A Coupled Viscoelasticity/Damage Model with Application to Swirl-Mat Composites

A comprehensive thermodynamics framework is proposed for modeling the continuum damage behavior of viscoelastic materials. The thermodynamic framework is formulated in a general form that accounts for the possibility of a permanent deformation component in the behavior. Therefore, the total strain is decomposed into viscoelastic and permanent components. The effect of damage on the constitutive behavior is introduced through direct coupling between damage and the internal state variables representing deformation of the undamaged (virgin) material. This approach accounts for time-dependent damage as well as damage-induced changes in material symmetry. The proposed viscoelastic constitutive model is formulated for the case of damage coupled with linear viscoelasticity and is applied to experimental data for swirl-mat polymeric composites.