Relative displacement measurements for two-body problems

Abstract

While high-sensitivity moire interferometry is very effective for displacement measurements in continuous bodies, special difficulties arise with two-body problems. Fringes may become discontinuous at the boundary between the bodies and as a result the relative displacements cannot be extracted from the fringe patterns. In this work, flexible bridges are used between the bodies to provide a continuous path for fringe counting. The bridges are made of relatively low modulus material and have a low stiffness geometry, such that they deform under minimal load. The experimental methods used for obtaining relative displacement measurements in two-body problems are described for the two cases; dovetail joint in turbo-machinery, and thick adherend lap joint.