbon was investigated experimentally and numerically. Single SMA ribbons (55% Ni, 45% Ti) were pre-strained to 1% and then embedded in a room-temperature-cured epoxy resin. The embedded ribbons were heated resistively to a temperature above the austenite start temperature to induce transformation. The development of displacements and strains due to transformation were measured in situ using moire interferometry. Analysis of the resulting fringe patterns at steady-state temperature and after cool down indicated that most of the phase transformation in the embedded SMA ribbon was restricted to a region close to the edge of the sample. Numerical simulation of the embedded ribbon was carried out using a fully-coupled thermomechanical SMA constitutive model. Numerical predictions were in good agreement with both the measured displacements and strains in the ribbon and confirmed that only the outer edges of the ribbon transform due to the constraint imposed by the polymer matrix.