Swelling and mechanical stretching of elastomeric materials

The equilibrium stress-stretch behavior of elastomeric materials can be captured by statistical mechanics treatments of rubber elasticity. Gaussian statistics is known to capture the essence of the stress-strain behavior; however, discrepancies between Gaussian theory and experiment are recognized to occur at both small to moderate stretch levels and at large stretch levels. These discrepancies are further amplified in studies of the effects of swelling on stress-stretch behavior. A brief review of the various approaches used to represent the stress-stretch behavior of elastomers and the effect of swelling on this behavior is given. Then, a hybrid constitutive model composed of the Flory-Erman constrained chain model and the Arruda-Boyce non-Gaussian eight-chain model is presented and found to capture the stress-stretch behavior from small to large stretch levels. Furthermore, the Flory-Erinan/Arruda-Boyce hybrid model is also found to successfully predict the effect of swelling on the stress-stretch behavior from small to large stretches using only three material constants.