Infrared interferometry for rough surface measurements: application to failure characterization and flaw detection

Jaydeep K. Sinha Hareesh V. Tippur Auburn University Department of Mechanical Engineering 202 Ross Hall Auburn, Alabama 36849-5341 E-mail: [email protected] Abstract. A real-time, full-field, noncontacting infrared Twyman-Green interferometer for performing deformation measurements has been developed. The choice of the wavelength offers the advantage of using the interferometer with structural components with little or no surface preparation. The limitation on the surface roughness/texture commonly encountered when using visible light is circumvented through a favorable roughness-to-wavelength ratio. Planar objects with a surface roughness up to sa'1 mm (or surfaces prepared using fixed abrasives with mean grit sizes up to 250 mm) have been examined. Capability of the interferometer for quantifying deformations when dealing with rough surface measurements is demonstrated. Examples of defect detection as well as elastoplastic crack-tip-field mapping are provided. © 1997 Society of PhotoOptical Instrumentation Engineers. [S0091-3286(97)03908-1]