High-stress

One aspect of pressure vessel design which has received considerable attention in recent years is the design of threaded closures where, due to the high stress concentration at the root of the first active thread, a fatigue crack may quickly initiate and propagate in the radial—circumferential plane. Stress intensity factors for this type of crack are difficult to compute (112,113), and more geometries need to be examined before the factors can be used with confidence. 

Cycloaliphatics. Synthesized cycloahphatics are generally not utilized as hydrauhc fluids. Cycloahphatics are synthesized for use as traction lubricants because, under high stress, they have high traction coefficients and excellent stabihty. A typical cycloahphatic used as a synthetic traction fluid is 2,3-dicydohexyl-2,3-dimethylbutane [5171 -88-0] ... 

A simple, low cost steel for high temperature service in electric power generation (qv) is the C—0.5% Mo steel known as carbon—half moly, which was widely used for many years. The power industry and oil refineries have turned to 1.25% Cr—0.5% Mo and 2.25% Cr—1% Mo steels for high stress and high temperature service, because these steels have improved resistance to graphitization and oxidation, as weU as higher creep and mpture strength. 

Frame-Mounted. For medium and severe appHcations, when nozzle loads and thermal transients tend to impose high stresses and internal deflections inside the pump, frame-mounted designs are used. Typically, these designs use conventional impellers, but recessed impeller designs are also available (Fig. 5). 

Calcium—Silicon. Calcium—silicon and calcium—barium—siUcon are made in the submerged-arc electric furnace by carbon reduction of lime, sihca rock, and barites. Commercial calcium—silicon contains 28—32% calcium, 60—65% siUcon, and 3% iron (max). Barium-bearing alloys contains 16—20% calcium, 9—12% barium, and 53—59% sihcon. Calcium can also be added as an ahoy containing 10—13% calcium, 14—18% barium, 19—21% aluminum, and 38—40% shicon These ahoys are used to deoxidize and degasify steel. They produce complex calcium shicate inclusions that are minimally harm fill to physical properties and prevent the formation of alumina-type inclusions, a principal source of fatigue failure in highly stressed ahoy steels. As a sulfide former, they promote random distribution of sulfides, thereby minimizing chain-type inclusions. In cast iron, they are used as an inoculant. 

Typically, ozone cracking initiates at sites of high stress (flaws) on the mbber surface. Thus, in general, mbber articles should be designed to rninirnize potential sites of high elongation such as raised lettering. Similarly, the use of clean molds helps to reduce the incidence of surface flaws. 

The performance of a tool material in a given appHcation is dictated by its response to conditions at the tool tip. High temperatures and stresses can cause blunting from the plastic deformation of the tool tip, whereas high stresses alone may lead to catastrophic fracture. In addition to plastic deformation and fracture, the service life of cutting tools is deterrnined by a number of wear processes, some of which are shown in Figure 2. 

The mechanism of subcritical crack growth is the reaction of the corrosive medium with highly stressed bonds at the crack tip. In siUca, in the absence of stressed bonds, the rate of the reaction between the bonds and corrosive media such as water is very low. The introduction of strain energy into crack tip bonds increases the activity of the bond. For siUca glass in water, attack and bond breakage occurs by the following reaction (47) ... 

If there is particle—particle interaction, as is the case for flocculated systems, the viscosity is higher than in the absence of flocculation. Furthermore, a flocculated dispersion is shear thinning and possibly thixotropic because the floccules break down to the individual particles when shear stress is appHed. Considered in terms of the Mooney equation, at low shear rates in a flocculated system some continuous phase is trapped between the particles in the floccules. This effectively increases the internal phase volume and hence the viscosity of the system. Under sufficiently high stress, the floccules break up, reducing the effective internal phase volume and the viscosity. If, as is commonly the case, the extent of floccule separation increases with shearing time, the system is thixotropic as well as shear thinning. 

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