Engineering components

Similar exercises must be performed to identify synthetic nanocomponents. Considerations include suitability for the proposed environment, synthesis and handling properties, polydispersity, structural / chemical properties, as well as amenability to assembly into higher order structures. For medical devices, tolerability and safety of the structural materials is also an issue. Current materials technology offers powerful, but limited capacity to engineer an off the shelf approach to nanostructures. 

After device construction, structural and functional analysis are critical. One might argue that only the second issue matters, but structural data often give insights into why devices perform suboptimally, and provide important clues about how to improve device function. We routinely use protein analytics (matrix-assisted laser desorption-ionization mass spectroscopy, amino acid composition analysis, gel electrophoresis, Western blotting, circular dichroism, vari- 

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Fatigue. Engineering components often experience repeated cycles of load or deflection during their service fives. Under repetitive loading most metallic materials fracture at stresses well below their ultimate tensile strengths, by a process known as fatigue. The actual lifetime of the part depends on service conditions, eg, magnitude of stress or strain, temperature, environment, surface condition of the part, as well as on the microstmcture. 

Chemically Functional. Refractory coatings are used for corrosion-resistant high temperature service in gas turbine and diesel engines, components such as cmcibles, thermocouple protection tubing, valve parts, etc. 

These coatings are also employed as soHd lubricants in engine components. Refractory materials such as M0S2 and WSe2 are lamellar compounds and provide very effective soHd-state lubrication in spacecraft bearings and components used in radiation environments where conventional organic Hquid lubricants are not stable (see Lubrication and lubricants). 

High Temperature. The low coefficient of thermal expansion and high thermal conductivity of sihcon carbide bestow it with excellent thermal shock resistance. Combined with its outstanding corrosion resistance, it is used in heat-transfer components such as recuperator tubes, and furnace components such as thermocouple protection tubes, cmcibles, and burner components. Sihcon carbide is being used for prototype automotive gas turbine engine components such as transition ducts, combustor baffles, and pilot combustor support (145). It is also being used in the fabrication of rotors, vanes, vortex, and combustor. 

Carbon steel heat exchangers, cast iron water boxes, screens, pump components, service water system piping, standpipes, fire protection systems, galvanized steel, engine components, and virtually all non-stainless ferrous components are subject to significant corrosion in oxygenated water. 

The air/fuel ratio can be varied, usually in the range 0.8 (rich) to 1.1 (lean), and a typical limit of the compression ratio is set at about 10 1 by the tendency of the engine to knock at higher ratios, leading to severe mechanical stresses in the engine components. 

Figure 4.21 Typical load histories for engineering components/systems...

The first and most important steps in the design process are to define clearly the purpose and function of the proposed product and to identify the service environment. Then one has to assess the suitability of a range of candidate materials. The following are generally regarded as the most important characteristics requiring consideration for most engineering components. 

The previous section has considered the in-plane deformations of a single ply. In practice, real engineering components are likely to be subjected to this type of loading plus (or as an alternative) bending deformations. It is convenient at this stage to consider the flexural loading of a single ply because this will develop the method of solution for multi-ply laminates. 

Using iodine as their starting point, they experimented with a series of compounds including the anilines and a series of metals near the bottom of the periodic table. Lead turned out to be the most effective of the additives tested. But lead alone caused a number of problems, including the accumulation of Its oxide in engine components, and particularly the cylinders, valves, and spark plugs. 

This type of damage is dealt with comprehensively in Section 8.8. It can be particularly severe in seawater giving rise to cavitation corrosion or cavitation erosion mechanisms, and hence can be a considerable problem in marine and offshore engineering. Components that may suffer in this way include the suction faces of propellers, the suction areas of pump impellers and casings, diffusers, shaft brackets, rudders and diesel-engine cylinder liners. There is also evidence that cavitation conditions can develop in seawater, drilling mud and produced oil/gas waterlines with turbulent high rates of flow. 

Tin-lead can be substituted for tin for other purposes, although the toxicity of lead limits the field of application. The corrosion resistance is usually no better than that of unalloyed tin, but there may be some saving of cost in applications such as wash-boilers and other vessels for non-potable liquids and light engineering components formed from sheet metal. Heavily coated terne-plates may be used for the fuel tanks of stoves and vehicles. 

The CRC-Elsevier materials selector , 2nd edition, N.A. Waterman, and M.E Ashby CRC Press (1996) ISBN 0412615509. (Now, also available on CD-ROM). Basic reference work. Three-volume compilation of data for all materials includes selection and design guide. The Materials Selector is the most comprehensive and up-to-date comparative information system on engineering materials and related methods of component manufacture. It contains information on the properties, performance and processability of metals, plastics, ceramics, composites, surface treatments and the characteristics and comparative economics of the manufacturing routes which convert these materials into engineering components and products. 

High-temperature gas-turbine components. Diesel-engine components. 

Most metals and many refractory compounds can be thermal-sprayed. Applications include coating of gas-turbine components for aircraft and industrial use, components of steam turbines and diesel engines, components for the oil and gas industry, paper and pulp industry, and chemical processing industry. 

Hessel, V., Lowe, H., Micro chemical engineering components - plant concepts -user acceptance Part III, Chem. Eng. Technol. 26, 5 (2003) 531-544. 

HESSELy.howEll., Microchemical engineering components—plantconcepts— useracceptance.Partll, Chem.Eng. Tedmol. 26,4 ( 2003)391 08. 

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