The measurement is taken between the two points that are furthest apart the front and rear extremities , along the length of the aircraft. The length is measured along a horizontal plane. It is the distance between a vertical plane striking the front of the nose, and a vertical plane striking the rear of the tail. Wingspan is the total distance spanned by both wings. The span is measured as a straight line between the two wingtips. Overall height measures how tall the aircraft is.
The dimension is measured vertically between the underside of the wheels and a horizontal plane striking the top of the tail. Maximum fuselage width is the external width of the aircraft's body- how wide it is, measured horizontally between vertical planes striking the outside faces of the fuselage. Maximum cabin width states the maximum internal width, measured between the inside faces of the fuselage.
The measurement is equivalent to the external width , less the thickness of the fuselage at each side of the aircraft. Notes: When written, the words dimension and dimensions are often abbreviated to dim and dims. Span is also used to describe the distance s crossed by a bridge, between its supports.
If a bridge has a support at its centre as well as at each end , then it has two spans. However, a surface which is flat is not necessarily horizontal. A flat surface may be vertical, or inclined sloping at an angle to the horizontal or vertical plane. Faces that are vertical, such as those of the walls of buildings, are described by engineers as being plumb.
Structures that are slightly inclined from vertical are said to be out of plumb. I height overall thickness span width Look at A and B opposite to help you. The conductors are suspended from the supports by rods, called insulators. On straight sections of line, the insulators are 2 level 1 plumb, hanging vertically from the supports.
At supports where the direction of the line changes, pairs of insulators are used. In this situation, the insulators are 3 inclined j striking from the vertical plane, as they are pulled 4 plumb 1 out of plumb by the conductors pulling in different directions. The higher the voltage being transmitted by the line, the greater the required distance between the conductor and the support, in order to provide effective insulation.
The 5 length I width of insulators therefore varies, depending on the voltage. Higher voltages also mean that conductors must be located at a greater minimum 6 height 1 thickness above the ground, for safety. This distance is measured between the ground and the lowest point of the cable. Can you answer the questions? On long suspension bridges, when the distance between the vertical centres of the towers at either side of the bridge is measured horizontally, the distance between the tops of the two towers will be several millimetres longer than the distance between their bases.
Does this mean the towers are out of plumb? Why is there a difference? What dimensions would need to be specified on a drawing in order to allow the product to be manufactured?
The distances between the holes can be shown as running dimensions or as chain dimensions. In both cases, the centreline CL - a line through the centre of the hole- is marked drawn , and the distances between the centrelines are given. The holes below are at mm centres. These can be measured from, in order to locate -that is, give the position of- points on components. The measurements are offset from the centreline - each is at a certain distance from it, and the offsets are measured at a right-angle to the centreline at 90 degrees to it.
Note: We can say at a right-angle to X, at 90 degrees to X, or at right-angles to X. The gridlines have numbers and letters. All numbered gridlines are parallel with one another- that is, they are straight, and are regular distances apart. Lettered lines also run parallel with one another, and are perpendicular to at a right-angle to the numbered lines. The plan below shows part of the floor of an office building. The perpendicular gridlines intersect at cross at the centres of columns.
An opening hole in the floor is shown using coordinate dimensions. These allow the site engineer to set out mark the position of the opening by squaring off the gridlines- marking lines that run at a right-angle to them- and then measuring along these lines using a tape measure.
A theodolite- an optical device used for measuring angles- can be used to square off gridlines accurately. To double-check dimensions- that is, carry out an extra check- diagonal measurements can be used, as in the engineer's sketch below.
The length of diagonals can be calculated using Pythagoras's Theorem. Replace the underlined words and expressions with alternative words and expressions from A opposite. Complete the sentences using the words in the box. In civil engineeri ng, the following precautions can help to prevent costly setting-out mistakes. Describe it, using language from A and B opposite. You could also give approximate measurements.
Then imagine you are designing the object or the part of the building. What dimensions and lines will be needed on the drawings in order to locate its features?
During the talk, she mentions a number of dimensions relating to circles. The circumference of outside of tyre outer circle in the diagram is the outside of the L tyre, and the inner circle - the circle with the smaller diameter - represents both the inside of the tyre and the outside of the wheel. And, clearly, the inner circle is right in the middle of the outer circle - it's exactly in the centre. So because it's central, that means the inside and outside of the tyre form concentric circles.
