Abstract
This article reports on the relation between the surface topography and the optical reflectance, both total and diffuse, of different samples of AISI 430 ferritic stainless steel. Gaussian filters with different cutoff wavelengths were applied to the height maps of the surface topography of the samples, to separate the different scales of surface roughness involved in optical scattering in the visible range of the spectrum. Significant anisotropy, related to the rolling process, was found in the topography. An effective roughness slope parameter was defined from the dependence of the ratio between the root mean square height and the autocorrelation length on the cutoff wavelength. This roughness slope demonstrated an exceptionally good linear relationship with CIE 1931 luminance, which was calculated from the diffuse reflection spectra. The color uniformity of the samples was analyzed based on their CIE L*a*b* coordinates under daylight and LED illumination. The results confirmed the strong influence of manufacturing process on the surface characteristics of AISI 430 ferritic stainless steel sheet products with a bright finish.
Highlights
Quality control of the visual appearance of surfaces is a key issue in industrial fields dealing with paints, coatings, texturing, and finishing [1,2,3,4,5,6,7]
The optical scattering distribution function is a topic of interest in engineering applications such as the manufacture of high-quality mirrors for scientific use [8], and knowledge of this topic has been supported by the development of infographics and surface rendering [9,10,11,12]
A number of theoretical approaches developed to model the bidirectional reflectance distribution function (BRDF) and the most complete bidirectional scattering-surface reflectance distribution function (BSSRDF) is presented in the review by Frisvad et al [13], which provides a comprehensive analysis of the approaches that can be found in the literature
Summary
Quality control of the visual appearance of surfaces is a key issue in industrial fields dealing with paints, coatings, texturing, and finishing [1,2,3,4,5,6,7]. A number of theoretical approaches developed to model the bidirectional reflectance distribution function (BRDF) and the most complete bidirectional scattering-surface reflectance distribution function (BSSRDF) is presented in the review by Frisvad et al [13], which provides a comprehensive analysis of the approaches that can be found in the literature. All of them have limitations in the goodness of the model according to the roughness scale Some of these models explicitly consider surface microgeometry, making them better suited to modelling the optical scattering produced by small-scale (nano/micro) roughness. These models are based on the Rayleigh–Rice approach [14,15] and are valid for smooth surfaces fulfilling the so-called Rayleigh criterion:
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