In Situ Damage Progression in General Layup Composites

In this- paper, a methodology for progressive matrix cracking-delamination interaction is proposed. Two damage variables and a five-layer equivalent constraint model (ECM) are introduced. After a mesoscopic stress analysis is conducted for the ECM, concepts of continuum damage mechanics are applied to obtain the effective moduli by the approach proposed by Fan and Zhang in 1993. The critical matrix cracking densities at which the transition from matrix cracking to delamination occurs are found to be dependent on the number of plies of the weakest layer and almost independent of the layups. These numerical results of general layups are consistent with those obtained by Nairn and Hu in 1992 for cross-ply laminates. Results also show connections between the calculated energy release rates with the experimental data of the least required energy for damage initiation of T300/976 composite beams.