The full potential of fiber-reinforced composite laminate can be realized by developing optimum design methodology that is fundamentally different from that with isotropic materials. In this paper, strength characteristics of multidirectional laminates are studied first. Laminates are assumed to be symmetric about the midplane surface and to consist of plies with 0, 90, 45 and -45 degree fiber orientations. A simple transformation was introduced to normalize the combined loading data and express all of them in the closed stress space. Strength discontinuities of multidirectional laminates are pointed out, which should be taken into consideration during the process of ply thickness optimization of multidirectional laminates. Computer codes were developed to find the optimal combination of a maximum of four ply groups to obtain the maximum strength for a given set of general in-plane stresses. The numerical results obtained using T300/5208 graphite/epoxy composite material showed the strength of optimized laminate was about six times as high as that of the quasi-isotropic one at the highest point.
