ABSTRACT
All experimental studies for propagating cracks based on caustics assumed the existence of a static solution for the stress field at the vicinity of the crack tip valid also for the respective dynamic case, as well as of the approximate invariability of the mechanical and optical properties of the material used in the tests. Since it was established that the mechanical and optical properties of the materials used in the tests were changed considerably with the velocity of application of the external loading or the propagation of the crack, a basic improvement in the method was the introduction not only of some standard dynamic values for the moduli and optical constants, but, more accurately, their exact values found experimentally for the special dynamic conditions holding each particular test (6,7).
