Application of genetic algorithm for optimum design of bolted composite lap joints

The genetic algorithm (GA), a powerful optimization technique for multiple extrema functions in multidimensional search spaces, is applied in conjunction with stress analysis to achieve optimum designs of bolted composite lap joints. The objective of the optimization is to ensure the highest strength of the joint. In this study, the laminate thickness, laminate lay-up, bolt location, bolt flexibility, and bolt size are considered as design variables. The contact stresses (bolt loads) are determined by a combined complex potential and variational formulation. In this formulation, the equilibrium equations are satisfied exactly and the boundary conditions are enforced by minimizing the total potential. The contact stresses as well as the contact region are determined through an iterative procedure as part of a solution method that accounts for the effects of finite geometry and by-pass loading. The fitness function for the GA optimization is based on the average stress failure criterion for predicting net-section, shear-out, and bearing failure modes in bolted lap joints.