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Silicon Nitride Ceramics have attracted particular interest for high performance structural applications due to their excellent mechanical properties at elevated temperature and their good resistant to wear, corrosion and thermal shock. However, understanding of their fracture behaviour and mechanical characteristics is essential in order to design with these materials and to further improve their ability to respond to stresses. Failure in ceramics rarely occurs from flaws that are only subjected to pure tensile loading. It is necessary therefore, to study the effect of mixed mode stressing. In the present work 2 different types of precracks were used for measuring the mixed mode fracture behaviour of a hot pressed Si(3)N(4) material. Knoop indentation surface flaws, placed on the tensile face of flexural bars, at various angles to the longitudinal axis of the bar and single edge, through thickness precracks. The specimens with both types of precracks were tested under 4 point bending at room temperature. Knoop indented samples were polished or annealed before testing in order to remove the residual stress field produced by the indentation. The precrack dimensions were measured on the fracture surface using scanning electron microscopy. For both types of precracks the geometrical functions for the calculation of the stress intensity factors K(I) and K(II) were determined numerically using finite element analysis and experimentally using compliance calibration curves. The effect of loading rate in the mode mixity was also evaluated within the frame of the present work.

Additional information

Authors: KOSTOPOULOS V, JRC Petten (NL);PETEVES S D, JRC Petten (NL);STEEN M, JRC Petten (NL)
Bibliographic Reference: Paper presented: 6th International Symposium on Fracture Mechanics of Ceramics, Karlsruhe (DE), July 18-20, 1995
Availability: Available from (1) as Paper EN 39568 ORA
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