The Application of the Process Capability Index (PCI) in a Fatigue Test of a Tidal Turbine Blade Using Historic and Real-Time Load Data

Fatigue testing of composite tidal turbine blades aims to stimulate the damage of a specimen, which it would experience over the lifetime of its subsea deployment. The mechanical response of the blade is monitored as it undergoes thousands of stress cycles. The experiment results are subsequently used to evaluate the design and manufacturing processes by comparing them against theoretical results and industry standards. Therefore, it is essential for the credibility of the test that the loads exerted on the specimen match the desired loading values.
Process Capability Indices (PCIs) provide a straightforward measure of how well the achieved process outcomes match the desired quality specifications. They serve as a valuable tool to a) assess whether contractual obligations have been met, b) compare the performance of various assets on-site, or c) monitor the change in the system's performance in time. In our work, we consider fatigue tests of a tidal turbine blade carried out at FastBlade, a dedicated research facility for regenerative testing of full-scale structures. We discuss the benefits of incorporating a PCI for performance monitoring purposes and decide on the index type best suited for evaluating the accuracy and consistency of exerted loads. We subsequently apply the measure to historical load data and integrate it directly into the control system of the fatigue test rig. The experimental results are used to determine the change in the consistency and accuracy of applied loads between the tests run at various stages of facility development and to find out how fidelity to the desired values in a fatigue test changes throughout its duration. The data findings are also used to determine the quality discrepancies between individual actuators. Finally, the wider implementation of PCIs in full-scale tests of tidal turbine blades is considered.