<title>Application of high-speed holographic microscopy to study rapid crack propagation</title>

A method of angle-multiplexing holography is applied to develop high-speed holographic microscopy, which can take three successive photographs of a fast propagating crack. The crack speed is at several hundred m/sec. The optical system for holographic recording has three pulsed ruby lasers as light sources. When the crack is propagating in the observation area in a plate specimen, the three ruby lasers oscillate successively. The time interval of the laser oscillation is about 1 microsecond or longer. Varying the angle of incidence of reference beams, the optical system records the crack as three holograms which are superimposed on a holographic plate. Illuminated with a He- Ne laser beam, the three holograms reconstruct for three crack images. Lens assisted holography with spatial filters are utilized to reconstruct the three crack images separately. The spatial resolution of the reconstructed images is more than 120 lines/mm. Along a crack, one can measure the crack opening displacement (COD), that is of the order of ten microns. The dynamic stress intensity factor can be obtained from the COD measurement. The high-speed holographic microscopy is useful to study the rapid fracture phenomena in microseconds.© (1997) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.