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ASTM Selected Technical Papers
Composite Materials: Testing and Design (Fifth Conference)
SW Tsai
SW Tsai
Senior Scientist
Air Force Materials Laboratory, Wright-Patterson Air Force Base
Ohio 45433, editor
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ASTM International
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Fatigue is one of the most critical design considerations for a helicopter, especially its rotor blades. The acceptance of glass fiber reinforced composites for the rotor blade structure has created a need for fatigue data. The fatigue testing described here was undertaken to determine which of the many raw material variables could contribute to improving this specific property. A series of thirty curves, alternating stress versus cycles to failure (S-N), have been developed for a number of the raw material variables in nonwoven glass fiber reinforced epoxy composites. These variables include glass type, glass fiber finish, glass fiber suppliers, fiber bundle size, and resin studies. Both an all unidirectional, 0-deg, and a bias, ±45-deg, orientation were used in the tensile-tensile fatigue tests performed. The S-N curves indicate differences in the reproducibility and data scatter in the two orientations studied. The 0-deg orientation gave greater scatter in data than the ±45-deg. Of the two orientations used, the ±45-deg orientation gave greater spread between the variables being studied. The variation between the poorest and best materials tested was 85 percent. There were significant differences noted due to glass finish, fiber bundle size, and resins in this study.

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