机械毕业设计英文外文翻译490我国自卸车

Mechanical engineering1.The porfile of mechanical engineeringEngingeering is a branch of mechanical engineerig,itstudies mechanical and power generation especially power and movement.2.The history of mechanical engineering18th century later periods,the steam engine invention hasprovided a main power fountainhead for the industrialrevolution,enormously impelled each kind of mechznicalbiting.Thus,an important branch of a newEngineering –separated from the civil engineering tools andmachines on the branch-developed together with Birmingham andthe establishment of the Associantion of Mechanical Engineersin 1847 had been officially recognized.The mechanicalengineering already mainly used in by trial and error methodmechanic application technological development into professional engineer the scientific method of which in theresearch,the design and the realm of production used .From themost broad perspective,thedemend continuously to enhance theefficiencey of mechanical engineers improve the quality of work,and asked him to accept the history of the high degreeof education and training.Machine operation to stress not only economic but also infrastructure costs to an absolute minimun.3.The field of mechanical engineeringThe commodity machinery development in the develop country,in the high level material life very great degree is decided each kind of which can realize in the mechanical engineering.Mechanical engineers unceasingly will invent the machine next life to produce the commodity,unceasingly will develop the accuracy and the complexity more and more high machine tools produces the machine.The main clues of the mechanical development is:In order to enhance the excellent in quality and reasonable in price produce to increase the precision as well as to reduce the production cost.This three requirements promoted the complex control system development.The most successful machine manufacture is its machine and the control system close fusion,whether such control system is essentially mechanical or electronic.The modernized car engin production transmission line(conveyer belt)is a series of complex productions craft mechanization very good example.The people are in the process of development in order to enable further automation of the production machinery ,the use of a computer to store and handle largevolumes of data,the data is a multifunctional machine tools necessary for the production of spare parts.One of the objectives is to fully automated production workshop,threerotation,but only one officer per day to operate.The development of production for mechanical machinery must have adequate power supply.Steam engine first provided the heat to generate power using practical methods in the old human,wind and hydropower,an increase of engin .New mechanical engineering industry is one of the challenges faced by the initial increase thermal effciency and power,which is as big steam turbine and the development of joint steam boilers basically achieved.20th century,turbine generators to provide impetus has been sustained and rapid growth,while thermal efficiency is steady growth,and large power plants per kW capital consumption is also declining.Finally,mechanical engineers have nuclear energy.This requires the application of nuclear energy particularly high reliability and security, which requires solving many new rge power plants and the nuclear power plant control systems have become highly complex electroonics,fluid,electricity,water and mechanical parts networks All in all areas related to the mechanical engineers.Small internal combustion engine,both to the type(petrol and diesel machines)or rotary-type(gas turbines and Mong Kerr machine),as well as their broad application in the field of transport should also due to mechanical enginerrs.Throughout the transport,both in the air and space,or in the terrestrial and marine,mechanial engineers created a variety of equipment and power devices to their increasing cooperation with electrical engineers,especially in the development of appropration control systems.Mechanical engineers in the development of military weapons technology and civil war ,needs a similar,though its purpose is to enhance rather than destroy their productivity.However.War needs a lot of resources to make the area of techonlogy,many have a far-reaching development in peacetime efficiency.Jet aircraft and nuclear reactors are well known examples.The Biological engineering,mechanical engineering biotechnology is a relatively new and different areas,it provides for the replacement of the machine or increase the body functions as well as for medical equipment.Artficial limbs have been developed and have such a strong movement and touch response function of the human body.In the development of artificial organ transplant is rapid,complex cardiac machines and similar equipment to enable increasingly complexsurgery,and injuries and ill patients life functions can be sustained.Someenviromental control mechanical engineers through the initial efforts to drainage or irrigation pumping to the land and to mine and ventilation to control the human environment.Modern refrigeration and air-conditioning plant commonaly used reverse heat engine,where the heat from the engine from cold places to more external heat.Many mechanical engineering products,as well as other leading technology development city have side effects on the environment,producingnoise,water and air pollution caused,destroyed land and landscape.Improve productivity and diver too fast in the commodity,that the renewable natural forces keep pace.For mechanical engineers and others,environmental control is rapidly developing area,which includes a possible development and production of small quantities of pollutants machine sequnce,and the development of new equipment and teachnology has been to reduce and eliminate pollution.4.The role of mechanical engineeringThere are four generic mechanical engineers in common to the above all domains function.The 1st function is the understanding and the research mechanical sciencefoundation.It includes the power and movement of the relationship dynamics For example,in the vibration and movement of the relationship;Automaticcontrol;Study of the various forms of heart,energy,power relations between the thermodynamic;Fluidflows; Heat transfer; Lubricant;And material properties.The 2nd function will be conducts the research,thedesing and the development,this function in turn attempts to carry on the essential change to satisfy current and the future needs.This not only calls for a clear understanding of mechanical science,and have to break down into basic elements of a complex system capacity.But also the need for synthetic and innovative inventions.The 3rd function is produces the product and the power,includeplan,operation and maintenance.Its goal lies in the maintenance either enhances the enterprise or the organization longer-tern and survivabilaty prestige at the same time,produces the greatest value by the least investments and the consumption.The 4th function is mechanical engineer’s coordinated function,including the management,theconsultation,as well as carries on the market marking in certain situation.In all these function,one kind unceasingly to use thescience for a long time the method,but is not traditional or the intuition method tendency,this is a mechanical engineering skill aspect which unceasingly grows.These new rationalization means typical names include:The operations research,the engineering economics,the logical law problem analysis(is called PABLA) However,creativity is not rationalization.As in other areas,in mechanicalengineering, to take unexpected and important way to bring about a new capacity,still has a personal,markedcharacteristice.5.The design of mechanical engineeringThe design of mechanical is the design has the mechanical property the thing or the system,suchas:the instrument and the measuring appliance in very many situations,the machine design must use the knowledge of discipline the and so on mathematics,materials science and mechanics.Mechanical engineering desginincludeing all mechanical desgin,but it was a study,because it also includes all the branches of mechsnicalengineering,such as thermodynamics all hydrodynamics in the basic disciplines needed,in the mechanical engineering design of the initial stude or mechanical design.Designstages.The entire desgin process from start to finish,in the process,a demand that is designed forit and decided to do the start.After a lot of repetition,the final meet this demand by the end of the design procees and the plan.Designconsiderations.Sometimes in a system is to decide which parts needs intensity parts of geometric shapes and size an important factor in this context that we must consider that the intensity is an important factor in the design.When we use expression design considerations,we design parts that may affect the entire system design features.In the circumstances specified in the design,usually for a series of such functions must be taken into account.Howeever,to correct purposes,we should recognize that,in many cases the design of important design considerations are not calculated or test can determine the components or systems.Especiallystudents,wheen in need to make important decisions in the design and conduct of any operation that can not be the case,they are often confused.These are not special,they occur every day,imagine,forexample,a medical laboratory in the mechanical design,from marketing perspective,people have high expectations from the strength and relevance of impression.Thick,and heavy parts installed together:to produce a solid impression machines.And sometimes machinery and spare parts from the design style is the point and not theother point of view.Our purpose is to make those you do not be misled to believe that every design decision will need reasonable mathematical methods.Manufacturing refers to the raw meterials into finished products in the enterprise.Create three distinct phases.Theyare:input,processingexprot.The