凸轮设计外文翻译参考文献

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1、外文文献翻译 (含：英文原文及中文译文) 英文原文 Failure Analysis, Dimensional Determination And Analysis , Applications Of CamsINTRODUCTIONIt is absolutely essential that a design engineer know how and why parts fail so that reliable machines that require minimum maintenance can be designed. Sometimes a failure can be se

2、rious, such as when a tire blows out on an automobile traveling at high speed. On the other hand, a failure may be no more than a nuisance. An example is the loosening of the radiator hose in an automobile cooling system. The consequence of this latter failure is usually the loss of some radiator co

3、olant, a condition that is readily detected and corrected. The type of load a part absorbs is just as significant as the magnitude . Generally speaking , dynamic loads with direction reversals cause greater difficulty than static loads, and therefore, fatigue strength must be considered. Another con

4、cern is whether the material is ductile or brittle. For example, brittle materials are considered to be unacceptable where fatigue is involved.Many people mistakingly interpret the word failure to mean the actual breakage of a part . However , a design engineer must consider a broader understanding

5、of what appreciable deformation occurs. A ductile material, however will deform a large amount prior to rupture. Excessive deformation, without fracture, may cause a machine to fail because the deformed part interferes with a moving second part . Therefore , a part fails(even if it has not physicall

6、y broken)whenever it no longer fulfills its required function . Sometimes failure may be due to abnormal friction or vibration between two mating parts. Failure also may be due to a phenomenon called creep, which is the plastic flow of a material under load at elevated temperatures. In addition, the

7、 actual shape of a part may be responsible for failure . For example , stress concentrations due to sudden changes in contour must be taken into account . Evaluation of stress considerations is especially important when there are dynamic loads with direction reversals and the material is not very du

8、ctile.In general, the design engineer must consider all possible modes of failure, which include the following. Stress Deformation Wear Corrosion Vibration Environmental damage Loosening of fastening devicesThe part sizes and shapes selected also must take into account many dimensional factors that

9、produce external load effects , such as geometric discontinuities , residual stresses due to forming of desired contours, and the application of interference fit joints.Cams are among the most versatile mechanisms available . A cam is a simple two-member device. The input member is the cam itself, w

10、hile the output member is called the follower. Through the use of cams, a simple input motion can be modified into almost any conceivable output motion that is desired. Some of the common applications of cams are : Camshaft and distributor shaft of automotive engine Production machine tools Automati

11、c record players Printing machines Automatic washing machines Automatic dishwashersThe contour of high-speed cams (cam speed in excess of 1000 rpm) must be determined mathematically. However , the vast majority of cams operate at low speeds(less than 500 rpm) or medium-speed cams can be determined g

12、raphically using a large-scale layout . In general, the greater the cam speed and output load, the greater must be the precision with which the cam contour is machined.DESIGN PROPERTIES OF MATERIALSThe following design properties of materials are defined as they relate to the tensile test .Static St

13、rength. The strength of a part is the maximum stress that the part can sustain without losing its ability to perform its required function. Thus the static strength may be considered to be approximately equal to the proportional limit , since no plastic deformation takes place and no damage theoreti

14、cally is done to the material.Stiffness . Stiffness is the deformation-resisting property of a material. The slope of the modulus line and , hence , the modulus of elasticity are measures of the stiffness of a material .Resilience . R esilience is the property of a material that permits it to absorb

15、 energy without permanent deformation. The amount of energy absorbed is represented by the area underneath the stress-strain diagram within the elastic region.Toughness . Resilience and toughness are similar properties. However , toughness is the ability to absorb energy without rupture. Thus toughn

16、ess is represented by the total area underneath the stress-strain diagram , as depicted in Figure 2. 8b . Obviously , the toughness and resilience of brittle materials are very low and are approximately equal. Brittleness . A brittle material is one that ruptures before any appreciable plastic defor

