Dissertation
SHOCK COMPRESSION AND RELEASE OF MAGNESIUM SINGLE CRYSTALS: ANISOTROPY AND TIME-DEPENDENT INELASTIC RESPONSE
Doctor of Philosophy (PhD), Washington State University
01/2017
Handle:
https://hdl.handle.net/2376/111870
Abstract
To gain insight into the inelastic deformation mechanisms for shocked and released hexagonal close-packed (hcp) metals, high purity magnesium single crystals were subjected to shock compression and release along c-axis [0001], a-axis [112 ̅0] and a low-symmetry (LS) axis [101 ̅2] to two different impact stresses. For Mg, c- and a-axes Mg are “specific” directions and, hence, propagate purely longitudinal two-waves (elastic-plastic) followed by release. Wave profiles, measured using laser interferometry, for these orientations showed a sharply peaked elastic wave followed by stress relaxation suggesting a time-dependent response. The c-axis unloading showed a distinct elastic-inelastic feature, while a-axis unloading was smooth and featureless. LS-axis Mg is a “non-specific” direction and, hence, propagates quasi-longitudinal and quasi-shear waves. The combination of LS-direction and elastic-plastic deformation leads to complex loading/unloading profiles. Wave profiles, measured using laser interferometry, for LS-axis Mg showed a small elastic precursor followed by two plastic waves (second plastic wave significantly slower when shocked to a lower stress). The measured release wave profiles for LS-axis Mg exhibit a structured unloading response when released from higher peak stress and a somewhat smooth release response when released from lower stress.
The wave profiles obtained along the different orientations show significant differences (qualitatively and quantitatively) in both compressive and release wave profiles suggesting that Mg single crystals exhibit strong anisotropy under both shock compression and release. The role of crystal anisotropy was observed in the measured elastic wave amplitudes, in the decay of the elastic wave amplitudes, and in the release wave profiles.
Numerical simulations of the measured wave profiles using a time-dependent anisotropic modelling framework, that incorporated both dislocation slip and deformation twinning, provided considerable insight into the inelastic deformation response of Mg single crystals shocked and released along c-, a-, and LS-axes. The inelastic deformation mechanisms governing both shock compression and release of Mg single crystals can be understood in terms of dislocation slip on basal, prismatic, pyramidal I and pyramidal II planes, and deformation twinning along (101 ̅2) twinning planes. These inelastic deformation mechanisms are the same as those previously observed for Mg single crystals under quasi-static loading/unloading.
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Details
- Title
- SHOCK COMPRESSION AND RELEASE OF MAGNESIUM SINGLE CRYSTALS: ANISOTROPY AND TIME-DEPENDENT INELASTIC RESPONSE
- Creators
- Prithachakaran Renganathan
- Contributors
- Yogendra M Gupta (Advisor)David P Field (Committee Member)Jow-Lian Ding (Committee Member)
- Awarding Institution
- Washington State University
- Academic Unit
- School of Mechanical and Materials Engineering
- Theses and Dissertations
- Doctor of Philosophy (PhD), Washington State University
- Number of pages
- 189
- Identifiers
- 99900581824901842
- Language
- English
- Resource Type
- Dissertation