On Direct Measurements of Strain and Rotation in Holographic Interferometry Using the Line of Complete Localization

The interpretation of the fringe pattern formed by a double-exposed hologram of a deformed object leads first to the displacement of a point of the object surface. Further, if one desires to know the strains and the rotations at this point without numerical differentiation, the concept of the line of complete localization may be used. Associated to each point of the surface there is a locus in space where the light waves reflected by the vicinity of this point have all the same phase shift. Points of this curve may be determined by a criterion concerning the direction of the fringes and by use of a special device based upon it. Linear equations yield then directly and in general cases the sought strains and rotations. Some experimental results are given which attempt to show the applicability of this method. Further developments should permit the investigation of the constitutive equation of any non-transparent body.