- Springer Science+Business Media, LLC 2012. All rights reserved. Damage treated here is a multitude of surfaces formed within a composite that permanently change its response to external impulses. Examples of such damage are matrix cracking at different scales, fiber breakage, fiber/matrix debonding, and interply cracking (delamination). The response affected could be mechanical (stiffness properties), thermal (expansion and conductivity), time-dependent (viscoelastic), and in general any that is sensitive to the presence of internal surfaces. The representation of damage is by internal variables and the response functions are formulated in a thermodynamics framework. Although specific cases considered here are composite laminates with multiple sets of intralaminar cracks, the formulation has sufficient generality to treat other composite configurations and other energy-dissipating mechanisms such as thermal oxidation and radiation-induced morphological changes in polymers.