Elasticity foam cell

This low pressure process, also known as elastic reservoir molding, consists of making basically a sandwich of plastic-impregnated open-celled flexible polyurethane foam between the face layers of fibrous reinforcements. When this plastic composite is placed in a mold and squeezed, the foam is compressed, forcing the plastic outward and into the reinforcement. The elastic foam exerts sufficient pressure to force the plastic-impregnated reinforcement into contact with the heated mold surface. Other plastics are used. 

The shape of foam films and border profiles in large interval of foam expansion ratio from 10 to 1500 has been experimentally studied in [83], A regular pentagonal dodecahedron made up of transparent organic glass with an elastic rubber balloon inside it which took the shape of a sphere at inflation (Fig. 1.10) was used as a model of foam cell. 

All this makes foam cells stable and is an essential difference between foams and emulsions. This fact was not taken into account in many papers, e.g., in [214,438]. The foam cell does not loose its individuality even if it remains alone on the liquid surface [429]. The two-sided envelope provides sufficient rigidity and elasticity of foams [249]. 

Since the boundary of a foam cell is a multilayer film [429], the elasticity of this shell is many times larger than the elasticity of the adsorption layer. 

The point is that the lamella [429] has a complex multilayer structure (see Figure 7.2). It consists of two boundaries of foam cells, two direct plate micellae [413], and a liquid film, which is a part of the continuous phase of the foam. All in all, the lamella has six parallel adsorption layers. Hence, its modulus of elasticity must be many times larger than that of a simple adsorption layer. 

Hard, scanihard and soft elastic foams Closed-cell, open-cell and mixed-cell... 

Another model was presented by Gibson and Ashby [1], based on a cubic cell model for a closed-cell foam, which takes into account the enclosed gas. As shown in Figure 1, the thickness of the edges and the faces of PP foam cell are approximately equal, which means there is no accumulation of material in the corners. Therefore, the main deformation mechanisms are the stretching of the cell walls and the compression of the enclosed gas. As a result, the elastic properties of the closed-cell foam are described by ... 

Their results indicated that non-atherosclerotic tissue, non-calcified atherosclerotic plaque and calcified atherosclerotic plaque all give different Raman spectra, and hence this technique can differentiate these three states of a vessel wall. Microscopic Raman spectra were obtained to study the chief constituents of the vessels under examination elastic laminae, collagen fibres, smooth muscle cells, fat cells, foam cells, necrotic cores, cholesterol crystals, p-carotene containing crystals, and calcium mineralisations. The results indicate different levels of each depending on which arterial sample was being observed. For example, calcified atherosclerotic plaques contained a lot more foci of calcium... 

Polyurethane foam synthesis can be modified by additions of PEG in such a way that an open-cell, very flexible, highly elastic foam is produced, for example, for upholstery. 

The creep behavior and mechanism of several visco-elastic foams were analyzed in this paper to understand the stmcture property relationship. The creep behavior and recoverability of these foams were characterized by the compression set, short time creep test, as well as hysteresis with an optical extensometer. The creep mechanism was analyzed and explained based on foam cell structure (cell orientation and uniformity) and material properly. Material parameters and cell stmcture that possibly control the creep and recoverability of visco-elastic foams are also discussed. 

The results of meehanieal analysis of two viseo-elastic foams analyzed in this paper show clearly differentiation in stress strain behavior, ereep and eompression srt, and recoverabihty. It was known that mechanical property of foam depends on material chemieal structure, phase morphology, strut dimension, eell structure, and cell orientation and imiformity. The question is why these two visco-elastic foams have different eonqjressive stress strain behavior and compression set. For foam 1 we observed an elastomeric behavior under the compressive stress up to 60% of strain. The foam shows visco-elastic behavior when it was loaded and unloaded at different strain levels. However, for foam sample 2 under the compressive loading we observed elastic deformation, plateau due to possible localized buckling, and densification. 

When a foam is compressed, the stress-strain curve shows three regions (Fig. 25.9). At small strains the foam deforms in a linear-elastic way there is then a plateau of deformation at almost constant stress and finally there is a region of densification as the cell walls crush together. 

Fig. 25.11. When on elastomeric foam is compressed beyond the I inear region, the cell walls buckle elastically, giving the long plateau shown in Fig. 25.9.

Gas-filled plastics are polymer materials — disperse systems of the solid-gas type. They are usually divided into foam plastics (which contain mostly closed pores and cells) and porous plastics (which contain mostly open communicating pores). Depending on elasticity, gas-filled plastics are conventionally classified into rigid, semi-rigid, and elastic, categories. In principle, they can be synthesized on the basis of any polymer the most widely used materials are polystyrene, polyvinyl chloride, polyurethanes, polyethylene, polyepoxides, phenol- and carbamideformaldehyde resins, and, of course, certain organosilicon polymers. 

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