工程力学英文版课件00 Introduction
合集下载
工程力学双语课件ch13-Shear Force and Bending Moments in Beams
perpendicular to the section when the beam is bending.
2). Shearing force：Q
Internal force which the acting line in the cross-section parallel to the section, when the beam is bending.
symmetry, or the external forces do not act in a plane of symmetry of the beam with symmetric planes, this kind of bending is called unsymmetrical
bending. In later chapters we will mainly discuss the bending stresses and
Uniformly distributed force
P—
Concentrated force
5). Statically determinate and statically indeterminate beams
Statically determinate beams：Reactions of the beam can be determined only by static equilibrium equations，such as the above three kinds of basic beams. Statically indeterminate beams： Reactions of the beam cannot be determined or only part of reactions can be determined by static equilibrium equations.
工程力学英文版课件03 Nonconcurrent Forces
R' F' A F B C D O P'
M F AB OC F R, OA AB CD CD OC AB OA OC CD AB OA
18
R
P
OC M R CD R AB F AB M OA
A given couple may be moved about in its plane of action without changing its effect on a rigid body.
+
-
5
2. Transmissibility The force F acting on a rigid body has the properties of a sliding vector and can therefore act at any point along its line of action and still create the same moment about point O. This is the principle of transmissibility. It is important to realize that only the external effects, such as the body’s motion or the forces needed to support the body if it is stationary, remain unchanged after F is moved.
d F F F
13
d
F
The moment produced by a couple is called a couple moment. Its value can be determined by finding the sum of the moment of both couple forces about any arbitrary point.
工程力学英文版课件00 Introduction
Stability:
Capacity of a component or a structural element to retain the original state of equilibrium.
18
Under the requirement that the strength, rigidity, stability criteria are satisfied, provide the necessary fundamental theory and method of calculation for determining reasonable shape and dimension, choosing proper materials for the components with the most economic price.
21
Concentrated Force: A concentrated force represents the effect of a loading which is assumed to act at a point on a body. Force is defined as any action that tends to change the state of rest of a body to which it is applied. Three properties of force: Magnitude Direction Point of application
Transmissibility of Force The point of application of a force may be moved along its line of action without altering the effect of the force on any rigid body to which it is applied.
工程力学英文版课件04 Equilibrium of a Rigid Body
12
Equilibrium of a three-force body A body acted on by three forces is called a three-force body.
If a body is subjected to only three forces, then it is necessary that the forces be either concurrent or parallel for the body to be in equilibrium.
3
2. Construction of free-body diagrams Successful application of the equation of equilibrium requires a
complete specification of all the known and unknown external forces that act on the body. It is necessary to show all the forces and couple moments that the surroundings exert on the body so that these effects can be accounted for when the equations of equilibrium are applied. For this reason, a thorough understanding of how to draw a free-body diagram is of primary importance for solving problems in mechanics.
Equilibrium of a three-force body A body acted on by three forces is called a three-force body.
If a body is subjected to only three forces, then it is necessary that the forces be either concurrent or parallel for the body to be in equilibrium.
3
2. Construction of free-body diagrams Successful application of the equation of equilibrium requires a
complete specification of all the known and unknown external forces that act on the body. It is necessary to show all the forces and couple moments that the surroundings exert on the body so that these effects can be accounted for when the equations of equilibrium are applied. For this reason, a thorough understanding of how to draw a free-body diagram is of primary importance for solving problems in mechanics.
力学专业英语-Lecture_1_Introduction
• How are you doing? • How is life?
EVERY DAY GREETINGS
“Good morning”
“Good evening” “Good afternoon” “Good Night” “Goodbye”
What can you say to someone when you meet them for the first time?
Topics
Is greeting and introduction important?
What is a good greeting or introduction? How to make foreign friends?
Write your own opinion and submit it to qingheБайду номын сангаасao@.
Activities 2：
Using the above format, introduce the your partner at
a formal function.
FORMAL GREETINGS
Greeting
• Good Morning, Mr. Jack • Good Afternoon, Mr. Blue • Good Evening, Mommy
Listening
Most people are born with good hearing, but not good
listening skills. Listening must be learned. Listening is a mental process requiring effort, and we can learn how to be good listeners.
