力学专业英语Translation2.doc

G1 Die Life and Die Failure模具的寿命及其失效Proper selection of the die material and of the die （da n.模具）manufacturing technique determines, to a large extent, the useful life of forming dies.（直译法）模具材料的恰当选择及其制造工艺，在很大程度上决定了模具的使用寿命。 Dies may have to be replaced for a number of reasons, such as changes in dimensions due to wear or plastic deformation, deterioration（ dtrren n.变坏，退化，损耗 ） of the surface finish, breakdown of lubrication（ lubrken n.润滑）, and cracking or breakage.（直译法）模具可能会因为一系列原因被替换，比如由于磨损或塑性变形导致的尺寸变化，表面平整度变差，润滑故障，和裂纹即破裂。In hot impression die forging, the principal modes of die failure are erosion, thermal（ :rml adj.热的) fatigue （ fti n.疲劳）, mechanical fatigue and permanent (plastic) deformation.(直译法)在热压印模锻造中，模具失效的主要模式是腐蚀作用、热疲劳、机械疲劳和永久（塑性）变形。In erosion r()n, also commonly called die wear, material is actually removed from the die surface by pressure and sliding of the deforming material, wear resistance of the die material, die surface temperature, relative sliding speed at the die/material interface and the nature of the interface layer are the most significant factors influencing abrasive bresv die wear.（分句法+直译法）腐蚀，通常也称作模具磨损，实际上是材料受压从模具表面剥落的过程。变形材料的滑移，模具材料的抗磨性，模具表面温度，模具和材料接触表面的相对滑动速度以及接触层的性质，都是影响模具磨损的最显著因素。 Thermal m()l fatigue ftigoccurs on the surface of the die impression in hot forming and results in “heat checking”. (直译法）热疲劳发生在热成形中的模具模腔表面,并且最终导致“热裂”。 Thermal fatigue ( ftig (热)疲劳) results from cyclic yielding (jild 屈服) of the die surface due to contact with the hot deforming material.（逆序法）由于与热变形材料接触，在周期性屈服的模具表面引起了热疲劳。 This contact causes the surface layers to expand, and, because of the very steep ( stip 急剧的) temperature gradients, the surface layers are subject to compressive stresses. （直译法）这种接触导致表层膨胀，并且，由于温度梯度的急剧变化，表层会受到压应力。 At sufficiently high temperatures, these compressive stresses may cause the surface layers to deform. When the die surface cools, a stress reversal (rvsl 反向) may occur and the surface layers will then be in tension. （直译法）温度足够高时，这些压应力可引起表层变形。当模具表面冷却，可发生反向应力，表层此后处于受拉状态。After repeated cycling in this manner, fatigue ftig 疲劳will cause formation of a crack pattern that is recognized as heat checking热裂纹. （分句法）这种状态经过循环往复后，疲劳将导致裂纹图案形成。这被认为是热裂纹。 Die breakagebrekd 断裂 or cracking is due to mechanical fatigue and occurs in cases where the dies are overloaded and local stresses are high. （分句法）模具断裂或产生裂纹是机械疲劳的缘故，发生在模具超载和局部应力高的地方。 The dies are subjected to受到 alternating stresses交变应力 due to loading and unloading during the deformation process, and this causes crack initiation and eventual failure（直译法）模具由于在形变过程中的加载、卸载而受到交变应力，这导致了裂纹发生和最终的破坏。Die life and die failure are greatly affected by the mechanical properties of the die materials under the conditions that exist in a given deformation process.（状语前置）在给定的变形进程具有的条件下，模具的寿命及其失效很大程度上受模具材料机械性能的影响。 Generally, the properties that are most significant depend on the process temperature. Thus, die materials used in cold forming processes are quite different from those used in hot forming.（直译法+定语前置）通常，影响最大的特性取决于加工温度。因此，用冷成形加工而成的模具材料与用热成形加工而成的模具材料大有不同。 The design and manufacture of dies and the selection of die materials are very important in the production of discrete parts by use of metal forming processes.（状语前置）对于用金属成形加工生产的单个部件，模具的设计和制造及模具材料的选择非常重要。The dies must be made by modern manufacturing methods from appropriate die materials in order to provide acceptable die life at a reasonable cost.（逆序法）为了以合理的成本维持可接受的模具寿命，（上述的）模具必须用适当的模具材料经现代制造方法制成。 Often the economic success of a forming process depends on die life and die costs per piece produced.（直译法）通常，一个成形加工过程经济上的成功取决于模具寿命和生产每件模具的成本。 