Optimal shape of repair patches in composites

In recent decades, the increase in demand for advanced composites in the replacement of conventional materials, to both primary and secondary aircraft components, reached a concerning level. The safety and efficiency of composite aircraft components are significantly dependent on damage assessment and repair techniques. In this scenario, the use of composite repair patches for restoring and/or improving the original strength and stiffness conditions of damaged components is a viable option. This statement is particularly true when replacing the entire damaged component is not cost-effective. The present work proposes an optimization-based methodology for obtaining the best patch configurations for the repair of damaged laminate panels. A two-phase optimization was employed: first, the fiber orientation that maximizes the strength of the repair patch was defined, followed by the minimization of the repair surface. Circular and square repair patch shapes were tested. The parent plate was considered as a rectangular plane laminate with two different stacking sequences, and different boundary conditions were tested as well. The patch was modeled as an unbalanced fiber reinforced repair with a single layer. Linear programming was employed to solve both optimization problems: fiber orientation and shape area. The error concerning the first natural frequencies of the repaired component compared to the damaged one was considered as the objective function.