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1、精选优质文档-倾情为你奉上英文原文：1. Introduction to Mechanics of Materials Mechanics of materials is a branch of applied mechanics that deals with the behavior of solid bodies subjected to various types of loading. It is a field of study that is known by a variety of names, including “strength of materials” and “m
2、echanics of deformable bodies.” The solid bodies considered in this book include axially-loaded bars, shafts, beams, and columns, as well as structures that are assemblies of these components. Usually the objective of our analysis will be the determination of the stresses, strains, and deformations
3、produced by the loads; if these quantities can be found for all values of load up to the failure load, then we will have obtained a complete picture of the mechanical behavior of the body.Theoretical analyses and experimental results have equally important roles in the study of mechanics of material
4、s. On many occasions we will make logical derivations to obtain formulas and equations for predicting mechanical behavior, but at the same time we must recognize that these formulas cannot be used in a realistic way unless certain properties of the material are known. These properties are available
5、to us only after suitable experiments have been made in the laboratory. Also, many problems of importance in engineering cannot be handled efficiently by theoretical means, and experimental measurements become a practical necessity. The historical development of mechanics of materials is a fascinati
6、ng blend of both theory and experiment, with experiments pointing the way to useful results in some instances and with theory doing so in others. Such famous men as Leonardo da Vinci(1452-1519) and Galileo Galilei(1564-1642) made experiments to determine the strength of wires, bars, and beams, altho
7、ugh they did not develop any adequate theories (by todays standards) to their test results. By contrast, the famous mathematician Leonhard Euler(1707-1783) developed the mathematical theory of columns and calculated the critical load of a column in 1744, long before any experimental evidence existed
8、 to show the significance of his results. Thus, Eulers theoretical results remained unused for many years, although today they form the basis of column theory.The importance of combining theoretical derivations with experimentally determined properties of materials will be evident as we proceed with
9、 our study of the subject. In this section we will begin by discussing some fundamental concepts, such as stress and strain, and then we will investigate the behavior of simple structural elements subjected to tension, compression, and shear. 2. StressThe concepts of stress and strain can be illustr
10、ated in an elementary way by considering the extension of prismatic bar.A prismatic bar is one that has constant cross section throughout its length and a straight axis. In this illustration the bar is assumed to be loaded at its ends by axial forces P that produce a uniform stretching, or tension,
11、of the bar. By making an artificial cut (section mm) though the bar at right angels to its axis, we can isolate part of the bar as a free body. At the right-hand end the tensile force P is applied, and at the other end there are forces representing the removed portion of the bar upon the part that r
12、emains. These forces will be continuously distributed over the cross section, analogous to the continuous distribution of hydrostatic pressure over a submerged surface. The intensity of force, that is, the per unit area, is called the stress and is commonly denoted by the Greek letter . Assuming tha
