INFLUENCE OF A DAMAGE ZONE ON HIGH-TEMPERATURE CRACK-GROWTH IN BRITTLE MATERIALS

High temperature crack growth in ceramics often occurs by the nucleati on, growth and coalescence of cavities in a region ahead of the crack tip known as the damage zone. Models describing this type of behaviour generally assume that the presence of cavities does not affect the st ress distribution ahead of the crack tip. In this study, a crack growt h simulation has been developed which incorporates the effects of cavi ty nucleation, growth and coalescence on the stress field ahead of the crack. Cavity growth dominated both by grain boundary diffusion and b y surface diffusion has been modelled. The models follow both the tran sient effects which occur following initial loading and the developmen t of a steady-state regime under conditions of constant applied stress intensity factor K-1. In general, the wedging action due to cavity gr owth reduces the stress field near the crack tip. However, this is lar gely compensated for by an increase in the damage zone size, as a resu lt of load transfer from the crack tip to the end of the damage zone. We have therefore demonstrated that the established analytical models which do not account for stress redistribution give a much better desc ription of steady-state crack growth behaviour than one would expect.