17、mation takes place. Brittle materials are generally considered undesirable for machine components because they are unable to yield locally at locations of high stress because of geometric stress raisers such as shoulders, holes , notches , or keyways.Ductility . A ductility material exhibits a large

18、 amount of plastic deformation prior to rupture. Ductility is measured by the percent of area and percent elongation of a part loaded to rupture. A 5%elongation at rupture is considered to be the dividing line between ductile and brittle materials.Malleability . Malleability is essentially a measure

19、 of the compressive ductility of a material and, as such, is an important characteristic of metals that are to be rolled into sheets .Hardness . The hardness of a material is its ability to resist indentation or scratching . Generally speaking, the harder a material, the more brittle it is and, henc

20、e , the less resilient. Also , the ultimate strength of a material is roughly proportional to its hardness .Machinability . M achinability is a measure of the relative ease with which a material can be machined. In general, the harder the material, the more difficult it is to machine.Figure 2.8COMPR

21、ESSION AND SHEAR STATIC STRENGTHIn addition to the tensile tests, there are other types of static load testing that provide valuable information.Compression Testing. Most ductile materials have approximately the same properties in compression as in tension. The ultimate strength, however , can not b

22、e evaluated for compression . As a ductile specimen flows plastically in compression, the material bulges out , but there is no physical rupture as is the case in tension. Therefore , a ductile material fails in compression as a result of deformation, not stress.Shear Testing. Shafts, bolts , rivets

23、 , and welds are located in such a way that shear stresses are produced. A plot of the tensile test. The ultimate shearing strength is defined as the stress at which failure occurs. The ultimate strength in shear, however , does not equal the ultimate strength in tension . For example , in the case

24、of steel , the ultimate shear strength is approximately 75% of the ultimate strength in tension. This difference must be taken into account when shear stresses are encountered in machine components.DYNAMIC LOADSAn applied force that does not vary in any manner is called a static or steady load. It i

25、s also common practice to consider applied forces that seldom vary to be static loads. The force that is gradually applied during a tensile test is therefore a static load.On the other hand, forces that vary frequently in magnitude and direction are called dynamic loads. Dynamic loads can be subdivi

26、ded to the following three categories. Varying Load. With varying loads , the magnitude changes , but the direction does not . For example, the load may produce high and low tensile stresses but no compressive stresses .Reversing Load. In this case, both the magnitude and direction change. These loa

27、d reversals produce alternately varying tensile and compressive stresses that are commonly referred to as stress reversals.Shock 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

28、 times greater than the weight of the elevator, The same type of shock load occurs in automobile springs when a tire hits a bump or hole in the road.FATIGUE FAILURE-THE ENDURANCE LIMIT DIAGRAMThe test specimen in Figure 2.10a . , after a given number of stress reversals will experience a crack at th

29、e outer surface where the stress is greatest. The initial crack starts where the stress exceeds the strength of the grain on which it acts. This is usually where there is a small surface defect, such as a material flaw or a tiny scratch. As the number of cycles increases, the initial crack begins to

30、 propagate into a continuous series of cracks all around the periphery of the shaft . The conception of the initial crack is itself a stress concentration that accelerates the crack propagation phenomenon . Once the entire periphery becomes cracked , the cracks start to move toward the center of the

31、 shaft . Finally , when the remaining solid inner area becomes small enough , the stress exceeds the ultimate strength and the shaft suddenly breaks. Inspection of the break reveals a very interesting pattern, as shown in Figure 2.13. The outer annular area is relatively smooth because mating cracke

32、d surfaces had rubbed against each other . However , the center portion is rough, indicating a sudden rupture similar to that experienced with the fracture of brittle materials.This brings out an interesting fact. When actual machine parts fail as a result of static loads , they normally deform appr

33、eciably because of the ductility of the material.Thus many static failures can be avoided by making frequent visual observations and replacing all deformed parts. However , fatigue failures give to warning. Fatigue fail mated that over 90% of broken automobile parts have failed through fatigue.The f

