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Novel syntactic foams made of ceramic hollow micro-spheres and starch - theory, structure and properties

Novel syntactic foams made of ceramic hollow micro-spheres and starch - theory, structure and properties

as binder for syntactic foams has not been employed in the past despite the fact that starch has some advantages over other binders such as epoxies, phenolics, etc in some applications. It is readily available, environmentally friendly, and an inexpensive renewable polymeric binder although it is dimensionally unstable during manufacturing. The ceramic hollow micro- spheres used for this paper is also inexpensive and available as part of fly ash from coal-fire power stations.

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Characterisation of syntactic foams for marine applications

Characterisation of syntactic foams for marine applications

excellent permeation barrier to resist blistering in marine laminates. Some advantages of the vinyl esters, which may justify their higher cost, include superior corrosion resistance, hydrolytic stability, and excellent physical properties such as impact and fatigue resistance (Gupta et al., 2010). Vinyl ester resins are also widely used as thermoset matrices to fabricate a variety of reinforced structures including pipes, tanks, scrubber and ducts (Sultaniaa et al., 2010). In addition to these applications, vinyl esters are also being used in coatings, adhesives, moulding compounds, structural laminates, electrical applications, etc. Vinyl ester resins combine the best properties of epoxies and unsaturated polyesters. Vinyl ester resins based on epoxy novolac are used for chemical storage tanks, pipes and ducting, fume extraction systems and gas cleaning units, as this particular resin shows superior chemical resistance at high temperatures (Dwivedi et al., 2003). They have high tensile elongation along with better corrosion resistance, which makes them promising material for producing lining coating with outstanding adhesion to other types of plastics and conventional materials such as steel and concrete. Vinyl ester resins also find a variety of applications in optical fibre coating, topcoats for containers, as well as printed circuit boards. Hence, investigating the properties of vinyl ester matrix syntactic foams and developing structure-property correlations for these materials represent important challenges in this study.

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The application of thin wall shell model in plate problem of syntactic foams

The application of thin wall shell model in plate problem of syntactic foams

To reduce cost of calculations, the paper tries to de-dimension inclusions in according to classic Kirchhoff-Love thin-wall shell theorem, deducing the expression of strain and stiffness of inclusion under plate strain situation, discussing multi-points constraint relationship between inclusion and matrix, and then taking the equivalent modulus problem that at the time syntactic foams debond partly from interface as an example for checking.

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Characterisation of Aluminium Matrix Syntactic Foams under Dynamic Loading

Characterisation of Aluminium Matrix Syntactic Foams under Dynamic Loading

Previous studies have investigated the behaviour of metal matrix syntactic foams under dynamic compression loads (Luong et al., 2013; Tao et al., 2009). Low and high velocity impact tests have been carried out to characterise metal matrix syntactic foams and their behaviour has been studied using drop-weight and split pressure Hopkinson bar tests (Hopkinson, 1914; Tao et al., 2009). It was found that the yield strength of metal matrix syntactic foams under dynamic loading is approximately ten to thirty percent higher, as compared with quasi-static compression (Gupta et al., 2010). Additionally, samples of aluminium matrix syntactic foams were investigated under impact and it was reported that many oscillations appeared at the beginning of the stress–strain curve, where the strain was low due to the high vibration of the drop hammer (Zhang and Zhao, 2007). Tao and Zhao (2009) evaluated the behaviour of aluminium matrix syntactic foams under drop weight impact loading. The split pressure Hopkinson bar was used in order to characterise the behaviour of the material under dynamic loading. It was concluded that aluminium matrix syntactic foams at high strain-rates had 10-30% higher plateau stress and higher peak strengths compared to those measured during a quasi-static test.

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The processing and properties of syntactic Al foams containing low cost expanded glass particles

The processing and properties of syntactic Al foams containing low cost expanded glass particles

Aluminium syntactic foams are commonly made by isothermal infiltration of a bed of hollow spheres with molten metal. Whilst this is a convenient and potentially low cost route, deleterious reactions between the hollow spheres and the molten metal matrix are possible and the requirement for a packed bed of hollow spheres means that there is limited ability to vary the sphere volume fraction outside the range for loose and dense random packing (roughly 0.6-0.65). This leads to reasonably high densities for these materials (1.5-1.9 g cm -3 ) compared with conventional metal foams and

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Magnesium Matrix Composite Foams—Density, Mechanical Properties, and Applications

