Some effects of viscoelasticity on ability to model failure in composites

Abstract

The classical approach to modelling the thermomechanical response of composites employs a framework embodied within the concept of continuum mechanics. This approach may not always lead to success in that some failure mechanisms such as molecular scale phenomena may not be accurately captured by the continuum approximation. On the other hand, the continuum approach may be quite powerful and accurate for predicting failure in a variety of circumstances. For any continuum mechanics based approach to have hope of accuracy it is, however, necessary for that model to in some sense capture the physics of all of the cogent energy dissipative processes that are engendered in the actual application. The current paper takes the approach that failure due to fracture in viscoelastic composites can indeed be modelled entirely within the framework of continuum mechanics, but that in order to accurately predict failure due to fracture it is often necessary to deploy a model that is simultaneously cast within multiple length scales, each using the framework of continuum mechanics. This approach is taken for the simple reason that experimental observation suggests that in viscoelastic composites cracks form on the microscale, and these cracks eventually coalesce into macroscale cracks that cause the part to fail due to catastrophic facture. While predictions of these events may seem extraordinarily costly and complex, there are multiple structural applications where effective models would save considerable expense. The formulation for such an approach will be presented herein. This approach has been implemented into a finite element code and some example problems will be given in order to demonstrate the capabilities of the method.