Effects of contact pressure, loading frequency and number of loading cycles on the fretting induced damage of large scale annular flat-on-flat contact of 34CrNiMo6 — A study utilizing a novel fretting test rig

Abstract

Fretting fatigue and fretting wear are damage mechanisms that may activate when a contact experiences small amplitude oscillatory sliding known as fretting. The resulting damage depends on the contact conditions such as nominal contact area, contact pressure, loading frequency and number of loading cycles. An experimental study on the effects of these test parameters on fretting behavior of quenched and tempered steel in very large annular flat-on-flat contacts was done. The nominal contact size studied was 622 mm2. Sizes of local adhesive junctions, crack lengths and wear masses were increased when higher contact pressures were used. When a low loading frequency was used, the maximum values of coefficient of friction were depended on contact pressure unlike in higher loading frequency tests. A combination of low contact pressure and loading frequency caused near ideal Coulomb friction conditions whereas in other test conditions non-Coulomb fretting loops were observed. Cross section characterizations were done to evaluate sub surface damage. Long cracks and thick tribologically transformed structure-layers were observed after high contact pressure tests provided that tests were not stopped after too few loading cycles. Thicker third body layers were able to form in lower contact pressure conditions. The investigation indicates that the interactions of contact area, contact pressure and loading frequency, and their evolution over multiple loading cycles, merit further studies especially in the case of very large flat-on-flat contacts which are commonly used in industry.