Strain Separation on a Nonplanar Object Using a Luminescent Photoelastic Coating

This paper presents the theoretical modeling and corresponding experimental results of the oblique incidence response of a luminescent photoelastic coating (LPC) applied to a cylinder under load. LPC is a measurement technique to acquire full-field maximum shear strain and its principal strain direction. The technique uses an absorption dye and a luminescent dye within a photoelastic coating, and the coating is applied on the surface of the specimen using conventional aerosol techniques. On 3D objects, the response of the emission field is dependent on the excitation orientation due to the surface inclination of the structural component and the out-of-plane strain component within the coating. Full-field strain separated results have been previously demonstrated on a 2D specimen. The extension of the strain separation technique to a 3D specimen—a cylinder in bending—is the focus of this investigation. Two different responses were obtained from normal and oblique excitation. As a result, the principal strain was separated over ±56° of circumference of the cylinder with RMS error relative to the theoretical result of 87 μɛ for maximum principal strain and 78 μɛ for minimum.