Static fatigue crack growth tests of several silicon nitride ceramics with various microstructures were carried out by a constant moment method. Correlations between the static fatigue crack growth behavior and microstructures, such as the size and distribution of grains and the fraction of rod-like grains, were investigated.
The experimental results showed the following tendency. The larger average grain size, the higher fatigue crack growth resistance. The more uniform distribution of grain size, the higher gradient of fatigue crack growth resistance curve for crack length ranging to about 5mm. And the fraction of rod-like grains was not so correlative to crack growth resistance.
Furthermore, a grain bridging model which may explain the influence of microstructure on fatigue crack growth behavior was proposed. In this model, the bridging force reducing effective stress intensity is described as a function of crack opening displacement and size and interval of bridging grains. The simulation showed that the more uniform distribution of grain size, the higher fatigue crack growth resistance. Also, the larger average grain size and the more fraction of rod-like grains, the higher fatigue crack growth resistance. These results were conformed qualitatively by the experimental results.
