Assessing delamination initiation of angle-ply laminates from fiber and matrix properties

As a laminate is essentially bonded together from laminae by the matrix, any delamination of it must be initiated from a matrix failure. This article predicts the initiation of a laminate delamination through analyzing the matrix failure. A three-dimensional finite element approach is used to calculate the stress field of an angle-plied laminate under a uniaxial tension. The stresses in each lamina of the laminate are averaged with respect to the lamina thickness to eliminate a weak singularity near a free edge. Homogenized stresses in the matrix are then obtained through bridging model, which are further converted into true values by virtue of stress concentration factors of the matrix in the composite. Influence of any interface crack between the fiber and the matrix on the true stresses has been taken into account. A criterion for detecting the delamination initiation is proposed, which only involves the true stresses and the original strength data of the matrix. To assess the efficiency, comparisons between the predictions and available experiment data are made for a number of angle-plied laminates. Reasonable correlation has been found.