Effects of case hardening properties on the contact fatigue of a wind turbine gear pair

Abstract

Contact fatigue is an important issue in gear industry as it influences the reliabilities of mechanical equipment. Case-hardening processes could provide better mechanical properties by increasing the surface hardness and generating compressive residual stress. Yet these processes still cannot avoid contact fatigue problems and careful modeling is required. These processes generate gradients of mechanical properties below the surface, increasing complexities of contact analysis and fatigue life prediction. A numerical model is proposed to study the effect of the hardening layer on the carburized gear contact fatigue behavior. The gradients of the residual stress and the hardness are measured and the contact fatigue risk is evaluated using the concept of the material exposure. The effects of residual stress distribution, effective case depth, and surface-core hardness discrepancy on the contact fatigue performance of the gear are investigated. Results show that the contact fatigue of subsurface and the case- core transition area should both be evaluated to estimate the risk of pitting and tooth flank fracture.