Magnesium Matrix Composite Foams—Density, Mechanical Properties, and Applications

Abstract: Potential of widespread industrial applications of magnesium has been realized in recent years. A variety of magnesium alloy matrix composites are now being studied for mechanical properties. Since magnesium is the lightest structural metal, it can replace aluminum in existing applications for further weight savings. This review presents an overview of hollow particle filled magnesium matrix syntactic composite foams. Fly ash cenospheres are the most commonly used hollow particles for such applications. Fly ash cenospheres primarily have alumino-silicate composition and contain a large number of trace elements, which makes it challenging to study the interfacial reactions and microstructure in these composites. Microstructures of commonly studied AZ and ZC series magnesium alloys and their syntactic foams are discussed. Although only a few studies are available on these materials because of the nascent stage of this field, a comparison with similar aluminum matrix syntactic foams has provided insight into the properties and weight saving potential of magnesium matrix composites. Analysis shows that the magnesium matrix syntactic foams have higher yield strength at the same level of density compared to most other metal matrix syntactic foams. The comparison can guide future work and set goals that need to be achieved through materials selection and processing method development.

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Fuzzy graphs: Algebraic structure and syntactic recognition

Fuzzy graphs: Algebraic structure and syntactic recognition

Fuzzy graphs were defined as an extension of the notion given by Rosenfeld in [32], i.e., directed (hyper)graphs with fuzzy sets of nodes and fuzzy sets of edges. It turns out that the set of all fuzzy graphs can be structured into a magmoid with operations product (graph composition) and sum (disjoint union). By virtue of this algebraic structure we introduced a syntactic recognizability notion for sets of fuzzy graphs employing the syntactic magmoid in a role analogous to the syntactic monoid of string languages. This approach shall allow us to explore the fuzzy case for existing crisp graph theoretic methods and techniques involving formal verification [3, 4, 13] and natural language processing [31] as well as for the syntactic complexity of string and graph languages [14, 15, 22].

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Wall slip of bubbles in foams

Wall slip of bubbles in foams

The variation of the liquid area 共corresponding to vol- ume if the system is extended in the third dimension兲 with Ca may have relevance to dilatancy in foams. This is an increase of the amount of liquid in a foam with strain and/or strain rate, which has been introduced by Weaire and Hutzler. 31 This effect is more familiar in the mechanics of granular materials but may play a significant role in foams also. In particular it has been invoked as a possible factor in the explanation of convective instability. 32 The result shown in Fig. 12 pertains to what we might call surface dynamic dilatancy.

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Structure and energy of liquid foams

Structure and energy of liquid foams

Let us now consider disordered dry foams [1,22,28,36,42]. Fig. 7 to Fig. 9 summarise a few of their properties. Surface Evolver simulations (Section 5.2) of monodisperse disordered foams [36] show that their av- erage number of neighbours b N N is approximately 13.7, similar to the value found by Matzke in an experimental study in 1946 [41] (Fig. 7a and Table 1), and also close to the values for the Weaire – Phelan and the Kelvin structure. Increasing polydispersity in such simulations leads to a decrease in both b N N and E ̂ (Fig. 7b,c). Despite their random- ness, such packings feature a number of statistical correlations concerning their local structure [1,28]. For example, Fig. 8, based on sim- ulation data for large bubble clusters, shows that the number of neigh- bours of a bubble increases with its volume: the bigger a bubble, the more neighbours it has [28,32,43]. Also, on average, a large bubble is more likely to be surrounded by smaller bubbles [1,28,44], a correlation related to the Aboav – Weaire law for two-dimensional foams [1]. Fig. 5. The topology and geometry of foams in the dry limit (φ b 0.05) is governed by

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A. Mechanical Behaviours of Metal Foams

A. Mechanical Behaviours of Metal Foams

Among metal foams, titanium foams (Ti-foams) are preferred in many crucial applications including biomedical implants which biocompatibility is required. The main interests for using cellular metals come from the increase of the friction coefficient between the implant and the surrounding bone. It allows mechanical interlocking of bone with the implant by substantial bone in-growth and better long term stability. Additionally, stiffness of the implants can be tailored by varying porosity to reduce the stress shielding effect [5], [6]. One of promising biomedical application of Ti-foams is in dental implants.

