机械结构设计外文文献翻译中英文翻译机械设计外文翻译Word文档格式.docx

1、系 、 部： 机械系 * * 指导教师： 康煜华 职称 副教授 专 业： 机械设计制造及其自动化 班 级： 机本0704班 完成时间： 2011年6月 Augustine J.Fredrich摘要：结构设计是选择材料和构件类型，大小和形状以安全有用的样式承担荷载。一般说来，结构设计暗指结构物如建筑物和桥或是可移动但有刚性外壳如船体和飞机框架的工厂稳定性。设计的移动时彼此相连的设备（连接件），一般被安排在机械设计领域。 关键词：结构设计 ； 结构分析 ； 结构方案 ； 工程要求Abstract: Structure design is the selection of materials and

2、 member type ,size, and configuration to carry loads in a safe and serviceable fashion .In general ,structural design implies the engineering of stationary objects such as buildings and bridges ,or objects that maybe mobile but have a rigid shape such as ship hulls and aircraft frames. Devices with

3、parts planned to move with relation to each other（linkages） are generally assigned to the area of mechanical . Key words: Structure Design ； Structural analysis ；structural scheme ； Project requirements Structure Design Structural design involved at least five distinct phases of work: project requir

4、ements, materials, structural scheme, analysis, and design. For unusual structures or materials a six phase, testing, should be included. These phases do not proceed in a rigid progression , since different materials can be most effective in different schemes , testing can result in change to a desi

5、gn , and a final design is often reached by starting with a rough estimated design , then looping through several cycles of analysis and redesign . Often, several alternative designs will prove quite close in cost, strength, and serviceability. The structural engineer, owner, or end user would then

6、make a selection based on other considerations.Project requirements. Before starting design, the structural engineer must determine the criteria for acceptable performance. The loads or forces to be resisted must be provided. For specialized structures, this may be given directly, as when supporting

7、 a known piece of machinery, or a crane of known capacity. For conventional buildings, buildings codes adopted on a municipal, county , or , state level provide minimum design requirements for live loads （occupants and furnishings , snow on roofs , and so on ）. The engineer will calculate dead loads

8、 （structural and known, permanent installations ） during the design process. For the structural to be serviceable or useful , deflections must also be kept within limits ,since it is possible for safe structural to be uncomfortable “bounce” Very tight deflection limits are set on supports for machin

9、ery , since beam sag can cause drive shafts to bend , bearing to burn out , parts to misalign , and overhead cranes to stall . Limitations of sag less than span /1000 （ 1/1000 of the beam length ） are not uncommon . In conventional buildings, beams supporting ceilings often have sag limits of span /

10、360 to avoid plaster cracking, or span /240 to avoid occupant concern （keep visual perception limited ）. Beam stiffness also affects floor “bounciness,” which can be annoying if not controlled. In addition , lateral deflection , sway , or drift of tall buildings is often held within approximately he

11、ight /500 （1/500 of the building height ） to minimize the likelihood of motion discomfort in occupants of upper floors on windy days .Member size limitations often have a major effect on the structural design. For example, a certain type of bridge may be unacceptable because of insufficient under cl

12、earance for river traffic, or excessive height endangering aircraft. In building design, ceiling heights and floor-to-floor heights affect the choice of floor framing. Wall thicknesses and column sizes and spacing may also affect the serviceability of various framing schemes.Materials selection. Tec

13、hnological advances have created many novel materials such as carbon fiber and boron fiber-reinforced composites, which have excellent strength, stiffness, and strength-to-weight properties. However, because of the high cost and difficult or unusual fabrication techniques required , they are used on

14、ly in very limited and specialized applications . Glass-reinforced composites such as fiberglass are more common, but are limited to lightly loaded applications. The main materials used in structural design are more prosaic and include steel, aluminum, reinforced concrete, wood , and masonry . Struc

15、tural schemes. In an actual structural, various forces are experienced by structural members , including tension , compression , flexure （bending ）, shear ,and torsion （twist） . However, the structural scheme selected will influence which of these forces occurs most frequently, and this will influen

