机械制造专业英语课件
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机械设计制造及其自动化专业英语UnitMechanicalPropertiesofMaterialsPPT课件
• 当卸载时，变形消失。对于许多材料来说， 上述情况发生的应力极限值称为弹性极限σe 。
精品课件 10
Mechanical properties
• This is depicted [diˈpekt] by the straight line relationship and a small deviation [ˌdiviˈeʃən] thereafter, in the stress-strain curve (Fig. 3. 1).
• 而在这其中最重要的是腐蚀性，通俗的解释 是材料在特定大气中长期使用时，抵抗腐(败) 蚀的能力。
精品课件 5
Mechanical properties
• Mechanical properties include the strength properties like tensile, compression, shear, torsion, impact, fatigue and creep .
word
• cross-section 横截面 • ordinate n. 纵坐标 [ˈɔ:rdineit] • abscissa n. 横坐标 [əbˈsisə] • deviation n. 偏离；偏移 [ˌdi:viˈeiʃən] • time-lag 延时；落后；时滞 • yield n. ； v. 屈服 [ji:ld] • elongation n. 延伸率；伸长 [ˌi:lɔŋ'ɡeiʃən] • diminish n. 减小；缩小 [diˈminiʃ] • necking n. 颈缩；形成细颈现象 ['nekiŋ]
• 材料在加载时，随着载荷大小的变化，尺寸 会发生改变。
精品课件 9
Mechanical properties
精品课件 10
Mechanical properties
• This is depicted [diˈpekt] by the straight line relationship and a small deviation [ˌdiviˈeʃən] thereafter, in the stress-strain curve (Fig. 3. 1).
• 而在这其中最重要的是腐蚀性，通俗的解释 是材料在特定大气中长期使用时，抵抗腐(败) 蚀的能力。
精品课件 5
Mechanical properties
• Mechanical properties include the strength properties like tensile, compression, shear, torsion, impact, fatigue and creep .
word
• cross-section 横截面 • ordinate n. 纵坐标 [ˈɔ:rdineit] • abscissa n. 横坐标 [əbˈsisə] • deviation n. 偏离；偏移 [ˌdi:viˈeiʃən] • time-lag 延时；落后；时滞 • yield n. ； v. 屈服 [ji:ld] • elongation n. 延伸率；伸长 [ˌi:lɔŋ'ɡeiʃən] • diminish n. 减小；缩小 [diˈminiʃ] • necking n. 颈缩；形成细颈现象 ['nekiŋ]
• 材料在加载时，随着载荷大小的变化，尺寸 会发生改变。
精品课件 9
Mechanical properties
《机械类专业英语》课件
Skimming
This skill allows readers to quickly scan through the text to get a general understanding of the content It is often used to identify key information or main ideas
Learning significance and purpose
Learning significance and purpose
Learning significance: Mastering mechanical English is of great significance for enhancing personal competitiveness, broadening international perspectives, and promoting academic exchanges.
PPT courseware for Mechanical Professional English
• Introduction to Mechanical Professional English
• Mechanical English Vocabulary • Mechanical English Reading and
Outline
Skimming through the text to identify key information or ideas and creating an outline to organize them This helps readers understand the structure of the article and how different ideas are connected
This skill allows readers to quickly scan through the text to get a general understanding of the content It is often used to identify key information or main ideas
Learning significance and purpose
Learning significance and purpose
Learning significance: Mastering mechanical English is of great significance for enhancing personal competitiveness, broadening international perspectives, and promoting academic exchanges.
PPT courseware for Mechanical Professional English
• Introduction to Mechanical Professional English
• Mechanical English Vocabulary • Mechanical English Reading and
Outline
Skimming through the text to identify key information or ideas and creating an outline to organize them This helps readers understand the structure of the article and how different ideas are connected
机械制造技术英文PPT (18)
mould making： High-speed milling replaces traditional EDM forming with 3-5 times high
efficiency.（figure 3-34，figure 3-35 ）.
