微动磨损对弹条II型扣件弹条断裂的影响分析

弹条是实现弹条II型扣件功能的主要元件，传统的疲劳分析方法主要从弹条的应力、应变入手，这并不能反映真实情况，因为弹条在工作中与其它构件接触面表面之间存在微小的相互移动，即微动．应用非线性接触理论，采用库仑摩擦模型模拟弹条与周围接触元件之间的摩擦接触情况，计算出弹条各点的剪切应力τ、相对位移δ及二者乘积τ·δ的值；并采用离散裂缝模型来模拟扣件裂纹的生成及扩展．理论分析表明，若微动磨损在弹条疲劳断裂过程中起主要作用，则断口处应位于弹条中τ·δ值最大的点附件．扣件疲劳试验表明，弹条断口处位于弹条尾部与轨距挡板接触处，处于τ及τ·δ最大的点之间且更靠近τ·δ值最大的点．弹条尾部与轨距挡板之间由于微动磨损产生裂纹，形成污染源，反复作用下，裂纹扩展，最终导致弹条断裂．试验证明了弹条微动磨损理论分析的正确性，为改进弹条设计，提高其疲劳寿命提供科学依据．

Effect of Fretting Wear on Fracture of Type II Fastener Elastic Bar

The function of type II fastener is mainly achieved by the elastic bar. The traditional methods for the study of fatigue dealing with stress or strain do not reflect the true situation because the contact surface between the elastic bar at work and other with other components leads to tiny mutual movement, namely fretting. The shear stress（T） , relative displacement（δ） and the product of them（τ·δ） of the elastic bar are calculated by application of the nonlinear contact theory and the Coulomb friction model. A discrete crack model is then used to simulate the fastener crack generation and propagation. It is shown through theoretical analysis that the fatigue fracture should be located in a section close to the maximum value of theτ·δ if the fretting wear plays a major role. Fastener fatigue tests indicate that, a fracture is found at the tail of elastic bar and baffle contact, which is between points of the τ value and the maximum τ·δ value, while being a little closer to the latter one. The fret- ting wear between the tail elastic bar and baffle results in cracks, which are then propagated repeatedly and leads to the eventual fracture. The correctness of the fretting wear theory is proved by the experiment, which provides scientific basis for improving the fastener design and enhancing its wearability.