2.4Design against stress concentrations

尺寸优化方法综述Size optimization methods are crucial in various fields, including engineering, computer science, and manufacturing. These methods aim to reduce the size or dimensions of a product or system while maintaining or even improving its performance and functionality. 尺寸优化方法在各个领域都至关重要，包括工程、计算机科学和制造业。

这些方法旨在减小产品或系统的尺寸或尺寸，同时保持或甚至提高其性能和功能。

One commonly used size optimization method is topology optimization, which involves optimizing the material distribution within a given design space to achieve the best structural performance. Topology optimization algorithms iteratively remove material from non-critical areas and redistribute it to critical areas to achieve the desired objectives. 一个常用的尺寸优化方法是拓扑优化，这涉及优化给定设计空间内的材料分布，以实现最佳的结构性能。

拓扑优化算法通过迭代地从非关键区域移除材料，并将其重新分配到关键区域，以达到所需的目标。

Another approach to size optimization is shape optimization, which focuses on optimizing the geometric shape of a structure to improveits performance. Shape optimization methods involve modifying the geometry of a design to achieve desired outcomes such as reducing stress concentration, minimizing weight, or enhancing aerodynamic efficiency. 另一种尺寸优化的方法是形状优化，它着重于优化结构的几何形状以改善其性能。

英语课后重点短语LESSON 1(P15)1)the fundamental concept 基本概念2)cross section 横截面3)the internal stresses produced in the bar 棒内应力4)continuous distribution of bydrostatic pressure 净水压力的连续分布5)the tensile load 拉伸载荷6) a uniform distribution over the cross section 横截面上的均匀分布7)arbitrary cross-sectional shape 任意横截面形状8)tensile stress 拉应力9)compressive stresses 压应力10)a normal stress 正应力11)through the centroid of the cross sectional area 通过质心的横截面积12)the uniform stress condition 均应力状态13)the stress distribution at the end of the bar14)high localized stresses 局部高应力15)an axially loaded bar 轴向加载杆16)a tensile strain 拉伸应变17)an elongation or stretching of the material 延长或拉伸的材料18)a compressive strain 压应变19)the ratio of two lengths20)purely statical and geometrical considerations 从纯静态和几何关系考虑LESSON 2(P25)1)the main manifestations of capacity 功能的主要表现形式2)the maximum unit load(stress) 最大单位载荷3)stress-strain diagram 应力-应变图4)the simple tensile test 简单拉伸试验5)the percentage elongation at rupture 断裂延伸率6)the end of tensile specimens 拉伸试样的末端7)permanent deformation 永久变形8)the resulting load-displacement curve 所产生的载荷-位移曲线9) a substsntial yielding of the material 大量高产的物质10)yield point 屈服点11)the trainsition from elastic to plastic behavior12)material property table 材料性能表13)plastic defomation 塑性变形14)a specified standard length of the specimen 指定的标准试样的长度15)at the moment of rupture 在破裂时16)short cylindrical specimens 短圆柱试样17)ductile materials 任性材料18)high stress concentration 高应力集中19)ultimate tensile strength 极限抗拉强度20)strain hardening zone 应变硬化区LESSON 3(P37)1)circular cross section 圆截面2)the position of mountings 安装位置3)nominal size 标准尺寸4)length of shaft subjected to twist 轴的受扭长度5)minimize stress concentration 尽量减小应力集中6)from the standpoint of stress 从应力角度7)equations for a shaft in pure torsion 轴纯扭转的方程式8)diameter of solid shaft 实心轴的直径9)outside diameter of hollow shaft 空心轴的外径10)the amount of twist in a shaft 轴的扭转量11)torsional deflection 扭转变形12)shear modulus of elasticity 剪切弹性模量13)be closer to the vertical load 接近于垂直载荷14)the endurance limit 疲劳极限15)the allowable shearing stress 许用剪切应力16)equation for equivalent moments 方程的等效力矩17)the design stress values for flexure 设计弯曲应力值18)the angle of twist 扭转角19)antifricton bearings 滚动轴承20)the amount of twist in a shaft 轴的扭转量LESSOM 4(P51)1)herringbone gears 人字齿轮2)spiral gears 螺旋齿轮3)worn gears 蜗轮4)bevel gears 圆锥齿轮5)hypoid gears 准双曲面齿轮6)sizes of spur-gear teeth 齿轮轮齿的尺寸7)the automotive rear axle drives 汽车后桥驱动8)rack-and-pinion drives 齿条和小齿轮驱动器9)diametral pitch 径节10)pitch circle 节圆11)the tangency point 切点12)pressure angles 压力角13)an involute curve 渐开线14)the radial distant 径向距离15)at right angles 成直角16)the average number of teeth in contact17)the reciprocal of the diametral pitch 对等径节18)to change inches to millimeters 把英寸换算成毫米19)a line perpendicular to the centerlines 垂直中心线的直线20)center distance between two meshed gears 两个齿轮的中心距LESSION 5(P62)1)plate cams 盘形凸轮2)cylindrical cams 圆柱凸轮3)the cam assembles in automatic record players 汽车发动机上的凸轮组件4)cam profiles 凸轮轮廓5)make a full-scale template 制造一个实体样板6)in the course of several revolutions of the cam 在凸轮中转几圈7) a tangential plate cam 切向盘形凸轮8) a translation cam 移动凸轮9)the groove in the periphery of the cam 凸轮表面的槽10)a guided vertical reciprocated follower 做垂直运动的往复件11)a constant-diameter cam 等径凸轮12)automatic washing machines13)a face cam 面凸轮14)the edge of a pivoted follow 摆动从动件的边缘15)a reciprocating knife-edged follower 作往复运动的刀口式从动件16)miniature snap-action electrical switchies 小的速动开关17)a pivoted flat-faced follower 安装在摆臂上的滚子从动件18)air pilot values19)the abrupt change in cam profile 在凸轮轮廓上的突变20)a Scotch yoke mechanism 苏格兰的克机构LESSION 6(P73)1)developing and demanding industry 一个处在发展中社会需要的产业2)propeller shaft 传动轴3)suspension components4) a sliding splined type of joint 滑动花键连接5)two rear axle shafts 两个后半轴6)to mesh with a larger bevel gear 与更大的锥齿轮啮合7)the universal joint 万向节8) a steering wheel 转向轮9)unevenness of road surfaces 路面的不平度10)the transverse line of the axle shafts 后横半轴11)to cause excessive tyre wear 造成轮胎的过度磨损12)the exactly similar diameter 直径非常接近13)quarter-elliptic leaf springs 四分之一随圆形钢板板式弹簧14)the transmission of shock 冲击15)road surface variation 路面变化16)the final-drive gears 最终传动齿轮副17)the precise alignment of shaft 精确同轴18)a rotating drum 转动筒鼓19)a hand lever 手刹杆20)be locked in the one position 被固定某一位置LESSION 8(P99)1)bulk deformation of metals 金属的变形2)forging，rolling or extruding 锻造滚压挤压3)plastic deformation 塑性变形4)impact blows 冲击5)the recrystallization point of the mental6)hot working and cold working 热加工和冷加工7)better surface finish8)hammer forging 锤锻9)striking the hot metal 锻打热金属10)a slow squeezing action 缓慢加压11)open dies and closed dies 开模和闭模12)bevel gears with traight or helical teeth 用直齿或螺旋加工锥齿轮13)impression dies 型腔模14)each of several die cavities 每一个模膛15)mass production16)a homogeneous circumferential grain fiow 均匀的周向纤维流17)the three-dimensional description 三维描述18)computer simulation 计算机仿真19)hydraulic presses 液压压力20)be rough- and finished-machined 粗加工和精加工LESSION 9(P110)1)carrying high-amperage current 携带高安培电流2)the electrode and the work-piece 电机和工件3)the weld pool 焊接熔池4) a column of ionized gas called plasma 一个列的电离气体称为等离子体5)the oxides and nitrides 氧化物和氮化物6)the positive ions 阳离子7)deleterious substances 有害物质8)the newly solidified mental 刚凝固的金属9)in overhead welding 仰焊10)current density 电流密度11)deposition rate 沉积速率12)an unbalanced magnetic field 不平横磁场13)arc blow 电弧偏吹14)the electrode coating 电极涂层15)in overhead position 在仰焊的位置16)the cooling rate of the deposited metal 沉积金属的冷却速度17)a more homogeneous microstructure 更均匀的微观结构18)a smooth flow of molten metal 顺畅熔融19)cellulosic-coated electrodes 纤维质涂层的焊条20)perpendicular to the current path 与电路垂直LESSION 10(P123)1)plain carbon steel 碳素钢2)carbon content 碳含量3)low carbon steel 低碳钢4)medium carbon steel 中碳钢5)high carbon steel 高碳钢6)be cold worked 冷加工7)be heat treated 热处理8)contain 20 point of carbon 含20%的碳9)in the hot-rolled condition 在热轧条件下10)heat-treat-hardened plain carbon steel 热处理硬化普通碳钢11)free-machining steels 易切削钢12)hot short 热脆性13)cold shortness 冷脆性14)the isothermal transformation curves 等温移动曲线15)grain refinement 细化晶粒16)stainless steel 不锈钢17)AISI steels 美国钢铁协会钢18)Iron-carbon equilibrium diagram 铁碳平衡表19)Tool and die steel 工具钢和模具钢20)High corrosion chemical resistance 高耐腐蚀和耐化学性能LESSION 11(P134)1)allotropic materials 同素异晶材料2)plain low carbon steel 普通低碳钢3)hypoeutectiod steel 亚共析钢4)normalized steel 正火钢5)hypereutectoid steel 过共析钢6)eutectoid composistion 共析钢7)grain houndaries 晶界8)ferrite matrix 铁氧体矩阵9)about 60℃about the Ac1 temperature 大约Ac1温度以上60摄氏度10)the nose of the I-T curve I-T曲线鼻共处11)cooling rate 冷却速率12)quenching shock 淬火介质13)thermal stress 热应力14)thermal shock 热冲击15)a tempered steel 回火钢16)temper brittlement 回火脆性17)in the tempering or drawing proceduce 在回火阶段18)hardened steel 硬化钢19)full annealing 充分退火20)to dissolve all the cementite 溶解渗碳体LESSION 15(P177)1)turning，facing and boring 车削，车端面和镗孔2)split nut 对开螺母3) a single setup of the workplace 工件在一次性定位安装4)headstock assembly 主轴箱组件5)tailstock assembly 尾座组件6)carriage assembly 溜板箱组件7)lead screw and feed rod 丝杠和光杆8)two sets of parallel，longitudinal ways 两组平行的导轨9)to assure accuracy of alignment 为了保证装配的精确度10)a set of transmission gears 一套传动齿轮11)the maximum size of bar stock 棒料的最大尺寸12)gear box 齿轮箱13)a V-belt or silent-chain drive V型带和无声传动装置14)carbide and ceramic tools 硬质合金和金属陶瓷刀15)the inner ways of the end 床身的内侧导轨16)tailstock quill 尾座套筒17)a graduated scale 通常情况18)in the direction normal to the axis of rotation of the work 在垂直工件旋转轴线方向19)manual movement of the carriage 托盘的手工移动20)per revolution of the spindle 主轴旋转一周LESSION 16 (P188)1) a multiple-tooth cutter 多齿铣刀2)progressive formation 逐渐成形3)in a direction perpendicular to the axis of the cutter 在垂直刀具轴线的方向4)the metal removal rate 金属切除率5)produce good surface finish 产生好的表面光洁度6)in job-shop and tool and die work7)teeth located un the periphery of the cutter body8)slab milling 板铣9)face milling 端面铣削10)up milling 逆铣11)down milling 顺铣12)the direction of feed of the workpiece 工件的进给方向13)the clamping device 夹具14)the smoothness of the generated surface 铣削表面的平整度15)the sharpness of the cutter edges 切削刃的锋利程度16)at the end of the tooth engagement17) p rofile cutters 仿形铣刀18) c arbide- and ceramic- tipped cutters 硬质合金及陶瓷-硬质合金刀具19)negative-rake-angle cutters 负倾角刀20)arbor cutters and shank cutters 乔木刀和柄刀。

