Fatigue behaviour of mullite studied by the indentation flexure method

A systematic study has been performed of the use of the Indentation Flexure Fatigue (IFF) method to study crack growth in mullite at room temperature and high temperature (1300°C). The results obtained for a mullite have been compared with previous data generated on the same material, but using the more direct compact tension method. The material produces transgranular crack growth and consequently does not show R-curve behaviour, which considerably simplifies the comparison of the data generated by both methods. The IFF method can significantly overestimate the crack tip stress intensity factor because of the way in which the residual stress intensity produced by the indentation is estimated. The experimental details that influence the test results were investigated.