Scale-invariant analysis of wear particle morphology - a preliminary study

The importance of wear particle characterization is continuously growing, a s the need for prediction and monitoring of wear increases. Accurate analys is of wear particles can, however, be limited by problems associated with p article characterization, especially of the wear particles' surface morphol ogy. Since the shape and surface topography of wear particles often exhibit a fractal nature, fractal (scale-invariant) methods are, therefore, used i n their characterization. However, the methods used to date ignore the fact that all fractal objects can be described by a small set of mathematical r ules; although finding those rules which describe a particular fractal imag e is a difficult problem. No general solution exists to date and this paper attempts to redress this problem. A new analysis method, 'scale-invariant analysis', which is based on a partitioned iterated function system (PIFS), is proposed for the characterization of wear particle morphology. PIFS is a collection of contractive affine transformations. Each affine transformat ion transforms one part of a wear particle image onto another part of the s ame image. PIFSs were constructed for both computer generated and SEM image s of wear particles. Results obtained in this study clearly demonstrate tha t the morphology of wear particles can effectively be characterized using t he PIFS method. (C) 2000 Elsevier Science Ltd. All rights reserved.