And as the tyre is circular, simple geometry tells us that measurements of the radius, taken from the centre of the circle to different points on its edge diameter of wheel -points on the circumference- are equal. All the radii are the same. In other words, the tyre diameter of tyre has a constant radius. That means its geometry changes. So while the wheel - the inner circle - obviously remains round, the circumference of the tyre - the outer circle - changes shape.
It deforms. Before deformation, this part of the tyre forms an arc of the circle, between points A and B. The tyre becomes deformed between points A and B. It becomes a chord of the same chordl- ! So the design of the tyre has to allow for this change in shape- from a rounded edge to a straight edge. The width of the inside of a pipe is called the inside diameter ID. It can also be called the bore. The outside width is called the outside diameter OD.
When pipes are laid horizontally, the top of the outside of the pipe is called the crown, and the bottom of the inside of the pipe is called the invert. One question has two possible answers. Describe it using language from A opposite. This is because all production processes are imprecise to a certain extent.
Therefore, the sizes of several components produced from the same design will vary differ. Because engineers know that accuracy cannot be perfect, in designs they often specify tolerances -that is, acceptable variations in precision. Instead of giving one precise size, a tolerance specifies a range of acceptable sizes- an allowed amount of variation. This is often given as a deviation difference from a precise size. This means the diameter may deviate 0. Therefore, diameters of However, diameters of A large permissible deviation is a loose tolerance.
The key question is, how tightly or loosely should they fit together? This distance must be quite precise. If there is insufficient clearance - if the gap is too small - the component will fit too tightly. As a result, the component will bind - it will not be able to slide or turn freely. In other words, there will not be enough play. However, if there is too much clearance, there will be too much play and the component will be able to move too much.
This type of fit can be achieved by forcing the component into the hole. Alternatively, the metal around the hole can be heated so that it expands increases in size due to heat.
After sufficient expansion, the component is placed in the hole. The metal then cools and contracts decreases in size due to cooling. The contraction results in a tight fit. An example of an interference fit is a train wheel fitted on an axle. Sometimes there is more than one possible answer. Although these differences may only be One way round this problem if you have the cash is to have your engine blueprinted. The process is perfectly legal, as the sizes of all parts remain However, by carefully matching pairs standard engine spec seems obvious - everyone or groups of parts that are all in either the lower has the same power, so it's driving talent or upper half of the tolerance But things aren't a blueprinted engine is built to No two standard engines together very precisely, thanks to almost perfect are identical.
There will always be a slight Say what tolerances arc permissible, both for production not too tight du e to co sl , and for quality not ton loose. Say which parts require the tightest tnlcmntTS, and explain why. One of the company's engineers is giving his opinion on the idea in a meeting. For example, one millimetre is nought point nought three nine three seven inches as a decimal. So to be manageable, decimals have to be rounded up or down.
You'd probably round up that number to two decimal places, to give you zero point zero four. Now, you might say the difference is negligible- it's so small it's not going to affect anything. Ghes "" 0. Ghes - Addition, subtraction, multiplication and division During a TV programme about garden design, the presenter is explaining the calculations required to make a large setsquare which can be used for setting out.
I 've made This :, fee-t long. I 've made This one 4 fee-t long. SUWI of ihose -two numbers - so if I o. So, 2? Use one or two words from B opposite to fill each gap. The sizes of electrical wires are specified by a number which gives an area in square millimetres. For example, in a home, a 6 mm2 wire may be specified to supply an electric oven in a kitchen.
This number gives the cross-sectional area of the conductor. Increasing the cross-sectional area allows the conductor to carry more current safely, without overheating. Therefore, instead of using single cables with large sections for each conductor, power lines often use groups of two, three or four small-section cables, to give more surface area than a single, large-section cable. But in physics and in engineering, grams and kilograms are units of mass. Whether an object is on earth -where it is subjected to gravity the pull of the earth - or floating weightless in space, its mass is always the same.
