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, L_x and L_y, and fractal dimensions, D_x and D_y, is introduced to solve the morphologies with the same skewness Sk and kurtosis Ku as that of the textured specimen. The product value L_xL_y 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 S_a and L_xL_y, superior than the conventionally used S_a, 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 S_a and L_xL_y. Adhesive energy E_a((θ)_oil) is introduced to establish its connection with tribological parameters.