Effect of bolt size and fibre orientation on the bearing performance of resin-infused thermoplastic and thermoset 3D woven composite double-lap joints

This paper presents a comprehensive assessment of the effect of bolt size and fibre orientation on the bearing performance and damage mechanisms of single-bolt double-shear (SBDS) lap joints in 3D fibre-reinforced composites (FRC). The bearing performance of resin-infused thermoplastic 3D-FRC was evaluated along the on-axis (0° and 90°) and off-axis (45°) fibre orientations and compared with their thermoset counterparts. The resin-infused thermoplastic 3D-FRC joints exhibit superior bearing performance in terms of absorbed energy, bearing stiffness, ultimate bearing strength, and damage severity. In on-axis configurations, as the bolt size increases the bearing strength decreased by 26% and 21%, whereas the bearing stiffness increased by 46% and 48% in thermoset and thermoplastic 3D-FRC, respectively. In off-axis configuration, thermoplastic lap joints experience a significant increase of 116% in the bearing stiffness with a slight decrease of 12% in the bearing strength, while thermoset joints exhibit an increase of 21% in bearing stiffness with a reduction of 25% in bearing strength. Furthermore, the surface morphology of damaged specimens showed the main damage characteristics of thermoplastic bolted joints include plastic kinking while the damage characteristics of thermoset include undesirable damage modes, i.e., fibre/matrix debonding, transverse cracking and fibre brooming.