Abstract
A rapidly bifurcating crack in PMMA is photographed by high-speed holographic microscopy at about 5 s after bifurcation. Crack speed is 612m/s. Crack opening displacement, COD, is measured along two branch cracks as well as the mother crack. The COD of the mother crack is approximately proportional to the square root of the distance r from the crack tip. The COD of one of the two branch cracks is roughly proportional to √r, but not about the other branch crack. This is thought to be caused by the three-dimensional structure of the branch crack. Stress intensity factors and energy release rates of each of the two branch cracks are obtained from the CODs of the two branch cracks. Stress intensity factor and energy release rate of the whole bifurcated crack are obtained from the COD of the mother crack. The energy release rate of one of the two branch crack is about half of the entire energy release rate of the bifurcated crack.
