Читать книгу Materials for Biomedical Engineering - Mohamed N. Rahaman - Страница 179

Surface roughness is commonly quantified in terms of the vertical height of the surface relative to a mean or reference line, defined such that the area between the roughness profile and the mean line is the same above and below the line. While a variety of parameters are used to quantitate the topography of materials, the average roughness R_a and the root mean square roughness R_q are most often used. R_a is the arithmetic mean of the average values of the vertical deviation from the mean line of the roughness profile whereas R_q is the square root of the arithmetic mean of the square of the vertical deviation from the mean line. As these two parameters are primarily concerned with the relative departure of the roughness profile in the vertical direction only, they do not provide information about the slopes, shapes, and sizes of the surface asperities or about their spacing. It is possible for surfaces of widely different profiles to have approximately the same R_a or R_q values. In general, these two parameters are more useful for characterizing surfaces of the same type that are produced by the same method.