Original paper(Vol.48 No.11 pp.1288)
Probabilistic estimation of fracture strength considering loading time in ceramics/metal joints
Takahashi Manabu; Okabe Nagatoshi; Kobayashi Hideo
Abstract:Room and high temperature four point bend tests for Si3N4/SUS304 joints were carried out at various crosshead speeds. Ceramics/metal interface region and brazing zone were analyzed using a vickers hardness tester, SEM and EPMA to discuss the relation between strength of joints and microstructure. Furthermore, the fracture strength and the nature of its scatter were estimated based on the proposed model.
Failure of brazed Si3N4/metal joints occurred at a flaw in ceramics near bonding interface. Therefore, the bending strength of the joints was dominated by a magnitude and distribution of stress concentration induced in ceramic region. The magnitude of stress concentration induced in ceramic region was dependent on deformation resistance of interlayer. This buffer effect of interlayer depended on exposed time of the specimen at test temperature, which inversely corresponds to loading rate.
The dispersion of strengths of the joints was well described according to the Weibull distribution using unified estimation method. The estimation equation was proposed to evaluate the bending strength and its nature of scatter.
Key Words:ceramics/metal joints, silicon nitride, bending strength, stress concentration, deformation resistance, interlayer, heating time, unified estimation method