  Purpose - The purpose of this paper is to describe finite element modelling
for fracture and fatigue behaviour of zirconia toughened alumina
microstructures. Design/methodology/approach - A two-dimensional finite element
model is developed with an actual $Al{_2}O{_3}$ - 10 vol% $ZrO{_2}$
microstructure. A bilinear, time-independent cohesive zone law is implemented
for describing fracture behaviour of grain boundaries. Simulation conditions
are similar to those found at contact between a head and a cup of hip
prosthesis. Residual stresses arisen from the mismatch of thermal coefficient
between grains are determined. Then, effects of a micro-void and contact stress
magnitude are investigated with models containing residual stresses. For the
purpose of simulating fatigue behaviour, cyclic loadings are applied to the
models. Findings - Results show that crack density is gradually increased with
increasing magnitude of contact stress or number of fatigue cycles. It is also
identified that a micro-void brings about the increase of crack density rate.
Social implications - This paper is the first step for predicting the lifetime
of ceramic implants. The social implications would appear in the next few years
about health issues. Originality/value - This proposed finite element method
allows describing fracture and fatigue behaviours of alumina-zirconia
microstructures for hip prosthesis, provided that a microstructure image is
available.

Medical Physics