Estimation of toughening produced by ferroelectric/ferroelastic domain switching

An estimate is made of the upper limit of the toughening that might be expected by the crack tip stress induced reorientation of domains in ferroelectric ceramics. The calculation is based on obtaining the shielding stress intensity factor produced by the shear transformation of a zone surrounding the crack tip and extending over the crack surfaces. The estimate suggests that the toughening that might be expected is less than 10% even in the most ideal conditions. This case is contrasted with the much greater toughening which is expected from the crack tip stress induced phase transformations which are largely driven by the chemical, or bulk, free energy change of the transformation.