An ESPI system for determining in-plane deformations. Three-dimensional analysis of the carrier fringes and a proposal for analysis of transient in-plane deformations

In this work we report results on analysis of in-plane deformation using the symmetrical illumination technique. A single illumination source is doubled by means of a mirror placed perpendicular to the object being tested. Carrier fringes are introduced by displacing the symmetrical sources (one of which is virtual), a technique often used in contouring. We present a three-dimensional theoretical model for the generation of the carrier fringes and analyse the basic concepts of this model. Experimental results obtained using a cw laser are also presented. These results and the ones obtained by applying this technique to out-of-plane and shearing systems are the basis for proposing the application of the concept to analysis of in-plane transient deformation using a double cavity Nd:YAG laser. A convenient set-up for that purpose is described.