Analysis of the performance of carbon fiber patches on improving the failure strength of a damaged and repaired plate

Since the implementation of the composite patch bonding repair technique, this process has gradually replaced traditional bolting or welding methods. The correct choice of fiber type for the composite patch guarantees better durability of the repair. Carbon fiber composites, favored for the most advanced aeronautical and industrial applications, have shown great effectiveness in reducing stress at the damaged area. They are chosen for their high strength, low weight and high stiffness compared to other fibers. This work is part of this context, as the objective is to highlight, through a numerical analysis by finite elements, the interest of applying patches based on carbon fiber to reduce the stress concentration at the level of a damaged plate (a plate with a side crack and another plate with a crack emanating from a notch). Two types of carbon fiber were chosen, high modulus fiber and high strength fiber. Composite patches were bonded using Adekit A-140 adhesive to repair a 2024-T3 aluminum plate. The plate and the adhesive were introduced as materials with elastoplastic behavior where the adhesive was taken as being a third material. However, for the composite an orthotropic material was considered by introducing the respective engineering constants. The objective is to highlight the benefit of using high modulus (HM) or high strength (HS) carbon fibers compared to other fibers. The effects of crack size, presence of a notch, applied stress and the use of a hybrid composite (combination of HM fibers and HS fibers) were taken into consideration. The results showed clearly that the carbon fiber patch absorbs clearly a large amount of stress from the damaged area and ensures good resistance of the repaired plate.