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Erosion Response of Highly Anisotropic Silicon Nitride (2005)

Zhang, Yu ; Cheng, Yi-Bing ; Lathabai, Srinivasarao ; [et al.]

Oxford, UK : Blackwell Science Inc

Journal of the American Ceramic Society 88 (2005), S. 0

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ISSN: 1551-2916

Source: Blackwell Publishing Journal Backfiles 1879-2005

Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics

Notes: The erosion rates and impact damage of two sintered Si3N4 materials with identical compositions but different microstructures were determined using a gas-blast-type erosion rig. The erodent particles used were SiC grits and the impact angles investigated were 30° and 90°. It was found that the erosion behavior of the two materials could not be related to their mechanical properties, such as hardness and fracture toughness as predicted by the theoretical erosion models. In fact, a close relationship was identified between their microstructure and the erosion mechanism. Microstructures containing evenly dispersed and uniaxially oriented reinforcing whiskers promoted grain-pullout, while the randomly oriented elongated grains hindered it.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1111/j.1551-2916.2004.00014.x

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Fracture mechanics model for subthreshold indentation flaws (1991)

Lathabai, Srinivasarao ; Rödel, J. ; Dabbs, T. ; [et al.]

Springer

Journal of materials science 26 (1991), S. 2157-2168

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ISSN: 1573-4803

Source: Springer Online Journal Archives 1860-2000

Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics

Notes: Abstract A fracture mechanics model for subthreshold indentation flaws is. described. The model describes the initiation and extension of a microcrack from a discrete deformation-induced shear “fault” (shear crack) within the contact zone. A stress-intensity factor analysis for the microcrack extension in residual-contact and applied-stress fields is used in conjunction with appropriate fracture conditions, equilibrium in Part I and non-equilibrium in Part II, to determine critical instability configurations. In Part I, the K-field relations are used in conjunction with the Griffith requirements for crack equilibrium in essentially inert environments to determine: (i) the critical indentation size (or load) for spontaneous radial crack pop-in from a critical shear fault under the action of residual stresses alone; (ii) the inert strengths of surfaces with subthreshold or postthreshold flaws. The theory is fitted to literature data for silicate glasses. These fits are used to “calibrate” dimensionless parameters in the fracture mechanics expressions, for later use in Part II. The universality of the analysis in its facility to predict the main features of crack initiation and propagation in residual and applied fields will be demonstrated. Special emphasis is placed on the capacity to account for the significant increase in strength (and associated scatter) observed on passing from the postthreshold to the subthreshold domain.