工程力学课件(双语版)
(FS)
Sample problem 4-3 The spool in Fig. (a) weights 25N, and its center of gravity is located at the geometric center. The weight of block C is 50N. The coefficients of static friction at the two points of contact are as shown. Determine the largest horizontal force P that can be applied without disturbing the equilibrium of the system.
a. Static case (no P) No friction force, no relative motion, no tendency of relative motion. b. Static case (P <Fmax) No relative motion, but having the tendency of relative motion and a friction force existing. 0F =P<Fmax=SN S: coefficient of static friction c. Case of impending sliding (P=Fmax ) The surfaces on the verge of sliding. F =Fmax=SN d. Dynamic case (P>Fmax ) Surfaces sliding relative to each other. F=Fk=kN k: coefficient of kinetic friction s , k 的大小可由实验测定，它们与接触物体的材料和表 面状态有关。常用材料的s , k见表5－1。
工程力学专业外语60页PPT
Elastic Range: • Linear elastic: • Nonlinear elastic:
Plastic Range: • Yield point
• Yield strength • Ultimate strength
力学 mechanics 牛顿力学 Newtonian mechanics 经典力学 classical mechanics 静力学 statics 运动学 kinematics 动力学 dynamics 动理学 kinetics 宏观力学 macroscopic mechanics, macromechanics 细观力学 mesomechanics 微观力学 microscopic mechanics, micromechanics 一般力学 general mechanics 固体力学 solid mechanics 流体力学 fluid mechanics 理论力学 theoretical mechanics 应用力学 applied mechanics 工程力学 engineering mechanics 实验力学 experimental mechanics 计算力学 computational mechanics 理性力学 rational mechanics 物理力学 physical mechanics 地球动力学 geodynamics 分析力学 analytical mechanics
1. Stress and strain are related terms used to define the intensity of internal reactive forces in a deformed body and associated unit change of dimension, shape, or volume by externally applied forces.
(英汉双语)工程力学第零章 绪 论
12
Sun Xunfang is an engineering mechanist and mechanics educationist. He has engaged in the research of fracture, damage, fatigue and creep of solid mechanics .He is the first to apply fracture dynamics to practice and developed the method of analysis in elasto-plastic fracture dynamics with surface cracks and assessment in integrity .
Leonardo Da Vinci Galileo Galilei
He made a detailed study on the basic concepts of movement 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.
Strength、 rigidity、 stability
19
§0-2 材料力学的任务及与工程的联系
强度、刚度、稳定性
20
Strength :
Capacity to resist failure of a component or an element. Rigidity : Capacity to resist deformations of a component or an element. Stability : Capacity to remain the original state in equilibrium of a component or an element
工程力学专业英语翻译PPT课件
在轴向力作用下，梁的总伸长用希腊字母δ来表示[见图1(a)]， 单位伸长量或者说应变将由方程(2)决定，这里L是指梁的总长度。 注意，这里应变ε是一个无量纲量，只要应变在梁的长度上各处是 均匀的，那么它可以通过方程(2)精确获得。如果梁被拉伸，那么 得到拉应变，表现为材料的延长或者拉伸；如果梁被压缩，那么 得到压应变，意味着梁的横截面将彼此更加靠近。
Note that E has the same units as stress. The modulus of elasticity is sometimes called Young’s modulus, after the English scientist Thomas Young (1773-1829) who studied the elastic behavior of bars. For most materials the modulus of elasticity in compression is the same as in tension.
Eq.(1) can be regarded as the equation for the uniform stress in a prismatic bar. This equation shown that stress has units of force divided by area. When the bar is being stretched by the force 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 stress.
Note that E has the same units as stress. The modulus of elasticity is sometimes called Young’s modulus, after the English scientist Thomas Young (1773-1829) who studied the elastic behavior of bars. For most materials the modulus of elasticity in compression is the same as in tension.
Eq.(1) can be regarded as the equation for the uniform stress in a prismatic bar. This equation shown that stress has units of force divided by area. When the bar is being stretched by the force 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 stress.
工程力学英文版课件11 Shear Forces and Bending Moments in Beams
16
• The shear V is obtained by summing forces perpendicular to the beam’s axis. • The moment M is obtained by summing moments about the sectioned end of the segment.
P P/2 P/2
18
Shear and Moment Functions. The beam is sectioned at an arbitrary distance x from the support A, extending within region AB, and the free-body diagram of the left segment is shown in figure. The unknowns V and M are indicated acting in the positive sense on the right-hand face of the segment according to the established sign convention.
