济南大学专业英语考试

1 1 WhatWhat areare composites composites Characteristics Characteristics typestypes 什么是复合材料 特点 什么是复合材料 特点 类型 类型 p98p98 Composites Composites composites are hybrid 混合的 creations made of two or more materials that maintain their identities 身份 when combined They are combinations of materials assembled 组合的 together to obtain properties superior to those of their single constituent characteristics They are expensive compete with metal and polymers 高分子 because the manufacturing 制造 of composites involves many steps It s difficult to recycle Characteristics Characteristics 1 The properties of one constituent 成分 enhance the deficient 不足 properties of the other 2 Usually a given property of a composite lies between the values for each constituent 3 Sometimes the property of a composite is clearly superior to those of either of the constituents 4 Because manufacturing of composites involves many steps and is labour intensive 劳动力密集型产业 composites may be too expensive to compete with metals and polymers 5 Composites are usually difficult to recycle Types P96 Types P96 Composites are classified according to the nature of their matrix metal ceramic 陶瓷 polymer composite often designated 指定的 MMCs 金属基复合材料 CMCs 陶瓷基复合材料 PMCs 聚 合物基复合材料 2 2 classificationclassification ofof materialsmaterials 材料的分类 材料的分类 MaterialsMaterials Natural Inorganic Non Metallic Materials Ceramics Organic Materials Polymers blends 混纺 Metals Alloys Semiconductors Composites Biomaterials 生物材料 AccordingAccording toto theirtheir properties properties materialsmaterials cancan bebe broadlybroadly classi classifi eded intointo thethe followingfollowing groups groups Structural materials Functional materials Smart materials 智能材料 ScaleScale 数值范围 ofof MaterialsMaterials 1 Nanoscale sizes of about 1 to 100 nanometers 2 Microscale relevant for micro devices and microsystems having sizes of typically 1 to 1000 micrometers 微米 3 Macroscale materials 宏观材料 have the dimensions of all customary products devices and plants ranging from the millimeter 毫米 to the kilometer scale 3 3 PhysicalPhysical propertiesproperties names names 物理性质 名称 TheThe mechanicalmechanical propertiesproperties 机械性质 ofof material material bend test 弯曲试 验 ductility 延展性 elasticity 弹性 brittleness 脆性 Tensile test 抗拉试验 yield strength 屈服强度 tensile strength 抗张强度 Hardness test 硬度试验 hardness Impact test 冲击试验 toughness 韧性 under shock 冲击 Fatigue test 疲劳试验 fatigue behavior Stiffness 硬度 Creep test 蠕变试验 creep ThermalThermal properties properties thermal conductivity 热导率 specific heat capacity 比热容 OpticalOptical propertiesproperties 光学性质 reflection 反射 refraction 折射 dispersion 散射 ElectricalElectrical propertiesproperties 电学性质 conductivity 导电性 resistivity 电阻率 particle wave duality of light MagneticMagnetic properties properties perneabolity susceptibility 敏感性 magnetic induction 4 4 HowHow toto getget thethe stress strainstress strain curve curve WhatWhat areare thethe parametersparameters cancan wewe getget fromfrom thisthis curve curve 如何得到应力 应变曲线 我们从这个曲线得到什么参数 The result of a tensile test is commonly displayed in a stress strain diagram Y stress tensile stress X strain Under tensile stress the rod becomes longer in the direction of the applied force and eventually narrower perpendicular to that axis the change in longitudinal dimension in response to stress is called strain ParametersParameters 参数参数 1 yield strength 屈服强度 y 2 modulus of elasticity 弹性模量 E 3 tensile strength 抗张强度 t 4 necking 5 breaking Strength 力量 b 6 Stress 压力 7 strain 张力 5 5 whatwhat areare toughnesstoughness underunder shock shock fatiguefatigue behavior behavior creep creep 什么是冲击什么是冲击 韧性 疲劳行为 蠕变 韧性 疲劳行为 蠕变 p22 p22 ToughnessToughness underunder shock shock When subjected to a sudden blow some materials break at a lower stress than that measured using a tensile machine The impact tester investigates the toughness of materials by striking them at the center while fixing both ends Toughness is defined as the energy not the force required to break a material FatigueFatigue behavior behavior Materials even when stressed below the yield strength still may eventually break if a large number of tension and compression cycles are applied The fatigue test measures the number of bending cycles that need to be applied for a specific load until failure occurs Creep Creep The creep test measures the continuous and progressive plastic deformation of materials at high temperatures while a constant stress or a constant load below the room temperature yield strength