Network Evolution in Elastomers at Large Deformations and Elevated Temperatures: Experiments and Modeling

An overview is presented of a study of network evolution in elastomers due to scission and crosslinking at elevated temperature (90 to 150^oC for natural rubber) and large deformations. Experiments were performed on natural rubber specimens that exhibit finite elasticity, entropic stiffening with temperature, viscoelasticity, scission and oxygen diffusion/ reaction effects. Single-step and two-step uniaxial deformations and biaxial stretch using membrane inflation were used to determine the decrease of original network due to scission, the formation of new networks due to crosslinking and increasing permanent set. A three dimensional constitutive model is formulated based on a multi-network framework that extends previous work to account for kinetics of scission and crosslinking, arbitrary deformations and time-varying temperature histories and incorporates the effects of viscoelastic relaxation and diffusion limited oxidative scission. The model is calibrated to experiments performed on commercially available filled natural rubber material. Numerical simulations compare favorably to experiments for a variety of temperature histories. An example illustrates the use of the model to predict the lifetime of an elastomeric seal.