For a given application, selection of the appropriate die material depends on three types of variables:（直译法）对于给定的应用，模具材料的恰当选择取决于（以下）三种变量：(a) Variables related to the process itself, including factors such as size of the die cavity, type of machine used and deformation speed, initial stock size and temperature, die temperature to be used, lubrication, production rate and number of parts to be produced.（a）与加工工艺本身相关的变量，包括模腔尺寸、所用机器类型和变形速度，毛坯尺寸和温度，要用的模具温度、润滑、生产率和要生产的零件数量。(b) Variables related to the type of die loading, including speed of loading, i.e., impact or gradual contact time between dies and deforming metal (this contact time is especially important in hot forming), maximum load and pressure on the dies, maximum and minimum die temperatures, and number of loading cycles to which the dies will be subjected（b）与模具加载类型相关的变量，包括加载速度，即模具和变形中的金属冲击或者逐渐接触的时间（这段接触时间在热成型中尤为重要），模具上的最大荷载和压力，模具的最高和最低温度，以及模具将受到的加载循环次数。(c) Mechanical properties of the die material, including hardenability, impact strength, hot strength (if hot forming is considered) and resistance to thermal and mechanical fatigue. （c）模具材料的物理特性，包括硬度，冲击强度，热强度（若考虑热成形的话），抗热性和抵抗机械疲劳的性能。G2 Cold working and Hot WorkingThe above considerations provide the basis for classification of forging temperature ranges, namely, hot working (hot forging) and cold working (cold forging). 前面的想法给我们提供了用锻造温度范围进行分类的依据，也就是热加工（热锻造）和冷加工（冷锻造）。Hot working is considered to be plastic deformation that is accomplished above the recrystallization再结晶 temperature .热加工被定义为是在高于再结晶温度的温度下完成的塑性变形。The use of the term “hot working” usually implies that the material is heatedbut not always. For example, the recrystallization再结晶 of lead takes place at very low temperatures.热加工这个词的使用通常意味着材料是被加热的，但也有例外。举个例子，铅的再结晶过程就发生在非常低的温度下。By the above definition, lead铅 forged at room temperature is being hot worked.根据前面的定义，铅在室温下的锻造过程就是热加工。Cold working is defined as plastic deformation below the recrystallization再结晶 temperature. 冷加工的定义是在低于再结晶温度的温度下发生的塑性变形。Several common metals, or their alloys合金, have recrystallization temperatures in the order of 750-900.一些常见的金属以及他们的合金的再结晶温度在750-900的范围内。To improve properties性能, several of these alloys合金 are strain hardened by forging in the range of 550-700.为了提高性能，一些金属可以在550-700的温度范围内锻造来进行强化。Although by definition, this is truly “cold work”, it is often referred to as “warm work”温加工. 尽管在定义上这个过程是真正的冷加工，但是通常被称为“温加工”。The heating is done mainly to reduce the flow stress and thereby the forging锻造 force required. 热加工主要是作用于降低流动应力和因此所需的锻造力。Warm working“ operations must be very closely controlled if the ultimate最终的 improvement in properties is to be obtained.如果性能要得到最终的改善，温加工操作必须要精密地控制。The operation is normally followed by stress relieving应力消除处理 at a temperature below the forging temperature. 该操作之后通常需要进行低于锻造温度下的应力消除处理。The temperature of recrystallization for austenitic奥氏体 stainless steels不锈钢, higher temperature alloys合金, and many nonferrous无铁的 alloys can vary over a considerable range.奥氏体的不锈钢，更高温的合金，和很多无铁合金，他们的再结晶温度都可以在相当大的范围内变化。Factors influencing this temperature include the degree of strain hardening应变硬化 present, the time of annealing退火, the prior grain size晶粒度 and the solute溶质 atomic concentration in solid solution固溶体.影响该温度的因素包括应变硬化的程度，退火时间，原来的晶粒度和固溶体中的溶质原子浓度。The recrystallized重结晶 grain size at the instant of recrystallization is inversely相反的 proportional to the degree of deformation. This fact leads to the possibility of grain size refinement精致 by a combination of controlled deformation and recrystallization.再结晶的晶粒度在再结晶的瞬间是与变形的程度成反比的。这个现象导致了晶粒度的精制是有可能通过同时控制变形和再结晶来实现的。