Temporal damage behavior in SiC/SiC ceramic matrix composites

This study investigates stress relaxation behavior in SiC/SiC ceramic matrix composites (CMCs) under constant displacement loading, a phenomenon observed but not thoroughly explored in the literature. Tensile tests were conducted on macroscale dogbones using a ramped loading schedule, where samples were held at fixed displacements for up to an hour. Acoustic emission (AE) and digital image correlation (DIC) monitored damage evolution during the holds. Stress relaxation was observed during the displacement holds due to damage progression detected by both AE and DIC. The magnitude of stress relaxation increased with increasing stress. AE events occurred up to one hour into the displacement hold, with high energy AE events occurring early in the ramped loading schedule with AE energy magnitudes peaking near the proportional limit. DIC data showed surface strain redistributions occurring throughout the duration of a hold. These findings contribute to a deeper understanding of the time-dependent behavior of CMCs under load, crucial for their application in high-temperature environments like turbine engines.