Unit 3 Engineering Materials

1、FU RUIDevelopment History of Building MaterialsProperties of Building MaterialsConstruction Materials-WoodConstruction Materials-BricksConstruction Materials-Steel SectionsConstruction Materials-Cement ConcreteExercisesFU RUI The principal construction materials of earlier times were wood and masonr

2、y-brick, stone, or tile(瓦）, and similar materials. The courses or layers（砖层）were bound together with mortar or bitumen, a tarlike substance, or some other binding agent（粘合剂）. The Greeks and Romans sometimes used iron rods or clamps to strengthen their building. The columns of the Parthenon in Athens

3、（雅典的帕台农神庙）, for example, have holes drilled（钻孔） in them for iron bars that have now rusted away（锈蚀殆尽）. The Romans also used a natural cement called pozzolana, made from volcanic ash, that became as hard as stone under water.FU RUI早期主要的建筑材料是木材和砌体，如砖、石、瓦以及类似的材料。砖层之间通过砂浆、沥青（一种焦油状的物质）或其他一些粘合剂粘合在一起。希腊人和罗

4、马人有时用铁条或夹子来加固他们的房屋。例如，雅典的帕台农神庙柱子中曾钻孔以便加入铁条，如今都已锈蚀殆尽。罗马人也用称作白榴火山灰的天然水泥，它用火山灰制作，在水中会变得与石头一样坚硬。FU RUIBoth steel and cement, the two most important construction materials of modern times, were introduced（推广） in the nineteenth century. Steel, basically an alloy of iron （铁合金）and a small amount of carbon,

5、had been made up to that time（到那个时候） by a laborious（繁复的） process that restricted it to such special uses as sword blades（刀刃）. After the invention of the Bessemer process （贝塞麦炼钢法）in 1856, steel was available in large quantities at low prices. FU RUIThe enormous advantage of steel is its tensile stren

6、gth; that is, it does not lose its strength when it is under a calculated degree (适当的) of tension, a force which, as we have seen, tends to （往往）pull apart many materials. New alloys have further increased the strength of steel and eliminated some of its problems, such as fatigue, which is a tendency

7、 for it to weaken as a result of continual changes in stress（连续的应力变化）.FU RUI 作为现代两种最重要的建筑材料，钢材与水泥在十九世纪得到了推广。直到那个时候，钢材才通过繁复的过程制造出来，基本上是铁合金，并含有少量的碳，因而被限制在一些特殊的用途如刀刃。在1856年发明了贝塞麦炼钢法后，钢材才得以大量低价获得。钢材巨大的优势即是它的抗拉强度，也就是当它在适当的拉力下不会失去强度，正如我们所看到的，该力往往能够将很多材料拉开。新的合金进一步提高了钢材的强度，并消除了一些缺点，如疲劳，即在连续的应力变化下导致强度减弱的趋势。F

8、U RUIModern cement, called Portland cement, was invented in 1824. It is a mixture of limestone（石灰石） and clay, which is heated and then ground into a powder（磨成粉末）. It is mixed at or near the construction site （施工现场）with sand, aggregate (small stones, crushed rock, or gravel), and water to make concre

9、te. Different proportions of the ingredients （配料）produce concrete with different strength and weight. FU RUIConcrete is very versatile; it can be poured, pumped, or even sprayed into （喷射成）all kinds of shapes. And whereas steel has great tensile strength, concrete has great strength under compression

10、. Thus, the two substances complement each other（互补）.FU RUI现代水泥发明于1824年，称为波特兰水泥。它是石灰石和粘土的混合物，加热后磨成粉末。在或靠近施工现场，将水泥与砂、骨料（小石头、压碎的岩石或砾石）、水混合而制成混凝土。不同比例的配料会制造出不同强度和重量的混凝土。混凝土的用途很多，可以浇筑、泵送甚至喷射成各种形状。混凝土具有很大的抗压强度，而钢材具有很大的抗拉强度。这样，两种材料可以互补。FU RUIThe adoption of structural steel and reinforced concrete caused

