Generally, it is assumed that under any applied force there will always be some gap between the surfaces in a contact of rough elastic surfaces resulting in a discontinuous (i.e. multiply connected) contact. The presence of gaps along the line contact relates to the ability to form an adequate mechanical seal across an interface. This paper will demonstrate that for a twice continuously differentiable rough surface with sufficiently small asperity amplitude and/or sufficiently large applied load and/or sufficiently low material elastic modulus singly connected contacts exist. Solution of a contact problem for a rough elastic half-plane and a perfectly smooth rigid indenter with sharp edges is considered. First, considered a problem with artificially created surface irregularity and it is shown that for such a surface the contact region is always multiply connected. An exact solution of the problem for an indenter with sharp edges resulting in a singly connected contact region is considered and it is conveniently expressed in the form of a series in Chebyshev polynomials. A sufficient (not necessary) condition for a contact of an indenter with sharp edges and a rough elastic surface to be singly connected is derived. The singly connected contact condition depends on the surface micro-topography, material effective elastic modulus, and applied load. It is determined that in most cases a normal contact of a twice continuously differentiable rough surface with sufficiently small asperity amplitude and/or sufficiently large applied load is singly connected.
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