Properties of a single asperity and the interface between molecular dynamics and continuum mechanics: A commentary

摘要

The speakers in this session attempted to bridge the large spatial gap between the atomistic processes occurring at a sliding interface and the continuum description of such processes. This task is indeed formidable. One may ask why should we study such elementary processes at all if what we are really interested in is a global picture of friction. Real surfaces are uneven, impure, and may be covered by nasty things like lubricants specifically placed there to modify frictional behavior. Isn't the real world of friction too ''dirty'' to be studied by surface science techniques. Indeed, even if we were to understand the interaction of every geometry of single asperity under every environment, how to average this information to produce a model of friction is unknown. Does this mean that we shouldn't attempt to measure and calculate these simple processes. I think not. Understanding the response of a single asperity is an important essential element which will lead to a thorough predictive understanding of friction. But clearly our work cannot end with the study of single asperities. There are two critical phenomena which have to be added to a single asperity model: first the inclusion of a distribution in both size and location of single asperities and second the role of microstructure evolution. Clearly single asperities do not respond independently from each other. The proximity of two asperities changes both the local stress distribution as well as the contact area. I believe the greatest challenge that faces us is how to assemble the vast amount of single asperity data that we can generate and from it create useful engineering models.