Creep of Wool Fibers

Abstract

The molecular mechanical constant a which is directly related to flow hole volume is calculated for wool fibers exhibiting a range of stress-strain properties. It is found that the value of the stress developed at 30% strain (Sgo) is invese1y proportional to the value. of a and that the product of a and SgO is constant. This relationship suggests that the differences observed between wool fibers in water are due to variations in the number of~ow units per unit cross sectional area. These variations, in turn, offer an explanation of the large differences in creep behavior among wool fibers in water under constant stress.where lt is strain at time t, and a and b are constants. Now for each single fiber we have a series of creep curves under varying loads. The values of a are obtained for each fiber by plotting lilt against 1ft. The gradient of the straight line obtained by plottingIn a against load gives the value of a for each of this Sao value is employed, and the fibers are subjected to this load for a short time at 100% RH. The experiment can be repeated without permanent damage-to the fiber. Since our original experiments, however, we have noted that some fibers cannot be loaded for the time periods previously used [10] without the onset of permanent damage. If the experiment is limited to 3-min duration the fiber will survive three loadings provided a period of 24 hr is allowed to elapse between successive loadings. On recalibration the Sao value will lie within ±2% of the original. If shorter experiment times are used the number of loadings can be progressively increased. In the present work all experiments were carried out in distilled water at 20.0°C ± 0.2°C, and each fiber was subjected to loads of 70%, 75%, and 80% of its Sao value. Fibers were then recalibrated to ensure that they exhibited no signs of permanent damage.For short times Feughelman [4] has noted that creep curves obey the following relationship in the yield region.