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PUTTING IT TOGETHER – SCIENCE AND T
PUTTING IT TOGETHER – SCIENCE AND TECHNOLOGY OF COMPOSITE MATERIALS
Home / Education / Nova
Key text
This topic is sponsored by the Cooperative Research Centre for Advanced Composite Structures Ltd and the Australian Government's National Innovation Awareness Strategy.
Light, strong and corrosion-resistant, composite materials are being used in an increasing number of products as more manufacturers discover the benefits of these versatile materials.
In an advanced society like ours we all depend on composite materials in some aspect of our lives. Fibreglass, developed in the late 1940s, was the first modern composite and is still the most common. It makes up about 65 per cent of all the composites produced today and is used for boat hulls, surfboards, sporting goods, swimming pool linings, building panels and car bodies. You may well be using something made of fibreglass without knowing it.
What makes a material a composite?
Composite materials are formed by combining two or more materials that have quite different properties. The different materials work together to give the composite unique properties, but within the composite you can easily tell the different materials apart – they do not dissolve or blend into each other.
Composites exist in nature. A piece of wood is a composite, with long fibres of cellulose (a very complex form of starch) held together by a much weaker substance called lignin. Cellulose is also found in cotton and linen, but it is the binding power of the lignin that makes a piece of timber much stronger than a bundle of cotton fibres.
Not a new idea
Humans have been using composite materials for thousands of years. Take mud bricks for example. A cake of dried mud is easy to break by bending, which puts a tension force on one edge, but makes a good strong wall, where all the forces are compressive. A piece of straw, on the other hand, has a lot of strength when you try to stretch it but almost none when you crumple it up. But if you embed pieces of straw in a block of mud and let it dry hard, the resulting mud brick resists both squeezing and tearing and makes an excellent building material. Put more technically, it has both good compressive strength and good tensile strength.
Another well-known composite is concrete. Here aggregate (small stones or gravel) is bound together by cement. Concrete has good strength under compression, and it can be made stronger under tension by adding metal rods, wires, mesh or cables to the composite (so creating reinforced concrete).
Making a composite
Most composites are made up of just two materials. One material (the matrix or binder) surrounds and binds together a cluster of fibres or fragments of a much stronger material (the reinforcement). In the case of mud bricks, the two roles are taken by the mud and the straw; in concrete, by the cement and the aggregate; in a piece of wood, by the cellulose and the lignin. In fibreglass, the reinforcement is provided by fine threads or fibres of glass, often woven into a sort of cloth, and the matrix is a plastic.
The threads of glass in fibreglass are very strong under tension but they are also brittle and will snap if bent sharply. The matrix not only holds the fibres together, it also protects them from damage by sharing any stress among them. The matrix is soft enough to be shaped with tools, and can be softened by suitable solvents to allow repairs to be made. Any deformation of a sheet of fibreglass necessarily stretches some of the glass fibres, and they are able to resist this, so even a thin sheet is very strong. It is also quite light, which is an advantage in many applications.
Over recent decades many new composites have been developed, some with very valuable properties. By carefully choosing the reinforcement, the matrix, and the manufacturing process that brings 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 in 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.
Choosing materials for the matrix
For the matrix, many modern composites use thermosetting or thermosoftening plastics (also called resins). (The use of plastics in the matrix explains the name 'reinforced plastics' commonly given to composites). The plastics are polymers that hold the reinforcement together and help to determine the physical properties of the end product.
Thermosetting plastics are liquid when 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, as 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 shelf 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 the matrix for some highly specialised purposes. For example, ceramics are used when the material is going to be exposed to high temperatures (eg, heat exchangers) and carbon is used for products that are exposed to friction and wear (eg, bearings and gears).
Choosing materials for the reinforcement
Although glass fibres are by far the most common reinforcement, many advanced composites now use fine fibres of pure carbon. Carbon fibres are much stronger than glass fibres, but are also more expensive to produce. Carbon fibre composites are light as well as strong. They are used in aircraft structures and in sporting goods (such as golf clubs), and increasingly are used instead of metals to repair or replace damaged bones. Even stronger (and more costly) than carbon fibres are threads of boron.
Polymers are not only used for the matrix, they also make a good reinforcement material in composites. For example, Kevlar 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, structural body parts of an aircraft). Composite materials were not the original use for Kevlar – it was developed to replace steel in radial tyres and is now used in bulletproof vests and helmets.
Choosing the manufacturing process
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 to form the object. Pressure may be applied to force out any air bubbles, and the mould is then heated to make the matrix set solid.
The moulding process is often done by hand, but automatic processing by machines is becoming more common. One of the new methods is called pultrusion (a term derived from the words 'pull' and 'extrusion'). This process is ideal for 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 structure 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.
In many advanced composites (such as those used in the wing and body panels of aircraft), the structure may consist of a honeycomb of plastic sandwiched between two skins of carbon-fibre reinforced composite material. Such sandwich composites combine high strength, and particularly bending stiffness, with low weight. Like everything to do with aircraft, they can be very costly!
