physical and mathematical principle of the exper imental method of caustics in re-entrant corners

in this paper, the experimental method of caustics and its application to stress field and related studies in fracture mechanics is described. theocaris [1,2,3] has used the optical method of caustics to study stress intensity factors and the stress field around crack tips, in cracked transparent plates. many other researchers have also used this method to obtain stress intensity factors for different crack shapes in different materials. but a review of the available literature indicates that this method has not yet been used to study the singularities in plates with notch or re-entrant corners. the stress field at the roots of sharp notches has singularities of order a-l where a. depends on the notch angle. in this study the essential equations and parameters for the application of the method of reflected caustics to v-notched plates were developed . the equations obtained showed that the radius of the initial caustic curve was not a constant and depended on 8. it has also been shown that in many instances the variation of initial curve with respect to 8 is relatively small and can be ignored.