The uncertainty in selecting the length parameter (the maximum diameter) of a caustic image is investigated. A simple calibration method is used to determine the mode-I stress intensity factor KI at a crack tip. The accuracy is further improved by using white light. The effect of the pinhole size on the determination of KI is investigated. The accuracy of the proposed measurement location is demonstrated by comparing experimental results with theory.
Nashwan T. Younis,
Steven E. Egleston,
"Simple calibration method for determining KI using the method of caustics," Optical Engineering 33(9), (1 September 1994). https://doi.org/10.1117/12.177514