Laboratory Investigation of Wheel Rail Contact Stresses for U.S. Freight Cars

Importance of the wheel rail contact stresses in track degradation and safety of trains is discussed. Theroetical elastic contact stresses based on Hertz theory for various U.S. railroad cars are presented. These contact stresses were produced for simulation of different cars on the IIT-GM-EMD wheel rail simulation facility which is briefly discussed. Experimental measurements of contact areas at the facility for 55, 70, 95 and 125 ton cars, including changes due to the plasticity and wear effects are given. Based on these, the average contact stress variation with time is shown. It is observed that the contact stresses for cars stabilize at a nearly constant value within a range of 88–103 ksi. Due to increased plasticity effects under cyclic loading the stabilized contact stress levels for heavier cars are found to be at lower stress levels as compared to lighter cars. Stabilized contact stresses are compared with theroetical values predicted by Melan and Johnson under simplified load and material behavior conditions. Experimental values are somewhat higher as expected. Laboratory data on contact stresses is compared with contact stresses measured at the Facility for Accelerated Service Testing for 100 ton cars. Good corroboration with laboratory data was observed. A summary comparison of current industry design contact stresses with laboratory and field measurements shows that the contact stresses are too high and not stable for U.S. freight cars using the current AAR standard wheel rail designs. A concept of profile stability is proposed for future profile designs which are much needed for the heavy tonnage cars.