Jumplike variation of the contact area between randomly rough surfaces

A numerical model of the contact between two solid surfaces with statistically random roughness has been considered. As the two surfaces are brought in contact and pressed against each other, the real contact area initially increases in proportion to the normal force, with a proportionality factor dependent on the spectral density of the surface profile. As the pressing force grows further, the contact area exhibits two sequential jumps. This behavior is universal, being manifested for various spectral densities of the surface roughness in both two-and three-dimensional cases. The physical reasons for the observed features and their role in the mechanics of contact between soft materials (rubber, biological tissues) are discussed. The effect can be used for creating new adhesive systems capable of exhibiting strong adhesion upon application of a critical pressing force.