Novel Monitoring Method for Damage Evolution in GFRP Bolted Joints Using Bolt Inclination as a Local Kinematic Indicator

Abstract

Bolt inclination is investigated as a local kinematic indicator of the mechanical behaviour of glass fibber/epoxy bolted joint, monitored using a compact inertial sensor directly mounted on the bolt. The evolution of inclination is shown to be highly sensitive to variations in joint compliance and local load transfer mechanisms, enabling the early detection of damage not captured by the global force response. An analytical bolt bending model is introduced as a lower bound reference, highlighting the predominant role of joint compliance in the observed behaviour. Fatigue tests further support this interpretation through a progressive reduction in minimum force under cyclic loading. Post-mortem observations using optical microscopy and scanning electron microscopy (SEM) reveal localized damage in the vicinity of the bolt hole, confirming the proposed mechanism. Overall, bolt inclination emerges as a simple, robust, and highly sensitive parameter for monitoring the mechanical integrity of bolted composite joints.