16、ce the process of materials selection.Tension is the most efficient way to resist applied loads ,since the entire member cross section is acting to full capacity and bucking is not a concern . Any tension scheme must also included anchorages for the tension members . In a suspension bridge , for exa

17、mple ,the anchorages are usually massive dead weights at the ends of the main cables . To avoid undesirable changes in geometry under moving or varying loads , tension schemes also generally require stiffening beams or trusses. Compression is the next most efficient method for carrying loads . The f

18、ull member cross section is used ,but must be designed to avoid bucking ,either by making the member stocky or by adding supplementary bracing . Domed and arched buildings ,arch bridges and columns in buildings frames are common schemes . Arches create lateral outward thrusts which must be resisted

19、. This can be done by designing appropriate foundations or , where the arch occurs above the roadway or floor line , by using tension members along the roadway to tie the arch ends together ,keeping them from spreading . Compression members weaken drastically when loads are not applied along the mem

20、ber axis , so moving , variable , and unbalanced loads must be carefully considered. Schemes based on flexure are less efficient than tension and compression ,since the flexure or bending is resisted by one side of the member acting in tension while the other side acts in compression . Flexural sche

21、mes such as beams , girders , rigid frames , and moment （bending ） connected frames have advantages in requiring no external anchorages or thrust restrains other than normal foundations ,and inherent stiffness and resistance to moving ,variable , and unbalanced loads .Trusses are an interesting hybr

22、id of the above schemes . They are designed to resist loads by spanning in the manner of a flexural member, but act to break up the load into a series of tension and compression forces which are resisted by individually designed tension and have excellent stiffness and resistance to moving and varia

23、ble loads . Numerous member-to-member connections, supplementary compression braces ,and a somewhat cluttered appearance are truss disadvantages .Plates and shells include domes ,arched vaults ,saw tooth roofs , hyperbolic paraboloids , and saddle shapes .Such schemes attempt to direct all force alo

24、ng the plane of the surface ,and act largely in shear . While potentially very efficient ,such schemes have very strict limitations on geometry and are poor in resisting point ,moving , and unbalanced loads perpendicular to the surface.Stressed-skin and monologue construction uses the skin between s

25、tiffening ribs ,spars ,or columns to resist shear or axial forces . Such design is common in airframes for planes and rockets, and in ship hulls . it has also been used to advantage in buildings. Such a design is practical only when the skin is a logical part of the design and is never to be altered

26、 or removed .For bridges , short spans are commonly girders in flexure . As spans increase and girder depth becomes unwieldy , trusses are often used ,as well as cablestayed schemes .Longer spans may use arches where foundation conditions ,under clearance ,or headroom requirements are favorable .The

27、 longest spans are handled exclusively by suspension schemes ,since these minimize the crucial dead weight and can be erected wire by wire .For buildings, short spans are handled by slabs in flexure .As spans increase, beams and girders in flexure are used . Longer spans require trusses ,especially

28、in industrial buildings with possible hung loads . Domes ,arches , and cable-suspended and air supported roofs can be used over convention halls and arenas to achieve clear areas .Structural analysis . Analysis of structures is required to ensure stability （static equilibrium ） ,find the member forc

29、es to be resisted ,and determine deflections . It requires that member configuration , approximate member sizes ,and elastic modulus ; linearity ; and curvature and plane sections . Various methods are used to complete the analysis .Final design . once a structural has been analyzed （by using geomet

30、ry alone if the analysis is determinate , or geometry plus assumed member sizes and materials if indeterminate ）, final design can proceed . Deflections and allowable stresses or ultimate strength must be checked against criteria provided either by the owner or by the governing building codes . Safe

31、ty at working loads must be calculated . Several methods are available ,and the choice depends on the types of materials that will be used .Pure tension members are checked by dividing load by cross-section area .Local stresses at connections ,such as bolt holes or welds ,require special attention .

32、 Where axial tension is combined with bending moment ,the sum of stresses is compared to allowance levels . Allowable : stresses in compression members are dependent on the strength of material, elastic modulus ,member slenderness ,and length between bracing points . Stocky members are limited by materials strength ,while slender members are limited by elastic bucking . Design of beams can be checked by comparing a maximum bending stress to an allowable stress , which is generally controlled by the strength of the material, but may be limited if