The mass of an object is the object's volume multiplied by its density. The weight of an object is the force exerted on the object's mass by gravity. Some materials are very dense, and therefore very heavy. It has a radius of 40mm and it is 1,mm long. Complete the calculations using the words in the box. For the first phase, engineers are faced with the problem that every And each extra gram of That extra fuel, in turn, will With the cost of kilograms so high, the satellite must therefore be as In the second phase, with the orbiting satellite now As for the amount of space occupied, the situation is completely reversed.
The satellite's solar panels, which transform sunlight into battery power, must unfold to cover as wide an area as possible- opening out to cover an area of several Calculating the capacity of an electricity grid -the amount of energy it needs to supply to users -might seem simple. Just add up the power supplied over a given period of t ime to give the total amount consumed by users. Then, divide the cumulative amount of power used during the whole period by the number of hours in the period.
The result is an average level of consumption per hour. But there's one problem w it h this method -and it's a major one. The rate of power consumpt ion -the amount that's being consumed at a particular moment- is not constant.
In other words, consumption does not stay at the same level all the t ime. So electricity supply requireme nts ca nnot simply be averaged out over t ime.
People use more power at certain times of day, and less at other times, which means that demand for power fluctuates sign ificant ly. Generally, it rises to a maximum in the evening peak demand is at evening mea ltimes , and fa lls to its lowest levels during the night. These fluctuations are so big that at peak times consumption can be twice as high as it is during off-peak times. Clearly, the grid needs to have sufficient capacity to meet demand when consumption peaks.
But since each peak is brief, the grid w ill only run to capacity - at or close to its maximum capability- for a few moments each day. This means, most of the time, it has sign ificant spare capacity. As a res ult, there is a difference between input - the amount of energy put into the grid by power stations, and output - the amount used by consumers.
Bu t if electricity is generated at the place where it's consumed, and not transmitted through long-distance power lines, this loss can be avoided. One way to produce power loca lly is with photovoltaics PVs - often called solar panels. However, many PV installations are stil l con nected to the electricity grid. This means that when there is surplus power - when electricity is being produced by t he solar panels faster than it is needed in the home - it is fed into the grid.
If consumption exceeds production - if electricity is being used in the home faster than the solar panels can produce it - then power is taken from t he grid. Homes with low consumption may therefore become net prod ucers of power, producing more electricity t han they consume. Complete the explanation using the words in the box.
Of CCXJ. And le. So 5 hours of Unning a-t a lo So if we. Write figures to complete the comments. Water consumption fluctuated between A lot of heat is generated in this part of the process.
And all of that input I output is recycled- it provides a demand I supply of heat for the next stage of the process. So it's quite an efficient I inefficient system. At other times there isn't quite enough recycled heat to keep up with peak I off-peak demand for heat energy further along the process.
So there's a net loss I gain in total mass. Imagine you are starting a project to redesign it, in order to improve its efficiency. Is consumption constant or fluctuating? Describe any fluctuations, in terms of average and peak consumption.
What are the main reasons for inefficiencies? What are your first thoughts on how efficiency could be improved? They cannot be broken down into different constituents 'ingredients'. Examples of elements widely used in engineering materials are iron, carbon and aluminium AI.
An everyday example is water, which is a compound of hydrogen H and oxygen 0. A common example is steel, which is an iron-carbon alloy, and can include other alloying metals- metals which are added to alloys, in small quantities relative to the main metal. Examples of widely used alloying metals are chromium Cr , manganese Mn and tungsten W. Materials under the microscope: composites hen you think of examples of hi-tech materials, W composite materials come to mind- such as carbon-fibre, used in aerospace and Formula 1 cars.
But although we think of composites as hi-tech and highly expensive, that's not always true. The earliest examples of composite materials were bricks made from mud and straw. Or, to use the correct composite terms, from straw reinforcement- the structural network that reinforces the material inside, and a mud matrix- the material surrounding the reinforcement. These terms explain what a composite material is: a matrix with a reinforcing material inside it. A modern, everyday example is fibreglass- correctly called glass- reinforced plastic GRP -which has a plastic matrix reinforced with glass fibres.
Look at A opposite and Appendix IV on page to help you. However, using steel bars to Using a For example, 5 aluminium Look at A, B and C opposite to help you.
