Tensile test of sintered Si3N4 and the influence of process defects such as pores on fracture strength

Abstract

Tensile tests were carried out on sintered Si3N4 at room temperature under the ambient condition, and the influence of defects upon the fracture stress was discussed. As the surface of specimens was prepared carefully, fracture of 57 specimens out of 60 originated from the defects such as voids or inclusions which resulted from the sintering process. As a parameter to describe the size of the defect, √area was used which is the square root of the area of a 3-dimensional defect projected to the direction of the maximum principal stress. The results obtained are as follows. (1) √area of defects which caused fracture nearly conforms to the first asymptotic distribution of the largest value and the fracture strength conforms to Weibull distribution. (2) √area is a good parameter to describe the size of the defect from the standpoint of fracture. (3) Defects such as voids and inclusions act exactly as cracks of the same size. (4) The fracture strength can be estimated by using the distribution of √area, the fracture toughness and the mean grain size of Si3N4. © 1989, The Society of Materials Science, Japan. All rights reserved.