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A Preliminary Study on Fatigue Strength of High Toughness Thermoplastic Composite Material AS4/PEEK

고인성 열가소성 복합재료 AS4/PEEK의 피로강도에 관한 기초적 검토

  • Published : 2000.04.01

Abstract

First, various specimen geometries, namely, coupon type, waisted type and dog-bone type, were examined to determine appropriate fatigue specimen of thermoplastic composite material AS4/PEEK and the n, fatigue strength of smooth and notched specimens of AS4/PEEK [-45/0/+45/90]2s was investigated. Fatigue tests were performed under load controlled condition at a stress ratio of 0. 1 at a frequency of 5Hz. Stiffness degradation of specimens with fatigue cycling was monitored using an automated unloading compliance technique. The waisted type specimen is found appropriate for smooth fatigue specimen geometry of AS4/PEEK. As for the effect of stress concentration, it is found that fatigue strength is higher for a 2mm-diameter hole notched specimen than a 5mm-diameter one. Fatigue notch factor decreases with the increase of fatigue life. These results are far different from the trend of fatigue strength of metallic materials. The stiffness variation of smooth specimen was only 4% at maximum until final fracture. On the other hand, the stiffness of hole notched specimen was reduced by 45% at maximum. Notched fatigue strength was compared between thermoplastic composite AS4/PEEK and thermosetting composite Graphite/Epoxy. In long-life fatigue (>104), the AS4/PEEK composite shows superior fatigue strength, but in short-life fatigue, the fatigue strength of the Graphite/Epoxy composite is nearly equal or somewhat higher than that of the AS4/PEEK composite,

Keywords

Fatigue Strength;Thermoplastic Composite;Fatigue North Factor;Thermosetting Composite;Stiffness Degradation;Stress Redistribution

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