first phase includes the production of all products in line with market needs essential.First there must be the demand for the product,the necessary materials,while also needs such as energy,time,human knowledge and technology resourcess . Finall,the need for funds to obtain all the other resources. Lose one stage after the second phase of the resources of the processes to be distributed.Processing of raw materials into finished products of these processes.To complete the design,based on the design,and then develop plans.Plan implemented through various production processes.Management of resources and processes to ensure efficiency and productivity.Forexample,we must carefully manage resources to ensure proper use of funds.Finally,people are talking about the product market was cast.Stage is the final stage of exporting finished or stage.Once finished just purchased,it must be delivered to the users.According to productperformance,installation and may have to conduct further debugging in addition,someproducts,especially those very complex products User training is necessary.6.The processes of materials and maunfacturingHere said engineering materials into two main categories:metals and non-ferrous,high-performance alloys and power metals.Non-metallic futher divided into plastice,syntheticrubber,composite materials and ceramics.It said the production proccess is divided into several major process,includingshape,forging,casting/founding,heattreatment,fixed/connections ,measurement/ quality control and materalcutting.These processes can be further divide into each other’s craft.Various stages of the development of the manufacturing industry Over the years,the manufacturing process has four distinct stages of development, despite the overlap.These stages are:The first phase is artisanal,the second Phase is mechanization.The third phase is automation the forth Phase is integrated.When mankind initial processing of raw materials into finished products will be,they use manual processes.Each with their hands and what are the tools manusllyproduced.This is totally integrated production take shape.A person needsindentification,collectionmaterials,the design of a product to meet that demand,the production of such products and use it.From beginning to end,everything is focused on doing the work of the human ter in the industrial revolution introduced mechanized production process,people began to use machines to complete the work accomplished previously manual. This led to the specialization.Specialization in turn reduce the manufacture of integrated factors.In this stage of development,manufacturing workers can see their production as a whole represent a specific piece of the part of the production process.Onecan not say that their work is how to cope with the entire production process,or how they were loaded onto a production of parts finished.Development of manufacting processes is the next phase of the selection process automation.This is a computer-controlled machinery and processes.At this stage,automation island began to emerge in the workshop lane.Each island represents a clear production process or a group of processes.Although these automated isolated island within the island did raise the productivity of indivdualprocesses,but the overall productivity are often not change.This is because the island is not caught in other automated production process middle,but not synchronous withthem .The ultimate result is the efficient working fast parked through automated processes,but is part of the stagnation in wages down,causingbottlenecks.To better understand this problem,you can imagine the traffic in the peak driving a red light from the red Service Department to the next scene. Occasionally you will find a lot less cars,more than being slow-moving vehicles,but the results can be found by the next red light Brance.In short you real effect was to accelerate the speed of a red Department obstruction offset.If you and other drivers can change your speed and red light simultaneously.Will advance faster.Then,all cars will be consistent,sommthoperation,the final everyone forward faster.In the workshop where the demand for stable synchronization of streamlined production,and promoted integration of manufacturing development.This is a still evolving technology.Fully integrated in the circumstances,is a computer-controllrd machinery and processing.integrated is completed through computer.For example in the preceding paragraph simulation problems,the computer will allow all road vehicles compatible with the change in red.So that everyone can steady traffic.Scientific analysis of movement,timing and mechanics ofthe disciplines is that it is composed of two pater:statics and dynamics.Statics analyzed static system that is in the system,the time is not taken into account,research and analysis over time and dynamics of the system change.Dynameics from the two componets.Euler in 1775 will be the first time two different branches: Rigid body movement studies can conveniently divided into two parts:geometric and mechanics.The first part is without taking into account the reasons for the downward movement study rigid body from a designated location to another point of the movement,and must use the formula to reflect the actual,the formula would determine the rigid body every point position. Therefore,this study only on the geometry and,morespecifically,on the entities from excision.Obviously,the first part of the school and was part of a mechanical separation from the principles of dynamics to study movement,which is more than the two parts together into a lot easier.Dynamics of the two parts are subsequently divided into two separate disciplines,kinematic and dynamics,a study of movement and the movement strength.Therefore,the primary issue is the design of mechanical systems understand its kinematic.Kinematic studies movement,rather than a study ofits impact.In a more precise kinematic studies position,displacement,rotation, speed,velocity and acceleration of disciplines,foresample,or planets orbiting research campaing is a paradigm.In the above quotation content should be pay attention that the content of the Euler dynamics into kinematic and rigid body dynamics is based on the assumption that they are based on research.In this very important basis to allow for the treatment of two separate disciplines.For soft body,soft body shape and even their own soft objects in the campaign depends on the role of power in their possession.In such cases,should also study the power and movement,and therefore to a large extent the analysis of the increased complexity.Fortunately, despite the real machine parts may be involved are more or less the design of machines,usually with heavy material designed to bend down to the lowest parts.Therefore,when the kinematic analysis of the performance of machines,it is often assumed that bend is negligible,spare parts are hard,but when the load is known,in the end analysis engine,re-engineering parts to confirm this assnmption.机械工程1.机械工程简介机械工程是工程学的一个分支，它研究机械和动力的产，尤其是力和动力。

机械设计毕业设计翻译Introduction to Mechanical EngineeringMechanical engineering is the branch of engineering that deals with machines and the production of power. It is particularly concerned with forces and motion.History of Mechanical EngineeringThe invention of the steam engine in the latter part of the 18th century, providing a key source of power for the Industrial Revolution, gave an enormous impetus to the development of machinery of all types. As a result a new major classification of engineering, separate from civil engineering and dealing with tools and machines, developed, receiving formal recognition in 1847 in the founding of the Institution of Mechanical Engineers in Birmingham, England.Mechanical engineering has evolved from the practice by the mechanic of an art based largely on trial and error to the application by the professional engineer of the scientific method in research, design, and production.The demand for increased efficiency, in the widest sense, is continually raising the quality of work expected from a mechanical engineer and requiring of him a higher degree of education and training. Not only must machines run more economically but capital Costs also must be minimized.Fields of Mechanical EngineeringDevelopment of machines for the production of goods the high material standard of living in the developed countries owes much to the machinery made possible by mechanical engineering. The mechanical engineer continually invents machines to produce goods and develops machine tools of increasing accuracy and complexity to build the machines.The principal lines of development of machinery have been an increase in the speed of operation to obtain high rates of production, improvement in accuracy to obtain quality and economy in the product, and minimization of operating costs. These three requirements have led to the evolution of complex control systems.The most successful production machinery is that in which the mechanical design of the machine is closely integrated with the control system, whether the latter is mechanical or electrical in nature. A modern transfer line (conveyor) for the manufacture of automobile engines is a good example of the mechanization of a complex series of manufacturing processes. Developments are in hand to automate production machinery further, using computers to store and process the vast amount of data required for manufacturing a variety of components with a small number of versatile machine tools. One aim is a completely automated machine shop for batch production, operating on a three shift basis but attended by a staff for only one shift per day.Development of machines for the production of power Production machinery presuppose an ample supply of power. The steam engine provided the first practical means of generating power from heat to augment the old sources of power from muscle, wind, and waterOne of the first challenges to the new profession of mechanical engineering was to increase thermal efficiencies and