Feasibility Analysis of Bolted Joints with Composite Fibre-Reinforced Thermoplastics

The use of composite materials has shown steady growth in recent years due to their excellent specific mechanical properties and the possibility to reduce the weight of vehicles without impairing their safety and comfort. Continuous fibre-reinforced thermoplastic composites (CFRTP) show dynamic, acoustic, and damping properties far superior to steel and can be recycled and repaired. Their excellent properties make CFRTP good candidates for anti-vibration and shock absorbing components, however, out-of-plane mechanical properties hinder the anchoring to the vehicle's body by means of bolted connections. The results obtained in this study show how the maximum torque that can be applied without cracks or breakage phenomena is lower than in standard steel joints. Although the preload's value is admissible, this one is reduced over time due to relaxation phenomena associated with the viscoelastic behaviour of thermoplastic matrix. The results obtained can be improved with the integration of metal inserts in connections' areas. In this study, a case study of a gear mount replacing the steel core with CFRTP reinforced with inserts is carried out. The results show a reduction above 50% in weight, opening the possibility of lighter structures in the automotive sector.