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Aero Drive Systems - Gear Surface and Bending Fatigue
Research Objectives
The objective is to discover and validate methods to increase the power density of gears to allow for the lightest weight possible for a given application. This research area focuses on knowledge about the fatigue properties of gears. Research is directed towards two types of fatigue. Surface fatigue occurs on the contacting surface of the gear tooth profile. Bending fatigue occurs near the base of the gear tooth on the non-contacting region. Many aspects of this topic have been and continue to be studied including material composition and processing, gear geometry, lubrication technology, experimental assessments of fatigue life, stress analysis and fatigue theory, and statistical treatment of fatigue data.
Technical Challenges
  • Assessment of emerging research on new materials, steel alloying, material quality control and processing, control and manipulation of residual stress for application to gears
  • Testing of new technology to develop stress-cycle data for design and for comparison of competing technologies
  • Use of emerging surface engineering to enhance surface fatigue power density
Current Research
Gear Bending Fatigue Behavior Assessed
Low cycle fatigue behavior of AISI 9310 steel gears was established via single tooth bending fatigue testing and a recently developed alloy was tested and compared to the currently used AISI 9310 alloy. For more information refer to NASA research reports TM-2007-214914 and TM-2007-215009.

Gear bending fatigue data from two steel alloys

Above: Gear bending fatigue data from two steel alloys. The numbers in the left column indicate the "Bending Stress Index (GPa)" and the bottom numbers indicate the "Cycles to crack initiation".

Laboratory tool for gear tooth strains demonstrated
The capability to measure gear tooth strains during single tooth bending testing using a laser-based instrument was recently established.

Gear tooth under test
Above: Gear tooth under test
Measuring gear tooth strains
Above: Display of measured gear tooth strains as a crack begins to develop during gear durability testing.

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Last Updated: April 21, 2009