廖福宁 0904310110 装控091
专业英语翻译
unit 1
Static Analysis of Beams
A bar that is subjected to forces acting trasverse to its axis is called a beam. In this section we
Will consider only a few of the simplest types of beams, such as those shown in Flag.1.2. In every instance it is assumed that the beam has a plane of symmetry that is parallel to the plane of the figure itself. Thus the cross section of the beam occurs in that plane. Later we will consider a more general kind of bending in which the beam may have an unsymmetrical cross section.
The beam in Fig.1.2, with a pin support at one end and a roller support at the other, is called a
simply support beam ,or a simple beam . The essential feature of a simple beam is that both ends of the beam may rotate freely during bending, but the cannot translate in lateral direction. Also ,one end of the beam can move freely in the axial direction (that is, horizontal). The supports of a simple beam may sustain vertical reactions acting either upward or downward .
The beam in Flg.1.2(b) which is built-in or fixed at one end and free at the other end, is called
a cantilever beam. At the fixed support the beam can neither rotate nor translate, while at the free end it may do both. The third example in the figure shows a beam with an overhang. This beam is simply supported at A and B and has a free at C.
Loads on a beam may be concentrated forces, such as P1 and P2 in Fig.1.2(a) and (c), or
distributed loads loads, such as the the load q in Fig.1.2(b), the intesity. Distributed along the axis of the beam. For a uniformly distributed load, illustrated in Fig.1.2(b),the intensity is constant; a varying load, on the other hand, is one in which the intensity varies as a function of distance along
the axis of the beam.
The beams shown in Fig.1.2 are statically determinate because all their reactions can be
determined from equations of static equilibrium. For instance ,in the case of the simple beam supporting the load P 1 [Fig.1.2(a)], both reactions are vertical, and tehir magnitudes can be found by summing moments about the ends; thus, we find
L a L P R A )(1-=L
L P R B 1= The reactions for the beam with an overhang [Fig.1.2 (c)]can be found the same manner.
For the cantilever beam[Fig.1.2(b)], the action of the applied load q is equilibrated by a
vertical force RA and a couple MA acting at the fixed support, as shown in the figure. From a summation of forces in certical direction , we include that
qb R A =， And ,from a summation of moments about point A, we find
)2
(b a qb M A +=， The reactive moment MA acts counterclockwise as shown in the figure.
The preceding examples illustrate how the reactions(forces and moments) of statically
determinate beams requires a considerition of the bending of the beams , and hence this subject will be postponed.
The idealized support conditions shown in Fig.1.2 are encountered only occasionally in
practice. As an example ,long-span beams in bridges sometimes are constructionn with pin and roller supports at the ends. However, in beams of shorter span ,there is usually some restraint against horizonal movement of the supports. Under most conditions this restraint has little effect on the action of the beam and can be neglected. However, if the beam is very flexible, and if the horizonal restraints at the ends are very rigid , it may be necessary to consider their effects.
Example*
Find the reactions at the supports for a simple beam loaded as shown in fig.1.3(a ). Neglect
the weight of the beam.
Solution
The loading of the beam is already given in diagrammatic form. The nature of the supports is
examined next and the unknow components of reactions are boldly indicated on the diagram.
The beam , with the unknow reaction components and all the applied forces, is redrawn in Fig.1.3(b) to deliberately emphasiz this important step in constructing a free-body diagram. At A, two unknow reaction components may exist , since roller. The points of application of all forces are carefully noted. After a free-body diagram of the beam is made, the equations of statics are applied to abtain the sollution.
∑=0x F ，R Ax =0
∑+=0A M ，2000+100（10）+160（15）—R B =0，R B =+2700lb ↑
∑+=0B
M ,RAY(20)+2000—100（10）—160（5）=0，RAY=—10lb ↓ Check ：∑+↑=0FX ，—10—100—160+270=0
Note that ∑=0x F uses up one of the three independent equations of statics, thus only two
additional reaction compones may be determinated from statics. If more unknow reaction components or moment exist at the support, the problem becomes statically indeterminate.
Note that the concentrated moment applied at C enters only the expressions for summation
moments. The positive sign of RB indicates that the direction of RB has been correctly assumed in Fig.1.3(b). The inverse is the case of RAY ,and the vertical reaction at a is downward. Noted that a check on the arithmetical work is available if the caculations are made as shown.
Reading materia l
一条受力作用沿着横向坐标的轴类称作横梁。在这个部分，我们只考虑一些最简单的横
梁，例如那些展现的图1.2中的。假设每一个横梁都有水平面对称，和自身的线平行对称，因此，横梁的横截面又垂直的对称性。而且，假设负载沿水平方向均匀作用在横梁上，弯曲将会发生在水平面上。然后我们将要讨论那些更常见的不对称横截面横梁的弯曲
1.2 a 中的横梁，由一端固定另一端滚动组成的横梁，称为简单支撑横梁，或简单横梁，简单横梁主要的特征是两个末端在弯曲时都可以自由转动，但是不能转换。简单横梁可以支
撑向上或向下的反力。
图1.2 b 中的一端固定，一端自由运动的横梁，称为悬臂支撑横梁，固定端悬臂支撑不能旋转和转化，但是自由端可以。图表例子3中显示的是外伸横梁，由固定端A B和自由端C支撑。
负载加载在横杆上的力有可能是集中的载荷。就像图1.2a 1.2c 的P1 P2 ，如加载在例子1.2b中，分布载荷的特点在于他们的集中度已沿着横梁轴向单位距离表示力的单位，为了在例子1.2 b中图解一致性的分布载荷，且其变动载荷的强度是连续的，另一方面，强度大小的变化和横梁的轴向距离变化有关。
例1.2中的横梁是静定的，因为所有的力都可以通过平衡方程求出。例如1.2a中的简单横梁的负荷，两个反作用力都是垂直的，其大小也可以通过总结两边受力瞬间来确定。因此，我们发现Ra = P1(L-a)/L Rb=P1a/L
外伸横梁上的反作用力也可以通过相同的方式得到
对于1.2b的悬臂横梁，施加载荷使垂直力RA和力偶MA在固定端相等。如图所示，从合力方向垂直，我们可以总结Ra =qb 还有从A点得合力来看，我们发现MA=qb(a+b/2) 反作用力偶如图逆时针方向旋转。
之前的例子说明了静定横梁的作用效果可以通过方程计算静不定的横梁作用效果需要考虑到横梁的形变效果，此处这种研究方法教材以后会讨论。
图1.2中的理想化支撑条件只是偶尔在练习中遇到。举例，桥的大跨度横梁有时也会建造成铰链和滚动支撑。然而，在短一点的横梁，经常会有对支撑水平移动的制约力。大部分情况下，这种制约对横梁的效果很小，可以被忽略。当然，如果横梁非常容易弯曲，并且假如两端水平的制约力是非常有效果，那就又必要考虑他们共同作用的效果
例子
找出图1.3 a 中的简单横梁受力下的反作用力，忽略横梁自身的重量
横梁受力已经在图中给出。测试支撑力的性质和横梁的未知部件明显地在图中展示。有未知的反作用力和所有提供的力重新画在1.3b ，来可以强调构建这个自由体的重要步骤，在A中，由于一端是固定住，可能存在两个未知的反作用力。由于B端滚动，其他在只可能在垂直作用力上。所有的力量被认真标记处。当这个自由体的受力图表完成后，这个问题需要用静态方程求解。
∑Fx=0 Rax=0
∑MA=0+,2000+100(10)+160(15)-Ra(20)=0,RB=+2700lb
∑Mb=0+, Ray(20)+200-100(10)-160(5)=0 Ray=-101b
验证∑Fy=0，-10-100-160+270=0
注意∑Fx=0 用到了3个非静态方程中的一个，所以只有两个附加的反应力组成部分可能由方程中可以求出。但是如果有更多的反应力存在支撑结构中，问题成了静不定。
注意点C的中心的力集中瞬间只是出现在所有瞬间总和的表现。Rb的正向标记说明在1.3b中做出了正确的假设。Ra的情况相反，并且A点得垂直反作用力是向下的。注意假如计算如上那么计算过程中的验证是有效的。
UNIT 2
Reading material 2
Shear Force and Bending Moment in Beams
Let us now consider, as an example, a cantilever beam acted upon by an inclined load P at its free end [Fig.1.5(a)]. If we cut through the beam at a cross section mn and isolate the left-hand part of the beam as free body [Fig.1.5(b)], we see that the action of the removed part of the beam (that is, the right-hand part) upon the left-hand part must be such as to hold the left -hand part in equilibrium. The distribution of stresses over the cross section mn is not known at this stage in our study, but we do know that the resultant of these stresses must be such as to equilibrate the load P. It is convenient to resolve the resultant into an axial force N acting normal to the cross section and passing through the centroid of the cross section, a shear force V acting parallel to the cross section, and a bending moment M acting in the plane of the beam.
The axial force, shear force, and bending moment acting at a cross section of a beam are known as stress resultants. For a statically determinate beam, the stress resultants can be determined from equations of equilibrium. Thus, for the cantilever beam pictured in Fig. 1.5, we may write three equations of statics for the free-body diagram shown in the second part of the figure. From summations of forces in the horizontal and vertical directions we find, respectively,
N=Pcosβ V=Psinβ
and, from a summation of moments about an axis through the centroid of cross section mn, we obtain
β
M=
Px
sin
where x is the distance from the free end to section mn. Thus, through the use of a free-body diagram and equations of static equilibrium, we are able to calculate the stress resultants without difficulty. The stresses in the beam due to the axial force N acting alone have been discussed in the text of Unit.2; Now we will see how to obtain the stresses associated with bending moment M and the shear force V.
The stress resultants N, V and M will be assumed to be positive when they act in the directions shown in Fig.1.5(b). This sign convention is only useful, however, when we are discussing the equilibrium of the left-hand part of the beam. If the right-hand part of the beam is considered, we will find that the stress resultants have the same magnitudes, but opposite directions[see Fig.1.5(c)]. Therefore, we must recognize that the algebraic sign of a stress resultant does not depend upon its direction in space, such as to the left or to the right, but rather it depends upon its direction with respect to the material against which it acts. To illustrate this fact, the sign conventions for N, V and M are repeated in Fig.1.6, where the stress resultants are shown acting on an element of the beam.
