Thermomechanical Response of SMA Composite Beams with Embedded Nitinol Wires in an Epoxy Matrix

Nitinol shape memory wires were embedded in epoxy beams to study their thermomechanical behavior in the embedded state. Beams were made with ten wires placed below the geometric mid-plane. A room temperature cure epoxy was used to minimize residual stresses acting on the wires. The beams were placed in an oven and heated from room temperature to a temperature well above the austenitic finish temperature of the wires. The beams were photographed through a window in the oven door at periodic intervals during the experiment. The photographs were analyzed to measure beam deflections during the experiment resulting from thermal and shape memory transformational strains. A beam model was developed and predictions of beam curvature were compared to the experimental data. The results show that agreement between the model and the experimental data is dependent, and extremely sensitive to, an accurate knowledge of the thermomechanical properties of both the nitinol and epoxy phases. Large deflections of the beams were obtained and some evidence of a transformation front propagation from the edges to the center of the beam is shown.