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 per cent 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-to-density 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 electrical 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 proper ties are different depending on the orientation of the composite material. For example, if a PMC is fabricated so that all the fibres are lined up parallel to one another, then the 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 these anisotropic properties into account. 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 a lower cost than is now possible, accelerating the wider exploitation of these materials.

Assignments:

I. General understanding. Answer the questions:

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 filler or fibers in composites?

5. How are the composite materials with ceramic metal matrices called?

6. What are the advantages / disadvantages of composites?

7. Why should anisotropic properties of composites be taken into account?

II. Find the equivalents in the text:

Композитные материалы; параллельно друг другу; уникальные механические свойства; полимерные матричные композиты; составлять 60% объёма; углепластик; волокна; привлекательные качества; структура; подвергающиеся воздействию разнонаправленных сил.

III. Match a word in A with a word in B to fill the gaps in sentences 1-6.

1. A plastic is a type of synthetic or __________ _________.

2. Polymers can be moulded into various shapes or drawn into filaments that can be used as ___________ ___________.

3. Additives are added to improve the mechanical, physical, or __________ ________.

4. Products which have an __________ _________ of more than three years are known as durables.

5. __________ _________ that are used to treat or monitor patients are non-durables and are not expected to last longer than three years.

6. PET is clear, rough, and a good barrier to gas and moisture, so supermarkets find it ideal for __________ __________.

IV. In the supermarket, why is food wrapped in clear packaging?

1) Read the text and check your answer.

Green and Intelligent

Food shopping is changing and so too is the way food is wrapped for sale. Clear plastic wrapping allows the consumer to see the state of the food inside at the same time as preventing contamination from dust and bacteria. But now supermarkets are looking at new types of packaging.

Some supermarkets have decided to wrap their fresh fruit and vegetables in biodegradable plastic packaging instead of conventional plastic. Biodegradable plastic or bioplastics can be made from plant-based materials such as starch from corn, wheat, potatoes. In the environment, micro-organisms are able to break down these plastics easily and quickly to produce carbon dioxide and water. Biodegradable plastics can also be made by some bacteria that are capable of producing granules of plastic (PHA / PHB) in their cells. Biodegradable plastic packaging can be composted and allows customers to dispose of their own waste at home.

Active packaging is a new development that can interact with the product to improve it or provide the consumer with information about the freshness of the product. An American company has developed a label that indicates the temperature a package has been stored at. A chemical in the label polymerizes and becomes darker in color if the temperature rises.

Another company has developed a membrane wrapper which changes its permeability to oxygen and carbon dioxide as the temperature changes so that the best O₂ / CO₂ balance can be achieved inside the packaging.

2) Complete the table with the different packaging technologies mentioned and their advantages:

3) What effect do you think these new technologies will have on the environment? / the plastics industry? / the consumer?

V. 1) Information for curious ones. Read some interesting facts about the use of plastics in the automotive industry:

Reduced Weight:

The average new car in 1984 contained 8.5% plastics by weight. A similar car today contains around 11%. The increased use of plastics reduces the weight of vehicles and consequently emissions. The weight reductions brought about though the increased use of plastics has also offset the extra weight brought about by improved safety features such as airbags.

Energy Saving:

Using 100 kg of plastics in a car can replace between 200 – 300 kg of traditional materials. Over the average lifespan of a vehicle every 100 kg of plastics will reduce fuel consumption of the vehicle by 750 litres.

Comfort, Safety and Aesthetics:

Plastics are essential in the manufacture of many car parts. Plastics are used in air bags, seats, seat covers, insulation, electrics, under bonnet applications. The use of plastics also provides many aesthetic benefits both in the shapes and colors available.

Innovations:

The automotive sector is very dynamic in terms of research and development, and innovation. Automotive manufactures are always looking for ways to reduce weight and improve efficiency, and plastics provide great opportunities to reach these goals. In the future carbon-fibre is likely to play an important role in replacing traditional materials and could potentially reduce the weight of cars by a half.

www.bpf.co.uk

2) With a partner render this information in the form of an interview.

UNIT 5

Natural Fibers

Read the text:

Fibers

Fibers are probably the oldest engineering materials used by man. Jute, flax, and hemp have been used for “engineered” products such as rope, cordage, nets, water hose, and containers since antiquity. Other plant and animal fibers have been used for felts, paper, brushes, and heavy structural cloth.

The fiber industry is clearly divided between natural fibers (from plant, animal, or mineral resources) and synthetic fibers. Many synthetic fibers have been developed specifically to replace natural fibers, because synthetics often behave more predictably and are usually more uniform in size.

For engineering purposes, glass, metallic, and organically derived synthetic fibers are most significant. Nylon, for example, is used for belting, nets, hose, rope, parachutes, webbing, ballistic cloths, and as reinforcement in tyres.

