An Improved Diagnostic Method for Detection of Bolt loosening in Thermal Protection Panels

An improved analytical method was proposed to assess the fastener integrity of a bolted structure. A new unsymmetrical washer was designed and fabricated, taking full advantage of piezoelectric ceramics (PZT) to play both roles as actuators and sensors, and using energy as the only extracted feature. This method doesn't restricted by the materials of the bracket, panel and base structure. A series of experiments on metallic honeycomb sandwich panel TPS were completed to detect the bolt loosing. Studies show this method can be used not only to identify the location of loosening bolts rapidly, but also to estimate the torque levels of loosening bolts. It has been found that energy is the only extracted feature in this method, which making the computation process become very simple, so the operation speed rises greatly without impacting the accuracy of the results.