Contact Fatigue Life Investigations and Wear Mechanisms of Different Case Hardened Surfaces under Rolling Contact Loading for Gears

摘要

For many machine components well-defined standard codes exist concerning the conservative load-carrying capacity under rolling contact fatigue. The present work examines experimentally the local damage evolution and compares the differences in fatigue behaviour of different case-hardened depths layers under rolling contact fatigue (RCF). The RCF experiments are accompanied by damage assessments as well as accompanying two and three dimension finite element computations. Within the numerical finite element computations, special focus is put on a detailed assessment of the tensile stress peak at the edge of contact. In order to assess experimentally the extreme conditions line contact, the experiments were performed on a three-disc rolling contact fatigue test rig (3RCF) and a standardized gear test rig (FZG). With the material 20MnCr5 three case hardened depths from 0.5 - 1.25 mm were also compared on 3RCF and FZG test rig. Under high contact pressure an increase in case hardening depth has a higher lifetime as a lower depth, however under reduced contact pressures the low case hardened depth is beneficial. A system study for RCF was examined, and as a major result the 3RCF tests can comparatively be used instead of FZG tests. In FEM it was shown that it can be realized in a computational efficient way by combining two steps of discrimination. Starting with linear-elastic analysis, the simulation model is improved by introducing elasto-plastic material behaviour, and further by applying the compressive residual stresses from the heat-treatment process as obtained from X-ray diffraction. Results taken from fatigue testing, fracture assessment, change of cyclic material behaviour and evaluation of the highly-stressed region by FEM established a closed damage model for the RCF-analysis investigated.