Simultaneous displacement and strain measurements

Abstract: This paper introduces a novel experimental approach to simultaneously measure displacement and strain on an oscillating thin panel under high-speed fluid-structure interactions (FSI). Commonly, measurements like these have been determined using digital image correlation (DIC), which involves applying a speckle pattern to the panel and coordinating the panel's oscillation with a high-speed camera to capture multiple images for estimating out-of-plane displacement using stereo DIC. However, this method suffers from limited resolution and is prone to noise due to the numerical differentiation of displacement data. To address these issues, we have developed a unique setup that combines stereo-DIC with Photoelastic Coating (PEC) for strain measurement, allowing for direct, noise-free estimation of strain. This system utilizes a single light source to illuminate the PEC texture, which also serves as the speckle pattern, while a high-speed polarized camera captures the reflected light at different polarization angles. Our paper will detail this experimental setup, assess error margins, and compare the effectiveness of direct versus indirect strain measurement methods using PEC and stereo-DIC. Keywords: Digital image correlation, Photoelastic coatings, Fluid-structure-interactions