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（磚層）were bound together with mortar or bitumen, a tarlike substance, or some other binding agent（粘合劑）. The Greeks and Romans sometimes used iron rods or clamps to strengthen their building. The columns of the Parthenon in Athens

3、（雅典的帕臺農(nóng)神廟）, for example, have holes drilled（鉆孔） in them for iron bars that have now rusted away（銹蝕殆盡）. 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體，如磚、石、瓦以及類似的材料。磚層之間通過砂漿、瀝青（一種焦油狀的物質(zhì)）或其他一些粘合劑粘合在一起。希臘人和羅

4、馬人有時(shí)用鐵條或夾子來加固他們的房屋。例如，雅典的帕臺農(nóng)神廟柱子中曾鉆孔以便加入鐵條，如今都已銹蝕殆盡。羅馬人也用稱作白榴火山灰的天然水泥，它用火山灰制作，在水中會變得與石頭一樣堅(jiān)硬。FU RUIBoth steel and cement, the two most important construction materials of modern times, were introduced（推廣） in the nineteenth century. Steel, basically an alloy of iron （鐵合金）and a small amount of carbon,

5、had been made up to that time（到那個時(shí)候） by a laborious（繁復(fù)的） process that restricted it to such special uses as sword blades（刀刃）. After the invention of the Bessemer process （貝塞麥煉鋼法）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 (適當(dāng)?shù)? 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（連續(xù)的應(yīng)力變化）.FU RUI 作為現(xiàn)代兩種最重要的建筑材料，鋼材與水泥在十九世紀(jì)得到了推廣。直到那個時(shí)候，鋼材才通過繁復(fù)的過程制造出來，基本上是鐵合金，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年發(fā)明了貝塞麥煉鋼法后，鋼材才得以大量低價(jià)獲得。鋼材巨大的優(yōu)勢即是它的抗拉強(qiáng)度，也就是當(dāng)它在適當(dāng)?shù)睦ο虏粫?qiáng)度，正如我們所看到的，該力往往能夠?qū)⒑芏嗖牧侠_。新的合金進(jìn)一步提高了鋼材的強(qiáng)度，并消除了一些缺點(diǎn)，如疲勞，即在連續(xù)的應(yīng)力變化下導(dǎo)致強(qiáng)度減弱的趨勢。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 （施工現(xiàn)場）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 （噴射成）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（互補(bǔ)）.FU RUI現(xiàn)代水泥發(fā)明于1824年，稱為波特蘭水泥。它是石灰石和粘土的混合物，加熱后磨成粉末。在或靠近施工現(xiàn)場，將水泥與砂、骨料（小石頭、壓碎的巖石或礫石）、水混合而制成混凝土。不同比例的配料會制造出不同強(qiáng)度和重量的混凝土。混凝土的用途很多，可以澆筑、泵送甚至噴射成各種形狀?；炷辆哂泻艽蟮目箟簭?qiáng)度，而鋼材具有很大的抗拉強(qiáng)度。這樣，兩種材料可以互補(bǔ)。FU RUIThe adoption of structural steel and reinforced concrete caused

11、major changes in traditional construction practices（施工作業(yè)）. 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結(jié)構(gòu)鋼與鋼筋混凝土的采用使傳統(tǒng)的施工作業(yè)發(fā)生了明顯的變化。對多層建筑，再也沒必要采用厚的石墻或磚墻，且施工防火地面變?yōu)槿菀椎枚唷＿@些變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為可能。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（承重墻）. FU RUIToday, however, curtain walls are often made of lightweight material

14、s such as glass, aluminum, or plastic, in various combinations.由于現(xiàn)代結(jié)構(gòu)的重量由鋼或混凝土框架承受，墻體不再支承建筑物。它們成為幕墻，將日曬風(fēng)吹雨打阻擋在外，而讓光線進(jìn)入。在較早的鋼或混凝土框架建筑中，幕墻一般由砌體構(gòu)成；它們具有承重墻的結(jié)實(shí)外觀。但是今天，幕墻通常由輕質(zhì)材料組成，如玻璃、鋁或塑料，并形成不同的組合。FU RUIPhysical PropertiesMechanical PropertiesChemical PropertiesElectrical PropertiesMagnetic PropertiesOpt

15、ical PropertiesThermal PropertiesFU RUIBulk Density 容積密度Chemical Resistance 化學(xué)穩(wěn)定性Coefficient of Softening 軟化系數(shù)Density 密度Density Index 密度指數(shù)Porosity 孔隙率Specific Heat 比熱FU RUIThermal Conductivity 導(dǎo)熱率Thermal Capacity 熱容量Water Absorption 吸水性Permeability 滲透性FU RUIIt is defined as the mass per unit volume

16、of the material in its homogeneous(均勻的） state , i.e. neglecting the volume of pores and voids.材料在絕對密實(shí)狀態(tài)下單位體積的質(zhì)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.材料在自然狀態(tài)下單位體積的質(zhì)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.定義：材料體積內(nèi)被固體物質(zhì)充實(shí)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.材料中的孔隙體積與總體積的百分比成為孔隙率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.材料在外力作用下產(chǎn)生變形，當(dāng)外力去除后能完全恢復(fù)

20、到原始形狀的性質(zhì)稱為彈性彈性。FU RUIIt is the property of a material, by which no deformation vanishes, when it is relieved from the external load.材料在外力作用下產(chǎn)生變形，當(dāng)外力去除后，有一部分變形不能恢復(fù)，這種性質(zhì)稱為材料的塑性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，不發(fā)生明顯的變形而突然破壞的一種性能，稱為脆性FU RUIToughness is the property of a material that enables it to absorb energy without fracture(斷裂）.材料在外力作用下，能吸收大量的能量，并能承受較大的變形而不至于破壞的性能，稱為韌性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.材料在長期使用過程中，能保持其原有性能而不變質(zhì)、不破壞的性質(zhì)，統(tǒng)稱之為耐耐久性久性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(易潮濕的） 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 (澆鑄）clay（粘土） in rectangular blocks of uniform size, then by drying and burning these blocks in brick kilns（磚窯）.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 (排水溝）and arches（拱橋）Hollow bricks（bricks with cavities) are used for sound and heat insulation purposesFire bricks are used for insulating chimneys(煙囪） 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 (熱軋）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(鋼屋架）, 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（鋼架結(jié)構(gòu)）.FU RUIFU RUIWhen stone or gravel, sand, cement and water are mixed together, they form an easily workable plastic mixture（塑性漿體） 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簡寫砼（tong)，是當(dāng)代最主要的土木工程材料之一?；炷潦怯赡z結(jié)材料，骨料和水按一定比例配制，經(jīng)攪拌振搗成型，在一定條件下養(yǎng)護(hù)而成的人造石材。1824年Aspdin發(fā)明了波特蘭水泥（硅酸鹽水泥），以水泥作為膠凝材料的混凝土開始問世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