Crack tip switching zone in ferroelectric ferroelastic materials

A novel liquid crystal display was utilized to monitor electric surface potentials in front of a crack tip in a ferroelectric ferroelastic material, lead zirconate titanate (PZT). The electric potential could be converted to yield the radial stress and strain distribution in front of the crack which afforded determination of the domain switching zone as well as the hardening coefficient. This zone shape as well as its evolution during crack growth was monitored. In contrast to transformation toughening materials, the crack tip process zone size was demonstrated to first increase and then decrease with increasing crack length.