We see that a positive axial force is directed away from the surface upon which it acts (tension), a positive shear force acts clockwise about the surface upon which it acts, and a positive bending moment is one that compresses the upper part of the beam.
Example
A simple beam A
B carries two loads, a concentrated force P and a couple Mo,acting as
shown in Fig.1.7(a). Find the shear force and bending moment in the beam at cross sections
located as follows: (a) a small distance to the left of the middle of the beam and (b) a small
distance to the right of the middle of the beam.
Solution
The first step in the analysis of this beam is to find the reactions R A and R B . Taking
moments about ends A and B gives two equations of equilibrium, from which we find
L Mo P R A -=43 L
Mo P R B +=4 Next, the beam is cut at a cross section just to the left of the middle, and a free-body diagram is
drawn of either half of the beam. In this example we choose the left-hand half of the beam, and the corresponding diagram is shown in Fig.1.7(b). The force P and the reaction R A appear in this
diagram, as also do the unknown shear force V and bending moment M, both of which are shown in their positive directions. The couple Mo does not appear in the figure because the beam is cut to the left of the point where Mo is applied. A summation of forces in the vertical direction gives
L
Mo P P V R A --=-=4 which shows that the shear force is negative; hence, it acts in the opposite direction to that
assumed in Fig.1.7(b). Taking moments about an axis through the cross section where the beam is cut [Fig.1.7(b)] gives
2842Mo PL PL L
R A M -=-=
Depending upon the relative magnitudes of the terms in this equation, we see that the bending
moment M may be either positive or negative.
To obtain the stress resultants at a cross section just to the right of the middle, we cut the
beam at that section and again draw an appropriate free-body diagram [Fig.1.7(c)]. The only
difference between this diagram and the former one is that the couple Mo now acts on the part of
the beam to the left of the cut section. Again summing forces in the vertical direction, and also
taking moments about an axis through the cut section, we obtain
L Mo P V --=4 2
8Mo PL M += We see from these results that the shear force does not change when the cut section is shifted from left to right of the couple Mo, but the bending moment increases algebraically by an amount equal to Mo.
现在让我们考虑，举例，一个倾斜的载荷P 作用于一个悬臂杆的自由端。假如我们穿过杆件的横截面 MN ，使得左手边部分脱离杆件成为自由体，我们发现右边部分必须与左边部分保持力的平衡。在我们的分析学习中，我们并不知道压应力在mn 面的分配情况。但我们的确知道这个压应力是与载荷P 相平衡的。们可以简单地把其分解为一个通过轴心的轴向
力N，一个和截面平行的剪应力，和一个作用在轴上得弯矩M。
应力的必然结果是在截面产生了轴向力，剪应力和弯矩。对于一个静定的杆件，可由这三个要素确定其平衡方程。因此图中的悬臂梁，我们可以得到三个平衡方程，从受力图分析，水平和垂直两个方向上，我们可以得到以下两个方程，其依次为：N=PcosβV=Psinβ从通过质心截面我们总结M=Pxsinβ，X表示自由端到MN的距离。可见，通过对自由体进行受力分析以及解析方程，可以轻易地求取轴向力，剪切力和弯矩。对于轴应变力N是轴向应力单独作用的结果，现在我们将会发现压力和弯矩和剪应力V的关系
我们把N ,V,M但他们如图所示方向都设为正方向。当我们考虑梁的左边部分时，这样的分析方法很方便。对右边部分的考虑，结果是类似的，只是方向相反而已，如图[see Fig.1.5(c)].所示。因此，我们必须要注意到这些应力的代数关系并不依赖于它们的空间方向，而是取决于材料对它的作用。为了证明这一点，我们可以对N、V和M进行微元分析，如图Fig.1.6所示。
我们规定垂直截面向外的方向为轴力的正方向，顺时针方向为剪应力的正方向，而使得梁的上部材料被压的弯矩方向为正方向。
例子
简支梁AB受两个载荷，一个集中力P和一对力偶Mo，如Fig.1.7（a）。剪力和弯矩在梁截面的分布的特征是左右边都与中心面相距很小距离。
解决方法
第一步，先分析Ra和Rb，分别对A、B两点列力矩平衡方程，有
Ra=3P/4-Mo/L Bb=P/4+Mo/L
下一步，用一个假想的平面将梁分开，有以下两图。选左边来研究，如图Fig.1.7(b)，在我们的研究体系中存在力P和Ra，以及未知剪力V和弯矩M，两个均为正方向，因为我们只是取左边部分考虑，所以在这分析中不考虑Mo，故在垂直方向的合力为V=Ra-P=-P/4-Mo/L
剪应力为负值，说明它与假定方向相反。对被截面形心列力矩式，有
M=RaL/2-PL/4=PL/8-Mo/2
鉴于其中的相对性，方程中所求出的力矩有可能是正值，也有可能是负值。
为得到右半部分所受应力情况，同样是将其从中间分开，有图[Fig.1.7(c)]. 此图跟前一图的区别就是力矩Mo已经考虑在梁上。再次在垂直方向列力的平衡方程以及对截面形心列力矩平衡方程，有
V=-P/4-Mo/L M=PL/8+Mo/2
从结果分析，有以下结论：力矩Mo在梁上左右移动时，剪切力并没有改变，但弯矩和Mo 成线性比例关系。
unit 3 力学理论
Reading Material 3
Theories of strength
1. Principal stresses
The state of the stress at a point in a structural member under a complex system of loading
is described by the magnitude and direction of the principal stresses. The principal stresses are the maximum values of the normal stresses at the point; which act on the planes on which the shear stress is zero. In a two-dimensional stress system, Fig.1.11, the principal stresses at any pint are related to the normal stress in the x and y directions σx and σy and the shear stress τxy at the point by the following equation: Principal stresses,22214)(2
1)(21xy x y x y τσσσσσσ+-±+=??? The maximum shear stress at the point is equal to half the algebraic between the principal
stresses: Maximum shear stress,)(2
121max σστ-=
Compressive stresses are conventionally taken as negative; tensile as positive.
2. Classification of pressure vessels
For the purpose of design and analysis, pressure vessels are sub-divided into two classes
depending on the ratio of the wall thickness to vessel diameter : thin-wall vessels, with a thickness ratio of less than 1/10, and thick-walled above this ratio.
The principal stresses acting at a point in the wall of a vessel, due to a pressure load, are
shown in Fig.1.12. If the wall is thin, th e radial stress σ3 will be small and can be neglected in comparison with the other stresses , and the longitudinal and circumferential stressesσ1 andσ2 can be taken as constant over the wall thickness. In a thick wall, the magnitude of the radial stress will be significant, and the circumferential stress will vary across the wall. The majority of the vessels used in the chemical and allied industries are classified as thin-walled vessels. Thick-walled vessels are used for high pressures.
3. Allowable stress
In the first two sections of this unit equations were developed for finding the normal stress
and average shear stress in a structural member. These equations can also be used to select the size of a member if the member’s strength is known. The strength of a material can be defined in several ways, depending on the material and the environment in which it is to be used. One definition is the ultimate strength or stress. Ultimate strength of a material will rupture when subjected to a purely axial load. This property is determined from a tensile test of the material. This is a laboratory test of an accurately prepared specimen, which usually is conducted on a universal testing machine. The load is applied slowly and is continuously monitored. The ultimate stress or strength is the maximum load divided by the original cross-sectional area. The ultimate strength for most engineering materials has been accurately determined and is readily available.
If a member is loaded beyond its ultimate strength it will fail----rupture. In the most
engineering structures it is desirable that the structure not fail. Thus design is based on some lower
value called allowable stress or design stress. If, for example, a certain steel is known to have an ultimate strength of 110000 psi, a lower allowable stress would be used for design, say 55000 psi. this allowable stress would allow only half the load the ultimate strength would allow. The ratio of the ultimate strength to the allowable stress is known as the factor of safety :
Sa
Su n or stress allowable strength ultimate saf ety of Factor == We use S for strength or allowable and σ for the actual stress in material. In a design:
σ≤S A
This so-called factor of safety covers a multitude of sins. It includes such factors as the
uncertainty of the load, the uncertainty of the material properties and the inaccuracy of the stress analysis. It could more accurately be called a factor of ignorance! In general, the more accurate, extensive, and expensive the analysis, the lower the factor of safety necessary.
4. Theories of failure
The failure of a simple structural element under unidirectional stress (tensile or compressive)
is easy to relate to the tensile strength of the material, as determined in a standard tensile test, but for components subjected to combined stresses (normal and shear stress) the position is not so simple, and several theories of failure have been proposed. The three theories most commonly used are described below:
Maximum principal stress theory: which postulates that a member will fail when one of the
principal stresses reaches the f ailure value in simple tension,σ’e . The failure point in a simple tension is taken as the yield-point stress, or the tensile strength of the material divided by a suitable factor of safety.
Maximum shear stress theory: which postulates that failure will occur in a complex stress
system when the maximum shear stresses reaches the value of the shear stress at failure in simple
tension. For a system of combined stresses there are three shear stresses maxima:
22
11σστ-±=，23
22σστ-±=，21
33σστ-±= （1.10）
In the tensile test, 2'
e e στ=
The maximum shear stress will depend on the sign of the principal stresses as well as their
magnitude, and in a two-dimensional stress system, such as that in the wall of a thin-walled pressure vessel, the maximum value of the shear stress may be given by putting σ3 =0 in equations 1.10. T he maximum shear stresses theory is often called Tresca’s, or Guest’s theory.
Maximum strain energy theory: which postulates the failure will occur in a complex stress
system when the total strain energy per unit volume reaches the value at which failure occurs in simple tensile.
