Three-Dimensional Effective Moduli of Orthotropic and Symmetric Laminates

A simple and accurate method for estimating the three-dimensional effective moduli of symmetric and orthotropic laminated composites is presented. The method is based on obtaining the exact displacement field of three boundary value problems of laminated composites using the Airy stress function solution technique. The effective moduli are estimated by matching the boundary displacements of the equivalent homogeneous system with those of the laminated system. Among the estimated effective moduli, those associated with the interlaminar direction are of special interest. It is found that the effective interlaminar normal stiffness in extensional deformation is independent of laminae stacking sequence which is consistent with the finding of Pagano (1974). However, the laminate interlaminar shear stiffness is dependent on stacking sequence, and it is shown that the rule of mixtures can not predict the interlaminar shear stiffness accurately.