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P.F. Browning "Time Dependent Crack Tip Phenomena in Gas Turbine Disk Alloys" Ph.D. Thesis, Rensselaer Polytechnic Institute, Troy, NY, 1998
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Time dependent crack tip phenomena in gas turbine disk alloys
by Browning, Paul Frederick, Ph.D., Rensselaer Polytechnic Institute, 1998 , 212 pages; AAT 9918375
Abstract (Summary)
In the continuous quest for improved thrust-to-weight ratio and higher efficiency and power output, designers of aircraft engines and land based power systems subject gas turbine alloys to increasing service temperatures and stresses in aggressive environments. Under these conditions, the determination of component life increasingly requires a detailed understanding of time dependent crack tip phenomena and their ability to degrade fatigue resistance. At present, there is not consensus in the literature as to the mechanism(s) responsible for this environmental degradation. If we hope to reach consensus as to a damage mechanism, three fundamental issues must be addressed. These are identification of the damaging environmental species, determination of the damage location and determination of the rate-limiting step in the degradation process. It is the purpose of this thesis to address these three issues. Through a combination of advanced mechanical testing and materials characterization techniques, the phenomena occurring at the tip of a time dependent crack will be investigated. It will be shown that two environmental species, oxygen and water vapor, when present in sufficient quantity and combined with sufficient crack tip stress, facilitate environmental degradation. The location of environmental damage will be shown to extend no further than about one grain diameter from the crack tip, if it extends beyond the crack tip at all. Finally, through analysis of crack tip oxide scales and the crystallographic nature of cracked grain boundaries, the rate limiting step in the time dependent crack growth process will be identified as diffusion of oxygen through the oxide scale that forms at the crack tip. Implications of this new information for the users and developers of gas turbine disk alloys, and recommendations for further work to determine the damage mechanism, will also be presented.
Indexing (document details)
Advisor: Rajan, K.
School: Rensselaer Polytechnic Institute
School Location: United States -- New York
Keyword(s): Oxide scales, Crack tip, Gas turbine
Source: DAI-B 60/02, p. 788, Aug 1999
Source type: Dissertation
Subjects: Materials science, Mechanics, Aerospace materials, Mechanical engineering
Publication Number: AAT 9918375
ISBN: 9780599175051
ProQuest document ID: 734366391
