A phenomenological model to simulate various aspects of nonlinearity in creep behavior and to predict long-term creep strain

Abstract

In the present work, a thorough description of the creep response of polymers in both linear and nonlinear viscoelastic domains is presented. According to the proposed model, the polymeric structure is considered as an ensemble of meso-regions linked with each other while they can cooperatively relax and change their positions. Each meso-region has its own energy barrier that needs to be overcome for a transition to occur. It was found that the distribution function, followed by the energy barriers, attains a decisive role, given that it is associated with the distribution of retardation times and with their particular effect on the materials’ time evolution. The crucial role of the imposed stress in a creep experiment by its influence on the retardation time spectrum of the polymeric structure was extensively analyzed. The proposed model has been successfully validated by a series of creep data in a variety of temperatures and stress levels for polymeric materials, studied experimentally elsewhere. Furthermore, the model’s capability to predict the long-term creep response was analytically shown.