11、major changes in traditional construction practices（施工作业）. It was no longer necessary to use thick walls of stone or brick for multistory buildings, and it became much simpler to build fire-resistant floors（防火地面）. Both these changes served to（有利于） reduce the cost of construction. It also became poss

12、ible to erect（建造）buildings with greater heights and longer spans.FU RUI结构钢与钢筋混凝土的采用使传统的施工作业发生了明显的变化。对多层建筑，再也没必要采用厚的石墙或砖墙，且施工防火地面变为容易得多。这些变化有利于降低建筑的成本。它也使建造高度更高和跨度更大的建筑物成为可能。FU RUISince the weight of modern structures is carried（承受） by the steel or concrete frame, the walls do not support the buildin

13、g. They have become curtain walls, which keep out the weather and let in light. In the earlier steel or concrete frame building, the curtain walls were generally made of masonry; they had the solid look of bearing walls（承重墙）. FU RUIToday, however, curtain walls are often made of lightweight material

14、s such as glass, aluminum, or plastic, in various combinations.由于现代结构的重量由钢或混凝土框架承受，墙体不再支承建筑物。它们成为幕墙，将日晒风吹雨打阻挡在外，而让光线进入。在较早的钢或混凝土框架建筑中，幕墙一般由砌体构成；它们具有承重墙的结实外观。但是今天，幕墙通常由轻质材料组成，如玻璃、铝或塑料，并形成不同的组合。FU RUIPhysical PropertiesMechanical PropertiesChemical PropertiesElectrical PropertiesMagnetic PropertiesOpt

15、ical PropertiesThermal PropertiesFU RUIBulk Density 容积密度Chemical Resistance 化学稳定性Coefficient of Softening 软化系数Density 密度Density Index 密度指数Porosity 孔隙率Specific Heat 比热FU RUIThermal Conductivity 导热率Thermal Capacity 热容量Water Absorption 吸水性Permeability 渗透性FU RUIIt is defined as the mass per unit volume

16、of the material in its homogeneous(均匀的） state , i.e. neglecting the volume of pores and voids.材料在绝对密实状态下单位体积的质量FU RUIIt is defined as the mass per unit volume of material in its natural state, i.e. including volume of pores and voids.材料在自然状态下单位体积的质量FU RUIFor a sort of material, whats the relationshi

17、p between Density and Bulk Density?FU RUIThe ratio of bulk density of the material to its density is known as its density index.定义：材料体积内被固体物质充实的程度%100%100000mmVVDFU RUIThe degree by which the volume of material is occupied by pores is termed as porosity. It is the ratio of volume of voids to the tot

18、al volume of the specimen.材料中的孔隙体积与总体积的百分比成为孔隙率P%1001%1001%1000000PFU RUIThe ability of a material to absorb and retain water is termed as its water absorption. It is expressed either as percentage of weight or percentage of volume of dry material. It mainly depends on the bulk density and porosity

19、of the material.FU RUIAbrasionElasticityPlasticityStrengthImpact StrengthWearFatigueFU RUIHardnessBrittlenessDuctilityMalleabilityToughnessFU RUIThe property by which a material regains its original shape and position after the removal of external load is known as elasticity.材料在外力作用下产生变形，当外力去除后能完全恢复

20、到原始形状的性质称为弹性弹性。FU RUIIt is the property of a material, by which no deformation vanishes, when it is relieved from the external load.材料在外力作用下产生变形，当外力去除后，有一部分变形不能恢复，这种性质称为材料的塑性FU RUIWhats the difference between Elasticity and Plasticity?FU RUIA material is said to be brittle when it cannot be drawn in

