To receive reliable results for the VHCF behavior of case hardened gears in the VHCF regime, gears have to be tested in a high-speed rotational test rig. Therefore, the consortium member WZL developed and designed a high power back-to-back test rig for high rotational speeds, which goes beyond the current state of the art of gear fatigue testing. In a first step, the geometry of the test gear set was designed according to the ISO 6336 and checked regarding the critical failure modes using different standardized and highly detailed calculation methods. The gear design represents the best compromise for the given limits and derives a sufficient safety against unwanted damage types. Based on the final test gear geometry the test rig was designed and critical machine components were optimized. Using the detailed CAD-Model of the test rig, the drawings of the components were derived. For the reliable continuous operation of the test rig, the cooling infrastructure at the WZL has been enhanced. Since the power class of the new high-speed rotational test rig is beyond the state of the art, the available cooling capacity was not sufficient.
Based on the drawings of the test rig the external manufacturing of the housings, shafts and seals was tendered and commissioned. Due to the high estimated costs of these parts, an extensive tendering process was necessary. Furthermore, the other test rig components and components for test preparation, e.g. the oil aggregate, the drive motor and a balancing machine, were tendered and ordered. Performance analyses of the test rig were carried out. The thermal and dynamic operational behavior was simulated and the safe operation ensured.
The test rig components were manufactured and procured and the test rig was successfully assembled. The test rig was successfully commissioned up to a maximum speed of 12000 rpm.
During the final stages of commissioning, scuffing damage occurred to the axial journal bearing, which prevented the investigations from proceeding. The procurement of a replacement bearing went beyond the end of the project term. Accordingly, a short series of tests was carried out on the pulsator test rig for risk mitigation purposes in order to still have gear test data.
The manufacturing of the standard test specimens and the test gears from both materials was finished.
For the understanding of relevant local failure probabilities and mechanisms at up to 10^9 load cycles a VHCF model was developed by Leibniz-IWT. The experimental approach includes fatigue and crack growth investigations on simplified geometries to examine the influence of different carbon contents on the material properties of case-hardening steels under cyclic loading. The model taks into account the weakest link concept and was fully built up at the IWT. To build the model, compact tension tests and axial HCF tests were carried out with the different hardness states for both materials. On the part of the WZL, simulations of the local tooth root stress and a complete gear tooth characterization (hardness depth curves, residual stress measurements) contributed to the development of the material model.