13、t the stress has a uniform distribution over the cross section, we can readily see that its resultant is equal to the intensity times the cross-sectional area A of the bar. Furthermore,from the equilibrium of the body shown in Fig, we can also that this resultant must be equal in magnitude and oppos
14、ite in direction to the force P. Hence, we obtain (1)as the equation for the uniform stress in a prismatic bar. This equation shows that stress has units of force divided by area-for example, Newtons per square millimeter (N/mm) or pounds per square inch (psi). When the bar is being stretched by the
15、 forces P, as shown in the figure, the resulting stress is a tensile stress; if the forces are reversed in direction, causing the bar to be compressed, they are called compressive stresses.A necessary condition for Eq. (1) to be valid is that the stress must be uniform over the cross section of the
16、bar. This condition will be realized if the axial force P acts through the centroid of the cross section, as can be demonstrated by statics. When the load P does not act at the centroid, bending of the bar will result, and a more complicated analysis is necessary. Throughout this book, however, it i
17、s assumed that all axial forces are applied at the centroid of the cross section unless specifically stated to the contrary. Also, unless stated otherwise, it is generally assumed that the weight of the object itself is neglected.3. Strain The total elongation of a bar carrying an axial force will b
18、e denoted the Greek letter , and the elongation per unit length, or strain, is then determined by the equation (2)where L is the total length of the bar. Note that the strain is nondimensional quantity. It can be obtained accurately from Eq. (2) as long as the strain is uniform throughout the length
19、 of the bar. If the bar is in tension, the strain is a tensile strain, representing an elongation or a stretching of the material; if the bar is in compression, the strain is a compressive strain, which means that adjacent cross sections of the bar move closer to one another.翻译：1.材料力学的介绍 材料力学是应用力学的一
20、个分支，用来处理固体在不同荷载作用下所产生的反应。这个研究领域包含多种名称，如：“材料强度”，“变形固体力学”。本书中研究的固体包括受轴向载荷的杆，轴，梁，圆柱及由这些构件组成的结构。一般情况下，研究的目的是测定由荷载引起的应力、应变和变形物理量；当所承受的荷载达到破坏载荷时，可测得这些物理量，画出完整的固体力学性能图。在材料力学的研究中，理论分析和实验研究是同等重要的。必须认识到在很多情况下，通过逻辑推导的力学公式和力学方程在实际情况中不一定适用，除非材料的某些性能是确定的。而这些性能是要经过相关实验的测定来得到的。同样，当工程中的重要的问题用逻辑推导方式不能有效的解决时，实验测定就发挥实用
21、性作用了。材料力学的发展历史是一个理论与实验极有趣的结合，在一些情况下，是实验的指引得出正确结果而产生理论，在另一些情况下却是理论来指导实验。例如，著名的达芬奇(1452-1519)和伽利略(1564-1642)通过做实验测定钢丝，杆，梁的强度，而当时对于他们的测试结果并没有充足的理论支持（以现代的标准）。相反的，著名的数学家欧拉(1707-1783) ，在1744年就提出了柱体的数学理论并计算其极限载荷，而过了很久才有实验证明其结果的正确性。 因此，欧拉的理论结果在很多年里都未被采用，而今天，它们却是圆柱理论的奠定基础。随着研究的不断深入，把理论推导和在实验上已确定的材料性质结合起来研究的重
22、要性将是显然的。在这一节，首先。我们讨论一些基本概念，如应力和应变，然后研究受拉伸，压缩和剪切的简单构件的性能。2.应力通过对等截面杆拉伸的研究初步解释应力和应变的概念。等截面杆是一个具有恒定截面的直线轴。这里，假设在杆的末端施加轴向力P，产生均匀的伸展或拉伸。假设沿垂直于轴线的方向切割杆，我们就能把杆的一部分当作自由体隔离出来。张力P作用于杆的右端，在另一端就会出现一些力来代替杆被切除的那一部分。这些力连续地分布在横截面上，类似于作用在被淹没物体表面的连续的静水压力。力的密度，也就是单位面积上的力的大小，称为应力，一般用表示。假设应力是均匀分布在横截面上，易得出它的大小等于密度乘以杆的横截面
23、积A。另外，通过图中所示物体，也由力的平衡可得到它与力P等大反向。因此得到 （1）为等截面杆中平均应力的计算公式。从这个公式可以看出，应力的单位是力除以面积例如：牛每平方毫米(N/mm)或磅每平方英寸(psi)。当杆在力的作用下被拉伸时，如图所示，所产生的应力称为拉应力；当施加相反方向的力时，杆被压缩，这时所产生的应力称为压应力。方程（1）的必要条件是应力必须均匀分布在杆的横截面上。如果轴向力P通过截面的形心时，这个条件可以满足，同时也可以通过静力学验证。当载荷P不是作用在形心时，将会产生挠度，就需要更加复杂的分析了。如果没有特殊说明，本书中假定所有的轴向力都作用在横截面的形心。除非另有说明，否则物体本身的质量一般忽略不计。3.应变受轴向力时，杆的总伸长量用希腊字母表示。单位长度的伸长即应变，可以用 （2）计算得到。这里L是杆的总长度。注意应变是无量纲量，只要应变在杆上是均匀的，就可以通过方程（2）得到精确的结果。如果杆被拉伸，此时的应变称为拉应变，即材料伸长或被拉伸；如果杆被压缩，即为压应变，这就意味着杆的相邻截面间的距离变小。专心-专注-专业