power; this was done principally by the development of the steam turbine and associated large steam boilers. The 20th century has witnessed a continued rapid growth in the power output of turbines for driving electric generators, together with a steady increase in thermal efficiency and reduction in capital cost per kilowatt of large power stations. Finally, mechanical engineers acquired the resource of nuclear energy, whose application has demanded an exceptional standard of reliability and safety involving the solution of entirely new problems- The control systems of large power plank and complete nuclear power stations have become highly sophisticated networks of electronic, fluidic. Electric, hydraulic, and mechanical components, ail of these involving me province of the mechanical engineer.The mechanical engineer is also responsible for the much smaller internal combustion engines, both reciprocating (gasoline and diesel) and rotary (gas-turbine and Wankel) engines, with their widespread transport applications- In the transportation field generally, in air and space as well as on land and sea. the mechanical engineer has created the equipment and the power plant, collaborating increasingly with the electrical engineer, especially in the development of suitable control systems.Development of military weapons The skills applied to war by the mechanical engineer are similar to those required in civilian applications, though the purpose is to enhance destructive power rather than to raise creative efficiency. The demands of war have channeled huge resources into technical fields, however, and led to developments that have profound benefits in peace. Jet aircraft and nuclear reactors are notable examples.Biaengineering Bioengineering is a relatively new and distinct field of mechanical engineering that includes the provision of machines to replace or augment the functions of the human body and of equipment for use in medical treatment. Artificial limbs have been developed incorporating such lifelike functions as powered motion and touch feedback. Development is rapid in the direction of artificial spare-part surgery. Sophisticated heart-lung machines and similar equipment permit operations of increasing complexity and permit the vital functions in seriously injured or diseased patients to be maintained.Environmental control Some of the earliest efforts of mechanical engineers were aimed at controlling man's environment by pumping water to drain or irrigate land and by ventilating mines. The ubiquitous refrigerating and air-conditioning plants of the modem age are based on a reversed heat engine, where the supply of power "pumps" heat from the cold region to the warmer exterior.Many of the products of mechanical engineering, together with technological developments in other fields, have side effects on the environment and give rise to noise, the pollution of water and air, and the dereliction of land and scenery. The rate of production, both of goods and power, is rising so rapidly that regeneration by natural forces can no longer keep pace. A rapidly growing field for mechanical engineers and others is environmental control, comprising the development of machines and processes that will produce fewer pollutants and of new equipment and techniques that can reduce or remove the pollution already generated.Functions of Mechanical EngineeringFour functions of the mechanical engineering, common to all the fields mentioned, arecited. The first is the understanding of and dealing with the bases of mechanical science. These include dynamics, concerning the relation between forces and motion, such as in vibration; automatic control; thermodynamics, dealing with the relations among the various forms of heat, energy, and power; fluid flow; heat transfer; lubrication; and properties of materials.Second is the sequence of research, design, and development. This function attempts to bring about the changes necessary to meet present and future needs. Such work requires not only a dear understanding of mechanical science and an ability to analyze a complex system into its basic factors, but also the originality to synthesize and invent.Third is production of products and power, which embraces planning, operation, and maintenance. The goal is to produce the maximum value with the minimum investment and cost while maintaining or enhancing longer term viability and reputation of the enterprise or the institution.Fourth is the coordinating functioning of the mechanical engineering, including management, consulting, and, in some cases, marketing.In all of these functions there is a long continuing trend toward the use of scientific instead of traditional or intuitive methods, an aspect of the ever-growing professionalism of mechanical engineering. Operations research, value engineering, and PABLA (problem analysis by logical approach) are typical titles of such new rationalized approaches. Creativity, however, cannot be rationalized. The ability to take the important and unexpected step that opens up new solutions remains in mechanical engineering, as elsewhere, largely a personal and spontaneous characteristic.The Future of Mechanical EngineeringThe number of mechanical engineers continues to grow as rapidly as ever, while the duration and quality of their training increases. There is a growing: awareness, however, among engineers and in the community at large that the exponential increase in population and living standards is raising formidable problems in pollution of the environment and the exhaustion of natural resources; this clearly heightens the need for all of the technical professions to consider the long-term social effects of discoveries and developments. -There will be an increasing demand for mechanical engineering skills to provide for man's needs while reducing to a minimum the consumption of scarce raw materials and maintaining a satisfactory environment.Introduction to DesignThe Meaning of DesignTo design is to formulate a plan for the satisfaction of a human need. The particular need to be satisfied may be quite well defined from the beginning. Here are two examples in which needs are well defined:1. How can we obtain large quantities of power cleanly, safely, and economical/ without using fossil fuels and without damaging the surface of the earth?2. This gear shaft is giving trouble; there have been eight failures in the last six weeks. Dosomething about it.On the other hand, the statement of a particular need to be satisfied may be so nebulous and ill defined that a considerable amount of thought and effort is necessary in ( order to state it dearly as a problem requiring a solution. Here are two examples.-1. Lots of people are killed in airplane accidents.2. In big cities there are too many automobiles on the streets and highways.This second type of design situation is characterized by the fact that neither the need nor the problem to be solved has been identified. Note, too, that the situation may contain not one problem but many.We can classify design, too. For instance, we speak of:1. Clothing design 7. Bridge design2. Interior design 8. Computer-aided design3. Highway design 9. Heating system design.4. Landscape design 10. Machine design5. Building design 11. Engineering design6. Ship design 12. Process designIn fact, there are an endless number, since we can classify design according to the particular article or product or according to the professional field,In contrast to scientific or mathematical problems, design problems have no unique answers; it is absurd, for example, to request the "correct answer" to a design problem, because there is none. In fact, a "good" answer today may well turn out to be a "poor" answer tomorrow, if there is a growth of knowledge during the period or if there are other structural or societal changes.Almost everyone is Involved with design in one way or another, even in dally living, because problems are posed and situations arise which must be solved. A design problem is not a hypothetical problem at all. Design has an authentic purpose—the creation of an end result by taking definite action, or the creation of something having physical reality. In engineering, the word design conveys different meanings to different persons. Some think of a designer as one who employs the drawing board to draft the details of a gear, clutch, or other machine member. Others think of design as the creation of a complex system, such as a communications network. In some areas of engineering the word design has been replaced by other terms such as systems engineering or applied decision theory. But no matter what words are used to describe the design function, in engineering it is still the process in which scientific principles and the tools of engineering—mathematics, computers, graphics, and English—are used to produce a plan which, when carried out, will satisfy a human need.Mechanical Engineering DesignMechanical design means die design of things and systems of a mechanical nature machines, products, structures, devices, and instruments. For the most part, mechanical design utilizes mathematics, the materials sciences, and the engineering-mechanics sciences.Mechanical engineering design includes all mechanical design, but it is a broader study, because it includes all the disciplines of mechanical engineering, such as the thermal and fluids sciences, too. Aside from the fundamental sciences that are required, the first studies in mechanical engineering design are in mechanical design.The Phases of DesignThe complete process, from start to finish. The process W begins with a recognition of a need and a decision to do something about it. After much iteration, the process ends with the presentation of the plans for satisfying the need.Design ConsiderationsSometimes the strength required of an element in a system is an important factor in the determination of the geometry and the dimensions of the element. In such a situation we say that strength is an important design consideration. When we use the expression design