Experimental Investigation of Contact Stresses Between a U.S. Locomotive Wheel and Rail

Abstract

An experimental study of the real contact stresses for U.S. locomotives and rails including the effects of plasticity and wear has been performed under laboratory Hertzian simulation using the IIT-GMEMD wheel-rail simulation facility. Experiments were performed under both traction and braking conditions to account for differences observed earlier in the two modes. Wheel/rail tests were conducted using adhesion coefficients of 0.02, 0.15, and 0.25. Average contact stresses for various stages of wear were determined by measuring the contact areas. A synthesis of all the data generated showed that for operation of purely tractive wheels of a typical U.S. locomotive on a rail, the stabilized average contact stress ranges from approximately 100 to 25 ksi as the continuous operating adhesion coefficient ranges from 0 to 0.25. In order to determine the contact stresses for locomotives under field conditions, measurements of contact stresses were made on three different locomotives with wheels of different degrees of wear. Contact stresses for locomotives were found to be higher than stabilized contact stresses established by laboratory simulation tests. The locomotive wheel contact stresses were found to be closer to freight car wheel stabilized contact stresses established in an earlier study than for the laboratory locomotive simulation. It is suggested that this is due to the fact that 20 to 50 times as many cars operate on the same rails as do locomotives. On the basis of these experiments it is recommended that for U.S. locomotive wheels an average stabilized contact stress of approximately 65 ksi rather than the current 138 ksi would be quite stable. Profile and dynamic stability should be achieved simultaneously in such an approach. Currently available 2-D theories have been used to compare the experimental data showing poor agreement and reasons for discrepancy.