Characterization of cracks formed in large flat-on-flat fretting contact

Running-in in fretting, transition from near-stable friction regime to gross sliding

“…Smaller cracks were also encountered in all specimens. The biggest cracks formed a 'crack pair' similar to that found in previous tests [25]. Examples of the cracking and damage are shown in Fig.…”

“…At the lowest T RM value (0.55), clear crack pairs were found. The COF behaviour was similar compared to the gross sliding test with similar (gross sliding) parameters and without any running-in, and also the crack dimensions were at a similar level between these tests [25]. Thus, this suggests that the running-in phase should be done with sufficiently high loading in order to obtain reduction in the fretting-induced cracking.…”

“…General degradation layer (GDL) and TTS observations have been obtained typically using concentrated, Hertzian type, contacts producing high nominal load. In the case of flat-on-flat contact, the loads were nominally low; however, the fretting process itself leads to the formation of individual highly loaded 'spots', concentrating loads, where both TTS, GDL and cracking were present [24,25].…”

Avoiding the high friction peak in fretting contact

“…Material degradation [16] and nucleation of cracks [10] have already been observed at loading cycles within the initial friction peak. Those cracks can further propagate causing complete fracture.…”

Prediction of contact condition and surface damage by simulating variable friction coefficient and wear

“…Additionally, even if stable stick conditions are achieved, certain regions may already have been damaged. Even slight exposure for fretting may significantly impair the component's fatigue properties due to surface degradation and cracking [47]. Thus, there is a need for developing a model that considers non-uniform COF evolution and wear across the contact, and which can be used to utilize scientific laboratory findings in industrial-scale simulations.…”