Embedded area

Fig. 9.10 Plots of piullont force versus embedded area for (a) untreated ramie fiber (b) untreated kenaf fiber and (c) cOTresponding IFSS for both. Reproduced with the kind permissirai of the publishers of [39]...

In Fig. 9.10a, b, the critical embedded area was obtained by intersection of two linear regression lines one associated with the fiber pullout, whereas the other with the fiber fracture linear regression line. The corresponding IFSS were given as par plots, Fig. 9.10c, from which apparently values of 15.7 MPa for ramie fiber/epoxy and 9.7 MPa for kenaf fiber/epoxy may be found. 

These equations are taken by Watstien and Parsons. In Fig. 8.9a the embedment area Ab = abed = 2d b when under direct tension having a large depth D, consisting of two flanges each of area Ab = Id b as shown in Fig. 8.9c ... 

When the bars are fairly uniformly distributed over the embedment area. Brice suggests that the area Ab may be assumed to be made up of as many square areas as the number of bars with the bar embedded in the centre of each of these elemental areas. 

Ab =embedment area of concrete Act =area of concrete in tension zone... 

To limit the crack to 0.3 mm 3 no. GK60+ bars l ( ) are required in the embedded area on the tension side. Usually in RC structures, hair eraek size permissible with ordinary reinforcement having tensile strength of 20,000 psi is 0.15 mm. With the type of reinforcement provided in p.v and with the size of structure like pressure vessel, crack size at working permissible is assumed to be 0.3 mm. Therefore where greater tension in concrete is to be expected on the outside surface or haunches, the minimum number of bars <3. 

Taking 12 x 240 embedded area across the barrel thickness (excluding shutters)... 

In the final section, we will survey the different theoretical approaches for the treatment of adsorbed molecules on surfaces, taking the chemisorption on transition metal surfaces, a particularly difficult to treat yet extremely relevant surface problem [1], as an example. Wliile solid state approaches such as DFT are often used, hybrid methods are also advantageous. Of particular importance in this area is the idea of embedding, where a small cluster of surface atoms around the adsorbate is treated with more care than the surroundmg region. The advantages and disadvantages of the approaches are discussed. 

Computational solid-state physics and chemistry are vibrant areas of research. The all-electron methods for high-accuracy electronic stnicture calculations mentioned in section B3.2.3.2 are in active development, and with PAW, an efficient new all-electron method has recently been introduced. Ever more powerfiil computers enable more detailed predictions on systems of increasing size. At the same time, new, more complex materials require methods that are able to describe their large unit cells and diverse atomic make-up. Here, the new orbital-free DFT method may lead the way. More powerful teclmiques are also necessary for the accurate treatment of surfaces and their interaction with atoms and, possibly complex, molecules. Combined with recent progress in embedding theory, these developments make possible increasingly sophisticated predictions of the quantum structural properties of solids and solid surfaces. 

Surfaces exposed to water contained many localized areas of wastage (Fig. 6.22). Corroded areas were covered by brittle black or brown caps over irregular metal-loss regions. Many small fibers were embedded in corrosion products, and many more were wrapped around surfaces. Most fibers were about 0.001 in. (0.003 cm) in diameter and were hollow. 

Most of the surface is covered with a black corrosion product that is thicker in relatively low-flow areas near the hub. This layer of soft corrosion product can be shaved from corroded surfaces. Microstructural examinations revealed flakes of graphite embedded in iron oxide near the surfaces. 

As an example, a tank farm that is to be cathodically protected by this method is shown schematically in Fig. 11-4. As can be seen in the figure, injection of the protection current occurs with two current circuits of a total of about 9 A, via 16 vertically installed high-silicon iron anodes embedded in coke. These are distributed over several locations in the tank farm to achieve an approximately uniform potential drop. The details of the transformer-rectifier as well as the individual anode currents are included in Fig. 11-4. Anodes 4, 5 and 6 have been placed at areas where corrosion damage previously occurred. Since off potentials for 7/ -free potential measurements cannot be used, external measuring probes should be installed for accurate assessment (see Section 3.3.3.2 and Chapter 12). 

With damage of a large area, the concrete is removed down to the uppermost layer of the reinforcement then the first layer of sprayed concrete is applied (see Fig. 19-3a). The anode is fixed to this layer and is followed by a second layer of sprayed concrete. With large areas of old concrete which are still solid, the anodes can be attached to this and finally embedded with sprayed concrete (see Fig. 19-3b). The anodes must supply the required protection current and be structurally robust. The bond between the old concrete and sprayed concrete must not be damaged during the spraying process or in operation. 

The interiors of rhodopseudomonad bacteria are filled with photosynthetic vesicles, which are hollow, membrane-enveloped spheres. The photosynthetic reaction centers are embedded in the membrane of these vesicles. One end of the protein complex faces the Inside of the vesicle, which is known as the periplasmic side the other end faces the cytoplasm of the cell. Around each reaction center there are about 100 small membrane proteins, the antenna pigment protein molecules, which will be described later in this chapter. Each of these contains several bound chlorophyll molecules that catch photons over a wide area and funnel them to the reaction center. By this arrangement the reaction center can utilize about 300 times more photons than those that directly strike the special pair of chlorophyll molecules at the heart of the reaction center. 

Leach or extraction testing undertaken on anhydrous salts embedded in bitumen as a matrix indicates that rehydration of the embedded compound can occur. When the sample is soaked in water, the asphalt or bitumen can swell and split apart, thereby greatly increasing the surface area and rate of waste loss. 

Nail sickness Nail sickness is chemical decay associated with corroded metals in marine situations. Chemical degradation of wood by the products of metal corrosion is brought about by bad workmanship or maintenance, or unsuitable (permeable) timber species, all of which permit electrolyte and oxygen access which promotes corrosion. Chemical decay of wood by alkali occurs in cathodic areas (metal exposed oxygen present). Softening and embrittlement of wood occurs in anodic areas (metal embedded oxygen absent) caused by mineral acid from hydrolysis of soluble iron corrosion products. 

In reality, around an inclusion embedded in a matrix a rather complex situation develops, consisting of areas of imperfect bonding, permanent stresses due to shrinkage, high stress-gradients or even stress-singularities, due to the geometry of the inclusions, voids, microcracks etc. 

---