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.