34、atigue strength of a material is its ability to resist the propagation of cracks under stress reversals. Endurance limit is a parameter used to measure the fatigue strength of a material . By definition, the endurance limit is the stress value below which an infinite number of cycles will not cause

35、failure.Let us return our attention to the fatigue testing machine in Figure 2.9. The test is run as follows:A small weight is inserted and the motor is turned on. At failure of the test specimen , the counter registers the number of cycles N, and the corresponding maximum bending stress is calculat

36、ed from Equation 2.5. The broken specimen is then replaced by an identical one, and an additional weight is inserted to increase the load. A new value of stress is calculated, and the procedure is repeated until failure requires only one complete cycle . A plot is then made of stress versus number o

37、f cycles to failure. Figure 2.14a shows the plot, which is called the endurance limit or S-N curve. Since it would take forever to achieve an infinite number of cycles, 1 million cycles is used as a reference. Hence the endurance limit can be found from Figure 2.14a by noting that it is the stress l

38、evel below which the material can sustain 1 million cycles without failure.The relationship depicted in Figure 2.14 is typical for steel, because the curve becomes horizontal as N approaches a very large number. Thus the endurance limit equals the stress level where the curve approaches a horizontal

39、 tangent. Owing to the large number of cycles involved , N is usually plotted on a logarithmic scale, as shown in Figure 2.14b. When this is done , the endurance limit value can be readily detected by the horizontal straight line . For steel , the endurance limit equals approximately 50% of the ulti

40、mate strength . However , if the surface finish is not of polished equality , the value of the endurance limit will be lower. For example, for steel parts with a machined surface finish of 63 microinches ( in. ) , the percentage drops to about 40%. For rough surfaces (300in. or greater), the percent

41、age may be as low as 25%.The most common type of fatigue is that due to bending. The next most frequent is torsion failure, whereas fatigue due to axial loads occurs very seldom. Spring materials are usually tested by applying variable shear stresses that alternate from zero to a maximum value , sim

42、ulating the actual stress patterns.In the case of some nonferrous metals , the fatigue curve does not level off as the number of cycles becomes very large . This continuing toward zero stress means that a large number of stress reversals will cause failure regardless of how small the value of stress

43、 is. Such a material is said to have no endurance limit. For most nonferrous metals having an endurance limit, the value is about 25% of the ultimate strength.EFFECTS OF TEMPERATURE ON YIELD STRENGTH AND MODULUS OF ELASTICITYGenerally speaking , when stating that a material possesses specified value

44、s of properties such as modulus of elasticity and yield strength, it is implied that these values exist at room temperature. At low or elevated temperatures, the properties of materials may be drastically different. For example, many metals are more brittle at low temperatures. In addition , the mod

45、ulus of elasticity and yield strength deteriorate as the temperature increases . Figure 2.23 shows that the yield strength for mild steel is reduced by about 70% in going from room temperature to 1000o F .Figure 2.24 shows the reduction in the modulus of elasticity E for mild steel as the temperatur

46、e increases. As can be seen from the graph, a 30% reduction in modulus of elasticity occurs in going from room temperature to 1000o F . In this figure, we also can see that a part loaded below the proportional limit at room temperature can be permanently deformed under the same load at elevated temp

47、eratures.CREEP: 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 time. Creep also occurs at room temperature, but the process is so slow that it rarely becomes significant during

48、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 strength of a material is its ability to resist creep, and creep strength data can be obtained by conducting long-time cre

49、ep tests simulating actual part operating conditions. During the test , the plastic strain is monitored for given material at specified temperatures.Since creep is a plastic deformation phenomenon , the dimensions of a part experiencing creep are permanently altered. Thus , if a part operates with t

50、ight clearances, the design engineer must accurately predict the amount of creep that will occur during the life of the machine. Otherwise , problems such binding or interference can occur. Creep also can be a problem in the case where bolts are used to clamp tow parts together at elevated temperatu

