材料力學(xué)的介紹專(zhuān)業(yè)英語(yǔ)

1、1. Introduction to Mechanics of Materials 材料力學(xué)的介紹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 “mechanics of

2、 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 produced by

3、 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. 材料力學(xué)是應(yīng)用力學(xué)的一個(gè)分支，用來(lái)處理固體在不同荷載作用下所產(chǎn)生的反應(yīng)。這個(gè)研究領(lǐng)域包含多種名稱(chēng)，如：“材料強(qiáng)度”，“變形固體力學(xué)”。本書(shū)中研究的固體包括受軸向載荷的桿，軸，梁，圓柱及由這些構(gòu)件組成的結(jié)構(gòu)。一般情況下，研究的目的是測(cè)定由荷載引起

4、的應(yīng)力、應(yīng)變和變形物理量；當(dāng)所承受的荷載達(dá)到破壞載荷時(shí)，可測(cè)得這些物理量，畫(huà)出完整的固體力學(xué)性能圖。Theoretical analyses and experimental results have equally important roles in the study of mechanics of materials. On many occasions we will make logical derivations to obtain formulas and equations for predicting mechanical behavior, but at the same

5、 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 to us only after suitable experiments have been made in the laboratory. Also, many problems of importance in engineering cannot be handled

6、 efficiently by theoretical means, and experimental measurements become a practical necessity. The historical development of mechanics of materials is a fascinating blend of both theory and experiment, with experiments pointing the way to useful results in some instances and with theory doing so in

7、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, although they did not develop any adequate theories (by todays standards) to their test results. By contrast, the famous mathematician Leonhard

8、 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 to show the significance of his results. Thus, Eulers theoretical results remained unused for many years, although today they form the ba

9、sis of column theory.在材料力學(xué)的研究中，理論分析和實(shí)驗(yàn)研究是同等重要的。必須認(rèn)識(shí)到在很多情況下，通過(guò)邏輯推導(dǎo)的力學(xué)公式和力學(xué)方程在實(shí)際情況中不一定適用，除非材料的某些性能是確定的。而這些性能是要經(jīng)過(guò)相關(guān)實(shí)驗(yàn)的測(cè)定來(lái)得到的。同樣，當(dāng)工程中的重要的問(wèn)題用邏輯推導(dǎo)方式不能有效的解決時(shí)，實(shí)驗(yàn)測(cè)定就發(fā)揮實(shí)用性作用了。材料力學(xué)的發(fā)展歷史是一個(gè)理論與實(shí)驗(yàn)極有趣的結(jié)合，在一些情況下，是實(shí)驗(yàn)的指引得出正確結(jié)果而產(chǎn)生理論，在另一些情況下卻是理論來(lái)指導(dǎo)實(shí)驗(yàn)。例如，著名的達(dá)芬奇(1452-1519)和伽利略(1564-1642)通過(guò)做實(shí)驗(yàn)測(cè)定鋼絲，桿，梁的強(qiáng)度，而當(dāng)時(shí)對(duì)于他們的測(cè)試結(jié)果并沒(méi)有充足

10、的理論支持（以現(xiàn)代的標(biāo)準(zhǔn)）。相反的，著名的數(shù)學(xué)家歐拉(1707-1783) ，在1744年就提出了柱體的數(shù)學(xué)理論并計(jì)算其極限載荷，而過(guò)了很久才有實(shí)驗(yàn)證明其結(jié)果的正確性。 因此，歐拉的理論結(jié)果在很多年里都未被采用，而今天，它們卻是圓柱理論的奠定基礎(chǔ)。 The concepts of stress and strain can be illustrated in an elementary way by considering the extension of prismatic bar see Fig.1.4(a). 通過(guò)對(duì)等截面桿拉伸的研究初步解釋?xiě)?yīng)力和應(yīng)變的概念如圖1.4（a）。A pris

11、matic bar is one that has constant cross section throughout its length and a straight axis. 等截面桿是一個(gè)具有恒定截面的直線軸。In this illustration the bar is assumed to be loaded at its ends by axial forces P that produce a uniform stretching, or tension, of the bar. 這里，假設(shè)在桿的末端施加軸向力P，產(chǎn)生均勻的伸展或拉伸。By making an artific

12、ial cut (section mm) though the bar at right angels to its axis, we can isolate part of the bar as a free body Fig.1.4 (b). 假設(shè)沿垂直于軸線的方向切割桿，我們就能把桿的一部分當(dāng)作自由體隔離出來(lái)圖1.4（b）。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 ba

13、r upon the part that remains. 張力P作用于桿的右端，在另一端就會(huì)出現(xiàn)一些力來(lái)代替桿被切除的那一部分。These forces will be continuously distributed over the cross section, analogous to the continuous distribution of hydrostatic pressure over a submerged surface. 這些力連續(xù)地分布在橫截面上，類(lèi)似于作用在被淹沒(méi)物體表面的連續(xù)的靜水壓力。The intensity of force, that is, the p

14、er unit area, is called the stress and is commonly denoted by the Greek letter .力的密度，也就是單位面積上的力的大小，稱(chēng)為應(yīng)力，一般用表示。Assuming that the stress has a uniform distribution over the cross section see Fig.1.4(b), we can readily see that its resultant is equal to the intensity times the cross-sectional area A of

15、 the bar. 假設(shè)應(yīng)力是均勻分布在橫截面上如圖1.4（b），易得出它的大小等于密度乘以桿的橫截面積A。Furthermore, from the equilibrium of the body shown in Fig.1.4 (b), we can also that this resultant must be equal in magnitude and opposite in direction to the force P. 另外，通過(guò)圖1.4（b）中所示物體，也由力的平衡可得到它與力P等大反向。Hence, we obtain 因此得到 (1.3)as the equatio

