Andrew J. Eckel

Thermal Diffusivity Imaging of Ceramic Composites

Strong, tough, high temperature ceramic matrix composites are currently being developed for application in advanced heat engines. One of the most promising of these new materials is a SiC fiber-reinforced silicon nitride ceramic matrix composite (SiCf/Si3N4). The interfacial shear strength in such composites is dependant on the integrity of the fiber’s carbon coating at the fiber-matrix interface. The integrity of the carbon rich interface can be significantly reduced if the carbon is oxidized. Since the thermal diffusivity of the fiber is greater than that of the matrix material, the removal of carbon increases the contact resistance at the interface reducing the thermal diffusivity of the composite. Therefore thermal diffusivity images can be used to characterize the progression of carbon depletion and degradation of the composite. A new thermal imaging technique has been developed to provide rapid large area measurements of the thermal diffusivity perpendicular to the fiber direction in these composites. Results of diffusivity measurements will be presented for a series of SiCf/Si3N4 (reaction bonded silicon nitride) composite samples heat-treated under various conditions. Additionally, the ability of this technique to characterize damage in both ceramic and other high temperature composites will be shown.Copyright

Ceramic Matrix Composites for Rocket Engine Turbine Applications

A program to establish the potential for introducing fiber reinforced ceramic matrix composites (FRCMC) in future rocket engine turbopumps was instituted in 1987. A brief summary of the overall program (both contract and in-house research) is presented. Tests at NASA Lewis include thermal upshocks in a hydrogen/oxygen test rig capable of generating heating rates up to 2500 °C/sec. Post thermal upshock exposure evaluation includes the measurement of residual strength and failure analysis. Test results for monolithic ceramics and several FRCMC are presented. Hydrogen compatibility was assessed by isothermal exposure of monolithic ceramics in high temperature gaseous hydrogen plus water vapor.Copyright

Ceramic Composites Portend Long Turbopump Lives

Use of continuous fiber reinforced ceramic matrix composites (FRCMC) for turbopump hot section components offers a number of benefits. The performance benefits of incresed turbine inlet temperature are apparent and readily quantifiable. Perhaps less obvious are the potential benefits of incresed component life. At nominal turbopump operating conditions, FRCMC offer increased operating temperature margin relative to conventional materials. This results in potential for significant life enhancement. Other attributes (e.g., thermal shock resistance and high cycle fatigue endurance) of FRCMC provide even greater potential to improve life and reduce maintenance requirements. Silicon carbide (SiC) matrix composites with carbon fibers (C/SiC) do not degrade when exposed to hydrogen-rich steam for 10 hours at 1200 C. This FRCMC is resistant to thermal shock transients far in excess of those anticipated for advanced, high temperature turbomachinery. Orthogonal, two-dimensional (2D0, plain woven, C/SiC) also does not degrade when subjected to tensile-tensile fatigue at room temperature for 4 x 10(exp 5) cycles at 75% of the ultimate strength. Runout at greater than 10(exp 6) cycle occurs for axial specimens subjected to fully reversed strain controlled fatigue at ambient temperature and 0.3% strain.

Ceramic composites for rocket engine turbines

ABSTRACTUse of ceramic materials in the hot sectionof the fuel turbopump of advanced reusablerocket engines promises increased performanceand payload capability, improved component lifeand economics, and greater design flexibility.Severe thermal transients present duringoperation of the Space Shuttle Main Engine(SSME) push metallic components to the limit oftheir capabilities. Future engine requirementsmay be even more severe. In Phase I of thistwo Phase program, performance benefits havebeen quantified and continuous fiber reinforcedceramic matrix composite (FRCMC) components havedemonstrated a potential to survive the hostileenvironment of an advanced rocket engine turbo-pump.INTRODUCTIONReusable rocket engines for future missionsof earth-to-orbit and beyond must operate lon-ger, withstand more duty cycles, and be moreefficient than present generation engines.Today the most advanced reusable rocket engineof this type is the Space Shuttle Main Engine(SSME). Metal turbopump blades, stator vanesand other hot gas flow path components of thishydrogen/oxygen burning engine have limiteddurability. For improved efficiency, futureAdvanced Launch Systems (ALS) such as the SpaceTransport Booster Engine (STBE) and SpaceTransport Main Engine (STME) will requirematerials with greater temperature capability.Materials with potential to significantlyoutperform the currently used superalloysinclude ceramics, synthetic alloys such asintermetallics, and carbon/carbon. These mate-rials have a lower density and can operate athigher temperatures than superalloys (Fig. 1).Of the candidate materials, ceramics exhibitbetter potential for overall tolerance to theaggressive rocket engine environment. The loadcarrying capability of monolithic ceramics is,