Development of the evaluation Method for High Temperature Strength of Silicon Nitride

点击翻译按钮获取中文摘要

The purpose of this study was to establish appropriate and precise methods to evaluate the strength and the toughness of silicon nitride ceramics at room and high temperatures. The study was performed in two years from 1986 to 1987, in the Faculty of Science and Engineering, Ritsumeikan University.In 1986, testing equipments to evaluate the strength under monotonic tensile and three points bending load conditions were designed and fablicated. An attension was paid to obtain a precise allignment of the load transmission path in each case. Systematic experiments were conducted at room and high temperatures up to 1300 C on a number of silicon nitride ceramic specimens y using the developed loading equipments. Results obtained through the tests were analized statistically, and the following two points were mainly discussed; (1)temperature dependence of Weibull parameters, and (2) statistical propertirs of the strength under monotonic tensile and three points bending load conditions.In 1987, the experiments were carried out continuing to the previous year, and the results obtained in two years were summarized and discussed to establish the methods of how to evaluate the strength and the toughness of silicon nitride ceramics at room and high temperatures. The obtained results in addition to the above are as follows: (3) The strengthes under two types of load conditions can be well correlated when the effective volume concept is taken into account, (4) the fracture toughness at high temperature takes the same value as that at room temperature when a crack length increment due to slow crack growth is considered at high temperature, and (5) the liner fracture mechanics concept seems to be applicable to the fracture criterion even for small size inherent defects existing in silicon nitride, when the size of segregated Fe area around the fraxture origin is considered as the defect size.