26 - Tensile failure of composite scarf repair

Abstract

Composite repair is an integral and critical aspect in the service and maintenance of growing fleets in the civil aerospace, automotive, and marine composite–vehicle industries. Bonded repair and scarf repair are particularly attractive from strength restoration and technological standpoints, allowing one-sided access while only minimally affecting the outer shape of the structure. Mechanics of composite scarf repair under tensile loading, with and without overplies, were examined for the ply orientations of nontraditional patches. Three-dimensional nonlinear analysis was performed for composite repair failure prediction. A baseline was achieved by comparing open-hole scarfed panels with panels repaired using standard ply-by-ply replacement patch composition. Multidimensional optimization was performed to calculate the repair patch ply orientations that minimize von Mises stress in the adhesive. These optimal stacking sequences achieved significant reduction of stress levels and resulted in predictions of up to 60% and 90% strength restoration for flush and single-ply thickness overply repairs, respectively. These results, supported by experimental data, are intended to illustrate additional design variables available for efficient composite repair design, chiefly the composition of the repair patch.