Matrix-dominated performance of thick-section fiber composites for flywheel applications

摘要

An Achilles heel for the performance of thick-section, cylindrical fiber composite flywheels is the poor interlaminar properties of the material. Methods that have been used to minimize or eliminate radial tensile stresses include prestressing concentric cylinders and mass loading. There can also be significant interlaminar shear stresses at the edges of mass-loaded flywheels and in flywheels for high-power density applications where abrupt braking results in high torque levels. To specify adequate safety factors for thick-section flywheels used in these applications, the failure envelope and fatigue behavior under combined interlaminar stresses are required. Using a hollow cylindrical specimen, which was subjected to combined axial compression and torsion, results for fatigue and failure were generated for several flywheel material systems. Interlaminar compression resulted in significant enhancements to the interlaminar shear strength and results were compared to the predictions of proposed three-dimensional composite failure models. The interlaminar shear fatigue behavior of a carbon/epoxy system was also studied and compression was found to greatly enhance fatigue life. The results demonstrate that radial compression stresses can yield improvements in the interlaminar shear strength and fatigue lifetimes of composite flywheel rotors.