Prakt. Met. Sonderband 46 (2014) 315
FRETTING FATIGUE - THE FAILURE ANALYST'S WATERLOO
FRETTING - DES SCHADENSKUNDLERS WATERLOO
A. Neidel, E. Cagliyan, B. Fischer, S. Wallich
Siemens AG, Energy Sector, Gasturbinenwerk Berlin
ABSTRACT
There are many names for the phenomenon of fretting, fretting wear, fretting corrosion,
fretting fatigue, to name just a few. However, the generic term fretting is established now
internationally, particularly in the gas turbine and jet engine industries.
It is advisable to differentiate between the process of fretting as such and its causes.
Fretting in the word's sense means minute relative movements of fraying partners in a
tribological system. This in turn might trigger a number of material degradation processes,
such as fretting fatigue, fretting fatigue cracking, and fretting fatigue failure.
A prerequisite for fretting and its causes are minute relative movements of fraying
partners in a tribological system. Depending on the source, 0.1 - 50 ym of slip are
believed to be necessary. At lower or higher values of slip, fretting will no longer be
possible and other wear mechanisms take over. The relative motion might be translatory,
oscillatory, or complex in nature. Fretting is always a high-cycle process. Fretting fatigue
cracks that were forced open therefore always show the telltale signs of high cycle fatigue
fracture, since a crack induced by fretting fatigue will grow as a normal high cycle fatigue
crack once it propagated out of and away from the fretted zone.
Fretting Fatigue is a common failure mechanism in all engineering components that have
a mating partner in a tribological system and are excited by vibratory or other dynamic
loads. Particularly vulnerable are aircraft structures, aircraft engines, gas and steam
turbines, generators, chemical plants and automotive parts. Fretting can occur under both
dry and aqueous conditions and even in lubricated systems. Palliative measures
comprise anti-fretting coating systems or shot peening of one or both tribological partners
or both.
In some early works there are statements to the effect that the likelihood for fretting to
occur is so high in multi-component systems that are dynamically loaded, that the fatigue
behavior of those systems is entirely controlled by their susceptibility to fretting.
Fretting can affect almost all metallic materials that are used in the components described
above. One of the most dangerous causes of fretting is the marked drop in fatigue
resistance of fretted surfaces. Depending on the source, the drop could be as much as
