On-Site Monitoring of Composite Bolted Joints Looseness Using CB/PVP Nanocomposite Piezoresistive Sensor

Bolted joints play important roles in ensuring the integrity of composite structures. Information obtained through structural health monitoring (SHM) can be used to determine the health condition of composite bolted joints. However, integrating monitoring sensors with the composite bolted joints is an extremely challenging problem. In this study, a nanocomposite piezoresistive sensor made of carbon black (CB) and polyvinyl pyrrolidone (PVP) is applied to the composite bolted joints looseness monitoring. The change in the mass fraction of CB particles leads to different resistance values, which are measured to analyze the conductive property of the sensor. The mechanical properties of the sensor are demonstrated under pressure loading with different mass fractions of CB particles. The nanocomposite piezoresistive sensor is integrated with the carbon fiber reinforced plastics (CFRP) single-lap bolted joints, and the optimized electrode layout is presented by comparing the change of resistance and the sensitivity. The state of CFRP bolted joints looseness is represented by the change of relative resistance with different torques. The experimental results show that the CB/PVP nanocomposite piezoresistive sensor has great potential in SHM to realize the integration of the sensor and life-cycle monitoring of composite bolted joints.