3.8.1 Overview of high-speed processing ◆ Applications for high-speed processing
Mechanical Manufacturing Technology High Speed Cutting And Grinding
3.8.1 Overview of high-speed processing
◆ Overview
The famous "Salomon curve" given by the German physicist C.J. Salomom in his article on the principle of high-speed cutting in 1931——there is a critical cutting speed corresponding to a certain workpiece material, the cutting temperature gets higher with the cutting speed below the critical value. However, the cutting speed increases and the cutting temperature decreases above this critical value. Salomom"s theoretical and experimental results generated a great deal of interest and led to the concept of "High Speed Cutting (HSC)".
efficiency.（figure 3-34，figure 3-35 ）.
3.8.1 Overview of high-speed processing ◆ Applications for high-speed processing
Mechanical Manufacturing Technology High Speed Cutting And Grinding
3.8.1 Overview of high-speed processing
◆ Overview
The famous "Salomon curve" given by the German physicist C.J. Salomom in his article on the principle of high-speed cutting in 1931——there is a critical cutting speed corresponding to a certain workpiece material, the cutting temperature gets higher with the cutting speed below the critical value. However, the cutting speed increases and the cutting temperature decreases above this critical value. Salomom"s theoretical and experimental results generated a great deal of interest and led to the concept of "High Speed Cutting (HSC)".
机械制造技术英文PPT32
During rough machining, most of the allowance of the machined surface is removed. If any defect of the blank is found, it shall be scrapped in time to avoid the waste of working hours caused by the continuous machining.
The final heat treatment such as quenching should be arranged before finish machining, and its deformation can be eliminated by finish machining.
（4）helpful to find the defect of the blank as soon as possible（Such as sand hole and air hole of casting）
finish machining
superfinishing
Ensure the main surface precision and surface roughness.
to obtain high dimensional precision, reduce the surface roughness or strengthen the surface.
②Primary before secondary
The machining of primary surfaces such as assembly base and working surface of parts is arranged first，while the machining of secondary surfaces such as keyways, unthreaded or threaded holes for fastening is arranged finally.
The final heat treatment such as quenching should be arranged before finish machining, and its deformation can be eliminated by finish machining.
（4）helpful to find the defect of the blank as soon as possible（Such as sand hole and air hole of casting）
finish machining
superfinishing
Ensure the main surface precision and surface roughness.
to obtain high dimensional precision, reduce the surface roughness or strengthen the surface.
②Primary before secondary
The machining of primary surfaces such as assembly base and working surface of parts is arranged first，while the machining of secondary surfaces such as keyways, unthreaded or threaded holes for fastening is arranged finally.
机械制造技术英文PPT (34)
Dimension conversion
So lution： Three dimensions : 50, 10 and hole depth A0 constitute the dimensional chain.
The size is obtained indirectly, so it is a closed link, while 50 and the hole depth are component links.
Can also draw another arrow on the dimension chart to determine
Dimensional chain diagram
√Drawing method : f i r s t , determine the size of the formed indirectly as the closed link. Then from the closing link, draw the component links. The dimensions are connected head to t a i l , and arrows are drawn in one direction to form a closed figure
➢Closed A dimensional chain is a closed size group
➢Correlationthe component linthe closing link is the dependent variable.
√ For linear
tolerancesT0L
dimension chains
√ For statistical toleranceT0S
So lution： Three dimensions : 50, 10 and hole depth A0 constitute the dimensional chain.
The size is obtained indirectly, so it is a closed link, while 50 and the hole depth are component links.
Can also draw another arrow on the dimension chart to determine
Dimensional chain diagram
√Drawing method : f i r s t , determine the size of the formed indirectly as the closed link. Then from the closing link, draw the component links. The dimensions are connected head to t a i l , and arrows are drawn in one direction to form a closed figure
➢Closed A dimensional chain is a closed size group
➢Correlationthe component linthe closing link is the dependent variable.
√ For linear
tolerancesT0L
dimension chains
√ For statistical toleranceT0S
机械制造技术英文PPT30
comprehensive analysis
In the third scheme, the datum is basically coincident, the structure of the fixture is not too nvenient to install, so it should be used.
Fourth process, drilling, expanding and reaming the hole with Φ16H9 mm in diameter.
• （3）Three degrees of freedom are limited on the bottom, and two degrees of freedom are limited on the Φ32H7 hole.
• In addition to the accuracy requirements of the hole itself, the position requirements of this process shall be 4±0.1mm, 51±0.1mm and the parallelism of the two holes shall be 0.02mm.
