Doctoral Dissertations

Date of Award

12-2014

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Materials Science and Engineering

Major Professor

George M. Pharr

Committee Members

Yanfei Gao, Carl J. Mchargue, Madhu S. Madhukar

Abstract

This research aims at enhancing the fundamental understanding of mechanisms controlling the deformation and fracture of silicon carbide based ceramics (single- and poly-crystal). The role of microstructure and material properties on the energy absorption capability of SiC is studied. This research helps to improve the ability to quantitatively predict the initiation and propagation of fracture and the interaction between fracture and plasticity, which provides a step towards a mechanistic understanding of deformation and failure properties of ceramic single crystals and polycrystals. The validity of the indentation-cracking method for toughness measurement is examined using nanoindentation tests with different indenters (spherical, pyramidal). Pyramidal indenters with various centerline to face angles are used to produce a wide range of effective strains in the single and polycrystalline SiC. Crystal plasticity constitutive laws can be calibrated using below threshold indentation loads. Above threshold loads are used to construct a parametric map that delineates the dependence of the ratio of crack size and contact radius on indenter geometry, applied load, toughness, and hardness, thus providing important guidelines for the toughness measurement method. By examining the behavior of several SiC materials during nanoindentation experiments using spherical and pyramidal indenters, it is possible to make predictions about methods to improve the ductility and fracture toughness of SiC to optimize its energy absorption. The applicability of the area under the irreversible part of the indentation load displacement curve (energy dissipated during loading) to predict the performance of SiC under contact loading is examined.

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