Multi-scale simulations of the contact mechanics of lubricated, rough surfaces

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The applicants at UWO and General Motors of Canada (GM) will carry out collaborative research related to wear in aluminum engines.  Wear limits the life span of mechanical devices with moving parts such as cylinders and pistons in car engines.  Understanding and controlling wear is of obvious economic interest to companies and consumers alike. However, surprisingly little is known about the microscopic origins of wear.  One reason for this deficiency is that the distribution of local pressures in engineering contacts is difficult to predict.  Even highly polished surfaces turn out to be very rugged when looked at with sufficiently high resolution.  To complicate things, it is difficult to assess the behaviour of the lubricant immersed between the moving parts.  For example, it is very difficult to predict whether the lubricant gets squeezed out when two asperities (little bumps) of two opposed surfaces collide or whether it solidifies in response to the immense local pressures in these microscopic points of contact.  Things become even more complicated for modern, fuel-efficient, aluminium-based engines.  Not only are the surfaces rugged, but in order to harden the materials, little silicon crystals are embedded into the aluminium matrix.  These crystalites stick out of the surfaces and supposedly carry most of the load in sliding contacts. Unfortunately, very little is known as yet about the true pressure distribution. Conventional methods to describe contact mechanics break down for these systems.  By combining atomistic computation techniques with more conventional methods, we intend to assess what factors lead to favourable mechanical behavior. More specifically, the simulated stress distribution on a rough Al-Si surface promises to give valuable guidelines as to how one might want to optimize the geometry of surfaces, which lubricant properties are preferential (strong or weak pressure dependence of viscosity) and whether one would want good stick conditions of a lubricant on the aluminum and/or on the silicon-dominated grains.  This information can then be used to design aluminum engines for minimal sliding friction and high wear resistance.