13
Fig. (c)
qL a x2 Fig. (c)
Y qL Q2 q( x2 a ) 0
B
M2
Q2
Q2 q( x2 a L)
mB (Fi ) 0 , 1 qLx2 M 2 q( x2 a)2 0 2
1 2 M 2 q( x2 a) qLx2 2
4
Often beams are classified as to how they are supported. For example, a simply supported beam is pinned at one end and roller-supported at the other, whereas a cantilevered beam is fixed at one end and free at the other. Beams with overhanging end (ends) are overhanging beam. The actual design of a beam requires a detailed knowledge of the variation of the internal shear force V and bending moment M acting at each point along the axis of the beam.
• The shear V is obtained by summing forces perpendicular to the beam’s axis. • The moment M is obtained by summing moments about the sectioned end of the segment.
P P/2 P/2
18
Shear and Moment Functions. The beam is sectioned at an arbitrary distance x from the support A, extending within region AB, and the free-body diagram of the left segment is shown in figure. The unknowns V and M are indicated acting in the positive sense on the right-hand face of the segment according to the established sign convention.
13
Fig. (c)
qL a x2 Fig. (c)
Y qL Q2 q( x2 a ) 0
B
M2
Q2
Q2 q( x2 a L)
mB (Fi ) 0 , 1 qLx2 M 2 q( x2 a)2 0 2
1 2 M 2 q( x2 a) qLx2 2
4
Often beams are classified as to how they are supported. For example, a simply supported beam is pinned at one end and roller-supported at the other, whereas a cantilevered beam is fixed at one end and free at the other. Beams with overhanging end (ends) are overhanging beam. The actual design of a beam requires a detailed knowledge of the variation of the internal shear force V and bending moment M acting at each point along the axis of the beam.
工程力学ppt课件01(第一部分：第1-4章)
材料力学的性能分析
01
材料力学性能分析包括对材料的弹性、塑性、脆性、韧性 等性能的评估。
02
弹性是指材料在外力作用下发生形变，外力消失后能恢复 原状的能力；塑性是指材料在外力作用下发生形变，外力 消失后不能恢复原状但也不立即断裂的能力；脆性和韧性 则是描述材料在受力过程中易碎和抗冲击能力的性能。
03
力的分类
根据力的作用效果，可将力分为拉力、 压力、支持力、阻力、推力等。
静力学的基本原理
二力平衡原理
力的平行四边形法则
作用与反作用定律
三力平衡定理
作用在刚体上的两个力等大反 向，且作用在同一直线上，则 刚体处于平衡状态。
作用于物体上同一点的两个力 和它们的合力构成一个平行四 边形，合力方向沿两个力夹角 的角平分线，因为两个分力大 小不变，所以合力的大小也是 一定的。
材料力学性能分析对于工程设计和安全评估具有重要意义 ，是确定材料能否承受预期载荷并保持稳定性的关键依据 。
材料力学的应用实例
材料力学在建筑、机械、航空航 天、汽车、船舶等领域有广泛应 用。
例如，建筑结构中的梁和柱的设 计需要考虑到材料的应力分布和 承载能力；机械零件的强度和刚 度分析对于其正常运转和疲劳寿 命预测至关重要；航空航天领域 中，材料力学则涉及到飞行器的 轻量化设计以及确保飞行安全的 关键因素。
动力学的基本原理
牛顿第一定律
物体在不受外力作用时，将保持静止或匀速直线运动状态。
牛顿第二定律
物体受到的合外力等于其质量与加速度的乘积，即F=ma。
牛顿第三定律
作用力和反作用力大小相等、方向相反、作用在同一条直线上。
动力学的基本方法
动力学方程的建立
01
根据牛顿第二定律，建立物体运动过程中受到的合外力与加速
工程力学第一章ppt
绪论
工程力学
第一部分：静力学 第二部分：材料力学
▲ 静力学基础（静力学理论基础，物体受力分析） ▲ 力系的简化（各种力系的简化过程） ▲ 力系的平衡（各种力系的平衡条件及应用） ▲ 应用问题--桁架与摩擦（考虑摩擦的平衡）
静力学基本内容 静力学——研究物体受力及平衡规律。（只研究“力”） Statics 刚体、刚体系
F
sin
cos
Fy Fxy sin F sin sin
例2001-N1，图F3中=a3=00bN=，方m向，如c图= 。求m。各力力3 F在1 三= 1个00坐N标，轴F2上= 的2
投影。
例2001-N1，图F3中=a3=00bN=，方m向，如c图= 。求m。各力力3 F在1 三= 1个00坐N标，轴F2上= 的2
FF1 F2
1）直接分解法
FF1F2F3
F1 F co s
F
2
F
cos
F
3
F
cos
2）二次分解法
F F M F 3 F 1 F 2 F 3
FM F sin
F
1
F
sin
cos
F
2
F
sin
sin
F 3 F c o s
2.力的分解以及与力的投影的关系
将一个力分解为两个(或三个)分力(的过程) 问题：力的投影与力的分解是否相同？
作用在物体上同一点的两个力，可合成一个合力，合力的作用点仍在该点，其 大小和方向由以此两力为边构成的平行四边形的对角线确定。
矢量表示：
FR F1F2
1.2静力学公理
公理2 二力平衡条件：
矢量表示：
作用在刚体上的两个力，使刚体处于平衡的充要条件是，这两个力大小相等，方 向相反，且作用在同一直线上。
