Overview of Engineering Mechanics工程力学概述.docVIP

第三课 Overview of Engineering Mechanics工程力学概述 1、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 plastic. We know from experience that some things are better than others; they last longer, cost less, are quieter, look better, or 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 designed according to some set of “functional requirements” as perceived by the designers – that is, it has been designed 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 type of loading due to weight, inertia, pressure, etc. From the beams in our homes to the wings of an airplane, where must be an appropriate melding of materials, dimensions, and fastening to produce structures that will perform their functions reliably for 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 form, size, 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，安全和成本的反复考虑。 (2) When a device fails (unexpectedly) it is often necessary to carry out a study to pinpoint the cause of failure and to identify potential corrective measures. Our best designs often evolve through a 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 engineers, both of the above processes can prove to be absolutely fascinatin