Strain-Based Shape Reconstruction And Temperature Compensation For Fiber Bragg-Instrumented Rotor Blades

Abstract

A pre-series Kopter AW09 main rotor blade was instrumented with fiber Bragg gratings (FBGs). Static lab tests sup- ported by digital image correlation (DIC) were conducted to derive and evaluate mathematical relationships between the measured strain signals and structural quantities. These comprised the beam sectional strains, the elastic deforma- tion of the blade, and the sectional loads and stiffness properties. Additionally, the paper addresses the challenge of isolating these target variables from the influence of temperature variations. In order to evaluate cross-sectional strains due to thermal influences, full-scale rotor test rig data recorded in non-rotating conditions was used as the basis for an in-field calibration, taking advantage of natural temperature changes. This accounted for the effect of temperature and its spatial gradients on the sectional signals of the anisotropic rotor blade.