So why use composites?
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 (Box 1: Composites in Australia).
Modern aviation, both military and civil, is a prime example. It would be much less efficient without composites. In fact, the demands made by that industry for materials that are both light and strong has been the main force driving the development of composites. It is common now to find wing and tail sections, propellers and rotor blades made from advanced composites, along with much of the internal structure and fittings. The airframes of some smaller aircraft are made entirely from composites, as are the wing, tail and body panels of large commercial aircraft.
In thinking about planes, it is worth remembering that composites are less likely than metals (such as aluminium) to break up completely under stress. A small crack in a piece of metal can spread very rapidly with very serious consequences (especially in the case of aircraft). The fibres in a composite act to block the widening of any small crack and to share the stress around.
The right composites also stand up well to heat and corrosion. This makes them ideal for use in products that are exposed to extreme environments such as boats, chemical-handling equipment and spacecraft. In general, composite materials are very durable.
Another advantage of composite materials is that they provide design flexibility. Composites can be moulded into complex shapes – a great asset when producing something like a surfboard or a boat hull.
The downside of composites is usually the cost. Although manufacturing processes a
Home / Education / Nova
Key text
This topic is sponsored by the Cooperative Research Centre for Advanced Composite Structures Ltd and the Australian Government's National Innovation Awareness Strategy.
Light, strong and corrosion-resistant, composite materials are being used in an increasing number of products as more manufacturers discover the benefits of these versatile materials.
In an advanced society like ours we all depend on composite materials in some aspect of our lives. Fibreglass, developed in the late 1940s, was the first modern composite and is still the most common. It makes up about 65 per cent of all the composites produced today and is used for boat hulls, surfboards, sporting goods, swimming pool linings, building panels and car bodies. You may well be using something made of fibreglass without knowing it.
What makes a material a composite?
Composite materials are formed by combining two or more materials that have quite different properties. The different materials work together to give the composite unique properties, but within the composite you can easily tell the different materials apart – they do not dissolve or blend into each other.
Composites exist in nature. A piece of wood is a composite, with long fibres of cellulose (a very complex form of starch) held together by a much weaker substance called lignin. Cellulose is also found in cotton and linen, but it is the binding power of the lignin that makes a piece of timber much stronger than a bundle of cotton fibres.
Not a new idea
Humans have been using composite materials for thousands of years. Take mud bricks for example. A cake of dried mud is easy to break by bending, which puts a tension force on one edge, but makes a good strong wall, where all the forces are compressive. A piece of straw, on the other hand, has a lot of strength when you try to stretch it but almost none when you crumple it up. But if you embed pieces of straw in a block of mud and let it dry hard, the resulting mud brick resists both squeezing and tearing and makes an excellent building material. Put more technically, it has both good compressive strength and good tensile strength.
Another well-known composite is concrete. Here aggregate (small stones or gravel) is bound together by cement. Concrete has good strength under compression, and it can be made stronger under tension by adding metal rods, wires, mesh or cables to the composite (so creating reinforced concrete).
Making a composite
Most composites are made up of just two materials. One material (the matrix or binder) surrounds and binds together a cluster of fibres or fragments of a much stronger material (the reinforcement). In the case of mud bricks, the two roles are taken by the mud and the straw; in concrete, by the cement and the aggregate; in a piece of wood, by the cellulose and the lignin. In fibreglass, the reinforcement is provided by fine threads or fibres of glass, often woven into a sort of cloth, and the matrix is a plastic.
The threads of glass in fibreglass are very strong under tension but they are also brittle and will snap if bent sharply. The matrix not only holds the fibres together, it also protects them from damage by sharing any stress among them. The matrix is soft enough to be shaped with tools, and can be softened by suitable solvents to allow repairs to be made. Any deformation of a sheet of fibreglass necessarily stretches some of the glass fibres, and they are able to resist this, so even a thin sheet is very strong. It is also quite light, which is an advantage in many applications.
Over recent decades many new composites have been developed, some with very valuable properties. By carefully choosing the reinforcement, the matrix, and the manufacturing process that brings 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 in 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.
Choosing materials for the matrix
For the matrix, many modern composites use thermosetting or thermosoftening plastics (also called resins). (The use of plastics in the matrix explains the name 'reinforced plastics' commonly given to composites). The plastics are polymers that hold the reinforcement together and help to determine the physical properties of the end product.
Thermosetting plastics are liquid when 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, as 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 shelf 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 the matrix for some highly specialised purposes. For example, ceramics are used when the material is going to be exposed to high temperatures (eg, heat exchangers) and carbon is used for products that are exposed to friction and wear (eg, bearings and gears).
