Factorial Design Experiment to Analyze the Response of a Luminescent Photoelastic Coating

Abstract

A luminescent photoelastic coating is a relatively new technique to measure full-field surface strain and determine principal strain directions that has many potential applications in engineering. Generally, luminescent photoelastic coating technology uses an in situ strain gage measurement to calibrate the detected optical response to maximum shear strain. This calibration requires the determination of two coating parameters: the polarization efficiency and the coating characteristic. A better understanding and modeling of these two parameters, particularly the polarization efficiency, will enable a simpler a priori calibration and greater measurement accuracy. This paper presents a factorial design experiment that assesses the effect of four factors on the optical strain response of an luminescent photoelastic coating. The factors examined were substrate reflectance, luminescent dye concentration, absorption dye concentration and cure time. Results show the polarization efficiency is strongly correlated with the emission anisotropy of the coating. When the polarization efficiency is modeled as the measured emission anisotropy, the two most significant factors are the substrate reflectance and the luminescent dye concentration. Absorption dye concentration and reflectance-luminescence interaction are minor but significant effects. The most significant tested factors in modeling the coating coefficient are absorption dye concentration and substrate reflectance. The resulting uncertainties for the polarization efficiency and coating characteristic are 1.3 and 3.7%, respectively.