持续制动工况下轴装制动盘螺栓载荷演化规律

Variation of Bolt Loads of Axle Braking Disc under Continuous Braking Condition

制动盘螺栓紧固结构的完整性对于保证良好的制动性能至关重要。通过建立热-机耦合有限元分析模型,研究列车在长大下坡持续制动过程中轴装制动盘螺栓的载荷演化规律。结果表明,在制动表面产生的热量向制动盘内部及其他连接结构传递的过程中,制动盘中的温度梯度是导致螺栓载荷出现变化的主导因素。螺栓的轴向拉伸载荷出现先下降后反弹的演化规律,不均匀的温度场使螺栓内部出现弯曲载荷,且螺栓的周向弯曲载荷明显大于径向弯曲载荷。对流换热系数的增加可以减小螺栓轴向拉伸载荷和弯矩的变化,但当对流换热系数增加到一定值时,这种影响逐步减小。螺栓与周围结构热膨胀系数的差异会加剧螺栓载荷的变化,可能会导致螺栓自松的风险增加或者螺栓弯曲失效。螺栓预紧力对螺栓弯矩变化没有影响,而对螺栓轴力变化有一定的影响。

The integrity of bolted joint in braking disc system is critical to the good quality of braking performance. A thermo-mechanical coupling finite element model is established to investigate the load variation of bolted joint in axle braking disc of railway vehicle under continuous downhill braking condition. The transient temperature gradient in the brake disc is the key mechanism for the variation of bolt loads. The bolt tension drops firstly and then bounces back, while the bending moment is introduced in the bolt due to temperature non-uniformity. The circumferential bending moment is significantly higher than that in the radial bending direction. The bolt load variation decreases with the increase of the convection heat transfer coefficient, but the influence is gradually reduced when the convection heat transfer coefficient reach a certain value. The mismatch of thermal expansion coefficient of bolt with surrounding structure causes the increased variation of bolt tension and bending moment, which may cause either the loosening or the bending failure of bolt joint. The initial preload has no much influence on the thermally-induced bending moment but a moderate influence on the variation of tension.