An overview of contacts relevant to tribological load in aerospace is presented including examples from airplanes, helicopters and satellites. The specific requirements for different aircraft and space applications are explained.

This study places emphasis on the approach how to solve tribological problems (e.g. fretting, wear) in aerospace applications. The main focus relies on coatings for aerospace components. However tribological functions are also important for tools for the manufacturing of aerospace parts. In the frame of this approach different test methods with increasing level of complexity are used to determine the solution candidates.

A preselection of coatings can be made considering the process parameters of the coating deposition. It is mandatory to avoid changes of the substrate properties (hardness, microstructure, fracture toughness). These changes can be caused by temperature, special process gases or the coating material. Evaluation of the key parameters like loads, movements, contact partners, temperatures and environment during the use of the component enables the selection of relevant materials and/or coatings to be tested in standard lab-tests (e.g. pin-on-disc, Taber® Abraser). The results obtained from these tests give basic information (coefficient of friction, wear) under clean laboratory conditions with special contact geometry. Based on the results from laboratory testing a custom-built component test is designed with contact geometry and loads (surface pressure, vibration frequency) comparable to the real application. This test gives information about the behaviour of the coating or surface treatment under application related conditions. The reliability of the component test is investigated employing the materials in its initial stage as a reference (e.g. without coating). Coatings or surface treatments which meet the requirements are considered for flight tests. Two examples of laboratory and component test equipment for fretting and long amplitude wear are shown.

Furthermore some practical examples from different aerospace applications are discussed, which demonstrate the use of various coating technologies (PVD, hybrid coating, galvanic process, special grease) to work against existing tribological challenges.

We present the results of massively parallel molecular dynamics simulations of realistic AFM tips in contact with silica surfaces coated with self-assembled monolayers (SAMs). Detailed analysis demonstrates that the commonly applied JKR and DMT models do not accurately predict the contact mechanics of these systems. Shear simulations reveal the effects of varying tip radius (from 3 to 30 nm) and the addition of a SAM coating to the tip itself. We show that small applied loads are sufficient to damage the SAM, enabling the penetration of water which leads to further debonding of the coating. Our simulations of coated and uncoated tips additionally provide evidence supporting a recently proposed plowing mechanism of energy dissipation¹.

Sandia is a multiprogram laboratory operated by Sandia Corp., a Lockheed Martin Company, for the United States Department of Energy's National Nuclear Security Administration under Contract DE-AC04-94AL85000.

¹ E.E. Flater, W.R. Ashurst, R.W. Carpick, Langmuir, in press (2007).