Directional Signatures of Surface Texture

Surface texture affects adhesion, friction and wear. A key component in the studies of these effects is a multiscale and directional characterization of surfaces. However, this task is beyond the ability of standard methods currently used. Methods based on fractal geometry, quantifying the surface topography at individual scales and directions, have been developed to overcome this problem. In this study, we propose a unified approach for surface texture analysis comprising three steps: directional surface representation, directional surface dimension and computer implementation. To address longstanding issues of texture analysis of surfaces with directionality and studies of surface texture effects on contact behaviour of rough surfaces, a directional blanket curvature covering method was used. Peak curvature signatures (sets of peak dimensions) were calculated. Higher value of peak dimension represents higher peak curvature complexity. Isotropic (sandblasted) and anisotropic (abraded) titanium alloy (Ti–6Al–4V) surface images were generated. Statistically significant differences in peak dimension were found between isotropic and anisotropic surfaces at scales of 15 μm and 20 μm. Contact areas and pressures were calculated between rigid flat plates pressed against Ti–6Al–4V rough surfaces. For low loads at a scale of 15 μm, contact areas decreased with dimension, while at scale of 25 μm they decreased and then increased. Changes in contact pressures exhibited trends opposite to the areas. For high loads, there are virtually no changes. Results showed that the curvature covering method detects minute differences in surface anisotropy and allows for detailed study of contact behaviour.