3D Functional Parameters
Sdc(mr) (Inverse Areal Material Ratio)
The Inverse Areal Material ratio, Sdc(mr) is the height , c, which gives the specified material ratio, mr. The height c may be measured from the best fitting least squares mean plane or as a depth down from the maximum point of the Areal Material Ratio Curve.
Sdc(mr) might be used to assure that an optimum crevice volume is produced for a sealing surface to allow for some lubricant entrapment (to prevent running dry) but not be too deep to prevent leakage. For example, a specification such as -0.4 um <Sdc(100%)<-0.8 µm with a 1% peak and 1% valley offset, measured from the mean plane, would assure that the bottom 50% or the surface would extend at least 0.4 um below the mean plane but no greater than 0.8µm.