Choosing materials for the reinforcement
Although glass fibres are by far the most common reinforcement, many advanced composites now use fine fibres of pure carbon. Carbon fibres are much stronger than glass fibres, but are also more expensive to produce. Carbon fibre composites are light as well as strong. They are used in aircraft structures and in sporting goods (such as golf clubs), and increasingly are used instead of metals to repair or replace damaged bones. Even stronger (and more costly) than carbon fibres are threads of boron.
Polymers are not only used for the matrix, they also make a good reinforcement material in composites. For example, Kevlar 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, structural body parts of an aircraft). Composite materials were not the original use for Kevlar – it was developed to replace steel in radial tyres and is now used in bulletproof vests and helmets.
Choosing the manufacturing process
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 to form the object. Pressure may be applied to force out any air bubbles, and the mould is then heated to make the matrix set solid.
The moulding process is often done by hand, but automatic processing by machines is becoming more common. One of the new methods is called pultrusion (a term derived from the words 'pull' and 'extrusion'). This process is ideal for 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 structure 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.
In many advanced composites (such as those used in the wing and body panels of aircraft), the structure may consist of a honeycomb of plastic sandwiched between two skins of carbon-fibre reinforced composite material. Such sandwich composites combine high strength, and particularly bending stiffness, with low weight. Like everything to do with aircraft, they can be very costly!
So why use composites?
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 (Box 1: Composites in Australia).
Modern aviation, both military and civil, is a prime example. It would be much less efficient without composites. In fact, the demands made by that industry for materials that are both light and strong has been the main force driving the development of composites. It is common now to find wing and tail sections, propellers and rotor blades made from advanced composites, along with much of the internal structure and fittings. The airframes of some smaller aircraft are made entirely from composites, as are the wing, tail and body panels of large commercial aircraft.
In thinking about planes, it is worth remembering that composites are less likely than metals (such as aluminium) to break up completely under stress. A small crack in a piece of metal can spread very rapidly with very serious consequences (especially in the case of aircraft). The fibres in a composite act to block the widening of any small crack and to share the stress around.
The right composites also stand up well to heat and corrosion. This makes them ideal for use in products that are exposed to extreme environments such as boats, chemical-handling equipment and spacecraft. In general, composite materials are very durable.
Another advantage of composite materials is that they provide design flexibility. Composites can be moulded into complex shapes – a great asset when producing something like a surfboard or a boat hull.
The downside of composites is usually the cost. Although manufacturing processes a
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ĐẶT NÓ LẠI VỚI NHAU-KHOA HỌC VÀ CÔNG NGHỆ VẬT LIỆU COMPOSITETrang chủ / giáo dục / NovaVăn bản quan trọngChủ đề này được bảo trợ bởi Trung tâm nghiên cứu hợp tác xã cho nâng cao Composite cấu trúc Ltd và chiến lược nâng cao nhận thức sáng tạo quốc gia của chính phủ Úc. Ánh sáng, mạnh mẽ và khả năng chống ăn mòn, hỗn hợp vật liệu đang được sử dụng trong một số lượng ngày càng tăng của sản phẩm khi thêm các nhà sản xuất phát hiện ra những lợi ích của các vật liệu linh hoạtTrong một xã hội tiên tiến như chúng ta, chúng ta đều phụ thuộc vào các vật liệu composite trong một số khía cạnh của cuộc sống của chúng tôi. Bằng sợi thủy tinh, phát triển vào cuối những năm 1940, là hỗn hợp hiện đại đầu tiên và vẫn còn phổ biến nhất. Nó làm cho tăng khoảng 65 phần trăm của tất cả các vật liệu tổng hợp được sản xuất vào ngày hôm nay và được sử dụng cho thuyền vỏ, ván lướt sóng, thể thao hàng hoá, bơi lót, xây dựng tấm và các cơ quan xe hơi. Bạn có thể cũng sử dụng một cái gì đó làm bằng sợi thủy tinh mà không biết nó.