Mesoscopic dynamic characteristics and RCF damage evolution of high-speed transmission gear in wind turbine

Abstract

For the gears utilized in wind turbines, the main reason leading to malfunction is the crack initiation and propagation under cyclic loading. In the gear engagement process, the fatigue damage accumulates gradually and formulate visible microcrack if the fatigue parameter reaches to specified threshold. In order to simulate the fatigue evolution in wind turbine gears, a mesoscopic model is established, in which the Voronoi tessellation and cohesive elements are integrated, such that the crystal structure and grain boundary can be modeled. The dynamic stress distribution and fatigue evolution phenomenon are then investigated under different working conditions. The loading in the meshing region is simplified as moving load on a semi-infinite plane, so the shear stress distributions for per loading cycle are obtained. Furthermore, bilinear traction-separation law (TSL), Jump-in-Cycles (JIC) loading methodology and multi-axial fatigue criterion are involved to fulfill the damage accumulation simulation. As a result, the initiation location and propagation pattern of the fatigue crack are predicted, and the fatigue life curve is also obtained. Thereafter, the influence of wind speed and lubrication condition on fatigue damage evolution is also discussed. The results have shown that the wind loading mainly influences the magnitude of the maximum shear stress, whereas the contact width will determine the location of the maximum shear stress. When the whole fatigue evolution procedure is finished, the first two cracks initiate at the depth of 0.13 mm and 0.27 mm beneath the surface respectively, and then propagate into the substrate. Through comparative analyses of fatigue life curves, it can be concluded that higher wind speeds and poor lubrication conditions will reduce gear service life significantly.