Luminescent coating image analysis on a three dimensional grid

The luminescent photoelastic coating (LPC) technique is a method to measure the full-field strain on three-dimensional (3D) structural components. A luminescent dye within a photoelastic binder is excited with circular polarized light, and the corresponding emission intensity for coating is detected via a CCD camera. Images are then processed to find the relative change in emission with respect to camera analyzer position, and subsequently analyzed to determine maximum in-plane shear strain. Image alignment plays a crucial role to obtain accurate measurements, especially when implementing an oblique excitation approach to separate the principal strains while accounting for non-strain related polarization changes due to surface inclination. Image warping methods in the image two-dimensional (2D) coordinate system provides reasonable results for 2D or simple 3D specimens; however, for complex 3D structures with moderate movement or deflection in the field-of-view, the accuracy and efficiency of these methods are not optimal. An alternative approach is to perform the analysis on a 3D grid representation of the structures. This study will research the merit of such an approach and develop the analysis procedures to separate the principal strains on 3D structures. The theoretical results will be compared to experimental data from a 2D and a 3D specimens while assessing the accuracy of the approach.