Refinement细化 of grain size by means of controlled deformation is regularly practiced by the forging industry. However, there is hazard危险 inherent to this method.通过控制变形来细化晶粒度，这一方法经常被锻造业使用。然而，这种方法在本质上的有危险。Nearly all the alloys合金 are sensitive to a combination of strain hardening and temperature where very rapid grain growth (called “abnormal grain growth”) occurs. 几乎所有的合金都对应变硬化和晶粒快速生长（又名“晶体异常生长”）所发生的温度的结合非常敏感。The combination is normally referred to as critical strain临界应变 and usually occurs when the alloy is subjected to relatively small strains, although this is somewhat dependent on the prior grain size as well as the alloy.该结合通常被称为临界应变，而且通常发生在合金发生相对微小应变的时候，尽管这一定程度上取决于原来的晶粒度和合金(的种类)。Controlling grain size by recrystallization is not merely a matter of imparting strain hardening and recrystallization. 通过重结晶控制晶粒度，不仅仅是施加应变硬化和重结晶的问题。The critical zone临界应变 must be avoided by straining either more or less than the critical amount.还必须通过使应变多于或少于临界量来避开临界区域。The location of the critical one is of key importance and unfortunately it is not constant. Several factors can enlarge or change its position. 临界区域的位置是非常关键的，但遗憾的是它不是恒定的。有几个因素可以放大甚至改变其位置。G3 Viscous and inviscid flowsA fluid flow may be broadly classified as either a viscous flow or an inviscid flow.流体流动可以大致分为黏性流和无黏性流。An inviscid flow is one in which viscous effects do not significantly influence the flow and are thus neglected. 无黏性流是黏性作用不显著影响流动而因此被忽略的流动。In a viscous flow the effects of viscosity are important and cannot be ignored.在黏性流中黏性的影响重要而且不可被忽略。To model an inviscid flow analytically, we can simply let the viscosity be zero; this will obviously make all viscous effects zero. 要建模分析一个无黏性流，我们可以简单地让黏性为零；显然这会让所有黏性影响变为零。It is more difficult to create an inviscid flow experimentally, because all fluids of interest (such as water and air) have viscosity.在实验中要创造一个无黏性流体更为困难，因为所有流体（比如水和空气）都有黏性。The question then becomes: Are there flows of interest in which the viscous effects are negligibly small?然后问题就变成：是否存在黏性作用小到可以忽略不计的流动？The answer is yes, if the shear stresses in the flow are small and act over such small areas that they do not significantly affect the flow field. 答案是：“存在，如果流动中的剪切应力足够小而且作用范围小到对流场影响不显著的话。”This statement is very general, of course, and it will take considerable analysis to justify the inviscid flow assumption.当然这个结论很笼统，而且需要大量分析去判定无黏性流假设是否正确。Based on experience, it has been found that the primary class of flows, which can be modeled as inviscid flows, is external flows, that is, flows which exist exterior to a body.根据经验，可以被模拟分析为无黏性流的初等流动是外部流，就是存在于物体外部的流动。Inviscid flows are of primary importance in flows around streamlined bodies, such as flow around an airfoil or a hydrofoil.无黏性流在绕流线型物体的流动研究中非常重要，比如绕着机翼或者水翼的流动。Any viscous effects that may exist are confined to a thin layer, called a boundary layer, that is attached to the boundary, such as that shown in Fig.1-7;任何可能存在的黏性作用被限制于一个薄层，被称为边界层，紧贴物体表面，如1-7所示。the velocity in a boundary layer is always zero at a fixed wall, a result of viscosity.由于黏性的作用，边界层固定壁处的速度恒为0.For many flow situations, boundary layers are so thin that they can simply be ignored when studying the gross features of a flow around a streamlined body.对于许多流动情况，边界层很薄，当我们研究通过流线型物体的流动特点时可以忽略它。For example, the inviscid flow solution provides an excellent prediction to the flow around the airfoil, except inside the boundary layer and possibly near the trailing edge. 例如，对绕机翼的流动，除了边界层和可能接近机翼后缘的区域外，无黏流动解与实际情况很吻合。Inviscid flow is also encountered in contractions inside piping systems and in short regions of internal flows where viscous effects are negligible.管道系统内收缩段的流动及内部流动的黏性影响可忽略的小部分区域都可简化为无黏流动。