Prototyping a Conductive Polymer Steering Pad for Rail Freight Service

The AdapterPlus™ steering pad is a polymer component on a railcar that helps to reduce stresses on the axle as a railcar rounds a curve. One railway application requires a minimum of 240 mA to be passed through the steering pad to the rail, which activates air valves that control automated cargo gates. Currently, two copper studs are inserted into the pad to provide a conductive path. However, after continuous cyclic loading caused by normal service operation, the copper studs deform, wear, and eventually lose contact between the two surfaces rendering the pad nonconductive. One proposed solution to this problem is to create a steering pad made entirely from an electrically conductive material. The University Transportation Center for Railway Safety (UTCRS) research team has successfully created a conductive nanocomposite made from vapor grown carbon nanofibers (CNFs) and a modified form of Elastollan 1195A thermoplastic polyurethane (TPU). Previous attempts to create this material were promising but failed to produce an electrically conductive specimen when injection molded. Preliminary results have shown that the new material can be injection molded to create an electrically conductive test specimen. An injection molded insert was designed, fabricated, and incorporated into the existing steering pad design for further testing. Pressure measurement film had previously been used to find the points of maximum stress inside the pad to optimize the design of the composite insert. Characterization of the resistivity of the composite material was carried out in order to verify functionality in future iterations of this product. The resistance of the composite material is expected to be non-linear with a strong dependence on load and voltage. Conductivity tests were performed using a material testing system with a compressive load ranging from 1500 pounds to 5500 pounds. The voltage at each load was also varied between 10V to 20V and the nonlinear resistance of the material was examined. The results have shown that the CNF/TPU composite is a potential replacement for the current TPU used for the pad and, with minimal modifications, can be implemented in field service operation.