Stylus (X,Y) Rpk
The Rk parameters are derived from the bearing ratio curve (aka bearing ratio curve, or Abbot-Firestone Curve) based on the ISO 13565-2:1996 standard. For each profile, a bearing area curve is generated by simulating a horizontal line moving through the profile from the top down, evaluating the percentage of contact the line would make with the surface at each level.
Rpk, or Stylus (X,Y) Rpk, the Reduced Peak Height Along (X,Y), is a measure of the peak height above the core roughness.
Rvk, or Stylus (X,Y) Rvk, the Reduced Valley Depths Along (X, Y), is found from a measure of the valley depths below the core roughness.
Rk, or Stylus (X, Y) Rk, the Core Roughness Along (X, Y), is a measure of the core (peak to valley) roughness of the surface with the major peaks and valleys established by Stylus (X, Y) Rpk and Stylus (X, Y) Rvk removed.
Note that each profile in the X and Y directions are evaluated individually and the resulting average of a given parameter is reported.
Depiction of the bearing area calculation for the Stylus X and Stylus Y parameters (Rpk, Rk, Rvk).The contour plot (A) shows a line through the center over which the profile (B) is selected. The resulting bearing area curve (C) is constructed as described above for the 3D parameters.
A high Stylus (X, Y) Rpk implies a surface composed of high peaks providing small initial contact area and thus high areas of contact stress when the surface is contacted. Stylus (X, Y) Rpk may represent the nominal height of the material that may be removed during a running-in operation. Stylus (X, Y) Rvk is a measure of the valley depths below the core roughness and may be related to lubricant retention and debris entrapment. By comparing the various parameters along the different directions (X vs. Y) one may also assess the uniformity of the surface peak and valley distributions relative to a particular direction of interest. Stylus (X, Y) Rk is a measure of the nominal roughness (peak to valley) and may be used to replace parameters such as Stylus (X, Y) Ra, Stylus (X, Y) Rt, or Stylus (X, Y) Rz when anomalous peaks or valleys may adversely affect the repeatability of these parameters.