The Use of a Diffraction Grating as the Rubbing Surface in the Study of the Frictional Properties of Wool Fibers

Diffraction gratings with saw-toothed rulings at spacings of 4 to 25 microns have been used as surfaces against which to measure the frictional coefficients of wool fibers by the capstan method. The geometrical regularity of these surfaces improves the reproducibility of measurements on individual fibers (coefficient of variation between 2% and 5%), facilitates microscopic observation of the sliding process and simplifies the geometry of the system sufficiently to permit some features of the dependence of frictional behavior on such factors as load, grating spacing, and the nature of the surrounding medium to be explained. Some values of the coefficients in air and in soap solution are reported and discussed.