Stiff structure

The plastic insulants are rigid, homogeneous materials, suitable as the core of sandwich panels. Such a method of fahrication is facilitated when using foamed rigid polyurethane, since the liquids can he made to foam between the inner and outer panel skins and have a good natural adhesion, so making a stiff structural component [40]. 

The rigid chemical structure of a conjugated polymer helps in the movement of electrons. That stiff structure, however, has limited its use. They are like uncooked spaghetti and do not easily entangle themselves. Polymer chain entanglements are necessary to achieve high viscosities, which are required to create fibers out of these polymers. 

In the case of plastics, emphasis is on the way plastics can be used in these structures and why they are preferred over other materials. In many cases plastics can lend themselves to a particular field of application only in the form of a sophisticated lightweight stiff structure and the requirements are such that the structure must be of plastics. In other instances, the economics of fabrication and erection of a plastics lightweight structure and the intrinsic appearance and other desirable properties make it preferable to other materials. 

Pang, Li, and Barton indicated, based on viscosity data, that PAEs had a stiff structure in solution [43]. A PAE shows a Mark-Houwink constant as high as a= 1.92 [43], revealing that it has a very stiff structure, similar to rodlike poly-(pyridine-2,5-diyl) [65,66]. Liquid crystalline behavior of PAEs with a meso-gen has been reported [45]. The chemical properties of PAEs have also been investigated with oligomeric model compounds [67-76]. 

Because of the repulsion of the cyanide groups the polymer backbone assumes a rod-like conformation. The fibers derive their basic properties from this stiff structure of PAN where the nitrile groups are randomly distributed about the backbone rod. Because of strong bonding between the chains, they tend to form bundles. Most acrylic fibers actually contain small amounts of other monomers, such as methyl acrylate and methyl methacrylate. As they are difficult to dye, small amounts of ionic monomers, such as sodium styrene sulfonate, are often added to improve their dyeability. Other monomers are also employed to improve dyeability. These include small amounts (about 4%) of more hydrophilic monomers, such as -vinyl-2-pyrrolidone (Equation 6.69), methacrylic add, or 2-vinylpyridine (Equation 6.70). 

The kinked dicarboxy compounds obviously has considerable capability for decreasing the melt transitions with increasing substitution for the terephthalic acid. A decrease to below 300°C is already achieved with the diphenyl ether derivatives-(3,4 -0 and 4,4 -0) at a degree of substitution corresponding to 30%. For the corresponding diphenyl ketone derivatives (3,4 -K and 4,4 -K) a somewhat higher degree of substitution is required, 35-40%, to get a comparable melt depression. The more stiff structure of the ketones compared to the ethers may be connected with this kind of behaviour. However, further increase in the amounts has a very drastic effect on the melt transition. 

The biomechanical response of the body has three components, (1) inertial resistance by acceleration of body masses, (2) elastic resistance by compression of stiff structures and tissues, and (3) viscous resistance by rate-dependent properties of tissue. For low-impact speeds, the elastic stiffness protects from crush injuries whereas, for high rates of body deformation, the inertial and viscous properties determine the force developed and limit deformation. The risk of skeletal and internal organ injury relates to energy stored or absorbed by the elastic and viscous properties. The reaction load is related to these responses and inertial resistance of body masses, which combine to resist deformation and prevent injury. When tissues are deformed beyond their recoverable limit, injuries occur. 

Plastics products are most likely to fail in a brittle manner under impact conditions, both due to strain rate effects and because large forces can be generated by low energy impacts on stiff structures. A variety of impact tests are used. Usually a weight falls from a height of the order of Im to hit the test specimen with a velocity of about 5ms . This simulates the strain rates that occur when a product is dropped about a metre, but not the higher strain rates in vehicle collisions or ballistic impacts. The uses and limitations of three types of impact tests will be discussed. 

Figures Ic and Id show no advantage for boron-aluminum over boron-epoxy. There are some cryogenic applications, however, where a high electrical conductivity and a strong, stiff structure are required, e.g., in eddy-current shields in rotating superconducting machinery. The high thermal conductivity of boron-aluminum limits its cryogenic applications. The excellent properties and low property variability observed with boron-epoxy were also observed for boron-6061 aluminum at 4 K [ ].

The structure of PC with its carbonate and bisphenolic structures has many characteristics which promote its distinguished properties. The para substitution on the phenyl rings results in a symmetry and lack of stereospecificity. The phenyl and methyl groups on the quarte-nary carbon promote a stiff structure. The ester-ether carbonate groups —OCOO— are polar, but their degree of intermolecular polar... 

Overall settlement in both tests was a fraction of that observed with loose soil. The settlements did differ between the two structures with the stiff structure settling... 

The foundation of a flexible structure does not rotate as much as that of a stiff structure, due the ability of the flexible structure to dissipate energy internally. 

For obtaining a low -weight, high-bending-stiffness structure, sandwich constructions are a conunon choice for composite components. To make a sandwich, low-density materials are inserted as sandwich cores between two faces of the structural material itself (so in this case between two stacks of prepreg plies). Commonly used core materials are plastic foams (for example, made from PVC, PS, or PET) and balsa wood. Examples of core materials for more sophisticated, structured sandwich cores are honeycombs (made from aluminium, or resin-impregnated paper sheets), or fibre-reinforced foams. 

The increasing use of plastics in large structures such as radomes, space structures, and architectural structures particularly, has resulted in a number of interesting and unique types of stiff structures with a somewhat complicated geometry. These designs are also used in structures made of other materials such as reinforced concrete and in structures made of combinations of plastics and other materials. Some of these shapes are shown in Figs. 8-17, 8-18, 8-19 and 8-20. One of... 

The use of folded plates to form stiff structures has become one of the most important developments in architecture, as much because of the variety of interesting enclosures and support shapes possible as the efficient use of materials to impart stiffness. Benjamin gives a large number of examples of folded plate structures using FRP materials. They are one of the preferred materials for this type of construction because they can be readily fabricated into the required complex geometries. 

In addition, as the relation between Tsoil and Tstr. was expected to play a significant role on the overall response, two cases of this ratio were compared. For the first case, Tsoil coincides with Tstr. (implying a kind of resonance), while in the second case Tsoil is three times higher than Tstr. (representing a relatively stiff structure). In Figure 9 the soil amplification factors AFsoil (without the structure) and AF soil (with the structure) are compared for three surface points Bi behind the wall L/Ff = 0.2, 0.7, 1.2, or L = 1.6, 5.6, 9.6m, respectively. It is obvious that in the case... 

Some earthquake resistance improvement may be achieved by local dampers or relatively soft parts in an overall stiff structure (Bozorgnia and... 

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