consideration, we are referring to some characteristic which influences the design of the element or, perhaps, the entire system. Usually quite a number of such characteristics must be considered in a given design situation. Many of the important ones are as follows:1. Strength2. Reliability3. Thermal properties4. Corrosion5. Wear6. Friction7. Processing8. Utility9. Cost10. Safety11. Weight12. Life 13. Noise14. Styling15. Shape16. Size17. Flexibility18. Control19. Stiffness20. Surface finish21. Lubrication22. Maintenance23. V olume24. LiabilitySome of these have to do directly with the dimensions, the material, the processing, and the joining of the elements of the system. Other considerations affect the configuration of the total system.To keep the correct perspective, however, it should be observed that in many design situations the important design considerations are such that no calculations or experiments are necessary in order to define an element or system. Students, especially, are often confounded when they run into situations in which it is virtually impossible to make a single calculation and yet an important design decision must be made. These are not extraordinary occurrences at all; they happen every day. Suppose that it is desirable from a sales standpoint—for example, in medical laboratory machinery—to create an impression of great strength and durability. Thicker parts assembled with larger-than-usual oversize bolts can be used to create a rugged-looking machine. Sometimes machines and their parts are designed purely from the standpoint of styling and nothing else. These points are made here so that you will not be misled into believing that there is a rational mathematical approach to every design decision.ManufacturingManufacturing is that enterprise concerned with converting raw material into finished products. There are three distinct phases in manufacturing. These phases are as follows: input, processing, and output.The first phase includes all of the elements necessary to create a marketable product. First, there must be a demand or need for the product. The necessary materials must be (available. Also needed are such resources as energy, time, human knowledge, and human skills. Finally, it takes capital to obtain all of the other resources.Input resources are channeled through the various processes in Phase Two. These are the processes used to convert raw materials into finished products. A design is developed. Based on the design, various types of planning are accomplished. Plans are put into action through various production processes. The various resources and processes are managed to ensure efficiency and productivity. For example, capital resources must be carefully managed to ensure they are used prudently. Finally, the product in question is marketed.The final phase is the output or finished product. Once the finished product has been purchased it must be transported to users. Depending on the nature of the product, installation and ongoing field support may be required. In addition, with some products, particularly those of a highly complex nature, training is necessary.Materials and Processes in ManufacturingEngineering materials covered herein are divided into two broad categories:metals and nonmetals. Metals are subdivided into ferrous metals, nonferrous metals, high-performance alloys, and powdered metals. Nonmetals are subdivided into plastics, elastomers, composites, and ceramics. Production processes covered herein are divided into several broad categories including forming, forging, casting/molding, .heat treatment^ .fastening joining metrology/quality control, and material removal. Each of these is subdivided into several other processes.Stages in the Development of ManufacturingOver the years, manufacturing processes have- gone through four distinct, -although overlapping, stages of development. These stages are as follows: Stage 1 ManualStage 2 MechanizedStage 3 AutomatedStage 4 IntegratedWhen people first began converting raw materials into finished products, they used manual processes. Everything was accomplished using human hands and manually operated tools. This was a very rudimentary form of fully integrated manufacturing. A person identified the need, collected materials, designed a product to meet the need, produced the product, and used it. Everything from start to finish was integrated within the mind of the person who did all the work.Then during the industrial revolution mechanized processes were introduced and humans began using machines to accomplish work previously accomplished manually. This led to work specialization which, in turn, eliminated the integrated aspect of manufacturing. In this stage of development, manufacturing workers might see only that part of an overall manufacturing operation represented by that specific piece on which they worked. There was no way to tell how their efforts fit into the larger picture or their workpiece into the finished product.The next stage in the development of manufacturing processes involved the automation of selected processes. This amounted to computer control of machines and processes. During this phase, islands of automation began to spring up on the shop floor. Each island represented a distinct process or group of processes used in the production of a product. Although these islands of automation did tend to enhance the productivity of the individual processes within the islands, overall productivity often was unchanged. This was because the islands were sandwiched in among other processes that were not automated and were not synchronized with them.The net result was that workpieces would move quickly and efficiently through the automated processes only to back up at manual stations and create bottlenecks. To understand this problem, think of yourself driving from stoplight to stoplight in rush hour traffic Occasionally you find an opening and an: able to rush ahead of the other cars that are creeping along, only to find yourself backed up at the next light. The net effect of your brief moment of speeding ahead is canceled out by the bottleneck at the next stoplight. Better progress would be made if you and the other drivers could synchronize your speed to the changing of the stoplights. Then all cars would move steadily and consistently along and everyone would make better progress in the long run.This need for steady, consistent flow on the shop floor led to the development of integrated manufacturing, a process that is still emerging. In fully integrated settings, machines and processes are computer controlled and integration is accomplished through computers. In the analogy used in the previous paragraph, computers would synchronize the rate of movement of all cars with the changing of the stoplights so that everyone moved steadily and consistently along.The Science of MechanicsThat branch of scientific analysis which deals with motions, time, and forces is called mechanics and is made up of two parts, static’s and dynamics. Static’s deals with the analysis of stationary systems, i. e., those in which time is not a factor, and dynamics deals with systems which change with time.Dynamics is also made up. of tyro major disciplines, first recognized as separate entities by Euler in 1775.The investigation of the motion of a rigid body may be conveniently separated into two parts, the one geometrical, the other mechanical. In the first part, the transference of the body from a given position to any other position must be investigated without respect to the cause of the motion, and must be represented by analytical formulae, which will define the position of each point of the body. This investigation will therefore be referable solely to geometry, or rather to stereotomy.It is clear that by the separation of this part of the question from the other, which belongs properly to Mechanics, the determination of the motion from dynamical principles will be made much easier than if the two parts were undertaken conjointly.These two aspects of dynamics were later recognized as the distinct sciences of kinematics and kinetics, and deal with motion and the forces producing it respectively.The initial problem in the design of a mechanical system therefore understands its kinematics. Kinematics is the study of motion, quite apart from the forces which produce that motion. More particularly, kinematics is the study of position,displacement rotation, speed, velocity, and acceleration. The study, say of planetary or orbital motion is also a problem in kinematics.It should be carefully noted in the above quotation that Euler based his separation of dynamics into kinematics and kinetics on the assumption that they should deal with rigid bodies. It is this very important assumption that allows the two to be treated separately. For flexible bodies, the shapes of the bodies themselves, and therefore their motions, depend on the forces exerted on them. In this situation, the study of force and motion must take place simultaneously, thus significantly increasing the complexity of the analysis.Fortunately, although all real machine parts are flexible to some degree, machines are usually designed from relatively rigid materials, keeping part deflections to a minimum. Therefore, it is common practice to assume that deflections are negligible and parts are rigid when analyzing a machine's kinematics performance, and then, after the dynamic analysis when loads are known, to design the parts so that this assumption is justified.。

