Importance of twisted structure of textile fiber

Trelor in his Mather lecture, titled “Twisted Structures” adequately recognizes the role of twist in yarns and

the part it plays in the design of textile structures .He discusses the obvious necessity of twist in the natural and staple fibers by pointing out

“ Twist is essential to provide a certain minimum coherence between fibers, without a yarn having a significant tensile strength cannot be made. This coherence is dependent on the frictional forces brought into play by the lateral pressures between fibers arising from the application of a tensile stress along the yarn axis. With the introduction of continuous filament yarns, however, the role of twist must be reconsidered. In continuous filament yarns, twist is not necessary for the attainment of tensile strength (in fact, it reduces it) but it is necessary for the achievement of satisfactory resistance to abrasion, fatigue, or other types of damage associated with stresses other than a simple tensile stress, and typified by the breakage of individual filaments, leading ultimately to total breakdown of the structure. High twist produces a hard yarn, which is highly resistant to damage of this kind. The role of twist in continuous filament yarn is thus to produce a coherent structure that cannot readily be disintegrated by lateral stresses.

From the engineering standpoint, the interesting thing about this structural function of twist is that, in contrast to most structure-building techniques, it produces its effect without significantly increasing the flexural rigidity or resistance to bending of the system. A yarn of 100 filaments has only 100 times the flexural rigidity of single filament; if the filaments were all cemented together to form a solid rod, it would have 10,000 times the flexural rigidity of a single filament.

Extending this line of thought to woven fabrics, we find again that the stiffness of the fabric is of the same order as the total stiffness of all the filaments in a given cross section as shown by Livesey and Owen, and similar considerations apply, no doubt, to knitted or other types of fabric structure. We see, therefore, that the major processes of textile fabrication are concerned with the production of coherent structures having maximum flexibility or minimum resistance to bending stresses, and hence also to compressive or buckling stresses, while retaining, of course, the inherent strength of the original filament material under the action of tensile stresses. This objective is in curious contrast to that normally encountered in engineering structures, where the general problem is to produce maximum resistance to bending and compressive stresses, combined with maximum tensile strength. The engineer achieves his objective of maximizing the rigidity by the introduction of suitably disposed fixed linkages between the various components of the structure.

In textile structures, on the other hand, the objective of maximum flexibility is ingeniously achieved by the introduction of geometrical restrains, which, while strongly resisting forces of disruption do not interfere appreciably with the small relative movements of individual elements associated with bending or other types of lateral deformation. However, a difference of objective does not necessarily imply a difference in method of approach, and there is no reason why the design of textile structure should not be treated by the same rigorous analytical techniques as the design of any other engineering structures such as bridge or an airplane. The materials with which the textile engineer works have an inherent strength and other mechanical properties comparable with those of typical structural-engineering materials, and research is continually being concentrated on the improvement of these inherent properties. If these valuable characteristics are to be utilized to the fullest extent, it is equally important to see that the problem of design from the engineering standpoint receives something like the kind of attention.”

The study of twist, therefore, is very important for the textile engineers and technologists to understand the structure and behavior of yarns and their ultimate influence on the end-use properties of fabrics.