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

摘要

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 K-I and K-II 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.