附录附录1英文原文Rolling Contact BearingsThe concern of a machine designer with ball and roller bearings is fivefold as follows:(a) life in relation to load; (b) stiffness,ie.deflections under load; (c) friction; (d) wear; (e) noise. For moderate loads and speeds the correct selection of a standard bearing on the basis of a load rating will become important where loads are high,although this is usually of less magnitude than that of the shafts or other components associated with the bearing. Where speeds are high special cooling arrangements become necessary which may increase fricitional drag. Wear is primarily associated with the introduction of contaminants,and sealing arrangements must be chosen with regard to the hostility of the environment.Because the high quality and low price of ball and roller bearing depends on quantity production,the task of the machine designer becomes one of selection rather than design. Rolling-contact bearings are generally made with steel which is through-hardened to about 900HV,although in many mechanisms special races are not provided and the interacting surfaces are hardened to about 600HV. It is not surprising that,owing to the high stresses involved,a predominant form of failure should be metal fatigue, and a good deal of work is based on accept values of life and it is general practice in bearing industry to define the load capacity of the bearing as that value below which 90 percent of a batch will exceed life of one million revolutions.Notwithstanding the fact that responsibility for basic design of ball and roller bearings rests with the bearing manufacturer, the machine designer must form a correct appreciation of the duty to be performed by the bearing and be concerned not only with bearing selection but with the conditions for correct installation.The fit of the bearing races onto the shaft or onto the housings is of critical importance because of their combined effect on the internal clearance of the bearing as well as preserving the desired degree of interference fit. Inadequate interference can induce serious trouble from fretting corrosion. The inner race is frequently located axially by against a shoulder. A radius at this point is essential for the avoidance of stress concentration and ball races are provided with a radius or chamfer to follow space for this.Where life is not the determining factor in design, it is usual to determine maximum loadingby the amount to which a bearing will deflect under load. Thus the concept of "static load-carrying capacity" is understood to mean the load that can be applied to a bearing, which is either stationary or subject to slight swiveling motions, without impairing its running qualities for subsequent rotational motion. This has been determined by practical experience as the load which when applied to a bearing results in a total deformation of 0.0025mm for a ball 25mm in diameter.The successful functioning of many bearings depends upon providing them with adequate protection against their environment, and in some circumstances the environment must be protected from lubricants or products of deterioration of the bearing design. Moreover, seals which are applied to moving parts for any purpose are of interest to tribologists because they are components of bearing systems and can only be designed satisfactorily on basis of the appropriate bearing theory.Notwithstanding their importance, the amount of research effort that has been devoted to the understanding of the behavior of seals has been small when compared with that devoted to other aspects of bearing technology.LathesLathes are widely used in industry to produce all kinds of machined parts. Some are general purpose machines, and others are used to perform highly specialized operations.Engine lathesEngine lathes, of course, are general-purpose machine used in production and maintenance shop all over the the world. Sized ranger from small bench models to huge heavy duty pieces of equipment. Many of the larger lathes come equipped with attachments not commonly found in the ordinary shop, such as automatic shop for the carriage.Tracer or Duplicating LathesThe tracer or duplicating lathe is designed o produce irregularly shaped parts automatically. The basic operation of this lathe is as fallows. A template of either a flat or three-dimensional shape is placed in a holder. A guide or pointer then moves along this shape and its movement controls that of the cutting tool. The duplication may include a square or tapered shoulder, grooves, tapers, and contours. Work such as motor shafts, spindles, pistons, rods, car axles, turbine shafts, and a variety of other objects can be turned using this type of lathe.Turret LathesWhen machining a complex workpiece on a general-purpose lathe, a great deal of time isspent changing and adjusting the several tools that are needed to complete the work. One of the first adaptations of the engine lathe which made it suitable to mass production was the addition of multi-tool in place of the tailstock. Although most turrets have six stations, some have as many as eight.High-production turret lathes are very complicated machines with a wide variety of power accessories. The principal feature of all turret lathes, however, is that the tools can perform a consecutive serials of operations in proper sequence. Once the tools have been set and adjusted, little skill is require to run out duplicate parts.Automatic Screw MachineScrew machines are similar in construction to turret lathes, except that their heads are designed to hold and feed long bars of stock. Otherwise, their is little different between them. Both are designed for multiple tooling, and both have adaptations for identical work. Originally, the turret lathe was designed as a chucking lathe for machining small casting, forgings, and irregularly shaped workpieces.The first screw machines were designed to feed bar stock and wire used in making small screw parts. Today, however, the turret lathe is frequently used with a collect attachment, and the automatic screw machine can be equipped with a chuck to hold castings.The single-spindle automatic screw machine, as its name implies, machines work on only one bar of stock at a time. A bar 16 to 20 feet long is feed through the headstock spindle and is held firmly by a collect. The machining operations are done by cutting tools mounted on the cross slide. When the machine is in operation, the spindle and the stock are rotated at selected speeds for different operations. If required, rapid reversal of spindle direction is also possible.In the single-spindle automatic screw machine, a specific length of stock is automatically fed through the spindle to a machining area. At this point, the turret and cross slide move into position and automatically perform whatever operations are required. After the machined piece is cut off, stock is again fed into the machining area and the entire cycle is repeated.Multiple-spindle automatic screw machines have from four to eight spindles located around a spindle carrier. Long bars of stock, supported at the rear of the machine,pass though these hollow spindles and are gripped by collects. With the single spindle machines, the turret indexes around the spindle. When one tool on the turret is working, the others are not. With a multiple spindle machine, however, the spindle itself index. Thus the bars of stock are carried to the various end working and side working tools. Each tool operates in only one position, but tollsoperate simultaneously. Therefore, four to eight workpieces can be machined at the same time.Vertical Turret LathesA vertical turret is basically a turret lathe that has been stood on its headstock end. It is designed to perform a variety of turning operations. It consists of a turret, a revolving table, and a side head with a square turret for holding additional tools. Operations performed by any of the tools mounted on the turret or side head can be controlled through the use of stops.Machining CentersMany of today's more sophisticated lathes are called machining centers since they are capable of performing, in addition to the normal turning operations, certain milling and drilling operations. Basically, a machining center can be thought of as being a combination turret lathe and milling machine. Additional features are sometimes included by the versatility of their machines.Numerical ControlOne of the most fundamental concepts in the area of advanced manufacturing technologies is numerical control(NC). Prior to the advent of NC, all machine tools were manually operated and controlled. Among the many limitations associated with manual control machine tools, perhaps none is more prominent than limitation of operator skills. With manual control, the quality of the product is directly related to and limited to the skills of the operator. Numerical control represents the first major step away from human control of machine tools.Numerical control means the control of machine tools and other manufacturing systems through the use of prerecorded, written symbolic instructions. Rather than operating a machine tool, an NC technician tool to be numerically controlled, it must be interfaced with a device for accepting and decoding the programmed instructions, known as a reader.Numerical control was developed to overcome the limitation of human operators, and it has done so. Numerical control machines are more accurate than manually operated machines, they can produce parts more uniformly, they are faster, and the long-run tooling costs are lower. The development of NC led to the development of several other innovations in manufacturing technology:1.Electrical discharge machining.ser cutting.3. Electron beam welding.Numerical control has also made machines tools more versatile than their manually operated predecessors. An NC machine tool can automatically produce a wide variety of parts, each involving an assortment of widely varied and complex machining processes. Numerical control has allowed manufacturers to undertake the production of products that would not have been feasible from an economic perspective using manually controlled machine tools and processes.Like so many advanced technologies, NC was born in the laboratories of the Masschusetts Institute of Technology. The concept of NC was developed in early 1950s with funding provided by the U.S.Air force. In its earliest stages, NC machines were able to make straight cuts efficiently and effectively.However,curved paths were a problem because the machine tool had to be programmed