Original Date: 03/08/1999
Revision Date: 01/18/2007
Best Practice : Gear and Gear Materials Testing
The expense of operating a gear test facility is deterring many aircraft manufacturers from setting up in-house test capabilities. However, the Applied Research Laboratory at the Pennsylvania State University (ARL Penn State) has obtained the necessary equipment to provide gear and gear materials testing services to the aircraft industry. The laboratory offers power circulating gear tests for:
Surface Durability (pitting) and Wear The test strategy is to find loads that have an average life-to- failure durability of three- to six-million cycles for high loads and 12- to 15-million cycles for low loads. Six tests are conducted at each of these load levels with the specimen gear running at 900 rpm and the mating gear at 540 rpm. A Weibull statistical analysis of the results establishes the service life of 10%, 50%, and 90% failures with 50% and 90% confidence levels.
Low Speed Bending The test strategy is to use a standard 18-tooth specimen gear and a 30-tooth mating gear that have a life-to-bending failure of 250,000 to 500,000 cycles.
Scuffing The test strategy is to run the gear set at a low load and speed using a cold/room temperature lubricant for half an hour. Measurements for surface finish occur in 0.5-hour increments after each step, starting with a moderately high load, speed, and lubricant temperature. The load and/or lubricant temperature is increased with each step. The test concludes when surface roughness significantly increases and visible tears (scuff marks) occur at the tip of the driven gear.
Single-Tooth Bending Fatigue The test strategy is to identify a load that will cause a failure by using a single-tooth fatigue fixture with cycles of 50,000 to 100,000 and 250,000 to 500,000 cycles. Six tests are performed at each of these load levels.
Rolling/Sliding Contact Fatigue The test strategy is to determine the loads by a gear operating speed of 1330 rpm, using three- to six-million cycles for high loads and 12- to 15-million cycles for low loads.
Low overhead and accessibility enable the ARL Penn State to operate its gear test capabilities at a lower cost than industry. As a result, excellent gear and gear materials testing services are now available to manufacturers who cannot afford an in-house gear test facility.
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