The significance of non-elastic deformation in the fracture of heterogeneous ceramic materials

Abstract

The classification of refractory ceramic materials is considered according to the magnitude of their brittleness i.e. the ratio of the specific elastic energy stored in the specimen at the moment of fracture, to the total amount of deformation energy of the specimen prior to its fracture. The materials are classified as brittle ( x = I) and relatively brittle ( x < I). Deformation peculiarities of these materials are analysed and distinctive features of their mechanical behavior are pointed out. It is shown that macrononelasticity of relatively brittle materials is caused by microfractures. It is proved that these features must be taken into consideration when developing design criteria for these materials. The known thermal shock resistance criteria are considered and a new criterion is proposed in which brittleness is introduced as a parameter. The validity of the approach is confirmed by results of tests of single-phase and composite ceramic materials based on aluminium oxide, yttrium oxide, zirconium dioxide, and titanium carbide.