M. Ibbotson - Professional english in use engineering (794233), страница 11
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In each case, there is more thanone possi ble answer. Look at A opposite to help you.1 Engineered wood2 Softwood3 Solid woodcomes only from coniferous trees.comes only from decid uo us trees.can come from either conifero us or decidu ous trees.specifica lly describes single pieces of timber, not multiple pieces that have been bondedtogether.e is always made from multiple pieces or particles of wood.f may have knots in it.abcd1 7.2Complete the sentences below using words and expressions fro m B opposite.1 Wood has a smooth finish after it has been ...............................................................
.2 Wood cut with a circular saw is called ............................................................... timber.3 After timber is tested for strengths and weaknesses, it is given a ............................................................... .4 When tim ber is inspected by a person who looks for weaknesses, it is5 When timber is inspected by a machine which tests its strength, it is17.3Complete the article about the environmental considerations of wood using words from Band C opposite.From an environmental perspective, woodhas many advantages.
Firstly, it comes froma sustainable source. Coniferous trees growrelatively fast, providing a rapidly replaceablesource of (1) ................................ . Secondly, almostall the timber in a tree can be utilized, leavinglittle or no waste. The best quality wood can beused for structural applications, where solid,(2) ................................ sections are required byengineers; for high-strength elements such as(3) ................................ beams; and in the high-qualityplies used to make (4) .................................
Smallerstrands can be made into engineering wood withstructural properties, such as (5) ................................ .And small particles and fibres, including thosefrom waste timber, can go into cheapermaterials, like (6) ................................ board and(7) ................................ .Glue-laminated timber in the ScottishParliament building in Edinburgh, ScotlandOve,r .f-o tjoa . ,What types of timber are used in your horne and/or office, both as building materials and tomake fixtures and furniture within the building?Professional English in Use Engineering41rr.l,· Material properties 1IIU-Tensile strength and deformationWhen materials are exposed to forces, such as tension (stretching forces ~0~) andcompression (crusrung forces ~0~), they deform- that is, they change shape. The type ofdeformation 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 iscalled extension or elongation. It is especially important to understand the performance ofmaterials in tension, as their tensile strength (ability to resist tension) is usually lower thantheir compressive strength (ability to resist compression).-Elasticity and plasticitySome materials can extend significantly, but still return to their original shape.
A material'sability to do this is called elasticity. Rubber is an example of a very elastic material- it canbe elastically deformed to a considerable extent.If a material has very low elasticity, and is strong, engineers say it is stiff. If a material haslow elasticity and is weak, it is described as brittle- that is, it fractures (breaks, due totension) 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 saythese materials are plastic. Often, plasticity is described in specific terms. A material that can beplastically deformed by hammering or rolling- for example, lead (Pb)- is malleable. A materialthat can be drawn out (stretched) into a long length- for example, copper (Cu)- is ductile.-Stages in elastic and plastic deformationThe graph below shows the typical extension behaviour of ductile materials in tensile testing-where a sample bar is subjected to a progressively increasing tensile force.Points 0-1 The extension of the bar is proportional to the increase in tension.
For example,when tension increases by 10%, length increases by 10%.Point 1The bar reaches the limit of proportionality. Beyond this point, length begins toincrease at a slightly greater rate than tension.Point 2The elastic limit is reached. Beyond this point, the bar will no longer return toits original length. In many materials, the elastic limit occurs almost immediatelyafter the limit of proportionality.The bar reaches its yield point.
Once it yields, it continues to increase in length,Point 3even without a further increase in tension.Point 4This 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 5This is the fracture point, where the bar breaks in two.Tensile load203ExtensionElasticdeformation42Professional English in Use EngineeringPlasticdeformation18.1Complete the sentences using the words in the box. You will needLook at A opposite to help you.compressiOndeformationelongationextensiontouse one word twice.tension1 A stretching force is called ................................ .2 A crushing force is called ................................
.3 Extension is also called ................................ .4 Tension causes ................................ or ................................ .5 Tension or compression cause ................................ .1 8.2Match the two parts to make correct sentences. Look at B and C opposite to help you.If a material is stiff2 If a material is bri ttle3If a material is plastic4 If a material yields5 If a material fractures6 If a material is elastically deformedabcdef18.3ititititititis malleable and/or ductile.has low elasticity and low tensile strength.has low elasticity and high tensile strength.has been extended to a point before its elastic limit.has been loaded beyond its ultimate tensile strength.has been significantly plastically deformed, but not broken.Complete the magazine article about springs using words from A, B and C opposite.How are the springs used in car suspension made springy? It sounds like a sillyquestion, but thi nk about it fo r a moment.
In order for a spring to compressor extend, then return t o its original shape, it must be (1) ................................ .But spri ngs are made from wi re, and wire is made from very(2) ................................ met al (often cold drawn carbon steel) . Whenthe wire is manufactured, it is not only stretched beyondits (3) ................................................................
-meaning it willno longer return to its original length- but alsobeyond its (4) ................................................................ , wheresignificant, irreversible (5) ................................ occurs.The metal from which springs are made has thereforebeen (6) ................................
deformed and, consequently, needs to have its springiness put back .To do this, once a spring has been formed into a coil, it is tempered- a process in which it is heatedand kept at a high temperature for a sustained peri od . This 'resets' the atomic structure of themetal (partly, at least), so that after tempering, the spring will behave as it should - it can be(7) ................................ deformed and will subsequently return to its original shape .Ov~r .f-o 11o~·'J1Think about a device, vehicle or structure you're familiar with, and the materials used tomake it.
What properties do the materials have? Which properties are strengths in thissituation? Which properties are weaknesses, and how are these weaknesses overcome?Professional English in Use Engineering43Material properties 2HardnessThe hardness of a material affects its durability- that is, how long it will last. Generally, hardmaterials are more durable than soft materials, because they are better at resisting wearprogressively worsening damage- to their surfaces. Hardness can be defined in two main ways:•Scratch hardness describes a material's ability to resist being scratched.
Materia ls with ahigh degree of scratch hardness are said to have good abrasion resistance- they are goodat resisting damage due to abrasion (the action of two surfaces being rubbed together).•Indentation hardness describes a materia l's abil ity to resist indentations- that is,compressions in the surface of a material caused by impacts.Scratches-IndentationsFatigue, fracture toughness and creepThe article below is fro m an aviation magazine.In aircraft construction, special attention mustbe paid to two materials problems that arewell understood by mechanical and structuralengineers.One is fatigue, often called metal fatigue in metals.This problem is caused by cyclic loads- forces thatcontinually vary.
In aircraft, the wings are affectedby cyclic loading as they frequently flex, continuallybending up and down due to air turbulence. Theconsequence of fatigue is micro-cracking - theformation of cracks too small to see with the eye,and which worsen over time. The speed at whichfatigue cracking progresses depends on thematerial's fracture toughness.
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