LIFETIME PREDICTION OF CERAMICS - IMPORTANCE OF THE TEST METHOD

Experimental results of subcritical crack growth obtained by a direct method (the double torsion method) and an indirect method (the dynamic fatigue method) are compared. Dynamic fatigue tests have been simulat ed using the results of the double torsion tests. These simulations ex plain the differences between the results of both kinds of tests and s how that the results obtained with indirect methods cannot be used to calculate the lifetime of the pieces. Finally, the simulation is exten ded to thermal fatigue and the same conclusion is deduced, i.e. the us ual thermal fatigue tests give an average value of the stress exponent n which cannot be used to calculate the lifetime of ceramic parts.