Time-dependent fluid squeeze-out between solids with rough surfaces.

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. As an application we discuss fluid squeeze-out between a tire tread block and a road surface. Some implications for the leakage of seals are discussed, and experimental results are presented to test the theory. The theoretical prediction for the leak rate as a function of the fluid pressure difference is in good agreement with the experimental data for all fluid pressures up to "lift-off", where the fluid pressure equals the nominal rubber-substrate squeezing pressure.