Flywheel energy storage systems are mechanical devices used to store rotational kinetic energy for later use in energy management applications such as grid stabilization, backup power supply, and regenerative braking systems. The efficiency and lifespan of flywheel systems depend heavily on the selection of materials and the geometric design of the flywheel structure. Material properties determine the strength, density, fatigue resistance, and energy storage capability, while design geometry influences rotational stability, stress distribution, and energy density. The combination of both factors determines the overall performance and operational durability of the flywheel system in energy storage applications. Material selection plays a critical role in determining the maximum rotational speed and energy storage capacity of flywheel systems. Traditional flywheels were manufactured using metals such as steel and aluminum alloys due to their high strength and relatively low manufacturing cost. Steel flywheels are known for their high durability and ability to withstand repeated mechanical stress cycles. However, steel has relatively high density, which limits the maximum achievable rotational velocity because of the large centrifugal forces generated during high-speed operation. Since the energy stored in a flywheel is proportional to the square of rotational velocity, limiting rotational speed reduces the overall energy storage efficiency. Advanced flywheel systems increasingly use composite materials such as carbon fiber reinforced polymers. These materials offer significantly higher strength-to-weight ratios compared to metals. Carbon fiber composites can withstand extremely high tensile stress while maintaining low mass density. This allows flywheels constructed from composite materials to rotate at much higher speeds, thereby increasing stored energy capacity without requiring large physical dimensions. Additionally, composite materials exhibit superior fatigue resistance compared to metals, which is important because flywheels experience repeated loading and unloading cycles during operation. Another important material property affecting flywheel lifespan is fatigue strength. Flywheels are subjected to cyclic stress during acceleration and deceleration.