66,221 research outputs found
Flexible fire retardant polyisocyanate modified neoprene foam
Lightweight, fire resistant foams have been developed through the modification of conventional neoprene-isocyanate foams by the addition of an alkyl halide polymer. Extensive tests have shown that the modified/neoprene-isocyanate foams are much superior in heat protection properties than the foams heretofore employed both for ballistic and ablative purposes
Stochastic Metallic-Glass Cellular Structures Exhibiting Benchmark Strength
By identifying the key characteristic “structural scales” that dictate the resistance of a porous metallic glass against buckling and fracture, stochastic highly porous metallic-glass structures are designed capable of yielding plastically and inheriting the high plastic yield strength of the amorphous metal. The strengths attainable by the present foams appear to equal or exceed those by highly engineered metal foams such as Ti-6Al-4V or ferrous-metal foams at comparable levels of porosity, placing the present metallic-glass foams among the strongest foams known to date
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An Evaluation of Non-Stochastic Lattice Structures Fabricated Via Electron Beam Melting
Metal foam structures have many applications and can be used as structural supports, heat
exchangers, shock absorbers, and implant materials. Stochastic metal foams having different cell
sizes and densities have been commercially available for a number of years. This paper addresses
a different type of foams which are known as non-stochastic foams, or lattice structures. These
foams have a well defined repeating unit cell structure rather than the random cell structure in
commercially available stochastic foams. The paper reports on preliminary research on the
fabrication of non-stochastic Ti-6Al-4V alloy foams using the Electron Beam Melting process.
Behavior of the structures in compression, bending, and low cycle repeating load tests are
discussed, and recommendations about cell geometry and processing conditions are made.Mechanical Engineerin
Note and calculations concerning elastic dilatancy in 2D glass-glass liquid foams
When deformed, liquid foams tend to raise their liquid contents like immersed
granular materials, a phenomenon called dilatancy. We have aready described a
geometrical interpretation of elastic dilatancy in 3D foams and in very dry
foams squeezed between two solid plates (2D GG foams). Here, we complement this
work in the regime of less dry 2D GG foams. In particular, we highlight the
relatively strong dilatancy effects expected in the regime where we have
predicted rapid Plateau border variations.Comment: 12 pages, 3 tables, 5 figure
Thermal Degradation and Physical-mechanical Properties of Lignin-filled Rigid Polyurethane Foams
Nowadays, the synthesis of polymers from renewable resources, including polyurethane foams, has been actively investigated. In this work the potential application of lignin (CIMV, France) as non-reactive filler in tall oil amide (OH = 269 mg KOH/g, H2O = 0,2 wt.%) based rigid PU foams is studied.
It was concluded that introducing lignin to rigid PU foams systems can increase physico-mechanical properties of foams
Polyetherimide foams filled with low content of graphene nanoplatelets prepared by scCO2 dissolution
Polyetherimide (PEI) foams with graphene nanoplatelets (GnP) were prepared by supercritical carbon dioxide (scCO2) dissolution. Foam precursors were prepared by melt-mixing PEI with variable amounts of ultrasonicated GnP (0.1–2.0 wt %) and foamed by one-step scCO2 foaming. While the addition of GnP did not significantly modify the cellular structure of the foams, melt-mixing and foaming induced a better dispersion of GnP throughout the foams. There were minor changes in the degradation behaviour of the foams with adding GnP. Although the residue resulting from burning increased with augmenting the amount of GnP, foams showed a slight acceleration in their primary stages of degradation with increasing GnP content. A clear increasing trend was observed for the normalized storage modulus of the foams with incrementing density. The electrical conductivity of the foams significantly improved by approximately six orders of magnitude with only adding 1.5 wt % of GnP, related to an improved dispersion of GnP through a combination of ultrasonication, melt-mixing and one-step foaming, leading to the formation of a more effective GnP conductive network. As a result of their final combined properties, PEI-GnP foams could find use in applications such as electrostatic discharge (ESD) or electromagnetic interference (EMI) shieldingPostprint (published version
Using porous metals to enhance heat transfer in phase change materials (PCMs)
Heat transfer enhancement mechanism of Phase Change Materials (PCMs) by high-porosity metal foams was investigated in this study. The Darcy-Brinkman-Forchheimer modified flow model was employed in the
numerical simulations to consider the non-Darcy effects in metal foams: viscous flow resistance and inertia flow resistance. Local Non-Thermal Equilibrium (LNTE)
model was used to consider the temperature difference between PCM and metal foam. The results showed that in the solid and two-phase zone the heat transfer rate
in PCMs was significantly increased by metal foams, whilst in the liquid zone, natural convection was found to be weakened by the large flow resistance of metal
foams, despite which the overall heat transfer rate was still higher than the case where metal foams were not used. Metal foams of low porosity and high pore
density were found to perform better than the ones of high porosity and low pore density
The Jamming Perspective on Wet Foams
Amorphous materials as diverse as foams, emulsions, colloidal suspensions and
granular media can {\em jam} into a rigid, disordered state where they
withstand finite shear stresses before yielding. The jamming transition has
been studied extensively, in particular in computer simulations of
frictionless, soft, purely repulsive spheres. Foams and emulsions are the
closest realizations of this model, and in foams, the (un)jamming point
corresponds to the wet limit, where the bubbles become spherical and just form
contacts. Here we sketch the relevance of the jamming perspective for the
geometry and flow of foams --- and also discuss the impact that foams studies
may have on theoretical studies on jamming.
We first briefly review insights into the crucial role of disorder in these
systems, culminating in the breakdown of the affine assumption that underlies
the rich mechanics near jamming. Second, we discuss how crucial theoretical
predictions, such as the square root scaling of contact number with packing
fraction, and the nontrivial role of disorder and fluctuations for flow have
been observed in experiments on 2D foams. Third, we discuss a scaling model for
the rheology of disordered media that appears to capture the key features of
the flow of foams, emulsions and soft colloidal suspensions. Finally, we
discuss how best to confront predictions of this model with experimental data.Comment: 7 Figs., 21 pages, Review articl
Development and evaluation of hybrid aluminium matrix syntactic foams
A special class of metallic foams, the so called metal matrix syntactic foams was produced by pressure infiltration technique. Metal matrix syntactic foams consist of a light-weight metal matrix and a set of hollow spheres. Microstructural investigatons were done on polished specimens. The results showed almost perfect infiltration and thin interface layer between the matrix and the reinforcement. Quasi-static compression tests were also done to get basic information about the mechanical properties of metal matrix syntactic foam. The results showed outstanding mechanical properties among other metallic foams. The tests were performed in order to prepare pin-on-disc wear tests
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