Textile Research Journal

This paper is concerned with a mathematical analysis of the longitudinal rheological behavior of dimensionally and structurally variable fibers. At first, the general relation ships for the stress-strain behavior of such fibers are derived by ignoring time effects. The uniform and non-uniform fibers are compared for the case when stress and strain follow a power law relationship, and the stress-strain behavior of non-uniform wool fibers is calculated to illustrate the effect with actual fibers. Structural and dimensional non- uniformities are shown to have considerable significance. When both variabilities are present, the two non-uniformities may act additively or subtractively, depending on the relationships between them.

In considering time effects, the behavior of several rheological models is examined. The uniform and non-uniform specimens are compared for creep (constant load), stress relaxation (constant extension) and stress-strain behavior at constant rates of loading and straining. To illustrate the applications possible with actual fibers, the creep behavior of wet wool fibers is briefly treated.

Two methods of determination of the volumes of felted wool balls with considerable accuracy are described. The first is an indirect method by computation from the directly determined average diameter of a ball, and a measuring procedure is given whereby this average diameter can be obtained accurately even when the shape of the ball is not per fectly spherical. However, the method involves subjective personal judgment and hence suffers from some lack of precision due to operator errors which may be introduced. In the second method, the volume is determined directly by saturating the ball with water and weighing it in this condition; theory and practice are fully described. The method is simple, very accurate (± 0.01 cm³), free from operator bias, and requires only normal laboratory equipment.

The molecular structure of wool was modified by reactions with alkenylsuccinic and other anhydrides. This internal modification was accomplished under anhydrous condi tions in a special medium, dimethylformamide. Acid and alkali solubilities of the modi fied wool fabrics were interpreted as changes of the acid-base character of the wool and also in terms of' the anhydrite structure. Wool modified with long-chain alkenylsuccinic anhydrides had decreased strength but increased resistance to acid conditions and laundering shrinkage.

This paper examines the influence of two factors on the operation of a worsted spin ning set on the same input of work. The factors are the number of spinning frames in the set and the way in which the frames will be allotted to big lots. It uses the method of simulation on a simplified model of the set. Measures of the effect of changes in the factors are made in terms of delivery frequency and duration of delays and the in-process inventory. The effect of the fluctuating demand for frame time on the number of frames necessary to meet performance criteria is indicated.

A method is described for measuring lateral load-deformation relations of fibers. The results of tests on Lincoln wool fibers are given, for aqueous test liquids at pH 2.1, 6, and 9.1, and for fibers treated with formaldehyde, with an anionic detergent, and with mercuric acetate.

In water at 20° C the shear modulus (for loading times of several seconds) is near to 2 X 10⁸ dynes/cm² and does not vary greatly with the chemical treatment or the acidity of the test liquid.

As the temperature increases, the shear modulus slowly decreases. At a certain temperature, approximately 80° C for this Lincoln wool in water, the modulus starts to decrease much more rapidly with temperature. This transition is accentuated and dis placed to lower temperatures at pH 9.1 or by the treatment with mercuric acetate.

Measurements of viscous flow under constant load were also obtained. Between 70° and 100° C the native wool fibers show a viscosity of the order of 10¹¹-10¹² poise, with an activation energy of about 26 kcl/mole. Some structural implications of these phenomena are discussed.

If a textile yarn, marked at intervals along its length, is struck transversely by a rifle bullet, a flash photograph taken shortly after impact will reveal a shifting of the marks caused by passage of a strain wave. Analysis of these shifts provides data on the dis tribution of strain and strain velocity in the wave. Tests were performed on specimens of a high-tenacity nylon and a high-tenacity polyester yarn, to determine strain-velocity distributions at various times after impact and at various impact velocities. The observed distributions were then compared with the predictions of a theory which assumed that stress-strain behavior was independent of strain rate. From discrepancies between theo retical and observed results, it was concluded that at strain levels up to 9%, significant creep and stress relaxation occurred within 30 μ sec after impact, but in the time interval 30 μ sec to 300 μ sec, creep and stress relaxation were negligible. For strains of the order of 1%, the 30 μ sec creep and stress relaxations at the point of impact were of the order of 15% and 5%, respectively.

Heat is transferred to skin protected against intense thermal radiation by several mechanisms. Textile fabrics provide considerable protection but some of them tend to decompose, producing tars which condense on the skin. The amount of energy trans ferred by tars from cotton fabrics was estimated by determining the amount of tar deposited and the amount of energy required to re-evaporate the tar. Two fabrics were used; one untreated, the other fire resistant treated (FR) with brominated triallyl phosphate. The energy amounts to about 500 cal for each gram of tar evaporated and is about the same for the two fabrics. Over the range of interest, the amount of tar deposited increased with increase in exposure. For fabric in contact with a skin simu lant, the energy transferred by this mechanism varied up to 1 cal cm^-2 of fabric; for the spaced arrangement, up to 1.5 to 2 cal cm^-2. For low and intermediate exposures, the energies transferred by the tar were about the same for the two fabrics; at the highest exposures, the values were considerably greater for the FR treated fabric. At exposures which produce disabling burns, the heat transferred by the tars is negligible for fabric in contact with the skin but for fabrics spaced from the skin, the tars may account for a fourth or more of the total energy transferred. Without this energy, the burn would be greatly reduced.