Điều gì làm cho một vật liệu một hỗn hợp?Vật liệu composite được hình thành bằng cách kết hợp hai hay nhiều vật liệu có tính khá khác nhau. Các vật liệu khác nhau làm việc cùng nhau để cung cấp cho các đặc tính độc đáo tổng hợp, nhưng trong các composite bạn có thể dễ dàng cho các tài liệu khác nhau-họ không hòa tan hoặc pha trộn vào nhau.Vật liệu tổng hợp tồn tại trong tự nhiên. Một mảnh gỗ là một hỗn hợp, với dài sợi cellulose (một hình thức rất phức tạp của tinh bột) được tổ chức với nhau bằng một yếu hơn nhiều chất gọi là lignin. Cellulose cũng được tìm thấy trong bông và lanh, nhưng nó là ràng buộc sức mạnh của lignin mà làm cho một mảnh gỗ rất mạnh mẽ hơn so với một bó của bông sợi.Không phải là một ý tưởng mớiCon người đã sử dụng các vật liệu composite ngàn năm. Có bùn gạch ví dụ. Một bánh khô bùn là dễ dàng để phá vỡ do đó đặt một lực lượng căng thẳng trên một cạnh, nhưng làm cho một bức tường vững mạnh tốt, nơi tất cả các lực lượng được nén. Một mảnh rơm, mặt khác, có rất nhiều sức mạnh khi bạn cố gắng để kéo dài nó nhưng hầu như không có khi bạn crumple nó. Nhưng nếu bạn nhúng mẩu rơm trong một khối của bùn và để cho nó khô cứng, gạch bùn kết quả chống cả ép và rách và làm cho một vật liệu xây dựng tuyệt vời. Đặt hơn về mặt kỹ thuật, có cường độ nén tốt và độ bền tốt.Một nổi tiếng composite là bê tông. Ở đây, tổng hợp (đá nhỏ hoặc sỏi) ràng buộc với nhau bởi xi măng. Bê tông có sức mạnh tốt dưới nén, và nó có thể được thực hiện mạnh mẽ hơn theo căng thẳng bằng cách thêm vào thanh kim loại, dây điện, lưới hoặc cáp composite (do đó việc tạo ra bê tông cốt thép).Thực hiện một hỗn hợpHầu hết các vật liệu tổng hợp được tạo thành từ hai vật liệu. Một tài liệu (ma trận hoặc chất kết dính) bao quanh và gắn kết với nhau một cụm các sợi hoặc mảnh vỡ của một vật liệu mạnh mẽ hơn nhiều (tăng cường). Trong trường hợp của viên gạch bùn, hai vai trò được thực hiện bởi bùn và rơm; bê tông, xi măng và tổng hợp; trong một mảnh gỗ, bởi cellulose và lignin. Ở bằng sợi thủy tinh, tăng cường được cung cấp bởi chủ đề tốt đẹp hoặc loại sợi thủy tinh, thường dệt thành một loại vải, và ma trận là một nhựa.Các chủ đề của thủy tinh trong bằng sợi thủy tinh rất mạnh dưới căng thẳng nhưng họ cũng được giòn và sẽ chụp nếu cong mạnh. Ma trận không chỉ giữ các sợi với nhau, nó cũng bảo vệ chúng khỏi bị hư hại bằng cách chia sẻ bất kỳ căng thẳng trong số đó. Ma trận là mềm mại, đủ để được định hình với các công cụ, và có thể được làm mềm bằng các dung môi phù hợp để cho phép sửa chữa được thực hiện. Bất kỳ sự biến dạng của một tấm bằng sợi thủy tinh nhất thiết phải trải dài một số sợi thủy tinh, và họ có thể để chống lại điều này, vì vậy, ngay cả một tấm mỏng là rất mạnh mẽ. Nó cũng là khá ánh sáng, mà là một lợi thế trong nhiều ứng dụng.Trong thập kỷ gần đây nhiều vật liệu composite mới đã được phát triển, một số với tài sản rất có giá trị. Bởi cẩn thận chọn tăng cường, Ma trận, và quá trình sản xuất mang lại cho họ với nhau, kỹ sư có thể thay đổi các thuộc tính để đáp ứng yêu cầu cụ thể. Họ có thể, ví dụ, làm cho tấm hỗn hợp rất mạnh mẽ trong một hướng bằng việc xếp thẳng các sợi như vậy, nhưng yếu hơn theo hướng khác nơi mà sức mạnh không phải là rất quan trọng. Họ cũng có thể chọn các thuộc tính như chống nhiệt, hóa chất, và thời tiết bằng cách chọn một vật liệu ma trận thích hợp.Việc lựa chọn vật liệu cho ma trậnCho ma trận, nhiều vật liệu tổng hợp hiện đại sử dụng bọt hoặc nhựa thermosoftening (tiếng Anh thường gọi là nhựa). (Giải thích việc sử dụng nhựa trong ma trận tên 'nhựa gia cố' thường được trao cho vật liệu tổng hợp). Các sản phẩm nhựa là polyme có tổ chức tăng cường với nhau và giúp đỡ để xác định tính chất vật lý của sản phẩm cuối cùng.Chế biến nhựa bọt được lỏng khi chuẩn bị nhưng cứng lại và trở nên cứng nhắc (tức là, họ chữa) khi họ có hệ thống sưởi. Quá trình cài đặt là không thể đảo ngược, do đó các tài liệu này không trở thành mềm dưới nhiệt độ cao. Các nhựa cũng chống lại mặc và tấn công bằng hóa chất làm cho chúng rất bền, ngay cả khi tiếp xúc với môi trường khắc nghiệt.Thermosoftening nhựa, như tên của nó, là khó khăn ở nhiệt độ thấp nhưng làm mềm khi họ có hệ thống sưởi. Mặc dù họ được sử dụng ít phổ biến hơn chế biến nhựa bọt họ có một số lợi thế, chẳng hạn như lớn hơn vết vỡ độ dẻo dai, dài hạn sử dụng của nguyên liệu, năng lực để tái chế và một môi trường làm việc sạch