Optimization of disc geometry and hardness distribution for better transferability of fatigue life prediction from disc to FZG tests

Abstract

FZG tests have become a standard for the determination of fatigue lifetime and other key operational parameters in gear applications. This testing configuration is considered to be closer to the real-field application than other rigs such as twin disc testers, although FZG requires a significantly more complex sample preparation in addition to not allowing for the variation of key test parameters. Despite the fact that DIN 3990 recommends the use of disc tests if no other gear test results are available, it must be noted that the transferability of results from twin disc to FZG gear tests has not been properly assessed in the available literature.For the present study, gears made of case hardened 22MnCr5 with different carburisation depths were tested under lubricated conditions using a FZG test rig. The results, including S–N curves, were compared with twin-disc tests performed by the authors with modified disc geometries, in order to assess the transferability of the results between both configurations. Additionally, worn samples have been characterised in terms of residual stresses and microstructure for one case hardening depths in FZG tests at different tooth flank locations and compared with disc tests. It has been found that a good match between FZG and twin disc test rig results can be found for an appropriate twin disc sample geometry and hardness distribution, opening the way for transferability between both test configurations.