Introduction and application of modified surface roughness parameters based on the topographical distributions of peaks and valleys

A set of modified roughness parameters (N%‐Rpvʹs) is introduced based upon the separate distribution of peaks and valleys. These new measures of surface roughness are utilized to quantitatively evaluate the as‐rolled and deformation‐induced surface roughness of Al sheets. N%‐Rpv is defined as the difference between the average heights of the upper N% of peaks and the lower N% of valleys. As N decreases, the magnitude of N%‐Rpv tends to be more sensitive to the contribution from relatively large‐wavelength roughness components. The topographical difference between the transverse direction (TD) and the rolling direction (RD) roughness profiles of the as‐rolled surface is shown to be characterized more realistically by N%‐Rpv than the root‐mean‐square roughness (Rq). The result from this quantification of deformation‐induced surface roughness of the Al sheet at intermediate and macroscopic scales suggests that the presence of spatially organized macro‐roughening patterns can be characterized using the relative magnitudes of 100%‐Rpv and 10%‐Rpv. This suggests a possible link between the spatial distribution of surface roughness and the magnitude of N%‐Rpv.