to undertake a series of horizontal and vertical steps to produce a curve. The shorter is straight lines making up the steps, the smoother is the curve. Each line segment in the steps had to be calculated.This problem led to the development in 1959 of the Automatically Programmed Tools(APT) language. This is a special programming language for NC that uses statements similar to English language to define the part geometry, describe the cutting tool configuration, and specify the necessary motions. The development of the APT language was a major step forward in the further development of NC technology. The original NC systems were vastly different from those used today. The machines had hardwired logic circuits. This instructional programs were written on punched paper, which was later to be replaced by magnetic plastic tape. A tape reader was used to interpret the instructions written on the tape for the machine. Together, all of this represented a giant step forward in the control of machine tools. However, there were a number of problems with NC at this point in its development.A major problem wad the fragility of the punched paper tape medium. It was common for the paper tape containing the programmed instructions to break or tear during a machining process. This problem was exacerbated by the fact that each programmed instructions had to be return through the reader. If it was necessary to produce 100 copies of a given part,it was also necessary to run the paper tape through the reader 100 separate times. Fragile paper tapes simply could not withstand the rigors of a shop floor environment and this kind of repeated use.This led to the development of a special magnetic plastic tape. Whereas the paper tape carried the programmed instructions as a series of holes punched in the tape, the plastic tape carried the instructions as a series of magnetic dots. The plastic tape was much stronger than thepaper taps, which solved the problem of frequent tearing and breakage. However, it still left two other problems.The most important of these was that it was difficult or impossible to change the instructions entered on the tape. To make even the most minor adjustments in a program of instructions, it necessary to interrupt machining operations and make a new tape. It was also still necessary to run the tape through the reader as many times as there were parts to be produced. Fortunately, computer technology became a reality and soon solved the problem of NC associated with punched paper and plastic tape.The development of a concept known as direct numerical control(DNC)solved the paper and plastic tape problems associated with numerical control by simply eliminating tape as the medium for carrying the programmed instructions. In direct numerical control machine tools are tied, via a data transmission link, to a host computer. Programs for operating the machine tools are stored in the host computer and fed to the machine tool as needed via the data transmission linkage. Direct numerical control represented a major step forward over punched tape and plastic tape. However, it is subject to the same limitations as all technologies that depend o a host computer. When the lost computer goes down, the machine tools also experience downtime. This problem led to the development of computer numerical control.The development of the microprocessor allowed for the development of programmable logic controllers(PNC)and microcomputer. These two technologies allowed for the development of computer numerical control(CNC). With CNC, each machine tool has a PLC or a microcomputer that serves the same purpose. This allows programs to be input and stored at each individual machine tool. It also allows programs to be developed off-line and download at the individual machine tool. CNC solved the problems associated with downtime of the host computer, but it introduced another known as data management. The same program might be loaded on ten different being solved by local area networks that connect microcomputer for better data management.CNC machine tool feed motion systems CNC machine tool feed motion systems, especially to the outline of the control of movement into the system, must be addressed to the movement into the position and velocity at the same time the realization of two aspects of automatic control, as compared with the general machine tools, require more feed system high positioning accuracy and good dynamic response.A typical closed-loop control of CNC machine tool feed system, usually by comparing the location of amplification unit, drive unit, mechanical transmission components, such as feedbackand testing of several parts. Here as mechanical gear-driven source refers to the movement of the rotary table into a linear motion of the entire mechanical transmission chain, including the deceleration device, turning the lead screw nut become mobile and vice-oriented components and so on. To ensure that the CNC machine tool feed drive system, precision, sensitivity and stability, the design of the mechanical parts of the general requirement is to eliminate the gap, reducing friction, reducing the movement of inertia to improve the transmission accuracy and stiffness. In addition, the feeding system load changes in the larger, demanding response characteristics, so for the stiffness, inertia matching the requirements are very high.Linear Roller GuidesIn order to meet these requirements, the use of CNC machine tools in general low-friction transmission vice, such as anti-friction sliding rail, rail rolling and hydrostatic guideways, ball screws, etc.; transmission components to ensure accuracy, the use of pre-rational, the form of a reasonable support to enhance the stiffness of transmission; deceleration than the best choice to improve the resolution of machine tools and systems converted to the driveshaft on the reduction of inertia; as far as possible the elimination of drive space and reduce dead-zone inverse error and improve displacement precision.Linear Roller Guides outstanding advantage is seamless, and can impose pre-compression. By the rail body, the slider, ball, cage, end caps and so on. Also known as linear rolling guide unit. Use a fixed guide body without moving parts, the slider fixed on the moving parts. When the slider moves along the rail body, ball and slider in the guide of the arc between the straight and through the rolling bed cover of Rolling Road, from the work load to non-work load, and then rolling back work load, constant circulation, so as to guide and move the slider between the rolling into a ball.附录2中文翻译滚动轴承对于球轴承和滚子轴承，一个机械设计人员应该考虑下面五个方面：（a)寿命与载荷关系；（b）刚度，也就是在载荷作用下的变形；（c）摩擦；（d）磨损；（e）噪声。

Res Nondestr Eval(1996)8:83–100©1996Springer-Verlag New York Inc.Effect of Stress Concentration on Magnetic Flux Leakage Signals from Blind-Hole Defects in Stressed Pipeline Steel T.W.Krause,R.W.Little,R.Barnes,R.M.Donaldson,B.Ma,and D.L.Atherton Department of Physics,Queen’s University,Kingston,Ontario,K7L3N6,CanadaAbstract.Stress-dependent magneticflux leakage(MFL)signals of the normal surface compo-nent(radial)MFL signal from blind-hole defects in pipeline steel were investigated.Three different stress rigs with uniaxial stress andfield configurations were used.A double-peak feature in the MFL signal was defined quantitatively by a saddle amplitude,which was taken as the difference between the average of the double peaks and the corresponding saddle point.Results indicated that the saddle amplitude increased linearly with increasing tensile surface stress and decreased, or did not exist,for increasing compressive surface stress.The stress-dependent saddle amplitude was shown to increase with increasing defect depth.Finite-element calculations indicated that stress concentration also increased with increasing defect depth.The measurements and analy-sis demonstrate that the stress-dependent saddle amplitude behavior in the radial MFL signal is associated with surface-stress concentrations near the blind-hole defects.IntroductionMagneticflux leakage(MFL)techniques are commonly used for the in-line inspection of pipelines for metal loss defects such as corrosion pits[1].The in-service operating pressures of gas pipelines generate large circumferential stresses that may reach70%of the yield strength of the pipe.These in-service stresses affect theflux leakage patterns and have been studied previously[2]–[7].In the presence of stress,defects act as“stress raisers”[8].Dependent upon the defect depth[9],the defects may generate stress con-centrations that exceed the yield strength in their vicinity.Stress raising around defects also may lead to enhanced stress corrosion cracking[10].There are two effects that may contribute to the generation of the stress-dependent MFL signal:1)the bulk effect of stress on the magnetic properties[11]–[16]and2)the effect of the defect as a stress raiser that is also dependent on the depth of the defect [9].Metal loss resulting from increasing defect depth increases the level of magnetic saturation in the vicinity of the defect and,therefore,increases the MFL signal.Similarly, by affecting the stress-dependent magnetic properties of the steel in the vicinity of the defect,the application of a bulk stress also affects the peak-to-peak MFL(MFL pp) signal.Stress concentrations in the vicinity of the defect have a similar effect.From a previous consideration[17],under a bending stress the two-dimensional solution for a100%through-wall defect or hole generates a peak stress level at the edge of the84Krause et al. hole that is2.4times that of the nominal background stress[8,17].Finite-element calculations and stress measurements[17]indicate that,for the same bending stress,the stress concentration for a round-bottomed pit that is50%of the through-wall thickness is1.2times the nominal stress.For a plate under uniform tensile stress,the maximum stress at the edge of a full cylindrical through-hole is three times that of the nominal stress [8,18].Stress concentrations occur at the two edges of the defect that are tangential to the applied stress direction.An increase in the pipe wallflux density typically results in an increase in the MFL signal due to increased saturation of the steel in the defect region.The effect of stress on the MFL pp signal has been shown to increase for increasingflux densities in the range of 0.65to1.24T[9,13]–[16].It is expected,therefore,that stress concentration combined with increasingflux density may similarly affect the MFL signal.Observations of a double-peak feature that increases in amplitude with increasing applied tensile stress have been made for normal-surface component(radial)MFL signals for various uniaxial orientations of stress andfield applied to pipeline steel[5,11].In particular,the amplitude of the double-peak feature(hereafter referred to as the saddle amplitude)has been observed to increase linearly with increasing levels of applied stress and has been associated with stress patterns around the defect itself[12,14].In this paper we provide evidence that strongly supports this claim.Further,it is demonstrated that the double-peak feature in the MFL signal may be associated primarily with stress concentrations that appear in the vicinity of the defect near the surface of the steel pipeline sample,and also that the stress concentration and resultant saddle amplitude in the MFL signal increase with increasing defect depth.Experimental ApparatusThe experimental apparatus is described in detail elsewhere[11,12].The apparatus used to measure the radial component of theflux leakagefield from a defect on the same side of the sample as the measuring apparatus(near side)consisted of a Hall probe,an amplifier to amplify the Hall signal,and a computer for data acquisition.The radialflux leakage signal was measured at scanned positions set at1-mm intervals(0.5mm for the semicircular pipe section)across the area of the defect.The radialflux leakage signal was taken as the average of100measurements taken at each position.Pipeline Sample and Stressing ApparatusSamples of pipeline steel used in this study were cut from a610-mm(24-in.)diameter X70steel pipe of9-mm wall thickness.Thefirst sample used was a102-mm(4-in.)wide semicircular section cut in the pipe hoop direction.Other samples used were4.27-m long axial strips that were also102mm(4in.)wide.The pipeline steel composition is given elsewhere[17].There were three separate experimental test rigs.Thefirst apparatus is the semi-circular hoop bending rig shown in Fig.1.The second and third apparatus use the single-strip beam-bending arrangement and the composite beam-bending arrangement,Magnetic Flux Leakage Signals from Blind-Hole Defects85Fig.1.The semicircular pipe section and bending stress rig for the production of surface stress in semicircular sections of pipe steel.both described elsewhere[11,12].Surface stresses up to±300MPa were applied using the three stress rigs.This is below the yield stress of the pipe steel,which is at500MPa. All three sets of apparatus have a13-mm diameter ball-milled external pit machined to50%of the steel wall thickness.The composite beam apparatus also has two more 13-mm diameter ball-milled external pits machined to depths of25and75%.An area of about40mm by40mm around the defect was stripped of its epoxy coating to expose the pipe steel.The defect area was magnetized to a maximum axialflux density of1.6T using ferrite magnets.For the semicircular pipe section,steel hingedfingers were used to couple theflux from the magnets into the steel pipe,while for the two beams,steel brushes shaped to the curvature of the beams coupledflux into the steel samples. Semicircular Pipe Section Stress RigIn thefirst stress rig,shown in Fig.1,a semicircular pipe section is held stationary by a fixed clamp,while the other is connected to a movable clamp.The movable clamp is free to travel along a horizontal threaded rod as the rod is rotated with the handle,the result being the application of a hoop-bending stress.When the clamp is moved inward,tension is created on the outside and compression on the inside pipe surface,with the opposite being true if the clamp were to be moved outward.A“clamp position versus stress”calibration was obtained theoretically[17]and verified using strain gauges(placed well away from the defect region).86Krause et al. Single BeamThe single-strip beam is a102-mm wide strip of steel cut in the axial direction from the 610-mm diameter pipe with a thickness of9mm and a length of4.27m.The low rigidity of the single beam allows bending by simply hanging masses of about5kg from one end of the beam or supporting it at a raised height while the middle length of the beam is supported and the opposite end of the beam isfixed in position.Composite BeamThe third apparatus utilizes a composite beam and an arrangement to bend the beam [11,12].The composite beam is made from two axial strips of pipeline steel that are separated at afixed distance of29mm by an alternatingfiberglass–wood composite. The composite materials are bonded together with high-strength epoxy resin.Under a bending stress the neutral axis of the beam is outside the pipeline steel regions,so that nearly uniform stress is generated through the thickness of the steel walls.Because the composite beam is much more rigid,the beam is stressed by placing it parallel to a comparably rigid pipe section of equal length separated by a wood saddle in the middle. At one end the beam and pipe are held together by a clamp or chain,and at the other end the beam and pipe are pulled together by another clamp with a scissor jack.For tests using tensile stress the steel strip with the defect in it is on the side facing away from the rigid pipe,with the composite beam above the pipe.For compressive stress the steel strip is on the side facing toward the pipe and with the beam underneath the pipe,so that the detector can be placed on top of the beam.Stress CyclesThree different procedures of applyingfield and stress are used to perform the mea-surements:1)the“normal cycle,”which involves magnetizing the beam with no applied stress and maintaining the appliedfield during the stressing of the beam;2)the“opposite cycle,”which is similar to the“normal cycle”except that the magnetization is generated with thefield in the opposite polarity;and3)the“after-cycle,”which involves removing the magnet before each stressing increment and then replacing it so that the beam is remagnetized after each change of stress.In all three methods,the defects are scanned at fixed levels of stress.Of the three cycles,the after-cycle is the most similar to an actual pipeline pigging measurement.Measurements of the peak-to-peak magneticflux leakage(MFL pp)signal in the normal-cycle mode across a50%penetration round-bottomed blind-hole–simulated de-fect for various levels of applied tensile and compressive stress in the semicircular pipe section were performed using the hoop-bending stress rig shown in Fig.1.Starting from0MPa,tensile stress up to250MPa was applied followed by changes in stress to 250MPa compressive stress and,finally,back to a0-MPa stress level.The MFL signal was recorded at various levels of applied stress.The stress in the pipe section was ad-justed by varying the distance between the ends of the semicircular pipe section in the stress rig to various strain gauge calibrated settings.Magnetic Flux Leakage Signals from Blind-Hole Defects87 For the composite beam tensile stress scans were performed,first for all three defects and stress cycles,and then followed by compressive stress scans,since a reorientation of the beam was required.No compressive stress scans were performed for the single beam.Variation of Pipeline Steel Flux DensityThe totalflux density within the semicircular pipe section was measured by removing the magnetizing system,noting theflux change,reversing the polarity of the magnetizer, applying it again,and noting theflux change again.The average of the twoflux readings was taken and theflux density within the pipe and was found to be1.54T.The totalflux density within the single-beam stress rig was determined in the same manner and was found to be1.6T.Two techniques were used to vary theflux density within the composite beam pipe wall and are described in detail elsewhere[9,13].Thefirst technique consisted of changing the size of the magnets used,and the second involved the application of partial shorting bars.The steel bars diverted some of theflux from the magnets and therefore reduced theflux density in the pipe wall.An integrating voltagefluxmeter,connected to a13-turn coil wound around one section of steel beam and through a hole in the center of the composite beam assembly,was used to determine theflux density within the pipe wall. The four pipe wallflux densities generated within the composite beam pipe wall using these two techniques were0.65T,0.84T,1.03T,and1.24T.AnalysisThe peak-to-peak radial component of the magneticflux leakage(MFL pp)signal is ob-tained by taking the difference between the maximum(positive)and minimum(negative) components of the MFL signal.Positive saddle amplitude values are obtained from the MFL signal by evaluating the difference between the average of the two positive peaks and the positive saddle point.Negative saddle amplitude values are obtained in the same manner,except that the negative double MFL peaks and the negative saddle point are used for the evaluation.Both the variation of the MFL pp signal and the saddle amplitude as functions of stress were investigated.Finite-Element CalculationsA three-dimensionalfinite-element method was used to model the stress pattern surround-ing the defect.Finite-element modeling was performed using the ANSYS Revision4.4 by Swanson Analysis Systems.A ten-node tetrahedral element with three directional degrees of freedom at each node was used to mesh the solid model.The volumes were defined using a solid modeling approach,where the geometry of the object was described by specifying key points,lines,areas,and volumes.ANSYS thenfilled in the solid model with nodes and elements based on the user-defined element shape and size.88Krause et al.Fig.2.