104 research outputs found
Gravitational Geometric Phase in the Presence of Torsion
We investigate the relativistic and non-relativistic quantum dynamics of a
neutral spin-1/2 particle submitted an external electromagnetic field in the
presence of a cosmic dislocation. We analyze the explicit contribution of the
torsion in the geometric phase acquired in the dynamic of this neutral
spinorial particle. We discuss the influence of the torsion in the relativistic
geometric phase. Using the Foldy-Wouthuysen approximation, the non-relativistic
quantum dynamics are studied and the influence of the torsion in the
Aharonov-Casher and He-McKellar-Wilkens effects are discussed.Comment: 14 pages, no figur
Optimization of the Strength-Fracture Toughness Relation in Particulate-Reinforced Aluminum Composites via Control of the Matrix Microstructure
The article of record as published may be found at http://dx.doi.org/10.1007/s11661-998-0119-9The evolution of the microstructure and mechanical properties of a 17.5 vol. pct SiC particulatereinforced
aluminum alloy 6092-matrix composite has been studied as a function of postfabrication
processing and heat treatment. It is demonstrated that, by the control of particulate distribution, matrix
grain, and substructure and of the matrix precipitate state, the strength-toughness combination in the
composite can be optimized over a wide range of properties, without resorting to unstable, underaged
(UA) matrix microstructures, which are usually deemed necessary to produce a higher fracture toughness
than that displayed in the peak-aged condition. Further, it is demonstrated that, following an
appropriate combination of thermomechanical processing and unconventional heat treatment, the
composite may possess better stiffness, strength, and fracture toughness than a similar unreinforced
alloy. In the high- and low-strength matrix microstructural conditions, the matrix grain and substructure
were found to play a substantial role in determining fracture properties. However, in the intermediate-
strength regime, properties appeared to be optimizable by the utilization of heat treatments
only. These observations are rationalized on the basis of current understanding of the grain size
dependence of fracture toughness and the detailed microstructural features resulting from thermomechanical
treatments.United States Army Research OfficeArmy Research LabratoryUnited States Air Force Office of Scientific ResearchWright Materials LabratoryDWA Composite
Atomic Structures of Symmetric Tilt Grain Boundaries in Hexagonal Close-Packed (hcp) Crystals
The fracture behaviour of functionally graded piezoelectric materials containing collinear dielectric cracks
A numerical solution of the diffusion equation resulting from the void theory of the trapping of hydrogen in iron and steel
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