16、n for the uniform stress in a prismatic bar.為等截面桿中平均應(yīng)力的計(jì)算公式。This equation shows that stress has units of force divided by area-for example, Newtons per square millimeter () or pounds per square inch (psi). 從這個(gè)公式可以看出，應(yīng)力的單位是力除以面積例如：牛每平方毫米()或磅每平方英寸(psi)。When the bar is being stretched by the forces P,

17、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. 當(dāng)桿在力的作用下被拉伸時(shí)，如圖所示，所產(chǎn)生的應(yīng)力稱(chēng)為拉應(yīng)力；當(dāng)施加相反方向的力時(shí)，桿被壓縮，這時(shí)所產(chǎn)生的應(yīng)力稱(chēng)為壓應(yīng)力。A necessary condition for Eq. (1.3) to be valid is that the s

18、tress must be uniform over the cross section of the 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 analys

19、is is necessary. Throughout this book, however, it is 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, as .方程（1.3）的必要條件是

20、應(yīng)力必須均勻分布在桿的橫截面上。如果軸向力P通過(guò)截面的形心時(shí)，這個(gè)條件可以滿足，同時(shí)也可以通過(guò)靜力學(xué)驗(yàn)證。當(dāng)載荷P不是作用在形心時(shí)，將會(huì)產(chǎn)生撓度，就需要更加復(fù)雜的分析了。如果沒(méi)有特殊說(shuō)明，本書(shū)中假定所有的軸向力都作用在橫截面的形心。除非另有說(shuō)明，否則物體本身的質(zhì)量一般忽略不計(jì)，如討論圖1.4中的桿情況一樣。 The total elongation of a bar carrying an axial force will be denoted the Greek letter see Fig. 1.4(a), and the elongation per unit length, or st

21、rain, is then determined by the equation (1.4)where L is the total length of the bar. Note that the strain is nondimensional quantity. It can be obtained accurately from Eq. (1.4) as long as the strain is uniform throughout the length of the bar. If the bar is in tension, the strain is a tensile str

22、ain, 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.受軸向力時(shí)，桿的總伸長(zhǎng)量用希臘字母表示，如圖1.4（a）所示。單位長(zhǎng)度的伸長(zhǎng)即應(yīng)變，可以用計(jì)算得到。這里L(fēng)是桿的總長(zhǎng)度。注意應(yīng)變是無(wú)量綱量，只要應(yīng)變?cè)跅U上是均勻的，就可以通過(guò)方程（

23、1.4）得到精確的結(jié)果。如果桿被拉伸，此時(shí)的應(yīng)變稱(chēng)為拉應(yīng)變，即材料伸長(zhǎng)或被拉伸；如果桿被壓縮，即為壓應(yīng)變，這就意味著桿的相鄰截面間的距離變小。 (Selected from Stephen P.Timoshenko and James M.Gere,mechanics of materials,Van Nostrand Reinhold Company Ltd.,1978 )材料力學(xué)的介紹材料力學(xué)是應(yīng)用力學(xué)的一個(gè)分支，用來(lái)處理固體在不同荷載作用下所產(chǎn)生的反應(yīng)。這個(gè)研究領(lǐng)域包含多種名稱(chēng)，如：“材料強(qiáng)度”，“變形固體力學(xué)”。本書(shū)中研究的固體包括受軸向載荷的桿，軸，梁，圓柱及由這些構(gòu)件組成的結(jié)構(gòu)。一

24、般情況下，研究的目的是測(cè)定由荷載引起的應(yīng)力、應(yīng)變和變形物理量；當(dāng)所承受的荷載達(dá)到破壞載荷時(shí)，可測(cè)得這些物理量，畫(huà)出完整的固體力學(xué)性能圖。在材料力學(xué)的研究中，理論分析和實(shí)驗(yàn)研究是同等重要的。必須認(rèn)識(shí)到在很多情況下，通過(guò)邏輯推導(dǎo)的力學(xué)公式和力學(xué)方程在實(shí)際情況中不一定適用，除非材料的某些性能是確定的。而這些性能是要經(jīng)過(guò)相關(guān)實(shí)驗(yàn)的測(cè)定來(lái)得到的。同樣，當(dāng)工程中的重要的問(wèn)題用邏輯推導(dǎo)方式不能有效的解決時(shí)，實(shí)驗(yàn)測(cè)定就發(fā)揮實(shí)用性作用了。材料力學(xué)的發(fā)展歷史是一個(gè)理論與實(shí)驗(yàn)極有趣的結(jié)合，在一些情況下，是實(shí)驗(yàn)的指引得出正確結(jié)果而產(chǎn)生理論，在另一些情況下卻是理論來(lái)指導(dǎo)實(shí)驗(yàn)。例如，著名的達(dá)芬奇(1452-1519)和伽利略(1564-1642)通過(guò)做實(shí)驗(yàn)測(cè)定鋼絲，桿，梁的強(qiáng)度，而當(dāng)時(shí)對(duì)于他們的測(cè)試結(jié)果并沒(méi)有充足的理論支持（以現(xiàn)代的標(biāo)準(zhǔn)）。相反的，著名的數(shù)學(xué)家歐拉(1707-1783) ，在1744年就提出了柱體的數(shù)學(xué)理論并計(jì)算其極限載荷，而過(guò)了很久才有實(shí)驗(yàn)證明其結(jié)果