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We use the Cellular Potts Model (CPM) to study the contact angle (CA) hysteresis in multiphase (solid-liquid-vapour) systems. We simulate a droplet over the tilted patterned surface, and a bubble placed under the surface immersed in liquid. The difference between bubbles and droplets was discussed through their CA hysteresis. Dependency of CA hysteresis on the surface structure and other parameters was also investigated. This analysis allows decoupling of the 1D (pinning of the triple line) and 2D (adhesion hysteresis in the contact area) effects and provides new insight into the nature of CA hysteresis.

During the running-in process, a friction pair experiences drastic evolution in many of its tribological parameters, such as surface roughness, wear rate, and coefficient of friction until steady-state is attained. In this paper, we present a model for predicting the behavior of the running-in process. Specifically, we determine a general relationship between the wear loss and surface roughness during the running-in stage and test the validity of its prediction of wear rate by comparing to available experimental results. We show, by using a dimensional analysis and applying the Buckingham Pi theorem, that there exists a linear relationship between the transient dimensionless wear, the dimensionless initial surface roughness, and dimensionless running-in time.

We investigate the possibility of Turing-type pattern formation during friction. Turing or reaction-diffusion systems describe variations of spatial concentrations of chemical components with time due to local chemical reactions coupled with diffusion. Turing systems can lead to a variety of complex spatial patterns evolving with time. During friction, the patterns can form at the sliding interface due to the mass transfer (diffusion), heat transfer, various tribochemical reactions, and wear. We present simulation data showing the possibility of such pattern formation. On the other hand, existing experimental data suggest that in situ tribofilms can form at the frictional interface due to a variety of friction-induced chemical reactions (oxidation, the selective transfer of Cu ions, etc.). These tribofilms as well as other frictional "secondary structures" can form various patterns (islands or honeycomb domains). This mechanism of pattern formation can be attributed to the Turing systems.