Application of the Caustic Method to the Stress-Freezing Technique

The caustic method is a very powerful technique for measuring the value of the stress-intensity factor. The caustic pattern, however, cannot be obtained in frozen-stress models in immersion fluid by the conventional caustic technique. The cause of this phenomenon is studied by using the individual values of the optical constants. It is shown that the optical constants of the frozen-stress model, which determine the shape of the caustic pattern, have very different aspects from those at room temperature. The caustic pattern in the frozen-stress model is theoretically calculated by using those optical constants, and it is also confirmed experimentally. Some practical techniques for applying the caustic method to such a frozen-stress model are shown.