120噸六梁橋式起重機(jī)結(jié)構(gòu)設(shè)計(jì)畢設(shè)畢業(yè)論文-wenkub.com
2025-06-16 07:12 本頁面
【正文】 一般來說，軟的和低強(qiáng)度材料的性質(zhì)是塑性的，而堅(jiān)硬和高強(qiáng)度的材料的塑性是很小的。而塑性材料在應(yīng)力作用下有很長的塑性區(qū)域。例如鋼制彈簧就是靠彈性應(yīng)變來作用的。對于低應(yīng)力，在42000磅/以下，應(yīng)變和應(yīng)力成正比。把焊接試件夾在實(shí)驗(yàn)機(jī)的夾頭上，在伸長時(shí)逐漸加大加到試件上的載荷。實(shí)驗(yàn)機(jī)上巨大的標(biāo)度盤顯示出家到焊接試件上的拉伸載荷的大小。焊縫是在1/2英寸厚的板上進(jìn)行的完全熔透的雙面對接焊縫，試件在板上切出2英寸的寬度以實(shí)驗(yàn)焊縫的強(qiáng)度。因?yàn)閯傂院艽螅饘僭诤艽蟮膽?yīng)力下只會產(chǎn)生很小的應(yīng)變。容焊時(shí)常常產(chǎn)生翹曲也是一種應(yīng)變，如他明顯的表明焊后的金屬內(nèi)存在著應(yīng)力。請看一個(gè)用一根百棕繩拖一輛汽車的簡單例子。在這個(gè)非常重要的前提基礎(chǔ)之上才允許分別對待這兩門學(xué)科。 因此，設(shè)計(jì)機(jī)械系統(tǒng)的首要問題就是理解它的運(yùn)動學(xué)。第一部分在不考慮運(yùn)動原因的情況下來研究剛體從一個(gè)指定位置到另外任一點(diǎn)的移動，而且必須用解析公式來體現(xiàn)，公式將確定剛體每一點(diǎn)的位置。在此向他們表示崇高的敬意和感謝！由于是第一次做這么大的設(shè)計(jì)，自己的知識、經(jīng)驗(yàn)都很欠缺，在設(shè)計(jì)過程中出現(xiàn)了很多不足之處，請各位老師批評！ 張明明 2007年6月18日The scientific of MechanicsThe branch of scientific analysis which deals with motions,time ,and forces is called mechabics and is made up of two parts, statics and dynamics. Statics deals with the analysis of stationarys systerms,.,those in which time is not a factor,and dynamics deals with systerms which change with time .As shown jin ,dynamics is also made up of two major disciplines,first recgnized as separate entities by Euler in 1775.The investigation of the motion of a rigie body may be convenientnly separated into two parts,the one gemetical , the other mechanical .In the first part, the transference of the body from a given position to any other position must be investigated without respect to the cause of the motion , and must be represented by analytical formulae, which will define the position of the investigation will therefore be referable solely to geometry ,or rather to stereotomy.It is clear that by the separation of this part of the question from the other,which belongs properlywo Mechanics, the determination of the motion from dynamical principles will be made much easier than if the two parts were undertaken conjointly.These two aspects of dynamics were later recgnized as the distinct sciences of kinematics and kinetics ,and deal with motion and the forces producing it ,respectively.The initial problem in the design of a mechannical systerm is therefore understanding its kinenatics. Kinematics is the study of motiom,quite apart from the forces which produce that motion. More particularly,kinematics is the study of position , displacement, totation, speed, velocity ,and study ,say,of planetary or orbital motion is also a problem in kinematics.It should be carefully noted jin the above quotation that Euler based his seperation of dynamics into kinematics and kinetics on the assunption that they should deal with rigid bodies. It is this very important assumption that allows the two to be treated separately .For flexible bodies , the shapes of the bodies themselves, and therefor their motions ,deoend on the forces exterted on them .In this situation ,the study of force and motion must taken place sinultaneously, thus significantly increasing the plexity of the analysis,Formulately ,although all real machine parts are flixble to some degree,machines are usually designed from relatively rigid materials, keeping part deflections to a minimum. Therefore ,it is mon practice to assume that deflections are negligible and parts are rigid when analyzing a machine’s kinematic performance ,and then, after the dynamic analysis when loads are known, wo design the parts so that this assunption is justified. Stress and StrainStress and strain are noet the same bue are related in that either one will puoduce the other. Consider the simple example ofa manila rope used to tow an automaobile. The pull on the rope causes a stress or force in the rope fibers . After the pull ,or stess, on the rope is relaxed, the rope has been permanently stretched owing to this stress. The increase jin length is a deformation or strain .The warping that always acpanies fusion welding is a strain and clearly indicates that there are stresses jin the matal after welding.Stresses are calculated in pounds per square inch(psi) just like stress in psi is equal wo the load P dicided by the area supporting the load:There are three possible types of stresses():1. pression(crushing)2. tension(pull)3. shear(cutting)Al
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