• In this scheme, there is datum non coincidence error for dimension 4 ± 0.1mm, and the locating pin is long and thin with poor rigidity. So, this scheme is also not feasible.
• The datum of design size 4±0.1mm coincides. The process datum of size 51±0.1mm is the center line of hole Φ32H7, while the location datum is k plane, and the location dimension is 6±0.1mm, with datum non coincidence error, which is equal to 0.2mm. The parallelism of two holes is 0.02mm, with datum non coincidence error, which is equal to 0.03mm. It can be seen that the datum non coincidence error of this scheme has exceeded the allowable range. So, this scheme is not feasible.
机械制造技术英文PPT33
Axis of rotation
Axis of workpiece
The allowance for this operation must meet the following formula ： Bilateral allowance ：2Z ≥ 2（ Ra + Da）+ Ta + 2|ρa +εb | Unilateral allowance ：Z ≥ Ra + Da + Ta + |ρa +εb |
I Processing allowance and its influencing factors
1． Processing allowance
➢About processing allowance
Processing allowance Z： Thickness of metal layer cut during processing Operation allowance Zi： The difference in operation dimension between
two operations Total processing allowance： The difference between the blank size and the design size of the part drawing Due to the tolerance of the process size, the margin also changes
Refers to the determination of operation dimensions and tolerance when the operation benchmark, positioning benchmark and design benchmark are overlaped, and the surface is processed multiple times. ➢Such as opertions of outer circle and inner hole (multi-process).
机械制造技术英文PPT18
mould making： High-speed milling replaces traditional EDM forming with 3-5 times higher
efficiency.（figure 3-34，figure 3-35 ）.
3.8.1 Overview of high-speed processing Applications for high-speed processing
High-speed CNC machine and high-speed machining center are used to form a high-speed flexible production line to achieve efficient production of multiple varieties and small and medium batches.（figure 3-33）
depending on the workpiece material, see figure3-32 ➢ The range of cutting speeds for high-speed machining varies depending
➢on the machining method
plastic
10
100
1000 10000
cutting speed V（m/min）
figure 3-32 High and ultra-high cutting speed range
3.8.1 Overview of high-speed processing Features of high-speed processing
Low cutting heat：Rapid processing, more than 95% of the cutting heat is carried away by the chips, the workpiece accumulates very little heat, low temperature rise, suitable for processing low melting point, easy oxidation and easy to produce thermal deformation of the parts.
efficiency.（figure 3-34，figure 3-35 ）.
3.8.1 Overview of high-speed processing Applications for high-speed processing
High-speed CNC machine and high-speed machining center are used to form a high-speed flexible production line to achieve efficient production of multiple varieties and small and medium batches.（figure 3-33）
depending on the workpiece material, see figure3-32 ➢ The range of cutting speeds for high-speed machining varies depending
➢on the machining method
plastic
10
100
1000 10000
cutting speed V（m/min）
figure 3-32 High and ultra-high cutting speed range
3.8.1 Overview of high-speed processing Features of high-speed processing
Low cutting heat：Rapid processing, more than 95% of the cutting heat is carried away by the chips, the workpiece accumulates very little heat, low temperature rise, suitable for processing low melting point, easy oxidation and easy to produce thermal deformation of the parts.
机械制造专业英语课件 3 English to Chinese Translation
电子计算机的主要特点是计算准确而迅速。
三、翻译技巧
3.英语形容词—汉语动词 e.g. Grinding has better surface roughness than milling.
科技英语的语言特点
• • • • • • • • “三重三避三多” 重叙事逻辑上的连贯(Coherence) 重表达上的明晰(Clarity) 重表达上的畅达(Fluency) 避免行文晦涩 避免表露个人感情 避免论证上的主观随意性 专业词汇多
• 复杂长句多 • 被动语态多
科技英语的语言特点
• 专业词汇多--The main components of the lathe are the headstock and tailstock at opposite ends of a bed, and a tool post between them which holds the cutting tool． • 被动语态，强调主语，突出重要性 --Springs are used as cushions to absorb shock． • 被动语态，因不需要指出动作的执行者 --When a force is applied to a materia1. It produces a stress in the material. • 被动语态，因无法指出动作执行者 --In most machine members, the deformation must be kept low．
English to Chinese Translation for Mechanical Engineering
◇Basic requirements of technical translation ◇Basic process for technical translation ◇Common translation skills ◇Translation of long sentences ◇Fast Mastering English Vocabulary by comparison
三、翻译技巧
3.英语形容词—汉语动词 e.g. Grinding has better surface roughness than milling.
