Abstract:

Objectives

To investigate the mechanical properties， fatigue parameters and lifetime of IPS e.max Press material via dynamic fatigue experiments， and to obtain the lifetime under cyclic loading from equations.

Methods

Bar specimens were manufactured with IPS e.max Press material， and inert strength was measured via three-point bending method in silicon oil and analyzed with Weibull statistics. Dynamic fatigue experiments were performed at different stressing rates of 10 MPa/s， 1 MPa/s， 0.1 MPa/s and 0.05 MPa/s in artificial saliva environment to calculate the subcritical crack growth （SCG） parameters n， A and B. Strength-fracture probability-lifetime （SPT） predictions of the material were derived for a period of 10 years. Based on the SCG parameters， the theoretical number of cycles to fracture （N_f，0） was predicted and the Wöhler diagram was drawn.

Results

Inert fracture strength， characteristic strength σ₀ and Weibull modulus m were 425.7， 453.8 MPa and 7.4 respectively. The SCG parameters n， A and B were determined as 23.1， 3.4 × 10^-15 and 857.2 respectively. According to the SPT diagram，the characteristic strength of IPS e.max Press was predicted to decrease by 47% after 10 years. A calculated number of cycles to failure was determined as 690 447.

Conclusions

Humidity and loading rate have an obvious influence on fracture strength of the IPS e.max Press specimens.Predictive fracture strength of the material decreases gradually with the lapse of time. Numerical method can serve as a complementary approach to in vitro experiment. However， cyclic fatigue experiment and finite element modeling are needed for a much more accurate simulation.

Key words: Ceramic, Dynamic fatigue, Weibull statistics, Cyclic fatigue