The maximum shear-stress theory has been found to be suitable for predicting the failure of
ductile material under complex loading and is the criterion normally used in the pressure-vessel design.
阅读材料3
力学理论
1. 主应力
在一个复杂系统下的结构中某一点力的情况通常是由其主应力大小和方向来描述的。主应力为在一点的正应力的最大有效值，它作用于平面上，同时在平面上的抗剪应力为0。在二维力学系统里，图1.11中，任何一点的主应力与在x 和y 方向上的正应力σx 和σy ，以及作用于那一点、由下列公式确定的抗剪应力τxy 主应力22214)(2
1)(21xy x y x y τσσσσσσ+-±+=??? 那一点的最大抗剪应力是主应力的代数差的一半： 最大抗剪应力，τmax =2
1（σ1—σ2） 压缩应力是常见的但不是很明显，而拉伸应力则是很明显的。
2. 压力容器的分类
对于设计和分析的目的来说，压力容器根据壁厚与容器的直径比值主要分为两大类：厚度比小于1/10的薄壁压力容器，以及超过这个尺度的厚壁压力容器。
作用于容器壁上某点的主要压力源于压力负载，如图1.22所示。假如壁是薄的，放射状的压力σ3将会很小，并且通过与其他压力的比较是可以忽略的，而纵向的和圆周上的压力σ1和σ2就会被视为与壁厚无关的常数。在薄壁上，放射性压力的大小将会是很重要的，而圆周的压力将会绕容器壁变化。应用于化工和联合工业的主要压力容器被分为薄壁容器。厚壁容器主要应用于高压环境下。
3. 允许压力*
在本章节开始两个部分里，方程是为了找到结构中的主要压力和平均切向压力而产生
的。这些方程同样在结构力已知的情况下，可以被用于选择结构组成。材料强度可以在以下几方面的定义，依据材料自身和其使用环境。一种定义是其最大的强度和压力。最大强度是指当其受到纯轴向负载作用下发生断裂的压力。这项属性将会从材料的拉伸试验中测出。这是在一个具备普遍检测能力的机器上对某一准确制备的样品进行检测的实验室试验。负载缓慢增加，并且是始终处于监视之下。最大强度或压力是可以在原始交汇区域分开的最大负载。对于大多数的设计材料来讲，其最大强度是将会被准确测出并给出。
假如某一部分承受的载荷超过了他的最大强度值，它就将断裂。在大多数的设计结构中人们希望的是结构不会崩溃。所以，设计是基于更小的有效值，它通常被称作允许压力或设计压力。举个例子，假如一个确定的钢坯是已知有最大强度值110000每平方英寸磅，一个低一点的强度将会被用于其设计，比如55000每平方英寸磅，这个允许强度将会承认最大强度的一半。最大强度值与允许强度值的比值被称作安全系数
允许强度值
最大强度值安全系数= or A U S S =n 我们用S 表示最大强度或者最大允许压力，用σ表示材料受到的实际负载，即
σ≤S A
这个所谓的安全系数包括了很多缺点。其中包括负载的不确定性，材料性能的不确定性，以及压力分析的不准确度等因素。它可以更准确的被称为忽略系数！事实上，分析得更准确、更广泛、更昂贵，安全系数的必要性旧越小。
4. 失败理论
在单向结构下的简单结构因素的失败很容易就可以联系到材料的可伸长强度。就像在标
准的可伸长性试验中那么有决心，但对于组成物服从于复应力（正应力或剪应力）来说， 位置就不那么简单了，并且几个失败理论已经被提出了。三个最常用的理论如下所示：
最大主应力理论：当主应力中的一个达到简单张力σ’e 下的失败值时，那么假定的一
个成员也会失败.简单张力中的失败点被视为屈服点负载，或者是材料的伸长强度，它是被一个合适的安全系数划分的。
最大剪应力理论：假定当最大剪应力达到简单张力下的失败点的值时，失败会出现在复
杂的手里系统中。
对于一个有联合作用力的系统，存在以下三个剪应力最大值：
22
11σστ-±=，23
22σστ-±=，21
33σστ-±= （1.10）
在张力试验中， 2'e
e στ= （1.11）
最大剪应力取决于主应力的方向和大小，并且在二维的压力系统中，比如在薄壁压力容
器的壁上，剪应力的最大值可以从代入σ3=0到公式1.10中得到。最大剪应力理论经常会被称为“特雷斯卡理论”或“盖斯特理论”。
最大应变能理论：当单位体积所承受的应变力达到使其在简单张力中达到屈服点后，假
定的负载受力系统会崩溃.
最大剪应力理论已经被发现适合于预测易延展的材料在复杂载荷下的屈服点，并且也是
应用在压力容器设计中的普遍准则。
Reading material 4
Stresses in Cylindrical Shells due to Internal Pressure
The classic equation for determining stress in a thin cylindrical shell subjected to pressure is
obtained from Fig.1.16. Summation of forces perpendicular to plane ABCD gives
Lt r PL σθ22=? or t Pr =
σθ (1.17) where P = pressure, L = length of cylinder, σθ= hoop stress, r = radius, t = thickness.
The strain εθ is defined as ngth
OriginalLe ngth OriginalLe h FinalLengt -=εθ and from Fig.1.17. , rr
rr W r πππεθ22)(2-+=
or r W =εθ (1.18) Also, dr dW =εθ (1.19) The radial deflection of a cylindrical shell subjected to internal pressure is obtained by substituting
the quantity into Eq.(1.18). Hence for thin cylinders Et
P W r 2= (1.20) where w = radial deflection, E = modulus of elasticity.
Equations (1.17) and (1.20) give accurate results when t r >10. As decreases, however, a
more accurate expression is needed because the stress distribution through the thickness is not
uniform. Recourse is then made to the "thick shell" theory first developed by Lame. The derived
equations are based on the forces and stresses shown in Fig.1.18. The theory assumes that all
shearing stresses are zero due to symmetry and a plane that is normal to the longitudinal axes
before pressure is applied remains plane pressurization. In other words,
ε1 is constant at any cross section.
A relationship between σr and σθ can be obtained by taking a free-body diagram of
ring dr as shown in Fig.1.18b. Summing forces in the vertical direction and neglecting
higher-order terms, we then have
dr d r r σσσθ=-
(1.21)
A second relationship is written as )]()1([)21)(1()]
()1([)21)(1()]
()1([)21)(1(1111εεεεεεεσεεεσθθθθμμμμμμμμμμμμr r r r E E E ++--+=++--+=++--+=
(1.22) Substituting Eq.(1.18) and (1.19) into the first two expressions of Eq. (1.22) and substituting the
result into Eq.(1,21) results in 012
22=-+r r d dr d r d ωωω
A solution of this equation is r
B Ar +
=ω (1.23) where A and B are constants of integration and determined by first substituting Eq.(1.23) into the
first one of Eq.(1.22) and then applying the boundary conditions
p i r -=σ
at r i r = and p r οσ-= at r r ο= Expression (1.23) then becomes )])(1())(21([)(1222222221P P r r r P r P r r r i i i i i Er r οοοοομμμωμε-++----+
-=(1.24) Once ω is obtained, the values of σθ are determined from Eqs.(1.18), and (1.19), and (1.22)
and expressed for thick cylinders as r r r r r p p r p r p r
r r r r p p r p r p i i i i
i r i i i i i 22222222222222))(())((--+--=--+-=οοοοοοοοοοθσ
σ
(1.25) where σr = radial stress σθ = hoop stress p i = internal pressure. p ο = external pressure
r i
= inside radius r ο = outside radius r = radius at any point The longitudinal stress in a thick cylinder is obtained by substituting Eqs.(1.18), (1.19), and (1.24) into the last expression of Eqs.(1.22) to give r r r p r p i
i i E 222211)(2--+=οοομεσ This equation indicates that σ1 is constant throughout a cross section because ε1 is constant
and r does not appear in the second term. Thus the expression
σ1 can be obtained from
statics as r r r p r p i
i i 22221--=οοοσ (1.26) With σ1 known, Eq.(1.24) for the deflection of a cylinder can be expressed as
)()1()()21)((222
2222r r r r p p r p r p r i o o i o i o o i i Er -+-+--=μμω (1.27)
阅读材料4
圆筒柱体壳由内力引起的应力
对确定薄圆柱壳受到压力的压力方程经典是从Fig.1.16得出的。对垂直与平面ABCD 的合力有
Lt r PL σθ22=? 或 t Pr =
σθ 其中：P =压力，L=圆柱的长度，σθ=环向应力，r=半径，t=厚度。
应变定义为 n g t h
O r i g i n a l L e n g t h O r i g i n a l L e h F i n a l L e n g t -=εθ 由方程1.17.得 rr
rr W r πππεθ22)(2-+= 或 r W =εθ (1.18)
或 dr
dW =εθ (1.19) 代入方程1.18得到在内部压力作用下圆柱壳的径向变形。因此，薄柱体 Et
P W r 2= (1.20) 其中w =径向位移，E=弹性模量。 当t r >10时由方程（1.17）和（1.20）可以得到准确的结果。随着t r 降低，然而，就需
要一个更为准确的表达式，因为通过壁厚度应力分布的不均匀。于是Lame 首次提出了“厚壳”理论。派生方程是根据在Fig.1.18所示的力和应力得到的。该理论假设由于对称所有剪力都是零，由于平面是在正常压力作用于纵轴剪应力仍然平面加压。换句话说，就是应变发生在任何截面。
σr 和σθ之间的关系，可以由环何体在图所示1.18b 获得。忽视高阶条件的话在垂直方向的合力有 dr d r r σσσθ=- (1.21) 第二个关系写成：
)]()1([)21)(1()]
()1([)21)(1()]
()1([)21)(1(1111εεεεεεεσεεεσθθθθμμμμμμμμμμμμr r r r E E E ++--+=++--+=++--+=
(1.22) 把方程1.18和1.19带到1.22前两个方程表达式和代入方程，得到的结果再代入1.21式得
01222=-+r
r d dr d r d ωωω
这个方程的解 r B Ar +=ω (1.23) 其中A 和B 是积分常数并由1.23的第一代方程代入方程1.22的第一个决定，然后运用边界
条件确定有p i r -=σ
或 r i r = 和 p r οσ-= 或 r r ο= 表达1.23就写成：)])(1())(21([)(1
222
222221P P r r r P r P r r r i i i i i Er r οοοοομμμωμε-++----+-=(1.24) 一旦得出w ，
σθ的值由1.18和1.19和1.22确定，薄壁可以这么表达： r r r r r p p r p r p r r r r r p p r p r p i i i i i r i i i i i 2222222222222
2)
)(())((--+--=--+-=οοοοοοοοοοθσσ
其中σr =径向应力， σθ=圆周应力，p i
=内部压力， p ο=外部压力， r i =外半径，r ο=内半径， r =任何方向上的半径。
在厚圆筒纵向应力可以由 1.18，1.19和 1.24代入 1.22最后一个表达式得出：r r r p r p i
i i E 222211)(2--+=οοομεσ 这个方程表明，σ1在整个横截面内是恒定不变，因为ε1不变和r 并没有出现在。因此，可以由静态方程得出表达式：r r r p r p i
i i 22221--=οοοσ σ1已知，方程1.24为圆柱体的偏转方程可以表示为：)()
1()()21)((222
2222r r r
r p p r p r p r i
o o i o i o o i i Er -+-+--=μμω
Reading Material 5
static and Dynamic Balance 。f Rotating Bodies
The unbalance of a single disk can detected by allowing the disk to rotate on its ax1e between two parallel knife-edges ，as shown in Fig ．1．22．The disk will rotate and come to rest with the heavy side on the bottom ．This type of unbalance is called static unbalance ，since it can be detected by static means ．
Fig.1.22 System with static unbalance Fig ．1．23 System with dynamic unbalance In general ，the mass of a rotor is distributed along the shaft such as in a motor armature or an automobile —engine crankshaft ．A test similar to the one above may indicate that such parts are in static balance ，but the system may show a considerable unbalance when rotated ．
As an illustration ，consider a shaft with two disks ，as shown in Fig ．1．23．If the two unbalance weights are equal and 180 deg ．apart ，the system will be statically balanced about the axis of the shaft.However ，when the system is rotated ，each unbalanced disk would set up a rotating centrifugal force tending to rock the shaft on its bearings ．Since this type of
unbalance results only from rotation we refer to it as dynamic unbalance ．
