Design of Texture in Standard Surfaces

All engineering surfaces exhibit varying degrees of sharpness and roundedness, and this characteristic is commonly identified by the “feel” or touch of the surface under consideration. Model surfaces such as cubes, cones, and spheres demonstrate extremes of flatness, sharpness, and roundedness, respectively, and they have the dual advantage of simple mathematical definition and reproducibility. This paper describes a logical progression from model to random textures, and discusses the relative significance of mean void width and asperity size, shape, and spacing. An alternating mechanism of wear on road surfaces is shown to exist which preserves the macrotexture by successive flattening and rounding of individual asperities. It is concluded that the two fundamental requirements of any standard surface are minimal wear and reproducibility or repeatability of frictional results. These criteria demand some degree of compromise in establishing a desirable texture in a standard surface, whereas the resulting frictional performance of the final selection is of secondary importance.