This paper presents results from a thermal sensitivity study of a luminescent photoelastic coating. The investigation is part of larger research program to integrate luminescence sensing for strain measurement and health monitoring in civil, automotive and aerodynamic applications. Luminescent photoelasticity is a new approach to measure mechanically induced stress and/or strain, and corresponding principal directions on structural components. The technique incorporates a luminescent dye that partially preserves the stress-modified polarization state within a birefringent coating and provides high emission signal strength at oblique surface orientations. The optical strain response of the coating is a nonlinear function of the maximum shear strain in the plane perpendicular to the propagation of light. Several parameters may affect the strain response including luminescent polarization efficiency, optical sensitivity, coating absorptivity and effective excitation-emission wavelength. The temperature dependency of these parameters is important to characterize if the technique is extended to high-temperature or cyclic-temperature environments. A small thermal chamber was constructed with open optical access to test coated cantilevered specimens under a linearly varying bending stress. Results show that the optical strain response decreases as temperature increases. Over a temperature range spanning from 24 °C to 92 °C, the optical strain response decreased by 77%. Most of the percentage drop occurred between 35 °C and 80 °C, with relatively constant response for temperatures lower and higher. The primary source of the temperature dependency is the coating sensitivity coefficient which is a function of the modulus of elasticity. Higher strains tended to delay the transition, indicating strain-temperature coupling in the optical sensitivity coefficient.

Date Published: 8 April 2008
PDF: 9 pages
Proc. SPIE 6932, Sensors and Smart Structures Technologies for Civil, Mechanical, and Aerospace Systems 2008, 693222 (8 April 2008);

Published in SPIE Proceedings Vol. 6932:
Sensors and Smart Structures Technologies for Civil, Mechanical, and Aerospace Systems 2008
Masayoshi Tomizuka, Editor(s)