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Module-1: General Introduction M1: General Introduction M1.1 Introduction of Composites Historical Development / Historical overview: Past: After making and controlling fire and inventing the wheel, spinning of continuous yarns is probably the most important development of mankind, enabling him to survive outside the tropical climate zones and spread across the surface of the Earth. Flexible fabrics made of locally grown and spun fibres as cotton; flax and jute were a big step forward compared t
  Module-1: General IntroductionM1: General IntroductionM1.1 Introduction of Composites Historical Development / Historical overview:Past: After making and controlling fire and inventing the wheel, spinning of continuous yarns isprobably the most important development of mankind, enabling him to survive outside thetropical climate zones and spread across the surface of the Earth. Flexible fabrics made of locallygrown and spun fibres as cotton; flax and jute were a big step forward compared to animal skins.More and more natural resources were used, soon resulting in the first composites; strawreinforced walls, and bows (Figure M1.1.1 (a)) and chariots made of glued layers of wood, boneand horn. More durable materials as wood and metal soon replaced these antique composites. Figure M1.1.1 (a): Composite Korean bowPresent: Originating from early agricultural societies and being almost forgotten after centuries, a truerevival started of using lightweight composite structures for many technical solutions during thesecond half of the 20th century. After being solely used for their electromagnetic properties(insulators and radar-domes), using composites to improve the structural performance of spacecraft and military aircraft became popular in the last two decades of the previous century.First at any costs, with development of improved materials with increasing costs, nowadays costreduction during manufacturing and operation are the main technology drivers. Latestdevelopment is the use of composites to protect man against fire and impact (Figure M1.1.1 (b))and a tendency to a more environmental friendly design, leading to the reintroduction of naturalfibres in the composite technology, see Figure M1.1.1 (c). Increasingly nowadays, the success of composites in applications, by volume and by numbers, can be ranked by accessibility and  reproducibility of the applied manufacturing techniques. Some examples of use of natural fibersare shown in Figure M1.1.1 (d) and Figure M1.1.1 (e). Future: In future, composites will be manufactured even more according to an integrated design processresulting in the optimum construction according to parameters such as shape, mass, strength,stiffness, durability, costs, etc. Newly developed design tools must be able to instantaneouslyshow customers the influence of a design change on each one of these parameters. Concept of Composite:  Fibers or particles embedded in matrix of another material are the best example of modern-daycomposite materials, which are mostly structural. Laminates are composite material where different layers of materials give them the specificcharacter of a composite material having a specific function to perform. Fabrics have no matrixto fall back on, but in them, fibers of different compositions combine to give them a specificcharacter. Reinforcing   materials generally withstand maximum load and serve the desirableproperties.Further, though composite types are often distinguishable from one another, no cleardetermination can be really made. To facilitate definition, the accent is often shifted to the levelsat which differentiation take place viz., microscopic or macroscopic .In matrix -based structural composites, the matrix serves two paramount purposes viz., bindingthe reinforcement phases in place and deforming to distribute the stresses among theconstituent reinforcement materials under an applied force.The demands on matrices are many. They may need to temperature variations, be conductors orresistors of electricity, have moisture sensitivity etc. This may offer weight advantages, ease of handling and other merits which may also become applicable depending on the purpose forwhich matrices are chosen.Solids that accommodate stress to incorporate other constituents provide strong bonds for thereinforcing phase are potential matrix materials . A few inorganic materials, polymers andmetals have found applications as matrix materials in the designing of structural composites,with commendable success. These materials remain elastic till failure occurs and show decreasedfailure strain, when loaded in tension and compression.Composites cannot be made from constituents with divergent linear expansion characteristics.The interface is the area of contact between the reinforcement and the matrix materials. In somecases, the region is a distinct added phase. Whenever there is interphase , there has to be twointerphases between each side of the interphase and its adjoint constituent . Some compositesprovide interphases when surfaces dissimilar constituents interact with each other. Choice of fabrication method depends on matrix properties and the effect of matrix on properties of reinforcements. One of the prime considerations in the selection and fabrication of composites isthat the constituents should be chemically inert non-reactive. Figure M1.1.1 (f) helps to classifymatrices.    Figure M1.1 (f): Classification of Matrix Materials M1.2 Basic Definitions and Classifications of Composites M1.2.1 Classification of Composites Composite materials are commonly classified at following two distinct levels: ã   The first level of classification is usually made with respect to the matrix constituent. Themajor composite classes include Organic Matrix Composites (OMCs), Metal MatrixComposites (MMCs) and Ceramic Matrix Composites (CMCs). The term organic matrixcomposite is generally assumed to include two classes of composites, namely PolymerMatrix Composites (PMCs) and carbon matrix composites commonly referred to as carbon-carbon composites. ã   The second level of classification refers to the reinforcement form - fibre reinforcedcomposites , laminar composites and particulate composites . Fibre Reinforced composites(FRP) can be further divided into those containing discontinuous or continuous fibres. ã   Fibre Reinforced Composites are composed of fibres embedded in matrix material. Such acomposite is considered to be a discontinuous fibre or short fibre composite if its propertiesvary with fibre length. On the other hand, when the length of the fibre is such that any furtherincrease in length does not further increase, the elastic modulus of the composite, thecomposite is considered to be continuous fibre reinforced. Fibres are small in diameter andwhen pushed axially, they bend easily although they have very good tensile properties. Thesefibres must be supported to keep individual fibres from bending and buckling. ã   Laminar Composites are composed of layers of materials held together by matrix.Sandwich structures fall under this category. ã   Particulate Composites are composed of particles distributed or embedded in a matrix body.The particles may be flakes or in powder form. Concrete and wood particle boards areexamples of this category. M1.2.2 Organic Matrix Composites
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