Microscopic observations of the progressive wear on shoe surfaces that affect the slip resistance characteristics

In this study, progressive wear and surface alterations which take place on the shoe surfaces during the repetitive slip resistance measurements are o utlined in an attempt to formulate a general picture of the friction and we ar mechanisms involved. A theory on the different types of surface alterati ons and wear evolution of the shoe surface was then developed. The surface changes and wear progress were quantified using conventional surface roughn ess parameters as well as a set of visual examinations based on a scanning electron microscope and extended it to three-dimensional interpretation. Su rface profiles of the three different shoes were recorded using a laser sca nning confocal microscope. A number of surface roughness parameters, viz., the center lime average (CLA. R-a) and root mean square (RMS. R-q) roughnes s, maximum mean peak-to-valley height (R-tm), maximum mean peak height (R-p m). maximum mean depth (R-vm). and average asperity slope (Deltaa) were cal culated. The analysis showed that the surface textures of each shoe underwe nt marked variations during the entire rubbing processes. It was concluded from the surface roughness measurements that the R-a roughness parameter wa s correlated with the standard deviation of peak heights and also had a lin ear relationship with the average asperity slope. Results from the surface roughness parameters also indicated that variations in the geometry of the shoe heels had a major effect on the slip resistance characteristics. Furth ermore, it was found from the microscopic observations that the progressive wear as more ses ere than expected and initiated in the very early stage o f sliding. The progressive wear was initiated by ploughing after only a few rubbings and this mechanism immediately was followed by simultaneous ploug hing and abrasion. Micro-topographic information as described in this study may provide a useful information for the understanding of friction and wea r mechanisms and the interpretation of any slip resistance result. Relevance to industry Slipping and falling accidents are a major ergonomic and safety concern in the workplace and the general community. Prevention of slip hazard has focu sed on designing "slip resistant" footwear and floor surfaces. This study i s primarily concerned with surface alterations and wear detection of the sh oe soling from a microscopic point of view. Microscopic approaches may prov ide additional useful information on the analysis of slip resistance perfor mance. (C) 2001 Elsevier Science B.V. All rights reserved.