Fig.1.24 shows a general case where the system is both statically and dynamically Unbalanced. It will now be shown that the unbalanced forces P and Q can always be eliminated by the addition of two correction weights in any two parallel planes of rotation ．
Fig.1.24 Balancing of rotating bodies requires correction in two planes 。 Consider first the unbalance force P ，which can be replaced by two parallel forces Pa/l and Pb/l.In a similar manner Q can be replaced by two parallel forces Qc/l and
Qd/l ．The two forces in each plane can then be combined into a single resultant force that can be balanced by a single correction weight as shown ．The two correction weights C 1 and C 2 introduced in the two parallel planes completely balanced P and Q ，and the system is statically and dynamically balanced ．It should be further emphasized that a dynamically balanced system is also statically balanced ．The converse ，however ，is not always true ；a statically balanced system may be dynamically unbalanced ．
Example A rotor 4 in ．long has an unbalance of 3 oz ．in ．in a plane 1 in ．from the left end ．and 2 oz ．in ．in the middle plane ．Its angular position is 90 deg ．in the clockwise direction from the first unbalance when viewed from the left end ．Determine the corrections in the two end planes ，giving magnitude and angular
positions ．
Fig ．1．25
Solution ．The 3- oz ．in ．unbalance is equivalent to 2*1/4 oz.in.at the left end And3/4 oz.in.at the right end ，as shown in Fig ．1．25．The 2 oz ．in ．at the middle is obviously equal to 1 oz ．in ．at the ends ．
Combining the two unbalances at each end ，the corrections are:
Left end ：
()47.202512
21=+=C oz ．in ．to be removed '02425
.21tan 11o ==-θ clockwise from plane of first unbalance Right end ：
25.114322
2=+??? ??=C oz.in.to be removed o 5375
.01tan 11==-θClockwise from plane of first unbalance (Selected from ：William T ．Thomson ．Vibration Theory and Applications ．Prentice
Hall Inc ．,1965)
阅读材料5
旋转体的静态和动态平衡
失衡的单个圆盘允许在轮轴间的刀刃平行线上旋转，如图1.22所示。该圆盘将旋转和停止在底部的同一侧，这类失衡称为静不定，因为它可以用静态平衡来检测。
通常，一般的转子都会安装在前轴，例如电 动 机 电 枢 或汽 车 发 动 机 曲 轴，类似于上述的一个试验可以表明，这种零件处于静态平衡，但是当系统旋转时就失衡了。
举例说明，两个圆盘套在一根轴上，如图1.23，如果两个不等重的圆盘处于平衡，质心位于轴的两侧且两质心成180°，系统会沿轴处于静态平衡。然而，当系统旋转时，各个失衡的圆盘会受到一个离心力的作用而沿其轴承摆动。由于这类旋转而导致的不平衡我们称为动态失衡。
图1.24所示的是一般情况下系统的静态和动态的失衡。由图现在可看到不平衡的力P 和Q
总是会被去除而由另外两个校正用量处在任何两个平行平面旋转
不平衡的力P 可两个平行力P 和P 。类似的力Q 也可分解为两个平行的力Q 和Q 。每两个力又可在各自的面上合成一个力与单个校正重量平衡。 这两个校正重量C1和C2在两个平行的面上分别与力P 和Q 平衡，这时系统处于静态和动态的平衡。需要强调的是一个处于平衡的系统同时也会处于静态平衡。相反的情况可能就会不成立，处于平衡的系统可能会处于动态的失衡中。
举例 一个4英寸的转子在距离最左边一英寸的一个平面上有3盎司的重量，在中心面上有2盎司的重量，从左边看去第一个不平衡点顺时针方向两者成90°。校正重量分别在两个端面上，角度处于两不平衡点的角度里
解答 3盎司不平衡重量相当于左边平面2.24盎司的重量和右边的0.75盎司的重量，如图
1.25所示。中部2盎司的重量显然等于两端1盎司的重量之和。
分别合成两端的不平衡量，得校正量：
左端：
47.2)25.2(1c 221=+=
盎司 024tan '1125.21οθ==
- 第一个不平衡点的顺时针方向 右端： 25.11)43(c
222=+= 盎司 ?==-5375.01tan 12θ
第一个不平衡点的逆时针方向 (摘自：William T. Thomoson, 《振动理论及应用》普伦蒂斯霍尔公司 ,1965.）
Reading material 6
Stainless steel
Stainless steels do not rust in the atmosphere as most other steels do. The term "stainless" implies a resistance to staining, rusting, and pitting in the air, moist and polluted as it is, and generally defines a chromium content in excess of 11% but less than 30%. And the fact that the stuff is "steel" means that the base is iron.
Stainless steels have room-temperature yield strengths that range from 205 MPa (30 ksi) to more than 1725 MPa (250 ksi). Operating temperatures around 750 C (1400 F) are reached. At the other extreme of temperature some stainless steels maintain their toughness down to temperatures approaching absolute zero.
With specific restrictions in certain types, the stainless steels can be shaped and fabricated in conventional ways. They can be produced and used in the as-cast condition; shapes can be
produced by powder-metallurgy techniques; cast ingots can be rolled or forged (and this accounts for the greatest tonnage by far). The rolled product can be drawn, bent, extruded, or spun.
Stainless steel can be further shaped by machining, and it can be joined by soldering, brazing, and welding. It can be used as an integral cladding on plain carbon or low-alloy steels.
The generic term "stainless steel" covers scores of standard compositions as well as variations bearing company trade names and special alloys made for particular applications. Stainless steels vary in their composition from a fairly simple alloy of, essentially, iron with 11% chromium, to complex alloys that include 30% chromium, substantial quantities of nickel, and half a dozen other effective elements. At the high-chromium, high-nickel end of the range they merge into other groups of heat-resisting alloys, and one has to be arbitrary about a cutoff point. If the alloy content is so high that the iron content is about half, however, the alloy falls outside the stainless family. Even with these imposed restrictions on composition, the range is great, and naturally, the properties that affect fabrication and use vary enormously. It is obviously not enough to specify simply a "stainless steel".
Classification The various specifying bodies categorize stainless steels according to chemical composition and other properties. However, all the stainless steels, whatever specifications they conform to, can be conveniently classified into six major classes that represent three distinct types of alloy constitution, or structure. These classes are ferritic, martensitic, authentic, manganese-substituted authentic, duplex authentic terrific, and precipitation-hardening. Each class is briefly described below. (1) ferrous stainless s teels: This class is so named because the crystal structure of the steel is the same as that of iron at room temperature. The alloys in the class are magnetic at room temperature and up to their Curie temperature (about 750 C; 1400 F). Common alloys in the ferrous class contain between 11% and 29% chromium, no nickel, and very little carbon in the wrought condition. (2) Martensitic stainless steels; Stainless steels of this class, which necessarily contain more than 11% chromium, have such a great hardenability that substantial thickness will harden during air cooling, and nothing more drastic than oil quenching is ever required. The hardness of the as-quenched martensitic stainless steel depend on its carbon content. However, the development of mechanical properties through quenching and tempering is inevitably associated with increased susceptibility to corrosion. (3) authentic stainless steels: The traditional and familiar authentic stainless steels have a composition that contains sufficient chromium to offer corrosion resistance, together with nickel to ensure austerity at room temperature and below. The basic authentic composition is the familiar 18% chromium, 8% nickel alloy. Both chromium and nickel contents can be increased to improve corrosion resistance, and additional elements (most commonly molybdenum) can be added to further enhance corrosion resistance. (4) Manganese-substituted authentic stainless stee ls: The authentic structure can be encouraged by elements other than nickel, and the substitution of manganese and nitrogen produces a class that we believe is sufficiently different in its properties to be separated from the chromium-nickel authentic class just described. The most important difference lies in the higher strength of the manganese-substituted alloys. (5) Duplex authentic-ferrous stainless steles: The structure of these steels is a hybrid of the structures of ferrite and austerity; and the mechanical properties likewise combine qualities of each component steel type. The duplex steels combine desirable corrosion and mechanical properties, and their use is as a result increasing in both wrought and cast form. (6) Precipitation-hardening stainless steels: Stainless steels can be designed so that their composition is amenable to precipitation hardening. This class cuts across two of the other classes, to give us martensitic and authentic precipitation-hardening stainless steels. In this class we find stainless steels with the greatest useful strength as well as the highest useful operating temperature.
