Investigation of the mechanism of impact vibration enhancement at the joint of tongue rail in turnout based on the combination of displacement measurement with small-size cameras and finite element analysis

Impact vibration due to the train passage at the joint of tongue rail has been known to induce the fatigue fracture of the hinged lug of turnouts. The impact vibration is considered to be enhanced by the mismatch of rails, the gap between the tongue rail and the base plate, and the loss of the tightening force of the bolt at the joint plate. However, the detailed mechanism has been unrevealed since the direct observation of the joint during train passage is inaccessible. In this study, we first measure the displacements of the tongue rail at the joint during train passage using small-size cameras. We evaluate the turnout whose hinged lug was broken. Displacement measurements show that the heel of the tongue rail (close to the joint) moves vertically downward by 3.9 mm and the toe of the tongue rail moves vertically upward by 2.3 mm when the train passes through the joint. Finite element analysis reveals that the downward displacement of the heel is caused by the gap between the tongue rail and the base plate and the upward displacement of the toe is caused by the rotation of the tongue rail around the supporting base plate. Acceleration measurements show that two peaks of impact acceleration enlarge the acceleration amplitudes (4400–7500 m/s2). Finite element analysis reveals that the first and second peaks are caused by the collision between the tongue rail and the wheel and that between the tongue rail and the base plate, respectively. Our results indicate that the gap between the tongue rail and the base plate should be minimized in addition to the mismatch of rails to reduce the amplitude of the impact vibration.