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Kabirian F.,University of Maryland Baltimore County | Khan A.S.,University of Maryland Baltimore County | Gnaupel-Herlod T.,Center for Neutron Research
International Journal of Plasticity | Year: 2014

Mechanical responses and texture evolution of extruded AZ31 Mg are measured under uniaxial (tension-compression) and multiaxial (free-end torsion) loadings. Compression loading is carried out in three different directions: along the extrusion direction (ED), perpendicular to the extrusion direction (PED), and 45° to the extrusion direction (45ED) at temperature and strain rate ranges of 77-423 K and 10-4-3000 s-1, respectively. Texture evolution at different intermediate strains reveals that crystal reorientation is exhausted at smaller strains with increase in strain rate while increase in temperature retards twinning. In addition to the well-known tension-compression yield asymmetry, a strong anisotropy in strain hardening response is observed. However, this anisotropy is negligible at smaller strain so that compressive yield stress does not change with loading directions at each temperature and strain rate. Strain hardening during the compression experiment is intensified with decreasing and increasing temperature and strain rate, respectively. Even though the strain hardening response during the free-end torsion experiment resembles that in tension, the shear yield stress is significantly smaller than prediction of von-Mises criterion. This complex behavior is explained through the understanding roles of deformation mechanisms using the Visco-Plastic Self Consistent (VPSC) model. In order to calibrate the VPSC model's constants as accurate as possible, in contrast to previous studies, this paper employs the VPSC model to simulate a vast number of mechanical responses and crystallographic characteristics including stress-strain curves in tension, compression in three directions, and free-end torsion, texture evolution at different strains, lateral strains of compression samples, twin volume fraction, and axial strain during the torsion experiment. The modeling results show that depending on the number of measurements used for calibration, roles of different mechanisms in plastic deformation change significantly. © 2014 Elsevier Ltd. All rights reserved. Source


Khan A.S.,University of Maryland Baltimore County | Pandey A.,University of Maryland Baltimore County | Pandey A.,Johns Hopkins University | Gnaupel-Herold T.,Center for Neutron Research | Mishra R.K.,General Motors
International Journal of Plasticity | Year: 2011

In order to study the behavior of material under finite deformation at various strain rates, the responses of AZ31 Mg sheet are measured under uniaxial (tension and compression) and multiaxial (simple shear) loadings along rolling direction (RD), 45° to rolling direction (DD), 90° to rolling direction (TD), and normal to the sheet (ND) to large strains. The material exhibits positive strain rate sensitivity (SRS) at room and elevated temperatures; the SRS is more pronounced at high temperatures and lower strain rates. The r-value of the material under tensile loading at room temperatures is higher in TD at lower strain rate. Texture measurements on several failed specimens are reported under tension and simple shear after finite plastic deformation of about 20% equivalent strain. The as-received material exhibits a strong fiber with equal fractions of grains having the c-axis slightly tilted away from the sheet normal towards both +RD and -RD. Pole figures obtained after tensile loading along the rolling direction (RD) show that the texture of the material strengthens even at low strains, with c-axis perpendicular to the sheet plane and prism planes lining up in a majority of grains. However, the tensile loading axis along TD does not lead to similar texture strengthening; the c-axis distribution appears to be virtually unchanged from the virgin state. The pole figures obtained after in-plane compression along RD brings the c-axes of the grains parallel to the loading direction. The pole figures after simple shear loading show that the c-axis rotates to lie on the sheet plane consistent with a compression axis 45° away on the sheet plane. © 2010 Elsevier Ltd. All rights reserved. Source


Jackson A.J.,Center for Neutron Research | Jackson A.J.,University of Delaware | McGillivray D.J.,University of Auckland
Chemical Communications | Year: 2011

We show that casein protein micelles - a complex protein/inorganic phosphate structure - can be subjected to high pressures (up to 350 MPa) while making in situ structural measurements using (ultra-)small angle neutron scattering, to give insight to the protein structure, aggregation and stability under pressure. © 2011 The Royal Society of Chemistry. Source


Kumari H.,University of Missouri | Kline S.R.,Center for Neutron Research | Atwood J.L.,University of Missouri
Chemical Communications | Year: 2012

Solution structure of insulin templated C-methyl resorcin[4]arene nanocapsules has been investigated using neutron scattering. The insulin biotemplate has enhanced the limits of encapsulation and enabled formation of a larger spherical molecular host. © 2012 The Royal Society of Chemistry. Source


Heinrich F.,Center for Neutron Research | Losche M.,Carnegie Mellon University
Biochimica et Biophysica Acta - Biomembranes | Year: 2014

Neutron reflectometry (NR) is an emerging experimental technique for the structural characterization of proteins interacting with fluid bilayer membranes under conditions that mimic closely the cellular environment. Thus, cellular processes can be emulated in artificial systems and their molecular basis studied by adding cellular components one at a time in a well-controlled environment while the resulting structures, or structural changes in response to external cues, are monitored with neutron reflection. In recent years, sample environments, data collection strategies and data analysis were continuously refined. The combination of these improvements increases the information which can be obtained from NR to an extent that enables structural characterization of protein-membrane complexes at a length scale that exceeds the resolution of the measurement by far. Ultimately, the combination of NR with molecular dynamics (MD) simulations can be used to cross-validate the results of the two techniques and provide atomic-scale structural models. This review discusses these developments in detail and demonstrates how they provide new windows into relevant biomedical problems. This article is part of a Special Issue entitled: Interfacially Active Peptides and Proteins. Guest Editors: William C. Wimley and Kalina Hristova. © 2014 Elsevier B.V. Source

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