科技英语的语言特点
• • • • • • • • “三重三避三多” 重叙事逻辑上的连贯(Coherence) 重表达上的明晰(Clarity) 重表达上的畅达(Fluency) 避免行文晦涩 避免表露个人感情 避免论证上的主观随意性 专业词汇多
• 复杂长句多 • 被动语态多
科技英语的语言特点
• 专业词汇多--The main components of the lathe are the headstock and tailstock at opposite ends of a bed, and a tool post between them which holds the cutting tool． • 被动语态，强调主语，突出重要性 --Springs are used as cushions to absorb shock． • 被动语态，因不需要指出动作的执行者 --When a force is applied to a materia1. It produces a stress in the material. • 被动语态，因无法指出动作执行者 --In most machine members, the deformation must be kept low．
English to Chinese Translation for Mechanical Engineering
◇Basic requirements of technical translation ◇Basic process for technical translation ◇Common translation skills ◇Translation of long sentences ◇Fast Mastering English Vocabulary by comparison
机械制造技术英文PPT (32)
3．Arrangement of processing sequence
■（1）Arrangement of cutting process sequence • ①Rough before finish
• rough machining is arranged first, semi_finish machining is arranged in the middle, and finish machining and superfinishing are arranged finally.
■（5）To avoid damage to machined surfaces
If finish machining is arranged at the end, it can protect the finished surface from damage or damage less.
➢The division of machining stage is not absolute, it must be determined according to the requirements of processing precision and the rigidity of workpiece：
■（2）For proper use of equipment
rough machining requires the use of rigid, high efficiency and low precision machine tools, while finish machining requires high precision machine tools.
Processing method：diamond turning/boring，lapping，honing， superfinishing， mirror grinding， polishing，chipless process，etc.
机械制造技术英文PPT (36)
◆ 3 、Technological analysis of NC machining parts It includes two parts : part drawing analysis and structure technology analysis. (1) Part drawing analysis
The instructions of CNC system are compiled by the programmer according to the material of workpiece, machining requirements, characteristics of machine tool and the instruction format (CNC language or symbol) specified by the system.
①The dimension ing method on the part drawing should adapt to the characteristics of NC machining ②Analyze the design drawings of the processed parts ③The conditions (such as tangen cy, intersection, perpendicular ity and parallelism) of the geometric elements (points, lines and faces) that make up the contour of a part are the important basis of NC programming.
CNC machine too l : it is a machine tool controlled by computer.
机械制造技术英文PPT12
The model shown in Figure 1 illustrates the deformation of the cutting process. The plastic metal material under the action of the tool produces shearslip deformation along the direction of 45o with the force of action, and when the deformation reaches a certain limit value, shear-slip destruction occurs along the direction of deformation. If the tool moves continuously, the material above the dotted line will separate from the material below under the action of the tool. The process of metal cutting is essentially similar to the process described above.
I. The process of chip formation
Under the action of a cutter, the cutting layer metal undergoes a complex process to become a chip. In the process, the morphology of the cutting layer changes. The root cause of this change is the old deformation of the cutting layer metal under the action of the cutting tool. The deformation of the cutting process is accompanied by a series of physical phenomena such as cutting force, cutting heat, cutting temperature, tool wear, accumulation of psoriasis, etc. The deformation of the cutting process is the basis for the study of the cutting process.
