Strain Gages for SiC–SiC Ceramic Matrix Composite Engine Components

As increasingly more SiC-SiC ceramic matrix composites (CMCs) are being used in the hot sections of gas-turbine engines, there is a greater need for in situ strain measurement in these harsh conditions. Thin-film strain sensors are ideally suited for this task since they have minimal mass and are nonintrusive. However, if the bulk piezoresistive properties of SiC-SiC CMCs could be used instead of the thin-film piezoresistive properties, superior resolution and stability could be realized. Toward this end, we have fabricated strain gages in which the active strain element is the SiC-SiC CMC itself. As a result of this approach, a Pt:SiC CMC strain gage that is capable of operating at 500 °C for prolonged periods was demonstrated. The large piezoresistive responses associated with the SiC fibers and SiC matrix resulted in gage factors larger than 100. The performance of the Pt:SiC CMC strain gages under both tension and compression are reported, and the I-V characteristics of the strain gages, as well as the piezoresistive response as a function of temperature, are presented. In addition, the potential for embedded strain gages in advanced CMC engine components will be discussed.