(a)Surface and contour plots of the radial magneticflux leakage from the near side of a13-mm-diameter ball-milled50%defect in the semicircular pipe section under a tensile stress of250MPa during a normal cycle.Thefinite-element calculations modeled aflat plate with a ball-milled defect.The plate dimensions were taken as50mm×50mm with a thickness of9mm,which was the same as that of the pipeline steel samples.The radius of curvature of the ball-mill that generated the defect was taken as6.35mm.The full defect radius was,therefore,only attained at71%defect depth.This may have affected the calculations since the defect radius was changing continuously with respect to the mesh distribution up to71%of the wall thickness.Young’s modulus was taken as210GPa and Poisson’s ratio as0.28. Calculations were performed for a nominal stress of190MPa.ResultsSemicircular Pipe Section:MFL pp MeasurementsFigures2a and2b show surface and contour plots of the radial magneticflux density leakagefield over the defect for tensile and compressive stresses of250MPa,respectively. Both scans are from the normal-cycle procedure using constant magnetization.The amplitude of a signal is obtained by taking the difference between the maximum andMagnetic Flux Leakage Signals from Blind-Hole Defects89Fig.2.(b)Surface and contour plots of the radial magneticflux leakage from the near side of a13-mm-diameter ball-milled pit in the semicircular pipe section under compressive stress at250MPa during a normal cycle.minimum values offlux density over the area of the scan(MFL pp).The profile of the contours is typical for all scans,with slight variations with changing paring the two scans,a more pronounced double-peak feature is observed for the tensile surface stress case than for the compressive surface stress case.The MFL pp signal as a function of stress for the semicircular pipe section under bending-hoop stress is shown in Fig.3.Starting at0MPa,the variation of the MFL pp signal with surface stress demonstrates an initial increase with the application of tensile stress followed by a decrease and a large hysteresis loop as the stress is cycled from 250MPa to−250MPa.Under a compressive stress the variation of the MFL pp signal is smaller,as is the hysteresis.Thefinal zero-stress MFL pp signal is greater than the initial starting point.Arrows indicate the order in which the data were taken.Variation of Saddle Amplitude with StressResults obtained from an analysis of the positive and negative saddle amplitudes as a function of surface stress in the normal cycle are shown for the semicircular pipe section in Fig.4.Positive and negative saddle amplitudes are present for the zero-stress case.90Krause et al.Fig.3.Peak-to-peak MFL signal from the near side as a function of surface stress in the normal cycle for a13-mm-diameter ball-milled50%defect on the semicircular pipe section under hoop-bending stress with an applied pipe wallflux density of1.54Tesla at0MPa.Since hysteresis is present,arrows indicate the direction in which the data were taken.The positive saddle amplitude increases linearly from a minimum at250MPa compressive stress to a maximum at200MPa tensile stress.Some hystersis is evident.In comparison, the negative saddle amplitude is smaller in magnitude,more hysteretic,and slightly less linear.For the single-beam stress rig,observations of a saddle amplitude that depended linearly on stress were made for there tensile surface stress measurements equal to and greater than200MPa measured in the normal cycle.In this rig a saddle was not observed for zero or applied compressive stresses.As in the semicircular pipe section,the magnitude of the positive saddle amplitudes was greater than the corresponding negative saddle amplitudes.The variations of the positive and negative saddle amplitudes with stress for the composite beam for the three defect depths in the normal cycle at1.24T are shown in Fig.5for tensile stress values.For the composite beam no saddle was observed for any zero or compressive stress values,which is in contrast to the semicircular pipe section where a saddle amplitude that was a decreasing function of increasing compressive stress was observed.This result is considered further in the discussion.The results for the composite beam indicate an increasing variation of saddle amplitude with stress forMagnetic Flux Leakage Signals from Blind-Hole Defects91Fig.4.Positive(•)and negative( )saddle amplitudes as functions of surface stress using the semi-circular pipeline apparatus with afield of1.54T during the normal cycle are plotted for the13-mm ball-milled50%defect.increasing defect depth.For the25and50%depth defects the positive saddle amplitudes are greater in magnitude than the negative saddle amplitude values for equivalent levels of stress,while at75%this difference is not as great.The dependence of the positive and negative saddle amplitudes upon stress in the composite beam for the three different defect depths for measurements performed in the after-cycle at1.24T are shown in Fig.6.In contrast to the normal-cycle measurements for the25and50%defects,the magnitude of the negative saddle amplitudes is greater than that of the positive saddle amplitudes,while there is no observed difference between the magnitudes for the75%defect.The rate of change of the saddle amplitude with stress is greatest for the75%defect and least for the25%defect.Stress-Dependent Saddle Amplitude SlopesLinear bestfits were applied to the saddle amplitude data as a function of stress for the three different stress rigs.The slopes of saddle amplitude variation with stress for the normal cycle in the three different stress rigs are shown in Table1.Several observations can be made for the normal-cycle stress applied in the three different stress rigs.These92Krause et al.Fig.5.Saddle amplitudes as a function of stress in the composite beam apparatus from13-mm ball-milled defects in afield of1.24T in the normal cycle are plotted for the25%defect for the positive( ) and negative( ),for the50%defect for the positive( )and negative( ),and for the75%defect for the positive( )and negative(•)saddle amplitudes.Table1.Bestfit slopes for normal-cycle MFL pp and saddle amplitude with different defect depths in the composite beam and50%defect in the semicircular pipe section and single beam.%MFL pp vs.Stress-dependent Stress-dependent+Sad.amp.−Sad.amp. Defect stress slope saddle amplitude saddle amplitude MFL pp slope MFL pp slope depth(10−12T/Pa)pos.(10−13T/Pa)neg.(10−13T/Pa)(=col.3/col.2)(=col.4/col.2) Composite Beam(B=1.24T)25% 1.6210.130.0650% 5.1760.140.1275%11.019.119.50.1740.177 Semicircular Pipe Section(B=1.54T)50%—118——Single Beam(B=1.6T)50% 2.3 1.68±39±30.350.43Fig.6.Saddle amplitudes as a function of stress in the composite beam apparatus from13-mm ball-milled defects in afield of1.24T in the after-cycle are plotted for the25%defect for the positive( ) and negative( ),for the50%defect for the positive( )and negative( ),and for the75%defect for the positive( )and negative(•)saddle amplitudes.are:1)the slope directions of the positive and negative saddles as a function of stress are all positive;2)the rate of change of saddle amplitude as a function of stress for all three stress rigs is of the same order of magnitude,in contrast to the MFL pp signal variations with stress,which demonstrate little correlation between the three different stress rigs: 3)the magnitude of the saddle amplitudes obtained from the positive saddle curves is greater than the corresponding negative saddle curves in the normal cycle;4)no change in the saddle amplitudes was observed under compressive stress for bending stress applied in the axial direction in both the single and composite beams;5)the magnitudes of the saddle amplitudes for the semicircular pipe section are approximately four times greater than those observed for the single and composite beams,and do not go to zero even with the largest application of compressive stress;and6)there is a general increase in the positive and negative saddle amplitude slopes with increasing defect depth.The slopes obtained from the after-cycle and opposite-cycle also demonstrate an increasing saddle amplitude slope with increasing defect depth,although increased in-tercepts for the25and50%defects for the negative saddle amplitude variation are observed.This increase can be seen for the after-cycle in a comparison of Figs.5and6. The sum of the positive and negative saddle amplitude slopes(the total saddle amplitudeFig.7.The sum of positive and negative saddle amplitude stress slopes plotted as a function of% defect depth for the normal cycle( ),after-cycle,( )and opposite cycle( )in the composite beam (B=1.24T).The solid and dashed curves are lines to guide the eye.slope)obtained from the three stress cycle results are plotted as a function of percent defect depth in Fig.7.The total saddle amplitude slope is plotted as a function offlux density for the after-cycle in Fig.8.For all three cycles the results indicated an increasing total saddle am-plitude with increasingflux density.The stress concentration factor is a constant for constant defect depth and,therefore, may be related to the slope of the saddle amplitude variation with stress.However,for the zero-stress case,the radialflux leakage signal demonstrates a considerable increase with increasing defect depth[19,20].Therefore,to perform a comparison of the variation of the saddle amplitude with stress for different defect depths with calculated values of the stress concentration,it is necessary to normalize the stress-dependent saddle amplitude slopes by their respective zero-stress MFL pp signals.A comparison of the normalized saddle amplitude slopes with the maximum and surface maximum stress concentrations obtained fromfinite-element calculations is shown in Fig.9.The stress-dependent saddle amplitude slopes have been averaged over the three cycles,normalized by their respective zero stress MFL pp signals,and scaled to the calculated maximum surface stress at75% defect depth.The normalized and scaled saddle amplitude slopes have beenfitted in Fig.9with anFig.8.Sum of positive and negative saddle amplitude stress slopes plotted as a function of pipe wall flux density for the after-cycle( )in the composite beam(B=1.24T).The solid curve is simply a line to guide the eye.empirical formulation given byA=a sinh(bD),(1)where A is the sum of the positive and negative saddle amplitude slopes,D is the percent defect depth,and a and b arefitting parameters given by(a,b)=(0.71,0.018). Equation(1)holds in the limit of a0%defect since the total saddle amplitude A goes to zero as the MFL pp signal goes to zero.Thefinite-element calculations indicate that both the maximum and surface maximum stress concentration are increasing functions of percent defect depth.Starting at0%defect depth,the maximum stress concentration increases more rapidly than both the surface maximum and the normalized and scaled saddle amplitude slope values.Slower increases in thefinite-element calculations are observed in the vicinity of70%,which corresponds with the defect depth in thefinite-element model where the radius of the defect reaches its maximum of6.35mm.After90%the surface maximum concentration becomes the maximum stress concentration.The hyperbolic sine function,Eq.