Cluster Analysis of Acoustic Emission Signals From SiC/SiC CMCs Including the Introduction of Waveguides and the Effect of Material Changes Under Thermal Exposure

Ceramic matrix composites (CMCs) have received significant attention due to their advantageous material properties for engineering applications where temperatures approach or exceed the working limits of traditional metals and alloys. An understanding of the damage mechanisms that accumulate within the material under complex mechanical and thermal stress conditions is therefore essential. Acoustic emission (AE) is one form of non-destructive evaluation (NDE) that is routinely used for such assessment. This paper investigates the application of pattern recognition tools to AE data obtained from monotonic tensile testing of SiCf/BN/SiC CMCs under thermal exposure in a range between room temperature (RT) and 1100°C. Unsupervised pattern recognition in the form of k-means clustering was subsequently applied to the AE datasets in efforts to link different AE signal characteristics with damage mechanisms anticipated at specific stresses within the CMC. Due to elevated temperatures, AE waveguides were used in all tests. At RT, commonly occurring clusters were attributed to damage modes such as matrix cracking and interfacial debonding/sliding. At increasing temperatures, cluster activity remained broadly consistent until the effects of oxidation and thermally induced degradation of the material occurred between the temperature steps of400° and 600°C. Further differences were observed at 1100°C.