A repair algorithm for composite laminates to satisfy lay-up design guidelines

Composite materials, due to their high specific strength and stiffness, are commonly used to design lightweight structures. However, the anisotropy of composite laminates induces complex multi-modal failure mechanisms and often undesired mechanical couplings. For this reason, empirically-based design guidelines are generally employed to increase confidence in the laminates’ long-term structural performance and integrity. However, most laminate design and optimisation methods have difficulties enforcing these guidelines. As a result, laminates must be repaired a posteriori—i.e. modified to satisfy lay-up guidelines by changing fibre angles, shuffling and adding plies—generally leading to a loss in structural performance. That is because repair methods proposed in the literature typically enforce guidelines by altering the laminate lay-up with little to no consideration for structural performance. In an effort to address this issue, the authors propose a deterministic repair procedure guaranteeing satisfaction of aerospace laminate design guidelines whilst minimising degradation of structural performance. Enforcing all guidelines simultaneously is very challenging. Instead, the authors devise an astute decomposition of the repair problem into a sequential set of easily manageable repair steps. First, laminate ply orientations are modified to satisfy membrane constraints and optimise in-plane structural performance. A similar action is then carried out for out-of-plane constraints and properties. The proposed repair strategy is shown to perform well on a wide range of examples, with an average success rate of more than 88%, and a computational speed in the order of tenths of seconds for symmetric laminates of 150 plies.