Stribeckeffekten

Stribeckeffekten, often translated as the Stribeck effect, is a phenomenon observed in tribology, the study of friction, wear, and lubrication. It describes the relationship between the friction coefficient and the speed of relative motion between two surfaces under lubrication.

The effect is typically visualized through a Stribeck curve, which plots the friction coefficient on the y-axis against the Hersey number on the x-axis. The Hersey number is a dimensionless parameter that represents the degree of lubrication and is calculated as the product of viscosity, relative speed, and the inverse of the load per unit area.

At very low speeds or under high loads, the lubricant film is thin and easily squeezed out, leading to boundary lubrication. In this regime, friction is high due to direct contact between the asperities of the surfaces. As the speed increases or the load decreases, the lubricant film thickness grows.

The Stribeck curve typically exhibits three distinct regions. Initially, as speed increases from zero, the friction coefficient decreases sharply. This is the mixed lubrication regime, where both direct surface contact and hydrodynamic lubrication occur. Further increasing the speed leads to the hydrodynamic lubrication regime. In this region, the lubricant film is thick enough to completely separate the surfaces, and friction is relatively low and stable, primarily due to viscous shear within the lubricant. At even higher speeds, the friction coefficient may begin to increase again, often attributed to increased viscous dissipation and lubricant shear heating, which can reduce lubricant viscosity.

Understanding the Stribeck effect is crucial for designing bearings, gears, and other machine elements to ensure efficient and long-lasting operation by operating within optimal lubrication regimes.