Makoto Nishi

Strength Reliability Evaluation of Ceramics (3rd Report). Fatigue Characteristics of Ceramics with Multiple Cracks.:Fatigue Characteristics of Ceramics with Multiple Cracks

This paper describes the effects of the number of cracks and crack spacing on fatigue crack growth characteristics of PSZ ceramics, which are required in the strength reliability evaluation of ceramics component. Fatigue fracture toughness testing shows that the life of PSZ ceramics with multiple pre-cracks increases with increasing the number of cracks and the life of PSZ ceramics is changed by the crack spacing. Also as the crack spacing is larger, the growth of crack which does not lead to fracture is more significant. It is confirmed that a linear relationship between the fatigue crack growth rate da/dN and the stress intensity factor range Δ K is exhibited on a logarithmic scale for the PSZ ceramics with multiple cracks as in the case of a single crack. On the other hand, crack growth rate parameters m and -logC, for multiple cracks depend on the number of cracks and the crack spacing. Further, the effect of the number of cracks and crack spacing on statistical characteristics of crack growth rate parameters m and -logC, and fracture toughness value Kfc is discussed by Weibull distribution function.

Strength Reliability Evaluation of Ceramics (I)

The main objective of this study is to evaluate the strength reliability of ceramics for mechanical com-ponent applications based on fracture mechanics. This paper discribes an algorithm for the strength reliability evaluation of ceramics and prediction of the life of PSZ (Partially Stabirized Zirconia) components according to the proposed algorithm. Extensive crack growth is observed prior to the final fracture during cyclic three-point bending and it is confirmed that PSZ exhibits a linear relationship on logarithmic scale between the fatigue crack growth rate da/dN and the stress intensity factor range ΔK. Statistical charac-teristics of the crack growth rate parameters C, m and the fatigue fracture toughness value Kfc are also found to fit well with Weibull distribution. It was found that the estimated life of PSZ components decreases with increasing stress range and initial crack length and with decreasing fracture probability.