工程力学英文版课件05 Force Analysis of Structures and Machines
18
Joint C: From the free-body diagram of joint C,
FBC
45˚
Fx 0 FCA FBC cos 45 0
C Cy
FCA
Fy 0 C y FBC sin 45 0 FCA 500 N; C y 500 N
FBA
FBC
Since the force in member BC has been calculated, we can proceed to analyze joint C in order to determine the force in member CA and the support reaction.
FCD
FCB
45◦ 30◦
y
C x
Figure (a)
1.5 kN
From figure (a):
Joint A: From the free-body diagram of joint A,
FBA
Ax
A
FCA
Fx 0 FCA Ax 0; Ax 500 N Fy 0 FBA Ay 0; Ay 500 N
19
Ay
[Example 2] Determine the forces acting in all the members of the truss shown in figure.
14
• The correct sense of an unknown member force can in many cases be determined ‘by inspection’. In more complicated cases, the sense of an unknown member force can be assumed to be in tension; then, after applying the equilibrium equations, the assumed sense can be verified from the numerical results. • Orient the x and y axes such that the forces on the free-body diagram can be easily resolved into their x and y components and then apply the two equilibrium equations.
Joint C: From the free-body diagram of joint C,
FBC
45˚
Fx 0 FCA FBC cos 45 0
C Cy
FCA
Fy 0 C y FBC sin 45 0 FCA 500 N; C y 500 N
FBA
FBC
Since the force in member BC has been calculated, we can proceed to analyze joint C in order to determine the force in member CA and the support reaction.
FCD
FCB
45◦ 30◦
y
C x
Figure (a)
1.5 kN
From figure (a):
Joint A: From the free-body diagram of joint A,
FBA
Ax
A
FCA
Fx 0 FCA Ax 0; Ax 500 N Fy 0 FBA Ay 0; Ay 500 N
19
Ay
[Example 2] Determine the forces acting in all the members of the truss shown in figure.
14
• The correct sense of an unknown member force can in many cases be determined ‘by inspection’. In more complicated cases, the sense of an unknown member force can be assumed to be in tension; then, after applying the equilibrium equations, the assumed sense can be verified from the numerical results. • Orient the x and y axes such that the forces on the free-body diagram can be easily resolved into their x and y components and then apply the two equilibrium equations.
工程力学专业外语-.ppt
dx
dee x, differential x
dy
the first derivative of y with respect to x
dx
d2y
the second derivative of y with respect to x
dx 2
y
the first partial derivative of y with respect to x
4. Ultimate tensile strength is the maximum nominal tensile stress developed during increasing-load application, calculated from maximum applied load and original unstrained sectional area.
AX
AX AX
f (x)
A is not a subset of the set X; or A is not contained in the set X
A is a member of the set X; or A belongs to X A is not a member of the set X; or A does not belong to X function f of x
Shearing stress
Torsion
Torque
Shearing stress
Bending
Combined Loading and deformation
Shear force normal stress
Bending moment Shearing stress
工程力学双语课件ch06-ForceAnalysisofStructuresandMachines重点
[Example] h, a and P are given, determine the internal forces on the element 4, 5 and 6. [例] 已知：如图，h，a，P，求：4，5，6杆的内力。 I Solution: ① Study the whole I structure, determine the reaction forces.
