Optimization of Composite Laminates for Minimum Weight and Delamination Fatigue Crack Growth Rate using NSGA-II

An elitist non-dominated sorting genetic algorithm (NSGA-II) is used to optimize the local delamination growing from transverse matrix cracking in laminated composites subjected to in-plane biaxial fatigue loading. The objectives of this research are minimization of weight and delamination fatigue crack growth rate (DFCGR) simultaneously to achieve a damage tolerant structure with most delamination resistance and lightest weight among all possible choices. The fiber orientation, fiber volume fraction, ply thickness, and staking sequence are chosen as the design variables. To define the problem statement, we consider symmetric laminates which one of their layers contains a single matrix crack that induces local delamination at the ply interface. The DFCGR is characterized using a Paris law based on the energy release rate associated with local delamination growth. Utilizing a 2D shear-lag method, the stiffness degradation is evaluated by employing the equivalent constraint model (ECM) of the damaged lamina. The application of the approach is demonstrated for glass/epoxy and carbon/epoxy laminates to verify the effectiveness of the proposed method.