An Investigation into the Relation between Wheel/rail Contact and Bolt Tightness of Rail Joints Using a Dynamic Finite Element Model

Rail joints have a shorter service life than most other railway track components. The discontinuity between rail ends turns the rail joint into a weak spot, and consequently, into a track component demanding more frequent maintenance measures, which result in high maintenance costs. Moreover, difficulties are often found when assessing the damage condition of rail joints since damage conditions like cracks in the rail web or loose bolts cannot be detected by visual inspection. A better understanding of the damage mechanisms and degradation process of rail joints may help to develop adapted maintenance measures and to improve rail joint design. In this paper, a 3D Finite Element model is presented as base for rail joint study. The model represents accurately the main components (rail, sleeper, joint bars and wheel) and the interaction between them (contact). The model is validated between 150 and 800 Hz with measured axle box accelerations of resilient wheels. Higher frequencies may be reached with an improved model of the rubber. In the paper, the influence of the bolt tightness is studied. The results showed that contact force, specially its variation, is strongly affected by the bolt tightness; loose bolts cause higher contact forces. The effect of vehicle speed on wheel/rail contact is also significant mainly due to the interaction between rail and sleepers in the vicinity of the rail joint. Apart from bolt tightness conditions and vehicle speed, the validated model has the potential to study the influence of other track parameters and damage conditions.