Generally, the steel used in reinforced concrete will have previously been exposed to water and to the oxygen in the air. As a result, it will usually be partly corroded, being covered with a layer of iron oxide rust. However, once the steel is inside the hardened concrete, it will be protected from air and water, which prevents further rusting.
Additionally, the cement in concrete does not react aggressively with the iron in steel. Say whether the materials are elements, compounds, mixtures, al loys or composites. Steel is the most widely used engineering material.
Technically, though, this well-known alloy of iron and carbon is not as simple as one might think. Steel comes in a huge range of different grades, each with different characteristics. For the inexperienced, it can be difficult to know where to begin.
A good place to start is with the two main types of steel. The first, carbon steels, consist of iron and carbon, and contain no significant quantities of other metals. The second main category of steel is alloy steels, which consist of iron, carbon and one or more alloying metals. A widely used grade of tool steel is high-speed steel, which is used in cutting tools that operate at high temperatures, such as drill bits.
Notes : The terms carbon steel and alloy steel can cause confusion, as carbon steels are also alloys, and alloy steels also contain carbon. This reaction takes place between the iron in the steel and the oxygen 0 2 in the air, to form iron oxide.
When iron corrodes, we say that it rusts. In some metals, such as aluminiwn Al , the presence of corrosion is not a problem, as the layer of oxide around the metal remains hard, which prevents it from oxidizing any further.
However, when mild steel goes rusty, the rust on the surface comes off continuously, and a new rusty layer forms, progressively 'eating into' the metal.
Steel is an alloy of iron and carbon. Then use the words to complete the sentences below. There is more than one possible answer. Look at C opposite to help you. Verb Noun Adjective corroded oxidized I go rusty 1 When steel is exposed to air and water, it Generally, the only solution is either to apply a protective coating, or to use another There is, however, an alternative solution. So-called weathering steel is a special alloy suitable for outdoor use.
But rather than being completely protected from corrosion, the surface of the steel is allowed to go Once a layer of While not everyone may like the 'rusty look', weathering steel has been widely used in architectural applications and outdoor sculptures. How serious is the potential problem of corrosion?
How is it prevented or limited- for example, by using a specific grade of steel? Aluminium is widely used, often in alloy forms. An example is duralumin, an alloy used in aircraft manufacturing, which also contains copper 4.
Aluminium can also be alloyed with titanium to produce very strong, lightweight metals. Copper is an excellent electrical conductor, which makes it ideal for use in electric wires.
Good ductility also makes it suitable for pipes. Copper is widely used in alloys, notably brass copper and zinc and bronze copper and tin, and sometimes lead. Silver is a precious metal - a reference to its high cost.
It is a better electrical conductor than any other material, so it is often used for electronic connections. Another precious metal - gold - is also an excellent conductor, and is highly corrosion-resistant. Notes: For more on metals and alloys, see Unit For more on ductility, see Unit An example is galvanizing zinc plating. Steel can be hot-dip galvanized, by placing it in molten liquid zinc.
It can also be electro- galvanized, which is a type of electroplating. With this technique, the steel component is placed in a liquid often an acid - called the electrolyte- and connected to the negative terminal - of an electrical supply, to become the cathode the negative side. This then becomes the anode the positive side. An electric current then flows between the pieces of metal, through the electrolyte. This causes a chemical reaction, which deposits zinc on the cathode, plating the component.
A related process, called anodizing, is used to protect aluminium. The component to be anodized is connected to the positive terminal to become the anode and placed in an electrolyte, with a cathode.
As electricity flows, aluminium oxide is deposited on the anode. As this is harder than aluminium metal, it provides protection. You will need to write some names more than once. I Check that there is sufficient I Ensure that the component is connected to the During the I Ensure that the metal being used for plating- e. During the process, it should function as the Is electroplating common? If so, what kinds of metals are used for plating, and why are these specific metals chosen?
But what, exactly, is a polymer or a plastic? Polymers are compounds made up of several elements that are chemically bound. Most compounds consist of large numbers of tiny molecules, which each contain just a few atoms.
For example, a water molecule- H2 0- contains two hydrogen atoms and one oxygen atom. But the molecules of polymers contain huge numbers of atoms, joined together in long chains.
