A Macro-Mechanical Study for Capturing the Dynamic Behaviors of a Rate-Dependent Elastomer and Clarifying the Energy Dissipation Mechanisms at Various Strain Rates

A strain-rate-sensitive polyurethane elastomer is numerically investigated to reveal improved impact characteristics and analyze the concerned rate dependencies and dynamic energy dissipation features. A physical constitutive model in view of amorphous molecular structure of the elastomer is proposed by relating the macro-mechanical behaviors to micro-structural changes through molecular transitions and flow activations. Two distinct relaxation processes are considered because of entangled molecular networks, with each possessing a unique activation energy. Through calibration with experimental data, finite element simulations based on the model are conducted. Related to the loading rate, the structural entropy of molecular chain entanglements, rate-dependent yielding, plateau flow and densification are well predicted by the model. The investigations are extended further regarding the material recoverability and accordingly, strain energy absorptions are illustrated. A power law function is proposed for designing the energy absorption relation to the applied loading rate. Finally, the inherent mechanisms causing the dynamic energy absorptions are analyzed with notable clarifications of post-experimental observations obtained via scanning electron microscopy.