Characterisation of subcritical crack growth in ceramics using indentation cracks

The introduction of indentation cracks into brittle materials has proved to be a useful tool in characterising subcritical crack growth, notably in efficiently measuring the kinetic growth parameters and in defining whether the material exhibits a fatigue threshold. The accuracy of the subcritical crack growth parameters obtained using indentation mechanics can be excellent, provided the stress intensity factor associated with the indentation cracks is well characterised. Indentation cracks can also be used to measure crack velocity as a function of the applied stress intensity factor by direct observation. In such testing, it is critical that the changes in crack shape as the crack extends are known or accurately predicted. Numerical simulations suggest that the shape changes can be influenced not only by the testing geometry but also the growth kinetics. Finally, it is shown that the fatigue threshold can be determined by allowing median cracks to extend subcritically during indentation.