Rubber, thanks to its many uses from rubber A polymer chain bands to car tyres , is one of the best-known polymers. It comes from latex, a natural liquid which comes from rubber trees. Rubber is therefore a natural polymer. However, most of the polymers used in industry are not natural, but synthetic.
The term 'plastic' is generally used to refer to synthetic polymers- in other words, those that are manmade.
Note: Rubber can be natural natural rubber or synthetic synthetic rubber. Thermoplastics and thermosetting plastics The page goes on to look at types of polymer. Synthetic polymers can be divided into two main categories: Thermoplastics can be melted by heat, and formed in shaped containers called moulds. After the liquid plastic has cooled, it sets to form a solid material.
A thermoplastic is a type of plast ic that can be heated and moulded numerous times. Thermosetting plastics, also called thermosets, can be heated and moulded like thermoplastics. They may also be mixed from cold ingredients. However, during cooling or mixing, a chemical reaction occurs, causing thermosets to cure. This means they set permanently, and cannot be moulded again. If a thermoset is heated after curing, it will burn. Two more categories of polymer are engineering plastics and elastomers.
Engineering plastics are mostly thermoplastics that are especially strong, such as ABS and polycarbonate. Elastomers are very elastic polymers which can be stretched by force to at least twice their original length, and can then return to their original length when the force is removed. However, not all rubber comes from trees. Plastics are also polymers. Then decide whether the sentences below are true or false, and correct the false sentences.
By this stage of the process, the plastic is solid, and has fully cooled. Selected panels can now undergo quality-control testing, to check they are strong enough to cope with the tough conditions they will be exposed to in use.
Tests include tensile testing, where narrow lengths of panel are subjected to high tension loads to check they do not stretch or fracture. More tests are carried out to check the panels' resistance to impacts and scratching. Any products that fail the tests are returned to the beginning of the production process, melted down, and their material is reused. How are they used?
Which of the categories mentioned in A and B opposite do the polymers belong to? Minerals are quite pure. Rocks, on the other hand, can be mixtures of several minerals, and may also contain previously organic material. Examples of minerals include different types of ore- from which metal can be extracted- such as iron ore. Generally, inorganic, non-metallic materials that have been formed by heating are called ceramics.
Glass is therefore a ceramic. When materials are heated to extremely high temperatures to form ceramics that are glass- like - that is, with a structure like that of glass - we say that they are vitrified. Ceramic materials are used to make construction materials such as bricks.
These are made from clay, and are then fired in a kiln- that is, heated to a high temperature in an industrial oven. Clay can also be vitrified - for example, to make waterproof pipes. This refers to the manufacturing technique where molten glass is floated on molten tin, to produce flat sheets. Usually, after float glass has been formed, it's annealed - it's left to cool slowly. But if it's left in this state, and the glass later gets broken, it breaks into dangerous, sharp pieces.
So for most engineering and architectural uses, annealed glass is unsuitable. We need to use what we call safety glass. As the term suggests, the glass is tempered - it's heated and kept hot for a certain time, to change its structure. Then if tempered glass is broken, it shatters - it breaks into tiny pieces. These are a lot safer than the long, sharp pieces produced when annealed glass breaks.
The disadvantage of toughened glass is that it can't withstand impacts from small objects, such as flying stones. So, for instance, that makes it unsuitable for vehicle windscreens. So in cases where impacts are a problem, another type of safety glass -laminated glass- is generally used.
This is made by laminating glass with a polymer- in other words, making a glass and polymer 'sandwich', with a sheet of polymer in the middle and sheets of glass at either side. The advantage of having a laminated material is not just that it's very strong. The layers of glass are bonded to a layer of polymer- they're stuck to the polymer- so if the glass does break, the broken pieces are held together, and don't fly.
Then, change one word in each of the false sentences to correct them. You will need to use some words more than once. Sometimes, more than one word is possible. But technically speaking, how accurate is the term 'bulletproof glass'? Outside of Hollywood movies, can glass really stop bullets? The answer is, not on its own. But if several The technique of sandwiching polymer and glass is nothing unusual.
