Viscoelastic Behavior of Composites
A purely elastic material (for example, Hookean solid) differs widely in its deformational characteristics from a purely viscous material (for example, Newtonian fluid). The stress in a purely elastic material is a function only of the instantaneous magnitude of deformation (strain) whereas in a purely viscous material, the stress is a function only of the instantaneous rate of deformation. Also, purely elastic materials return to their natural or undeformed state upon removal of applied loads whereas purely viscous materials possess no tendency at all for deformational recovery. The term “viscoelastic” implies the simultaneous existence of viscous and elastic characteristics in a material. Thus, a material behavior that incorporates a blend of both viscous and elastic characteristics is called viscoelastic behavior.