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2 Current and Future Needs
Pages 12-19

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From page 12...
... 12 CMCs show promise in addressing all of these imperatives because they are inherently refractory, have low density, and have demonstrated damage tolerance in some applications, suggesting that they could be used in lightweight, thermally loaded structures. CMCs also have weaknesses, however, such as oxidation embrittlement in non-oxide ceramics and limited creep strength in oxide ceramics.
From page 13...
... Consequently, it is impossible to operate the combustor lean enough to remain below the NOx formation threshold. This problem could be solved using a CMC combustion liner that can withstand the temperature of the hot gas in the reaction zone without film air cooling.
From page 14...
... The greater challenges of using CMCs in inertially loaded components should be deferred until field experience has been gained for thermally loaded components. Because most CMC applications are dominated by thermal loads, the material temperature depends not only on the component environment (e.g., gas temperature in a turbine engine)
From page 15...
... 15 The following near-term, lower risk applications represent product insertions that could provide long-term experience with CMCs: . hot gas filters for pressurized fluidized bed combustion (PFBC)
From page 16...
... Aerospace Systems Aerospace applications can be divided into aircraft, missile, and space systems. Several aircraft programs are focused on tailoring CMCs to improve performance, reduce weight, improve fuel efficiency, and reduce undesirable emissions from gas turbine engines.
From page 17...
... stability at the goal temperatures indicated and, during thermal cycles, through lower temperatures resistance to chemical attack in the gas path flow sufficient strength/strain capability to survive normal operating conditions and periodic instances of damage (e.g., overstress) reproducible performance Even though exhaust nozzles in aircraft engines represent a lower temperature, near-term application, the requirements 17 FIGURE 2-3 3M Type 203 Nextel fiber-reinforced SiC matrix ceramic composite candle filter.
From page 18...
... Defining fiber performance requirements for a temperature-time domain is contingent upon CMC component designthrough the expected stress levels as elaborated below. General Considerations The performance of thermally loaded components (in the absence of inertial loading)
From page 19...
... Fiber and Interface Requirements Given the limited amount of field experience and the limited analysis of that experience, it is premature to be explicit about property requirements. Thermal loadings tend to be benign because inelastic strains redistribute the stresses caused by thermal expansion.


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