抄録
High-speed holographic microscopy is applied to take three successive photographs of fast propagating cracks at the moment of bifurcation. The cracks are propagated in PMMA plate specimens at a speed about 660m/s. From the photographs, crack opening displacement (COD) is measured along the cracks as a function of distance r from the crack tips. The measurement results show that the CODs are proportional to √<r> before bifurcation. After bifurcation, the CODs of mother cracks are proportional to √<r>, however, those of branch cracks are not always proportional to √<r>. The energy release rate and energy flux toward crack tips are obtained from the COD data, and are found to be continuous across the bifurcation point.
