FRICTION IN FIBROUS MATERIALS .2. EXPERIMENTAL-STUDY OF THE EFFECTS OF STRUCTURAL AND MORPHOLOGICAL FACTORS

In this part of the series, the effects of a number of structural and morphological factors on fiber friction are examined and rationalized on the basis of the structural model discussed in Part I. The factors are fiber cross-sectional shape, molecular orientation, annealing, and fiber type. Friction tests have been conducted using techniques that allow measurements in both the point contact and line contact modes. Selected tests have also been done with the contact regions immersed in water. The results show that the coefficient of friction mu is higher for annealed than unannealed structures and increases with increasing molecular orientation. Circular fibers exhibit higher values than noncircular fibers. The value of the friction index a varies in the same fashion as the value of the coefficient of friction mu in all cases, except when fiber orientation is the variable. The friction index n increases with orientation and is higher for circular fibers than for noncircular ones. Wetting of the contact region or annealing of the structure has no effect on the value of n. Results are explained in light of the structural model presented in Part I.