Abstract

In order to reduce the emissions of greenhouse gas (GHG), many industries are turning towards more environmentally friendly technologies. The aerospace industry is particularly targeted as gas turbine engines will be required to reduce their CO2 emissions to net zero. New challenges will arise regarding the conditions in which materials are expected to operate (e.g. high temperatures, high velocities, high pressures) in order to achieve this goal. More conventional metals and alloys currently used in engine manufacturing will most likely be limited by their mechanical and tribological properties and thus, proper selection of materials is primordial to ensure the performance and efficiency of engines. Fiber-Reinforced Polymer (FRP) composites have been widely used in the aerospace industry and is one alternative solution due to their lightweight and high-strength properties. However, when considering FRP for the purpose of gas turbine engines, it is also important to consider the orientation of the fibers. Since there are a lot of moving and contacting mechanical assemblies in the engines where a high quantity of elements such as bearings and seals are present, the orientation of the fibers in FRP play a crucial role in ensuring good tribological behaviour. Many different studies have previously performed extensive characterization of carbon reinforced polymer composites and have demonstrated the impact of the parallel and anti-parallel orientation of the fibers on the mechanical properties and tribological behavior of composites. However, FRP composite with fibers oriented in the normal direction, which have shown improved mechanical properties, have received little attention regarding the impact of orienting vertically the fibers on the tribological properties.
The purpose of this study is to fully capture the influence of the fiber direction (parallel, anti-parallel and normal direction) in fiber-reinforced composite, with an emphasis on carbon fiber/ PEEK composite, and the influence on its tribological behavior for the purpose of gas turbine engines. The research performed throughout this study is divided into two parts where the influence of fiber direction in FRP composites on the tribological behaviour have been critically examined. The main focus of the first study is to identify the influence of fiber orientation on the surface energy and tribological behavior of CF-PEEK systems for the Fan and LPC region of the gas turbine engine (i.e. room temperature). The focus of the second study is to identify the influence of temperature on the tribological behavior of carbon fiber-reinforced PEEK. The tribological tests were performed using a ball-on-disk tribometer where the samples were subjected to different testing parameters to simulate more accurately the operating environment the material would have to go through in the engine. This includes a high loading, an elevated testing temperature, and a high number of cycles. The characterization to obtain the interfacial phenomena of the different worn surfaces and counterfaces was done using Scanning Electron Microscopy (SEM), confocal laser scanning microscopy (CLSM), Energy Dispersive X-ray Spectroscopy (EDS) and Atomic Force Microscope (AFM). Overall, it was found that there is a clear benefit of using CF-PEEK reinforced with fibers in the normal direction since it showcases better tribological properties, a higher reliability and higher potential of integrations within the gas turbine engines.