ROLLING CONTACT FATIGUE CHARACTERIZATION OF GEAR MATERIALS USING TWIN-DISC TESTS

The ISO standard 6336 for the calculation of the load carrying capacity of gears provides design curves against contact fatigue, which allow a rough estimation of the gear durability based on a coarse classification of materials. For a more accurate assessment, the derivation of the permissible values of Hertzian pressure on the tooth flanks by means of tests is suggested. In order to evaluate the endurable stress of a material in a fast and cost-effective way, the ISO standard mentions the use of tests on pairs of discs in contact, choosing the geometries, loads and speeds in order to simulate as close as possible the working conditions of the actual gear pair. However, no information is given about the determination of gears durability from the results of tests on discs, and about an appropriate method for specimens design. In this paper a twin-disc test rig is presented along with the results of preliminary tests on through hardened steels. Finally, the criteria used to design the specimens in order to recreate the working condition experienced by sun gears of off-highway axles are discussed.