Potentiality of triboscopy to monitor friction and wear

Triboscopy was proposed over 20 years ago, but despite the powerful insight it brings to analyse friction and wear with temporal evolution of localised events, its use is still limited. In this paper, triboscopy has been further developed. A LVDT sensor measures the position of the counter-body inside the wear track in a reciprocating tribometer. A high frequency acquisition system allows 10 points to be acquired within the elastic contact width, calculated by Hertz equations. The necessary number of acquired points is computed as a function of reciprocating frequency and stroke length, which enables to represent inherent details of the phenomena involved without producing excessively large files. Triboscopic maps of the acquired data are generated, where colours quantify the Z variable under measurement, X is the position of the counter-body within the wear track and Y is the number of cycles. Four examples where the use of 3D colour maps has helped to visually phenomena that would be hard to detect otherwise are presented. First, sintered composites containing solid lubricant particles dispersed in a Fe-Si-C matrix were tested. Under dry sliding, triboscopic friction maps showed higher friction at the ends of the strokes, which was more significant for harder specimens. Evidence showed that this friction increase was due to the accumulation of wear debris at the ends of the wear tracks. Second, triboscopic images of reciprocating tests of DLC-CrN coatings clearly indicated the region of the wear tracks where spalling occurred. Third, bronze disks containing regularly distributed inserts composed of graphite particles dispersed in bronze presented triboscopic maps where friction decreased periodically following approximately the size and spacing of the graphite inserts. Fourth, starved lubrication tests of textured surfaces showed no effect of surface texturing on average friction, but triboscopic maps suggested a tendency for lower friction with texturing.