外文翻译英文原文Belt Conveying Systems Development of driving systemAmong the methods of material conveying employed，belt conveyors playa very important part in the reliable carrying of material over longdistances at competitive cost．Conveyor systems have become larger and more complex and drive systems have also been going through a process of evolution and will continue to do so．Nowadays，bigger belts require more power and have brought the need for larger individual drives as well as multiple drives such as 3 drives of 750 kW for one belt(this is the case for the conveyor drives in Chengzhuang Mine)．The ability to control drive acceleration torque is critical to belt conveyors’performance．An efficient drive system should be able to provide smooth，soft starts while maintaining belt tensions within the specified safe limits．For load sharing on multiple drives．torque and speed control are also important considerations in the drive system’s design.Due to the advances in conveyor drive control technology，at present many more reliable．Cost-effective and performance-driven conveyor drive systemscovering a wide range of power are available for customers’ choices[1].1 Analysis on conveyor drive technologies1．1 Direct drivesFull-voltage starters．With a full-voltage starter design，the conveyor head shaft is direct-coupled to the motor through the gear drive．Direct full-voltage starters are adequate for relatively low-power, simple-profile conveyors．With direct fu11-voltage starters．no control is provided for various conveyor loads and．depending on the ratio between fu11-and no-1oad power requirements，empty starting times can be three or four times faster than full load．The maintenance-free starting system is simple，low-cost and very reliable．However, they cannot control starting torque and maximum stall torque；therefore．they arelimited to the low-power, simple-profile conveyor belt drives．Reduced-voltage starters．As conveyor power requirements increase，controlling the applied motor torque during the acceleration period becomes increasingly important．Because motor torque 1s a function of voltage，motor voltage must be controlled．This can be achieved through reduced-voltage starters by employing a silicon controlled rectifier(SCR)．A common starting method with SCR reduced-voltage starters is to apply low voltage initially to take up conveyor belt slack．and then to apply a timed linear ramp up to full voltage and belt speed．However, this starting method will not produce constant conveyor belt acceleration．When acceleration is complete．the SCRs,which control the applied voltage to the electric motor． are locked in full conduction, providing fu11-line voltage to the motor．Motors with higher torque and pull—up torque，can provide better starting torque when combined with the SCR starters, which are available in sizes up to 750 KW．Wound rotor induction motors．Wound rotor induction motors are connected directly to the drive system reducer and are a modified configuration of a standard AC induction motor．By inserting resistance in series with the motor’s rotor windings．the modified motor control system controls motor torque．For conveyor starting，resistance is placed in series with the rotor for low initial torque．As the conveyor accelerates，the resistance is reduced slowly to maintain a constant acceleration torque．On multiple-drive systems．an external slip resistor may be left in series with the rotor windings to aid in load sharing．The motor systems have a relatively simple design．However, the control systems for these can be highly complex，because they are based on computer control of the resistance switching．Today，the majority of control systems are custom designed to meet a conveyor system’s particular specifications．Wound rotor motors are appropriate for systems requiring more than 400 kW ．DC motor．DC motors．available from a fraction of thousands of kW ，are designed to deliver constant torque below base speed and constant kW above base speed to the maximum allowable revolutions per minute(r/min)．with the majority of conveyor drives, a DC shunt wound motor is used．Wherein the motor’s rotating armature isconnected externally．The most common technology for controlling DC drives is a SCR device． which allows for continual variable-speed operation．The DC drive system is mechanically simple, but can include complex custom-designed electronics to monitor and control the complete system．This system option is expensive in comparison to other soft-start systems．but it is a reliable, cost-effective drive in applications in which torque,1oad sharing and variable speed are primary considerations．DC motors generally are used with higher-power conveyors，including complex profile conveyors with multiple-drive systems，booster tripper systems needing belt tension control and conveyors requiring a wide variable-speed range．1．2 Hydrokinetic couplingHydrokinetic couplings，commonly referred to as fluid couplings．are composed of three basic elements; the driven impeller, which acts as a centrifugal pump；the driving hydraulic turbine known as the runner and a casing that encloses the two power components．Hydraulic fluid is pumped from the driven impeller to the driving runner, producing torque at the driven shaft．Because circulating hydraulic fluid produces the torque and speed，no mechanical connection is required between the driving and driven shafts．The power produced by this coupling is based on the circulated fluid’s amount and density and the torque in proportion to input speed．Because the pumping action within the fluid coupling depends on centrifugal forces．the output speed is less than the input speed．Referred to as slip．this normally is between l% and 3%．Basic hydrokinetic couplings are available in configurations from fractional to several thousand kW ．Fixed-fill fluid couplings．Fixed-fill fluid couplings are the most commonly used soft-start devices for conveyors with simpler belt profiles and limited convex/concave sections．They are relativelysimple,1ow-cost,reliable,maintenance free devices that provide excellent soft starting results to the majority of belt conveyors in use today．Variable-fill drain couplings．Drainable-fluid couplings work on the same principle as fixed-fill couplings．The coupling’s impellers are mounted on the AC motor and the runners on the driven reducer high-speed shaft．Housing mounted to the drive base encloses the working circuit．The coupling’s rotating casing containsbleed-off orifices that continually allow fluid to exit the working circuit into a separate hydraulic reservoir．Oil from the reservoir is pumped through a heat exchanger to a solenoid-operated hydraulic valve that controls the filling of the fluid coupling．To control the starting torque of a single-drive conveyor system，the AC motor current must be monitored to provide feedback to the solenoid control valve．Variable fill drain couplings are used in medium to high-kW conveyor systems and are available in sizes up to thousands of kW ．The drives can be mechanically complex and depending on the control parameters．the system can be electronically intricate．The drive system cost is medium to high, depending upon size specified．Hydrokinetic scoop control drive．The scoop control fluid coupling consists of the three standard fluid coupling components：a driven impeller, a driving runner and a casing that encloses the working circuit．The casing is fitted with fixed orifices that bleed a predetermined amount of fluid into a reservoir．When the scoop tube is fully extended into the reservoir, the coupling is l00 percent filled．The scoop tube, extending outside the fluid coupling，is positioned using an electric actuator to engage the tube from the fully retracted to the fully engaged position．This control provides reasonably smooth acceleration rates．to but the computer-based control system is very complex．Scoop control couplings are applied on conveyors requiring single or multiple drives from l50 kW to 750 kW.1．3 Variable-frequency control(VFC)Variable frequency control is also one of the direct drive methods．The emphasizing discussion about it here is because that it has so unique characteristic and so good performance compared with other driving methods for belt conveyor． VFC devices Provide variable frequency and voltage to the induction motor, resulting in an excellent starting torque and acceleration rate for belt conveyor drives．VFC drives．available from fractional to several thousand(kW ), are electronic controllers that rectify AC line power to DC and，through an inverter, convert DC back to AC with frequency and voltage contro1．VFC drives adopt vector control or direct torque control(DTC)technology，and can adopt different operating speeds according to different loads．VFC drives can make starting or stallingaccording to any given S-curves．realizing the automatic track for starting or stalling curves．VFC drives provide excellent speed and torque control for starting conveyor belts．and can also be designed to provide load sharing for multiple drives．easily VFC controllers are frequently installed on lower-powered conveyor drives，but when used at the range of medium-high voltage in the past．the structure of VFC controllers becomes very complicated due to the limitation of voltage rating of power semiconductor devices，the combination of medium-high voltage drives and variable speed is often solved with low-voltage inverters using step-up transformer at the output，or with multiple low-voltage inverters connected in series．Three-level voltage-fed PWM converter systems are recently showing increasing popularity for multi-megawatt industrial drive applications because of easy voltage sharing between the series devices and improved harmonic quality at the output compared to two-level converter systems With simple series connection of devices．This kind of VFC system with three 750 kW /2．3kV inverters has been successfully installed in ChengZhuang Mine for one 2．7-km long belt conveyor driving system in following the principle of three-level inverter will be discussed in detail．2 Neutral point clamped(NPC)three-level inverter using IGBTsThree-level voltage-fed inverters have recently become more and more popular for higher power drive applications because of their easy voltage sharing features．1ower dv/dt per switching for each of the devices，and superior harmonic quality at the output．The availability of HV-IGBTs has led to the design of a new range of medium-high voltage inverter using three-level NPC topology．This kind of inverter can realize a whole range with a voltage rating from 2．3 kV to 4．1 6 kV Series connection of HV-IGBT modules is used in the 3．