A preliminary report on 3d effects on caustics

A modification to the standard caustic equations was made to include the effect of a mixed plane stress-plane strain state across the specimen thickness near the crack tip. By assuming the thickness of the plane stress surface layer to be of the size of the plastic zone along the crack axis, a K ~ D 5 6 dependence for the stress intensity factor K vs the caustic diameter D was obtained. This dependence contrasts the classical K ~ D 5 2 relationship based on plane stress considerations, but it is in good agreement with our experimental data. © 1990