is applied 6 6 WhatWhat areare phonons phonons HeatHeat capacitycapacity 什么是声子 热容 什么是声子 热容 p272 p272 TheThe heatheat capacity capacity C C is the amount of heat dQ that needs to be transferred to a substance in order to raise its temperature by a certain temperature interval The unit for the heat capacity is J K PhotonsPhotons During the absorption of light by intraband transitions an additional mechanism may take place It involves lattice vibration quanta called phonons They are quanta of the ionic displacement field which represent classical sound the word phonon conveys the particle nature of an oscillator 振子 7 7 illustratesillustrates lightlight interactioninteraction withwith mattermatter 说明说明 举例说明举例说明 光与物质的光与物质的 相互作用 相互作用 Absorption of light Emission of light refraction of light dispersion of light reflection of light transmission of light diffraction of light interference of light 8 8 luminescenceluminescence andand mechanism mechanism 发光和机制发光和机制 p259 What p259 What areare lasers lasers 什么什么 是激光 是激光 HowHow theythey areare obtained obtained 如何获得激光如何获得激光 P261 P261 Luminescence Luminescence The emission of light due to reversion of electrons from a higher energy state is called luminescence Mechanism Mechanism An electron once excited must eventually revert back into a lower empty energy state This occurs as a rule spontaneously within a fraction of a second and is accompanied by the emission of a photon and or the dissipation of heat phonons Laser Laser light amplification by stimulated emission of radiation Stimulated emission of light occurs when electrons are forced by incident radiation to add more photons to an incident beam 9 9 ThermoelectricityThermoelectricity andand piezoelectricity piezoelectricity ExamplesExamples andand applications applications 热电和压电 举例和应用热电和压电 举例和应用 p220 p212 p220 p212 Piezoelectricity Piezoelectricity The pressure is applied to a ferroelectric material a change in the just mentioned polarization may occur which results in a small voltage across the sample The slight change in dimensions causes a variation in bond lengths between cations and anions This effect is called piezoelectricity Examples Examples Quartz 石英 BaTiO3 in ZnO in PbZrTiO6 applications applications Piezoelectricity is utilized in devices that are designed to convert mechanical strain into electricity Those devices are called transducers Applications include strain gages microphones sonar detectors and phonograph pickups to mention a few Thermoelectricity Thermoelectricity Assume two different types of materials e g a copper and aniron wire which are connected at their ends to form a loop One of the junctions is brought to a higher temperature than the other Then a potential difference V between these two thermocouples is observed which is essentially proportional to the temperature difference T where V T S is called the thermoelectric power ExamplesExamples andand applications applications ThermocouplesThermocouples made of metal wires are utilized as rigid inexpensive and fast probes for measuring temperatures even at otherwise not easily accessible places ThermoelectricThermoelectric powerpower generatorsgenerators utilizing the above mentioned semiconductors are used particularly in remote locations of the earth Siberia Alaska etc 10 10 InfluenceInfluence ofof temperaturetemperature andand impurityimpurity onon resistenceresistence ofof metals metals ExplanationsExplanations 温度和杂质对金属电阻的影响 温度和杂质对金属电阻的影响 P187 P187 解释解释 The resistivity of metals essentially increases linearly with increasing temperature according to the empirical equation 经验方程 2 1 1 T2 T1 where is the linear temperature coefficient of resistivity and T1and T2 are two different temperatures Explanation Explanation At higher temperatures the lattice atoms increasingly oscillate about their equilibrium positions due to the supply of thermal energy thus enhancing the probability for collisions by the drifting electrons As a consequence the resistance rises with higher temperature At near zero temperature the electrical resistance dose not completely vanish and the residual resistivity is essentially temperature independent 11 11 bandband structurestructure ofof semiconductorssemiconductors 半导体的能带结构 半导体的能带结构 Intrinsic semiconductor has three electron bands which are valence band conduction band and forbidden band There is completely filled with valence electrons in valence band and conduction band contains no electrons The forbidden band is not allowed