Effect of temperature, width, and fiber angle on tensile behavior of a fiber-dominated carbon/epoxy composite

A test program was conducted to investigate the effects of specimen width, elevated temperature, and fiber angle on tensile strength and fatigue of a carbon/epoxy composite used in filament wound flywheel rotor rims. Test coupons were manufactured with three fiber orientations representative of flywheels and three specimen widths. In unidirectional and balanced angle-ply material, it was found that fiber angles of up to 5 deg. from the loading axis had a highly significant effect on quasi-static and fatigue strengths, but not on the elastic modulus. Fiber angle had a more significant effect on quasi-static strength than on fatigue lifetime. The quasistatic and fatigue strengths of the 12.7- and 24.5-mm wide specimens were slightly higher than those of the 12.7-mm-wide specimens, suggesting that cut axial ends of flywheels are potentially the critical locations to consider in the design of flywheel rims. Increases in the test temperature led to monotonically decreasing quasi-static strengths. The trends in fatigue strength versus temperature were not as clear, which indicates that temperatures up to values of approximately 30°C below the glass transition temperature of these materials do not affect their fatigue behaviors significantly.