Study of the Fatigue Behavior of the Unidirectional Zylon/epoxy Composite Used in Pulsed Magnets

The fatigue behavior of the Zylon/epoxy composite has been tested under quasi-static tensile and tensile fatigue loads. The distribution of the fatigue life at different stress was determined. The results show that the statistical characteristic of the static strength and the fatigue life can be satisfactorily described by the normal, lognormal or Weibull distribution model. The measured S-N curve exhibits a pronounced nonlinear behavior. Strains of the unidirectional specimens were monitored with a mechanical extensometer during the test. Three distinct stages of the strain evolutionary process were observed. The evolution curves show a sharp increase in the first stage, an approximately linear slow increasing in the middle stage and an unstable acceleration in the third stage before failure. Similar to the strain evolution, the three-stage stiffness of degradation was also observed. The maximal cycle strain is chosen as the indicator of damage evaluation. The experimental data of the damage parameters are fitted with the existing analytical model. The presented models have a good agreement with the tested results.