hơn, an toàn hơn vì dung môi hữu cơ là không cần thiết cho quá trình cứng.Gốm sứ, cacbon và kim loại được sử dụng như là ma trận cho một số mục đích chuyên môn cao. Ví dụ, đồ gốm được sử dụng khi các tài liệu sẽ được tiếp xúc với nhiệt độ cao (ví dụ:, trao đổi nhiệt) và carbon được sử dụng cho các sản phẩm được tiếp xúc với ma sát và mặc (ví dụ:, vòng bi và bánh răng).Việc lựa chọn vật liệu để tăng cườngMặc dù kính sợi của xa tăng cường phổ biến nhất, nhiều nâng cao vật liệu tổng hợp bây giờ sử dụng tốt sợi cacbon tinh khiết. Sợi carbon là rất mạnh mẽ hơn so với sợi thủy tinh, nhưng cũng đắt tiền hơn để sản xuất. Vật liệu composite sợi carbon được ánh sáng cũng như mạnh mẽ. Chúng được sử dụng trong cấu trúc máy bay và các hàng hóa thể thao (chẳng hạn như câu lạc bộ golf), và ngày càng được sử dụng thay vì kim loại để sửa chữa hoặc thay thế bị hư hỏng xương. Thậm chí mạnh mẽ hơn (và tốn kém hơn) hơn sợi carbon là chủ đề của Bo.Polyme không chỉ được sử dụng cho ma trận, họ cũng làm cho một vật liệu tăng cường tốt trong vật liệu tổng hợp. Ví dụ, Kevlar là một sợi polyme là vô cùng mạnh mẽ và cho biết thêm sự bền bỉ để một hỗn hợp. Nó được sử dụng như gia cố trong các sản phẩm composite yêu cầu xây dựng nhẹ và đáng tin cậy (ví dụ:, cấu trúc cơ thể một phần của một máy bay). Vật liệu composite không là sử dụng ban đầu cho Kevlar-nó đã được phát triển để thay thế thép trong lốp xuyên tâm và bây giờ được sử dụng trong áo chống đạn và mũ bảo hiểm.Việc lựa chọn quy trình sản xuấtLàm cho một đối tượng từ một vật liệu composite thường liên quan đến một số hình thức của nấm mốc. Vật liệu tăng cường cho lần đầu tiên được đặt trong khuôn mẫu và sau đó bán lỏng ma trận tài liệu phun hay bơm trong để tạo thành các đối tượng. Áp lực có thể được áp dụng để buộc ra bất kỳ bong bóng khí, và khuôn mẫu sau đó được đun nóng đến làm cho ma trận thiết lập vững chắc.Quá trình đúc thường được thực hiện bằng tay, nhưng tự động xử lý bởi máy ngày càng trở nên phổ biến hơn. Một trong những phương pháp mới được gọi là pultrusion (một thuật ngữ xuất phát từ từ 'kéo' và 'đùn'). Quá trình này là lý tưởng để sản xuất sản phẩm được thẳng và có một phần đường liên tục, chẳng hạn như dầm cầu.Trong nhiều cấu trúc mỏng với hình dạng phức tạp, chẳng hạn như cong tấm, cấu trúc hỗn hợp được xây dựng bằng cách áp dụng tờ dệt sợi cốt thép mềm, bão hòa với các vật liệu nhựa ma trận, trong một khuôn mẫu cơ sở hình một cách thích hợp. Khi bảng đã được xây dựng với một dày thích hợp, các vật liệu ma trận sau đó chữa khỏi.Trong nhiều vật liệu composite cao cấp (chẳng hạn như những người sử dụng trong bảng cánh và cơ thể của máy bay), cấu trúc có thể bao gồm một tổ ong kẹp giữa hai da nhiều vật liệu composite sợi carbon gia cố bằng nhựa. Các vật liệu tổng hợp bánh sandwich kết hợp cường độ cao, và đặc biệt là uốn cứng, với trọng lượng nhẹ. Giống như tất cả mọi thứ để làm với máy bay, họ có thể rất tốn kém!Vì vậy, tại sao sử dụng vật liệu tổng hợp?Lợi thế lớn nhất của vật liệu composite là sức mạnh và độ cứng kết hợp với nhẹ nhàng. Bằng cách chọn một sự kết hợp thích hợp của tăng cường và vật liệu ma trận, nhà sản xuất có thể sản xuất thuộc tính chính xác phù hợp với các yêu cầu cho một cấu trúc cụ thể cho một mục đích cụ thể (hộp 1: vật liệu tổng hợp tại Úc).Hiện đại aviation, quân sự và dân sự, là một ví dụ nguyên tố. Nó sẽ ít hơn nhiều hiệu quả mà không có vật liệu tổng hợp. Trong thực tế, các yêu cầu của ngành công nghiệp đó cho tài liệu mà là cả hai nhẹ và mạnh mẽ đã là lực lượng chủ lực lái sự phát triển của vật liệu tổng hợp. Nó là phổ biến bây giờ tìm thấy phần cánh và đuôi, cánh quạt và cánh quạt lưỡi được làm từ vật liệu composite cao cấp, cùng với phần lớn cấu trúc bên trong và phụ kiện. Khung máy bay của một số máy bay nhỏ hơn được thực hiện hoàn toàn từ vật liệu tổng hợp, như là các tấm cánh, đuôi và cơ thể của máy bay thương mại lớn.Trong suy nghĩ về máy bay, nó là giá trị ghi nhớ rằng vật liệu tổng hợp là ít có khả năng hơn so với các kim loại (chẳng hạn như nhôm) để phá vỡ hoàn toàn bị căng thẳng. Một vết nứt nhỏ trong một mảnh kim loại có thể lây lan rất nhanh chóng với các hậu quả rất nghiêm trọng (đặc biệt là trong trường hợp của máy bay). Sợi trong một hành động hỗn hợp để ngăn chặn sự mở rộng của bất kỳ vết nứt nhỏ và chia sẻ những căng thẳng xung quanh.Các vật liệu tổng hợp bên phải cũng đứng lên tốt để nhiệt và ăn mòn. Điều này làm cho chúng lý tưởng để sử dụng trong các sản phẩm được tiếp xúc với môi trường khắc nghiệt như tàu thuyền, xử lý hóa chất thiết bị và tàu vũ trụ. Nói chung, làm bằng vật liệu là rất bền.Một ưu điểm khác của vật liệu composite là họ cung cấp tính linh hoạt thiết kế. Vật liệu tổng hợp có thể được thùng thành các hình dạng phức tạp-một tài sản lớn khi sản xuất một cái gì đó giống như một surfboard hoặc một tàu thuyền.Nhược điểm của vật liệu tổng hợp thường là chi phí. Mặc dù quá trình sản xuất một
