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1、Mechanics of Materials,材料力学,第一章 绪 论,Chapter1 Preface,达芬奇说： “力学是数学的乐园，因为我们在这里获得了数学的果实。”,达芬奇,伽利略,伽利略创建了材料力学,Leonardo Da Vinci said: “ mechanics is a mathematic paradise, because we acquired mathematicss fruit here.“,Leonardo Da Vinci,Galileo Galilei,He made a detailed study on the basic concepts of mo
2、vement including the center of gravity ,speed and acceleration and came up with the rigid mathematic formulas .Especially the concept of acceleration is the milestone in the history of mechanics.,Galileo (15641642) is a German astronomer,mechanist and philosopher.He was born in Pisa onFeb15 1564 and
3、 died on Jan.8 1642 at the same place.,INTRODUCTION,INTRODUCTION,He once informally proposed law of inertia ,which established the foundation for Newton to propose formally the first law and the second law . It can be said that Galileo is the Pioneer of Newton in the settlement of the classical mech
4、anics . Galileo also brought up with the law of resultant and the rule of the parabolic motion and set up the principle of relativity . He is the first scientist to make a tot of achievements by the telescope .He kept on fighting with the idealism and church philosophy and suggested that we should s
5、tudy the law of nature by specific experiments and thought that experiences are the source of theory.,Galileo Galilei,Introduction,Here are his contributions to mechanics : he made a further study on the basis of Galileo Galilei and other people and concluded the three principles of objectsmovement
6、and made a firm foundation for mechanics.He is the discoverer of the gravitation law and set up the theoretical system of the classical mechanics.He also made profound contributions to the field of mathematics , optics and astronomy.is his most important work.He concluded many important discoveries
7、and study results in all his life in the book.,Isaac Newton (16421727) is a great British physicist ,mathematician and astronomer .He was born in a family of peasants in Lincoln on Dec25 1624 and died of Kidney stone in London on Mar20 1727.,Introduction,He began his creative work between 1903 and 1
8、906 and did research in the University in Germany every year supervised by famous scholars . He was a professor of colleges between 1907 and 1917.He came to America in 1922 and engaged in the study of mechanics.In 1928,he found “the mechanics department of ASME” and held ,various kinds of mechanics
9、seminars periodically .He has many works on applied applying mechanics . Especially since the year of late twenties he has written about 20 books applied such as , and except that he has done some work in teaching and training maters .,S.P is a Russian dynamicist with American nationality . He was b
10、orn in Ukraine on Dec.23 1878 and died in German on May.29 1972.,第一章 绪 论 (Preface),1-1 材料力学的任务及研究对象 (The tasks and research objects of mechanics of materials),1-2 变形固体的基本假设(The basic assumptions of deformable body ),1-3 力、应力、应变和位移的基本概念 ( Basic concepts of force、stress、 strain and displacement),1-4 杆
11、件变形的基本形式(The basic forms of deformation),1-1 材料力学的任务及研究对象 The tasks and research objects of mechanics of materials,一、任务 (task),材料力学是研究构件承载能力的一门学科。,承载能力(carrying capacity ),强度（strength),刚度（stiffness),稳定性（stability),1、强度（strength),构件抵抗破坏的能力,构 件 保 持 原 有 平 衡 状 态 的 能 力,3、稳定性（stability),材料力学的任务,在满足强度、刚度、稳
12、定性的要求下，以最经济的代价，为构件确定合理的形状和尺寸，选择适宜的材料，而提供必要的理论基础和计算方法。Under the request that the strength, rigidity, stability are satisfied, offer the necessary theoretical foundation and calculation method for determining reasonable shapes and dimensions, choosing proper materials for the components at the most ec
13、onomic price.,二、研究对象(research objects),1、构件(element),2、构件的分类 (classification of elements),(bar),材料力学以“梁、杆”为主要研究对象（the main research objective in mechanics of materials include axially-loaded bars, shafts, beams, and columns),工程中多为梁、杆结构,1-2 变形固体的基本假设 (The basic assumptions of deformable body ),一、连续性假
14、设 (continuity assumption),物质密实地充满物体所在空间，毫无空隙。,二、均匀性假设（homogenization assumption),物体内，各处的力学性质完全相同。,三、各向同性假设（isotropy assumption),组成物体的材料沿各方向的力学性质完全相同。,四、小变形假设（neglecting deformation assumption),材料力学所研究的构件在载荷作用下的变形与原始尺寸 相比甚小，故对构件进行受力分析时可忽略其变形。,一、外力（external force),1、按作用方式分,体积力 （body force),表面力 (surfac
15、e force ),集中力(concentrated force),分布力(distributed force),2、按随时间变化分,静载荷（static load),动载荷(dynamic load),交变载荷（alternate load),冲击载荷（impact load),1-3 力、应力、应变和位移的基本概念 ( Basic concepts of force, stress, strain, and displacement),1、定义： 指由外力作用所引起的、物体内相邻部分之间相互作用力（附加内力）。,二、内力（internal force),2、 内力的求法 截面法 (meth
16、od of sections ),步骤 (procedures for analysis), 截开 在所求内力的截面处， 假想地用截面将杆件 一分为二。,m,m,代替任取一部分，其弃去部分对留下部分的作用，用作用 在截面上相应的内力（力或力偶）代替。,平衡,对留下的部分建立平衡方程，根据其上的已知外力来计算杆在 截开面上的未知内力（此时截开面上的内力对所留部分而言是外力）。,m,m,三、应力（stress),1、定义 (definition)：由外力引起的内力的集度 （the intensity of internal force by external loads)。,2、 应力的表示,平均应力 (mean stress),全应力（总应力）(total stress),全应力分解为,四 、变形和位移（deformation and displacement),
