CHARACTERIZATION OF THE FRETTING WEAR OF UNLUBRICATED STEEL SURFACES BASED ON THE COMPARISON OF WEAR RESULTS OBTAINED BY DIFFERENT METHODS

Fretting wear is the typical wear form caused by small, oscillatory, t angential movements between two normally loaded surfaces. In the prese nt research a bearing ball is subjected to fretting against a flat sur face in gross-slip conditions. Because of the small wear volumes it is very difficult to quantify fretting wear accurately. In the present r esearch, fretting wear measurements on the fretting of a bearing ball against cold-drawn steel are carried out by various methods: thin laye r activation (TLA), spherical cap modelling (SCM), normal displacement measurement (ND), three-dimensional surface topography (3DST) and sca nning electron microscopy (SEM). It is concluded that TLA gives the mo st accurate measurements. SCM largely overestimates and 3DST underesti mates the fretting wear. ND is mainly influenced by particle escape fr om the contact zone. It is shown that the fretting process consists of two stages. During a running-in stage of about 200 000 cycles the wea r rate and the coefficient of friction are high. The wear particles re main trapped in the contact zone for about 8000 cycles. After 200 000 cycles a steady state stage of the fretting process starts, characteri sed by an increase of the wear scar area rather than the wear scar dep th, an increase in the wear of the harder, spherical specimen and read hesion of the wear particles to the surface of the flat specimen. (C) 1997 Elsevier Science S.A.