Luminescent Strain-Sensitive Coatings

Abstract

The use of novel luminescent coatings and digital imaging to map the in-plane strain field on structural components under static load is described. The technology, referred to as strain-sensitive skin by Visteon Corporation, employs two different approaches: the first uses a luminescent brittle coating (LBC), and the second uses a luminescent photoelastic coating (LPC). A coating consisting of a binder, generally polymeric in nature, and luminescent dye is applied to the surface of a test part by conventional aerosol techniques. The LBC is excited with incoherent ultraviolet or blue illumination, and the corresponding emission is imaged via a digital camera. The relative change in emission intensity is related to the in-plane volumetric strain response for moderate strain levels. The I,PC is excited by the same sources after being conditioned with polarizing and retarding optics to create circularly polarized light. The relative change in emission ellipticity, both in magnitude and phase as measured after passing through an analyzing polarizer, are related to the in-plane shear strain and its corresponding principal direction. These techniques offer quantitative, repeatable, and high spatial resolution measurements. Additionally, they are applicable to complex three-dimensional geometries, cost efficient to implement, and suitable to be integrated in the product design cycle in conjunction with finite element analysis tools. Results from a test conducted on an automobile suspension control arm under static loads are presented and discussed.