Study on Tooth Interior Fatigue Fracture Failure of Wind Turbine Gears

Gear contact fatigue has becoming a bottleneck restricting the safety and reliability of wind turbine transmission systems. Tooth interior fatigue fracture (TIFF) failure is commonly observed in case-hardened wind turbine gears. In this work, a contact fatigue model is developed to investigate the effect of design parameters and material properties on TIFF of wind turbine gears. The sub-surface stress field is obtained by superposing the load-introduced stress and initial residual stress. The hardness gradient of the hardened layer is measured by Vickers hardness tests. Based upon the stress field and material properties, a fatigue parameter analysis is presented to characterize the risk of TIFF by using the Dang Van multiaxial fatigue criterion. Results show that the risk of TIFF increases with increasing external load. Increasing pressure angle and residual compressive stress could reduce TIFF risk. The combination of high surface hardness, low core hardness, and large effective case depth could inhibit the crack initiation.