A composite approach for modeling deformation behaviors of thermoplastic polyurethane considering soft-hard domains transformation

Thermoplastic polyurethane elastomers (TPUs) are the most used engineering thermoplastics combining the properties for both elastomers and glassy materials. TPUs have good physical and mechanical properties, excellent chemical and abrasion resistances. Compared with typical thermoset rubbers, TPUs are easier to be processed and recycled. However, the deformation behaviors of TPUs are very complex due to their nonlinear, hysteresis, rate and temperature dependences, and softening properties. Therefore, development of a constitutive model with microstructure considerations is important for predicting the deformation behavior of TPUs under mechanical loading as well as during forming processes such as rolling and stretching. In this work, TPUs were taken as a two-phase material consisting of both hard and soft phases corresponding to their hard and soft domains. A new composite constitutive model for stress-strain response of TPUs was proposed taking into account the microstructure of TPUs as well as its evolution (hard to soft phase transformation) induced by deformation. Excellent agreement between model predictions and experimental results for the loading-unloading behaviors of two TPUs with different hard and soft segment contents confirmed the efficacy of our proposed composite constitutive model.