27
6.6 Method of she point A:
研究A点： Again Y 0 由Y 0
Sb cos45o P 0
28
Sb 2P
6.6 Method of sections
① 研究整体求支反力 解：
X 0 XA 0 MB 0
YA P
Y 3a P 2a P a 0
21
6.6 Method of sections
② Draw a cut I-I, study the leftA'
hand section of the truss.
24
6.6 Method of sections
3. The judgments of the internal forces of special elements 三、特殊杆件的内力判断 ① If no load acts on a two-element joint and the two elements are not collinear, the internal forces of them are zero, they are called zero elements. 两杆节点无载荷、且两杆不在 S1 S2 0 一条直线上时，该两杆是零杆。 ② If no load acts on a three-element joint and two elements of them are collinear, the third is a zero element. 三杆节点无载荷、其中两杆在一条 直线上，另一杆必为零杆 S S
27
6.6 Method of she point A:
研究A点： Again Y 0 由Y 0
Sb cos45o P 0
28
Sb 2P
6.6 Method of sections
① 研究整体求支反力 解：
X 0 XA 0 MB 0
YA P
Y 3a P 2a P a 0
21
6.6 Method of sections
② Draw a cut I-I, study the leftA'
hand section of the truss.
24
6.6 Method of sections
3. The judgments of the internal forces of special elements 三、特殊杆件的内力判断 ① If no load acts on a two-element joint and the two elements are not collinear, the internal forces of them are zero, they are called zero elements. 两杆节点无载荷、且两杆不在 S1 S2 0 一条直线上时，该两杆是零杆。 ② If no load acts on a three-element joint and two elements of them are collinear, the third is a zero element. 三杆节点无载荷、其中两杆在一条 直线上，另一杆必为零杆 S S
工程力学专业英语阅读 ppt课件
这些材料的特点是：绝缘性好，耐磨性强。
2、某些表示事物特征的形容词作表语时可将其转译成名词， 其后往往加上“性”、“度”、“体”等，带有定冠词的某些 形容词用作名词，应译成名词
The cutting tool must be strong, tough, hard, and wear resistant. 刀具必须具有足够的强度、韧性、硬度和耐磨性。
This communication system is chiefly characterized by its simplicity of operation and the ease with which it can be maintained.
这种通讯系统的主要特点是操作简单，容易维修。 2、修饰形容词的副词，由于形容词转换成名词，因而可相应 地转译成形容词
4、有时把名词译成形容词更符合汉语的表达习惯。 This experiment was a success. 这个试验是成功的。
转换成汉语副词
1、修饰名词的形容词，由于名词转换成动词，因而相应地 转译成副词
The application of computers makes for a tremendous rise in labor productivity.
使用电子计算机可以大大地提高劳动生产率。
2、为了译文符合汉语习惯，有时形容词、动词应转译为副词
A helicopter is free to go almost anywhere. 直升飞机几乎可以自由地飞到任何地方去。 Rapid evaporation at the heating-surface tends to make the steam wet. 加热面上的迅速蒸发，往往使蒸汽的湿度变大。
2、某些表示事物特征的形容词作表语时可将其转译成名词， 其后往往加上“性”、“度”、“体”等，带有定冠词的某些 形容词用作名词，应译成名词
The cutting tool must be strong, tough, hard, and wear resistant. 刀具必须具有足够的强度、韧性、硬度和耐磨性。
This communication system is chiefly characterized by its simplicity of operation and the ease with which it can be maintained.
这种通讯系统的主要特点是操作简单，容易维修。 2、修饰形容词的副词，由于形容词转换成名词，因而可相应 地转译成形容词
4、有时把名词译成形容词更符合汉语的表达习惯。 This experiment was a success. 这个试验是成功的。
转换成汉语副词
1、修饰名词的形容词，由于名词转换成动词，因而相应地 转译成副词
The application of computers makes for a tremendous rise in labor productivity.
使用电子计算机可以大大地提高劳动生产率。
2、为了译文符合汉语习惯，有时形容词、动词应转译为副词
A helicopter is free to go almost anywhere. 直升飞机几乎可以自由地飞到任何地方去。 Rapid evaporation at the heating-surface tends to make the steam wet. 加热面上的迅速蒸发，往往使蒸汽的湿度变大。
工程力学英文版课件04 Equilibrium of a Rigid Body
7
? Study Table 4-1
? Internal forces are never shown on the free-body diagram, since they occur in equal but opposite collinear pairs and therefore cancel out.
