Abstract
A fast propagating crack in a brittle material often bifurcates into two cracks when the propagation speed is high enough, about 650m/s for example. In the present study, two optical system of pulsed holographic microscopy are applied to take the photographs of rapidly bifurcating cracks in PMMA plate specimens. The photographs are simultaneously taken on both surfaces of specimen. The photographs show that some rapidly bifurcating cracks have apparently different shapes on the both specimen surfaces. Even in the case that the crack shapes are almost the same on the both specimen surfaces, the crack shapes are different near the bifurcation point. Crack opening displacements of branch cracks are measured from the photographs. The measurement result show that branch cracks have not always the same CODs on both specimen surfaces, even though they are thought to be through cracks. These facts indicate that the bifurcation of fast propagating cracks is not two-dimensional phenomenon but three-dimensional one.
