Search results for "SHELL"
showing 10 items of 748 documents
Shape restoration effect in Ag-SiO2 core-shell nanowires.
2014
The combination of two different materials in a single composite core–shell heterostructure can lead to improved or even completely novel properties. In this work we demonstrate the enhancement of the mechanical properties of silver (Ag) nanowires (NW) achieved by coating them with a silica (SiO2) shell. In situ scanning electron microscope (SEM) nanomechanical tests of Ag–SiO2 core–shell nanowires reveal an improved fracture resistance and an electron-beam induced shape restoration effect. In addition, control experiments are conducted separately on uncoated Ag NWs and on empty SiO2 shells in order to gain deeper insight into the peculiar properties of Ag–SiO2. Test conditions are simulate…
Thin-shell plastic lenses for space and laboratory applications
2004
We have identified an inexpensive, readily available, mechanically stable, extremely smooth, elastic, and mechanically uniform plastic suitable for thin film X-ray optics. Polyethylene terephthalate (PET) is easily deformed without losing its elastic properties or surface smoothness. Most important, PET can be coated with mono- or multilayers that reflect X-rays at grazing incidence. We have used these properties to produce X-ray optics made either as a concentric nest of cylinders or as a spiral. We have produced accurately formed shells in precisely machined vacuum mandresl or used a pin and wheel structure to form a continuously wound spiral. The wide range of medical, industrial and sci…
Luminescent silicon nanocrystals produced by near-infrared nanosecond pulsed laser ablation in water
2014
Abstract We report the investigation of luminescent nanoparticles produced by ns pulsed Nd:YAG laser ablation of silicon in water. Combined characterization by AFM and IR techniques proves that these nanoparticles have a mean size of ∼3 nm and a core–shell structure consisting of a Si-nanocrystal surrounded by an oxide layer. Time resolved luminescence spectra evidence visible and UV emissions; a band around 1.9 eV originates from Si-nanocrystals, while two bands centered at 2.7 eV and 4.4 eV are associated with oxygen deficient centers in the SiO 2 shell.
Friction and wear of lubricated M3 Class 2 sintered high speed steel with and without TiC and MnS additives
2005
Abstract M3/2 sintered high speed steel and composite materials processed by initial admixing of 5 wt.% TiC (to decrease wear) and 5 wt.% MnS (to minimise friction) powders, singly and in combination, were assessed in pin-on-disc tribometers specially constructed to simulate use in the automotive valve train. Pins were of the sintered materials and the mating tribological material discs of T1 high speed steel. For comparison with existing conventional materials, identical tests were performed with discs and pins of two types of spheroidal cast iron. Testing at ∼110 °C, employing a few drops of fresh Shell Helix Standard SAE: 15W-40, API: SJ/CF oil, in daily segments of 5000 m of sliding dis…
Molluscan biomineralization: The proteinaceous shell constituents of Pinna nobilis L.
2005
Abstract The shell of molluscs is a remarkable example of a natural composite biomaterial, synthesized at ambient temperature. Consequently, many consider it as a model for trying to develop at little cost new biomimetic materials of superior mechanical properties. The peculiar resistance of shells to fracture lies in an organic matrix, which is closely associated with the mineral phase. This matrix regulates the crystal growth, by allowing nucleation of the crystals only where appropriate, by favoring crystal elongation in privileged directions, and by inhibiting their growth. This matrix is a mixture of glycoproteins and polysaccharides, the primary structure and function of which are poo…
Investigations on Load Capacity and stability of deformation of rubber cylindrical shells under internal pressure
1994
The paper presents a wide analysis of conditions under which a loss of deformation stability can be observed as well as local bulges form in axially-symmetric (rotational) shells of any length. Analytical relations of the theory of shells were used for the analysis. If the maximum pressure in the shell was exceeded, the deformation process was investigated too. In such a case, strains begin to develop more intensely in the central part of a long cylindrical shell and, owing to that, one or more superimposed bulges (blisters) form. Symmetry of the shell deformation in relation to the centre of its length can be disturbed. A set of algebraic equations was derived for determination of critical…
Nonlinear Structural Mechanics Based Modeling of Carbon Nanotube Deformation
2003
A nonlinear structural mechanics based approach for modeling the structure and the deformation of single-wall and multiwall carbon nanotubes (CNTs) is presented. Individual tubes are modeled using shell finite elements, where a specific pairing of elastic properties and mechanical thickness of the tube wall is identified to enable successful modeling with shell theory. The effects of van der Waals forces are simulated with special interaction elements. This new CNT modeling approach is verified by comparison with molecular dynamics simulations and high-resolution micrographs available in the literature. The mechanics of wrinkling of multiwall CNTs are studied, demonstrating the role of the …
Nuclear charge radii of potassium isotopes beyond N=28
2014
We report on the measurement of optical isotope shifts for 38, 39, 42, 44, 46–51 K relative to 47 K from which changes in the nuclear mean square charge radii across the N = 28 shell closure are deduced. The investigation was carried out by bunched-beam collinear laser spectroscopy at the CERN-ISOLDE radioactive ion-beam facility. Mean square charge radii are now known from 37K to 51K, covering all ν f7/2-shell as well as all νp3/2-shell nuclei. These measurements, in conjunction with those of Ca, Cr, Mn and Fe, provide a first insight into the Z dependence of the evolution of nuclear size above the shell closure at N = 28
F4E load transfer procedure among finite element models different in topology or in discretization
2019
Abstract In this paper, a methodology developed in Fusion for Energy (F4E) for interpolating mechanical loads both between compatible (i.e. from solid to solid models different in discretization) and incompatible (e.g. from solid models to shell/beam models) FE models is described. This novel procedure is able of transferring a force vector field (i.e. Lorentz forces) from a three-dimensional solid mesh (e.g. electromagnetic model) onto a target mesh (e.g. mechanical model), being it either three-dimensional solid or simplified beam/shell model. This interpolation procedure is developed with the aim of preserving both the global and local mechanical equilibrium of the system in terms of res…
A discontinuous Galerkin formulation for nonlinear analysis of multilayered shells refined theories
2023
A novel pure penalty discontinuous Galerkin method is proposed for the geometrically nonlinear analysis of multilayered composite plates and shells, modelled via high-order refined theories. The approach allows to build different two-dimensional equivalent single layer structural models, which are obtained by expressing the covariant components of the displacement field through-the-thickness via Taylor’s polynomial expansion of different order. The problem governing equations are deduced starting from the geometrically nonlinear principle of virtual displacements in a total Lagrangian formulation. They are addressed with a pure penalty discontinuous Galerkin method using Legendre polynomial…