Experimental and theoretical study of the peculiarities of the thermo‐mechanical behavior of semicrystalline polymers

A mathematical model for semicrystalline polymers is proposed to predict the specific features of thermal and deformation phenomena, which are realized in the processes of phase (crystallization) and relaxation (glassy‐type) transitions. To describe deformation phenomena, constitutive equations for evolution of the stress–strain state have been constructed within the framework of the phenomenological theory of continuum mechanics. The equations take into account the influence of phase and relaxation transitions on deformation processes. The polymeric material is approximated as a continuum consisting of two components, one representing the amorphous state of the material and the other the crystalline state of the material. Numerical experiments have indicated that the system of constitutive equations describes the peculiarities of the thermomechanical behavior of semicrystalline polymers in a broad temperature range that includes high elasticity, glass transition, and crystallization intervals. Based on the obtained results, a program for physical thermomechanical experiments has been developed which makes it possible to find the parameters of constitutive equations. In the experiments, two types of polymers exhibiting the characteristic behavior of semicrystalline materials, namely high‐pressure polyethylene (HPPE) with a crystalline phase content of 50% and polyamide PA‐6, were investigated. POLYM. COMPOS., 36:1055–1062, 2015. © 2015 Society of Plastics Engineers