ANALYSIS OF FRACTURE STRENGTH OF SI3N4 USING WEIBULL MULTIMODAL DISTRIBUTION

A maximum likelihood method for estimating multimodal Weibull parameters from the data of strength and fracture origin for different types of specimens was studied. Three kinds of 4-point bending test and one kind of tensile test were carried out for Si3N4 ceramics and the fracture origin of each specimen was investigated. A set of multimodal Weibull parameters of the Si3N4 ceramics was estimated by the maximum likelihood method. In this method parameters can be determined so as to maximize the likelihood function which is the product of the individual likelihood functions of each type of specimen. The strength distributions calculated from those parameters were in good agreement with the experimental results. It is indicated that the probability of failure can be predicted by collecting the size effects for every kind of fracture origin. The probability of failure after eliminating a critical fracture origin was estimated for each type of specimen.