SMA-induced snap-through of unsymmetric fiber-reinforced composite laminates

A theory is developed and experiments designed to study the concept of using shape memory alloy (SMA) wires to effect the snap-through of unsymmetric composite laminates. The concept is presented in the context of structural morphing, that is, a structure changing shape to adjust to changing conditions or to change operating characteristics. While the specific problem studied is a simplification, the overall concept is to potentially take advantage of structures which have multiple equilibrium configurations and expend power only to change the structure from one configuration to another rather than to continuously expend power to hold the structure in the changed configuration. The unsymmetric laminate could be the structure itself, or simply part of a structure. Specifically, a theory is presented which allows for the prediction of the moment levels needed to effect the snap-through event. The moment is generated by a force and support arrangement attached to the laminate. A heated SMA wire attached to the supports provides the force. The necessary SMA constitutive behavior and laminate mechanics are presented. To avoid dealing with the heat transfer aspects of the SMA wire, the theory is used to predict snap-through as a function of SMA wire temperature, which can be measured directly. The geometry and force level considerations of the experiment are discussed, and the results of testing four unsymmetric laminates are compared with predictions. Laminate strain levels vs. temperature and the snap-through temperatures are measured for the these laminates. Repeatability of the experimental results is generally good, and the predictions are in reasonable agreement with the measurements.