Measurement of the Surface Friction of Fibers by an Electro-Mechanical Method

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Abstract
A torsion-wire instrument, built for the measurement of frictional force, is described. Its operation depends on the angular deflection of a beam when a slider on the beam passes axially along the test specimen. The frictional force involved is registered elec tronically through a capacitive transducer and a bridge circuit. Means have been taken to minimize the influence of noise-producing sources on the delicate transducer. Typical chart recordings obtained on the frictional-force system are presented, showing that, under the conditions of these experiments, the frictional passage of an edge along a textile fiber is an irregular succession of "stick-slip" cycles. Two param eters, taking into account this irregularity, are introduced to characterize the frictional behavior of a fiber. Results of measurements in these terms are given for two man- made fibers, with and without finish, and for a camel-hair sample. At the traversing speeds employed in the present experiments, finishes on man-made fibers appear to have little effect on frictional behavior. In general, no correlation was found between the geometric roughness and frictional parameters. However, in the case of the camel hair, which exhibits the differential frictional effect (D.F.E.), a cor relation was found, in that both the roughness and frictional parameters have higher values when measured in the "against-scale" direction. Measurements made on a nylon sample, with and without finish, at various normal forces, showed that one of the frictional parameters, average maximum force, is (quite strictly) proportional to the normal force, in agreement with Amonton's law.

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