Slow crack growth of brittle materials with exponential crack velocity under cyclic fatigue loading

The life prediction analysis to determine life as a function of applied stress for brittle materials was made numerically based on an exponential crack velocity formulation. The results were examined using the experimental data on advanced structural ceramics tested under cyclic fatigue loading at ambient and elevated temperatures. The data fit to the obtained relation of ln(time to failure) versus maximum applied stress was very reasonable and compares well with that of the more widely utilized power-law crack velocity. It was also found that life prediction from one loading configuration (static fatigue) to another (cyclic fatigue) in the exponential formulation resulted in a similar degree of accuracy as compared with that in the power-law formulation. The major limitation in the exponential crack-velocity formulation, however, was that inert strength of a material must be known priori to evaluate the important slow-crack-growth parameter n, a significant drawback/burden as compared with the conventional power-law crack-velocity formulation.