Fractal shape analysis of tire debris particles and applications

Tire debris is produced by the normal wear of vehicle tire treads. Preliminary results are presented, which aim at characterizing the shape of debris particles by means of fractal analysis. Materials and Methods. Silica and carbon black filled styrene - butadiene rubber debris coming from controlled laboratory wear tests is being analyzed. The binarized images of individual debris particles obtained from a white light microscope are processed by an algorithm [1], which determines the perimeter (P) as a function of the chosen unit of length (yardstick, L). The fractal dimension (D) of the contour is deduced from the Log[P] vs. Log[L] plot [2]. Results. Some sets of wearing conditions (abrader type, pressure, velocity) yield particles in a homogeneous class, described by one value of $D$ in the explored yardstick range. Example: coarse particles similar to those of [3] have $D=1.3$. Particles produced under different conditions need not be homogeneous: Log-Log plots either yield one value of $D$ or exhibit a corner point at a characteristic yardstick length $L_c$. . In this case particles have both a textural and a structural fractal dimension. Interpretation. Particle morphology is the response to wearing conditions mediated by material inhomogeneities at the micrometer scale of length [3, 4, 5]. These results may provide information about crack initiation and tear dynamics [6] in filled elastomers. Applications. Beyond being relevant to the diagnostics of rubber wear processes and to product quality assessment, fractal shape analysis provides a non destructive means, other than analytical electron microscopy [7], of characterizing and identifying tire debris particles in heterogeneous, environmental specimens. With reference to this last application, morphological analysis has to be cross validated by a different method: indeed, the elastomer contents is determined by a purposedly developed, high sensitivity technique, which relies on IR absorption spectroscopy. Results from this technique will be presented as well. [1] V. Kindratenko et al., Env. Science and Technol., 28 (1994) 2197-2202. [2] B. Mandelbrot, 1983, "The Fractal Geometry of Nature", Freeman: New York. [3] A. N. Gent, Rubber Chem. and Technol., 62 (1989) 750-756 [4] A. Goldberg and D. R. Lesuer, Rubb. Chem. and Technol., 62 (1989) 272-287 [5] M. Klueppel and G. Heinrich, Rubb. Chem. and Technol., 68 (1995) 623-651. [6] R. L. B. Selinger and J. M. Corbett, MRS Bulletin 25 (2000) 46-50 [7] M. Camatini et al., to appear in J. Bentley et al., Eds., "Advances in Materials Problem Solving with the Electron Microscope" MRS Proc. vol. 589, MRS: Warrendale, PA, 2000. AIX Cartan0 2.1 2 Wed May 17 23:28:19 MET 2000