Feasibility Evaluation of Optoelectronic Strain Measurement for Flywheel Rotors

The rotor is a core element of a Flywheel Energy Storage System (FESS) and its condition has to be monitored continuously to assure safe operation. Modern flywheel rotors are usually made of carbon-fiber-reinforced polymer (CFRP) composites because of their high inherent specific energy density. Throughout the service life the stress state inside the rotor changes due to long-term effects of the material. Therefore, the strain profile is an interesting measure for the rotor’s health condition. The chosen measurement principle requires a surface finish of the rotor with a periodic pattern of contrasting areas. A preliminary evaluation of the feasibility of different optoelectronic measurement setups with focus on different rotor materials, surface finishes and the high rotational speed of the rotor was conducted. Adhesion properties and influences of different rotor surface finishes as well as the influence of the photodiode’s rise time are investigated.