Tensile behavior of filament-wound composites in medium vacuum

In order to design the most efficient flywheel energy systems using fiber-r einforced polymer composite rotors, design allowables for the rotor materia l in a realistic environment and under realistic stresses must first be est ablished. As a first step, this investigation characterizes the 0-deg tensi le behavior of unidirectional T700 carbon and E-glass reinforced epoxy comp osites both as received and after conditioning at a pressure of 15 mtorr an d a temperature of 20 to 25 degreesC. Constant-amplitude tension-tension cy clic fatigue tests were carried out on half the specimens in a similar medi um vacuum environment. Weights of specimens were tracked with immeasurable changes noted due to vacuum conditioning for up to 300 days' duration. E-gl ass/epoxy specimens had a higher quasi-static strength following conditioni ng, but this difference was not evident on an absolute stress basis in the fatigue tests. At the baseline comparison point of 10(5) cycles to failure, there was little difference in fatigue strength of as-received and conditi oned E-glass/epoxy specimens. In the case of T700/epoxy, little difference between conditionings was noted in quasi-static tests, but as-received spec imens had slightly higher fatigue strength at a lifetime of 10(5) cycles. M icroscopic inspection of fracture surfaces following quasi-static and fatig ue failures revealed no significant differences due to the type of loading or conditioning.