Variation of Longitudinal Modulus with Twist for Yarns Composed of High Modulus Fibers

Abstract

Variations of longitudinal and transverse moduli with twist for twisted yarns and twisted yarn-resin composite strands composed of fibers covering a wide range of tensile moduli are investigated using a sonic pulse propagation method. For twisted yarns composed of fibers relatively low in tensile modulus, the longitudinal modulus decreases with increasing twist in accordance with the cos²α model. For twisted yarns composed of high modulus fibers such as aramid and carbon, however, the reduction of the longitudinal modulus with twist is abrupt, and deviates largely from the prediction of the cos²α model. The relationship between the longitudinal modulus of twisted yarns and the twist angle is derived on the basis of a model that takes into account the anisotropic elasticity of the filaments. The analytical results of the proposed model are quantitatively consistent with the experimental results for various twisted yarns and twisted yarn-resin composite strands.

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References

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