Effect of geometry and adhesion on the performance of fiber reinforced thermoplastic composite joints with metal inserts

Joints for laminated composite structures using mechanical fasteners or adhesives often face issues such as reduced strength from fiber breakage in mechanically fastened joints and complex preparation for adhesive joints. Additionally, adhesive joints require compatibility between the adhesive and the composite matrix, limiting their suitability for many thermoplastics. To address these challenges, this study explores a technique that uses metal inserts embedded during the consolidation of laminated thermoplastic composites. It investigates how the geometry of metal inserts and their adhesion to the fiber-reinforced thermoplastic composite affect the joint's performance under out-of-plane loads. Results indicate that while mechanical locking assists in load transfer, the adhesion between the metal insert and the composite is crucial for the joint's failure mechanism and overall performance. Strong adhesion delays final failure by requiring fiber breakage through the composite's entire thickness, while weak adhesion leads to failure through fiber breakage on the bearing side.