Damage resistance of dispersed-ply laminates

This paper presents the design procedure of a quasi-isotropic (QI) laminate employing dispersion of ply orientations. The goal is to improve damage resistance of a laminate under low velocity impact (LVI). The LVI is treated as a quasi-static loading and instead of a plate a laminated beam is considered. Therefore, this situation simplifies the problem to an interlaminar shear (ILS) test. Although the specimen might experience several failure mechanism, only delamination which influence the load carrying capability of it drastically under compression after impact (CAI) is considered here. By studying the interlaminar shear stresses through the thickness of the laminate, initiation of crack can be inspected in every layer using a quadratic initiation criterion (QIC). Finally, employing a modified ant colony optimization (ACO) algorithm (two-pheromone ACO algorithm) a fully dispersed QI laminate is designed. The domain of the orientation angles is between -85o to 90o with a 5o interval. The results showed that the interface angles does not present a decisive influence on the crack onset. On the other hand, the dispersion tends to have as large as possible angles near the middle of the laminate to minimize the maximum value of QIC, and some small angles in the outside to provide enough bending stiffness.