Local displacements and load transfer of shape memory alloys in polymeric matrices

Shape memory alloy (SMA) materials can be embedded in a host matrix to induce active shape control, alter the stiffness, or change the modal response and provide vibration control. The interaction between the SMA and the host material is critical to applications requiring transfer of loads or strain from the SMA to the host. Although there has been a significant amount of research dedicated to the characterizing and modeling of SMAs alone, little research has been focused on the transformation behavior of embedded SMAs. The phase transformation in an SMA is a function of both stress and temperature. Since an SMA in a composite is subject to a complex stress field by the surrounding matrix, the embedded behavior is significantly different from that of a free SMA. Various experimental techniques were utilized to obtain insight into the behavior of embedded SMAs and to provide quantitative data for evaluation of theoretical models.; Average interfacial bond strength between an embedded SMA and an epoxy matrix were measured using pullout tests. The effects of various mechanical and chemical surface treatments on the bond strengths were examined. In-situ out-of-plane displacements of two-way trained SMA wires in epoxy were measured using heterodyne microinterferometry. The interfacial bond strengths from the pullout tests were correlated with the maximum wire displacements. The transient load transfer behavior of a one-way SMA ribbon in a room temperature cured polymer matrix was quantified using two-dimensional photoelasticity. The effects of residual stress were examined using high temperature cured matrices. In-plane displacements of room temperature cured SMA ribbon composites were obtained using moire interferometry. Displacements due to thermal expansion were separated from displacements due to SMA actuation. An experimental value for the velocity of propagation of the SMA actuation front was calculated. A finite element model based on one-dimensional constitutive equations was developed for ribbon composites. Displacements and stresses in the ribbon were compared with experimental values.