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PUTTING IT TOGETHER – SCIENCE AND TECHNOLOGY OF COMPOSITE MATERIALS
Home / Education / Nova
Key text
This topic is sponsored by the Cooperative Research Centre for Advanced Composite Structures Ltd and the Australian Government's National Innovation Awareness Strategy.
Light, strong and corrosion-resistant, composite materials are being used in an increasing number of products as more manufacturers discover the benefits of these versatile materials.
In an advanced society like ours we all depend on composite materials in some aspect of our lives. Fibreglass, developed in the late 1940s, was the first modern composite and is still the most common. It makes up about 65 per cent of all the composites produced today and is used for boat hulls, surfboards, sporting goods, swimming pool linings, building panels and car bodies. You may well be using something made of fibreglass without knowing it.
What makes a material a composite?
Composite materials are formed by combining two or more materials that have quite different properties. The different materials work together to give the composite unique properties, but within the composite you can easily tell the different materials apart – they do not dissolve or blend into each other.
Composites exist in nature. A piece of wood is a composite, with long fibres of cellulose (a very complex form of starch) held together by a much weaker substance called lignin. Cellulose is also found in cotton and linen, but it is the binding power of the lignin that makes a piece of timber much stronger than a bundle of cotton fibres.
Not a new idea
Humans have been using composite materials for thousands of years. Take mud bricks for example. A cake of dried mud is easy to break by bending, which puts a tension force on one edge, but makes a good strong wall, where all the forces are compressive. A piece of straw, on the other hand, has a lot of strength when you try to stretch it but almost none when you crumple it up. But if you embed pieces of straw in a block of mud and let it dry hard, the resulting mud brick resists both squeezing and tearing and makes an excellent building material. Put more technically, it has both good compressive strength and good tensile strength.
Another well-known composite is concrete. Here aggregate (small stones or gravel) is bound together by cement. Concrete has good strength under compression, and it can be made stronger under tension by adding metal rods, wires, mesh or cables to the composite (so creating reinforced concrete).
Making a composite
Most composites are made up of just two materials. One material (the matrix or binder) surrounds and binds together a cluster of fibres or fragments of a much stronger material (the reinforcement). In the case of mud bricks, the two roles are taken by the mud and the straw; in concrete, by the cement and the aggregate; in a piece of wood, by the cellulose and the lignin. In fibreglass, the reinforcement is provided by fine threads or fibres of glass, often woven into a sort of cloth, and the matrix is a plastic.
The threads of glass in fibreglass are very strong under tension but they are also brittle and will snap if bent sharply. The matrix not only holds the fibres together, it also protects them from damage by sharing any stress among them. The matrix is soft enough to be shaped with tools, and can be softened by suitable solvents to allow repairs to be made. Any deformation of a sheet of fibreglass necessarily stretches some of the glass fibres, and they are able to resist this, so even a thin sheet is very strong. It is also quite light, which is an advantage in many applications.
Over recent decades many new composites have been developed, some with very valuable properties. By carefully choosing the reinforcement, the matrix, and the manufacturing process that brings 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 in 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.
