This chapter deals with quantitative characterization of damage. The objective is to define variables which appropriately and with sufficient accuracy represent damage in composite materials as internal structural rearrangements. For this purpose the mechanisms of damage in composite materials are described and it is argued that the desired representation will be given by vectorial fields or by higher order tensorial fields. For the sake of representing the state of damage, but not its evolution, vectorial fields are considered sufficient and a particular representation is adopted. A continuum damage theory based on thermodynamics with internal variables is then developed. For initially orthotropic composite laminates, stiffness-damage relationships are derived. Evaluation of the phenomenological constants entering the relationships is discussed in detail and ample examples are given to demonstrate the usefulness and accuracy of the method in predicting changes in composite stiffness arising from damage. 1991, Elsevier Inc. All rights reserved.