Properties In selection of stainless steels, three kinds of properties have to be considered:
(1) Physical properties: density, thermal conductivity, electrical resistivity, and so on; (2) Mechanical properties: strength, ductility, hardness, creep resistance, fatigue, and so on; and (3) corrosion-resistant properties. Note that properties of stainless steels are substantially influenced by chemical composition and microstructure. Hence specifications include chemical composition, or, more correctly, an analysis of the most important elements (traces of unreported elements also may be present) as well as a heat treatment that provides the optimum structure.
Applications Since stainless steels were first used in cutlery industry, the number of applications has increased dramatically. The relative importance of the major fields of application for flat and long stainless steel products is shown in Table 1. Chemical and power engineering is the largest market for both long and flat products. It began in about 1920 with the nitric acid industry. Today, it includes an extremely diversified range of service conditions, including nuclear reactor vessels, heat exchangers, oil industry tubular, components for the chemical processing and pulp and paper industries, furnace parts, and boilers used in fossil fuel electric power plants.
阅读材料6
不锈钢
不锈钢不像大多数其他钢一样在大气中会生锈。术语“不锈钢”意味着抵抗染色，生锈，和在空气中的潮湿、污染，一般定义铬含量大于11％，但低于30％，。而事实是“钢”基本体是指铁。
不锈钢的室温屈服强度，范围从205兆帕（30 ksi）的超过1725兆帕（250 ksi）的。操作温度达到约750℃（1400 F）。在一些温度下不锈钢韧性下降到零的一个极端。
由于在某些类型的特定限制，不锈钢制成了能够用常规方法制备。它们可以生产和铸条件下使用;形状可以通过粉末冶金技术生产;铸锭可以扎制或锻造（目前此数量是最大）。轧制产品可以得出，弯曲，挤压，或旋转。不锈钢可以进一步塑造加工，并且可以加入了焊，钎焊，焊接。它可以作为对普通碳钢或低合金钢积分包围。
通用术语“不锈钢”包括数十标准成分的变化以及轴承公司，贸易名称和特定的应用作出特殊合金。不锈钢的组成各有不同，从一个相当简单的合金，基本上，11％的铬铁，其中包括30％的铬，镍的大量，以及50个其他有效成分复杂的合金。在高铬，高镍范围最后他们融入其他群体热耐热合金，一个要一个任意的分界点。如果合金含量像铁含量的一半左右如此之高的话，就不属于合金不锈钢家庭。即使对这些构成限制，范围是大的，自然的属性影响制造和使用有很大不同。这显然是不够的，规定仅仅是“不锈钢”。
分类机构的分类是根据不锈钢的化学成分和其他结构。但是，所有不锈钢，只要他们符合规格，可方便地分为6个不同类型结构的主要类别。这些类是铁素体，马氏体，奥式体，锰代奥式体，奥氏体—铁素体和沉淀硬化体。每一类下面简要介绍。（1）黑色不锈钢：这
个类是这样命名的，因为钢材的晶体结构是和在室温下的铁的结构是相同。此类的磁性合金在室温达到他们的居里温度（约750C; 1400 F）。在有色金属类普通合金含有11％至29％的铬，无镍，以及很少的碳造成的。（2）马氏体不锈钢;这一类，它必然包含超过11％的铬不锈钢，有这样一个大的淬透性的使它在空气冷却变硬，也不需要多的油淬要求。作为淬马氏体不锈钢的硬度取决于其碳含量。然而，通过淬火发展的机械性能和锻炼无可避免会出现腐蚀的易感性的增加。（3）奥氏体不锈钢：相似和传统奥氏体不锈钢有一个组成，其中包含提供足够耐腐蚀的铬和镍，确保在室温下紧缩。基本真实的组成是熟悉的18％的铬，镍合金8％。双方铬和镍含量可提高可改善耐腐蚀性，和（最常见的钼）添加可以到进一步提高耐腐蚀性。（4）锰代铬奥氏体不锈钢：在奥氏体的结构可以通过其他的元素，镍，锰和氮生成的类，我们认为有足够的不同，在其属性是从铬镍分离真正替代的描述。最重要的区别在于锰取代合金高强度。（5）奥氏体—铁素体双相不锈钢：这些钢的结构是一个紧缩的铁素体和混合结构和力学性能同样结合每个组件的钢种质量。双相钢抗腐蚀和机械性能的理想结合，其用途是作为增加锻造和铸造的形式。（6）沉淀硬化型不锈钢：此不锈钢设计可以使他们的组成是经得起沉淀硬化。在其他类的两个类削减，给我们马氏体和奥氏体的沉淀硬化不锈钢。在这个类，我们找到最有用的实力以及有益的工作温度最高的不锈钢。
属性不锈钢的选择有3种的属性，必须考虑：（1）物理性能：密度，导热系数，电阻率，等等;（2）机械特性：强度，塑性，硬度，抗蠕变，疲劳等;（3）耐腐蚀特性。请注意，不锈钢性能大幅化学成分和显微组织的影响。因此，规范包括化学成分，或者更正确，一个最重要的因素分析（痕迹也可能存在未报告的内容）以及热处理，提供了最佳的结构。
应用由于不锈钢餐具首次在工业中，用的人数剧增。对平面和长的不锈钢产品，如表1所示的应用的主要领域的相对重要性。化工，电力工程是在长期和平板产品的最大市场。它始于1920年左右与硝酸行业。今天，它包括了服务条件极为多样化，包括核反应容器，换热器，石油行业的管道，用于化学加工和纸浆和造纸工业，炉零件组件的范围，并在化石燃料的发电厂使用的锅炉。
表1
Reading Material 7
Standard Mechanical Texts
To summarize the previous discussion, it is very important to know the strength of a material, both for its eventual use and also to determine the forces required to shape it. Since it is impracticable to test every article after it has been designed and made, several simple general tests are used to measure the mechanical properties of the stock material before, during and after manufacture of the final product.
(1)Tensile Tests
The simplest and most widely accepted tensile test requires a cylindrical (or flat) bar with enlarged ends. This tensile specimen is subjected to a steadily increasing tensile force along its
axis, and the extension of a gauge length is accurately measured as the load-extension curve, according to the appropriate standard. The results usually required are the maximum tensile stress, the yield stress, the percentage elongation to fracture and the reduction of
cross-sectional area at fracture. In addition, the Young’s Modulus of Elasticity, or Young Modulus may be measured.
(2)Compression Tests
It is important for metal forming calculations to know the yield stress at much higher strains than can be obtained in tension. Axial compression of a short cylinder may be used, with suitable correction for the frictional resistance on the flat ends, but a more accurate result is obtained by the transverse plane strain compression of a well-lubricated strip
(3)Hardness Testing
Tensile and compression tests are destructive of the sample, but it is often important to check the strength properties of stock material or finished components, without destruction. There are several types of hardness test for this purpose, which make only a small indentation in the surface.
The oldest and best known hardness tests in the U.K are the Brinell test in which a standard ball (usually 10 mm dia.) is pressed into a metal under a prescribed load, typically 330kgf (=29.42 kN or 6615lbf), and the Vickers test. The brinell Hardness Number (BHN or HB) is defined as the load in kgf divided by the actual spherical surface area of the indentation in mm2.Likewise, the Vickers Hardness Number (VHN or HV) is the load in kgf divided by the pyramidal surface area (again in mm2) of the indentation.
In the U.S.A., the Rockwell test is favored. In that test the depth of the indentation is measured whilst the load is still being applied (rather than the lateral dimensions). The Rockwell Hardness Number is designated as HR.
(4)Fatigue Tests
A very important phenomenon is called fatigue. It has been recognized for many years that static tensile of compressive testing is not adequate for predicting the strength of components subjected to vibration or repeated loading. These can fail at much lower stress levels, and there is a general relationship (due to Goodman) which shows the allowable oscillating stress level for a given mean stress. Fatigue testing needs considerable time, since each point n the final graph of applied stress S against the number N of cycles to failure requires a new specimen and N is usually between 106 and 108. For many non-ferrous alloys the S-N curve falls steadily, but for steels there is often a leveling off after some 106 to 107 cycles. It the stress does not exceed this endurance limit, the specimen will last indefinitely.
Another very important failure phenomenon is that of high-stress low-cycle fatigue which is potentially dangerous in materials as disparate as animal bone and aerospace components.
(5)Impact Testing
Another important subject is that of the behavior of relatively brittle materials such as cast iron, which may fail under ever a single impact. Since it may be very important to avoid this type of fracture, impact tests have been devised in which a notched specimen is hit by a heavy pendulum. The energy absorbed is measured from the height of follow-through of the pendulum.
(6)High-Temperature tests
At high temperature the plastic deformation of materials is dominated by diffusion processes which, for metals, become evident above about 2/3 of the absolute melting temperature T m. tensile, compression or hardness tests may all be used at elevated temperatures.