Choosing materials for the matrix
For the matrix, many modern composites use thermosetting or thermosoftening plastics (also called resins). (The use of plastics in the matrix explains the name 'reinforced plastics' commonly given to composites). The plastics are polymers that hold the reinforcement together and help to determine the physical properties of the end product.
Thermosetting plastics are liquid when 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, as 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 shelf 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 the matrix for some highly specialised purposes. For example, ceramics are used when the material is going to be exposed to high temperatures (eg, heat exchangers) and carbon is used for products that are exposed to friction and wear (eg, bearings and gears).
Choosing materials for the reinforcement
Although glass fibres are by far the most common reinforcement, many advanced composites now use fine fibres of pure carbon. Carbon fibres are much stronger than glass fibres, but are also more expensive to produce. Carbon fibre composites are light as well as strong. They are used in aircraft structures and in sporting goods (such as golf clubs), and increasingly are used instead of metals to repair or replace damaged bones. Even stronger (and more costly) than carbon fibres are threads of boron.
Polymers are not only used for the matrix, they also make a good reinforcement material in composites. For example, Kevlar 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, structural body parts of an aircraft). Composite materials were not the original use for Kevlar – it was developed to replace steel in radial tyres and is now used in bulletproof vests and helmets.
Choosing the manufacturing process
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 to form the object. Pressure may be applied to force out any air bubbles, and the mould is then heated to make the matrix set solid.
The moulding process is often done by hand, but automatic processing by machines is becoming more common. One of the new methods is called pultrusion (a term derived from the words 'pull' and 'extrusion'). This process is ideal for 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 structure 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.
In many advanced composites (such as those used in the wing and body panels of aircraft), the structure may consist of a honeycomb of plastic sandwiched between two skins of carbon-fibre reinforced composite material. Such sandwich composites combine high strength, and particularly bending stiffness, with low weight. Like everything to do with aircraft, they can be very costly!
So why use composites?
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 (Box 1: Composites in Australia).
Modern aviation, both military and civil, is a prime example. It would be much less efficient without composites. In fact, the demands made by that industry for materials that are both light and strong has been the main force driving the development of composites. It is common now to find wing and tail sections, propellers and rotor blades made from advanced composites, along with much of the internal structure and fittings. The airframes of some smaller aircraft are made entirely from composites, as are the wing, tail and body panels of large commercial aircraft.
In thinking about planes, it is worth remembering that composites are less likely than metals (such as aluminium) to break up completely under stress. A small crack in a piece of metal can spread very rapidly with very serious consequences (especially in the case of aircraft). The fibres in a composite act to block the widening of any small crack and to share the stress around.
The right composites also stand up well to heat and corrosion. This makes them ideal for use in products that are exposed to extreme environments such as boats, chemical-handling equipment and spacecraft. In general, composite materials are very durable.
Another advantage of composite materials is that they provide design flexibility. Composites can be moulded into complex shapes – a great asset when producing something like a surfboard or a boat hull.
The downside of composites is usually the cost. Although manufacturing processes a
Home / Education / Nova
Key text
This topic is sponsored by the Cooperative Research Centre for Advanced Composite Structures Ltd and the Australian Government's National Innovation Awareness Strategy.
Light, strong and corrosion-resistant, composite materials are being used in an increasing number of products as more manufacturers discover the benefits of these versatile materials.
In an advanced society like ours we all depend on composite materials in some aspect of our lives. Fibreglass, developed in the late 1940s, was the first modern composite and is still the most common. It makes up about 65 per cent of all the composites produced today and is used for boat hulls, surfboards, sporting goods, swimming pool linings, building panels and car bodies. You may well be using something made of fibreglass without knowing it.
What makes a material a composite?
Composite materials are formed by combining two or more materials that have quite different properties. The different materials work together to give the composite unique properties, but within the composite you can easily tell the different materials apart – they do not dissolve or blend into each other.
Composites exist in nature. A piece of wood is a composite, with long fibres of cellulose (a very complex form of starch) held together by a much weaker substance called lignin. Cellulose is also found in cotton and linen, but it is the binding power of the lignin that makes a piece of timber much stronger than a bundle of cotton fibres.
Not a new idea
Humans have been using composite materials for thousands of years. Take mud bricks for example. A cake of dried mud is easy to break by bending, which puts a tension force on one edge, but makes a good strong wall, where all the forces are compressive. A piece of straw, on the other hand, has a lot of strength when you try to stretch it but almost none when you crumple it up. But if you embed pieces of straw in a block of mud and let it dry hard, the resulting mud brick resists both squeezing and tearing and makes an excellent building material. Put more technically, it has both good compressive strength and good tensile strength.
Another well-known composite is concrete. Here aggregate (small stones or gravel) is bound together by cement. Concrete has good strength under compression, and it can be made stronger under tension by adding metal rods, wires, mesh or cables to the composite (so creating reinforced concrete).
