A mechanical model for the lateral compression of woven fabrics is derived from Van Wyk's compression law for fiber assemblies. The pressure ( P ) and thickness (v) relationship is P = a/ ( v -v')3. The parameter v' refers to the core of the fabric, which is incompressible over the pressure range 2-5000 gf/cm 2 . The parameter a refers to the compressible surface layers and is dependent on the mass of fibers in the surface layers and their orientation.A comparison is made of the results obtained with the KES-F fabric compression tester and the standard fabric thickness tester. The energy of compression is proportional to the cube root of the parameter a. The compressibility of the fabric is proportional to the energy of compression per unit volume of fabric. The changes that occur in the fabric surface layers during a typical fabric finishing process are investigated.The measurement of the lateral or thickness compression properties of fabrics forms an integral part of objective measurements currently being considered internationally for wool fabrics [ 12,17]. These objective measurements are intended to help maintain consistent quality in finished wool fabrics and to aid in product engineering of wool fabrics. An early paper [2] described the thickness-compression curve of fabrics. The effects of finishing treatments on the lateral compression curves of fabrics have been described [3,9,13], but the thickness-compression curves of fabrics have not been analyzed mechanically. An analysis of the mechanics of fabric compression may help in developing compression test methods and interpreting results. In this paper, we present a mechanical model that describes the compression curves measured on a large number of woven fabrics over the pressure range of 2-5000 gf/cm2. The model reduces the fabric to three layers -a relatively incompressible core layer in contact with a much more compressible surface layer on either side. The model is reconciled with both electron microscope evidence and optical measurements made on the fabrics.The model indicates that the DIN standard [6] for measuring fabric compression is very simply related to the compression test performed on the Kawabata evaluation system for fabrics . The change in the compression properties of wool fabrics in some commercial worsted fabric finishing processes is presented and interpreted in terms of the model.
The design principles, construction, and operation of an instrument designed for the rapid measurement of the distribution of fiber fineness of wool are described. The instrument is based on an electro-optical measurement of the amount of light scattered from a directed beam by fiber snippets. The snippets are transported through the beam dispersed in a moving liquid. The relation of the measurement parameter to fiber fineness and the problems of calibrating the instrument against the projection microscope method are discussed.
A model is developed to calculate the residual set in a helical fiber axis after it has been wrapped around a mandrel, set into this shape, and released. The theory used is linear viscoelasticity in conjunction with the bending and twisting equations for thin rods. The model may be applied equally well to calculate the snarling behavior of twisted yams. An example of this is presented to confirm predictions made by the model. Two cases in the setting of helices are analyzed. In the first case the released helix is not in contact with the mandrel. In this case the bending and torsional set in the helical fiber axis follows quite simply from principles of linear viscoelasticity. In the second case, the released helix is constrained to lie on the surface of the mandrel.Results of this second case are more complex, but have been computed and presented in tabular form.If wool fibers are wrapped around a mandrel into the shape of a close-coiled helix, set, and released [ 14], the shape of the released fiber depends on wool fiber type [ 14]. The differences observed have been attributed to variations in the mechanical properties of the fiber substances [ 14] or to the initial fiber crimp shape. It is the aim of this paper to enable calculations to be made of the set in the fibers in such a test, and thereby to examine whether the differences observed between wool fiber types are due to fiber substance or crimp.The fiber is assumed to have an initial helical crimp. This assumption simplifies the analysis because the shape of the fiber around the mandrel is then also helical, as is the shape of the released fiber. Fibers that have a planar crimp can be approximated by circular arcs joined together. Each of these arcs is part of a plane, close-coiled helix, and the helical solution may be easily modified to that of a planar crimped fiber by including a torsional contribution.First, for a helical fiber, setting in bending and torsion is simply related to the fiber stress relaxation in bending and torsion, respectively. Second, the equations of equilibrium for a helix forced to lie on the surface of a mandrel by a constraining couple are established by means of the principle of minimum energy [3,4]. Third, the effect of inserting twist into the helical fiber axis, prior to wrapping it around the mandrel, is included in the analysis. In this way the effect of planar fiber crimp may be deduced.A special case of inserting pretwist into a helix and then wrapping it around a mandrel is that of the snarling of a twisted yarn. In this case the pretwisted cylinder is allowed to wrap around itself, the mandrel radius corresponding to the radius of the twisted cylinder or yarn. The snarling twist predicted by the model agrees with that found experimentally [ 1,2].The theory is then used to predict the setting of a helix around a mandrel. Assuming that a crimped wool fiber can be represented by a helical shape, the apparent difference in setting behavior of straight Lincoln wool and crimped Merino wool can be largely explained by the d...
An Instrument ls described for the rapid measurenent of the staple length of greasy wool. The staple travels through an optical plane of detection, where the ends of the staple are recognized. The distance travelled hy the staple while in this plane ls the staple length.The Instruaent is suitable for use with an automatic-feed device, and the length data can be fed into a computer.Advantage has been taken of these attrihutes to include lt as the length-neasuring system for the CSIRO Autonatic Tester for Length and Strength (ATLAS).
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