When two macroscopically smooth surfaces come into contact, initially they only touch at a few of these asperity points.Friction and wear originate at these points, and thus understanding their behavior becomes important when studying materials in contact.It has been reported that an increased roughness may under certain circumstances result in weaker frictional interactions while smoother surfaces may in fact exhibit high levels of friction owing to high levels of true contact.[3] The Archard equation provides a simplified model of asperity deformation when materials in contact are subject to a force.Due to the ubiquitous presence of deformable asperities in self affine hierarchical structures,[4] the true contact area at an interface exhibits a linear relationship with the applied normal load.
The top image shows asperities under no load. The bottom image depicts the same surface after applying a load.
