Date of Publication


Document Type

Master's Thesis

Degree Name

Master of Science in Mechanical Engineering

Subject Categories

Energy Systems | Mechanical Engineering


Gokongwei College of Engineering


Mechanical Engineering

Thesis Advisor

Aristotle T. Ubando
Jeremias A. Gonzaga

Defense Panel Chair

Laurence A. Gan Lim

Defense Panel Member

Gerardo L. Augusto
Conrad Allan Jay R. Pantua


There are many reasons to improve the utility of renewable energy sources. The use of clean energy sources makes it possible to cut the global carbon emissions and solves the energy crisis due to the depleting fossil fuel reserves. However, the use of renewable energy sources has its shortcomings in its consistency of supply. To solve this problem, energy storage systems are employed to store the energy surplus and supply it when there is scarcity. Among the energy storage systems, the study focused on improving the flywheel for its environmentally friendly features. However, this mode of energy storage is still not preferred over other types because it has higher capital costs, relatively lower efficiency, and it has moving parts that are vulnerable to fatigue failure. This research attempted improve the design of the flywheel by studying its crack growth behavior. This would allow the flywheel to run as fast as possible to store and release more energy while considering the growth of surface cracks. With this, higher energy density and efficiency for the rotor while utilizing its structural capacity could be achieved. A three-dimensional model of the flywheel was developed from the specifications provided in the work of Kale et al. (2021). The model was validated using mesh independence tests and statistical methods to test the consistency of its results. Using the J-integral as the crack energy release rate criterion, the parameters where crack tends to propagate most was evaluated. The growth of the three-dimensional semi-elliptical crack was also predicted using stress intensity factors. The developed model has shown minimal difference in the stress distributions from the work of Kale et al. (2021). It was found that the maximum energy release rate for the given geometry can be found at the site closest to the center, while the speed is the highest possible, and the crack aspect ratio is the smallest possible. The crack was observed to have mixed loading for any angle of orientation, except for radially oriented cracks where pure mode I loading was observed. The crack front tends to separate at the bottom for shallow cracks, while deeper cracks tend to propagate at both crack tips. The crack fronts tend to slide parallel to each other the most at its deepest site for all aspect ratios. Out of plane shear of the crack fronts for the length of the crack were observed to completely reverse. This means that the crack front tends to move in one direction for one half, and the other direction for the other half. The findings of the study would be useful in determining the regions in the rotor that should be improved for structural integrity. It would also be useful in developing monitoring systems for flywheels. The data on the behavior of the crack would be helpful in the containment of cracks to prevent possible rotor burst. The methodology developed could also be useful in investigating crack development in other flywheel materials.

Abstract Format





Energy storage; Flywheels—Fatigue; Rotors—Fatigue

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