Fractal parameters developed to evaluate the effects of laser textured surface on oil contact angle and tribological parameters

Steel specimens are textured by controlling laser peak fluence F0 and overlap ratio, OR. A 3D fractal model with the characteristic (periodic) lengths, Lx and Ly, and fractal dimensions, Dx and Dy, is introduced to solve the morphologies with the same skewness Sk and kurtosis Ku as that of the textured specimen. The product value LxLy shows its correlation with Sk and is used as a surface pattern parameter with its value proportional to asperity's plateau area. Areal mean surface roughness Sa and LxLy, superior than the conventionally used Sa, Sk, and Ku, become the controlling factors that are more efficient to interpret their role on contact angle (θ)oil formed at textured surfaces with various patterns. Effects of F0 and OR on (θ)oil are efficiently evaluated through the correlations of texturing conditions of laser power and overlap ratio with Sa and LxLy. Adhesive energy Ea((θ)oil) is introduced to establish its connection with tribological parameters.