金属材料专业英语 材料科学 材料科学定义 [m???'] 加工性能 .[?θ] 强度 & .[k?'r????n] &['?] .[ '?r?'b?l?t?] 抗腐蚀及耐用金属特性 , & 抗敏感及环境保护[?'l??] 化学元素'?] 元素的原子序数 原子及固体物质 原子的组织图['k?] 周期表[?'?]. 周期的；定期的 原子键结合 金属与合金['?l?i, ?'l?i] & 铁及非铁金属['?s]. [化]亚铁的；铁的，含铁的金属的特性 晶体结构['?l]n. 水晶；结晶，晶体；水晶饰品 . 水晶的；透明的，清澈的 , & 晶体结构，定向格子及单位晶格['l?]n. 格子；格架；晶格 . 使成格子状
X – X线结晶分析法[,?n?'?l] 金属结晶格子 点阵常数 's 米勒指数 金相及相律 固熔体 置换固熔体[?:??n?l] 间隙固熔体[?'??l]n. 填隙原子；节间 . 间质的；空隙的；填隙的 金属间化合物[?'t?]['k?, k?m']. 混合；合成；和解妥协；搀合 . 妥协；和解 n. 化合物；复合词；混合物 . 复合的；混合的 转变 转变点 磁性转变[m?ɡ'] 同素转变[m?ɡ']. [化]同素异形的 热平衡['θ??l]. 热的，热量的 n. 上升暖气流. 热的，热量的['?m] 自由度 临界温度
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1、应力和应变 应力和应变的概念可以通过考虑一个棱柱形杆的拉伸这样一个简单的方式来说明。一个棱柱形的杆是一个遍及它的长度方向和直轴都是恒定的横截面。在这个实例中，假设在杆的两端施加有轴向力F，并且在杆上产生了均匀的伸长或者拉紧。 通过在杆上人工分割出一个垂直于其轴的截面mm，我们可以分离出杆的部分作为自由体【如图1(b)】。在左端施加有拉力P，在另一个端有一个代表杆上被移除部分作用在仍然保存的那部分的力。这些力是连续分布在横截面的，类似于静水压力在被淹没表面的连续分布。 力的集度，也就是单位面积上的力，叫做应力，通常是用希腊字母，来表示。假设应力在横截面上是均匀分布的【如图1(b)】，我们可以很容易的看出它的合力等于集度，乘以杆的横截面积A。而且，从图1所示的物体的平衡，我们可以看出它的合力与力P必须的大小相等，方向相反。因此，我们可以得出 等式(1)可以作为棱柱形杆上均匀应力的方程。这个等式表明应力的单位是，力除以面积。当杆被力P拉伸时，如图所示，产生的应力是拉应力，如果力在方向是相反，使杆被压缩，它们就叫做压应力。 使等式(1)成立的一个必要条件是，应力，必须是均匀分布在杆的横截面上。如果轴向力P作用在横截面的形心处，那么这个条件就实现了。当力P 没有通过形心时，杆会发生弯曲，这就需要更复杂的分析。目前，我们假设所有的轴向力都是作用在横截面的形心处，除非有相反情况特别说明。同样，除非另有说明，一般也假设物体的质量是忽略的，如我们讨论图1的杆一样。
轴向力使杆产生的全部伸长量，用希腊字母δ表示【如图1(a)】，单位长度的伸长量，或者应变，可以用等式来决定。 L是杆的总长。注意应变ε是一个无量纲的量。只要应变是在杆的长度方向均匀的，应变就可以从等式(2)中准确获得。如果杆处于拉伸状态，应变就是拉应变，代表材料的伸长或者 ，那么应变就是压应变，这也就意味着杆上临近的横截面是互相靠近的。 当材料的应力和应变显示的是线性关系时，也就是线弹性。这对多数固体材料来说是极其重要的性质，包括多数金属，塑料，木材，混凝土和陶瓷。处于拉伸状态下，杆的应力和应变间的线性关系可以用简单的等式来表示。E 是比例常数，叫做材料的弹性模量。 注意E和应力有同样的单位。在英国科学家托马斯·杨(1773 ~ 1829)研究杆的弹性行为之后，弹性模量有时也叫做杨氏模量。对大多数材料来说，压缩状态下的弹性模量与处于拉伸时的弹性模量的一样的。 2、拉伸应力应变行为 一个特殊材料中应力和应变的关系是通过拉伸测试来决定的。材料的试样通常是圆棒的形式，被安置在测试机上，承受拉力。当载荷增加时，测量棒上的力和棒的伸长量。力除以横截面积可以得出棒的应力，伸长量除以伸长发生方向的长度可以得出应变。通过这种方式，材料的完整应力应变图就可以得到。 图1所示的是结构钢的应力应变图的典型形状，轴向应变显示在水平轴，对应的应力以纵坐标表示为曲线OABCDE。从O点到A点，应力和应变之间是直接成比例的，图形也是线性的。过了A点，应力应变间的线性关系就不存
修改过程装备与控制工程专业英语翻译Unit 16 压力容器及其部件 压力容器时不泄露的容器。它们有各种尺寸。最小的直径不到一英寸，最大的直径能达到150英尺甚至更大。某些是埋在地下或海洋深处，多数是安放在地上或支撑在平台上，还有一些实际上是在航天飞行器中的贮槽和液压装置中。 由于内部压力，容器被设计成各种形状和尺寸。内部的压力可能低到1英寸，水的表面压力可能达到300000多磅。普通的单层表面建筑压力是15到5000磅，虽然有很多容器的设计压力高出或低于这个范围。ASME锅炉和压力标准中第八卷第一节指定一个范围从15磅在底部到上限，然而，内部压力在3000磅以上，ASME 标准，第八卷第一节，指出考虑特殊设计的情况是必要的。 压力容器的典型部件描述如下: 圆柱壳体在石化工业中对于结构压力容器圆柱壳体是经常被用到的，它是很容易制造、安装并且维修很经济。虽然在一些场合应用载荷和外压控制，要求的厚度通常由内压决定。其他因素如热应力和不连续压力可能有要求厚度决定。 成型的封头许多的端封头和过度部分有设计工程师选择。用一种结构相对另一种依靠很多因素，如成型方法、材料成本、和空间限。一些经常应用的成型封头是: 带凸缘的封头这些封头通常在较低压力的压力设备中，例如汽油罐和锅炉。有些也应用在较高压力的但是较小直径的设备中。设计和结构的许多细节在ASME 标准，第八卷第一节中给出。 半球形封头通常，在一个给定温度和压力下半球形的要求厚度是相同直径和材料圆柱壳体的一半。假如我们用镍和钛昂贵的合金建造实心或覆盖形半球形封头，这样是很经济的。假如使用碳钢，然而，由于这高价的制造费用就不比凸缘形
材料科学与工程专业英语第三版翻译以及答案 Document serial number【KK89K-LLS98YT-SS8CB-SSUT-SST108】
UNIT 1 一、材料根深蒂固于我们生活的程度可能远远的超过了我们的想象，交通、装修、制衣、通信、娱乐（recreation）和食品生产，事实上（virtually），我们生活中的方方面面或多或少受到了材料的影响。历史上，社会的发展和进步和生产材料的能力以及操纵材料来实现他们的需求密切（intimately）相关，事实上，早期的文明就是通过材料发展的能力来命名的（石器时代、青铜时代、铁器时代）。 二、早期的人类仅仅使用（access）了非常有限数量的材料，比如自然的石头、木头、粘土（clay）、兽皮等等。随着时间的发展，通过使用技术来生产获得的材料比自然的材料具有更加优秀的性能。这些性材料包括了陶瓷（pottery）以及各种各样的金属，而且他们还发现通过添加其他物质和改变加热温度可以改变材料的性能。此时，材料的应用（utilization）完全就是一个选择的过程，也就是说，在一系列有限的材料中，根据材料的优点来选择最合适的材料，直到最近的时间内，科学家才理解了材料的基本结构以及它们的性能的关系。在过去的100年间对这些知识的获得，使对材料性质的研究变得非常时髦起来。因此，为了满足我们现代而且复杂的社会，成千上万具有不同性质的材料被研发出来，包括了金属、塑料、玻璃和纤维。 三、由于很多新的技术的发展，使我们获得了合适的材料并且使得我们的存在变得更为舒适。对一种材料性质的理解的进步往往是技术的发展的先兆，例如：如果没有合适并且没有不昂贵的钢材，或者没有其他可以替代（substitute）的东西，汽车就不可能被生产，在现代、复杂的（sophisticated）电子设备依赖于半导体（semiconducting）材料四、有时，将材料科学与工程划分为材料科学和材料工程这两个副学科（subdiscipline）是非常有用的，严格的来说，材料科学是研究材料的性能以及结构的关系，与此相反，材料工程则是基于材料结构和性能的关系，来设计和生产具有预定性
United 1 材料科学与工程 材料在我们的文化中比我们认识到的还要根深蒂固。如交通、房子、衣物，通讯、娱乐和食物的生产，实际上，我们日常生活中的每一部分都或多或少地受到材料的影响。历史上社会的发展、先进与那些能满足社会需要的材料的生产及操作能力密切相关。实际上，早期的文明就以材料的发展程度来命名，如石器时代，铜器时代。早期人们能得到的只有一些很有限的天然材料，如石头、木材、粘土等。渐渐地，他们通过技术来生产优于自然材料的新材料，这些新材料包括陶器和金属。进一步地，人们发现材料的性质可以通过加热或加入其他物质来改变。在这点上，材料的应用完全是一个选择的过程。也就是说，在一系列非常有限的材料中，根据材料的优点选择一种最适合某种应用的材料。直到最近，科学家才终于了解材料的结构要素与其特性之间的关系。这个大约是过去的 60 年中获得的认识使得材料的性质研究成为时髦。因此，成千上万的材料通过其特殊的性质得以发展来满足我们现代及复杂的社会需要。很多使我们生活舒适的技术的发展与适宜材料的获得密切相关。一种材料的先进程度通常是一种技术进步的先兆。比如，没有便宜的钢制品或其他替代品就没有汽车。在现代，复杂的电子器件取决于所谓的半导体零件. 材料科学与工程有时把材料科学与工程细分成材料科学和材料工程学科是有用的。严格地说，材料科学涉及材料到研究材料的结构和性质的关系。相反，材料工程是根据材料的结构和性质的关系来设计或操纵材料的结构以求制造出一系列可预定的性质。从功能方面来说，材料科学家的作用是发展或合成新的材料，而材料工程师是利用已有的材料创造新的产品或体系，和/或发展材料加工新技术。多数材料专业的本科毕业生被同时训练成材料科学家和材料工程师。“structure”一词是个模糊的术语值得解释。简单地说，材料的结构通常与其内在成分的排列有关。原子内的结构包括介于单个原子间的电子和原子核的相互作用。在原子水平上，结构包括原子或分子与其他相关的原子或分子的组织。在更大的结构领域上，其包括大的原子团，这些原子团通常聚集在一起，称为“微观”结构，意思是可以使用某种显微镜直接观察得到的结构。最后，结构单元可以通过肉眼看到的称为宏观结构。 “Property”一词的概念值得详细阐述。在使用中，所有材料对外部的刺激都表现出某种反应。比如，材料受到力作用会引起形变，或者抛光金属表面会反射光。材料的特征取决于其对外部刺激的反应程度。通常，材料的性质与其形状及大小无关。实际上，所有固体材料的重要性质可以概括分为六类：机械、电学、热学、磁学、光学和腐蚀性。对于每一种性质，其都有一种对特定刺激引起反应的能 力。如机械性能与施加压力引起的形变有关，包括弹性和强度。对于电性能，如电导性和介电系数，特定的刺激物是电场。固体的热学行为则可用热容和热导率来表示。磁学性质
