Reflection Type High-speed Holographic Microscopy to Photograph Bifurcation of Fast Propagating Cracks.

Abstract

Reflection type high-speed holographic microscopy is applied to photograph the bifurcation of fast propagating cracks in PMMA. The cracks are of the opening mode. Spatial resolution is more than 180 lines/mm, frame interval is 5μs and the number of frames is three. A crack at bifurcation is recorded as three successive holograms on one photographic plate by means of angle-multiplexing holography. Lens assisted reconstruction method is used to reconstruct separately the three crack images from the holograms. The reconstructed crack images are magnified and photographed through a conventional microscope. The photographs show that, at bifurcation, several crack tips are running simultaneously in a small region about 1 mm in diameter. And also shown is dynamic three dimensional behavior of crack front edges or microcracks at bifurcation.