Practical issues of activating self-repairing bolted joints

An investigation of self-sensing and self-repairing bolted joints is presented. The goal of the self-sensing and self-repairing joint is to reduce the likelihood of failure due to self-loosening and to reduce the cost of maintenance of critical bolted joints. The concept combines piezoelectric-based health-monitoring techniques with shape memory alloy (SMA) actuators to restore tension in a loose bolt. The objective of this study is to enhance the practicality of the self-healing bolted joint. One of the primary issues is the actuation of the SMA actuators. The relatively large mass of the shape memory washer and low resistance because of the washer's short length make resistive heating particularly difficult. A series of models was developed to assess the viability of resistive heating and provide an estimate for the power requirements for effective actuation. Modeling and experimental testing have shown that an external heater can be used to actuate a shape memory alloy actuator with conventional power sources. By making the shape memory alloy washer substantially easier to actuate, this method provides a convenient alternative to resistive heating, and aids the practical implementation of the concept of self-sensing, self-repairing joints.