Electrical monitoring of crack propagation during quasi-static loading and ballistic impact of alumina plates

An electrical methodology has been developed to monitor crack advance during ballistic impact. Velocities of radial cracks can be measured and information about development of the crack pattern can be obtained. This is done via a grid of thin gold tracks, printed onto the front or back surfaces of the sample. These elements were incorporated into an electrical circuit and high speed data acquisition was carried out during impact. The fracture behaviour of two grades of alumina has been examined. Hard spherical projectiles were used, with a range of impact velocities. An increase in radial crack velocity was detected with increasing impact velocity, within this range. Differences in crack velocities were also noted between the two types of alumina. Crack speed values are in good agreement with data reported previously for similar systems, obtained using high speed photography. The methodology proposed here looks to be reliable, convenient and economically attractive.