各专业课程英文翻译(精心整理) 生物及医学专业课程汉英对照表 应用生物学 Applied Biology 医学技术 Medical Technology 细胞生物学 Cell Biology 医学 Medicine 生物学 Biology 护理麻醉学 Nurse Anesthesia 进化生物学 Evolutionary Biology 口腔外科学 Oral Surgery 海洋生物学 Marine Biology 口腔/牙科科学 Oral/Dental Sciences 微生物学 Microbiology 骨科医学 Osteopathic Medicine 分子生物学 Molecular Biology 耳科学 Otology 医学微生物学 Medical Microbiology 理疗学 Physical Therapy 口腔生物学 Oral Biology 足病医学 Podiatric Medicine 寄生物学 Parasutology 眼科学 Ophthalmology 植物生物学 Plant Physiology 预防医学 Preventive Medicine 心理生物学 Psychobiology 放射学 Radiology 放射生物学 Radiation Biology 康复咨询学 Rehabilitation Counseling 理论生物学 Theoretical Biology 康复护理学 Rehabilitation Nursing 野生生物学 Wildlife Biology 外科护理学 Surgical Nursing 环境生物学 Environmental Biology 治疗学 Therapeutics 运动生物学 Exercise Physiology 畸形学 Teratology 有机体生物学 Organismal Biology 兽医学 Veterinary Sciences 生物统计学 Biometrics 牙科卫生学 Dental Sciences 生物物理学 Biophysics 牙科科学 Dentistry 生物心理学 Biopsychology 皮肤学 Dermatology 生物统计学 Biostatistics 内分泌学 Endocrinology 生物工艺学 Biotechnology 遗传学 Genetics 生物化学 Biological Chemistry 解剖学 Anatomy 生物工程学 Biological Engineering 麻醉学 Anesthesia 生物数学 Biomathematics 临床科学 Clinical Science 生物医学科学 Biomedical Science 临床心理学 Clinical Psychology 细胞生物学和分子生物学 Celluar and Molecular Biology 精神病护理学 Psychiatric Nursing 力学专业 数学分析 Mathematical Analysis 高等代数与几何 Advanced Algebra and Geometry 常微分方程 Ordinary Differential Equation 数学物理方法 Methods in Mathematical Physics 计算方法 Numerical Methods 理论力学 Theoretical Mechanics 材料力学 Mechanics of Materials 弹性力学 Elasticity 流体力学 Fluid Mechanics 力学实验 Experiments in Solid Mechanics 机械制图 Machining Drawing 力学概论 Introduction to Mechanics 气体力学 Gas Dynamics 计算流体力学 Computational Fluid Mechanics 弹性板理论 Theory of Elastic Plates 粘性流体力学 Viscous Fluid Flow 弹性力学变分原理 Variational Principles inElasticity 有限元法 Finite Element Method 塑性力学 Introduction of Plasticity
CQ螺纹球阀CQ Thread Ball Valves L形三通式L-pattern three way T形三通式T-pattern three way 安全阀Safety valve 暗杆闸阀Inside screw nonrising stem type gate valve 百叶窗; 闸板shutter 百叶窗式挡板louver damper 摆阀式活塞泵swing gate piston pump 保温式Steam jacket type 报警阀alarm valve 报警阀; 信号阀; 脉冲阀sentinel valve 背压调节阀back pressure regulating valve 背压率Rate of back pressure 本体阀杆密封body stem seal 波纹管阀Bellows valves 波纹管密封阀bellow sealed valve 波纹管密封式Bellows seal type 波纹管平衡式安全阀Bellows seal balance safety valve 波纹管式减压阀Bellows reducing valve
波纹管式减压阀Bellows weal reducing valve 薄膜thin film 薄膜; 隔膜diaphragm 薄膜式减压阀Diaphragm reducing valve 薄型闸阀Thin Gate Valves 不封闭式Unseal type 槽车球阀Tank Lorry Ball Valves 颤振Flutter 常闭式Normally closed type 常开式Normally open type 超低温阀门Cryogenic valve 超高压阀门Super high pressure valve 超过压力Overpressure of a safety valve 衬胶隔膜阀rubber lined diaphragm 衬胶截止阀rubber lined globe valve 垂直板式蝶阀Vertical disc type butterfly valve 磁耦合截止阀Magnetic Co-operate Globe Valves 带补充载荷的安全阀Supplementary loaded safety valve 带辅助装置的安全阀Assisted safety valve
UNIT 1 一、材料根深蒂固于我们生活的程度可能远远的超过了我们的想象，交通、装修、制衣、通信、娱乐（recreation）和食品生产，事实上（virtually），我们生活中的方方面面或多或少受到了材料的影响。历史上，社会的发展和进步和生产材料的能力以及操纵材料来实现他们的需求密切（intimately）相关，事实上，早期的文明就是通过材料发展的能力来命名的（石器时代、青铜时代、铁器时代）。 二、早期的人类仅仅使用（access）了非常有限数量的材料，比如自然的石头、木头、粘土（clay）、兽皮等等。随着时间的发展，通过使用技术来生产获得的材料比自然的材料具有更加优秀的性能。这些性材料包括了陶瓷（pottery）以及各种各样的金属，而且他们还发现通过添加其他物质和改变加热温度可以改变材料的性能。此时，材料的应用（utilization）完全就是一个选择的过程，也就是说，在一系列有限的材料中，根据材料的优点来选择最合适的材料，直到最近的时间内，科学家才理解了材料的基本结构以及它们的性能的关系。在过去的100年间对这些知识的获得，使对材料性质的研究变得非常时髦起来。因此，为了满足我们现代而且复杂的社会，成千上万具有不同性质的材料被研发出来，包括了金属、塑料、玻璃和纤维。 三、由于很多新的技术的发展，使我们获得了合适的材料并且使得我们的存在变得更为舒适。对一种材料性质的理解的进步往往是技术的发展的先兆，例如：如果没有合适并且没有不昂贵的钢材，或者没有其他可以替代（substitute）的东西，汽车就不可能被生产，在现代、复杂的（sophisticated）电子设备依赖于半导体（semiconducting）材料 四、有时，将材料科学与工程划分为材料科学和材料工程这两个副学科
户外用品整理 个人装备Personal equipment ＝＝＝＝＝＝＝＝＝＝＝＝＝＝登山靴Climbing boots 防寒运动靴Snow training shoes 攀岩鞋Climbing shoes 毛衬衫Woolen Shirt 登山裤Climbing trousers 运动衣裤Training wear 毛内衣裤Woolen undershirts 毛袜Woolen socks 毛手套Woolen glove 丝手套Silk glove 棉手套Cotton glove 毛衣Sweater 冲锋衣Jaket(Windbreaker) 外裤Over-trousers 外手套Over-gloves 外鞋罩Long spats 防寒帽Bataclave 高处帽High altitude cap 太阳帽Glacier cap 太阳镜Sunglasses 睡垫Mattress 鸭绒睡垫Down sleeping bag 鸭绒衣Down jacket 鸭绒裤Down trousers 鸭绒背心Down vest 鸭绒袜Down tent shoes/slippers 睡袋套Sleeping bag cover 背包Duffel bag 整理袋Stuff bag 冰爪Grampons 冰爪带Grampons strap 冰爪袋Grampons case 外靴Over-shoes 安全帽Helmet 冰镐Ice axe(PIckel) 安全带Harness 铁锁Carabiner with safety ring 铁锁Carabmer 小绳套Sling 下降器Eight rings
Unit1： 交叉学科interdiscipline 介电常数dielectric constant 固体性质solid materials 热容heat capacity 力学性质mechanical property 电磁辐射electro-magnetic radiation 材料加工processing of materials 弹性模量（模数）elastic coefficient 1.直到最近，科学家才终于了解材料的结构要素与其特性之间的关系。It was not until relatively recent times that scientists came to understand the relationship between the structural elements of materials and their properties . 2.材料工程学主要解决材料的制造问题和材料的应用问题。Material engineering mainly to solve the problem and create material application. 3.材料的加工过程不但决定了材料的结构，同时决定了材料的特征和性能。Materials processing process is not only to de structure and decided that the material characteristic and performance. 4.材料的力学性能与其所受外力或负荷而导致的形变有关。Material mechanical properties with the extemal force or in de deformation of the load. Unit2： 先进材料advanced material 陶瓷材料ceramic material 粘土矿物clay minerals 高性能材料high performance material 合金metal alloys 移植implant to 玻璃纤维glass fiber 碳纳米管carbon nanotub 1、金属元素有许多有利电子，金属材料的许多性质可直接归功于这些电子。Metallic materials have large numbers of nonlocalized electrons，many properties of metals are directly attributable to these electrons. 2、许多聚合物材料是有机化合物，并具有大的分子结构。Many of polymers are organic compounds,and they have very large molecular structures. 3、半导体材料的典型特征介于导体材料（如金属、金属合金）与绝缘体（陶瓷材料和聚合体材料）之间。Semiconductors have electrical properties that are intermediate between the electrical conductors ( viz. metals and metal alloys ) and insulators ( viz. ceramics and polymers ). 4、生物材料不能产生毒性，并且不许与人体组织互相兼容。Biomaterials must not produce toxic substances and must be compatible with body tissues. Unit3： 微观结构microstructure 宏观结构macrostructure 化学反应chemical reaction 原子量atomic 电荷平衡balanced electrical charge 带正电子的原子核positively charge nucleu 1、从我们呼吸的空气到各种各样性质迥异的金属，成千上完中物质均是由100多种院子组成的。These same 100 atoms form thousands of different substances ranging from the air we breathe to the metal used to support tall buildings.