21、to a wire by tension. A brittle material fails suddenly under pressure without appreciable deformation preceding the failure. 材料在外力作用下，不发生明显的变形而突然破坏的一种性能，称为脆性FU RUIToughness is the property of a material that enables it to absorb energy without fracture(断裂）.材料在外力作用下，能吸收大量的能量，并能承受较大的变形而不至于破坏的性能，称为韧性F

22、U RUIThe property of a material to resist the combined action of atmospheric and other factors is known as its durability. The life and maintenance cost of any structure depends upon the durability of the materials which it is composed of.材料在长期使用过程中，能保持其原有性能而不变质、不破坏的性质，统称之为耐耐久性久性FU RUITimber is a fo

23、rm of wood suitable for building or engineering purposes. It is obtained from trees. FU RUISpecific gravity: Wood is a very light material its specific gravity being always less than one. Woods show good deal of variation in their specific gravity. This depends on their structure and presence of por

24、es in them.Moisture content: All woods are hygroscopic(易潮湿的） in nature. They gain moisture from atmosphere. Wood may absorb moisture more than 2-2.5 times than its own weight.FU RUIIt is used for door and window frames, shutters of doors and windows, roofing materials , etc.It is used for making fur

25、niture, agricultural instruments, sports goods, musical instruments, etc.It is used for making railway coach wagons.It is used for railway sleepers, packing cases, etc.It is used for temporary bridges and boat constructionFU RUIThe common brick is one of the oldest building materials and it is exten

26、sively used at present because of its durability, strength, reliability, low cost, etc.Bricks are obtained by moulding (浇铸）clay（粘土） in rectangular blocks of uniform size, then by drying and burning these blocks in brick kilns（砖窑）.FU RUIFU RUIBricks should have perfect edges, well-burnt in kilns, cop

27、per(赤褐色） coloured, free from cracks with proper rectangular shape and of standard size(19x9x9 cm)Bricks should have low thermal conductivity and should be soundproof.The minimum crushing strength of bricks must be 3.5N/mmFU RUIThe construction of walls to carry the loads from roofs to the foundation

28、The construction of gutters (水槽), drains (排水沟）and arches（拱桥）Hollow bricks（bricks with cavities) are used for sound and heat insulation purposesFire bricks are used for insulating chimneys(烟囱） and ovensFU RUISteel is a structural material which consists mostly of iron and carbon. It can, however, con

29、tain other additives which might change the steels properties. Steel can be hot rolled (热轧）or cold formed into structural shapes, such as the familiar I beam known today as a wide flange. Steel has the same strength in tension as it has in compression, unlike concreteFU RUIAngle sections may be of e

30、qual legs or unequal legs.Angle sections are used in the construction of steel roof trusses(钢屋架）, steel beams and as stiffeners in huge girders(大梁）. It is mainly used in the construction of steel bridge.FU RUIFU RUIFU RUIA channel section consists of a web with two equal flanges.Typically a channel

31、section is designated by the height of web and the width of flangeChannel sections are widely used as structural members of the steel-framed structures（钢架结构）.FU RUIFU RUIWhen stone or gravel, sand, cement and water are mixed together, they form an easily workable plastic mixture（塑性浆体） which can be m

32、oulded and cast into desired shapes or structures. This cement and water in the plastic mixture undergo a chemical combination in a few hours after the mixing results in a solidification and gradual hardening. This mixture is called concrete. FU RUIConcrete is a structural material which consists of

33、 Portland cement, aggregate (sand and rock), and water (to make the chemical reaction called hydration occur).Concrete can sometimes contain other substances, such as fly ash(粉煤灰） from industrial smoke stacks, which can change its properties.FU RUI简写砼（tong)，是当代最主要的土木工程材料之一。混凝土是由胶结材料，骨料和水按一定比例配制，经搅拌振捣成型，在一定条件下养护而成的人造石材。1824年Aspdin发明了波特兰水泥（硅酸盐水泥），以水泥作为胶凝材料的混凝土开始问世FU RUIFU RUIConcrete is a very strong material when it is placed in compression. It is, however, extremely weak in tension. It is for this