the electrons reside in the gap Since the filled valence band possesses no allowed empty energy states in which the electrons can be thermally excited and then accelerated in an electric field and since the conduction band contains no electrons at all silicon at 0 K is an insulator Two electron bands the lower of which at 0 K is completely filled with valence electrons called the valence band It is separated by a small gap from the conduction band which at 0 K contains no electrons Further quantum mechanics stipulates that electrons essentially are not allowed to reside in the gap between these bands called the forbidden band Since the filled valence band possesses no allowed empty energy states in which the electrons can be thermally excited and then accelerated in an electric field and since the conduction band contains no electrons at all silicon at 0 K is an insulator 12 12 types types application application machenismsmachenisms ofof magneticmagnetic materialsmaterials names names differences differences 磁性材料的类型 应用和机理 磁性材料的类型 应用和机理 名字 差异名字 差异 paramagnetics diamagnetics ferromagnetics ferriamgnetics and antiferromagnetics A qualitative as well as a quantitative distinction between these types can be achieved in a relatively simple way by utilizing a method proposed by Faraday Magnetic material to be investigated is suspended from one of the arms of a sensitive balance and is allowed to reach into an inhomogeneous magnetic field Diamagnetic materials are expelled from this field where para ferro antiferro and ferrimagnetics are attracted in different degrees FIGURE 12 2 Schematic representation of magnetic field lines in and around different types of materials a Para or ferromagnetics 铁磁 体 The magnetic induction B B 磁感应强度 inside the material consists of the free space component 0H H plus a contribution by the material 0M M see Eq 12 5 b The magnetic field lines outside a material point from the north to the south poles whereas inside of para or ferromagnetics B B and 0M M point from south to north in order to maintain continuity 连续性 c In diamagnetics 反磁性体 the response of the material counteracts 抵消 weakens the external magnetic field d In a thin surface layer of a superconductor a supercurrent 超电流 is created below its transition temperature which causes a magnetic field that opposes the external field As a consequence the magnetic flux lines are expelled 消除 from the interior of the material Compare to Figure 11 27 Fig 3 3 Materials types with examples of materials attributes and characterization 表征 methods Grain size 结晶粒度 Computational modelling 计算模拟 Probabilistic simulation 概率仿真 Wear resistance 耐磨性 Figure 3 3 lists the main conventional 常规的 families 族 of materials together with examples of classes 种类 members and attributes 属性 For the examples of attributes sufficient 充分的 characterization methods are named From a technological point of view the materials categorized in Fig 3 3 as families have different characteristics 特性 relevant for engineering applications Fig 3 6 Materials and their characteristics result from the processing of matter Processing 处理 Manufacturing 制造 Machining 加工 Forming 成型 actuator 制动器 Nanoscale manipulation 纳米级处理 Assembly 组装 According to their properties materials can be broadly classified into the following groups Structural materials engineered materials with specific 特殊的 mechanical or thermal properties Functional materials engineered materials with specific electrical magnetic or optical properties Smart materials engineered materials with intrinsic 固有的 or embedded 植入的 sensors 传感器 and actuators which are able to react in response to external loading aiming at optimising the materials behaviour according to given requirements for the materials performance It must be emphasized that the characteristics of engineered structural functional and smart 灵敏的 materials depend essentially on their processing and manufacture as illustrated in a highly simplified 简化的 manner 方式 in Fig 3 6 Table 3 1 Application examples of materials in energy systems and relevant materials properties Heat engine热力发动机 Electricity generator发电机 Nuclear pressure vessel核压力容器 Solar energy太阳 能 Superconductor超导体 Conservation保存 crack growth裂纹发展 magnetic quenching磁猝灭 From the materials cycle which applies to all branches of technology it is obvious that materials and their properties to be determined through measurement and testing are of crucial importance for the performance of technical products This is illustrated in Table 3 1 for