Making a composite
Most composites are made up of just two materials. One material (the matrix or binder) surrounds and binds together a cluster of fibres or fragments of a much stronger material (the reinforcement). In the case of mud bricks, the two roles are taken by the mud and the straw; in concrete, by the cement and the aggregate; in a piece of wood, by the cellulose and the lignin. In fibreglass, the reinforcement is provided by fine threads or fibres of glass, often woven into a sort of cloth, and the matrix is a plastic.
The threads of glass in fibreglass are very strong under tension but they are also brittle and will snap if bent sharply. The matrix not only holds the fibres together, it also protects them from damage by sharing any stress among them. The matrix is soft enough to be shaped with tools, and can be softened by suitable solvents to allow repairs to be made. Any deformation of a sheet of fibreglass necessarily stretches some of the glass fibres, and they are able to resist this, so even a thin sheet is very strong. It is also quite light, which is an advantage in many applications.
Over recent decades many new composites have been developed, some with very valuable properties. By carefully choosing the reinforcement, the matrix, and the manufacturing process that brings 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 in 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.
Choosing materials for the matrix
For the matrix, many modern composites use thermosetting or thermosoftening plastics (also called resins). (The use of plastics in the matrix explains the name 'reinforced plastics' commonly given to composites). The plastics are polymers that hold the reinforcement together and help to determine the physical properties of the end product.
Thermosetting plastics are liquid when 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, as 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 shelf 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 the matrix for some highly specialised purposes. For example, ceramics are used when the material is going to be exposed to high temperatures (eg, heat exchangers) and carbon is used for products that are exposed to friction and wear (eg, bearings and gears).
Choosing materials for the reinforcement
Although glass fibres are by far the most common reinforcement, many advanced composites now use fine fibres of pure carbon. Carbon fibres are much stronger than glass fibres, but are also more expensive to produce. Carbon fibre composites are light as well as strong. They are used in aircraft structures and in sporting goods (such as golf clubs), and increasingly are used instead of metals to repair or replace damaged bones. Even stronger (and more costly) than carbon fibres are threads of boron.
Polymers are not only used for the matrix, they also make a good reinforcement material in composites. For example, Kevlar 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, structural body parts of an aircraft). Composite materials were not the original use for Kevlar – it was developed to replace steel in radial tyres and is now used in bulletproof vests and helmets.
Choosing the manufacturing process
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 to form the object. Pressure may be applied to force out any air bubbles, and the mould is then heated to make the matrix set solid.
The moulding process is often done by hand, but automatic processing by machines is becoming more common. One of the new methods is called pultrusion (a term derived from the words 'pull' and 'extrusion'). This process is ideal for 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 structure 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.
In many advanced composites (such as those used in the wing and body panels of aircraft), the structure may consist of a honeycomb of plastic sandwiched between two skins of carbon-fibre reinforced composite material. Such sandwich composites combine high strength, and particularly bending stiffness, with low weight. Like everything to do with aircraft, they can be very costly!
So why use composites?
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 (Box 1: Composites in Australia).
Modern aviation, both military and civil, is a prime example. It would be much less efficient without composites. In fact, the demands made by that industry for materials that are both light and strong has been the main force driving the development of composites. It is common now to find wing and tail sections, propellers and rotor blades made from advanced composites, along with much of the internal structure and fittings. The airframes of some smaller aircraft are made entirely from composites, as are the wing, tail and body panels of large commercial aircraft.
In thinking about planes, it is worth remembering that composites are less likely than metals (such as aluminium) to break up completely under stress. A small crack in a piece of metal can spread very rapidly with very serious consequences (especially in the case of aircraft). The fibres in a composite act to block the widening of any small crack and to share the stress around.
The right composites also stand up well to heat and corrosion. This makes them ideal for use in products that are exposed to extreme environments such as boats, chemical-handling equipment and spacecraft. In general, composite materials are very durable.
Another advantage of composite materials is that they provide design flexibility. Composites can be moulded into complex shapes – a great asset when producing something like a surfboard or a boat hull.
The downside of composites is usually the cost. Although manufacturing processes a
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- nevermind what i've said
- necklace
- A day of work
- never mind what i've said
- gia đình là điều tuyệt vời nhất
- Steal 100000000 glold
- 梁珊下来的时候,看到左放与傅自喜言笑晏晏的景象,稍稍惊讶了一下.不过,傅自喜本来
- But how
- Từ thành phố cực nam nước úc là Hobart
- To produce you need a total energy (proc
- A day is work
- Email Alerts
- nó nghe rất vui tai
- tự nhận thức đúng đắn về trách nhiệm sản
- avoid the christmas rush
- pháo hoa trong tết xưa và tết nay
- chỉ là tôi cảm thấy như vậy
- tôi không hiểu, tôi phải đến trường ngây
- financially
- thu phí
- tết xưa và tết nay : pháo hoa
- tôi đã mắc lỗi về thời gian làm việc
- full day of work
- Tại hội nghị các đại học úc-á về môi trư