Metal fibers are used in high strength, high temperature, light-weight composite materials for aerospace applications. Fiber composites improve the strength-to-weight ratio of base materials such as titanium and aluminium. Metal-fiber composites are used in turbine compressor blades, heavy duty bearings, pressure vessels and spacecraft re-entry shields. Boron, carbon, graphite, and refractory oxide fibers are common materials used in high-strength fiber composites.

Glass fibers are probably the most common of all synthetic engineering fibers. These fibers are the finest of all fibers. Glass fibers are used for heat, sound, and electrical insulation; filters; reinforcement for thermoplastics and thermoset resins and for rubber (such as in tyres); fabrics, and fiber optics.

Assignments:

I. General understanding. Answer the questions:

1. Which two types are fibers divided into?

2. What purpose were synthetic fibers developed for?

3. What types are synthetic fibers divided into?

4. What are the uses of glass, metallic and organically derived synthetic fibers?

II. Find synonyms to the following words in the text:

Aim; to displace; as a rule; important; make better; normal; strengthening; general; artificial; perhaps; thin; distinctly; use; foundation.

III. Find antonyms to the following words in the text:

The youngest; the present; low; natural; make worse; unimportant; synthetic; heavy; specific; light.

IV. Fill in the table using the information from the text:

V. Render the text in English:

Пластмассы в музее

Всем известна неприятная особенность пластиковой упаковки: она очень устойчива и медленно разлагается в окружающей среде. Однако есть случаи, когда можно только сожалеть о том, что и пластмассы все же не вечны. Речь идет о сохранности музейных экспонатов, выполненных из пластиков. Вполне возможно, что до потомков не дойдут не только произведения искусства, выполненные из полимеров или из материалов на их основе (например, кинофильмы, грампластинки), но и повседневные предметы обихода, способные рассказать людям будущего о жизни наших современников.

Недавно проведенная ревизия лондонских музеев показала, что примерно один из каждых восьми пластиковых экспонатов несёт признаки разрушения – трещины, выцветание, деформации. В Национальном музее искусства и дизайна насчитали более 8000 предметов из пластмасс, в основном это детские игры, игрушки и куклы, предметы одежды и обуви, полимерные детали мебели и ювелирных украшений. Хотя в этих изделиях стали широко применять лишь 80 лет назад, 15% из них уже находятся в плохом или катастрофическом состоянии. Еще 17% несут признаки химических изменений: более половины из них стали хрупкими, 20% утратили окраску.

Разрушение полимеров, как правило, необратимо. Зачастую оно начинается с выпотевания на поверхность пластмассовых изделий добавок, придающих полимерам пластичность, - глицерина, фталатов и других пластификаторов. К выступившей маслянистой жидкости прилипает грязь, удаляемая с трудом. После этого под действием атмосферного кислорода, света (особенно ультрафиолетового), различных загрязнений воздуха материал начинает терять окраску и трескаться.

Некоторые полимеры при разрушении выделяют опасные вещества. Так, ацетилцеллюлоза (материал кинопленки) при старении выделяет уксусную кислоту, разъедающую сам экспонат и окружающие предметы. Целлулоид – старейшая пластмасса, изобретенная в 60-х годах XIX века для замены слоновой кости в бильярдных шарах, - выделяет азотную кислоту.

В 2008 году восемь стран Европейского союза начали дорогостоящую программу по изучению проблемы. Участвующие в ней музеи, университеты и правительственные учреждения намерены исследовать причины разрушения полимеров, разработать способы хранения, чистки и реставрации пластмассовых экспонатов, а также неразрушающие методы анализа пластмасс.

«Наука и жизнь»

Use the words and phrases given below:

Медленно разлагаться в окружающей среде - decompose slowly in the environment; сохранность музейных экспонатов – museum exhibits safety; потомок – descendant; выцветание - bleaching; необратимо – irreversibly; выпотевание – dewetting; глицерин – glycerol; выделять опасные вещества - extract hazardous substance; ацетилцеллюлоза - acetyl cellulose; уксусная кислота - acetic acid; азотная кислота - nitric acid; изучение проблемы - case study; разработать способы хранения, чистки и реставрации - work out the ways of keeping, cleaning and restoration.

VI. 1) How could you comment upon this statement?

“The world’s annual consumption of plastic materials has increased from around 5 million tonnes in the early 1950s to nearly 100 million tonnes today”.

Technology 2, Eric H Glendinning and Alison Pohl

2) Make a brief class discussion on the topic “Plastics’ consumption and application”. Reporters should prepare short presentations about plastics. Don’t forget about a presentation structure (Part I Unit 6) and clichés (Appendix 2).

Date: 2015-12-12; view: 1986; Нарушение авторских прав