A State-of-Ease Analysis of Shape Memory Elastomers

A state-of-ease model is developed to predict the time-dependent mechanical behavior of a shape memory elastomer. The model assumes continuous mechanical equilibrium between applied stress and stresses of entropic origin arising from a permanent network and a second, independent network composed of reversible bonds. Bonds forming the reversible network are assumed to rearrange at a constant rate, and newly formed bonds are created in a stress-free state. This gives rise to a time-dependent distribution of bond ages and corresponding stresses, and both are accounted for in the model using a delay integral approach. The model is capable of describing creep, stress relaxation, and shape memory responses. The model will be fit to experimental data for a poly(butyl acrylate) shape memory elastomer, and results will be compared to a simpler dashpot-spring model.