High speed fracture in brittle materials: Supersonic crack propagation

Microcircuit resistance grids were deposited on the surface of glass and glass-ceramic single edge notched beam (SENB) specimens. The individual strips were as small as ~ 10 μm in width. The specimens were broken in bending and the signal from the grids was captured using a waveform recorder. It was observed that the crack began to propagate with a nonzero initial velocity provided the initial notch was blunt. With continued crack propagation, the crack velocity decreased. In specimens with sharp notches, the crack began propagating with a near zero velocity and the velocity increased with increasing crack length. In some glass specimens with blunt notches, the initial crack velocity was found to be considerably greater than the sound velocity thereby showing that supersonic crack propagation can occur.