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Shock compression of polyurethane foams

Shock compression of polyurethane foams

Polyurethane foams are a common class of polymeric foams used extensively as structural components and shock mitigating materials. As such, there have been several previous studies focused on their impact or shock compres- sion response and dynamic compaction behaviours. How- ever, earlier studies have been limited to a few low initial densities as well as fully dense polyurethane. Here, we present new Hugoniot data for polymethylene diisocyanate (PMDI)-based polyurethane foam at a range of initial densities designed to fill in the gap in literature shock data in the density regime between 0.35 and 0.9 g/cm 3 . We also

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Auxetic foams for sports applications

Auxetic foams for sports applications

Chapter 2: Literature Review Page 32 D3O market the Trust Helmet Pad System [234] incorporating pads with a re-entrant auxetic geometry that are claimed to provide increased fit to the head. Although double curvature (Figure 2.7b) is a clear benefit in auxetics, the utilised re-entrant cells are large and it is unclear whether double curvature will be realised in a continuum, rather than a discontinuous, manner. More products are likely to emerge if the increased level of comfort and protection offered by auxetic materials can be further demonstrated, justifying investment in the development of stiffer, more appropriate auxetic materials (such as closed cell [140] or shear thickening fluid impregnated [207] auxetic foams, or novel impact hardening auxetic polymers [235]). The emergence of sports products including auxetic materials could be assisted by the development of a commercially-viable (low cost, large scale) auxetic foam production process [111,132]. ‘Felted’ foams, fabricated by uniaxial compression, are already commercially produced and exhibit auxetic behaviour in one loading direction [108]). Alternatively AM is becoming a commercially viable option [225] to provide fine control over cell structure for auxetic foam-like structures.

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Chapter 16: The structure of liquid foams

Chapter 16: The structure of liquid foams

The polydisperse foam of Figure 16.1 is typical for examples found in nature or many industrial applications. In fundamental research, there is often a preference for studying monodisperse foams, consisting of bubbles with a polydispersity of less than 5%. The right photograph in Figure 16.1 shows an example of such a monodisperse foam, again sitting on top of the foaming solution. Such foams have a tendency to order when confined into tubes of width of only a few bubble diameters. They can also order spontaneously in bulk when produced from bubbles that are smaller than the capillary length, resulting in a crystalline wet foam. For more details, see Section 16.5 and [4–7].

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A Review of the Syntactic Priming—A Research Method in Sentence Production

A Review of the Syntactic Priming—A Research Method in Sentence Production

The implicit learning mechanism indicates that the syntactic priming is the process of strengthening the syn- tactic representation link. When producing or comprehending a syntactic structure, the user has to know how to map the sentence meaning to the functions (which is the subject, and which is the object), and how to map the functions to the component sequence, and the syntactic priming can reinforce the mapping. There are four cha- racteristics illustrating the point that the syntactic priming is implicit: (1) the priming has no relationship with the explicit memory (Bock, Loebell, & Morey, 1992); (2) the anterograde amnesia patients who suffer from the middle of the temporal injury and whose explicit memory has been injured seriously can have the syntactic priming effect (Ferreira, Bock, Wilson, & Cohen, 2005); (3) the syntactic priming has the inverse preference ef- fect, which means that the low-frequency sentences can make larger priming effect (Hartsuiker & Kolk, 1998), being correlative with the error-based implicit learning calculations; (4) Chang’s series of large-scale computer simulation studies proved that the syntactic priming was implicit (Chang, 2002; Chang, Dell, & Bock, 2006; Chang, Dell, Bock, & Griffin, 2000). The researchers who believe in the implicit learning deemed that: (1) the syntactic priming’s syntactic structure was composed of the abstract syntactic frame; (2) the priming was related to long term memory; (3) the concrete words were filled into the syntactic frame during the speech production; (4) the promoting function of the word repetition was in relation to the sentence meaning, which was a short time phenomenon.

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Models of wet two dimensional foams

Models of wet two dimensional foams

The structure and rheology of foams, emulsions and similar soft packings without static particle friction in the ‘‘deeply jammed’’ regime has recently been investigated by several simulations and models on the particle scale, 9,10,27 and we hope that our results may help to develop them further. Fig. 2 illustrates that for large strains, many contacts can persist in a droplet packing even though they should be disconnected according to two-body interaction models. Such changes of the coordination in the packing can modify the yielding and non- affine local deformation behavior. Moreover, since the nonlinear viscous friction between particles 9,10 in flowing samples is governed by contact forces, their modification by many-body effects needs to be considered in models of energy dissipation in foams and emulsions.