Car windscreens are made by If a stone hits a windscreen, even though a small section of the glass on the outside may crack, the polymer behind it will stop the stone, and also ensure the entire piece of glass doesn't Bullet-resistant glass uses the same principle, but must be much tougher. A stronger polymer is therefore used - often polycarbonate - as well as a greater number of What types of material arc used, and why? It consists of a very fine powder. When water is added to cement, a chemical reaction occurs, and the cement begins to set - it starts to become solid.
The most widely used cement-based material is concrete, which is made from cement, fine aggregate sand , coarse aggregate gravel and water. After concrete has set, it needs time to reach its structural strength - the strength needed to perform effectively. Generally, engineers consider that this strength is reached after 28 days - a point called day strength.
Concrete mix designs, which are specified by engineers, state the proportions of cement, fine aggregate and coarse aggregate to be used for specific structures. For example, a one- two-four mix consists of one part cement, two parts fine aggregate and four parts coarse aggregate. For mixing precise quantities- known as hatching- proportions are measured by weight.
Mix designs also specify the water-cement ratio - the amount of water added relative to the amount of cement used. Excess water reduces the strength of concrete, so the quantity of water is kept to a minimum. But as drier concrete is more difficult to work with, an additive added chemical substance called a plasticizer is often used. This helps the concrete to flow more easily.
Other additives can also be used- for example, a retarder may be added to delay setting, which gives workers more time to pour place the concrete. Reinforced concrete Reinforced concrete RC structures contain steel bars. Steel reinforcement is needed mainly because concrete is weak in tension - that is, bad at resisting stretching forces.
As steel is strong in tension, reinforcing bars overcome this weakness. In order to form the different parts of structures, formwork - sometimes also called shuttering - is used. This consists of moulds of the required size and shape, made from steel or timber, which are used to contain the concrete until it has set. In-situ reinforced concrete being poured When wet concrete is cast placed in its final position, it is called in-situ concrete.
Instead of being cast in-situ, reinforced concrete elements can also be precast- cast at a factory - then delivered to the construction site ready for assembly.
Sometimes, precast concrete is also prestressed. With prestressing, tension is applied to the reinforcing bars, by machine, usually before the concrete is poured. The bars are then held in tension while wet concrete is poured around them. After the concrete has fully set, the bars become 'trapped' in tension. This increases the concrete's ability to resist bending forces. Look at B opposite to help yo u. This form of prestressing is called pre-tensioning, as tension is applied before the concrete is poured.
The technique is often used in the manufacture of floor components, which are small enough to fit on the back of a truck, and can therefore be A less common prestressing technique is post-tensioning applying tension after the concrete has set. This is more suitable for large elements, especially long beams, which cannot be transported, and therefore need to be poured Before the concrete is poured, ducts usually plastic tubes are placed inside the These ducts contain steel cables.
After the concrete has been This is only possible because the cables are free to move within the ducts- it is not possible with pre-tensioned reinforcing bars, which are held fast by the hard The ends of the cables are then permanently anchored at either end of the beam.
In what sequence do you think it was built? Do you think it was poured in-situ, or were its parts precast? In American Engl ish, tim ber genera lly means wood that is still growing in trees. Solid structural timber The text below is from a technical handbook about structural timber- wood intended to support loads in a structure. Generally, timbe r is cut to th e requ ired section- the width and depth tha t determin e its cross- section -at a sawmill, whe re a range of section sizes are produced.
Timber from sawm ills is generally supplied in rough-sawn sections. Thi s refers to the surface te xture produced by sawing timber with a circular saw. If the timber needs to have a smooth finish - for exa mple, because it will be visible in the structure- it can subsequ ently be planed to smooth its surface. Because the strength of wood varies , structural timber must be stress-graded. Th is means its strength is tested in order to give it a stress grade- a stand ard strength value which an engineer can use for design calculations.
Timber can be mechanically stress-graded, where its strength is checked by machin e. It can also be visually stress-graded , where the wood is exam ined by an inspector w ho looks for pote ntial weaknesses- in part icular, the position of knots. Engineered wood Engineered wood covers a range of softwood and hardwood materials. In each case, there is more than one possi ble answer.
From an environmental perspective, wood has many advantages. Firstly, it comes from a sustainable source. Coniferous trees grow relatively fast, providing a rapidly replaceable source of Secondly, almost all the timber in a tree can be utilized, leaving little or no waste.
