Damage in composite laminates with off-axis plies

Damage in off-axis Flies of composite laminates is studied by examining the configuration [0/ +/- theta(4)/0(1/2)], with theta = 25, 40, 55, 70 and 90 subjected to tensile loading in the axial direction. It is found that for the values of theta, where the stress in the off-axis plies normal to the f ibers is tensile, ply cracks lying along fibers initiate and increase in nu mber, while for other theta values the plies do not undergo this damage, as expected. However, the overall laminate elastic moduli are also found to c hange for the a values where no ply cracks exist. It is postulated that a s hear-induced degradation of the off-axis plies is responsible for the obser ved laminate moduli changes. The prediction of changes in these moduli by u sing the ply shear modules measured on [+/-theta(4)](s) appears to support this postulate. For the case of moduli changes caused by ply cracks the rec ently proposed synergistic damage-mechanics approach [1] is applied. The im plications of the findings of this work on a class of continuum damage-mech anics formulations proposed in the literature are discussed. (C) 1999 Elsev ier Science Ltd. All rights reserved.