A theoretical basic scheme is presented to desclibe how the deformation properties of random fiber masses are affected by the slippage of fibers at their contact points. The constituting fibers are modeled by chains of hypothetical short elements variously oriented, each of which has a length equaling the mean free-fiber-length depending on the respective direction in the mass and a circular curvature corresponding to the local fiber crimpiness ; the elements are treated as if they were nonlinear elastic springs characterized by their orientation and curvature at each stage of deformation. The force that tends to induce fiber slippage or to oppose it at a fiber contact point is related to the relative recovery force between two elemental springs connected at the contact. The elastic response of the system to external force is formulated by the scheme that was earlier given by the present authors to the deformation mechanics of fiber assemblies. Several typical model analyses of the uniaxial compression of an isotropic mass predict the followings : hysteresis appears in the stress-strain curve as well as in the Poisson's ratio-strain relation when the mass is unloaded after compression ; a greater friction coefficient of fibers gives to the assembly a higher elasticity and a lower Poisson's ratio.

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In order to improve yarn strength and to diversify yarn structure, a multi-core twin spun yarn made by using the experimental ring-spinning frame was produced. The tensile properties and the thickness variation of various core twin spun yarns were examined, and the effects of insertion of core filaments into a twin spun yarn made from two different types of staple fibers were discussed. It was found that the insertion of multi-core filaments was accompanied by the fasciation of some staple fibers in the yarn andthe prevention of irregular drafting in the almost-twistless zone from front roller nip to strand convergence point.

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Frictional force patterns of shingosen were measured by KES-SE frictional force measurement system. Power spectra of the frictional forces were obtained by FFT method. The power spectra denoted that the vibrational components of the frictional forces can be divided into two groups. One group was related to the density of yarn and the other was related to the. spacing of piano wires on the surface of the probe. It was found that the former components decrease and the latter components increase with increasing randomness of spacing of yarns by a calculation with a simple model of interaction between a friction probe and fabrics. These vibrational components had various intensity and formed a characteristic spectrum pattern in each sample. Some relation were observed qualitatively between the spectrum patterns of frictional force and the handles of the fabrics. Then it was suggested that the frequency analysis of the frictional force can be used as ameasuring method by which the subtle differences in frictional properties among shingosen fabrics can be detected.

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