《工程力学结论》PPT课件.ppt

1、工程力学 双语课件,辽宁省第八届教育软件大赛参赛作品,Chapter 1 Exordium,工 程 力 学,engineering mechanics,第一章 绪论,本章目标 chapter objectives,工程力学研究什么问题 ? What is the contents of engineering mechanics?,工程力学怎样研究问题？ How to study the knowledge of engineering mechanics?,工程力学的研究对象是什么？ What is the studied object of engineering mechanics?,工

2、程力学的研究对象 The studied objects of engineering mechanics,刚体 rigid body,就是在力的作用下，大小和形状都不变的物体,There is no deformation whenever a body subjected to any force,变形体,deformable body,在外力作用下，一切固体都将发生变形（尺寸和形状）,故称为变形体。,It will tend to create the change of shape and size whenever a body subjected to any force,we c

3、aller the changes deformation and the body is called deformable solid body.,如图所示桥式起重机的主梁、吊钩、钢丝绳；悬臂吊车架的横梁AB， 斜杆CD都是工程力学的研究对象，工程上称为构件 。,The crane is shown as in Fig 1-1,the principle beam, pothook,steel cord ,the beam AB and the member CD are all studied bodies ,they are called elements in engineering

4、.,工程力学的研究内容 The contents of engineering mechanics,静力学 statics,主要研究刚体在力作用下的平衡问题，即根据力系平衡条件 分析平衡刚体的受力情况，确定各未知力的大小和方向，是 构件承载能力计算的基础。,Statics deals with the equilibrium of bodies,that is ,those that are either at rest or move with a constant velocity.the first step to solving most mechanics problems requ

5、ires drawing a diagram ,this step is particularly important when solving equilibrium problems,and for this reason drawing free-body diagrams is strongly emphasized throughout the book.,物体的受力分析 the analysis of forces acted to the bodies,力系的等效简化 equivalent reduction of force systems,本篇主要研究三方面问题 we wil

6、l study three problems in this part,力系的平衡条件及其应用 conditions and applying of equilibrium of force systems,工程静力学（statics）的理论和方法不仅是工程构件静力设计 的基础，而且在解决许多工程技术问题中有着广泛应用。,The principles and methods of statics are the basis of design, They are widely applied in many engineering technology problems.,建立的力学模型 fo

7、rce model established,发动机原理图 Work principle of motor,静力学分析过程 procedures of analysis of statics,NA,NB,NO,NA,M,N1,N2,NB,构件承载能力计算(材料力学),The analysis of ability of the members subjected to the loads,主要研究变形固体的强度和刚度问题，为机械零件确定合理的 材料、截面形状和尺寸，为达到既安全又经济的目的提供理论 基础。,Mechanics deals with the problems of strength

8、 and rigidity,to determine reasonable materials ,to design reasonable shape and size of sections, it provides necessary theory basis for safety and economy.,构件承载能力分析的内容 the contents of analysis of ability of members subjected to loads,对构件的三项基本要求 Three fundamental requests,强度构件在外载作用下，具有足够的抵抗断裂破坏的能力。例

9、 如储气罐不应爆破；机器中的齿轮轴不应断裂失效等。,构件拉伸破坏1 tension failure,构件拉伸破坏2 tension failure,Strength the ability of members resist loads not failure,构件拉伸破坏强度问题 tension failure -strength problems, 强度失效,刚度构件在外载作用下，具有足够的抵抗变形的能力。如机 床主轴变形不应过大，否则影响加工精度,Stiffness the ability of members that resist ductile deformation,未变形,变形

10、, 刚度失效,某些构件在特定外载， 如压力作用下，具有足够的保持其原有 平衡状态的能力。例如千斤顶的螺杆等。,稳定性,Stability the ability that slender members remain the line equilibrium State subjected to axial compressive loads, 屈曲失效,材料力学的任务,Task of mechanics,研究构件的强度、刚度和稳定性 To study the strength,stiffness and stability of elements,研究材料的力学性能 To study the

11、 mechanical properties of materials,为合理解决工程构件设计中安全与经济之间的矛盾提供力 学方面的依据 To provides mechanics theory basis for solving the conflict between safety and economy,变形固体的基本假设,Fundamental assumptions of deformable body,均匀连续性假设： 假定变形固体内部毫无空隙地充满物质，且各点处的力学性能都是相同的。 The homogenous and continues assumption :the bod

12、y has the same physical and mechanical properties throughout its volume without any interspaces among points.,各向同性假设: 认为物体内在各个不同方向上的力学性能相同 Isotropic assumption:the body has the same mechanical properties in all directions.,弹性小变形条件 The conditions of elastic small deflection,弹性变形: elastic deformation,

13、卸载后能够消失的变形 The disappeared deformation when the loads are taken down.,塑性变形: plastic deformation,卸载后不能消失的变形 The rudimental deformation when the loads are taken down.,构件的承载能力分析主要研究微小的弹性变形问题，称为 弹性小变形,The analysis of ability of members subjected to loads deals with Minute elastic deformation ,we called

14、it elastic small deformation.,杆件变形的基本形式 Fundamental deformation forms of members,根据其几何形状构件可以简化为四类 the elements can be divided into four classes based on the geographic shape of the elements bar (杆) 、plate (板) 、shell (壳) 、body (块) 。,1、拉伸tension和 压缩compression,2、剪切shear：演示,3、扭转torsion,4、弯曲bend,运动与动力分析

15、研究力与物体运动之间的关系。 Kinematics and kinetics show that the relation between Forces and motion subjected bodies.,.工程力学的研究方法 methods to study engineering mechanics,观察和实验是理论发展的基础 Discovery and test are the basis of the development of theory.,在观察和实验的基础上，用抽象的方法建立力学模型 Establish the mechanics models by ideal met

16、hod based on the discoveries and tests.,在建立力学模型的基础上，根据公理、定律和基本假设，借助数学工具，通 过演绎、推理的方法，考虑到问题的具体条件，得到各种形式的具有物理意 义和实用价值的定理和结论,Obtain different forms theories and resultants with physical and useful value after establish The mechanics models,based on some assumptions, maths calculation and considered the conditions of problems by the deduction methods .,小结 summarize,绪论课讲授时应用2课时，重点内容是让学生大致了解该课程 的内容，更重要的是培养学生对这门课的兴趣。,This class arrange two cla