Rate-dependent compressive behavior of EPDM insulation: Experimental and constitutive analysis

To fully characterize the compressive behavior of ethylene propylene diene monomer (EPDM), quasi-static and dynamic compression experiments were conducted for EPDM with a universal testing machine and split Hopkinson bar (SHPB), respectively. Dynamic experimental data employing the two-wave method were used to obtain the stress-strain curves, and the dynamic results were validated. The polymer was compressed under different strain rates varying from 10−4 to 103. The results indicate that the mechanical properties of EPDM insulation are obviously dependent on the strain rate. An improved Zhu-Wang-Tang (ZWT) nonlinear visco-hyperelastic constitutive model, in which the standard elastic component was replaced by the Mooney-Rivlin hyperelastic model, was developed to predict the mechanical behaviors of EPDM under quasi-static and dynamic impact loading. The model parameters were determined by fitting the model to the experimentally obtained curves by means of the least squares method. The stress-strain curves obtained from the improved ZWT model show good agreement with the experimental curves. This research will further improve the design of the internal insulation structure in solid rocket motors.