Overview-of-Engineering-Mechanics工程力学概述精品名师资料

1、第三课 overview of engineering mechanics工程力学概述1、as we look around us we see a world thingsfullof；machines,devices, tools; things that wehave designed, built, and used; things made of wood, metals, ceramics, and plastic. we knoexperience that some things are better than others; they last longer, cost le

2、ss, are quietor are easier to us.当我们观察我们周围就会发现世界充满“物品”：机器，设备，工具；我们已经设计，建造， 并使用的物品； 木头，金属，陶瓷和塑料制品。根据我们使用的经验知道，有些物品比其它 物品更好；他们使用寿命较长，费用较低，噪音更低，更好看，或者更方便我们使用。 2、ideally,however, every such item has been designedaccordingto some setof “functional requirements”as perceivedby the designersthatis,ithas bee

3、n designedso as to answer the question,“exactlywhat functionshould itperform?”in the world of engineering,the majorfunction frequently is to support some type of loading due to weight, inertia, pressure, ebeams in our homes to the wings of an airplane, where must be an appropriate melding of madimen

4、sions,and fasteningto produce structuresthatwillperform theirfunctionsreliablyfor a reasonable cost over a reasonable lifetime.然而，在理想的情况下，每一件产品都是设计人员工具其对某些“功能要求”的理解而设计出来的，也就是说，在设计过程中，应该回答这样的问题，即“它应该具有哪种确切的功能？” 在工程领域，主要功能通常是承受由于重力，惯性力，压力等作用的一些类型的载荷。从我们居住房屋的梁到飞机机翼，都必须有一个适当的材料，尺寸，在较合理的寿命基础上具有较合理的成本并能可靠

5、地完成其功能的产品结构连接的组合。3、in practice, the engineering mechanics methods are used in two quite different ways: 在实践中，工程力学方法常被应用在两个完全不同领域：(1) the development of any new device requires an interactive, iterative consideration of materials, loads, durability, safety, and cost.任何新装置的研发都需要对其结构，尺寸，材料，载荷，耐久性，安全和成本

6、的反复考虑。(2)when a devicefails(unexpectedly)itisoftennecessaryto carryout a studyto pinpointthecause of failure and to identify potential corrective measures. our best designs often evoa successive elimination of weak points.当一个装置（意外地）发生失效后，通常需要进行研究，找出失效的原因，并找出潜在的纠 正措施。最好的设计往往都是不断排除薄弱环节的演变过程。4、to many

7、engineers,both of the above processescan prove to be absolutelyfascinatingand enjoyable, not to mention (at times) lucrative.对许多工程师来说，上述过程既可以令人非常的陶醉又可以使人非常的愉快，更何况（有时） 对我们是有利的。5、in any“real”problem there is never sufficient good, useful information; we seldom know tactual loads and operating conditio

8、ns with any precision, and the analyses are seldom exacour mathematics may be precise, the overall analysis is generally only approximate, and diskilledpeoplecan obtaindifferentsolutions.in the studyof engineeringmechanics,most of the problems will be sufficiently“idealized”topermit unique solutions

9、, but it should be clear that “real world”isfar less idealized, andyouthatusually will haveperformto some idealization in order to obtain a solution.对于任何实际的问题，总是缺乏足够完整和有用的信息。我们很少准确地知道实际荷载和工作状态，因此，所做的分析工作也很少是精确的。虽然我们的数学可以准确，全面的分析一般只能近似，而且不同技术水平的人能得到不同的解。在工程力学研究领域，大多数问题要想得到唯一解就要充分的理想化，但应该清楚，“现实世界”远不非理

10、想化程度，因此为了得到问题的解决方案不得不进行一些理想化假设。6、the technical areas we will consider are frequently“staticscalled”and“strengthofmaterials”,“statics”referring to the study of forces acting on stationary devices,“strengthofandmaterials”referring to the effects of those forces on the structure (deformations, load lim

11、its, etc.我们要考虑的技术领域通常被称为“静力学”和“材料力学”，“静力学”，指的是研究作用在 固定装置上的作用力，“材料力学”指的是施加到结构的力（变形，载荷限制等）的影响。 7、while a greatmany devicesarenot,in fact,static,themethods developedhereareperfectlyapplicable to dynamic situations if the extra loadings associated with the dynamics are taaccount,whenever the dynamic for

12、cesare small relativeto the staticsloadings,the system is usually considered to be static.但是，事实上很多设备都不是静态的，如果与动力学有关的额外负荷被考虑了的话，那么静 力学的研究方法完全适用于动态的情况，只要动态力相对静态载荷较小，系统通常被认为是 静态的。8、in engineering mechanics, we appreciate the various type of approximations that are inhany real problem:在工程力学中，我们非常重视与实际问题

13、本质有关的各种类型的近似方法。primarily, we will be discussing things which“equilibriumarein,”i.e.,not accelerating. however,if we look closely enough, everything is accelerating. we will consider many structural mebe “weightless”but they never are. we will deal with forces “thatpoint”act,butatallforcesact over an

14、 area. we will consider some parts“rigidto”bebutallbodies will deform under load.首先，我们将要讨论处于“均衡”的事情，也就是说，不是加速的事情。但是，如果我们仔细观察，一切事情都是加速的。我们会认为许多结构单元是无质量的-但情况从来不是这样的。 我们会处理作用在某个点上的力，但所有力都作用在某个区域上。我们将考虑某些零件是“刚性的”-但是所有机构都将在负载下变形。we will make many assumptions that clearly are false. but these assumptions

15、should alwaysthe problem easier, more tractable. you will discover that the goal is to make as many simassumptions as possible without seriously degrading the result.很明显，我们将做出许多虚假的假设。但这些假设总是使问题变得更容易，更容易处理。你会发现，我们的目标是使许多简化假设尽可能不严重地使结果退化。9、 generallythereisno clearmethod to determinehow completely,r h

16、ow precisely,to treat problem:ifour analysisistoo simple,we may not geta pertinentanswer;ifour analysis stoo detailed, we may not be able to obtain any answer. it is usually preferable to start with simple analysis and then add more detail as required to obtain a practical solution. 一般没有明确的方法来确定如何完全，或者如何准确地处理一个问题：如果我们的分析过于 简单，我们可能无法获得相关的答案，如果我们的分析是过于详细，我们可能无法获得任何 答案。它通常是最好开始用一个相对简单的分析，然后根据需要添加更多的细节获得一个实 用的解决方案。10、 during the past two decades,therehas been a tremendous growth in the availability ofcomputerized methods for solving problems that previously were be