Investigation of Self-Monitoring and Self-Healing Bolted Joints

摘要

The bolted joint is of great importance in structures. Its loosening mode of failure is a mode common in the failure of structures. This paper is a report of an initial investigation into the real-time condition monitoring and active control of bolted-joints in civil structures and components. The impedance-based health monitoring technique, which utilizes the electromechanical coupling property of piezoelectric materials, has been used to detect and identify bolt-connection damage. When damage occurs, temporary adjustments of the bolt tension can be achieved actively and remotely using shape memory alloy actuators in order to restore lost torque for continued operation. Specifically, the actuator is a cylindrical Nitinol washer that expands axially when heated, according to the shape memory effect. The washer is actuated in response to a decrease in torque. Upon actuation, the stress generated by its axial strain compresses the bolted members and creates a frictional force that has the effect of generating a preload. The structure in question was monitored in all stages of testing using piezoelectric impedance analysis. Through experimentation, we have documented a successful actuation of the shape memory element. Due to complexity of constitutive modeling, qualitative analysis by the impedance method is used to illustrate the success. Additional considerations encountered in this initial investigation are made to guide further thorough research required for the successful commercial application of this promising technique.