some examples of products and technical systems from the energy sector FIGURE 2 4 Schematic representation 示意图 of a stress strain diagram for a ductile material The result of a tensile test is commonly displayed in a stress strain diagram as schematically depicted in Figure 2 4 Several important characteristics are immediately 直接地 evident During the initial stress period the elongation 延长 of the material responds to in a linear fashion 方式 the rod 棒 reverts 回复 back to its original length upon relief of the load This region is called the elastic range Once the stress exceeds however a critical 临界的 value called the yield strength y some of the deformation of the material becomes permanent In other words the yield point separates the elastic region from the plastic range of materials The highest force or stress that a material can sustain is called the tensile strength T Figure 2 4 At this point a localized 局 部的 decrease in the cross sectional area starts to occur The material is said to undergo 经历 necking 颈缩 as shown in Figure 2 6 Because the cross section is now reduced a smaller force is needed to continue deformation until eventually the breaking strength B is reached The slope in the elastic part of the stress strain diagram Figure 2 4 is defined to be the modulus of elasticity E or Young s modulus FIGURE 14 6 Schematic representation of the potential energy 势能 U r for two adjacent 临近的 atoms as a function of internuclear 原 子 核间的 separation r We turn now to a discussion of a possible mechanism that may explain thermal expansion from an atomistic point of view The lattice atoms absorb thermal energy by vibrating about their equilibrium position In doing so a given atom responds with increasing temperature and vibrational amplitude 振幅 to the repulsive 排斥的 forces of the neighboring atoms Let us consider for a moment two adjacent atoms only and let us inspect 考察 their potential energy as a function of internuclear separation We understand that as two atoms move closer to each other strong repulsive forces are experienced between them As a consequence the potential energy U r curve rises steeply 险 峻地 with decreasing r On the other hand we know that two somewhat 稍微 separated atoms also attract each other in some degree This results in a slight decrease in U r with decreasing r At low temperatures a given atom may rest 静止 in its equilibrium position r0 i e at the minimum of potential energy If however the temperature is raised the amplitude of the vibrating atom also increases Since the amplitudes of the vibrating atom are symmetric 相对称的 about a median position 中心位置 and since the potential curve is not symmetric a given atom moves farther apart from its neighbor that is the average position of an atom moves to a larger r say rT as shown in Figure 14 6 In other words the thermal expansion is a direct consequence of the asymmetry 不对称 of the potential energy curve The same arguments 论点 hold true if all of the atoms in a solid are considered FIGURE 2 7 Schematic representations of stress strain diagrams for various materials and conditions a brittle diamond ceramics thermoset 热固性 polymers versus ductile metals alloys materials b definition of the offset yield strength 残余变形屈服强度 条件屈服 强度 c upper and lower yield points observed for example in iron and low carbon steels d thermoplastic 热塑性的 polymer and e variation 变化 with temperature a brittle materials have no separate yield strength tensile strength or breaking strength And break already before the yield strength is reached Ductile materials withstand a large amount of permanent deformation before they break b Many materials essentially display no well defined yield strength in the stress strain diagram One therefore defines an offset yield strength at which a certain amount of permanent deformation 0 2 has occurred and which can be tolerated for a given application c Some materials such as rubber deform elastically to a large extent but cease to be linearly elastic after a strain of about 1 Other materials iron display a sharp yield point As the stress is caused to increase to the upper yield point no significant plastic deformation is encountered From now on the material will yield concomitantly with a drop in the flow stress resulting in a lower yield point and plastic deformation at virtually constant stress d A few polymeric materials such as nylon initially display a linear and subsequently a nonlinear viscoelastic region in the stress strain diagram Moreover beyond the yield s