J. W. S. Hearle

Physical properties of textile fibres

Introduction to fibre structure Testing and sampling Fibre fineness and transverse dimensions Fibre length Fibre density Thermal properties Equilibrium absorption of water Heats of sorption Rate of absorption of moisture The retention of liquid water Swelling Theories of moisture sorption Tensile properties The effects of variability Elastic recovery Rheology Directional effects Thermo-mechanical responses Fibre breakage and fatigue Theories of mechanical properties Dielectric properties Electrical resistance Static electricity Optical properties Fibre friction.

High-performance Fibres

Aramids Gel-spun high-performance polyethylene fibres Other high modulus-high tenacity (HM-HT) fibres Carbon fibres Glass fibres Ceramic fibres Chemically resistant fibres Thermally resistant fibres.

29—THE MECHANICS OF TWISTED YARNS: THE INFLUENCE OF TRANSVERSE FORCES ON TENSILE BEHAVIOUR

An idealized theoretical model of a yarn is assumed, and, after considering the stresses acting on a small element of the yarn, the conditions for radial equilibrium in the yarn are worked out. This leads to expressions for the tensile and transverse stresses in the fibres as functions of (i) the position in the yarn, (ii) the stress which would be present in fibres under the same extension as the yarn, (iii) the twist angle of the yarn, and (iv) the Poissons ratio of the fibres. Integration of the components of these stresses parallel to the yarn axis gives an expression for yarn tension. Finally, the behaviour when fibres start to break is considered.

Yarn texturing technology

The origins of texturing Scientific and engineering principles in twist-texturing Scientific and engineering principles in other texturing processes False-twist process False-twist textured yarns BCF processes and yarns Air-jet texturing and yarns Quality assurance Textile yarn logistics Retrospect and prospect.

15—The Mechanics of Twisted Yarns: Theoretical Developments

The assumptions used in theoretical predictions of the tensile properties of twisted continuous-filament yarns are critically discussed. A modified theory, based on constant yarn volume during extension, is derived, and theoretical and experimental values of modulus are compared. Expressions for yarn extension and breakage at large extensions, and also taking account of deviations from Hooke’s law, are derived and compared with experimental results.

39—INTERCHANGE OF POSITION AMONG THE COMPONENTS OF A SEVEN-PLY STRUCTURE: MECHANISM OF MIGRATION

The migration pattern in a seven-ply structure is predicted theoretically on the assumption that the centre filament moves to an outer layer only when it is slack. The frequency of migration is dependent on the twist, the twisting tension, the free length in the twisting zone, the tension resulting from an extension of the yarn, and the degree of buckling needed to initiate migration. If the tension is high enough, migration will be prevented. The theoretical predictions were confirmed by a study of the twisting of seven lOO-denier twisted viscose rayon yarns on an apparatus specially constructed to twist model yarn samples. The order of migration indicated that, of the six yarns in the outer layer, the yarn which had last migrated had a low, but not zero, probability of moving back to the centre, but that the other five had equal probability. Subsidiary experiments were performed on Courlene monofilaments and zerotwist rayon yarns.

6—THE MECHANICS OF TWISTED YARNS : TENSILE PROPERTIES OF CONTINUOUS-FILAMENT YARNS

The theories ofthe extension of yarns which have been proposed by Gegauff1 Platt 2,3, and Hearle4 and the assumptions on which they are based are considered. Experimental studies of the tensile properties of twisted continuous-filament yarns are reviewed. A range of yarns has been twisted, and their tensile properties determined. Reasons for the variation of stress-strain curves, modulus, limit of proportionality, breaking extension, and tenacity are discussed, and the results compared with theoretical predictions. The effects of processing conditions, and deviations of yarn structure from an idealized model are also mentioned.

23—THE MECHANICS OF TWISTED YARNS : FURTHER STUDIES OF THE TENSILE PROPERTIES OF CONTINUOUS-FILAMENT YARNS

This paper reports continued studies of the tensile properties of twisted continuous-filament viscose rayon, Tenasco, acetate, nylon and Terylene yarns, with particular reference to the influence of twisting tension, the differences between ring-twisted and uptwisted yarns, values of the work of rupture and the yarn contraction due to twisting, the change of yarn diameter during extension, the measurement of properties of filaments extracted from the yarns, and a study of glued and unglued model yarns.

13—THE TRANSMISSION OF TRANSVERSE STRESSES IN FIBRE ASSEMBLIES

The paper reports a study of the Iransverse pressure exerted horizontally by a specimen held under a vertical applied load in a rectangular trough. The materials tested are cotton and Fibro sliver, Fibro roving, nylon yarn and monofilaments. and metal wires and rods. The results are discussed in relation to the forces in a twisted yarn.