Elucidating the contact mechanics of aluminum silicon surfaces with Green's function molecular dynamics

We study the contact mechanics of a flat, elastic wall pressed against a rigid substrate with Green's function molecular dynamics. The substrate's height profiles are parametrized from atomic force microscope topography measurements of two different aluminum-silicon alloys. In both samples, roughness lives on disparate length scales, i.e., on relatively large scales defined by size and mean separation of load-bearing silicon particles and on much smaller scales associated with the roughness on top of individual particles. The major differences between the two alloys are their silicon content and the typical silicon particle geometry. These differences lead to quite different stress distributions on both mesoscale and microscale in our calculations. A common feature is that the stress distribution decays exponentially for large stresses sigma and not like a Gaussian. Persson's contact mechanics theory is generalized to the case where contact can only occur on silicon particles. This generalization predicts relatively accurate microscopic mean square stresses, however, it fails to predict accurate numbers for mean square stresses on the mesoscopic scales. Local overlap models are not accurate either, because they fail to describe the contact morphology. (c) 2007 American Institute of Physics.