A study on the strength improvement of the multi-bolted joint

The joining of composite materials has traditionally been achieved by adhesive bonding or mechanical fastening. Mechanically fastened composite joints are free from surface treatments, and they are unaffected by the service temperature, humidity and other environmental conditions. Most aircraft bolt joints consist of multiple bolts, and they may share the load unequally due to the relatively brittle nature of the composites. In this paper, a new method for improving the strength of the multi-bolted composite joint was evaluated. Multi-bolted composite joints with five bolts were manufactured and tested. The differences of displacement between the bolts were calculated by finite element analysis by applying a uniform load to each bolt of the multi-bolted joint. When these values were used for the positive clearances of the multi-bolted joints, it was experimentally demonstrated that the load acted upon all of the bolts uniformly compared to the multi-bolted joint without the clearance. Additionally, the failure strength of the joint specimen was improved by more than 13.1–21.8%.