FRACTAL GEOMETRY MODELING WITH APPLICATIONS IN SURFACE CHARACTERIZATION AND WEAR PREDICTION

Manufactured surfaces such as those produced by electrical discharge m achining, waterjet cutting and ion-nitriding coating can be characteri zed by fractal geometry. A modified Gaussian random fractal model coup led with structure functions is used to relate surface topography with fractal geometry via fractal geometry via fractal dimension (D) and t opothesy (L). This fractal characterization of surface topography comp lements and improves conventional statistical and random process metho ds of surface characterization, Our fractal model for surface topograp hy is shown to predict a primary relationship between D and the bearin g area curve, while L affects this curve to a smaller degree. A fracta l geometry model for wear prediction is proposed, which predicts the w ear rate in terms of these two fractal parameters. Using this model we show that the wear rate V(r) and the true contact area A(r) have the relationship V(r) (A(r))m(D), where m(D) is a is a function of D and h as a value between 0.5 and 1r. We next study the optimum (ie the lowes t wear rate) fractal dimension in a wear process. It is found that the optimum fractal dimension is affected by the contact area, material p roperties, and scale amplitude. Experimental results of bearing area c urves and wear testing show good agreement with the two models.