Silicon carbide (SiC) Ceramic Matrix Composites (CMCs) offer a considerable weight and temperature advantage over existing nickel-based superalloy systems used for hot section components in the gas turbine engine. By having approximately 1/3 of the density and 20% higher operating temperatures, the use of CMCs could significantly reduce the fuel consumption of commercial flights, resulting in a decrease in harmful emissions.
 
CMCs have significantly improved toughness when compared to monolithic ceramic materials due to a well-planned interphase layer between the fibres and the matrix. This interphase enables matrix cracks to deflect around the fibres promoting fibre pull-out to occur prior to failure. This mechanism allows additional energy absorption before fracture and helps prevent rapid catastrophic failure. However, once the matrix becomes saturated with microcracks, internal oxidation can cause degradation of the interphase layer resulting in embrittlement and premature failure. As a result, there is a growing need for reliable non-destructive evaluation (NDE) methods that are able characterise changes in material integrity, whether that be oxidation or the formation and accumulation of matrix cracks and/or fibre fractures.
 
Acoustic Emission (AE) has proven itself to be a reliable technique for evaluating the onset and propagation of transverse matrix cracks in SiCf/SiC CMCs, considered for high temperature gas turbine applications. As a technique it involves capturing sound waves and their corresponding information to relate AE signals to specific damage types, locations, or failure mechanisms. By capturing AE events during mechanical testing, it can be possible to deduce the condition of samples, providing information about damage progression in CMCs.
 
In this body of work, a two-channel AE system has been used to capture data from SiCf/SiC CMC specimens during different types of fatigue testing. Two different peak load dwell times have been investigated, as well as implementing a stepped fatigue loading regime, up to a final intended load. Extensometry has also been used alongside AE to correlate signatures with mechanical parameters during the testing.