3 kV and 4．1 6 kV devices．The 2．3 kV inverters need only one HV-IGBT per switch[2,3].2．1 Power sectionTo meet the demands for medium voltage applications．a three-level neutral point clamped inverter realizes the power section．In comparison to a two-level inverter．the NPC inverter offers the benefit that three voltage levels can be supplied to the output terminals，so for the same output current quality，only1/4 of the switching frequency is necessary．Moreover the voltage ratings of the switches in NPC inverter topology will be reduced to 1/2．and the additional transient voltage stress on the motor can also be reduced to 1/2 compared to that of a two-level inverter．The switching states of a three-level inverter are summarized in Table 1．U．V and W denote each of the three phases respectively；P N and O are the dc bus points．The phase U，for example，is in state P(positive bus voltage)when theswitches S1u and S2uare closed，whereas it is in state N (negative bus voltage)when the switches S3u and S4uare closed．At neutral point clamping，the phase isin O state when either S2u or S3uconducts depending on positive or negative phasecurrent polarity，respectively．For neutral point voltage balancing，the average current injected at O should be zero．2．2 Line side converterFor standard applications．a l2-pulse diode rectifier feeds the divided DC-link capacitor．This topology introduces low harmonics on the line side．For even higher requirements a 24-pulse diode rectifier can be used as an input converter．For more advanced applications where regeneration capability is necessary, an active front．end converter can replace the diode rectifier, using the same structure as the inverter．2．3 Inverter controlMotor Contro1．Motor control of induction machines is realized by using a rotor flux．oriented vector controller．Fig．2 shows the block diagram of indirect vector controlled drive that incorporates both constant torque and high speed field-weakening regions where the PW M modulator was used．In this figure，the command flux is generated as function of speed．The feedback speed is added with the feed forward slip command signal . the resulting frequency signal is integrated and then the unit vectorsignals(cos and sin )are generated．The vector rotator generates the voltage and angle commands for the PW M as shown．PWM Modulator．The demanded voltage vector is generated using an elaboratePWM modulator．The modulator extends the concepts of space-vector modulation to the three-level inverter．The operation can be explained by starting from a regularly sampled sine-triangle comparison from two-level inverter．Instead of using one set of reference waveforms and one triangle defining the switchingand frequency， the three-level modulator uses two sets of reference waveforms Ur1and just one triangle．Thus, each switching transition is used in an optimal Ur2way so that several objectives are reached at the same time．Very low harmonics are generated．The switching frequency is low and thus switching losses are minimized．As in a two-level inverter, a zero-sequence component can be added to each set of reference waveform s in order to maximize the fundamental voltage component．As an additional degree of freedom，the position of the reference waveform s within the triangle can be changed．This can be used for current balance in the two halves of the DC-1ink．3 Testing resultsAfter Successful installation of three 750 kW /2．3 kV three-level inverters for one 2．7 km long belt conveyor driving system in Chengzhuang Mine．The performance of the whole VFC system was tested．Fig．3 is taken from the test，which shows the excellent characteristic of the belt conveyor driving system with VFC controller．Fig．3 includes four curves．The curve 1 shows the belt tension．From the curve it can be find that the fluctuation range of the belt tension is very smal1．Curve 2 and curve 3 indicate current and torque separately．Curve 4 shows the velocity of the controlled belt．The belt velocity have the“s”shape characteristic．A1l the results of the test show a very satisfied characteristic for belt driving system．4 ConclusionsAdvances in conveyor drive control technology in recent years have resulted in many more reliable．Cost-effective and performance-driven conveyor drive system choices for users．Among these choices，the Variable frequency control (VFC) method shows promising use in the future for long distance belt conveyor drives due to its excellent performances．The NPC three-level inverter using high voltage IGBTsmake the Variable frequency control in medium voltage applications become much more simple because the inverter itself can provide the medium voltage needed at the motor terminals，thus eliminating the step-up transformer in most applications in the past．The testing results taken from the VFC control system with NPC three．1evel inverters used in a 2．7 km long belt conveyor drives in Chengzhuang Mine indicates that the performance of NPC three-level inverter using HV-IGBTs together with the control strategy of rotor field-oriented vector control for induction motor drive is excellent for belt conveyor driving system．中文译文：带式输送机及其牵引系统在运送大量的物料时，带式输送机在长距离的运输中起到了非常重要的竞争作用。

本科毕业论文（设计）外文翻译学院：机电工程学院__________专业：机械工程及自动化姓名：高峰指导教师：李延胜2011年05月10日教育部办公厅Failure An alysi§ Dime nsional Determ in ati on And An alysis Applicati ons Of Cams INTRODUCTIONIt is absolutely essential that a design engineer know how and why parts fail so that reliable mach ines that require minimum maintenance can be desig nedbmetimes a failure can be serious such as when a tire blows out on an automobile traveling at high speOn the other hand a failure may be no more than a nuisanceAn example is the loosening of the radiator hose in an automobile cooling systemThe consequence of this latter failure is usually the loss of some radiator coo la^a con diti on that is readily detected and correctedThe type of load a part absorbs is just as sig nifica nt as the magn itude Gen erally speak ing dyn amic loads with directi on reversals cause greater difficulty tha n static loads and therefore, fatigue strength must be considered Another concern is whether the material is ductile or brittleFor example brittle materials are considered to be unacceptable where fatigue is invo IvedMany people mistak in gly in terpret the word failure to mean the actual breakage of a part. However, a design engineer must consider a broader understanding of what appreciable deformation occur s A ductile material, however will deform a large amount prior to rupture . Excessive deformation without fracture, may cause a machine to fail becausethe deformed part interferes with a moving second part. Therefore, a part fails(eve n if it has not physically broke n) whe never it no Ion ger fulfills its required function. Sometimesfailure may be due to abnormal friction or vibration between two mating parts Failure also may be due to a phenomenon called creepwhich is the plastic flow of a material under load at elevated temperaturesIn addition, the actual shape of a part may be responsiblefor failure. For example stressconcentrationsdue to sudden cha nges in con tour must be take n into acco unt Evaluatio n of stress con siderati on sis especially importa nt whe n there are dyn amic loads with directi on reversals and the material is not very ductileIn general, the design engineer must consider alpossible modes of failure, which in clude the followi ng.StressDeformati on---- Wear---- Corrosi on---- Vibrati on---- En viro nmen tal damage---- Loose ning of faste ning devicesThe part sizes and shapesselectedalso must take into acco unt many dime nsional factors that produce external load effects, such as geometric discontinuities residual stresses due to formi ng of desired con toqrsa nd the applicati on of in terfere nee fit joi ntsCams are among the most versatile mechanisms available A cam is a simple two-member device The in put member is the cam itsejfwhile the output member is called the follower. Through the use of cams a simple in put motio n can be modified in to almost any con ceivable output moti on that is desired Some of the com mon applicati ons of cams are---- Camshaft and distributor shaft of automotive engine---- Productio n mach ine toolsAutomatic record playersPrinting machines---- Automatic washi ng mach ines---- Automatic dishwashersThe con tour of high-speed cams (cam speed in excess of 1000 rpm) must be determined mathematicall y However, the vast majority of cams operate at low speeds(less than 500 rpm) or medium-speedcams can be determined graphicallyusing a large-scale layout. In gen era, the greater the cam speed and output load the greater must be the precisi on with which the cam con tour is machi nedDESIGN PROPERTIES OF MATERIALSThe following design properties of materials are defined as they relate to the tensile test.Figure 2.7Static Strength The strength of a part is the maximum stressthat the part can sustain without losing its ability to perform its required function. Thus the static strength may be con sidered to be approximately equal to the proporti on al lirps ince no plastic deformatio n takes place and no damage theoretically is done to the materialStiff ness Stiff ness is the deformati on-resisti ng property of a materiaThe slope of the modulus line and, hence the modulus of elasticity are measuresof the stiffness of amateria lResilienee Resilienee is the property of a material that permits it to absorb energy withoutpermanent deformation The amount of energy absorbed is represented by the area undern eath the stress-strain diagram within the elastic regi onToughness Resilienee and toughness are similar propertiesHowever, toughness is the ability to absorb energy without rupture. Thus toughness is represented by the total area undern eath the stress-stra in diagramas depicted in Figure 28b. Obviously, the tough ness and resilienee of brittle materials are very low and are approximately equalBrittleness A brittle material is one that ruptures before any appreeiableplastie deformatio n takes plaee Brittle materials are gen erally eon sidered un