Fatigue behavior of high performance fiber yarns

The fatigue behavior of a variety of commercial high performance fiber yarns has been investigated. A general semiogrithmic law governs the relationship between fatigue lifetime and normalized load amplitude. Fatigue behavior is characterized by fatigue strength and fatigue strength index. The fatigue resistance of different fibers ranked as: Kevlar 29 ∼ Kevlar 119, Vectran HS ∼Technora, Spectra 900. A fatigue failure model is proposed to support a fatigue law which suggests that the cyclic maximum strain can be used to monitor the development of fatigue damage. Twisting as a means of improving fiber performance is studied and an optimum twist is observed. Axial splitting is seen in all fatigue fractured surfaces. Structural changes measured by X-ray diffraction and thermomechanical analysis(TMA) support the conclusion that the strength of the material is depleted with the fatigue.