Health-Monitoring Strategies for Non-Oxide High Temperature Composites and Structures Utilizing Electrical Resistance
Abstract
The use of non-oxide ceramic matrix composites is gaining momentum as it is introduced into more defense and commercial applications. There is much to understand regarding these new materials as to the mechanisms that lead to property degradation and end-of-life scenarios. Part of what is needed to better understand CMC degradation are health-monitoring techniques whichcan be tied to material degradation mechanisms. In particular, matrix cracking, oxidation and fiber-breakage all contribute to end-of-life. One such technique that is relatively simple in principle is the change in electrical resistance (more commonly known as electric potential drop in metals). This technique takes advantage of the electrical conduction properties of a material, i.e., if damage mechanisms alter the electrical properties of the material then this can be used to monitor damage. The electrical resistivity of a composite is dependent on the constituents (fiber,matrix and interphase) and their respective electrical resistivities. If the most conductive part of the composite is the matrix (as is the case with Si in MI composites), then the composite is very electrically sensitive to matrix cracking. If there are other phases such as C which is possibly the case as the fiber or interphase, then oxidation of C due to oxidation via oxygen transport throughmatrix cracks would increase resistance. For other mechanisms such as higher rate oxidation,corrosion or erosion a loss of area would result that would also increase resistance. Much work has already been done to understand the electrical response of composites with different constituents. However, more advanced understanding or use of electrical resistance properties towards components is envisioned for this proposal. Specifically, two areas are put forward forfurther investigation: (1) the use of monofilament fibers with carbon cores to act as internal electrical ???sensors??? for SiC/SiC composites especially geared towards aero engine applications and (2) the use of electrical resistance to monitor damage in more complex sandwich structures where the structure is made up of a SiC/C-based faceplate and a SiC/C-based foam core. In the first concept, a few carbon core monofilaments can extend through the hot section of a part andrelate any local stressed-oxidation damage that may occur due to the loss of carbon in that location. In the second concept, multiple lead attachments on the structure can be utilized to understand if damage and/or oxidation mechanisms occurred either on the faceplate in the core or at the core/faceplate interface during and after an applied thermal-mechanical load. A variety of ambient and elevated temperature tests are put forward, including those with local stressconcentrators, in order to assess the feasibility and effectiveness of ER to monitor damagelocally. This understanding can then be used to couple the damage mechanism determined from microstructural analysis with the change in the local circuit in order to model the change in resistance from which life-expectancy types of models can be utilized.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Jul 27, 2018
- Source ID
- N000141812646
Entities
People
- Gregory Morscher
Organizations
- Office of Naval Research
- United States Navy
- University of Akron