Numerical characterization of wear particles morphology and angularity of particles and surfaces

Abstract

The morphology of wear particles, in terms of their shape, size and surface texture, reflects the complex nature of wear processes involved in particle formation. Currently, wear particle morphology is usually assessed qualitatively based on microscopy observations. This procedure, since it relies upon the `expert's' experience, is not always objective and it can also be expensive. Hence, recent research efforts concentrate on the development of numerical descriptors and the application of computer technology and image analysis techniques to the assessment of particle morphology. Wear particle boundaries often exhibit rugged characteristics and fractal methods appear to be suitable for their description. Another problem is associated with the characterization of particle surface texture. In this case, fractal methods also seem to give promising results, especially in characterizing the surface anisotropy and directionality. An inherent feature of many tribological systems are abrasive particles. It is intuitively felt that the shape of abrasive particles is related to their abrasivity and subsequently influences the wear rates. Research efforts have been directed to the development of new parameters relating the particle shape to its ability to abrade. It is also intuitively recognized that the shape of surface profiles, i.e. surface texture, affects the abrasive wear rates. Recently, new parameters relating the angularity of both the particles and surface profiles (i.e. surface texture) to their abrasivity have been developed. In this paper an overview of recent advances and developments in the numerical characterization of wear debris, surface profiles and abrasive particles is presented, with particular emphasis on fractal methods. The advantages and limitations of fractal techniques used in the characterization of both boundaries and surfaces of wear particles found in tribological systems are examined and discussed. The relationship between the angularity of abrasive particles, surface textures and abrasive wear is also demonstrated. Practical implications of these developments are briefly discussed.