The determination of fractal dimensions of blast-cleaned steel substrates by means of comparative cross-section image analysis and contact stylus instrument measurements

Abstract

Morphological parameters of substrate surfaces determine the adhesion of coatings and pressure-sensitive adhesives. This paper is concerned with the assessment of fractal parameters by means of cross-section images and contact stylus instrument measurements of blast-cleaned substrates. Mild steel samples were prepared with different abrasive materials. Images were taken from a total of 12 surface configurations with an optical microscope. From each of the cross-section, a 2D profile of the steel surface was derived using the ImageJ image manipulation software. The fractal dimensions of these profiles were estimated by means of the box-counting method and then compared fractal values for 2D profiles taken from contact stylus measurements. Design of Experiment (DoE) was applied to statistically analyze the relationships. The factors considered included abrasive type, surface preparation grade, surface roughness, and most importantly for this paper, the surface profile evaluation method. The profile evaluation methods included cross-section analysis and contact stylus instrument measurements. Regardless of the method used to determine the surface profile, identical relative trends resulted for both measurement variants, with normalised values approximately twice as high for the cross-section profiles compared to the ones from contact stylus data.