In-situ damage monitoring of a SiC/SiC ceramic matrix composite using acoustic emission and digital image correlation

Continuous ceramic fiber reinforced ceramic matrix composites (CMCs) offer an innovative damage tolerant structural material for temperature regimes inaccessible to high temperature metals. However, when subjected to application environments, these materials exhibit damage and degrade over time depending on the severity of those conditions. The ultimate strength of CMCs is dictated by the properties of the load bearing fibers, but matrix cracking weakens the composite and can expose the load bearing fibers to harsh environments. The objective of the work performed was to develop a methodology for linking in situ detection of localized damage to final failure in continuous fiber reinforced CMCs. Initiation and growth of matrix cracking are measured and located linearly along the gage length via acoustic emission (AE) detection. High amplitude events at relatively low static loads can be associated with initiation of large matrix cracks. When there is a localization of high amplitude events in a given area, a measurable effect on the strain field can be observed. Full field surface strain measurements were obtained using digital image correlation (DIC). An estimation of the matrix cracking stress as well as localized areas of initiation were measured in real time.