Flexible-stiff

Monomers are primarily used to lower the viscosity of the uncured material to facilitate application. The monomer must be matched with the resin to give the desired set of properties with respect to adhesion to the substrate and bulk properties such as flexibility, stiffness, cure behavior, and durability. Early radiation curable monomers had problems associated with toxicity and skin sensitivity newly developed monomers have been significantly improved in this respect. 

Flexibility Stiffness capacity Cutting capacity Risk of vascular injury... 

As a second example cylindrical brush polymers, often called bottle brushes, are described (Sect. 3). Cylindrical brush polymers usually consist of a flexible main chain, densely grafted by flexible, stiff or dendritically branched side chains. The latter are known as dendronized polymers and have been fi equently investigated by both theory and experiment. In the present review, we focus on brush polymers with linear side chains. 

Leather-hard state The state of a body, typically clay or clay-like, in which it resembles leather in flexibility, stiffness, and ductility. 

N. Note that the stiff and flexible excess free energy of mixing are opposite signs, which implies that the flexible (stiff) chain is destablized (stabilized) upon transfer from the melt to the blend. Such behavior... 

Hardness of an adhesive is not important in itself, but for the sealant it may be important because it may be damaged if it is too soft, for instance, when the sealant joint is on the floor and should withstand traffic. Hardness is measured in a classic way as rubber hardness with a Shore durometer. There are of course relationships between hardness, flexibility, stiffness, etc. Hardness may also be used sometimes as an indication of the degree of cure. 

The conformation plot is the scaling law between macromolecule size and molecular weight (i.e., the chain length) and it is very useful in studying the stiffness (flexible, stiff, or compact conformation) of polymers. Also branching, degree of functionalization, or derivatization could be studied using the conformation plot of the polymer. Therefore, it is very useful in the molecular characterization of polymers. 

This type of coil was prepared from copper cladded printed circuit board material by applying photolithographic techniques. The p.c. board material is available with difierent copper thicknesses and with either a stiff or a flexible carrier. The flexible material offers the opportunity to adapt the planar coil to a curved three dimensional test object. In our turbine blade application this is a major advantage. The thickness of the copper layer was chosen to be 17 pm The period of the coil was 100 pm The coils were patterned by wet etching, A major advantage of this approach is the parallel processing with narrow tolerances, resulting in many identical Eddy current probes. An example of such a probe is shown in fig. 10. 

Crystallinity. Generally, spider dragline and silkworm cocoon silks are considered semicrystalline materials having amorphous flexible chains reinforced by strong stiff crystals (3). The orb web fibers are composite materials (qv) in the sense that they are composed of crystalline regions immersed in less crystalline regions, which have estimates of 30—50% crystallinity (3,16). Eadier studies by x-ray diffraction analysis indicated 62—65% crystallinity in cocoon silk fibroin from the silkworm, 50—63% in wild-type silkworm cocoons, and lesser amounts in spider silk (17). 

Textile fibers must be flexible to be useful. The flexural rigidity or stiffness of a fiber is defined as the couple required to bend the fiber to unit curvature (3). The stiffness of an ideal cylindrical rod is proportional to the square of the linear density. Because the linear density is proportional to the square of the diameter, stiffness increases in proportion to the fourth power of the filament diameter. In addition, the shape of the filament cross-section must be considered also. For textile purposes and when flexibiUty is requisite, shear and torsional stresses are relatively minor factors compared to tensile stresses. Techniques for measuring flexural rigidity of fibers have been given in the Hterature (67—73). 

In the manufacture of highly resident flexible foams and thermoset RIM elastomers, graft or polymer polyols are used. Graft polyols are dispersions of free-radical-polymerized mixtures of acrylonitrile and styrene partially grafted to a polyol. Polymer polyols are available from BASF, Dow, and Union Carbide. In situ polyaddition reaction of isocyanates with amines in a polyol substrate produces PHD (polyhamstoff dispersion) polyols, which are marketed by Bayer (21). In addition, blending of polyether polyols with diethanolamine, followed by reaction with TDI, also affords a urethane/urea dispersion. The polymer or PHD-type polyols increase the load bearing properties and stiffness of flexible foams. Interreactive dispersion polyols are also used in RIM appHcations where elastomers of high modulus, low thermal coefficient of expansion, and improved paintabiUty are needed. 

Surfa.cta.nt-TypeAntista.ts, Inherently conductive antistats have the advantage of not being dependent on atmospheric moisture to function. Thek drawbacks include expense, coloration of the plastic, and alteration of the mechanical properties of the plastic. The added stiffness caused by conductive fillers may not be a problem with a rigid container, but it can be a problem for a flexible bag. 

Fig. 4. The effect of blade loading on the wet-coating thickness in flexible blade coating where ( ) represents a less stiff blade (B) represents a stiffer...

Blends with styrenic block copolymers improve the flexibiUty of bitumens and asphalts. The block copolymer content of these blends is usually less than 20% even as Httie as 3% can make significant differences to the properties of asphalt (qv). The block copolymers make the products more flexible, especially at low temperatures, and increase their softening point. They generally decrease the penetration and reduce the tendency to flow at high service temperatures and they also increase the stiffness, tensile strength, ductility, and elastic recovery of the final products. Melt viscosities at processing temperatures remain relatively low so the materials are still easy to apply. As the polymer concentration is increased to about 5%, an interconnected polymer network is formed. At this point the nature of the mixture changes from an asphalt modified by a polymer to a polymer extended with an asphalt. 

Link-Suspended Basket Centrifuges In centrifuges with diameters larger than 762 mm (30 in), the basket, curb, curb cover, and drive form a rigid assembly flexibly suspended from three fixed posts (also known as a three-column centrifuge). The three suspension members may be either chain hnks or stiff rods in ball-and-socket joints and are spring-loaded. The suspended assembly has restrained freedom to oscillate to compensate for a normal out-of-balance condition. The drive is vertical with more efficient power transmission compared to the base-bearing type. 

Engineering design with polymers starts with stiffness. But strength is also important, sometimes overridingly so. A plastic chair need not be very stiff - it may be more comfortable if it is a bit flexible - but it must not collapse plastically, or fail in a brittle manner, when sat upon. There are numerous examples of the use of polymers (luggage, casings of appliances, interior components for automobiles) where strength, not stiffness, is the major consideration. 

The S -shaped flexible elements were required to keep the stiffness and stresses low, due to the relatively heavy rotor weight as evident by the finite element stress analysis shown in Figure 6-30. The wire EDM teehnology allows the produetion of sueh a damper deviee, whieh ean be easily designed with an offset to eompensate for the defleetion due to rotor weight. 

Critical speeds of a turbine operating below its first critical should be at least 20% above the operating speed range. The term commonly used for units operating below their first critical is that the unit has a stiff shaft, while units operating above their first critical are said to have a flexible shaft. There are many exciting frequencies that need to be considered in a turbine. Some of the sources that provide excitation in a turbine system are ... 

The previous section discussed the flexible shaft with rigid bearings. In the real world, the bearings are not rigid but possess some flexibility. If the flexibility of the system is given by Ki, then each support has a stiffness of Ki,/2. In such a system, the flexibility of the entire lateral system can be calculated by the following relationship ... 

It can be observed from the previous expression that when rigid support), then Lu t = lu or the natural frequency of the rigid system. For a system with a finite stiffness at the supports, or K/, = Kr, then lu is less than Lu t. Hence, flexibility causes the natural frequency of the system to be lowered. Plotting the natural frequency as a function of bearing stiffness on a log scale provides a graph as shown in Figure 5-15. 

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