机械工程专业英语-施平-没翻译课文补充

机械工程专业英语-施平-没翻译课文补充4、工程机械概述As we look around us we see a world full of “things”: machines, devices, tools;things that we have designed, built, and used; things made of wood, metals, ceramics,and plastics. We know from experience that some things are better than others; theylast longer, cost less, are quieter, look better, or are easier to use.正如我们环;;情况.Ideally, however, every such item has been designed according to some set of“functional requirements” as perceived by the designers — that is, it has beendesigned so as to answer the question, “Exactly what function should it perform?”In the world of engineering, the major function frequently is to support some typeof loading due to weight, inertia, pressure, etc.这样的项目已按设计一些“功能要求From the beams in our homes to the wings of an airplane, there must be anappropriate melding of materials, dimensions, and fastenings to produce structuresthat will perform their functions reliably for a reasonable cost over a reasonablelifetime.一生中其职能可靠。

In practice, engineering mechanics methods are used in two quite different ways:(1) The development of any new device requires an interactive, iterativeconsideration of form, size, materials, loads, durability, safety, and cost.(2) When a device fails (unexpectedly) it is often necessary to carry out a studyto pinpoint the cause of failure and to identify potential corrective measures. Ourbest designs often evolve through a successive elimination of weak points.1.cost.2.潜在的纠正措施。

我们最优秀的设计往往演变的To many engineers, both of the above processes can prove to be absolutelyfascinating and enjoyable, not to mention (at times) lucrative.In any “real” problem there is never sufficient good, useful information; weseldom know the actual loads and operating conditions with any precision, and theanalyses are seldom exact. While our mathematics may be precise, the overall analysisis generally only approximate, and different skilled people can obtain differentsolutions. In the study of engineering mechanics, most of the problems will besufficiently “idealized” to permit unique solutions, but it should be clear thatthe “real world” is far less idealized, and that you usually will have to performsome idealization in order to obtain a solution.在命令必须执行一些理想化获得一个解决方案。

The technical areas we will consider are frequently called “statics” and“strength of materials,” “statics” referring to the study of forces acting onstationary devices, and “strength of materials” referring to the effects of thoseforces on the structure (deformations, load limits, etc.).静”备作用力学风和“材料力学”指的是这些部队在结构上的影响。

While a great many devices are not, in fact, static, the methods developed hereare perfectly applicable to dynamic situations if the extra loadings associated withthe dynamics are taken into account (we shall briefly mention how this is done).static开发的方法是完全适用于动态的情况如果.Whenever the dynamic forces are small relative to the static loadings, the systemis usually considered to be每当动态势力相对较小的静态负荷被认为是静态的。

In engineering mechanics, we will appreciate the various types of approximationsthat are inherent in any real problem:Primarily, we will be discussing things which are in “equilibrium,” i.e., notaccelerating. However, if we look closely enough, everything is accelerating. Wewill consider many structural members to be “weightless” — but they never are.We will deal with forces that act at a “point” —but all forces act over an area.We will consider some parts to be “rigid” — but all bodies will deform under load.在一个区域的行为。

我们会考虑的某些部分“刚We will make many assumptions that clearly are false. But these assumptionsshould always render the problem easier, more tractable. You will discover that thegoal is to make as many simplifying assumptions as possible without seriouslydegrading the result.简化假设没有严重退化的结果。

Generally there is no clear method to determine how completely, or how precisely,to treat a problem: If our analysis is too simple, we may not get a pertinent answer;if our analysis is too detailed, we may not be able to obtain any answer. It is usuallypreferable to start with a relatively simple analysis and then add more detail asrequired to obtain a practical solution.一般法获得任何答案。

它通常是最好先从相对简单的实际的解决办法。

During the past two decades, there has been a tremendous growth in theavailability of computerized methods for solving problems that previously werebeyond solution because the time required tosolve them would have been prohibitive.At the same time the cost of computer capability and use has decreased by ordersof magnitude. We are experiencing an influx of “personal computers” on campus,in the home, and in business.了几个数量级。