Viscous flows include the broad class of internal flows, such as flows in pipes and conduits and in open channels.黏性流动包括大部分情况的内流（内流中很大部分情况属于黏性流动），如管道流、暗渠流和明渠流。In such flows viscous effects cause substantial “losses” and account for the huge amounts of energy that must be used to transport oil and gas in pipelines.在这样的流动中黏性作用造成重大的“损失”，这解释了在管道运输中石油和天然气耗费大量的能源。The no-slip condition resulting in zero velocity at the wall, and the resulting shear stresses, lead directly to these losses.在无滑移条件下，使壁面处的速度为0，由此产生的切应力直接导致这些损失产生。G4A viscous flow can be classified as either a laminar flow or a turbulent flow. In a laminar flow the fluid flows with no significant mixing of neighboring fluid particles. 黏性流动可分为两种：层流和紊流。在层流中流体与相邻的流体质点没有显著混合。If dye were injected into the flow, it would not mix with the neighboring fluid except by molecular activity; it would retain its identity for a relatively long period of time. Viscous shear stresses always influence a laminar flow. The flow may be highly time dependent or be steady.如果在层流中注入染料，除了因为分子运动以外，染料不会与相邻流体混合，而会在相对长的时间内能清楚地看到它。粘性剪应力总是会影响层流。层流可以是高度非定常的，也可以是定常的。In a turbulent flow fluid motions vary irregularly so that quantities such as velocity and pressure show a random variation with time and space coordinates. The physical quantities are often described by statistical averages.在紊流中流体运动相当不规则，所以速度和压力等参量随着时间和空间坐标的改变而随机变化。在这当中，物理量用统计平均值来表示。In this sense we can define a steady turbulent flow: a flow in which the time-average physical quantities do not change in time. A dye injected into a turbulent flow would mix immediately by the action of the randomly moving fluid particles; it would quickly lose its identity in this diffusion process. 在这层意义上说，我们可以将“定常”紊流定义为：时间平均物理量不随时间变化的一种流动。在紊流中注入染料，染料会因为流体质点的随机移动而瞬间混合。所以染料会在扩散过程中很快消散而变得无法识别。A laminar flow and a turbulent flow can be observed by performing a simple experiment with a water faucet. Turn the faucet on so the water flows out very slowly as a silent stream. This is laminar flow. Open the faucet slowly and observe the flow becoming turbulent. Note that a turbulent flow develops with a relatively small flow rate. 层流和紊流可以被轻易观察到，只要用一个水龙头做实验就可以了。打开水龙头，让水流缓慢安静地流出，这就是层流。慢慢地开大水龙头，观察它从层流变为紊流。注意，从层流转变为紊流只需增加一个相对小的流量。The flow regime depends on three physical parameters describing the flow conditions.流动状态依赖于三个描述流动条件的物理参数。The first parameter is a length scale of the flow field, such as the thickness of a boundary layer or the diameter of a pipe. If this length scale is sufficiently large, a flow disturbance may increase and the flow may be turbulent.第一个参数是流场的特征长度，如边界层厚度或管道直径。如果这个特征长度尺度足够大，流动中的扰动可能会逐渐增大，从而使得流动转变为紊流。The second parameter is a velocity scale such as a spatial average of the velocity; for a large enough velocity the flow may be turbulent. The third parameter is the kinematic viscosity; for a small enough viscosity the flow may be turbulent.第二个参数是特征速度，如空间平均流速，足够大的流速将导致紊流的产生。第三个参数是运动黏度，流体的黏性越小，紊流的可能性越大。The three parameters can be combined into a single parameter that can serve as a tool to predict the flow regime. This quantity is the Reynolds number, named after Osborne Reynolds, a dimensionless parameter, defined as Re=VL/v, where L and V are a characteristic length and velocity, respectively, and v is the kinematic viscosity; for example, in a pipe flow L could be the pipe diameter and V could be the average velocity. 上述三个参数可以整理成一个参数，用于预测流动状态。这个参数就是雷诺数，以奥斯本雷诺的名字命名，该参数为无量纲参数，定义为Re=VL/v，式中，L和V分别为特征长度和特征速度，v为运动黏度。例如，在管道流中，L为管径，V为平均速度。 If the Reynolds number is relatively small, the flow is laminar; if it is large, the flow is turbulent. This is more precisely stated by defining a critical Reynolds number, Recrit, so th