Fiber-Reinforced Superalloys For Rocket Engines
High pressure turbopumps for advanced reusable liquid propellant rocket engines such as that for the Space Shuttle Main Engine (SSME) require turbine blade materials that operate under extreme conditions of temperature, hydrogen environment, high-cycle fatigue loading, thermal fatigue and thermal shock. Such requirements tax the capabilities of current blade materials. Based on projections of properties for tungsten fiber reinforced superalloy (FRS) composites, it was concluded that FRS turbine blades offer the potential of a several fold increase in life and over a 200 C increase in temperature capability over the current SSME blade material. FRS composites were evaluated with respect to mechanical property requirements for SSME blade applications. Compared to the current blade material, the thermal shock resistance of FRS materials is excellent, two to nine times better, and their thermal fatigue resistance is equal to or higher than the current blade material. FRS materials had excellent low and high-cycle fatigue strengths, and thermal shock-induced surface microcracks had no influence on their fatigue strength. The material also exhibited negligible embrittlement when exposed to a hydrogen environment.
Fatigue life prediction of an intermetallic matrix composite at elevated temperatures
FATIGUE LIFE PREDICTION OF AN INTER -METALLIC MATRIX COMPOSITE ATELEVATED TEMPERATURESPaul A. BartolottaNational Aeronautics and Space AdministrationLewis Research CenterCleveland, Ohio 44135ABSTRACTA strain-based fatigue life prediction method is proposed for anintermetallic matrix composite (IMC) under tensile cyclicloadings at elevated temperatures. Styled after the "UniversalSlopes" method, the model utilizes the composite's tensileproperties to estimate fatigue life. Factors such as fiber volumeratio (Vr), number of plys and temperature dependence arcimplicitly incorporated into the model through these properties.The model constants are determined by using unidirectionalfatigue data at temperatures of 425 and 815 °C. Fatigue livesfrom two independent sources are used to verify the model attemperatures of 650 and 760 "C. Cross-ply lives at 760 *C arealso predicted. It is demonstrated that the correlation betweenexperimental and predicted lives is within a factor of two.INTRODUCTIONFatigue life prediction of composite materials has been a topicof research for the past two decades. There are manyprediction methods but most can be categorized into twoclasses, either modulus (stiffness) degradation theories (1-8) orresidual strength degradation theories (9-14).The residual strength degradation theories assume that due tocyclic damage accumulation, the composite's residual strengthwill continuously decrease as a function of applied cycles.Failure is assumed to occur when the residual strength of thecomposite is equal to the applied stress. These methods haveproven quite successful in predicting fatigue lives (9-14).However, the difficulty in this type of approach is that in orderto characterize the model, information about the relationshipbetween residual strength with respect to cyclic loading isrequired. That is, one needs to know if the composit¢'s residualstrength degrades as a linear function or some other type offunction with respect to cyclic loading. To obtain thisinformation, several fatigue tests are conducted at the samecondition. The tests are interrupted at various predeterminedcycles and subsequently the specimens are tensile tested toobtain the residual strength of the composite. This process istime consuming and requires a large number of specimens.Also, it should be noted that this relationship between residualstrength degradation and cycles is highly material dependent.The modulus degradation theories are based on the fi_ct thatunder cyclic loading, the stiffness of the composite decreases asa function of cycles. The method used to track the stiffnessdegradation is highly dependent on the model. In some cases.the unloading tangent modulus is used. In others, the secantmodulus is used. A new concept, the fatigue modulus, which isthe slope of the line from the point of origin to the maximumtensile peak of each cycle on a stress-strain plot has recentlybeen proposed (3). Once again there are a multitude ofmaterial dependent functions to describe how the modulusdegrades with respect to cyclic loads. Failure criterion is alsodependent on the model. Some of the models use a percentagedecrease in the modulus and some others use the point wherethe secant modulus degrades to the static modulus as thecondition when failure occurs. The advantage of this approachover the residual strength degradation models is that themodulus degradation behavior can be experimentally obse_'edin a nondestructive manner with a single specimen for a givenload condition. In contrast, the strength degradation modelsrequires testing of several specimens for the same loadcondition.The models in the above two classes of composite lifeprediction have shown to provide good correlations betweenexperimental and predicted fatigue lives in each of theirrespective studies (1-14). All of the models have well definedtheories that are backed up by observed physical phenomena.Most of the models are statistical based, typically utilizing two-or three-parameter Weibull distributions. Like life predictionmodels for monolithic materials, all of them require extensive
Concentrated solar energy in materials processing
Solar energy, which is available in abundant in nature, is least utilised. As per primary energy product, solar energy conversion can be of three different ways: solar fuels, solar electricity, and solar thermal systems. These three approaches are presently not being fully utilised. Concentrated solar energy (CSE) is an alternative to other types of energy for modifying the surfaces of metallic materials. Attempt has been made to overview the current status of CSE in materials processing technology. In this paper, applications of CSE through solar furnace and Fresnel lens for hardening, coatings, sintering, nitriding, synthesis and welding are discussed.