Experimental investigation of bolt loosening detection in thermal protection panels at high temperature

The integrity of thermal protection systems (TPS) is crucial to ensure a successful mission of future high-speed aerospace vehicles. Therefore, research and development efforts are underway to provide structural health monitoring systems for the TPS, but most of studies are carried out at room temperature, that was out of accord with fact. In this study the active embedded piezoelectric element was integrated into the TPS used as an actuator to generate the propagating waves as well as a sensor to receive the diagnostic waves. A series of experiments were completed lo demonstrate the feasibility of detecting loose fasteners in a TPS, and all the experiments were carried out at high temperature environment from 20°C to 300°C, which is heated by the quarlz lamp array. So an improved analytical method was proposed to assess ihe fastener integrity of a bolted structure; the computing process was simplified greatly by only using energ} as the extracted features. The durability of Ihe health monitoring system was also verified. Experimental results show that this method and health monitoring system is capable of locating the loosened bolts, as well as quantifying the degree of panel and bracket bolt loosening.