材料科学与工程专业英语ppt课件.ppt

材料专业英语翻译,主讲：林建国,课程简介：,课堂6学时，课后14学时考试：开卷，当堂完成,主要内容及课时安排,Introduction to materials science and engineering(4学时)Metallic materials and alloys（4学时）Ceramics（2学时）Composites（2学时）Nanostructured materials（2学时）,Part 1 Introduction to materials science and engineering,Unit 1 Physical and chemical properties of materialsUnit 2 Mechanical properties of materials,Unit 1 Physical and chemical properties of materials,Physical properties are those that can be observed without changing the identity of the substance. The general properties of matter such as color, density, hardness, are examples of physical properties. Properties that describe how a substance changes into a completely different substance are called chemical properties. Flammability and corrosion/oxidation resistance are examples of chemical properties.,In general, some of the more important physical and chemical properties from an engineering material standpoint include phase transformation temperatures, density, specific gravity, thermal conductivity, linear coefficient of thermal expansion, electrical conductivity and resistivity, magnetic permeability, and corrosion resistance, and so on.,磁导率,Phase Transformation Temperatures,When temperature rises and pressure is held constant, a typical substance changes from solid to liquid and then to vapor. Transitions from solid to liquid, from liquid to vapor, from vapor to solid and visa versa are called phase transformations or transitions. Since some substances have several crystal forms, technically there can be solid to another solid from phase transformation.,Melting point: the phase transition temperature where a solid changes to a liquidBoiling point: the temperature at which the vapor pressure of a liquid equals 1 atm (101.3 kPa),Some materials, such as many polymers, do not go simply from a solid to a liquid with increasing temperature. Instead, at some temperature below the melting point, they start to lose their crystalline structure but the molecules remain linked in chains, which results in a soft and pliable material. The temperature at which a solid, glassy material begins to soften and flow is called the glass transition temperature.,Density,Mass can be thinly dsitrbuted as in a pillow, or tightly packed as in a block of lead. 质量可以像枕头似地稀疏地分布，也可以像铅那样紧紧地堆积在一起。The space the mass occupies is its volume, and the mass per unit of volume is its density.,Mass (m) is a fundamental measure of the amount of matter. Weight (w) is a measure of the force exerted by a mass and this force is produced by the acceleration of gravity.Therefore, on the surface of earth, the mass of an object is determined by dividing the weight of an object by 9.8 m/s2 (the acceleration of gravity on the surface of the earth).,因此，在地球表面，物体的质量由物体的重量和重力加速度所决定。Since we are typically comparing things on the surface of the earth, the weight of an object is commonly used rather than calculating its mass.,The density (r) of a material depends on the phase it is in and the temperature (the density of liquids and gases is very temperature dependent). Water in the liquid state has a density of 1 g/cm3 at 4 . Ice has a density of 0.917 1 g/cm3 at 0 , and it should be noted that this decrease in density for the solid phase is unusual. For almost all other substances, the density of the solid phase is greater than that of the liquid phase. Water vapor has a density of 0.051 g/cm3.,Specific Gravity,Specific gravity is the ratio of density of a substance compared to the density of fresh water at 4 . At this temperature the density of water is at its greatest value and equal to 1 g/mL. Since specific gravity is a ratio, so it has no units. An object will float in water if its density is less than the density of water and sink if its density is greater than that of water.,Similarly, an object with specific gravity less than 1 will float and those with a specific gravity greater than 1 will sink. Specific gravity values for a few common substances are Au, 19.3; mercury, 13.6; alcohol, 0.7893; benzene, 0.8786. Note that since water has density of 1 g/cm3, the specific gravity is the same as the density of the material measured in g/cm3.,Magnetic Permeability,Magnetic permeability or simply permeability is the ease with which a material can be magnetized. It is a constant of proportionality that exists between magnetic induction and magnetic field intensity.,磁感应强度,磁场强度,This constant is equal to approximately 1.25710-6 Henry per meter (H/m) in free space (a vacuum). In other materials it can be much different, often substantially greater than the free-space value, which is symbolized 0 .其他材料却截然不同，通常远大于真空值。