An optical method for measuring mixed-mode stress intensity factors for an arbitrarily oriented crack in cylindrical shells

Abstract

This paper deals with the measurement of mixed-mode stress intensity factors for an arbitrarily oriented crack in cylindrical shells using an optical method based on a new theory of caustics. Completely analytical expressions are derived for caustic curves as well as for initial curves around the tip of an arbitrarily oriented crack in a cylindrical shell under mixed-mode conditions. The effects of mixed-mode condition, radius of curvature, shell thickness and crack angle on the caustic pattern are investigated, respectively. New procedures for the extraction of stress intensity factors KI and KII are presented using the characteristic dimensions of caustic patterns. A series of uniaxial tensile tests are performed on cylindrical shells containing an edge crack which is inclined to the axis of load by a different angle. The mixed-mode stress intensity factors obtained from the method of caustics developed here show a good agreement with previous theories and finite element results under K-dominant assumption.