Strength properties of Ceramics depend upon the shapes, sizes and location of initial flaws, and so they have the strength of significant different levels and dispersions owing mainly to the difference of testing modes or the shapes and sizes of specimens even though the material was taken from the same lot. Therefore, an estimating method for ceramic strength, based on a modified Weibull analysis, was studied in this paper for finding the common property parameters as material constants independent of testing methods or shapes and sizes of specimens. Common Weibull modulus m0 was estimated by Weibull analysis for the values of fracture strength normalized by a mean value of that by each testing method, and was applied to analyze the effective volume of specimens in each test. Finally the strength property parameter σ0 was derived from scale parameter. Weibull modulus m0 was treated as a determined value and the confidence of measured values was considered only about σ0. Consequently, by using these two parameters m0 and σ0, the fracture strength of ceramics can be estimated with regard to failure probability Pf, confidence level 1-γ and sample size n as follows.
σf=σ0m0√2nln(1-Pf)-1/Veffχ2(2n, 1-γ)
The estimating method proposed in this paper is very useful for estimating the design allowable stress and determining safety factor in ceramic structural design based on reliability engineering.
