Studying Strain Localization in Brittle Materials during the Brazilian Test
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STUDYING STRAIN LOCALIZATION IN BRITTLE MATERIALS DURING THE BRAZILIAN TEST S. N. Kulkov, I. Yu. Smolin, V. A. Mikushina, T. Yu. Sablina, I. N. Sevostyanova, and V. V. Gorbatenko
UDC 539.422.3 + 539.375
Sintered yttrium-stabilized zirconia is numerically and experimentally investigated during the Brazilian test. The strain and fracture of homogeneous and inhomogeneous cylindrical specimens under diametral compression are numerically simulated within the framework of mechanics of continuum mechanics. The specimen inhomogeneity is phenomenologically described by random assignment of the strength characteristics in computational cells. Unlike a homogeneous specimen, the strain localization and the formation of numerous fragments at fracture are observed in an inhomogeneous specimen. It is established that the zirconia strain is macroscopically localized. It is shown that sizes of coherently diffracting domains of the tetragonal phase and microdistortion of the lattice after sintering change compared to the initial state and differ for different fragments of a fractured specimen. The internal microstresses on different fragment surfaces change in the range 245–320 MPa depending on the arising strain inhomogeneity. The strain localization correlates with the inhomogeneity of the microstresses arising in the material undergoing deformation. The quantitative and qualitative agreement of the calculated results with the experimental data is observed. Keywords: digital images correlation, diametral compression, zirconia, macroscopic strain localization, x-ray phase analysis, numerical simulation.
INTRODUCTION Nowadays, many works (for example, see [1–3]) are devoted to a study of plastic flow localization under active loading and of macroscopic strain localization patterns in metals, alloys, and brittle materials. Experimental data have been obtained for more than ten substances [1, 4]; however, the problems of universal classification and establishing patterns of strain macrolocalization remain unsolved. The problem of strain localization in plastic materials has been studied in detail by both experimental [1, 4] and numerical methods [5]. These processes have been studied in different metals and alloys under quasistatic and dynamic loading. Analogous investigations of brittle materials, such as rocks and ceramics, are rare. The method of double-exposure speckle photography was used in [6] to record the spatiotemporal distributions of local components of the distortion tensor under active deformation by compression of a brittle material – nanocrystalline ceramics based on partially stabilized zirconia ZrO2(Y). Strain localization patterns were recorded, and the special features of the macroscopic strain inhomogeneity were studied for elastic behavior of the material. It was shown that during compression, the deformation in the specimen was distributed inhomogeneously. Moreover, in spite of the fact that unlike metals, ceramics are not subjected to a significant plastic flow, the process of macroscopic strain
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