(1),coincides with the finite-element calculations above75%defect depth and with the theoretical fractional change in stress concentration at100%defect depth.Fig.9.Normalized change in maximum stress( )and maximum surface stress(⊕)as a function of%defect depth as obtained fromfinite-element calculations.The total saddle amplitude stress slopes ( )for the composite beam normalized by their respective zero-stress MFL pp signals and averaged over the three different stress cycles have been scaled to the maximum surface stress(SurfaceσMAX)finite-element calculations at75%defect depth.The dashed lines are spline curves through the pointsobtained from thefinite-element calculations and the solid line is a bestfit of the empirical relation,Eq.(1).DiscussionSemicircular Pipe Section:MFL pp MeasurementsThe application of a bending stress in the semicircular pipe section complicates the prediction of the magneticflux leakage stress behavior of the pipe since,if the upper surface of the pipe with the near-side defect is under tensile stress,then the inner surface will be under compressive stress.A further complication in this system is the direction of the magnetic easy axis with respect to the direction of the applied stress.The magnetic easy axis is at90◦to the direction of the applied stress,and,therefore,the magnetic properties of the pipeline steel are different[21]from those where the stress and easy axis are aligned in the same direction[22].Geometric properties of the semicircular pipe stress rig also may play a role in affecting the stress-dependent variation of the MFL pp signal,since the radius of curvature and therefore the length of theflux path in the semicircular pipe section changes as a function of stress with respect to thefixed length of the magnetizer.Furthermore,different levels of pipe wallflux density at equivalent stress levels for increasing and decreasing applied stresses may arise because of hystereticflux coupling in the hingedfinger–semicircular stress system.This may explain the severe hysteresis observed in the radial MFL pp signal for the semicircular pipe section under tensile stress shown in Fig.3.The application of a hoop-bending stress that is either tensile or compressive results in an overall decrease of the MFL pp signal for either surface tensile or surface compressive applied stress.However,there is an initial increase of the MFL pp signal under a surface tensile stress of50MPa.This may be attributed to the presence of a residual compres-sive surface stress present within the pipe.This suggestion is supported by spring-back measurements observed when the pipe section was cut in half[22].Stress-Dependent Saddle Amplitude:Stress Concentration FactorsThe variation of the MFL pp signal with stress appears to be associated primarily with the bulk effects of stress[9],[11]–[13]and pipe wallflux density[9,13]on the magnetic properties of steel in the general vicinity of the defect.However,we propose that the double-peak feature in the MFL pp signal and the variation of the saddle amplitude with stress is associated with the near-surface variation of stress in the immediate vicinity of the defect,which acts as a local stress raiser[17].Measurements of the MFL pp signal with almost uniform bulk stress in the composite beam stress rig indicate an increase of the MFL pp signal with increasing uniaxial tensile stress[9,13].Similarly,the variation of the saddle amplitude as a function of stress at the near-side surface of the defect demonstrated the same positive dependence.The rate of change of the saddle amplitude as a function of stress was also of the same order of magnitude in all three apparatus.Since it is the surface stress in all three apparatus that is monitored,we associate the saddle amplitude behavior as a function of stress with the corresponding variation of surface stress in the pipeline steel in the vicinity of the defect.Normalization of the stress-dependent saddle amplitude variation by the stress-de-pendent MFL pp slope for the case of the composite beam is shown in Table1.The results indicate that the saddle amplitude increases with defect depth faster than the stress-dependent MFL pp signal.Also shown in Table1are the positive and negative saddle amplitude slopes for the single beam normalized by the stress-dependent MFL pp slope for the50%defect.The values for the normalized saddle amplitude slopes obtained in this manner are more than twice those obtained for the50%defect in the composite beam. Normalization of the semicircular pipe section stress-dependent saddle amplitude by the corresponding MFL pp stress-dependent signal generates a nonlinear stress variation since the MFL pp signal varies nonlinearly over the applied tension–compression stress cycle.As was shown elsewhere[9,13],the single and composite beams demonstrate a compressive stress dependence,while no saddle amplitude is observed in this applied stress region.These results demonstrate that the variation of the MFL pp signal as a function of the bulk stress effect cannot explain the observed stress-dependent variation of the saddle amplitude.Furthermore,the slope of the saddle amplitude as a function of measured surface stress for the50%defect in the three different stress rigs,two of which are under a bending surface stress,are all of the same order.These points indicate。

土木工程材料（civil engineering materials）Question: what are the effects of porosity, pore size and pore size on the properties of the material (such as strength, heat insulation, impermeability, frost resistance, corrosion resistance, water absorption, etc.)?.The larger the porosity of the material is, the lower the strength of the material is, the worse the impermeability and corrosion resistance are, and the stronger the water absorption is. The insulation property and frost resistance of the material are related to the pore structure of the material. The more content of the small hole and the non communicating hole, the better the thermal insulation property and the frost resistance of the material..Question: a multi-storey residential building interior plastering is lime mortar, after the delivery of the wall generally bulging cracking, try to analyze the reasons. 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But the cement particles are too small, too large specific surface area of cement paste to demand the same flow too much, but the impact of the cement strength..Question: why is it necessary to make cement standard consistency before determining the setting time and soundness of cement?.The setting time stability of cement is related to the water cement ratio of cement paste. Although the water consumption is too large, the hydration speed of cement increases, but the distance between the cement particles increases and the setting time of the cement increases. When the cement stability betweenqualified and unqualified, and increase the water cement ratio, the soundness of cement performance is qualified. Therefore, the water content of cement standard consistency is determined first, and the setting time and soundness of cement are determined by the same conditions..Question: why concrete is not the amount of cement as much as possible?.When the amount of cement is too large, the shrinkage of concrete is greater and the hydration heat is larger, which leads to the cracking of concrete. At the same time waste cement, increase project costs..Question: why is it necessary to add a certain amount of cementitious material to cement mortar?.Because the cement is used for making mortar, the mark of the cement is much larger than the strength grade of the mortar, so a small amount of cement can meet the requirement of strength. However, when the amount of cement is less (such as less than 350 kg), the fluidity and water holding capacity of mortar are often poor, especially the water retention. Therefore, the construction quality of mortar is seriously affected, so it is necessary to add some other cheap cementing material to improve the fluidity of mortar, especially the water retention..Question: under the condition that the amount of cement slurry is certain, why is the rate of sand too small and too big tomake the fluidity of mixture become worse?.The dosage of cement slurry under certain conditions, when the void volume rate of sand is not enough to fill the number of hours of gravel or little surplus, in this case, the stone mortar at the contact point is too little, flowing mixture is very small. When