desirable for maeh ine eomp onents beeause they are un able to yield loeally at loeati ons of high stress beeause of geometrie stress raisers sueh as shouldeholes, notehes, or keywaysDuetility . A duetility material exhibits a large amount of plastie deformatio n priorto rupture . Duetility is measured by the pereent of area and pereent elongation of a part loaded to rupture A 5%elongation at rupture is eonsidered to be the dividing line between duetile and brittle materialsMalleability. Malleability is essentiallya measure of the eompressiveduetility of a material and, as sueh is an important eharaeteristie of metals that are to be rolled into sheetsHardness The hardness of a material is its ability to resist indentation or scratchi ng Gen erally speak ing the harder a material the more brittle it is and hence the less resilient Also, the ultimate strength of a material is roughly proportional to its hard nessMach in ability. Mach in ability is a measure of the relative ease with which a material canbe machi ned In gen era] the harder the material the more difficult it is to mach ineFigure 2.8COMPRESSION AND SHEAR STATIC STRENGTHIn addition to the tensile tests there are other types of static load testing that provide valuable in formatio nCompressi on Test ing Most ductile materialshave approximatelythe same properties in compression as in tension The ultimate strength, however, can not be evaluated for compression As a ductile specimen flows plastically in compressionthe material bulges out, but there is no physical rupture as is the case in tensionherefore, a ductile material fails in compressi on as a result of deformatio nnot stressShear Testi ng Shafts bolts, rivets, and welds are located i n such a way that shear stresses are produced plot of the tensile test The ultimate shearing strength is defined as the stress at which failure occursThe ultimate strength in shearhowever, does not equal the ultimate strength in tension. For example in the caseof stee, the ultimate shear stre ngth is approximately 75% of the ultimate stre ngth in ten sionThis differe nee must be take n into aeeo unt whe n shear stresses are encoun tered in maehi ne compo s e ntsDYNAMIC LOADSAn applied force that does not vary in any manner is called a static or steady」oads alsocom mon practice to con sider applied forces that seldom vary to be static loadsThe force that is gradually applied duri ng a ten sile test is therefore a static .loadOn the other hand, forces that vary freque ntly in magn itude and direct ion are called dynamic loads Dynamic loads can be subdivided to the following three categoriesVarying Load. With vary ing loads, the magn itude cha nges but the directi on doesnot. For example the load may produce high and low tensile stresses but no compressive stressesRevers ing Load I n this case both the magn itude and direct ion cha nge These load reversalsproduce alternatelyvaryi ng ten sile and compressivestressesthat are com mon ly referred to as stress reversalsShock Load This type of load is due to impact One example is an elevator dropping on a nest of springs at the bottom of a chute The resulting maximum spring force can be many times greater tha n the weight of the elevatorThe same type of shock load occurs in automobile spri ngs whe n a tire hits a bump or hole in the roadFATIGUE FAILURE-THE ENDURANCE LIMIT DIAGRAMThe test specimen in Figure 2.10a , after a given number of stress reversalswill experie nee a crack at the outer surface where the stress is greateThe in itial crack starts where the stress exceeds the strength of the grain on which it actsThis is usually where there is a small surface defectsuch as a material flaw or a tiny scratchAs the number of cycles in creases the initial crack begi ns to propagate into a con ti nu ous series of cracks all around the periphery of the shaft. The conception of the initial crack is itself a stress concentration that acceleratesthe crack propagation phenomenon. Once the entire periphery becomes crackedhe cracks start to move toward the cen ter of the shaFti nally, whe n the remai ning solid inner area becomes small en oug h e stress exceeds the ultimate strength and the shaft suddenly breaks Inspection of the break reveals a very interesting patter n,as show n in Figure 2.13The outer annu lar area is relatively smooth because mati ng cracked surfaces had rubbed against each otheHowever, the center portion is rough indicating a sudden rupture similar to that experieneed with the fracture of brittle materialsThis brings out an interesting fact When actual machine parts fail as a result of static loads, they normally deform appreciably because of the ductility of the materialFigure 2.13Thus many static failures can be avoided by making freque nt visual observati ons and replacing all deformed partsHowever, fatigue failures give to warning Fatigue fail mated that over 90% of broke n automobile parts have failed through fatigueThe fatigue strength of a material is its ability to resist the propagation of cracks under stress reversals En dura nee limit is a parameter used to measure the fatigue stre ngth of a materia l By definition, the enduraneelimit is the stressvalue below which an infinite nu mber of cycles will not cause failureLet us return our attention to the fatigue testing machine in Figure 2.9The test is run as follows： A small weight is inserted and the motor is turned on. At failure of the test specimenthe coun ter registers the nu mber of cycles, Na nd the corresp onding maximum bending stress is calculated from Equation 2.The broken specimen is then replaced by an iden tical one and an additi onal weight is in serted to in crease the loAdnew value of stress is calculated and the procedure is repeated until failure requires only one complete cycle plot is then made of stress versus number of cycles to failurFigure 2.14a shows the plot which is called the endurance limit or S-N curv.e Since it would take forever to achieve an infinite number of cycles 1 million cycles is used as a referencHence the endurance limit can be found from Figure 2.14a by noting that it is the stress level below which the material can susta in 1 milli on cycles without failure The relati on ship depicted in Figure 2.14 is typical for steebecause the curve becomes horiz on tal as N approaches a very large nu mbeThus the en dura nce limit equals the stress level where the curve approaches a horiz on tal tan geOtw ing to the large nu mber of cycles invoIved, N is usually plotted on a logarithmic scajeas shown in Figure 2.14.bWhen this is done,the endurance limit value can be readily detected by the horizontal straight Foe stee, the endurance limit equals approximately 50% of the ultimate strengtHowever, if the surface finish is not of polished equality the value of the enduraneelimit will be lower. For example for steel parts with a machined surface finish of 63 microinches ( 卩助，.the percentage drops to about 40%For rough surfaces (300 or greater).the perce ntage may be as low as 25%The most com mon type of fatigue is that due to bending The n ext most freque nt is torsi on failure, whereas fatigue due to axial loads occurs very seldoSpri ng materials are usually tested by appl ying variable shearstressesthat alternatefrom zero to a maximum value,simulating the actual stress patternsIn the caseof some non ferrous metals the fatigue curve does not level off as the nu mber of cycles becomes very largeThis continuing toward zero stress means that a large number of stress reversalswill causefailure regardlessof how small the value of stress is. Such a material is said to have no en dura nee linFior most non ferrous metals hav ing an en dura nee limit the value is about 25% of the ultimate stre ngthEFFECTS OF TEMPERATURE ON YIELD STRENGTH AND MODULUS OF ELASTICITY Gen erally speak ing, when stat ing that a material possessesspecified values of properties such as modulus of elasticity and yield stre ngth it is implied that these values exist at room temperatureAt low or elevated temperaturesthe properties of materials may be drastically different For example many metals are more brittle at low temperature" addition, the modulus of elasticity and yield strength deteriorate as the temperature in creases Figure 2.23 shows that the yield stre ngth for mild steel is reduced by about 70%in going from room temperature to 100°F.Figure 2.24 shows the reduct ion in the modulus of elasticity E for mild steel as the temperature in creases As can be see n from the graph, a 30% reduct ion in modulus of elasticity occurs in going from room temperature to 10°F). In this figure, we also can see that a part loaded below the proportional limit at room temperaturecan be permanently deformed un der the same load at elevated temperaturesFigure 2.24CREEP: A PLASTIC PHENOMENONTemperature effects bring us to a phenomenon called creep which is the increasing plastic deformation of a part under constant load as a function of timCreep also occurs at room temperature but the process is so slow that it rarely becomes significant during the expected life of the temperature is raised to 300o C or more, the increasing plastic deformation can become significant within a relatively short period of time. The creep stre ngth of a material is its ability to resist creea nd creep stre ngth data can be obta ined by con duct ing Ion g-time creep tests simulati ng actual part operat ing con diti ons During the test, the plastic strain is monitored for given material at specified temperaturesSince creep is a plastic deformation phenomenon, the dimensions of a part experiencing creep are permanently altereThus, if a part operates with tight clearances the desig n engin eer must accurately predict the amount of creep that will occur duri ng the life of the machine Otherwise, problems such binding or interferenee can occurCreep also can be a problem in the case where bolts are used to clamp tow parts together at elevated temperaturesThe bolts, under tension, will creep as a function of time. Since the deformation is plastic loss of clamping force will result in an