On the dependence of the leak-rate of seals on the skewness of the surface height probability distribution

Seals are extremely useful devices to prevent fluid leakage. We present experimental result which show that the leak-rate of seals depend sensitively on the skewness in the height probability distribution. The experimental data are analyzed using the critical-junction theory. We show that using the top-power spectrum result in good agreement between theory and experiment.Comment: 5 pages, 9 figure

Leak-rate of seals: effective medium theory and comparison with experiment

Seals are extremely useful devices to prevent fluid leakage. We present an effective medium theory of the leak-rate of rubber seals, which is based on a recently developed contact mechanics theory. We compare the theory with experimental results for seals consisting of silicon rubber in contact with sandpaper and sand-blasted PMMA surfaces.Comment: 8 pages, 11 figure

Leak-rate of seals: comparison of theory with experiment

Seals are extremely useful devices to prevent fluid leakage. We present experimental results for the leak-rate of rubber seals, and compare the results to a novel theory, which is based on percolation theory and a recently developed contact mechanics theory. We find good agreement between theory and experiment.Comment: 6 pages, 10 figure

Fluid flow at the interface between elastic solids with randomly rough surfaces

I study fluid flow at the interface between elastic solids with randomly rough surfaces. I use the contact mechanics model of Persson to take into account the elastic interaction between the solid walls and the Bruggeman effective medium theory to account for the influence of the disorder on the fluid flow. I calculate the flow tensor which determines the pressure flow factor and, e.g., the leak-rate of static seals. I show how the perturbation treatment of Tripp can be extended to arbitrary order in the ratio between the root-mean-square roughness amplitude and the average interfacial surface separation. I introduce a matrix D(Zeta), determined by the surface roughness power spectrum, which can be used to describe the anisotropy of the surface at any magnification Zeta. I present results for the asymmetry factor Gamma(Zeta) (generalized Peklenik number) for grinded steel and sandblasted PMMA surfaces.Comment: 16 pages, 14 figure

Heat transfer between elastic solids with randomly rough surfaces

We study the heat transfer between elastic solids with randomly rough surfaces. We include both the heat transfer from the area of real contact, and the heat transfer between the surfaces in the noncontact regions. We apply a recently developed contact mechanics theory, which accounts for the hierarchical nature of the contact between solids with roughness on many different length scales. For elastic contact, at the highest (atomic) resolution the area of real contact typically consists of atomic (nanometer) sized regions, and we discuss the implications of this for the heat transfer. For solids with very smooth surfaces, as is typical in many modern engineering applications, the interfacial separation in the non-contact regions will be very small, and for this case we show the importance of the radiative heat transfer associated with the evanescent electromagnetic waves which exist outside of all bodies.Comment: 23 pages, 19 figure

Fluid squeeze-out between rough surfaces: comparison of theory with experiment

We study the time dependency of the (average) interfacial separation between an elastic solid with a flat surface and a rigid solid with a randomly rough surface, squeezed together in a fluid. We use an analytical theory describing the fluid flow factors, based on the Persson contact mechanics theory and the Bruggeman effective medium theory, to calculate the removal of the fluid from the contacting interface of the two solids. In order to test this approach, we have performed simple squeeze-out experiments. The experimental results are compared to the theory predictions.Comment: 8 pages, 13 figure

Contact mechanics with adhesion: Interfacial separation and contact area

We study the adhesive contact between elastic solids with randomly rough, self affine fractal surfaces. We present molecular dynamics (MD) simulation results for the interfacial stress distribution and the wall-wall separation. We compare the MD results for the relative contact area and the average interfacial separation, with the prediction of the contact mechanics theory of Persson. We find good agreement between theory and the simulation results. We apply the theory to the system studied by Benz et al. involving polymer in contact with polymer, but in this case the adhesion gives only a small modification of the interfacial separation as a function of the squeezing pressure.Comment: 5 pages, 4 figure

Interfacial separation between elastic solids with randomly rough surfaces: comparison of experiment with theory

We study the average separation between an elastic solid and a hard solid with a nominal flat but randomly rough surface, as a function of the squeezing pressure. We present experimental results for a silicon rubber (PDMS) block with a flat surface squeezed against an asphalt road surface. The theory shows that an effective repulse pressure act between the surfaces of the form p proportional to exp(-u/u0), where u is the average separation between the surfaces and u0 a constant of order the root-mean-square roughness, in good agreement with the experimental results.Comment: 6 pages, 10 figure