A NEW THEORY OF RAIL-WHEEL INTERACTION

Nature has clearly distinguished the complex rail-wheel interaction zone by endowing it with very high frequency vibrations of such order that the magnitude is 100 to 1,000 times more than those obtained in other linked masses like ballast or vehicle suspension. This is taken advantage of in formulating a simple hypothesis from fundamental principle of physics and vibrating masses, to estimate dynamic wheel load variations at the wheel rail interacting zone and is validated by comparing with actual field data available involving diverse vehicles starting from 4-wheel and 8-wheel freight stock to diesel and electric locomotives on different track structures. The theory takes into account rail and sleeper masses, their connectivity, the dimension of contact area, the rail top radius and wheel radius and the wheel load along with speed but overlooks vehicle suspension characteristics as well as ballast and formation characteristics. Using the theory the coefficient of dynamic component and high accelerations in rail in case of TGV train of SNCF at 300 km/h are predicted and shown to agree fairly well with values obtained in the field. The transient but heavy peak loads recorded by JNR for their 951 type train at 210 km/h as also their reduction is also their reduction is also explained. A parametric study is done using the theory to show that lightly loaded coaching stock may become critical at speeds in excess of 110km/h on tracks not provided with elastic fastenings.