Volume 25, Issue 2 (March 1997)
Precision Profilometry of Wear Scars on Curved Surfaces
Wear scars less than 1 μm in depth are a challenge to measure accurately by surface profilometry, particularly if they are formed on a curved surface. The resultant curved traces limit the use of the vertical scale enlargements necessary for the detection and measurement of minimal wear scars. Profilometer traces on the surface of an internal combustion engine cylinder, for example, commonly yield curved traces even when the stylus moves parallel to the cylinder axis because of (a) the difficulty in orienting the profilometer trace precisely along an element of the cylindrical surface and (b) small departures from a true cylindrical form in most manufactured cylinders. A simple procedure has been devised that permits a curved trace to be “straightened” and scaled to facilitate the determination of wear scar depths and cross sections in the sub-micron range. In some cases, wear scars within the original surface roughness can be detected and measured. The procedure will be illustrated on wear scar depths of 1 μm and less in cylindrical surfaces.