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On the Scaling of Fracture Toughness with Relative Density in Sintered Alumina by Sandeep Das Gupta

By: Contributor(s): Material type: TextTextPublication details: IIT Jodhpur Department of Metallurgical & Materials Engineering 2020Description: xvi,39p. HBSubject(s): DDC classification:
  • 620.112 G977O
Summary: Among boron-rich solids boron carbide come third in hardness when compared to diamondlike structures and has been the subject of research in recent decades. They possess superior industrial manufacturability, low density, and high hardness as compared to other ceramics such as alumina and silicon carbide. Despite of these properties, an ordinary pernicious attribute called “pressure-induced softening", limits their performance in high-velocity projectile applications. This thesis highlights this characteristics of amorphized states of boron carbide, an ordinary icosahedral boron-rich ceramic, intending to understand the mechanistic layout of this softening. Shock studies of B4C have suggested phase transformation at high pressures, but to date, no convincing proof has been affirmative to prove the existence of new high-pressure phases. To help uncover the failure mechanism, we used methods based on ab-intio calculations to carry out a simulation on B11C-CBCp polytype, results of which is later compared to B12-CCC stoichiometric boron carbide. For structural characterization, we have calculated non-resonant Raman spectra, which has been evaluated using first-principles calculations considering the macroscopic view of Raman Spectra. Our simulation suggests that softening is the consequence of structural changes associated with the three-atom chain’s bending. Carefull analysis of the calculated Raman spectra suggested shifts in the peak position and intensity with the variation of pressure. Calculations of the elastic constants (Ci jkl) are also being carried out following a homogeneous deformation method, to understand its mechanical behaviour under pressure variation.
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Thesis Thesis S. R. Ranganathan Learning Hub Course Reserve Reference 620.112 G977O (Browse shelf(Opens below)) Not For Loan TM00201
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Among boron-rich solids boron carbide come third in hardness when compared to diamondlike structures and has been the subject of research in recent decades. They possess superior industrial manufacturability, low density, and high hardness as compared to other ceramics such as alumina and silicon carbide. Despite of these properties, an ordinary pernicious attribute called “pressure-induced softening", limits their performance in high-velocity projectile applications. This thesis highlights this characteristics of amorphized states of boron carbide, an ordinary icosahedral boron-rich ceramic, intending to understand the mechanistic layout of this softening. Shock studies of B4C have suggested phase transformation at high pressures, but to date, no convincing proof has been affirmative to prove the existence of new high-pressure phases. To help uncover the failure mechanism, we used methods based on ab-intio calculations to carry out a simulation on B11C-CBCp polytype, results of which is later compared to B12-CCC stoichiometric boron carbide. For structural characterization, we have calculated non-resonant Raman spectra, which has been evaluated using first-principles calculations considering the macroscopic view of Raman Spectra. Our simulation suggests that softening is the consequence of structural changes associated with the three-atom chain’s bending. Carefull analysis of the calculated Raman spectra suggested shifts in the peak position and intensity with the variation of pressure. Calculations of the elastic constants (Ci jkl) are also being carried out following a homogeneous deformation method, to understand its mechanical behaviour under pressure variation.

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