Oberflächenermüdungsbruch

Oberflächenermüdung, often translated as surface fatigue, is a phenomenon that occurs in materials subjected to repeated cyclic stresses on their surface. This type of fatigue differs from bulk fatigue, which initiates and propagates cracks from within the material. Surface fatigue is primarily driven by surface-related phenomena such as contact pressure, wear, and environmental interactions.

The process typically begins with the formation of microscopic cracks at or very near the surface. These cracks can originate from stress concentrations caused by surface imperfections, subsurface defects, or the applied cyclic loading. Under continued stress, these cracks propagate both laterally along the surface and downwards into the material. Eventually, these propagating cracks can link up, leading to the detachment of material fragments.

Common examples of where surface fatigue is observed include rolling element bearings, gears, and rail surfaces. In bearings, the repeated contact between the rolling elements and the raceways generates high contact stresses, which can lead to the formation of spalling – the characteristic pitting or flaking of the surface. Similarly, gears experience surface fatigue due to the meshing of teeth, which involves sliding and rolling contact under load.

The susceptibility of a material to surface fatigue depends on several factors, including its hardness, microstructure, surface finish, and the presence of any surface treatments like case hardening or nitriding. Lubrication also plays a crucial role in mitigating surface fatigue by reducing friction and preventing direct metal-to-metal contact, thereby reducing the severity of the stresses and the potential for wear.