The best quality wood can be used for structural applications, where solid, Smaller strands can be made into engineering wood with structural properties, such as And small particles and fibres, including those from waste timber, can go into cheaper materials, like The type of deformation depends on the type of force that is applied.
When a material is subjected to tension, its length will increase by a certain amount. This is called extension or elongation. It is especially important to understand the performance of materials in tension, as their tensile strength ability to resist tension is usually lower than their compressive strength ability to resist compression. A material's ability to do this is called elasticity.
Rubber is an example of a very elastic material- it can be elastically deformed to a considerable extent. If a material has very low elasticity, and is strong, engineers say it is stiff.
If a material has low elasticity and is weak, it is described as brittle- that is, it fractures breaks, due to tension very easily. Glass is an example of a brittle material. Some materials can change shape significantly, but do not return to their original shape. We say these materials are plastic. Often, plasticity is described in specific terms. A material that can be plastically deformed by hammering or rolling- for example, lead Pb - is malleable.
A material that can be drawn out stretched into a long length- for example, copper Cu - is ductile. Points The extension of the bar is proportional to the increase in tension.
Point 1 The bar reaches the limit of proportionality. Beyond this point, length begins to increase at a slightly greater rate than tension. Point 2 The elastic limit is reached. Beyond this point, the bar will no longer return to its original length.
In many materials, the elastic limit occurs almost immediately after the limit of proportionality. Point 3 The bar reaches its yield point. Once it yields, it continues to increase in length, even without a further increase in tension. Point 4 This is the ultimate tensile strength UTS of the material.
Beyond this point, a waist a narrower section appears at a point along the length of the bar, signalling that it is about to fracture. Point 5 This is the fracture point, where the bar breaks in two. You will need to use one word twice. Look at B and C opposite to help you. How are the springs used in car suspension made springy? It sounds like a silly question, but thi nk about it fo r a moment. In order for a spring to compress or extend, then return t o its original shape, it must be But spri ngs are made from wi re, and wire is made from very When the wire is manufactured, it is not only stretched beyond its The metal from which springs are made has therefore been To do this, once a spring has been formed into a coil, it is tempered- a process in which it is heated and kept at a high temperature for a sustained peri od.
This 'resets' the atomic structure of the metal partly, at least , so that after tempering, the spring will behave as it should - it can be What properties do the materials have? Which properties are strengths in this situation? Which properties are weaknesses, and how are these weaknesses overcome?
Generally, hard materials are more durable than soft materials, because they are better at resisting wear- progressively worsening damage- to their surfaces. Materia ls with a high degree of scratch hardness are said to have good abrasion resistance- they are good at resisting damage due to abrasion the action of two surfaces being rubbed together.
Scratches Indentations - Fatigue, fracture toughness and creep The article below is fro m an aviation magazine. In aircraft construction, special attention must and which worsen over time. The speed at which be paid to two materials problems that are fatigue cracking progresses depends on the well understood by mechanical and structural material's fracture toughness.
This is a measure engineers. One is fatigue, often called metal fatigue in metals. This problem is caused by cyclic loads- forces that Another problem is creep - where components continually vary.
In aircraft, the wings are affected become permanently deformed stretched, for by cyclic loading as they frequently flex, continually example , due to loads. Creep increases over bending up and down due to air turbulence. The time. The problem is made worse by heat, so is consequence of fatigue is micro-cracking - the a major issue in engines, where both loads and formation of cracks too small to see with the eye, temperatures are high. Basic thermal properties Some materials conduct carry or transmit heat better than others.
Therefore, thermal conductivity varies, depending on the material. Copper, for example, is an excellent thermal conductor. Polystyrene, on the other hand, is an excellent thermal insulator and so a very poor thermal conductor. As temperature increases, most materials expand increase in size due to heating , and as temperature falls, they contract decrease in size due to cooling. The extent to which expansion and contraction occur is measured by a material's coefficient of thermal expansion - that is, its change in size for a given change in temperature.