机械制造技术基础英文课件cha
process sets the foundation for the subsequence manufacturing processes, ensuring that the final product is within the desired tolerance and specifications
目录
contents
Quality control of mechanical manufacturingAutomation and Intelligence of Mechanical ManufacturingDevelopment Trends and Prospects of Mechanical Manufacturing
Destructive testing
Testing a sample of the product to ensure it meets quality standards
Preparing and implementing quality policies and procedures
Monitoring and controlling the manufacturing process to ensure quality standards are met
Common types of machine tools include lathes, milling machines, drill pressures, and grinding machines
The selection of the appropriate machine tool depends on the type of cutting operation to be performed and the size and shape of the workpiece
目录
contents
Quality control of mechanical manufacturingAutomation and Intelligence of Mechanical ManufacturingDevelopment Trends and Prospects of Mechanical Manufacturing
Destructive testing
Testing a sample of the product to ensure it meets quality standards
Preparing and implementing quality policies and procedures
Monitoring and controlling the manufacturing process to ensure quality standards are met
Common types of machine tools include lathes, milling machines, drill pressures, and grinding machines
The selection of the appropriate machine tool depends on the type of cutting operation to be performed and the size and shape of the workpiece
机械制造技术英文PPT13
(1) Index formula for calculating cutting force
The higher the strength and the hardness the workpiece material is, the greater the cutting force needed. When cutting brittle materials, the plastic deformation of the cut material and its friction with the rake face are relatively small, so its cutting force is relatively small.
When metal cutting, the tool cuts into the workpiece to deform the processed material of the workpiece and becomes the chip. The force is called cutting force.
in the base plane. That is, the component force in the direction of the knife.
Feed Resistance Force Ff：Parallel to the feed movement direction in the base
Where, Fc—main cutting force, N; Vc—Cutting speed, m / min.
The power PE of the main motor can be calculated or checked according to the cutting power Pc (unit: kW):
The higher the strength and the hardness the workpiece material is, the greater the cutting force needed. When cutting brittle materials, the plastic deformation of the cut material and its friction with the rake face are relatively small, so its cutting force is relatively small.
When metal cutting, the tool cuts into the workpiece to deform the processed material of the workpiece and becomes the chip. The force is called cutting force.
in the base plane. That is, the component force in the direction of the knife.
Feed Resistance Force Ff：Parallel to the feed movement direction in the base
Where, Fc—main cutting force, N; Vc—Cutting speed, m / min.
The power PE of the main motor can be calculated or checked according to the cutting power Pc (unit: kW):
机械设计制造及其自动化专业英语UnitMechanicalPropertiesofMaterialsPPT课件
• 在这个区域中，金属遵守胡克定律—阐述了 在加载的弹性范围内，应力和应变成比例关 系（材料在卸载后，能够完全回复它原来的 尺寸）。
精品课件 14
Mechanical properties
• In the actual plotting of the curve, the proportionality limit is obtained at a slightly lower value of the load than the elastic limit.
• torsion n. 扭转；转矩 [ˈtɔ:rʃən]
• impact n. 冲击；冲力；影响 [ˈɪmpækt]
• fatigue n. 疲劳 [fəˈti:ɡ]
• creep n. 蠕变 [kri:p]
•
specimen
n.
试件；试样 精品课件
[ˈspesimin]
1
Mechanical Properties of Materials
• Physical properties
Density or specific gravity, moisture [ˈmɔɪstʃə] content, etc., can be classified under this category [ˈkætəgɔ:ri].
• 材料特性主要分为三类：(i)物理特性，(ii)化学 特性，(iii)力学性或碱性，活性和腐蚀性。
精品课件 4
Chemical properties
• The most important of these is corrosion which can be explained in layman’s [ˈlemən] terms as the resistance of the material to decay [dɪˈke] while in continuous use in a particular atmosphere.
精品课件 14
Mechanical properties
• In the actual plotting of the curve, the proportionality limit is obtained at a slightly lower value of the load than the elastic limit.
• torsion n. 扭转；转矩 [ˈtɔ:rʃən]
• impact n. 冲击；冲力；影响 [ˈɪmpækt]
• fatigue n. 疲劳 [fəˈti:ɡ]
• creep n. 蠕变 [kri:p]
•
specimen
n.
试件；试样 精品课件
[ˈspesimin]
1
Mechanical Properties of Materials
• Physical properties
Density or specific gravity, moisture [ˈmɔɪstʃə] content, etc., can be classified under this category [ˈkætəgɔ:ri].
• 材料特性主要分为三类：(i)物理特性，(ii)化学 特性，(iii)力学性或碱性，活性和腐蚀性。
精品课件 4
Chemical properties
• The most important of these is corrosion which can be explained in layman’s [ˈlemən] terms as the resistance of the material to decay [dɪˈke] while in continuous use in a particular atmosphere.
