Vibration Analysis Using Moire Interferometry

Abstract

Moire interferometry extends the applications of conventional moire into a realm of higher sensitivity. It has been quite extensively used for in-plane displacement measurement and an excellent review of some of this work is given in ref. 1. In these applications, a high frequency (600 ℓ /mm or 1200ℓ /mm) phase grating is replicated on the specimen via a thin layer of epoxy. This is then interrogated with an optically generated reference grating of twice the frequency to reveal the in-plane isothetics with a sensitivity of 0.83 µ/fringe or 0.417 µ/fringe. The use of an optically generated reference grating facilitates the creation of mismatch fringes, which enables optical differentiation of two patterns to remove any initial pattern or for strain determination.