Large strain micromechanics of thermoplastic elastomers with random microstructures

Thermoplastic polyurethanes (TPU) are block copolymeric materials composed of plastomeric "hard" and elastomeric "soft" domains, by which they exhibit highly resilient yet dissipative large deformation features depending on volume fractions and microstructures of the two distinct domains. In this work, we present a new methodology to address the microscopic deformation mechanisms in TPU materials with highly disordered microstructures. We propose new micromechanical models for randomly dispersed (or occluded) as well as randomly continuous hard domains, each within a continuous soft structure as widely found in representative TPU materials over a wide range of volume fractions of hard and soft components. The micromechanical modeling results are compared to experimental data on the macroscopic large strain behaviors reported in our prior work (Cho et al., Polymer, 128 (16), 2017; https://doi.org/10.1016/j.polymer.2017.08.065). We explore the role of the dispersed vs. continuous nature of the geometric and topological features of the random microstructures on shape recovery and energy dissipation at the microstructural level in this important class of phase-separated copolymeric materials.