机械制造技术英文PPT11
(1) Orthogonal plane reference system 1) The base plane Pr passes through the plane perpendicular to the cutting
speed at the selected point on the cutting edge. The base surface of the turning tool is the plane parallel to the bottom surface through the selected point of the cutting edge, and the base surface of the milling cutter and drill is the axial section of the tool.
3) The orthogonal plane Po passes through the plane selected by the cutting edge and is perpendicular to both the base plane and the cutting plane.
Orthogonal plane reference system
Basic knowledge of tool cutting
一、 The composition of the cutting part of the tool
• There are many types of tools used in metal cutting, and their shapes and uses are different. Among them, the turning tool is a basic tool that is widely used. Other tools can be regarded as the evolution or combination of turning tools. The outer turning tool is taken as an example to illustrate the basic concept of the tool composition and the geometric parameters of the cutting part of the tool.
机械制造技术英文PPT14
Chip Tool
Workpiece
Fig.1 Generation and transmission of cutting heat
When cutting ductile materials, the deformation and friction are greater, so more heat is generated. When its cutting speed is increased, because the deformation of chips are smaller, so the percentage of heat generated by plastic deformation is reduced, but the percentage of friction generated heat is much higher. When cutting brittle materials, the percentage of heat generated by friction on the flank surface increases.
④ The contact length of the cutter face is narrow, so the temperature rise and fall on the workpiece surface is completed in a very short time. When the tool passes, the machined surface is subjected to a thermal shock .
Chip Tool
① In the shear zone, the temperature of each point along the shear plane is almost the same, but the temperature gradient in the direction perpendicular to the shear plane is very large.
机械制造技术英文PPT (22)
outer ring
outer ring
outer ring
outer ring inner ring
inner ring inner ring
rolling body
(a) shape error of Inner ring raceway
(b) shape error of outer ring raceway
as shown in the figure.
齿面鱼鳞斑:
Machin ing errors caused by machine t ool 鱼鳞状的凹凸斑点,主要由于预先热处理(调质)后硬度较高,如果非终加工齿轮,该缺陷不是大问题. 检查滚刀装夹端面、纵向跳动，减小跳动偏差， 工作回转台与涡杆间隙
Mechanical Manufacturing Technology
Influence of machine tool geometric error on machining accuracy and its control
Influence of machine tool geometric error on machining accura源自y and i t s control
Three aspects of machine tool error: manufacturing, wear and ins of the machine tool itself
Static error: Various errors measured without cutting load;
偏大。。
spindl e revolving e rrors
√Different machining methods cause different machining errors caused by spindle revolving errors
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fastening (another components) so as that there is a factor of safety．Usually the designer assumes an allowable working
stress of only half the yield stress for the material.
interests of safety not only increases the initial material costs，but also the operating costs. For example，the stronger and heavier the structure members of an aircraft，the fewer passengers it can carry and the more fuel it consumers．Therefore a balance has to be maintained between safety，initial cost and operating costs．The
The stress in the bolt is made up of two elements. Firstly, the stress imparted by the initial tightening of the bolt; secondly， the stress imparted by the load on the fastening in service．The sum of these stress must not be allowed to approach，let alone exceed，the yield stress for the material of it will cease to act in an elastic manner．Therefore the designer proportions the
designer is constantly striving to improve the former whilst reducing the latter．
Allowable working stress is taken as a proportion of the yield or proof stress；that is，the component is only stressed within its elastic range when in service．For example, consider the screwed
If the fastening shown in Fig. 1.1 is overstressed by applying excess torque to the nut (for example，by extending the length of the spanner with a tube)，the bolt will be stressed beyond its elastic range．Once the yield stress for the bolt has been exceeded it exhibits plastic properties and takes a permanent set that is，it becomes permanently lengthened，the “spring back” is seriously reduced and the joint faces are no longer held firmly together. Thus for critical assemblies，the designer will seek to control the stress in the fastening and associated components by specifying the torque to be applied to the nut as it is tightened by the use of a “torque spanner” set to a specific value.
