Caustics in plane strain—evaluation of COD and the core region

The method of reflected caustics, which is believed up-to-now to apply only for plane-stress problems, was extended in this paper to elastic fields under conditions of plane-strain, containing any type of singularity due either to the mode of loading, or to the geometry of the stress field. The optical far-field theory valid in such types of fields was developed and experimental criteria were given for the first time, for deciding under what conditions the elastic field around a crack or any discontinuity is in a pure state of plane-stress or in a plane-strain, or in a mixed mode (triaxial) of deformation. Examples with transverse edge cracks of varying length in plates under uniaxial mode of loading corroborate the results of the theory.Finally, a technique was introduced for the accurate evaluation of the crack-opening displacement at the tip of the crack, as well as of the area covered by the core region for specimens under conditions of plane strain.