undesirable loosening of the bolted joint The extent of this particular phenomenon called relaxation can be determ ined by running appropriate creep stre ngth testsFigure 2.25 shows typical creep curves for three samples of a mild steel part un der a consta nt ten sile loadNotice that for the high-temperature case the creep tends to accelerate until the part fails . The time line in the graph (the x-axis) may represent a periodof 10 years the anticipated life of the productFigure 2.25SUMMARYThe machine designer must understand the purpose of the static tensile strength test. This test determ in esa nu mber of mecha ni calproperties of metalsthat are used in desig n equati ons Such terms as modulus of elasticjtyproporti on al limit, yield stre ngth, ultimate strength, resilienee and ductility define properties that can be determined from the ten sile test Dyn amic loads are those which vary in magn itude and direct ion and may require an investigation of the machine part ' s resisSmeestoeveurals may require thatthe allowable desig n stress be based on the en dura nee limit of the material rather tha n on the yield strength or ultimate strengthStress concen trati on occurs at locati ons where a mach ine part cha nges,sizech as a hole in a flat plate or a sudden change in width of a flat plate or a groove or fillet on a circular shaf t Note that for the case of a hole in a flat or ba, the value of the maximum stress becomes much larger in relation to the averagestress as the size of the hole decreases Methods of reducing the effect of stress concentration usually invoIve making the shape cha nge more gradual Mach ine parts are desig ned to operate at some allowable stress below the yield stre ngthor ultimate strength This approach is used to take care of such unknown factors as material property variati ons and residual stresses produced duri ng manu facture and the fact that the equati ons used may be approximate rather that exadthe factor of safety is applied to the yield stre ngth or the ultimate stre ngth to determ ine the allowable stressTemperature can affect the mecha ni cal properties of metals ncreases in temperature may cause a metal to expand and creep and may reduce its yield strength and its modulus of elasticity. If most metals are not allowed to expa nd or con tract with a cha nge in temperature then stresses are set up that may be added to the stresses from the lTais phe nomenon is useful in assembli ng parts by means of in terfere nce.fiA hub or ring has an in side diameter slightly smaller tha n the mati ng shaft or p.osithe hub is the n heated so that it expa nds eno ugh to slip over the shaW/he n it cools, it exerts a pressure on the shaft result ing in a strong frict ional force that preve nts loose ningTYPES OF CAM CONFIGURATIONSPlate Cams This type of cam is the most popular type becauseit is easy to design and manufacture Figure 6. 1 shows a plate camNotice that the follower moves perpendicular to the axis of rotation of the camshaf t All cams operate on the principle that no two objects can occupy the same space at the same .tiTheis, as the cam rotates ( in this case coun terclockwise ) the follower must either move upward or bind in side the guidWe will focus our attention on the prevention of binding and attainment of the desired output follower moti on. The spri ng is required to mai ntain con tact betwee n the roller of the follower and the cam con tour whe n the follower is movi ng dow nwardThe roller is used to reduce frict ion and hence wear at the contact surfacFor each revolutio n of the cam the follower moves through two strokes-bottom dead cen ter to top dead cen ter (BDC to TDC) and TDC to BDC .Figure 6.2 illustrates a plate cam with a poin ted follower . Complex motio ns can be produced with this type of follower becausethe point can follow precisely any sudden cha nges in cam con tour However, this desig n is limited to applicati ons in which the loads are very light; otherwise the con tact point of both members will wear prematurely with subseque nt failure Two additional variations of the plate cam are the pivoted follower and the offset sliding follower, which are illustrated in Figure 6.3A pivoted follower is used when rotary output motion is desired Referring to the offset follower; note that the amount of offset used depe nds on such parameters as pressure an gle and cam profile flatnwhich will be covered later A follower that has no offset is called an in-line followerFigure 6..3Translation Cams Figure 6.4 depicts a translation canThe follower slides up and down as the cam translates motion in the horizontal direction Note that a pivoted follower can be used as well as a sliding-type follower. This type of action is used in certain production machines in which the pattern of the product is used as the cam variation on this design would be athree-dimensional cam that rotates as well as translates For example a hand-constructed rifle stock is placed in a special lathe This stock is the pattern, and it performs the function of a cam As it rotates and translatesthe follower controls a tool bit that mach ines the product ion stock from a block of woodFigure 6.4Positive-Moti on Cams In the forego ing cam design,the con tact betwee n the cam and the follower is en sured by the action of the spri ng forces duri ng the retur n strokedowever, in high-speed cams the spri ng force required to maintain con tact may become excessive whe n added to the dyn amic forces gen erated as a result of accelerationsis situati on can result in un acceptablylarge stress at the con tact surface which in turn can result in premature wear Positive-motion cams require no spring because the follower is forced to con tact the cam in two directi ons There are four basic types of positive-moti on cams: the cylindrical cam thegrooved-plate cam ( also called a face cam Xhe matched-plate cam and the scotch yoke cam Cylindrical Cam The cylindrical cam shown in Figure 6.5 produces reciprocating follower motion, whereas the one shown in Figure 6.6 illustrates the application of a pivoted follower. The cam groove can be designedsuch that several camshaft revolutions are required to produce one complete follower cycleGrooved-plate Cam In Figure 6.8 we see a matched-plate cam with a pivoted follow e r although the design also can be used with a translation follower. Cams E and F rotate together about the camshaft B Cam E is always in con tact with roller C , while cam F mai ntai ns con tact with roller D Rollers C and D are moun ted on a bell-cra nk levewhich is the follower oscillating about point A Cam E is designed to provide the desired motion of roller C, while cam F provides the desired motion of roller DScotch Yoke Cam This type of cam, which is depicted in Figure 6.,consists of a circular cam moun ted ecce ntrically on its camshafThe stroke of the follower equals two times the ecce ntricity e of the cam . This cam produces simple harm on ic motio n with no dwell times. Refer to Secti on 6.8 for further discussi onCAM TERMINOLOGYBefore we become invoIved with the design of cams it is desirable to know the various terms used to identify important cam design parameters The following terms refer to Figure 6.11. The descriptions will be more understandableif you visualize the cam as stati onary and the followeras movi ng around the camTrace Point. The end point of a knife-edge follower or the center of the roller of a roller-type follower.Cam Con tour. The actual shape of the camBase Circle The smallest circle that can be draw n tangent to the cam con to us cen ter is also the center of the camshaft The smallest radial size of the cam stars at the base circlePitch Curve. The path of the trace point assuming the cam is stationary and the follower rotates about the camPrime Circle The smallest circle that can be drawn tangent to the pitch curves center is also the cen ter of the camshaftPressure An gle The an gle betwee n the direct ion of moti on of the follower and the normal to the pitch curve at the point where the center of the roller liesCam Profile. Same as cam con tourBDC . Bottom Dead Center, the position of the follower at its closest point to the cam hub .Stroke. The displaceme nt of the follower in its travel betwee n BDC and TDCRise. The displacement of the follower as it travels from BDC to TDCReturn. The displacement of the follower as it travels from TDC or BDCEwell. The actio n of the follower whe n it remai ns at a con sta nt dista nce from the cam hub while the cam turnsA clearer understandingof the significance of the pressureangle can be gained by referring to Figure 6.12 Here F T is the total force acting on the rollerIt must be normal to the surfaces at the con tact point Its directi on is obviously not parallel to the directi on of motio n of the follower. In stead, it is in dicated by the an gle the pressure a glemeasured from the line represe nting the directi on of motio n of the follower Therefore, the force F T has a horizontal component Fand a vertical component F. The vertical component is the one that drives the follower upward and therefore, neglecting guide friction equals the follower F load. The horizontal component has no useful purpose but it is unavoidabJeIn fact, it attempts to bend the follower about its guiderhis can damage the follower or cause it to bind in side its guide. Obviously, we want the pressurea ngle to be as possible to mini mize the side thrust F. A practical rule of thumb is to desig n the cam con tour so that the pressure angle does not exceed 30 The pressure angle in general depends on the followi ng four parameters:---- Size of base circleAmount of offset of followerSize of roller---- Flat nessof cam con tour ( which depe ndson follower stroke and type of follower motio n used )Some of the preceding parameters cannot be changed without altering the cam requireme nts such as space limitationsAfter we have lear ned how to desig n a cawe will discuss the various methods available to reduce the pressure an gle故障的分析、尺寸的决定以及凸轮的分析和应用前言介绍：作为一名设计工程师有必要知道零件如何发生和为什么会发生故障，以便通过进行最低限度的维修以保证机器的可靠性。