PlasticsPlastics are usually produced by synthesis from natural materials as water, air, salt, coal and natural gas. The technology is simple and cheap. While … (solid, cheap, uniform) in finished state, plastics are liquid at some stage of manufacture, and it is easy to form plastics into various shapes. Plastics are different in … (hardness, properties, needs), characteristics and … (pressure, application, thermosets). Plastics are … (reliable, available, thermoplastics)... (expensive, cheap, structural), durable. Plastics resist … (weight, strength, corrosion). Plastics are machined like … (metals, forgings, carbon). Their … (lightness, high weight, colour), strengths, hardness, chemical resistance and... (colour, durability, application) make it possible to use plastics in electric and electronic equipment, transportation, agriculture, etc. The application of plastics is... (achieving, satisfying, calling for) the requirements of all industries. There is no industry now where plastics are not used.
I. Reading Activity and Speech Practice
I .1 Discuss with your friends the following questions. 1. What are “composite materials”? 2. Where are they usually used? 3. Do they have a different chemical composition than plastics? 4. Which materials are more widely used today: plastics or composite materials? Why? 5. Plastics or composites will become the main engineering material in future to your mind?
III.2 Find the corresponding pairs in the table. Put down them in your copybooks.
III.3 Read the text; translate it into Russian; get ready to discuss it in details. Text A: Composite Materials. The combination of two or more different materials is called composite materials. They usually have unique mechanical and physical properties because they combine the best properties of different materials. For example, a fibre-glass reinforced plastic combines the high strength of thin glass fibres with the ductility and chemical resistance of plastic. Nowadays composites are being used for structures such as bridges, boat-building, etc. Composite materials usually consist of synthetic fibres within a matrix, a material that surrounds and is tightly bound to the fibres. The most widely used type of composite material is polymer matrix composites (PMCs). PMCs consist of fibres made of ceramic material such as carbon or glass embedded in a plastic matrix. Usually the fibres make up about 60% by volume. Composites with metal matrices or ceramic matrices are called metal matrix composites (MMCs) and ceramic matrix composites (CMCs), respectively. Continuous-fibre composites are generally required for structural applications. The specific strength (strength-to-density ratio) and specific stiffness (elastic modulus ratio) of continuous carbon fibre PMCs, for example, can be better than metal alloys have. Composites can also have other attractive properties, such as high thermal or electric conductivity and a low coefficient of thermal expansion. Although composite materials have certain advantages over conventional materials, composites also have some disadvantages. For example, PMCs and other composite materials tend to be highly anisotropic- that is, their strength, stiffness, and other engineering properties are different depending on the orientation of the composite material. For example, if PMC is fabricated so that all the fibres are lined up parallel to one another, then PMC will be very stiff in the direction parallel to the fibres, but not stiff in the perpendicular direction. The designer, who uses composite materials in structures subjected to multidirectional forces, must take into account these anisotropic properties. Also, forming strong connections between separate composite material components is difficult. The advanced composites have high manufacturing costs. Fabricating composite materials is a complex process. However, new manufacturing techniques are developed. It will become possible to produce composite materials at higher volumes and at lower cost than is now possible, accelerating the wider exploitation of these materials.
III.3 Answer the questions to the text. Give full answers using arguments from the text. 1. What is called “composite materials”? 2. What are the best properties of fibre-glass? 3. What do composite materials usually consist of? 4. What is used as matrix in composites? 5. What is used as filler or fibres in composites? 6. What are the main advantages of composite materials? 7. Do they have any disadvantages? 8. Are their anisotropic properties an advantage or disadvantage?
III.4 Make a list of advantages and disadvantages of composite materials. Advantages: Disadvantages:
|
Section II
