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In fibreglass, the reinforcement is provided by fine cl mg or fibres of glass, often woven into a sort of cloth, and the matrix is a cl mg. The threads of glass in fibreglass are very strong under tension but they are also ng and will snap if cl mg sharply.

The matrix not only holds the fibres together, it also protects them from damage by по этому сообщению any stress GLOSSARY stressForce per unit area. It is measured in the same units as pressure, namely pascals (Pa).

The matrix is soft enough to be shaped with tools, and can be softened cl mg suitable solvents to cl mg repairs to be made. Any deformation of a sheet of fibreglass necessarily stretches some of the cl mg fibres, and they are able to resist this, so even a thin sheet ,g very strong. It is also quite light, which is an advantage in many applications. Over recent decades many cl mg composites have been developed, some with very valuable properties.

By carefully choosing the reinforcement, the matrix, посетить страницу источник the manufacturing process that ng them together, engineers can tailor the properties to meet specific requirements.

They can, for example, make the composite sheet very strong in one direction by aligning the fibres that way, but weaker cl mg another direction where strength is not so important. They can also select properties such as resistance to heat, chemicals, and weathering by choosing an appropriate matrix material.

For the matrix, many modern composites use thermosetting or thermosoftening plastics (also called resins). The plastics are polymers GLOSSARY polymersLarge molecules that are made up of many units (monomers) linked together in a chain.

There are naturally occurring polymers (such as starch and DNA) and synthetic polymers (such as nylon and silicone). Thermosetting plastics are liquid cl mg prepared but harden and become rigid (ie, they cure) when they are heated. The setting process is irreversible, so that these materials do not become soft under high temperatures. These plastics also resist wear and attack by chemicals making them very durable, even when exposed to extreme environments.

Thermosoftening plastics, cl mg the name implies, are hard at low temperatures but soften when they are heated. Although they are less commonly used than thermosetting plastics they do have some advantages, such as greater fracture toughness, long mt life of the raw material, capacity for recycling and a cleaner, safer workplace because organic solvents are not needed for the hardening process.

Ceramics, carbon and metals are used as cl mg matrix for some highly specialised purposes. For example, ceramics are used when посетить страницу источник material is going to be exposed to high temperatures (such as heat exchangers) and carbon is used for products that cl mg exposed to friction and wear (such as bearings and gears).

Although glass fibres are by far the most common reinforcement, many advanced composites now use fine fibres of pure carbon. These are both pure carbon, but the carbon atoms are arranged in different crystal configurations. The bonds holding the hexagons together are very strong, but the bonds cl mg the sheets of hexagons together are quite weak, which cl mg what makes graphite soft.

Carbon nanotubes are made by taking a single sheet of graphite (known mmg graphene) and rolling it into a tube. This produces an extremely strong structure. Carbon fibre composites are light and much stronger than glass fibres, but are also more expensive.

Of the two, graphite fibres are cheaper and to produce than carbon nanotubes. They are used in aircraft structures and in high performance sporting equipment like golf clubs, tennis rackets and rowing boats, and are increasingly being used instead of metals to repair or replace damaged bones. Even stronger (and more xl than carbon fibres are threads of boron.

Nanotubes of boron nitride have the additional advantage of being much more resistant to heat than carbon fibres. They also cl mg piezoelectric qualities, which means they can generate electricity when cl mg pressure gm applied cl mg them, such as twisting or stretching. Polymers can also be used as the reinforcement material in composites.

For example, Kevlar, originally developed to replace steel in radial tyres but best known for its use in bullet-proof vests and helmets, is a polymer fibre that is immensely strong and adds toughness to a composite.

It is used as the reinforcement in composite products that require lightweight and reliable construction (eg, cl mg body parts cl mg an aircraft). Even stronger than Kevlar is a substance made from a combination of graphene and carbon nanotubes.

View video cl mg and transcript. Making an object from a composite material usually involves some form of mould. The reinforcing material is first placed in the mould and then semi-liquid matrix material is sprayed or pumped in stomach definition form the object.

Cl mg may be applied to force out any air bubbles, and читать статью mould is then heated to make the cl mg set solid. The moulding process is often done by hand, but automatic processing by machines is becoming more common. One of these methods is called pultrusion GLOSSARY pultrusionA continuous moulding process that mechanically aligns long strands of reinforcements for a composite material then passes cl mg through a ,g of thermosetting resin.

The coated strands are then assembled by a mechanical guide before the curing process. This cl mg is ideal cll manufacturing products that are straight and have a constant cross section, such as bridge beams. In many thin structures with complex shapes, such as curved panels, the composite cl mg is built up by applying sheets of woven fibre reinforcement, saturated with the plastic matrix material, over an appropriately shaped base mould. When the panel has been built to an appropriate thickness, the matrix material is then cured.

Many new types of composites are not made by the matrix and reinforcement method but by laying down multiple layers of material. The structure of many composites (such as those used in the wing and body panels xl aircraft), consists of a honeycomb of plastic sandwiched between two skins of carbon-fibre reinforced cl mg material.

These sandwich composites combine high strength, and c, bending stiffness, with low weight. Other methods involve simply laying down several alternating layers of different substances (for example, graphene and metal) to make the composite. The greatest advantage of composite materials is strength and stiffness combined with lightness. By choosing an appropriate combination of reinforcement and matrix material, manufacturers can produce properties that exactly fit the requirements for a particular structure for a particular purpose.

At the same time researchers want to improve the performance of the composites, such as making them more resistant to impact. Cl mg of the reinforcing fibres being put jg place individually, which is slow and costly, they can be knitted or woven cl mg to make a sort of cloth. This can even be three-dimensional rather than flat. The spaces between and around the textile fibres are then filled with the matrix material (such as a resin) to make the product.

This process can quite easily be done by machines rather than by hand, making it faster and cheaper. Connecting all the fibres together also means that the composite is less likely to be damaged when struck.



03.03.2020 in 08:39 Ия:
Эээ, а объясните, пожалуйста, а то я что то не совсем в тему въехал, это как?