Research and Development
Fatigue and Fracture Simulation of Energy Storage Flywheel

A structural integrity and damage tolerance analysis were carried out as part of research and development of an energy storage flywheel for a light rail transportation system. The flywheel prototype strength was assessed by using a detailed 3-D finite element analysis that included the interaction between the flywheel components (disks, flange and bolts) and by using contact surfaces and submodelling techniques. Critical areas were identified near the bolt holes and it was conceived that failure might occur due to fracture under extreme conditions (such as overspeed).
At the critical locations, an elastic and elastic-plastic fracture analysis was carried out. Initially the stress intensity (K) was calculated by conducting simulations for different crack lengths and considering possible crack orientations. Using the simulated K values, the material R-curves were compared to the finite element results and critical initial crack lengths to cause fracture, were obtained. The critical cracks were then used to predict the fatigue life of the flywheel employing fatigue crack growth material relation. The results were incorporated into the design process for further development.