A new solution to an old problem: designing an ultralow wear polymeric solid lubricant for bearing applications in challenging environments
Date
2018
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Publisher
University of Delaware
Abstract
A necessity of tribological systems in aerospace applications is functioning with long lifetimes and high efficiencies. Such demanding applications can prohibit the use of traditional lubricants due to physical, chemical, thermal, or other environmental challenges. This dissertation proposed to fulfill the need for advanced performing bearing materials in challenging conditions by using the body of knowledge gathered on a particular alumina-PTFE composite to improve tribomaterials design. ☐ The current model for alumina-PTFE necessitates a hard filler with multi-scale functionality and an operating environment that supports beneficial tribochemistry. This study proposed to satisfy the current model requirements by replacing alumina with a soft micro-sized filler that also supports tribochemistry in any environment. Several materials could meet these filler requirements, including micro-sized PEEK. A tribology study on PEEK-PTFE composites was implemented to test the proposed model for a relatively soft filler in lubricious matrix to display advanced bearing performance in conditions representing terrestrial and space operating environments. ☐ To conduct the proposed investigation, prior work was necessary to increase sample testing capacity and improve assessment of results. First, there existed a logistical limitation to the number of polymer materials that could undergo tribology testing in a timely manner. This barrier was overcome by designing, fabricating, prototyping, and implementing a wear testing tribometer with high-throughput capabilities. Second, it was necessary to establish a standard for numerically assessing the success or failure of polymer materials in bearing applications. This goal was achieved by studying common polymers and polymer composites, with a wide range in bearing performance, to identify a quantitative metric to reliably predict polymer wear rate. Finally, the equipment and methodologies developed in this dissertation were applied to testing PEEK-PTFE composites. ☐ This study identified PEEK-PTFE as the first solid lubricant to demonstrate ultralow wear rates and moderate friction in both dry and humid conditions, which support the high potential for this tribomaterial to fulfill the needs of the aerospace industry. The outcomes of this investigation have enhanced the understanding of tribological mechanisms driving the success of polymeric solid lubricants, and opened avenues for designing more composites to display advanced bearing performance in challenging environmental conditions.
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Keywords
Pure sciences, Applied sciences, Polymer tribology, Solid lubricant, Transfer film, Wear rate