Experimental investigation of layer number, fiber architecture, orientation, and areal density on the mechanical behavior and failure mechanism of FRP adhesive joints

In recent years, fiber-reinforced polymer (FRP) composites have found extensive application in aerospace, automotive, and construction industries owing to their high strength-to-weight ratio and excellent corrosion resistance. Among the factors influencing the performance of FRP structures, the joining method plays a critical role. Adhesive bonding is often preferred over mechanical fastening as it avoids drilling, maintains structural integrity, and provides a more uniform stress distribution. This study examines the mechanical performance of adhesively bonded joints in glass fiber-reinforced polymer composites. Reinforcement materials at the bonding interface included woven carbon fiber, woven glass fiber, and unidirectional glass fiber. Key variables investigated were the number of composite layers (one, three, and five), fiber orientation angles (0°, 30°, 45°, and 90°), and areal densities (200 and 300 g/m2). Samples were manufactured via vacuum infusion using a two-component epoxy resin system (Duratek-DTE 1200) with hardener (Duratek-DTS 1151), and cured under ambient conditions. Mechanical testing was performed at a displacement rate of 1 mm/min. The results showed that reinforcement architecture, fiber orientation, layer number, and areal density all had a significant impact on joint strength. Increasing the number of layers generally reduced joint strength due to higher shear and peel stresses, while certain orientations, particularly 45°, enhanced load-bearing capacity. Woven fiber reinforcements improved adhesive bonding and strength compared to other configurations. Lower areal density fibers in the adhesive region yielded higher strength, likely due to reduced peel stresses. Conversely, higher areal densities increased adherend thickness, promoting bending effects that could reduce joint performance.