51、res. The 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 determined by running appropriate creep strength

52、 tests.SUMMARYThe machine designer must understand the purpose of the static tensile strength test . This test determines a number of mechanical properties of metals that are used in design equations. Such terms as modulus of elasticity, proportional limit, yield strength, ultimate strength, resilie

53、nce , and ductility define properties that can be determined from the tensile test.Dynamic loads are those which vary in magnitude and direction and may require an investigation of the machine parts resistance to failure. Stress reversals may require that the allowable design stress be based on the

54、endurance limit of the material rather than on the yield strength or ultimate strength.Stress concentration occurs at locations where a machine part changes size, such 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 shaft. Note that for the c

55、ase of a hole in a flat or bar, the value of the maximum stress becomes much larger in relation to the average stress as the size of the hole decreases . Methods of reducing the effect of stress concentration usually involve making the shape change more gradual.Machine parts are designed to operate

56、at some allowable stress below the yield strength or ultimate strength. This approach is used to take care of such unknown factors as material property variations and residual stresses produced during manufacture and the fact that the equations used may be approximate rather that exact . The factor

57、of safety is applied to the yield strength or the ultimate strength to determine the allowable stress. Temperature can affect the mechanical properties of metals. Increases in temperature may cause a metal to expand and creep and may reduce its yield strength and its modulus of elasticity . If most

58、metals are not allowed to expand or contract with a change in temperature , then stresses are set up that may be added to the stresses from the load. This phenomenon is useful in assembling parts by means of interference fits. A hub or ring has an inside diameter slightly smaller than the mating sha

59、ft or post. The hub is then heated so that it expands enough to slip over the shaft. When it cools, it exerts a pressure on the shaft resulting in a strong frictional force that prevents loosening.中文译文失效分析，尺寸确定与分析，凸轮的应用引言设计工程师知道如何以及为什么部件出现故障是绝对必要的，这样可以设计出需要最少维护的可靠机器。有时候失败会非常严重，例如轮胎在高速行驶的汽车上爆胎。另一方面，失

60、败可能不过是一种滋扰。汽车冷却系统中散热器软管的松动就是一个例子。后一种故障的后果通常是散热器冷却剂的损失，这种情况很容易被发现和纠正。部件吸收的负载类型与幅度一样重要。一般而言，带有方向反转的动载荷比静载荷造成更大的难度，因此必须考虑疲劳强度。另一个问题是该材料是否具有韧性或脆性。例如，涉及疲劳的脆性材料被认为是不可接受的。许多人错误地将单词故障解释为一个零件的实际损坏。但是，设计工程师必须考虑更广泛的理解发生什么样的变形。然而，韧性材料在破裂之前会变形很大量。过度变形，没有断裂，可能会导致机器失效，因为变形部分会干扰移动的第二部分。因此，只要零件不再满足其要求的功能，零件就会失效（即使它没

61、有物理损坏）。有时故障可能是由于两个配合部件之间的摩擦或振动异常造成的。失效也可能是由于称为蠕变的现象造成的，蠕变是材料在高温下承受载荷的塑性流动。另外，零件的实际形状可能是造成故障的原因。例如，必须考虑由轮廓突然变化引起的应力集中。当存在方向反转的动态载荷并且材料的韧性不是很好时，评估应力考虑尤为重要。一般来说，设计工程师必须考虑所有可能的故障模式，其中包括以下内容。- 压力- 变形- 穿- 腐蚀- 振动- 环境破坏- 松开紧固装置选择的零件尺寸和形状也必须考虑许多尺寸因素，这些尺寸因素会产生外部载荷效应，例如几何不连续性，由于形成所需轮廓而产生的残余应力以及干涉配合接头的应用。凸轮是可用的