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Dynamic indentation on layered polypropylene foams

Dynamic indentation on layered polypropylene foams

In this present study, authors proposed to study the behavior of homogeneous and multi-layered PP foams at the macroscopic and the mesoscopic scales under dynamic loadings. The key point of this research work is to deter- mine the influence of the scale of variability – mesoscopic (variability in the beads) or macroscopic (variability in the layers of the foam) – on the macroscopic behavior. Experimental investigations had been led by Bouix et al. [8] to characterize the behavior of the foam subjected to uniaxial compressive tests at different strain rates and for different values of density.

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Auxetic Foams for Sport Safety Applications

Auxetic Foams for Sport Safety Applications

Peak accelerations were ~3 times lower for auxetic foam in comparison to its conventional counterpart. Similar peak accelerations were observed for both foams at the lowest impact energy of 2.2 J, but the auxetic samples performed better as impact energy increased to the maximum of 5.6 J. The auxetic foam performed better because it deformed less during impact, preventing the high accelerations observed when the conventional samples bottomed out. Quasi-static compression confirmed different stress-strain relationships for the two foams. The auxetic foam resisted cell-wall buckling with an almost linear stress-strain profile, which is likely to be why these samples deformed less during impact.

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Thermal-insulation performance of low density polyethylene (LDPE) foams: Comparison between two radiation thermal conductivity models

Thermal-insulation performance of low density polyethylene (LDPE) foams: Comparison between two radiation thermal conductivity models

T he loss of energy, especially in industrial and residential buildings is one of the main reasons of increased energy consumption. Improving the thermal insulation properties of materials is a fundamental method for reducing the energy losses. Polymeric foams are introduced as materials with excellent thermal insulation properties for this purpose. In the present study, a deep theoretical investigation is performed on the overall thermal conductivity of low-density polyethylene (LDPE) foams. The thermal conductivity by radiation is predicted using two different methods. The most appropriate model is selected through comparing results with experimental data. The results show that the theoretical model has an appropriate agreement with the experimental results. The effects of foam characteristics including foam density, cell size, and cell wall thickness on the overall thermal conductivity are investigated. The results indicate that by decreasing the cell size and increasing the cell wall thickness, the overall thermal conductivity is decreased significantly. Also, there is an optimum foam density in order to achieve the smallest thermal conductivity. The lowest overall thermal conductivity achieved in the studied range is 30 mW/ mK at a foam density of 37.5 kg.m -3 , cell size of 100 μm, and cell wall thickness of 6 μm. Polyolefins J (2019) 6:

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Processing and Development of an Ultra-Light, High Strength Material through Powder Metallurgy

Processing and Development of an Ultra-Light, High Strength Material through Powder Metallurgy

Digital images from cut sections of various composite foams that have been produced are shown in Figure 50. The visible pores are the interior cavities of the spheres, separated by the thickness of the sphere walls and the matrix. As can be seen, the spheres have a good distribution and a high packing density. There is little or no visible porosity between the spheres and the matrix which has filled the entire volume between the spheres, appears solidly formed and bonded to the spheres. The spheres have all remained spherical and show no signs of deformation as a result of processing. Careful inspection of the spheres reveals that none of the spheres have been penetrated by the matrix and they are all still hollow. Some spheres appear to have some material in them, but this is a consequence of the cutting and grinding process. This process can smear or press the thin metal shell of the sphere across the cavity of the sphere, making it appear filled. This material is mostly removed with further polishing, although manual removal is sometimes necessary.

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Low density nanoporous iron foams synthesized by sol gel autocombustion

Low density nanoporous iron foams synthesized by sol gel autocombustion

difficult work [12]. Tappan et al. have recently reported a cyanogel-based synthesis of macroporous refractory metals well below their melting point [23,24]. Several transition metal porous foams have been obtained by heating the cyanogel under an inert atmosphere. However, as men- tioned in the references, there are several disadvantages in their synthesis metrology: firstly, the by-products in their thermal processing contain very toxic hydrogen cyanide and cyanogen; secondly, the metal complexes with ener- getic ligand bistetrazolamine used in the process are expensive and complex to be synthesized; and thirdly, ele- mental analysis confirmed that the Fe foams contain only approximately 50% Fe, and the iron foams are not percept- ibly magnetic prior to heat treatment under a flow of Ar or H 2 gas [23,25]. In this communication, we demonstrate

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