? If a support prevents translation of a body in a particular direction, then thethat direction.
? If rotation is prevented, then the support exerts a couple moment on the body.
6
IMPORTANT POINTS ? No equilibrium problem should be solved without first drawing
the free-body diagram, so as to account for all the forces and couple moments that act on the body.
Identify each loading and give dimensions. The forces and couple moments that are known should be labelled with their proper magnitudes and directions. Letters are used to represent the magnitudes and direction angles of unknown forces and couple moments. Establish an x, y coordinate system so that these unknowns can be identified.
? Study Table 4-1
? Internal forces are never shown on the free-body diagram, since they occur in equal but opposite collinear pairs and therefore cancel out.
? If a support prevents translation of a body in a particular direction, then thethat direction.
? If rotation is prevented, then the support exerts a couple moment on the body.
6
IMPORTANT POINTS ? No equilibrium problem should be solved without first drawing
the free-body diagram, so as to account for all the forces and couple moments that act on the body.
Identify each loading and give dimensions. The forces and couple moments that are known should be labelled with their proper magnitudes and directions. Letters are used to represent the magnitudes and direction angles of unknown forces and couple moments. Establish an x, y coordinate system so that these unknowns can be identified.
工程力学-第1章工程静力学基础PPT课件
• 各分支学科间的交叉结果又产生粘弹性理论、流 变学、气动弹性力学等。
.
14
• 静力学 • 材料力学 • 结构力学 • 流体力学 • 弹性力学 • 断裂力学
• ……
工程力学
.
15
第一篇 静力学
第一章 静力学基本概念与物体受力分析 第二章 平面任意力系
.
16
引言
静力学是研究物体在力系作用下平衡规律的科学。
F
G
FN2
G
约束力 特 点：
①大小常常是未知的；
FN1
②方向总是与约束限制的物体的位移方向相反；
③作用点在物体与约.束相接触的那一点。
31
二、约束类型和确定约束反力方向的方法： 1. 柔索：由柔软的绳索、链条或皮带构成的约束
绳索类只能受拉， 约束反力作用在接触点， 方向沿绳索背离物体。
.
32
约束力方向与所能限制的物体运动方向相反。
固定铰支座
上摆
销钉
下摆
.
42
固定铰支座
.
43
固定铰支座
铰
.
44
固定铰支座
.
45
中间铰
铰
.
46
中间铰
. 销钉
47
约束力表示：
简化表示：
.
48
4 活动铰支座（辊轴支座）
在固定铰链支座的底部安装一排滚轮，可使 支座沿固定支承面滚动。
.
49
活动铰支座
上摆
销钉
滚轮
底板
.
50
活动铰支座
.
51
• 17世纪末牛顿继承和发展前人的研究成果(特别是 开普勒的行星运动三定律)，提出力学运动的三条 基本定律，使经典力学形成系统的理论。
.
14
• 静力学 • 材料力学 • 结构力学 • 流体力学 • 弹性力学 • 断裂力学
• ……
工程力学
.
15
第一篇 静力学
第一章 静力学基本概念与物体受力分析 第二章 平面任意力系
.
16
引言
静力学是研究物体在力系作用下平衡规律的科学。
F
G
FN2
G
约束力 特 点：
①大小常常是未知的；
FN1
②方向总是与约束限制的物体的位移方向相反；
③作用点在物体与约.束相接触的那一点。
31
二、约束类型和确定约束反力方向的方法： 1. 柔索：由柔软的绳索、链条或皮带构成的约束
绳索类只能受拉， 约束反力作用在接触点， 方向沿绳索背离物体。
.
32
约束力方向与所能限制的物体运动方向相反。
固定铰支座
上摆
销钉
下摆
.
42
固定铰支座
.
43
固定铰支座
铰
.
44
固定铰支座
.
45
中间铰
铰
.
46
中间铰
. 销钉
47
约束力表示：
简化表示：
.
48
4 活动铰支座（辊轴支座）
在固定铰链支座的底部安装一排滚轮，可使 支座沿固定支承面滚动。
.
