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Advances in military and commercial propulsion systems are directly tied to advances in material systems. Industry and government have identified the need for high temperature materials, that is, materials which maintain their physical or engineering properties at temperatures above present superalloy capability. Ceramics have been proposed to fulfill these needs. However, after approximately 15 years of research, no dominant life prediction tools or design codes have been generated for the structural application of ceramic materials. This is in part due to the continuous evolution of ceramics, which has made data base generation difficult, and the lack of tools to adequately describe the mechanical behavior. The accurate characterization of the fracture process is a critical element to the successful implementation of ceramics in a structural application.
A test method has been developed at ARL VTC, with the support of NASA LeRC, which permits the study and characterization of slow crack growth behavior in monolithic ceramics. Conventional loading techniques require the specimen to be a critical link in the loading system. Uncontrollable strain energy, stored in all the components of a loading system, becomes available to the fracture process as a crack is initiated. This energy is sufficient to cause rapid and catastrophic failure of the specimen. The approach developed at ARL VTC places the specimen in a parallel loading path, removing it as a critical link. This permits the controllable release of energy used to initiate and propagate cracks in the fracture process. The objective of the research, done at NASA LeRC, is to accumulate data which characterizes material behavior and is suitable for structural analysis codes.
POC: David N. Brewer
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Updated: March 12, 2004