Pages 149-150
Pulsed holographic microscopy was applied to take photographs of rapidly bifurcating cracks on the both surfaces of PMMA plate specimens. The cracks were of the opening mode and propagated at a speed more than 600m/s. From the photographs, crack opening displacement (COD) of crack branches were measured along themselves. The results show that, two crack branches have different COD. This means that the bifurcation of crack was asymmetric. And each of the crack branches has the same COD on both side near the crack tip, that imply crack branches have two dimensional crack fronts. Even in this case, however, the CODs of one of the two branches on the both side were not same in the vicinity of bifurcation point. This fact indicates that crack bifurcation was three dimensional and bifurcated cracks retain three dimensional structure at bifurcation point after bifurcation.
