Modelling crack propagation during relaxation of viscoelastic material

Abstract

A viscoelastic material which is stretched and is then held at constant elongation, normally results in decreasing stresses till the equilibrium has been reached. With the decreasing stresses a crack propagation is not expected as the energy of the system is decreasing. However, an initial damage could lead to an increase in the mechanical load on the undamaged chains during relaxation, leading to material degradation and crack propagation. While experimental investigations have been presented in the literature, modelling such an effect has not been thoroughly investigated. In this work, an initial framework for modelling the damage evolution during relaxation is presented. A mechanical model is coupled with a phase field to model the crack propagation. For simplicity, a linear viscoelastic model is implemented for the mechanical part. A mobility constant is employed to model the evolution of the phase field with the changing mechanical energy during relaxation. The evolution of phase field can be interpreted as the evolution with which the polymer chains get damaged. Different load conditions and geometries are simulated, which shows that the proposed framework is able to model the damage evolution during viscoelastic relaxation. Thus, with the help of the numerical model a physical explanation for the failure during relaxation is presented.