介观尺度下风电齿轮的疲劳损伤演化机理

Fatigue Damage Evolution Mechanism of Transmission Gears in Wind Turbine at Mesoscopic Scale

为了全面解析风电齿轮的疲劳损伤演化机理,以某1.5 MW风力发电机高速级齿轮为研究对象,基于Voronoi图与多晶体组织的几何相似性,建立介观尺度下的齿面模型,采用内聚力单元模拟晶界对基体的割裂作用,引入双线性分离曲线作为评判损伤的依据.采用周期跳跃的加载方式模拟齿面接触载荷的循环累积效应,仿真预测接触疲劳裂纹的萌生位置及其疲劳寿命,并探讨风速变化和齿面间摩擦因数对疲劳裂纹演化的影响.结果表明,齿轮在疲劳损伤初期的演化速率较慢,随着损伤量的不断累积,其损伤速率逐渐加快.针对研究对象,在距齿面深度0.13、0.27 mm处最先出现裂纹,并伴随接触应力的循环加载逐渐扩展,最终于齿面形成典型的剥落破坏.此外,通过对比分析还可以发现,高风速和齿间润滑不良均显著降低齿轮的寿命.

To comprehensively illustrate the fatigue damage evolution mechanism,a pair of high-speed gears in a 1.5 MW wind turbine was selected as the research object.Based on the geometric similarity between Voronoi diagram and polycrystalline structure,a mesoscopic tooth surface model was established with Voronoi tessellation.Cohesive elements were inserted in the model to simulate the fragmented effect of grain boundary on matrix.The bilinear-separation curve being related to cohesive elements was used to evaluate whether the damage originates or not.Then,jumping-in-cycles(JIC)loading method was applied to simulate the cyclic cumulative effect of contact loading due to gear meshing.As a result,the initiation location and initiation life of contact fatigue crack were simulated and predicted,and the effects of wind speed change and friction coefficient on crack evolution were discussed.Results show that the damage evolution rate is relatively slow at the initial stage,and gradually increases with the loading process and damage accumulation.For the investigated gear and its working conditions,the first two cracks appear at the depth of 0.13 mm and 0.27 mm under the gear surface.Initial cracks grow gradually under cyclic loading of contact stress,and finally form typical surface spalling failure.Additionally,higher wind speed and worse lubrication condition will significantly reduce the life of wind turbine gears.