附录：外文翻译 5.1Introduction Cylindrical shells are used innuclear,fossil and petrochemical industries. They are also used in heat exchangers of the shell and tube type.Generally.These vessels are easy to fabricate and install and economical to maintain. The design procedures in pressure vessel codes for cylindrical shells are mostly based on linear elastic assumption,occasionally allowing for limited inelastic behavior over a localized region.The shell thickness is the major design parameter and is usually controlledby internal pressure and sometimes by external pressure which can produce buckling.Applied loads are also important in controlling thickness and so are the disconti-nuity and thermal stresses.The basic thicknesses of cylindrical shells are Based on simpli?ed stress analysis and allowable stress for the material of construction.There are some variations of the basic equations in various design codes.Some of the equations are based on thick-wall Lame equations.In this chapter such equations will be discussed.Also we shall discuss the case of cylindrical shells under external pressure where there is a propensity of buckling or collapse. 5.2 Thin-shell equations A shell is a curved plate-type structure.We shall limit our discussion to Shells of revolutions.Referring to Figure5.1 this is denoted by anangle ?,The meridional radius r1 and the conical radius r2,from the center line.The horizontal radius when the axis is vertical is r. If the shell thickness is t,with z being the coordinate across the thickness,following the convention of Flugge, We have the following stress resultants: ?-+ = 2 2 1 1) ( t t dz r z r N θ θ σ(5.1) ?-+ = 2 2 2 2) ( t t dz r z r N φ φ σ(5.2) ?-+ = 2 2 2 2) ( t t dz r z r N θφ θφ σ(5.3)
法学 Law Study 英语 English 日语 Japanese 信息与计算科学 Information and Computation Science 应用物理学 Applied Physics 冶金工程 Metallurgical Engineering 金属材料工程 Metallic Materials Engineering 无机非金属材料 Inorganic Nonmetallic Materials 材料成型及控制工程 Material Formation and controlEngineering 高分子材料与工程 Multimolecular Materials and Engineering 工业设计 Industrial Disign 建筑学 Architecture 城市规划 City Planning 艺术设计 Artistical Disign 包装工程 Packaging Engineering 机械设计制造及自动化Machine Disign,Manufacturing,and Automation 热能与动力工程 Thermal and Power Engineering 水利水电工程 WaterConservance and Electro-power Engineering 测控技术与仪器 Technique and Instrumentation of Measurements 电气工程及其自动化 Electric Engineering and its Automation 自动化 Automation 通信工程 Communication Engineering 电子信息科学与技术 Sience and Technology of Electronic Information 计算机科学与技术 Computer Sience and Technology 土木工程 Civil Engineering
目录 英文缩写词 钢号中所采用的缩写字母及其涵义 常见材料学专业名词中英文对译 对文中使用的英文缩写词说明如下： 缩写英文原文中文翻译 CQ Commercial Quality 普通级 DQ Drawing Quality 冲压级 DDQ Deep Drawing Quality 深冲级 EDDQ Extra Deep Drawing Quality 超深冲级 CSP Compact Srip Production 紧凑式带钢生产 IF Interstitial Free (Steel) 无间隙原子(钢) LC Low Carbon 低碳(钢) DSA Dynamic Strain Aging 动态应变老化 MFS Mean Flow Stress 平均流动应力 YS Yield Stress 屈服应力 DRC Dynamic Recovery 动态回复 DRX Dynamic Recrystallization 动态再结晶 SRX Static Recrystallization 静态再结晶 SRC Static Recovery 静态回复 Ti-IF Ti Interstitial Free (Steel) 含钛无间隙原子(钢) Ti-Nb IF Ti-Nb Interstitial Free (Steel) 含钛铌无间隙原子(钢) ULC Ultra Low Carbon(Steel) 超低碳钢 DSP Direct Strip Production 带钢直接生产 FTSR Flexible Thin Slab Rolling 灵活性薄板坯轧制 C.C.T Continuous Cooling Transformation 过冷奥氏体连续转变曲线 T.T.T Time Temperature Transformation 过冷奥氏体等温转变曲线SPSS Statistical Package for the Social Science 社会科学统计软件包 钢号中所采用的缩写字母及其涵义
力学的基本概念 对运动，时间和作用力作出科学分析的分支被称为力学，它由静力学和动力学两部分组成。静力学对静止系统进行分析，即在静力学系统中不考虑时间这个因素，而动力学是对随时间变化的系统进行分析。 通过配合表面作用力被传送到机器的各个部件，例如从齿轮传到轴或者是从一个齿轮通过啮合传递到另一个齿轮，从三角皮带传到皮带轮，或者从凸轮传到从动件。由于很多原因，我们必须知道这些力的大小。在边界或啮合表面作用力的分布一定要合理，他们的大小必须在构成配合表面材料的工作极限以内。例如，如果施加在滑动轴承的作用力太大，那么它就会将油膜挤压出来，并且造成金属和金属的接触，使温度过高，使滑动轴承失效。如果作用在齿轮轮齿上的力过大，就会将油膜从齿间挤压出来。这将会导致金属表层的破裂和剥落，噪音增大，运动不精确，直至报废。在力学研究中，我们主要关心力的大小，方向和作用点。 当一些物体连接在一起形成一个组合或者系统时，在两个接触的物体之间作用和反作用的力被称之为约束力。这些力约束各个物体使其处于特有的状态。作用在这个物体系统外部的力叫做外力。 电力，磁力和重力是不需要直接接触就可以施加的力的实例。不是全部但是大多数，与我们有关的力都是通过直接的实际接触或者是机械接触才能产生的。 力是一个矢量。力的要素就是它的大小，它的方向和作用点，一个力的方向包括力的作用线的概念和它的指向。因此，沿着力的作用线，力的方向有正副之分。 沿着两条不重合的平行线作用在一个物体上的两个大小相等、方向相反的作用力不能合并成一个合力。任何作用在一个刚体上的两个力构成一个力偶。力偶臂就是这两个力的作用线之间的垂直距离。 力偶矩也是一个矢量，用M表示，垂直于力偶面；M的方向主要依据右手螺旋定则确定。力矩的大小是力偶臂与其中一个力的大小的乘积。 如果一个刚体满足下列条件，那么它处于平衡状态： （1）作用在它上面的所有外力的矢量和等于零。 （2）作用在它上面的所有外力对于任何一个轴的力矩之和等于零。在数学上这两个条件被表示为 所使用的术语“刚体”可以是整台机器，一个机器中几个相互连接
Unit 19 Types of Heat Exchangers Heat exchangers are equipment primarily for transferring heat between hot and cold streams.They have separate passages for the two streams and operate continuously.The most versatile and widely used exchangers are the shell-and-tube types but various plate and other types are valuable and economically competitive or superior in some applications.These other types will be discussed briefly but most of the space following will be devoted to the shell-and-tube types primarily because of their importance but also because they are most completely documented in the literature.Thus they can be designed with a degree of confidence to fit into a process.The other types are largely proprietary and for the most part must be process designed by their manufacturers. Plate-and-Frame Exchangers Plate-and-frame exchangers are assemblies of pressed corrugated plates on a frame. Gaskets in grooves around the periphery contain the fluids and direct the flows into and out of the spaces between the plates.Close spacing and the presence of the corrugations result in high coefficients on both sides several times those of shell-and-tube equipment and fouling factors are low.he accessibility of the heat exchange surface for cleaning makes them particularly suitable for fouling services and where a high degree of sanitation is required as in food and pharmaceutical processing.Operating pressures and temperatures are limited by the natures of the available gasketing materials with usual maxima of 300 psig and 400 F. Since plate-and-frame exchangers are made by comparatively few concerns most process design information about them is proprietary but may be made available to serious engineers.Friction factors and heat transfer coefficients vary with the plate spacing and the kinds of corrugations.Pumping costs per unit of heat transfer are said to be lower than for shell-and-tube equipment.1n stainless steel construction the plate-and-frame construction cot is 50%-70% that of the shell-and-tube. Spiral Heat Exchangers In spiral heat exchangers the hot fluid enters at the center of the spiral element and flows to the periphery; flow of the cold liquid is countercurrent entering at the periphery and leaving at the center.Heat transfer coefficients are high on both sides and there is no correction to the log mean temperature difference because of the true countercurrent'action. These factors may lead to surface requirements 20% or so less than those of shell-and-tube exchangers. Spiral types generally may be superior with highly viscous fluids at moderate pressures. Compact (Plate-Fin) Exchangers Compact exchangers are used primarily for gas service.Typically they have surfaces of the order of 1200 m2 /m3 corrugation height 3.8-11.8 mm corrugation thickness 0.2-0.6 mm and fin density 230-700 fins/m.The large extended surface permits about four times the heat transfer rate per unit volume that can be achieved with shell-and-tube construction.Units have been designed for pressiIres up to 80 atm or so.The close spacings militate against fouling https://www.doczj.com/doc/1e14842032.html,mercially compact exchangers are used in cryogenic services and also for heat recovery at high temperatures in connection with gas turbines.For mobile units as