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Technical Paper

The Reliability Evaluation of Transmission Gears

Pitting fatigue of gear teeth, if allowed to progress through continued operation, will result in tooth breakage and loss of drive. Laboratory test gears were run to determine their probability of failure under this mode. It was found that the dispersion or scatter of life values depends upon the gear surface contact stress; thus, there is less scatter at higher stress and, conversely, more scatter at lower stress. A cumulative damage method of evaluating transmission duty cycles is presented, with particular application to gear pitting fatigue, in a form adaptable to digital computer calculation.
Technical Paper

The Design of Boron/Epoxy Turboprop Reduction Gear Case

This paper describes the structural design of a composite material front housing for the T56 turboprop reduction gear case. The objective of the composite gear case is demonstration of the feasibility of composites for stiff, lightweight gear reduction cases and the advancement of structural and material technology. Turboprop reduction gear assemblies have typically used magnesium or aluminum for the case structure. Magnesium has reasonable strength properties and low density but the modulus is also low; furthermore, it exhibits poor corrosion resistance. Aluminum has sufficient strength but the specific stiffness, E/ρ, is similar to magnesium so the case is heavy for many applications. In addition to these disadvantages, the mounting requirements for propellers, engine, and transmissions dictate high loads on the gear case structure.
Technical Paper

Advanced Coatings on Superalloy Blades and Vanes for Hot Corrosion and Oxidation Resistance

The need for surface protection of nickel base alloys to prevent hot corrosion and/or sulfidation is discussed. Results of controlled engine test cycling and the rig testing of turbine blades are discussed to establish laboratory test correlation. The relative corrosion resistance of a number of commercial alloys is shown, and the response of these alloys to corrosion resistance with protective coating is covered in relation to their limitation in erosion/oxidation deterioration. Finally, some technology results and general methodology applied to electrophoretic processing for applying coatings of aluminum and combinations with chromium are described. The processing advantages and disadvantages of this coating process and general results are compared with present production.
Technical Paper

Comparative Evaluation of Protective Coatings for High Temperature Alloys

Recently there have been many new developments in aluminum-base diffusion coatings as well as with other coating materials for protection of metal parts in high temperature oxidizing environments. Evaluation is described of many of these coatings on three separate laboratory test devices, for determining (1) resistance to erosion in a high velocity high temperature oxidizing atmosphere, (2) resistance to cracking and oxidation in a thermal fatigue test, and (3) sensitivity to light impact damage at elevated temperatures. Experience with diffused aluminum base coatings on some turbine engine components is discussed, and limitations of the evaluated coatings are cited.