Optimization of fiber orientations near a hole for increased load-carrying capacity of composite laminates

Abstract

In this paper, a procedure for optimizing the fiber orientations near a hole in a single layer of multilayer composite laminates for increased strength is presented. A symmetric six-layer [(C-0)/+45/-45]_s laminate with central hole is considered. Within the ±45^° layers, the fiber orientations are fixed. The C-0 layer is divided into two fields: a small near field around the hole and a relatively large far field away from the hole. In the far field, the fiber orientations are fixed at 0^°, and in the near field, the fiber orientations are assumed to have continuous distribution represented by piecewise bilinear interpolation functions. The Tsai–Wu-criterion-based failure load magnitudes of [(C-0)/+45/-45]_s and [C-0]₆ designs are maximized by iteratively alternating between a gradient-based search and a genetic algorithm. The results show that the load-carrying capacity of composite laminates with hole can be greatly increased through the optimization of continuous fiber orientation distribution within a small area around the hole in the C-0 layer, and the optimum fiber orientation distribution pattern in the C-0 layer is similar to that of the corresponding principal stress orientation distribution. The [(C-0)/+45/-45]_s design is only a few percent weaker than the [C-0]₆ design, which is important for carrying off-design loadings.