Monitoring energy recovery in a full-scale fatigue test

A fatigue test aims to subject a specimen to a multitude of loading cycles to stimulate damage. This way objects such as beams, columns, or blades can be tested at an accelerated pace, and their degradation patterns can be examined before they are commissioned for mass production/service. Fatigue tests are energy-expensive processes due to the vast number of cycles required. Some tests benefit from energy savings when the specimen, such as a wind turbine blade, can be actuated at its natural frequency and resonance occurs. However, stiffer objects, such as polymer composite tidal turbine blades or aircraft wings, have a much higher resonant frequency and the specimen would suffer degradation due to overheating, rather than cyclic loading. FastBlade, a test facility at the University of Edinburgh, incorporates a novel energy recovery system for fatigue tests, opening the door to efficient testing of stiffer specimens. In this work, we introduce the principle of operation of the proprietary energy recovery system and describe the associated condition monitoring hardware. We then discuss various ways of quantifying hydraulic system efficiency. Running an offline test, it was found that more than 60% of the mechanical energy stored in the system was transferred into producing useful actuation work by the hydraulic system, while the electric motors driving the pumps were unpowered. We subsequently suggest system upgrades that can be integrated for more accurate energy savings estimation in real-time.