62、最通用的机制之一。凸轮是一个简单的双成员设备。输入构件是凸轮本身，而输出构件称为从动件。通过使用凸轮，可以将简单的输入动作修改为几乎任何想要的可想象的输出动作。凸轮的一些常见应用是：- 汽车发动机的凸轮轴和分配轴- 生产机床- 自动唱机- 印刷机- 自动洗衣机- 自动洗碗机高速凸轮的轮廓（凸轮速度超过1000 rpm）必须从数学上确定。然而，绝大多数凸轮以低速运行（小于500转/分钟）或中速凸轮可以使用大规模布局以图形方式确定。通常，凸轮速度和输出负载越大，加工凸轮轮廓的精度就越高。材料的设计性能定义材料的以下设计属性，因为它们涉及拉伸测试。静强度。零件的强度是零件在不失去执行其所需功能的能力

63、的情况下可承受的最大应力。因此，静态强度可以被认为近似等于比例极限，因为没有发生塑性变形，理论上对材料没有损伤。刚度。刚度是材料的抗变形性能。模量线的斜率以及因此弹性模量是材料刚度的度量。弹性。可靠性是一种材料的特性，允许它吸收能量而不会永久变形。吸收能量的数量由弹性区域内的应力 - 应变图下方的面积表示。坚韧。韧性和韧性是相似的性质。然而，韧性是吸收能量而不破裂的能力。因此韧性由应力 - 应变图下方的总面积来表示，如图2所示。显然，脆性材料的韧性和弹性非常低，几乎相等。脆弱。脆性材料是在发生明显的塑性变形之前破裂的材料。脆性材料通常被认为不适合于机器部件，因为它们由于诸如肩部，孔，凹口或键槽

64、等几何应力提升器而不能在高应力位置局部屈服。延展性。延展性材料在破裂之前表现出大量的塑性变形。延性是通过加载到破裂的部分的面积百分比和伸长百分比来测量的。断裂伸长率为5被认为是韧性材料和脆性材料之间的分界线。可塑性。可加工性基本上是材料的压缩延展性的量度，并且因此是要卷成片材的金属的重要特征。硬度。材料的硬度是其抵抗压痕或刮擦的能力。一般而言，材料越硬，它越脆，因此弹性越小。而且，材料的极限强度与其硬度大致成比例。可加工性。可加工性是对材料进行加工的相对容易程度的量度。一般来说，材料越硬，加工越困难。图2.8压缩和剪切静态强度除拉伸测试外，还有其他类型的静态负载测试可提供有价值的信息。压缩测试

65、。大多数韧性材料具有与拉伸中大致相同的压缩性能。但是，最终的强度无法评估压缩。当可塑性试样在压缩状态下塑性流动时，材料凸出，但不存在拉伸情况下的物理破裂。因此，由于变形而不是压力，延性材料不能压缩。剪切测试。轴，螺栓，铆钉和焊缝的位置应产生剪切应力。拉伸测试图。最终剪切强度定义为发生破坏的应力。然而，剪切力的极限强度并不等于拉力的极限强度。例如，在钢的情况下，极限抗剪强度约为拉伸极限强度的75。在机器组件中遇到剪切应力时，必须考虑到这种差异。动态负载不以任何方式变化的施加力被称为静态或稳态载荷。考虑很少变化的应用力是静态载荷也是常见的做法。因此，在拉伸测试过程中逐渐施加的力是静态负载。另一方面，大小和方向频繁变化的力称为动态载荷。动态负载可以细分为以下三类。变化的负载。随着负载变化，幅度变化，但方向不变。例如，载荷可能产生高和低的拉应力但不产生压应力。反向加载。在这种情况下，量值和方向都会改变。这些负载反转交替产生变化的拉伸应力和压缩应力，通常称为应力反转。冲击负载。这种类型的负载是由于影响。一个例子是电梯落在斜槽底部的弹簧座上。由此产生的最大弹簧力可能比电梯的重量大许多倍。当轮胎碰撞道路上的凹凸或孔时，汽车弹簧中会出现相同类型的冲击载荷。疲劳失效 - 耐力极限图图2.