On the fracture toughness of ferroelastic materials

The toughness enhancement due to domain switching near a steadily growing crack in a ferroelastic material is analyzed. The constitutive response of the material is taken to be characteristic of a polycrystalline sample assembled from randomly oriented tetragonal single crystal grains. The constitutive law accounts for the strain saturation, asymmetry in tension versus compression, Bauschinger e5ects, reverse switching, and strain reorientation that can occur in these materials due to the non-proportional loading that arises near a propagating crack. Crack growth is assumed to proceed at a critical level of the crack tip energy release rate. Detailed 7nite element calculations are carried out to determine the stress and strain 7elds near the growing tip, and the ratio of the far 7eld applied energy release rate to the crack tip energy release rate. The results of the 7nite element calculations are then compared to analytical models that assume the linear isotropic K-7eld solution holds for either the near tip stress or strain 7eld. Ultimately, the model is able to account for the experimentally observed toughness enhancement in ferroelastic ceramics. ? 2003 Elsevier Science Ltd. All rights reserved.