Bertil Olofsson

Measurement of Friction Between Single Fibers

a fiber mixture, a top, or a yarn have been the object of several scientific studies. One of the practical aspects has been the felting properties of wool, which are assumed to be due to the difference in frictional coefficients of the wool fiber when it is moved in different directions (towards root or tip). Another operation in the textile industry where the friction between the fibers should be of essential

Measurement of Friction Between Single Fibers: V. Frictional Properties of Viscose Rayon Staple Fibers

In a previous communication by Gralén and Olofsson [2~ a description was given of a new apparatus for the measurement of single-fiber friction, its construction, and theory. Some preliminary results were also given. In the case of wool fibers a very great dispersion of the separate readings was found, as regards antiscale friction. The reason for this is that relatively small differences in the height and the shape of the scales can give rise to rather large differences in friction. Smooth fibers give less dispersion of the values. Using the stick-slip apparatus is more time-consuming and laborious than using the twist friction meter described by Lindberg and Gralen [6], but in other respects the former has some advantages over the latter apparatus. Firstly, the distribution of the load on the contact surface is

Measurement of Friction Between Single Fibers VI. A Theoretical Study of Fiber Friction

8. The electrical conductivity of rayon fibers is only slightly influenced by the application of spinning auxiliaries if the amount of auxiliary added is not very great. 9. A theoretical study of the influence of frictional properties on sliver movement in drawing frames was made. 10. The variation of frictional coefficients meaS7 ured on a bulk of fibers is always significantly higher than the variation of measurements on one fiber.

Measurement of Friction Between Single Fibers: Part VII: Physicochemical Views of Interfiber Friction

D URING the last few years, interest in the frictional properties of textile materials has increased steadily. The importance of frictional properties in textile processes, such as carding, drawing, spinning, and fulling, is recognized, and their importance for the properties of finished products, such as breaking strength and elastic properties of yarns and fabrics, handle, creasing, and abrasion of fabrics, has been pointed out. At the Swedish Institute for Textile Research, we have concentrated on the interfiber friction-

Fatigue of Aramid Cords in Conveyor Belts

A theoretical study of strains and stresses in cycling of conveyor belts strengthened by two layers of high modulus cord (Kevlar®) was performed. Experimental belts were then built with cords of varying twist and their behavior in fatigue investigated. The significance of cord compression was especially clarified, but the results yield much further information on engineering these fiber composite products.

Filament Bending Recovery and Fabric Crease Recovery

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Theoretical Aspects of the Evaluation of Wrinkles in Fabrics

In the &dquo;conical wrinkling&dquo; method of TEFO, the (maximum) wrinkle height h is measured as a fundamental wrinkling parameter. But for fabrics of varying thickness and area weight u,, this parameter was observed to rank fabrics in poor agreement with a visual ranking [1]. Appreciably better correlation was obtained by using h/I’U’ as the ranking parameter. To get some explanation for this and other alternatives, the analysis presented here was made. For fabrics of varying thickness, the bulk volume of wrinkling compression at some arbitrary load was roughly proportional to the fabric thickness 1, especially at the 2-kg load. Assuming that the wrinkle pattern is similar for a thin or light fabric (index 1) and a thick or heavy fabric (index h), it is concluded that the bulk volume per wrinkle is proportional to 1. And as a heavy fabric also has a larger bending stiffness than a light fabric, i.e., smaller bending deformation at a specific load this difference in volume is not attributed to the height h of the wrinkle, but to the width which is thus equal to k.1 (E:ig. 1). For a sharply wrinkled fabric, it is expected, that the wrinkle appearance correlates with the wrinkle angle a, and a measure of the angle sharpness is evidently h/k.1 ( H ig. 1) and, consequently, hill, is larger than lr~l~~; also, for /<< = 1~~. In addition, the thin fabric might appear &dquo;worse&dquo; in wrinkling than the thick because of its higher wrinkle density which is io inverse proportion to k-I t

The Effect of a Curved Configuration of a Fiber on the Critical Extension Force for Yield or Break

If an initially bent fiber is extended, the very skew strain distribution in the plane of bending will cause a corresponding skewness of stress distribution. And if there is a critical stress (for yield etc.), this stress is attained at~ the points of maximum compression or extension (concave or convex side of the fiber) at a level of the external force which decreases with increasing~ initial curvature. The technical consequences are rather important. It has, for instance, been proved that setting of the randomly deformed wool fibers in stockdyeing [2] and also simple dry-fiber setting at large bending deformation ‘[ 1 ] give significant decrease in tenacity. In setting creases at high temperatures, a linear relationship between crease angle and strength has been observed (V. K6pke, persona! communication).. And there are indications that increasing, wave crimp , gives increasing loss of strength also for a flat setting. To get a quantitative idea’ of these relationships, the following derivation was made.

Walking, Running, Jumping — An Interaction of Two Rheological Systems

At the Department of Textile Technology we have been working together with a group from the Orthopedic-Surgical Hospital Department at the Gothenburg University on relationships between injuries in sports as football and properties of ground as well as shoes, preventive tapes etc. The present paper presents some fundamental rheology of the ground and its context with the rheological activity of the human being (player, athlet).

Comparison of stress-activated models and linear spectral models for visco-elasticity

SummaryAn analytical comparison is made of a stress-activated nonlinear model (E) and a linear spectral model (M) for visco-elastic bodies in relaxation, creep, relaxation-creep recovery, constant strain-rate extension and periodic strain. A special reason for this is an observed “invariance” in relaxation (eq. [1]). Significant parameters are the frequency functionH for (M) and the rate constantα for (E).H should be roughly constant in relaxation and in still rougher approximation also in creep recovery, whileα should be inversely proportional to the stress and in additionα (creep-recovery)/α (relaxation) ≈ 22. For strain extension both models predict similar results but none takes the plastic creep of large rate in consideration. Regarding periodic strain model (M) gives a conventional behaviour, while model (E) predicts significant time dependent frequency effects.Possible physical mechanisms for explanation of the results obtained are discussed.ZusammenfassungEin analytischer Vergleich von einem spannungsaktivierten nichtlinearen Modell (E) und einem linearen Spektralmodell (M) für visco-elastische Körper in Relaxation, Kriechen, Relaxationkriecherholung, Dehnung mit konstanter Geschwindigkeit und periodische Dehnung wird gemacht. Eine spezielle Ursache dafür ist eine „Invarianz“ in der Relaxation [1]. Signifikante Parameter sind die FrequenzfunktionH für (M) und die Geschwindig-keitskonstanteα für (E).H sollte in grober Näherung in der Relaxation konstant sein und in noch gröberer Näherung auch in Kriecherholung.α sollte aber im inversen Verhältnis zur Spannung stehen, und weiter sollteα (Kriecherholung)/α (Relaxation) ≈ 22 sein. Für Dehnung geben beide Modelle ungefähr dieselben Resultate, keines nimmt aber das plastische Kriechen von größerer Geschwindigkeit in Betracht. Für periodische Dehnung sieht (M) ein konventionelles Verhalten voraus, für (E) findet man aber signifikante zeitabhängige Frequenzeffekte.Mögliche physikalische Mechanismen zur Erklärung der Resultate werden diskutiert.