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Many freight railcars rest on polymer adapter pads made of injection-molded Thermoplastic Polyurethane (TPU) polymers which feature two copper studs to provide electrical conductivity through the pad. This design feature allows signal transmission from the track to the onboard systems, including cargo gates and pneumatic actuators. While in service, the polymer pads experience impact and cyclic loading that produce shear, resulting in the abrasive wear and plastic compression of the copper studs which leads to signal interruptions and loss of function requiring the periodic replacement of these polymer pads. This causes increased downtime due to maintenance and reduced reliability in the automated systems since pad failure is unpredictable. This limitation in current designs is the driving concern behind the effort to create an electrically conductive polymer adapter pad that would provide a durable conductive path between the rail and freight car side-frame.

To that end, the University Transportation Center for Railway Safety (UTCRS) has been working on developing a conductive composite blend of TPU and Carbon Nano Fibers (CNF) to create injection-molded polymer composite inserts that can provide the necessary conductivity without the need for the copper studs that are susceptible to wear. Previous work done on this project was successful in creating a TPU-CNF composite insert that provided the required electrical conductivity at full railcar loads but was inconsistent at empty railcar loads. Thus, current work presented here focused on studying the fiber orientation that would produce consistent conductivity at all railcar loads. Based on these findings, a new mold was fabricated to create injection-molded polymer composite inserts with the effective fiber orientation. Laboratory test results show that the newly created composite inserts provide approximately double the needed conductivity required for a 24-Volt railcar valve to actuate when tested under the minimum load conditions an adapter would experience in field service. This paper summarizes the work done on fiber alignment and the results of the testing performed on the UTCRS dynamic bearing test rigs.


© 2022 by ASME. Original published version available at

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Proceedings of the 2022 Joint Rail Conference. 2022 Joint Rail Conference





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