Mechanisms of plastic deformation in molecular crystal cyclotetramethylene-tetranitramine (β-HMX)
Authors
Khan, Mohammad Jane Alam
ORCID
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Other Contributors
Picu, Catalin R.
Blanchet, Thierry A.
Maniatty, Antoinette M.
Shi, Yunfeng
Blanchet, Thierry A.
Maniatty, Antoinette M.
Shi, Yunfeng
Issue Date
2020-12
Keywords
Mechanical engineering
Degree
PhD
Terms of Use
This electronic version is a licensed copy owned by Rensselaer Polytechnic Institute, Troy, NY. Copyright of original work retained by author.
Full Citation
Abstract
Shear localization happens when dislocation motion cannot accommodate the high strain rates imposed in the crystal. Shear localization is observed to be more frequent in β-HMX at higher pressures when dislocation motion is hindered by steric shielding. This study evaluates the shear band viscosity as a function of the applied pressure, temperature, and shear strain rate using atomistic models of the HMX crystal. It is observed that the viscosity of a fully formed shear band decreases as a power function of the strain rate (shear thinning) and decreases linearly with increasing temperature. The non-Arrhenius dependence of the viscosity on temperature is due to the high strain rates involved and the high non-equilibrium conditions in which the band operates. Pressure increases the viscosity of the fully formed band significantly. The band behavior is observed to be independent of the crystallographic orientations. It is shown that viscosity can be expressed exclusively in terms of the density of the non-crystalline material in the band, and hence, the results can be explained in terms of the excess free volume theory previously developed for shear bands in metallic glasses. The stress required to nucleate a shear band from a straight pre-existing dislocation is also reported as a function of the applied pressure, temperature, and shear strain rate.
Description
December 2020
School of Engineering
School of Engineering
Department
Dept. of Mechanical, Aerospace, and Nuclear Engineering
Publisher
Rensselaer Polytechnic Institute, Troy, NY
Relationships
Rensselaer Theses and Dissertations Online Collection
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