Ключевые слова: керамика, скалывание кромки, краевая вязкость разру шения, индентирование.Introduction. Ceramics are widely used in industry, medicine, and everyday life. Being brittle materials, they can undergo catastrophic failure in operation, e.g., even first efforts to manufacture ceramic gas-turbine blades have revealed this critical tendency [1]. An increased sensitivity to stress concentrations and low resistance of the edges to flaking, which can account for uncontrolled failure, also cause certain concern.With an improvement in the characteristics of ceramics and a continuous growth in production volumes of ceramic items, fracture resistance of these materials attracts the particular attention

Results obtained for a new material, namely, zirconia crystals stabilized by Y203 and CeO2 and containing a technological addition of neodymium oxide, tested at room temperature are described. Special features of the surfaces of the crystal blocks grown and the distribution of the additions introduced into the charge over their height are investigated. The dependences of the amounts of the stabilizing components and the fracture properties of the investigated material on its strength are determined. Certification results for the mechanical characteristics of the material are presented (mean four-point bending strength 1250 MPa, crack resistance in bending of a notched bar 11.43 MPa-m ~n at an elasticity modulus of 366 GPa for the crystallographic direction <100>). The crystals are investigated in the crystallographic plane { 100} by applying Vickers and Knoop indenters, and their hardness at different loads (beginning with 0.1 N) is determined. It is established that zones of phase transformations are formed near the indentations in addition to radial and lateral cracks. Problems of change in the specific features of the mechanical behavior of the crystals with change in the valence of cerium (most experiments were conducted for Ce203 ), with the heat treatment, etc. are considered. The results are analyzed using data of fractographic investigations and the new data obtained in tests of similar crystals partially stabilized by yt~ium and terbium oxides.It was established in the early 1980s [1] that crystals of partially stabilized zirconia possess relatively high mechanical parameters and other advantages that make them applicable for various purposes at temperatures up to 1600°C. However, these materials are not used in industry, although a technology for producing coarse crystals with high strength and crack resistance has been devised [2]. This can be explained by the fact that potential users have insufficient information on these crystals and that it is sometimes impossible to prepare materials with uniform structure and properties in an amount sufficient for practical purposes. In growing the crystals it is difficult to eliminate the appearance of cracklike defects, and in long-term storage they sometimes break spontaneously due to internal stresses. This shows that attention to investigating zirconia crystals for structural applications is insufficient. This especially concerns the interdependence of the technological regimes for preparing them, the phase composition, the structure, the laws governing their mechanical behavior, etc. On the whole, data that would make it possible to improve the production technology for these crystals and realize their potentialities are very scarce. As a continuation of previous work in this field [3], we present results of an investigation of crystals whose charge, in addition to zirconia (ZrO 2 ), contained Y203 and CeO 2 plus neodymium oxide 3 (Nd203 ) as a technological addition. These crystals were denoted Y-Ce-PSZ-K.Materials and methods. The experiments were conduct...

Fracture resistance of technical quartz and normal window glasses was investigated in testing polished rectangular parallelepipeds by edge flaking their long edges with Rockwell and Vickers indenters (EF method) and by scratching the specimen surface with a Rockwell indenter followed by flaking its edge (S+EF method). It was established that the fracture of those glass specimens in their edge flaking with a Rockwell indenter was started with the formation of a Hertzian ring crack and their corresponding chip scars had the form of Hertzian "quasi-cones." Fractographic data were used in analysis of test results.Introduction. One can hardly find any field of human activities where silicate glasses are not in use. Despite brittleness and inconsiderable deformability inherent in such materials, they turn out indispensable for many technical and other fields of application. This gives impetus to studies on the mechanical behavior of those materials and, in particular on their ability to resist fracture. Their fracture toughness was evaluated by different methods, including fracture of the specimen surface with sharp and blunt indenters [1]. As a result, a great body of experimental data was accumulated, which contributed to the enhancement of glass capabilities and to the gain in reliability of glass items in operation.As was mentioned earlier [2], glass is a material very complicated for comprehension. Its fracture behavior is still not clearly understood, and the choice of an optimum method for determining its fracture resistance is unresolved as yet. Therefore, the investigation of glass fracture in flaking the edges of rectangular parallelepipeds with standard indenters was carried out, which turned out to be an effective approach to studying different ceramics and allowed new information on their behavior under loading to be obtained [3].Materials and Methods. This investigation was targeted for getting the general notion of glass behavior in its edge flaking. For this purpose the two types of glass varying in their compositions were taken: "normal" (silica contents are less than 70-75%) and "anomalous", i.e., containing up to 99.9% silica [4]. The mechanical behavior of the former is believed to be similar to the behavior of other brittle materials, while glass of the second type exhibits certain differences associated with its structure. Therefore, both technical quartz glass, containing about 90-95% silica doped with Na 2 O and Al 2 O 3 , and normal window glass with about 72% silica were studied. Experiments were also performed on industrial hardened sheet glass. Those glasses were manufactured commercially, thus, their correct compositions, being "know-how" of enterprises, are unknown.The tests made use of specimens in the form of polished rectangular beams of standard sizes (3 4 × -mm

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