49
活动铰支座
上摆
销钉
滚轮
底板
.
50
活动铰支座
.
51
• 17世纪末牛顿继承和发展前人的研究成果(特别是 开普勒的行星运动三定律)，提出力学运动的三条 基本定律，使经典力学形成系统的理论。
- 1、下载文档前请自行甄别文档内容的完整性，平台不提供额外的编辑、内容补充、找答案等附加服务。
- 2、"仅部分预览"的文档,不可在线预览部分如存在完整性等问题,可反馈申请退款(可完整预览的文档不适用该条件!)。
- 3、如文档侵犯您的权益，请联系客服反馈,我们会尽快为您处理(人工客服工作时间：9:00-18:30)。
kilogram(kg) (N)
second(s)
lb s 2 slug( ) pound(lb) ft
Quantity FPS
Force Mass Length lb slug ft
Equals
SI
4.4482 N 14.5938 kg 0.3048 m
28
29
This subject is also concerned with computing the deformations of the body, and it provides a study of the body’s stability when the body is subjected to external forces.
25
Superposition Law Two equal, opposite, collinear forces, being in equilibrium, can be superimposed on, or removed from, any given force system without altering the action of that system on any rigid body.
1
Why Engineering Mechanics
Suspension bridge
2
Steel cables
3Байду номын сангаас
Bridge pier
4
5
6
7
8
Finite element modelling of car crash
9
10
11
12
Gears
13
Artificial bone
Transmissibility of Force The point of application of a force may be moved along its line of action without altering the effect of the force on any rigid body to which it is applied.
26
For a rigid body, three properties of force are: Magnitude Direction Line of application
27
Systems of Units
Name Length Time
second(s)
Mass
Force
SI meter(m) U.S. Customary foot(ft) (FPS)
19
Idealizations:
Models or idealizations are used in mechanics in order to simplify the application of the theory.
Particle: A particle has a mass, but a size that can be neglected. When a body is idealized as a particle, the principles of mechanics reduce to a rather simplified form since the geometry of the body will not be involved in the analysis of the problem.
17
Strength：
Capacity of a component or a structural element to resist failure.
Rigidity (Stiffness)：
Capacity of a component or a structural element to resist deformation.
Stability:
Capacity of a component or a structural element to retain the original state of equilibrium.
18
Under the requirement that the strength, rigidity, stability criteria are satisfied, provide the necessary fundamental theory and method of calculation for determining reasonable shape and dimension, choosing proper materials for the components with the most economic price.
15
Statics:
The subject deals with the equilibrium of rigid bodies, that is, it is used to determine the forces acting either external to the body or within it necessary to keep the body either at rest or moving with a constant velocity. The general problem of statics consists in reducing a given system of forces to its simplest equivalent, i.e., to its resultant.
14
Introduction
Mechanics can be defined as that branch of the physical sciences concerned with the state of rest or motion of bodies that are subjected to the action of forces. This semester, two very important branches of mechanics, namely, statics and mechanics of materials will be studied.
21
Concentrated Force: A concentrated force represents the effect of a loading which is assumed to act at a point on a body. Force is defined as any action that tends to change the state of rest of a body to which it is applied. Three properties of force: Magnitude Direction Point of application
Concurrent forces in a plane：
All coplanar forces acting on the body have the same point of application or the lines of action of the forces intersect at a common point.
Coplanar force systems Non-coplanar force systems (Force systems in space)
23
Coplanar force systems:
Concurrent forces in a plane Non-concurrent forces in a plane
22
Force system：
If several forces are applied to a body at various points and acting in various directions, we have a system of forces.
Force systems including：
24
Basic Laws of Force
Parallelogram Law Theorem of Three Forces Law of Action and Reaction Equilibrium Law If two forces applied to a body at a point are equal in magnitude, collinear in action, and opposite in direction, these two forces are said to be in equilibrium.
16
Mechanics of materials:
The subject studies the relationships between the external loads and the intensity of internal forces acting within the body.
20
Rigid Body: A rigid body can be considered as a combination of a large number of particles in which all the particles remain at a fixed distance from one another both before and after applying a load. As a result, the material properties of any body that is assumed to be rigid will not have to be considered when analyzing the forces acting on the body. In most cases the actual deformations occurring in structures, machines, mechanisms, and the like are relatively small, and the rigidbody assumption is suitable for analysis.