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Saturday, January 3, 2015

Materials in Aerospace Engineering - 1

Working of materials
Structures used in aerospace are made out of metals and alloys that are cut, shaped, bored, bent, and formed by tools and machines operated manually or, increasingly, under the control of CNC machines to provide greater precision than can normally be provided by humans.
For avionics, electrical and electronic fabrication are done by robots for insertion of components into circuit boards, wave soldering (an automated process for securing components to circuit boards with a standing wave of molten solder) for rapid, uniform connections, and photolithography (photographic transfer of a pattern to a surface for etching) for making circuit boards and multichip modules.
The fabrication method and safety controls depend upon the materials used. For example, beryllium, whose combination of light weight, high strength, and high melting point makes it a valuable structural material, yields dust and chips during machining. Because exposure to beryllium particles can cause adverse health effects, special care is required to preclude their contamination of personnel or atmosphere. Polymer-matrix composites also require special contamination protection because of the toxic character of the resins involved.
Many of the structures in aerospace need to bear high loads yet be as light as possible. Aerospace engineers have developed techniques for modifying the characteristics of a material. The most notable example is the so-called honeycomb sandwich, which is far lighter than a metal plate of comparable thickness and has greater resistance to bending. The sandwich consists of a honeycomb core, composed of rows of hollow hexagonal cells, bonded between extremely thin metal face sheets. Aluminium is the most extensively used metal in both core and face sheets, but the technique is applicable to a large variety of metallic and non-metallic materials. Sandwich construction is now employed to some degree in almost every type of flight vehicle.
Polymer composites are used extensively in the aerospace industry for their stiffness, lightness, and heat resistance.They are fabricated materials in which carbon or hydrocarbon fibres (and sometimes metallic strands, filaments, or particles) are bonded together by polymer resins in either sheet or fibre-wound form. In the former, individual sheet elements are layered in metal, wood, or plastic moulds and joined with adhesives. Applications for sheet composites include wing skins and fuselage bulkheads in aircraft and the underlying support for solar arrays in satellites. In fibre-wound forms, tubular or spherical shapes are fabricated by winding continuous fibre on a spinning mould with high-speed, computer-programmed precision, injecting liquid resin as the part is formed, and then curing the resin. This process is used for forming rocket motor casings; spherical containers for fuels, lubricants, and gases; and ducts for aircraft environmental systems.

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This topic will continue in Part - 2

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