,Materials that cause the lines of flux to move farther apart, resulting in a decrease in magnetic flux density compared with a vacuum, are called diamagnetic. Materials that concentrate magnetic flux by a factor of more than one but less than or equal to ten are called paramagnetic; materials that concentrate the flux by a factor of more than ten are called ferromagnetic. The permeability factors of some substances change with rising or falling temperature, or with the intensity of the applied magnetic field.,Exercises,Translate the following into Chinese Phase transformation temperaturesSpecific gravityThermal conductivityThe melting pointThe acceleration of gravityMagnetic permeabilityMagnetic lines of fluxferromagnetic,Unit 2 Mechanical Properties of Materials,The mechanical properties of a material are those ones that involve a reaction to an applied load.The common properties considered are strength, ductility, hardness, impact resistance, and fracture toughness.,强度、延展性、硬度、冲击强度、断裂韧性,Most structural materials are anisotropic, which means that their material properties vary with orientation. The variation in properties can be due to directionality in the microstructure (texture) from forming or cold working operation, the controlled alignment of fiber reinforcement and a variety of other causes. Mechanical properties are generally specific to product form such as sheet, plate, extrusion, casting, forging, and etc.,Additionally, it is common to see mechanical property listed by the directional grain structure of the material. In products such as sheet and plate, the rolling direction is called the longitudinal direction, the width of the product is called the transverse direction, and the thickness is called the short transverse direction. longitudinal lnditju:dinl 轴向Transverse trnsv:s 横向,The mechanical properties of a material are not constant and often change as a function of temperature, rate of loading , and other conditions. For example, temperatures below room temperature generally cause an increase in strength properties of metallic alloys; while ductility, fracture toughness, and elongation usually decrease. Temperatures above room temperature usually cause a decrease in the strength properties of metallic alloys. Ductility may increase or decrease with increasing temperature depending on the same variables,It should be also be noted that there is often significant variability in the values obtained when measuring mechanical properties. Seemingly identical test specimen from the same lot of materials will often produce condsideralbe different results. Therefore, multiple tests are commonly conducted to determine mechanical properties and values reported can be an average value or calculated statistical minimum value. Also, a range of values is sometimes reported in order to show variability.,loading,The application of a force to an object is known as loading. Materials can be subjected to many different loading scenarios and a materials performance is depent on the loading conditions. There are five fundamental loading conditions: tension, compression, bending, shear, and torsion.scenarios:情况 情节,Tension is the type of loading in which the two sections of material on either side of a plane tend to be pulled apart or elongated. Compression is the reverse of tensile loading and involves pressing the material together.Loading by bending involves applying a load in a manner that causes a material to curve and results in compressing the material on one side and stretching it on the other.,Shear involves applying a load parallel to a plane which caused the material on one side of the plane to want to slide across the material on the other side of the plane. Torsion is the application of a force that causes twisting in a material.,If a material is subjected to a constant force, it is called static loading. If the loading of the material is not constant but instead fluctuates, it is called dynamic or cyclic loading. The way a material is loaded greatly affects its mechanical properties and largely determines how, or if, a component will fail; and whether it will show warning signs before failure actually occurs.,Stress,The term stress (S ) is used to express the loading in terms of force applied to a certain cross-sectional area of an object. From the perspective of loading, stress is the applied force or system of forces that tends to deform a body. From the perstective of what is happening within a material, stress is the internal distribution of forces within a body that balance and react to the loads applied to it. The stress distribution may or may not be uniform, depending on the nature of the loading condition.,For example, a bar loaded in pure tension will essentially have a uniform tensile stress distribution. However, a bar loaded in bending will have a stress distribution that changes withDistance perpendicular to the normal axis.,垂直的,Strain,Strain is the response of a system to an applied stress. When a material is loaded with a force, it produces a stress, which then causes a material to deform. Engineering strain is defined as the amount of deformation in the direction of the applied force divided by the initial length of the material. The results in a unitless number, although it is often left in the unsimplified form, such as inches