The coefficient for aluminium, for example, is 0. This means that for an increase in temperature of one degree Celsius, a one-metre length of aluminium will increase in length by 0. This figure can also be referred to as the coefficient of linear expansion, since it describes change in length a linear measurement. These will allow the operator to see the cutting wheel at all times, and will shield the operator from flying metal fragments. The guards must therefore be constructed from material with a high degree of As the guards will require regular cleaning, the action of wiping away metal fragments will result in The guards must, therefore, have sufficient When comparing copper and aluminium as materials for electrical wires, it is necessary to consider their thermal properties.
For instance, in situations where high temperatures are involved, it is important to understand how quickly wires In this regard, the In the example above, a designer might therefore prefer aluminium wiring over copper wiring.
Another issue is thermal movement- the extent to which the metals In situations where temperature continually rises and falls, the resulting In this regard, copper has a Copper therefore has the advantage in this respect, as it is less susceptible to movement.
Ove,r 1-o 't. What materials were chosen as a result of these considerations? Casting involves heating metal until it becomes molten liquid and pouring it, or forcing it under pressure, into a mould called a die.
Instead of being cast, metal components can be formed by sintering. This is done by using metal powder instead of molten metal. The powder is placed in a die and compressed into a solid mass. It is then heated though not melted until it becomes sintered - that is, the powder particles join together structurally, due to the heat. Metal can also be shaped by extruding it into long lengths. Extrusion involves heating metal until it is molten, then forcing it at high pressure through a shaping tool- also called a die- to form bars or tubes, for example.
At the same time, the metal cools and becomes solid. The metal was then worked- in other words, shaped by hammering it. Working metal using compression for example, hammering is also called forging. The same basic technique is still in use today, especially with steel. However, large, automated machines are now used.
Metal is often worked or forged when hot hot forged , but may also be worked when it is cold cold forged. A common forging technique is drop forging, where a heavy hammer is dropped onto a piece of metal.
A die fixed to the hammer compresses the metal into the required shape. Rollers can also be used to apply compression, with or without heat, to produce hot rolled or cold rolled metal.
Forging also increases the hardness of metal. This is called work hardening. Metal becomes work hardened because its structure is changed by compression. The same result can be achieved without hammering or rolling - and therefore without changing the component's shape - by shot-peening.
This involves firing small metal balls metal shot at the surface of components when cold , at high speed. After components have been shot-peened, their surface is significantly harder. Dro p forged steel - Heat treating metal The properties of a metal can be changed by heat treating it- that is, heating and cooling the metal.
The table below, from the technical information section of a steel supplier's website, summarizes the main types of heat treatment. Type of heat treatment Description of process Properties of treated metal quenching Metal is heated, then di pped in water or Quenched metal is harder, but tends to oil to cool it ra pidly.
The first stage in manufacturing the blades for the cutting tools is to form them into an approximate shape by 1 a process of squeezing molten metal through a die. Before the blades have cooled, they are then 2 hammered while still at a high temperature - a process which not only flattens them into their final shape, but also ensures the metal becomes 3 harder as a result of the hammering action.
The blades are then 4 cooled quickly in water. Finally, they are 5 bombarded with small metal balls in order to further increase their surface hardness. Suggest different ways of obtaining these properties by forging or heat treating the steel. When steel and other metals are produced, they are made into blocks called ingots, which can subsequently be melted and cast. Very large steel ingots are called blooms. One standard size for steel blooms is mm x mm x 6 m. Steel can also be supplied in smaller blocks, of various sizes, called billets.
These can be round bars or rods which have a circular section. They may also be square bars, with a square section, and flat bars, with a flat, rectangular section. A bar is generally made of metal, but a rod can be made of any material. Other materials supplied in sheets include plastic, glass and wood. However, sheets of wood are often called boards.
When sheets of metal or metal sheets are delivered in large quantities, they can be supplied in rolls called coils. Non-metals, such as glass, plastic or wood, are not usually called plates; even if these materials are thicker than 3 mm, they are usually called sheets. See Appendix Von page for types of structural section. The most common types are round tubes, but square tubes and rectangular tubes are also produced.
Pipes are specifically for carrying liquid or gas. A pipe is therefore just one type of tube. They are usually supplied in coils. Several wires can be combined to form a cable. An electrical wire is a single conductor covered with insulation. The conductor can be a single wire called a solid wire or several strands of wire grouped together called a stranded wire.
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