Effect of patch geometry and resin type on mechanical properties of repairing deep scratch damage to aircraft composites

Abstract This study investigated the effects of patch geometry and resin type on mechanical properties in repairing small damages, such as deep scratches, on the exterior surfaces of composite components, such as fuselages, wings, tail stabilizers, and aircraft doors. A handheld prototype device was developed to impregnate glass roving with epoxy resin and apply a repair filler to damaged areas. To simulate the fuselage outer layer, 6 twelve-layer 2–3 mm thick composite plates (V f ≈ 55%) were produced by hot pressing using Duratek® epoxy and 300 g m −2 woven glass fabric. Tensile and flexural samples were prepared from plates per standard. U and V cross-section artificial scratch damage was created on samples with 40% of their thickness using two milling cutter types on a CNC router, resulting in three test samples: undamaged and two damage types. Three epoxy resins (Loctite®, Duratek®, and Polisan®) were applied to the U and V damaged areas with a handheld device, and 6–9 layers of filling patches were made using impregnated 300 tex glass roving. The repaired samples were cured at 23 °C for 24 h, under an infrared lamp at 40 °C for 4 h, and at 60 °C for 2 h. Tensile and flexural tests on the original and repaired samples showed a tensile strength recovery of up to 94%, tensile modulus of 89%, flexural strength of 65%, and flexural modulus of 99%. The U-patched samples demonstrated higher tensile and flexural strengths than the V-patches, with Duratek® epoxy proving advantageous for tensile properties and Loctite® for flexural properties.