Contact holographic interferometers for investigation of elastoplastic problems

A full understanding of the plastic zone formation in a stress concentration region of homogeneous and polycrystalline bodies, has long been a goal of researchers in experimental mechanics. Although some analytical and numerical models have been proposed to predict the formation of plastic zones, no satisfactory correlation has been obtained with experimental results due to the complexity of measurement procedures.^1-3 The purpose of this paper is to develop a simple experimental technique to investigate strains and stresses in a plastic zone in engineering materials by using contact holographic interferometers. Contact holographic interferometer is presented as an assembly of the object, surface section and holographic plate in an immediate vicinity to the object.^4,5 This technique is used to determine in-plane and out-of-plane displacements of the tested object. If a hologram is recorded at a metallized grating surface it restores information peculiar to some optical methods: holographic interferometry, speckle photography, holographic moiré and mirror-optical method. For the interpretation of interference patterns simple analytical equations are obtained. Contact holographic interferometers are used effectively to solve some elasto-plastic deformation measurement problems of isotropic and polycrystalline materials. It is specially designed to permit the accurate measurement of the in-plane component of strain in the immediate vicinity of stress concentrators in plates. Some research results of plane static and signvariable load elasto-plastic problems are considered.