In this paper, tensile properties of textured yarns will be analysed. First, the property is calculated on the basis of a "independent fiber model" where each fiber contributes independently to the yarn tensile property, i.e., no mechanical interactions among fibers are considered.One of the purpose of this paper is to examine the accuracy of this no-interaction assumption for making distinct the mechanical interaction among fibers. Second, the tensile property of a crimped single fiber is calculated by applying the so-called "strain additive method"~l~ to a helical coil model of a fiber. Then the tensile property of a textured yarn is introduced by summing up the tensile property of each crimped fiber. A good agreement between the calculated and the observed values is obtained over a wide range of the tensile atrain of the yarn by assuming the independent model. No interaction is observed except the small deformation region.The hysteresis behavior observed at the repeated extension is also examined, and it is confirmed that the independent model is still suitable for this case. The experimental results agree well with the calculated results with good accuracy, too.

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Investigation was made on the relation between the temperatures (Tmax) at which the maximum thermal stress was observed and the equilibrium thermal shrinkage in free state.The results obtained are as follows :1. A fiber contains frozen strains when the polymer molecules take the nonequilibrium configu ration in the production process.The thermal shrinkage of a fiber may be caused by disorienting effect due to breakdown of either crystallites or secondary bonds among the oriented molecular chains in the amorphous region.According to Boltzmann, the probability that a restrictive energy E.c is released, is proportionalSo, assuming that the equilibrium thermal shrinkage (%) in free state is owing to breakdown of these secondary bonds and crystallites, the following formula may be obta ined ;where, IT is the equilibrium thermal shrinkage (%) in free state at Tom.The first term on the right hand side of the above equation represents the frozen energy released at T < Tmax, and the second term is the frozen energy released at T > Tmex (°K). Assuming that the latter is larger than the former, the following results are obtained.

Considering the scarceness of papers treating of the lateral behaviour of the helical spring of textile materials, in this paper is studied its lateral compressive behaviour when the helical spring is made of heat-set nylon gut.It has been revealed that the lateral compressive force P per one pitch of the helix can be expressed as follows :where P1 is the force due to the bending deformation, P2 the force due to the torsional deformation and Po the negative force due to the original curvature.

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