A Pulsed Holographic Optical System for The Accurate COD Measurement of Fast Propagating Cracks

A holographic optical system developed which is used to photograph fast propagating crack tips in PMMA. The cracks are in the opening mode and propagate at a speed of several hundred m/s. At a point during crack propagation in a PMMA plate specimen, illumination light beams, emitted from a pulsed ruby laser, enter into the specimen through its side boundaries. Total reflection occurs at the specimen's surfaces as the light beams travel throughout the inside. When the beams reach the opened crack light is emitted, and is recorded on a holographic plate as the object light. The optical system is applicable only to cracks whose surfaces are "mirror" like and which propagates through transparent specimens. The optical system, however, makes it possible to measure in every photograph the crack opening displacement as a function of distance form the tip, even near the tip where craze appears.