the sand ratio is too large, set the total surface area and void material consumption rate increases, the fine aggregate used for wrapping the surface of cement mortar increased, cement sand at the point of contact is insufficient, even not enough to cover all the sand slurry, the dry mortar, liquidity mixture becomes worse..Question: what is the yield point of the material instead of its tensile strength as a basis for the design of the structure?.Yield strength and ultimate tensile strength are two important indexes to evaluate the strength of steel. Ultimate tensile strength is the maximum stress that a test piece can bear. In the structural design, the component is required to work within the elastic deformation range, even if a small amount of plastic deformation should be avoided, so the yield strength of the steel is taken as the basis for design stress. Tensile strength can not be fully utilized in structural design, but the ratio of yield strength to tensile strength (bending strength ratio) has some significance. The smaller the yield strength ratio is, the higher the structural safety is..Question: why is the elongation of steel an important technical performance index for construction steel?.Steel in use, in order to avoid the normal stress at the defect stress concentration due to brittle fracture, its plasticity is good, which has a certain elongation, the defect can be more than the yield point of the material, with the plastic deformation and the stress redistribution, and avoid the premature failure of steel. At the same time, under normal temperature, the steel is processed into a certain shape, and it also requires a certain plasticity. But the elongation can not be too large, otherwise it will allow the use of steel in excess of the allowable deformation value..Question: why does cold working hardening of steel have side effects of plasticity and brittleness?.Steel processing and plastic deformation, the plastic deformation of grains within the region have a relative slip, the slip surface of grain crushing, lattice deformation, a sliding surface is uneven, and the distortion to the difficult. Therefore, the plasticity decreases and the brittleness increases..Question: what are the similarities and differences between porous bricks and hollow bricks?.The two kinds of brick porosity requirements are equal to or greater than 15%; the brick hole size is small and the number of hollow brick the size of the hole and the number of small; the porous brick used in load-bearing hollow brick, often used for non load bearing parts..Question: in a water aerated concrete block masonry wall immediately after pouring mortar plastering mortar layer, prone to cracking and hollowing and why?.Aerated concrete block of the pores are mostly "ink bottle" structure, only a small part of the pores formed by evaporation of water, small belly, capillary action is poor, so water absorption heat conduction slow. Ordinary brick fired water easily absorb enough water, and aerated concrete surface watering a lot, but in fact, water absorption is not much. In general the mortar plastering of aerated concrete is easy to absorb moisture, and is easy to produce cracking and hollowing. Therefore, the water can be divided into several times, and the mortar with good water retention and high bond strength is adopted..Question: why should lightweight aggregate concrete small hollow block be used for expansion joint when wall is used?.This is because the temperature deformation and dry shrinkage deformation of lightweight aggregate concrete small hollow block are larger than that of sintered common brick. In order to prevent cracks, the expansion joint can be set according to specific conditions, and the structural reinforcement is added to the necessary parts..Question: are stone materials available for underground foundations?.Not always。

Concentration1. IntroductionConcentration refers to the ability to focus one’s attention on a specific task or object for an extended period of time. It is an essential cognitive skill that plays a crucial role in various aspects of our lives, including work, education, and daily activities. Theability to concentrate effectively can significantly improve productivity, learning outcomes, and overall well-being.2. The Importance of Concentration2.1 Enhancing ProductivityConcentration is directly linked to productivity. When we can concentrate on a task without distractions, we are more likely to complete it efficiently and effectively. By maintaining a high level of focus, we can prioritize our tasks, avoid procrastination, and accomplish our goals in a timely manner.2.2 Improving LearningConcentration is especially important in the context of education. Students who can concentrate well in the classroom are more likely to absorb and retain information. They are also better equipped to actively participate in discussions and engage with the learning materials. Improved concentration leads to better academic performance and a deeper understanding of the subject matter.2.3 Heightening Mental ClarityConcentration allows us to clear our minds from unnecessary thoughts and distractions. When we can focus our attention without being easily swayed by external factors, we can think more clearly and make betterdecisions. Enhanced mental clarity enables us to solve problems more effectively and approach tasks with a greater level of efficiency.2.4 Cultivating MindfulnessConcentration is closely related to mindfulness, which refers to the state of being fully present and aware of the current moment. When we concentrate on the present task at hand, we immerse ourselves in the experience, leading to a heightened sense of mindfulness. This can reduce stress, increase self-awareness, and improve overall mental well-being.3. Factors Affecting ConcentrationSeveral factors can significantly impact our ability to concentrate effectively. It is essential to identify and address these factors to optimize our concentration levels.3.1 DistractionsDistractions, both external and internal, can disrupt our concentration. External distractions include noises, interruptions, and environmental factors, while internal distractions may involve worries, personal concerns, or even daydreaming. Minimizing distractions and creating a conducive environment can help maintain focus.3.2 Fatigue and SleepLack of sleep and fatigue can severely affect concentration. When our bodies and minds are tired, it becomes challenging to sustain focus and attention. Prioritizing quality sleep, maintaining a regular sleep schedule, and adopting healthy lifestyle habits can improve concentration levels.3.3 Stress and AnxietyHigh levels of stress and anxiety can impair concentration. When we are overwhelmed by worry or pressure, our minds tend to wander, making itdifficult to concentrate on the task at hand. Practicing stress management techniques, such as meditation or deep breathing exercises, can alleviate these effects and enhance concentration.3.4 MultitaskingContrary to popular belief, multitasking can hinder concentration rather than enhance it. Dividing our attention among multiple tasks reduces our ability to concentrate on any one task fully. Prioritizing tasks, focusing on one task at a time, and practicing mindfulness can help avoid the pitfalls of multitasking.4. Strategies for Improving ConcentrationTo enhance concentration abilities, various strategies and techniques can be employed. Experimenting with different methods and identifying what works best for each individual is essential.4.1 Time ManagementEffectively managing time can positively impact concentration. Breaking down tasks into smaller, manageable chunks and allocating dedicated time slots for each task can make it easier to maintain focus. Using tools such as timers or productivity apps can assist in structuring and managing time effectively.4.2 Mindfulness and MeditationPracticing mindfulness and meditation can improve concentration by training the mind to stay present and focused. These practices involve redirecting attention back to the present moment whenever the mind wanders. Regular mindfulness exercises can improve overall concentration abilities and reduce the impact of distractions.4.3 Regular Breaks and Physical ActivityTaking regular breaks during prolonged periods of work or study can counteract mental fatigue and improve concentration. Engaging inphysical activity or exercise during these breaks can further enhance focus and cognitive performance. Physical movement increases blood flow to the brain and promotes a heightened sense of alertness.4.4 Mindful EatingNutrition plays a significant role in concentration and cognitive function. Adopting mindful eating habits, such as consuming a balanced diet and staying adequately hydrated, can support optimal brain functioning. Avoiding excessive sugar, caffeine, and processed foods can prevent energy crashes and promote sustained focus.4.5 Environment OptimizationCreating an environment conducive to concentration is vital. Minimizing distractions, organizing workspaces, and utilizing tools such as noise-cancelling headphones or white noise generators can help create an atmosphere that promotes focus. Personalizing the environment to suit individual preferences also contributes to an increased sense of comfort and concentration.ConclusionConcentration is a crucial cognitive skill that significantly impacts our productivity, learning capabilities, and overall well-being. By understanding the importance of concentration and implementingstrategies to enhance it, individuals can unlock their full potential and achieve success in various areas of life. It is an ongoing process that requires practice and dedication, but the rewards of improved concentration are well worth the effort.。