per inch or meters per meter.,工程应变可定义为：所施加力方向上的材料的改变量与材料原始长度的比值,For example, the strain in a bar that is being stretched in tension is the amount of elongation or change in length divided by its original length. As in the case of stress, the strain distribution may or may not be uniform in a complex structural element, depending on the nature of the loading condition.,If the stress is small, the material may only strain a small amount and the material will return to its original size after the stress is released. This is called elastic deformation, because of liking elastic, it returns to its unstressed state. Elastic deformation only occurs in a material when stresses are lower than a critical stress called the yield strength. If a material is loaded beyond it elastic limit, the material will remain in a deformed condition after the load is removed. This is called plastic deformation.,Tensile properties,Tensile properties indicate how the material will react to forces being applied in tension. A tensile test is a fundamental mechanical test where a carefully prepared specimen is loaded in a very controlled manner while measuring the applied load and the elongation of the specimen over some distance. Tensile tests are used to determine the modulus of elasticity, elastic limit, elongation, proportional limit, reduction in area, tensile strength, yield point, yield strength and other tensile properties.,拉伸试验是一种基本的力学测试，它是对所制备好的样品施加一种可以控制的负荷，来测量所施加的负荷和在一段距离内样品的拉长。,Hardness,Hardness is the resistance of a material to localized deformation. The term can apply to deformation from indentation, scratching, cutting or bending. In metals, ceramics and most polymers, the deformation considered is plastic deformation of the surface. For elastomers and some polymers, hardness is defined at the resistance to deformation of the surface.,The lack of a fundamental definition indicates that hardness is not be a basic property of a material, but rather a composite one with contributions from the yield strength, work hardening, true tensile strength, modulus, and other factors.Hardness measurements are widely used for the quality control of materials because they are quick and considered to be nondestructive tests when the marks or indentations produced by the test are in low stress areas.,Toughness,The ablity of a metal to deform plastically and to absorb energy in the process before fracture is termed toughness. The emphasis of this definition should be placed on the ablity to absorb energy before fracture. Recall that ductility is a measure of how much something deforms plastically before fracture, but just because a material is ductile does not make it tough.,The key to toughness is a good combination of strength and ductility. A material with high strength and high ductility will have more toughness than a material with low strength and high ductility. Therefore, one way to measure toughness is by calculating the area under the stress strain curve from a tensile test. This value is simply called “material toughness” and it has units of energy per volume. Material toughness equates to a slow absorption of energy by the material.,Exercises,Translate the following into Chinesethe service life the longitudinal directionthe transverse directiondynamic or cyclic loadingthe initial length of the material elastic deformationplastic deformationlocalized doformation,Part Metallic Materials and Alloys,Unit 3 Metals and Their Applications,Introduction to Metals and Alloys,In chemistry, a metal is defined as an element that readily loses electrons to form positive ions (cations) and forms metallic bonds between other metal atmos (forming ionic bonds with non-metals).,The metals of the periodic table are formally defined as lithium, beryllium, sodium, magnesium, aluminium, potassium, calcium, scandium, titanium, vanadium, chromium, zirconium, niobium, molybdenum, technetium, ruthenium, rhodium, palladium, silver, cadmium, indium, tin, antimony, caesium, barium, lanthanum, hafnium, tantalum, tungsten, rhenium, osmium, iridium, platinum, gold, mercury, thallium, lead and bismuth.,berilim 铍,liim 锂,sudim 钠,mgni: zim 镁,.ljuminim 铝,tsim 钾,klsim 钙,skndim钪,taiteinim 钛,vneidim 钒,krumim 铬,z:kunim 锆,naiubim 铌,mlibdinm钼,tekni:im 锝 Tc,ru:i:nim 钌,rudim 铑,leidim 钯,silv 银,kdmim 镉,indim 铟,tin 锡,ntimni 锑,si:zim 铯,brim 钡,lnnm镧,hfnim铪,tntlm 钽,tstn 钨,ri:nim 铼,zmim 锇,airidim 铱,ltinm 铂,m:kjuri 汞,lim 铊,li:d 铅,bizm 铋,Metals are sometimes described as a lattice of positive ions surrounded by a cloud of delocalized electrons. Metals are one of the three groups of elements as distinguished by their ionization and bonding properties, along with the metalloids and nonmetals.ionization：.ainaizein,.ainzein离子化，电离 metalloid: metlid,metl.id 类金属,An alternative definition of metals is that they have overlapping conduction bands and valence bands in their electronic structure. This definition opens up the category for metallic polymers and other organic metals, which have been mad