Study of deformation and fracture of ZrO2+3%Y2O3 ceramics by wedge splitting of a chevron-notched specimen

摘要

A method for determination of crack resistance of a material based on the test data of small-sized chevron-notched double cantilever beam specimens by wedge splitting is proposed. Specific fracture energy for small-sized chevron-notched double cantilever beam specimens is calculated using analytical expressions derived on the basis of the beam theory with a correction for elastic deformation of the ligament of a double cantilever beam specimen. A proper transition is performed from the pressing force on a wedge to the deflection force of cantilevers with account for the deformation of the ligament of a chevron-notched double cantilever beam specimen and the friction coefficient between the wedge and the specimen. An analytical formula that allows determination of friction coefficient during an experiment is worked out. New data have been obtained when testing ceramics based on ZrO2 + 3mol%Y2O3. The ceramics' loading diagrams reveal an extensive inelastic stage of deformation that precedes specimen fracture. It is shown to be associated with the alpha - beta polymorphic transformation in the chevron notch zone. The displacement contributed from inelastic deformation is >= 21% at the moment of specimen fracture for tested specimens. The obtained evidence indicates the dislocation-free mechanism of inelastic behavior of ZrO2 + 3%Y2O3 ceramics. In chevron-notched specimens, the alpha - beta transformation is performed under the action of stress concentration without a crack in the chevron notch zone. The paper points out the necessity to use the value of "nonelastic" displacement of chevron notch sides as an additional characteristic of crack resistance of a material when studying and modelling deformation and fracture of small-sized specimens.