第一篇 专业英语基础
第1章 绪 论
1.1 概述
1. 课程教学目的
培养学生对专业语言的理解能力和应用能 力；让学生承担专业阅读必需的基本技能和 知识，使学生能够以英语为工具获取专业科 技知识及其他与专业有关的信息。
2. 专业英语的起源 最初出现于20世纪50年代。
3. 专业英语的教学特点 语言教学密切结合专业知识，教材大都
continuously at their maximum allowable stress. This is done by
employing a factor of safety. Unfortunately，increasing the strength of a component in the来自1.2 专业英语的基本特点
为了了解专业英语的特点，我们先阅读下面一段关于许用应力的课文。
Despite the tests described in Chapters 1l and 12，materials may still fail in service，sometimes with disastrous results (e.g. when the failure occurs in aircraft．bridges，ships，etc.). To try to avoid such disastrous occurring，the designer avoids using materials
来源于相关的专业文献。
4. 专业英语的学习方法
专业英语阅读与普通英语的快速阅读的方 法也所不同，专业英语阅读要把准理解放在 首位，在准确理解的基础上提高阅读速度。 和其他的英语能力—祥，专业英语阅读能力， 需要通过长期的实践才能获得，不可能一蹴 而就，多读多练是提高专业英语阅读能力的 最有效的方法。
fastening shown in Fig. 1.l. When the nut is tightened normally the bolt is stretched slightly and，providing it is stressed within its elastic range，it will behave like a very powerful spring and will pull the joint faces together very firmly．
stress of only half the yield stress for the material.
interests of safety not only increases the initial material costs，but also the operating costs. For example，the stronger and heavier the structure members of an aircraft，the fewer passengers it can carry and the more fuel it consumers．Therefore a balance has to be maintained between safety，initial cost and operating costs．The
The stress in the bolt is made up of two elements. Firstly, the stress imparted by the initial tightening of the bolt; secondly， the stress imparted by the load on the fastening in service．The sum of these stress must not be allowed to approach，let alone exceed，the yield stress for the material of it will cease to act in an elastic manner．Therefore the designer proportions the
designer is constantly striving to improve the former whilst reducing the latter．
Allowable working stress is taken as a proportion of the yield or proof stress；that is，the component is only stressed within its elastic range when in service．For example, consider the screwed
If the fastening shown in Fig. 1.1 is overstressed by applying excess torque to the nut (for example，by extending the length of the spanner with a tube)，the bolt will be stressed beyond its elastic range．Once the yield stress for the bolt has been exceeded it exhibits plastic properties and takes a permanent set that is，it becomes permanently lengthened，the “spring back” is seriously reduced and the joint faces are no longer held firmly together. Thus for critical assemblies，the designer will seek to control the stress in the fastening and associated components by specifying the torque to be applied to the nut as it is tightened by the use of a “torque spanner” set to a specific value.
第一篇 专业英语基础
第1章 绪 论
1.1 概述
1. 课程教学目的
培养学生对专业语言的理解能力和应用能 力；让学生承担专业阅读必需的基本技能和 知识，使学生能够以英语为工具获取专业科 技知识及其他与专业有关的信息。
2. 专业英语的起源 最初出现于20世纪50年代。
3. 专业英语的教学特点 语言教学密切结合专业知识，教材大都
continuously at their maximum allowable stress. This is done by
employing a factor of safety. Unfortunately，increasing the strength of a component in the来自1.2 专业英语的基本特点
为了了解专业英语的特点，我们先阅读下面一段关于许用应力的课文。
Despite the tests described in Chapters 1l and 12，materials may still fail in service，sometimes with disastrous results (e.g. when the failure occurs in aircraft．bridges，ships，etc.). To try to avoid such disastrous occurring，the designer avoids using materials
来源于相关的专业文献。
4. 专业英语的学习方法
专业英语阅读与普通英语的快速阅读的方 法也所不同，专业英语阅读要把准理解放在 首位，在准确理解的基础上提高阅读速度。 和其他的英语能力—祥，专业英语阅读能力， 需要通过长期的实践才能获得，不可能一蹴 而就，多读多练是提高专业英语阅读能力的 最有效的方法。
fastening shown in Fig. 1.l. When the nut is tightened normally the bolt is stretched slightly and，providing it is stressed within its elastic range，it will behave like a very powerful spring and will pull the joint faces together very firmly．