Holographic recording of caustic light beams of fast propagating cracks.

Abstract

A pulsed holographic technique is described which records and reconstructs caustic light beams of fast propagating cracks in polymethylmethacrylate (PMMA). A caustic light beam of a fast propagating crack is recorded as a hologram at an instant during its propagation with a pulsed holographic recording system. Illuminated with reconstruction light, the hologram reconstructs the caustic light beam, and diameters of caustics at various distances from the specimen are measured from the reconstructed caustic light beam. Values of dynamic stress intensity factor K1 and initial curve radii are calculated from the caustic diameters. The initial curve radius at which calculated K1 values deviate from the real K1 value gives the scale of the three-dimensional stress field which appears around the fast propagating crack tip. In the case of cracks propagating through specimens 3mm in thickness, the 3-D stress field spreads as far as the distance of half of the specimen's thickness from the tip.