Frequency Effects on the Fatigue of Glass Reinforced Plastics

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Abstract
An experimental investigation has been conducted to determine the effects of cyclic frequency on the tensile fatigue characteristics of glass fiber (non-woven) reinforced plastics. A 3-M material was used, XP251, and the fiber orientations thus far studied include cross-ply (0°-90°) and isotropic (-60°, 0°, + 60°). The surface temper atures of the specimens were carefully recorded during the fatigue testing and studied as a function of frequency over the range from 1 cps to 40 cps. The hystersis has also been determined for a single cycle closed loop tension test. Analyses have been conducted and equations developed to predict the temperature distribution due to hystersis heating, the time to achieve steady state at interior points and the steady state surface temperatures. Surface temperatures as high as 265°F have been measured for the isotropic material. The hystersis heat generated in a cyclic fatigue test for a given material is dependent on the product σ 2f. The temperature difference be tween the center of a specimen (thickness-2a) and its surface is a function of (ασ) 2f. The fatigue life of these materials is lowered with increasing cyclic frequency, the effect becoming more pronounced at lower stress levels.

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