Crack growth in non-homogeneous transformable ceramics. Part II: Crack deflection

Abstract

Crack growth in transformation toughened ceramics is studied using a micromechanics based continuum model which accounts for both dilatant and shear transformation strain components. In the computations, the transformable phase is taken to be distributed non-homogeneously in order to model Zirconia Toughened Aluminas that have not been optimally mixed, or Duplex Ceramics in which large zirconia inclusion are dispersed in an untransformable matrix. The small scale transformation problem is solved using a finite element approach. The influence of the transformation strains around the propagating crack on the stress intensity at the crack tip is computed using the transformation domain integral. The crack is modelled as a missing row of mesh elements and crack growth is simulated by nullifying the stiffness of a crack tip element. In contrast to Part I of this paper [1], this part is concerned with cases where the transformable phase is not distributed symmetrically with respect to the x 1-axis, which causes the crack to deflect from its original crack path due to a local shear stress intensity factor at the crack tip. A computational method is developed which is capable of simulating this, assuming that the deflections from the original crack path are small. A parametric study is carried out of the effect of crack deflection and crack meandering on the overall crack growth resistance.