Ceramic strain gages for propulsion health monitoring

A robust ceramic strain gage has been developed for propulsion health monitoring which is capable of measuring both static and dynamic strains at temperatures up to 1400°C. These thin film sensors are ideally suited for in-situ strain measurement in harsh environments such as those encountered in the hot sections of gas turbine engines. The sensors are non-intrusive and robust enough to withstand the high “g” loading associated with rotating engine components. Since gage thickness is considerably less than the boundary layer thickness, these sensors do not adversely affect the gas flow path through the engine. Results of recent laboratory tests have shown that these strain gages can meet many of the current demands of high performance propulsion engines. Specifically, static strain tests have been performed at temperatures as high as 1400°C, which have resulted in a relatively large and reproducible piezoresistive response. In addition, high frequency dynamic strain tests were performed at temperatures up to 500°C and at frequencies up to 2000 Hz to simulate conditions that would be encountered during high cycle fatigue. The results indicated that not only did these sensors survive severe testing conditions, including an applied strain of ±500 με, but that they were sensitive enough to isolate possible causes of high cycle fatigue. The results of both the static and dynamic strain measurements at elevated temperature using these ceramic strain gages are presented and the prospects of using these strain gages for structural health monitoring are discussed