机械设计专业术语的英语翻译1机械设计专业术语的英语翻译1 柔性自动化flexibleautomation 润滑油膜lubricantfilm润滑装置lubricationdevice润滑lubrication润滑剂lubricant三角形花键serrationspline三角形螺纹vthreadscrew三维凸轮three - dimensionalcamto stheorem 三心定理kennedy砂轮越程槽grindingwheelgroove砂漏hour glass少齿差行星传动planetarydrivewithsmallteethdifference设计方法学designmethodology设计变量designvariable设计约束designconstraints深沟球轴承deepgrooveballbearing生产阻力productiveresistance升程rise升距lift实际廓线camprofile十字滑块联轴器doubleslidercoupling oldham'scoupling矢量vector输出功outputwork输出构件outputlink输出机构outputmechanism输出力矩outputtorque输出轴outputshaft输入构件inputlink数学模型mathematicmodel实际啮合线actuallineofaction双滑块机构double - slidermechanism, ellipsograph双曲柄机构doublecrankmechanism双曲面齿轮hyperboloidgear双头螺柱studs双万向联轴节constant - velocityordoubleuniversaljoint 双摇杆机构doublerockermechanism双转块机构oldhamcoupling双列轴承doublerowbearing双向推力轴承double - directionthrustbearing松边slack side顺时针clockwise瞬心instantaneouscenter死点deadpoint四杆机构four - barlinkage速度velocity速度不均匀波动系数coefficientofspeedfluctuation速度波动speedfluctuation速度曲线velocitydiagram速度瞬心instantaneouscenterofvelocity塔轮steppulley踏板pedal台钳、虎钳vice太阳轮sungear弹性滑动elasticityslidingmotion弹性联轴器elasticcoupling flexiblecoupling弹性套柱销联轴器rubber - cushionedsleevebearingcoupling 套筒sleeve梯形螺纹acmethreadform特殊运动链specialkinematicchain特性characteristics替代机构equivalentmechanism调节modulation, regulation调心滚子轴承self - aligningrollerbearing调心球轴承self - aligningballbearing调心轴承self - aligningbearing调速speedgoverning调速电动机adjustablespeedmotors调速系统speedcontrolsystem调压调速variablevoltagecontrolGovernor regulator, governorFerromagnetic fluid seals ferrofluidseal Parking phase, stoppingphaseStopping dwellSynchronous belt Synchronousbelt Synchronous belt drive synchronousbeltdrive Convex body convexCam camCam reverse mechanism inversecammechanism Cam mechanism cam, CamMechanismCam profile camprofileCam profile drawing layoutofcamprofile Theoretical profile of cam pitchcurve Flange coupling flangecouplingAtlas and Atlas AtlasGraphical method graphicalmethodPushing distance riseThrust ball bearing thrustballbearing Thrust bearing thrustbearingCutter toolwithdrawalgrooveAnnealed annealGyroscope gyroscopeV band VbeltExternal force externalforceOuter ring outerringOutline size boundarydimensionUniversal coupling Hookscoupling universalcoupling External gear externalgearBending stress beadingstressBending moment bendingmomentWrist wristReciprocating reciprocatingmotionReciprocating seal reciprocatingsealDesign on-netdesign online, ONDInching screw mechanism differentialscrewmechanism Displacement displacementDisplacement curve displacementdiagramPose pose, positionandorientationStable operation stage, steadymotionperiodRobust design robustdesignWorm wormWorm drive mechanism WormgearingNumber of worm heads numberofthreadsDiameter coefficient of worm diametralquotient Worm and worm gear wormandwormgearWorm cam stepping mechanism wormcamintervalmechanism Worm rotation handsofwormWorm gear wormgearPower spring powerspringStepless speed change device steplessspeedchangesdevices Infinity infiniteTie crankarm, planetcarrierField balancing fieldbalancingRadial bearing radialbearingCentripetal force centrifugalforceRelative velocity relativevelocityRelative motion relativemotionRelative clearance relativegapQuadrant quadrantClay plasticineFine tooth thread finethreadsPin pinConsuming consumptionPinion pinionPath minordiameterRubber spring balataspringModified trapezoidal acceleration motion law modifiedtrapezoidalaccelerationmotionCorrection of motion law of sinusoidal accelerationmodifiedsineaccelerationmotionHelical gear HelicalGearCross key, hook head wedge key taperkeyLeakage leakageHarmonic gear harmonicgearHarmonic drive harmonicdrivingHarmonic generator harmonicgeneratorEquivalent spur gear of helical gear equivalentspurgearofthehelicalgearMandrel spindleTravel speed variation factorcoefficientoftravelspeedvariationTravel speed ratio coefficient advance-toreturn-timeratio Planetary gear unit planetarytransmissionPlanet gear planetgearPlanetary gear change gear planetaryspeedchangingdevices Planetary gear train planetarygeartrainForm closed cam mechanismpositive-driveorform-closedcammechanismVirtual reality virtualrealityVirtual reality technology virtualrealitytechnology, VRT Virtual reality design, virtualrealitydesign, VRDVirtual constraint redundantorpassiveconstraintAllowable imbalance quantity allowableamountofunbalance Allowable pressure angle allowablepressureangleAllowable stress allowablestress, permissiblestressCantilever structure cantileverstructureCantilever beam cantileverbeamCyclic power flow circulatingpowerloadRotational torque runningtorqueRotary seal rotatingsealRotational motion rotarymotionType selection typeselectionPressure pressurePressure center centerofpressureCompressor compressorCompressive stress compressivestressPressure angle pressureangleInlay couplings jawteethpositive-contactcouplingJacobi matrix JacobimatrixRocker rockerHydraulic transmission hydrodynamicdriveHydraulic coupler hydrauliccouplersLiquid spring liquidspringHydraulic stepless speed change hydraulicsteplessspeedchanges Hydraulic mechanism hydraulicmechanismGeneralized kinematic chain generalizedkinematicchainMoving follower reciprocatingfollowerMobile sub prismaticpair, slidingpairMobile joints prismaticjointMoving cam wedgecamProfit and loss work incrementordecrementworkStress amplitude stressamplitudeStress concentration stressconcentrationStress concentration factor factorofstressconcentration Stress diagram stressdiagramStress strain diagram stress-straindiagramOptimum design optimaldesignOilbottle cupI oilcanOil groove seal oilyditchsealHarmful resistance uselessresistanceBeneficial resistance usefulresistanceEffective pull effectivetensionEffective circumferential force effectivecircleforce Harmful resistance detrimentalresistanceCosine acceleration motion cosineaccelerationorsimpleharmonicmotionPreload preloadPrime mover primermoverRound belt roundbeltBelt drive roundbeltdriveArc tooth thickness circularthicknessCircular cylindrical worm hollowflankwormRounded radius filletradiusDisc friction clutch discfrictionclutchDisc brake discbrakePrime mover primemoverOriginal mechanism originalmechanismCircular gear circulargearCylindrical roller cylindricalrollerCylindrical roller bearings cylindricalrollerbearingCylindrical pair cylindricpairCylindrical cam stepping motion mechanism barrelcylindriccamCylindrical helical tension spring cylindroidhelical-coilextensionspringCylindrical helical torsion spring cylindroidhelical-coiltorsionspringCylindrical helical compression spring cylindroidhelical-coilcompressionspringCylindrical cam cylindricalcamCylindrical worm cylindricalwormCylindrical coordinate manipulator cylindricalcoordinatemanipulator Conical spiral torsion springconoidhelical-coilcompressionspringTapered roller taperedrollerTapered roller bearing taperedrollerbearingBevel gear mechanism bevelgearsTaper angle coneangleThe original drivinglinkBound constraintConstraint constraintconditionConstraint reaction force constrainingforceJump jerkJump curve jerkdiagramInversion of motion, kinematicinversionMotion scheme design kinematicpreceptdesign Kinematic analysis kinematicanalysisKinematic pair kinematicpairMoving component movinglinkKinematic diagram kinematicsketchKinematic chain kinematicchainMotion distortion undercuttingKinematic design kinematicdesignMotion cycle cycleofmotionKinematic synthesis kinematicsynthesisUneven coefficient of operation coefficientofvelocityfluctuationKinematic viscosity kenematicviscosityLoad loadLoad deformation curve load - DEFORMATIONCURVE Load deformation diagram load - deformationdiagram Narrow V band narrowVbeltFelt ring seal feltringsealThe generating method of generatingTensioning force tensionTensioner tensionpulleyVibration vibrationVibration torque shakingcoupleVibration frequency frequencyofvibration Amplitude amplitudeofvibrationTangent mechanism tangentmechanismForward kinematics directforwardkinematics Sinusoidal mechanism sinegenerator, scotchyoke Loom loomNormal stress and normal stress normalstress Brake brakeSpur gear SpurGearStraight bevel gear straightbevelgearRight triangle righttriangleCartesian coordinate manipulator CartesiancoordinatemanipulatorCoefficient of diameter diametralquotient Diameter series diameterseriesStraight profile hourglass worm gear hindleyworm Linear motion linearmotionStraight axis straightshaftMass massCentroid centerofmassExecution component executivelink workinglinkProduct of mass and diameter mass-radiusproduct Intelligent design, intelligentdesign, IDIntermediate plane mid-planeCenter distance centerdistanceVariation of center distance centerdistancechange Center wheel centralgearMedium diameter meandiameterTerminate the meshing point finalcontact, endofcontact Week Festival pitchPeriodic velocity fluctuation periodicspeedfluctuation Epicyclic gear train epicyclicgeartrainElbow mechanism togglemechanismAxis shaftBearing cap bearingcupBearing alloy bearingalloyBearing block bearingblockBearing height bearingheightBearing width bearingwidthBearing bore bearingborediameterBearing life bearinglifeBearing ring bearingringBearing outer diameter bearingoutsidediameterJournal JournalBush and bearing lining bearingbushShaft end retaining ring shaftendringCollar shaftcollarShoulder ShaftShoulderAxial angle shaftangleAxial axialdirectionAxial profile axialtoothprofileAxial equivalent dynamic load dynamicequivalentaxialload Axial equivalent static load staticequivalentaxialload Axial basic rated dynamic load basicdynamicaxialloadrating Axial basic rated static load basicstaticaxialloadrating Axial contact bearing axialcontactbearingAxial plane axialplaneAxial clearance axialinternalclearanceAxial load AxialLoadAxial load factor axialloadfactorAxial component axialthrustloadActive component, drivinglinkDriving gear drivinggearDriving pulley drivingpulleyRotating guide rod mechanism whitworthmechanismRevolute pair revoluteturningpairThe speed is swivelingspeed rotatingspeedRotating joint revolutejoint Rotating shaft revolvingshaftRotor rotorRotor balance balanceofrotor Assembly condition assemblycondition Bevel gear bevelgearCone top commonapexofconeCone distance conedistanceCone wheel bevelpulley bevelwheel。