AN INVESTIGATION ON THE CYCLIC TENSILE AND IMPACT STRAINING OF YARNS

Abstract

In general the textile materials are subjected to repeated strains of various forms, the cyclic strains, during their manufacture and in their use by which they get fatigued at different levels. This is true of both industrial and domestic textiles. The various forms of cyclic strains are tensile, torsional, bending, compression, impact etc. The characteristic behaviour of the textile materials changes with time in its life cycle as per the nature of the cyclic strain it encounters. This dissertation is based on cyclic straining of yarns and has been designed to accommodate a number of variables at various levels, the straining amplitude, straining speed, straining cycles, their cumulative application, specimen length, testing parameters, material construction and chemical treatments along with interaction between forms of straining. Among the various forms of straining, the cyclic tensile and cyclic impact straining of yarns were selected in order to study their effects on yarn characteristics. The cyclic tensile and impact straining of ring, rotor and compact yarns have been carried out and their effects on the tensile breaking load, breaking extension and impact breaking load values were studied. In order to carry out these straining operations the following machines were designed and fabricated. a) Cyclic tensile straining cum strength tester for yarn, b) Cyclic impact straining machine for yarn and c) Impact strength tester for yarn.

An investigation on the influence of various cyclic tensile straining parameters, extension level, extension rate and straining cycles at five different levels, on the tensile breaking load and breaking extension characteristics of compact yarn of count 14.75 Tex has been carried out. The extension level of 8 mm, the extension rate of 400 mm/min and the number of straining cycles of 2500 have resulted in the maximum drop in the breaking load and extension values of the yarn which are 30.4% and 40.25% lower than the average breaking load and extension values of the unstrained yarn. The investigation on the influence of yarn specimen length, in cyclic tensile straining, on the tensile characteristics of compact yarn exhibits higher resistance when it is strained at shorter gauge lengths. The cumulative application of the extension levels and extension rates on compact yarn in cyclic tensile straining has resulted in the following findings. The loss % in breaking load and breaking extension values are low in cumulative straining as compared to the normal straining. Among the two types of cumulative straining, the extension level type exhibits minimum loss in the breaking load and breaking extension properties. An investigation has been carried out to compare the cyclic tensile strained and unstrained ring and compact yarns of count 9.85 Tex for tensile breaking load and extension characteristics tested at different extension rates and gauge lengths. It is observed that the rate of increase of breaking load and breaking extension values of strained ring and compact yarns, with increase in extension rate, is lower than that of unstrained yarns. On the other hand it is found that the rate of decrease of breaking load and breaking extension

values of strained ring and compact yarns, with increase in gauge length, is higher than that of unstrained yarns. An investigation on the influence of various cyclic longitudinal impact straining parameters, yarn tension, dropping height and straining cycles, at five different levels, on the impact breaking load values of compact yarn of count 14.75 Tex is carried out. The yarn tension of of 1.6 cN, the dropping height of 15 cm and the number of straining cycles of 2500 have resulted in the maximum drop in the impact breaking load value of the yarn which is 23.5 % lower than the average breaking load value of the unstrained yarn. The cumulative application of the yarn tensions and dropping heights on compact yarn, in cyclic impact straining, has resulted in the following findings. The loss % in impact breaking load is low in both types of cumulative straining as compared to the normal straining. Among the two types of cumulative straining, the yarn tension type exhibits minimum loss in the impact breaking load value. An investigation on the influence of cyclic tensile and impact straining of compact yarn of 14.75 Tex, at the selected straining parameters, on the tensile and impact characteristics has been carried out. The loss % of the tensile breaking load value at various straining cycles is lesser than the loss % of impact breaking load values. An investigation on the influence of cyclic mixed straining (tensile and impact) of compact yarn of 14.75 Tex, at the selected straining parameters, on the yarn tensile and impact characteristics has been carried out. Higher proportion of tensile straining in

the mixed straining has good impact on the loss % of the tensile breaking load, breaking extension and impact breaking load values. An investigation on the cyclic tensile straining of ring and rotor yarns of 29.5 Tex on the tensile and impact characteristics has been carried out. It is seen that for both ring and rotor yarns the loss % in tensile breaking load value is lower than that of impact breaking load value at all the strain cycles studied. The loss % of the tensile as well as the impact breaking load values in ring yarn is lower than that of rotor yarn at all the strain cycles studied. The loss % of the tensile breaking extension in ring yarn is marginally higher than that of rotor yarn at all the strain cycles studied. An investigation on the influence of the cyclic impact straining of ring and rotor yarns of 29.5 Tex on the tensile and impact characteristics has been carried out. Similar trend is observed as that of cyclic tensile straining. Finally the investigation of the influence of chemical treatments on the tensile and impact characteristics of the ring and rotor yarns, in cyclic tensile and impact straining, has resulted in the following finding. Out of the chemically treated yarns, the mercerized yarn shows good resistance to cyclic tensile and impact straining.