Interactions between contacting fibers

To investigate the nature of the forces involved in mechanical contact between fibers in a fluid, the interaction between a polymeric fiber settling under the influence of gravity and a fixed strand of the same material was observed. Initially after impact, the sedimenting fiber rotated about a fixed point. When the fiber came sufficiently close to vertical alignment so that the tangential component of gravity overcame the static friction, it slid along the surface of the fixed strand. The orientation of the fiber and its velocity were measured as a function of time, and compared to a simple model. The static coefficient of friction was found to be 0.38±0.06, in good agreement with published values. However, the velocity of the fiber after the onset of sliding was slower than that predicted by a theory incorporating friction and smooth cylinder lubrication, and an additional velocity-dependent resistance was required to model the fiber’s sliding motion. A possible source of this resistance is the coupling of normal and tangential lubrication forces as roughness elements are forced to lift past each other.