Modeling of contact fatigue damage behavior of a wind turbine carburized gear considering its mechanical properties and microstructure gradients
Carburized gears are commonly used in heavy-duty machines such as wind turbines, ships and high-speed rails. The gradient characteristics of mechanical properties and microstructure from the case to the core and the complex subsurface stress state in service make it very challenging to understand the contact fatigue performance of the carburized gears. In this study, a numerical model considering the effects of mechanical properties and microstructure gradients is developed to investigate the contact fatigue damage behavior of a wind turbine carburized gear. The hardness gradient in the case depth is modelled using Thomas empirical equation. The microstructure gradient is considered in terms of the grain size variation adopting the technique of Voronoi tessellation. The damage-coupled elastic-plastic material constitutive relations are developed to capture the intergranular mechanical response and the progressive fatigue damage under repeated gear meshing. The results indicate that the shear stress reversal is not uniformly distributed along the grain boundaries of the same depth. The critical subsurface depth of crack initiation and the fatigue damage evolution obtained from the calculation model compare well to the experimental and numerical results readily available in literature. With the developed framework, the influences of normal load and case carburization on the fatigue damage behavior of the carburized gear are also investigated and discussed in detail.