Experimental, Analytical and Finite Element Studies of the Nanoindentation Technique to Investigate Material Properties of Surface Layers Less Than 100 Nanometers Thick

Scuffing as a phenomenon has been studied for many years, however, the mechanism underlying scuffing remains unexplained. Recent findings suggest that the most significant changes occur in the top 50 ??? 100 nm of the surface, not at the micron level as previously suggested. The goal of this study is to identify different layers and their material properties on Al390-T6 disk surface and incorporate them into a thermomechanical Finite Element model to compare with tribological testing in a High Pressure Tribometer that simulates the contact in actual air conditioning compressor surfaces. Experimental, analytical and Finite Element studies of the nanoindentation technique are developed and used to investigate the material properties of surface layers less than 100 nm thick. All the methods are first verified in simple cases such as homogeneous materials and deposited thin film, then applied to rougher engineering Al390- T6 sample. The thin surface layers and the corresponding properties obtained from the above studies are then integrated into a thermomechanical FEM model to study the scuffing mechanism for the Al390-T6 disk and steel shoe sliding contact condition experienced in the High Pressure Tribometer that simulates realistic tribological contact in air conditioning compressor surfaces. It is shown that the FEM for nanoindentation is very useful as it is able to obtain additional properties and quantify properties of layers. It is found that a simple thermomechanical macro model does not provide sufficient information about the cause of scuffing. A FEM asperity-based micromodel is then built and successfully shows that the local contact stress and temperature increase could be extremely high under the critical loading. Also, it shows that scuffing should be a combination effect of stress and temperature increase.Air Conditioning and Refrigeration Project 12