Stiffeners types

Lugs are an improvement of the ear type by the addition of an element to provide lateral stiffening which also serves to improve load-carrying capacity and lateral strength. In high temperature services, unless heavily insulated, lugs are susceptible to distortion. 

Valve Problems. The primary solution to valve problems has been implantable replacement valves. The introduction of these devices necessitates open-heart surgery. There are two types of valves available tissue (porcine and bovine) and mechanical. The disadvantage of tissue valves is that these have a limited life of about seven years before they calcify, stiffen, and have to be replaced. The mechanical valves can last a lifetime, but require anticoagulant therapy. In some patients, anticoagulants may not be feasible or may be contraindicated. Of the valves which require replacement, 99% are mitral and aortic valves. The valves on the left side of the heart are under much greater pressure because the left ventricle is pumping blood out to the entire body, instead of only to the lungs. Occasionally, two valves are replaced in the same procedure. 

Determine the bounds on E for a dispersion-stiffened composite material of more than two constituents, i.e., more than one type of particle is dispersed in a matrix material. 

We usually must go beyond the simple concept of a monocoque or single-thickness skin for whatever structure we design. That is, we must usually consider the bending stiffness, and, to achieve structural efficiency, we often must stiffen a structure in some manner. We will first address the terminology of stiffening and how it is used. Then, we will consider the types of stiffeners that could be used. Next, an important issue that arises in the design of stiffeners is whether the stiffener has an open- or a closed-cross section. Then, we will address some of the... 

Figure 7-26 Metal Versus Composite Stiffener Characteristics 7.4.2.2 Types of Stiffeners...

Most of what has been described so far for stiffener design involves shape and size of the stiffener. Those issues involve selection of the type of stiffener, H-shaped cross section, blade, hat-shaped, etc. as well as the specific dimensions and material makeup of each stiffener element. Other obvious factors in the design of a stiffener include how far apart we space them, at what orientation we place them, and, perhaps most obviously in connection with what we addressed in Section 7.3, out of what material we make the elements. As you saw in some of the previous sketches for stiffeners, we are able with a composite stiffener to use different materials in different places very easily and to essentially optimize our materials usage so that the stiffening comes out to be as good as we can possibly make it. 

A hard-and-fast rule to be followed by all intending to use plastics is to design for plastics. As an example, for the same-size cross-section the strength of conventional plastics (not the high-performance reinforced types) is considerably less than that of most metals. The designer will thus find it necessary to increase thickness, introduce stiffening webs, and/or possibly use design inserts of various types of threads to secure the proposed product. The process will in some instances also require modification to the shape of the equipment used to produce the product. 

Another type of gel expands and contracts as its structure changes in response to electrical signals and is being investigated for use in artificial limbs that would respond and feel like real ones. One material being studied for use in artificial muscle contains a mixture of polymers, silicone oil (a polymer with a (O—Si—O—Si—) — backbone and hydrocarbon side chains), and salts. When exposed to an electric field, the molecules of the soft gel rearrange themselves so that the material contracts and stiffens. If struck, the stiffened material can break but, on softening, the gel is reformed. The transition between gel and solid state is therefore reversible. 

The width of the support ring for sectional plates will normally be 50 to 75 mm the support ring should not extend into the downcomer area. A strip of unperforated plate will be left round the edge of cartridge-type trays to stiffen the plate. 

In one of several important studies on dendronized polymers [4c, 4d]. Schluter and coworkers explored the stiffening of polystyrene chains through the incorporation of Frechet-type dendrons as side chains [28, 29]. While the G-l and G-2 dendrons were not sufficiently bulky to effectively stiffen the polystyrene chain, the G-3 dendron provides enough steric bulk to force the hybrid polymer into adopting a cylindrical shape in solution [28b], In a complementary study, Neubert and Schluter demonstrated that adding charges to the dendritic wedges leads to an expansion of the chains of the hybrid copolymer in aqueous solution [29],... 

Type IV reactions are due to chemicals added during manufacture of NRL, which include accelerators, antioxidants, antiozo-nants, emulsifiers, stabilizers, extenders, colorants, retarders, stiffeners, and biocides. Accelerators primarily control the rate, uniformity, and completeness of vulcanization. The most common accelerators include thiurams, carbamates, and mercaptobenzothiazoles. These chemicals are covered in detail in their specific monographs in this volume. 

Most admixtures of this type do not significantly alter the rheology of cement pastes at early ages. The quicker stiffening of accelerated pastes will, of course, result in higher viscosities at a later age. More complex formulations occasionally include water-reducing admixtures to reduce the water-cement ratio, and their effect will be a function of the water-reducing admixture type and content (see Section 1.3.1). 

Accelerating admixture type Stiffening time (h) for penetration resistance of 0.5 N mm- 3.5 N mm-2... 

Another type of supramolecular interaction of DNA is the intercalation of fused aromatic compounds into the stacked base pairs in double-stranded DNA (see Figure 6). Intercalation induces not only dehydration from the polar groups in intercalator but also concomitant unwinding, lengthening, dehydration, and stiffening of the DNA double helix. 

---