Identifier

etd-08312005-104009

Degree

Master of Science in Mechanical Engineering (MSME)

Department

Mechanical Engineering

Document Type

Thesis

Abstract

At high temperatures, stresses well below the material’s tensile yield strength can induce permanent deformation over a period of time. This time-dependent progressive deformation of a material at constant stress is called Creep and is observed in both crystalline and non-crystalline solids. The principal deformation processes contributing to creep deformation are slip, sub-grain formation and grain-boundary sliding. Mechanisms involving creep of crystalline materials involve either dislocation motion or diffusional flow of atoms or both. Extensive studies have been done to ascertain the creep mechanism in various regimes of temperature and applied stresses. At low stresses and high temperatures, grain boundary sliding accommodated diffusion creep i.e. Coble creep is the dominating mechanism. Apart from the experimental investigations, various analytical models have been proposed to explain the underlying principles of this process. However, these studies have been limited to small idealized microstructures. Computational models involving complex mathematical formulations have been developed to study Coble creep in homogeneous microstructures. The present study is to investigate the effect of microstructural inhomogeneity on the stress concentrations in the microstructure and the strain rate. These stress concentrations at grain boundaries arising from microstructural inhomogeneity affect the mechanical properties of polycrystalline materials. Moreover, since the strain rate in Coble creep is dependent on grain size, it is imperative to study the strain-rates in inhomogeneous microstructures to get a realistic idea of the deformation process. Our simulation results indicate that not only creep rate is lowered by the presence of inhomogeneities, but the stress concentrations are also significantly altered giving rise to tensile stresses as high as three times the external applied stress on the system.

Date

2005

Document Availability at the Time of Submission

Release the entire work immediately for access worldwide.

Committee Chair

Dorel Moldovan

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