Uzay sistemlerinde paslanmaz çelik çekme çubuklarının davranışı
Başlık çevirisi mevcut değil.
- Tez No: 55855
- Danışmanlar: PROF.DR. NESRİN YARDIMCI
- Tez Türü: Yüksek Lisans
- Konular: İnşaat Mühendisliği, Civil Engineering
- Anahtar Kelimeler: Belirtilmemiş.
- Yıl: 1996
- Dil: Türkçe
- Üniversite: İstanbul Teknik Üniversitesi
- Enstitü: Fen Bilimleri Enstitüsü
- Ana Bilim Dalı: Belirtilmemiş.
- Bilim Dalı: Belirtilmemiş.
- Sayfa Sayısı: 39
Özet
ÖZET İnşaat alanında, malzeme ekomomisi ve hafif yapı, günümüz ihtiyaçlarındandır. Bu yüzden mimarlık, mühendisliğe her zamankinden daha fazla bağlıdır. Yüklerin dağılımı, kuvvetlerin ayrımı, eğilme momentlerinin azaltılması ve malzemenin lımitlerıyle kullanılması öncelikle üzerinde durulması gereken konulardır. Bunun yanında büyük dizayn özgürlüğü sağlayan, yapı birleşim elemanlarının standardize edilebilmesi ve prefabrike olması, bunların sonucunda da hızlı, güvenilir şekilde mşa edilebilen yapıların önemi artmaktadır. Uzay sistemler, rıjıdliğı, bir elemanın yetersizliği durumunda mukavemet ihtiyatı sağlayan yüksek mertebeden hiperstatikliği, hazır yapım ve montaj kolaylıkları, sökme ve değiştirme kolaylıkları, biçimlendirmede ve çizimde büyük özgürlük sağlamasıyla, günümüz ihtiyaçlarına cevap vermektedir. Özellikle, 1950'li yıllardan beri hareketli yüklen az olan çatı ve benzen bina bölümlerinde, büyük açıklıkları aşmak için yaygın olarak kullanılmaktadır. Türkiye açısından uzay sistemlerin kullanımına bakacak olusak; uzay sistem kullanımının üstel bir fonksiyon gösterdiğini söylemek mümkündür. Uzay kafes sistemler, gerek çubuk enkesıt formları ve gerekse düğüm noktalarının düzenleme biçimleri açılarından oldukça değişik şekilde çözümlenebilirler. Türkıyede sayıları onbeş civarında olan uzay sistem firmalarının büyük bir bölümü, tepelen dik açılı bir çubuklar ağı ile birleşen dikdörtgen tabanlı pramitlerın yanyana konulmasıyla düzenlenen ve birbirine dik iki doğrultuda çalışan uzay sistem türünü kullanırlar. Düğüm noktalarının teşkilinde ise, Mero tıpı benzen düğüm noktasını tercih ettikleri görülmektedir. Bu tip düğüm noktaları, eksenleri birbirine dik, üç doğrultuda ve bunların açı ortaylarında olan, diş açılmış onsekiz deliğe sahip masif kürelerden oluşur. Boru kesitli çubukların uçlarına hareketli bir bulon, bunun üzerine bağlı bir somun-manşon bulunur. Bu çalışmada, Mero Tipi benzeri düğüm noktası detaylarında, paslanmaz çelik malzeme kullanılması durumunda, ortaya çıkabilecek problemlerin araştırılması ve paslanmaz çeliğin teorik mukavemet değerlen ile deney sunucunda elde edilen mukavemet değerlen arasındaki ilişkinin belirlenmesi amaçlanmıştır. Bunun için iki farklı çapta ve her birinden üçer adet olamak üzere toplam altı adet çekme deneyi yapılmıştır. vıı
Özet (Çeviri)
SUMMARY AN EXPERIMENTAL RESEARCH ON THE BEHAVIOUR OF STAINLESS STEEL TENSIAL MEMBERS IN SPACE FRAMES. Light construction and economy in material are current requirements in the building field, therefore, architecture is dependent upon engineering today more than ever before. The dıstrubutıon of loads, spreading of forces, the reduction of bending moments and the utilization of material to its limits, these are the tendencies that become more and more decisive for the architects and cıvıl engineers. Construction must give them greater freedom of design and in many instance led to lower costs through prefabrication and standardisation of component parts. Espacially during the last decade, space structures have mflunced the architectural scene all over the world. The reason for the interest in space structure is due to several factors; - intruduction and wide spread use of high-speed electronic computers. - development of highly efficient standardised connections. - a truly remarkable amount of recent scientific research into the elastic and non-elastic behaviour of space structures and determination of modes of their failure under excessive loading. If we look at marking a change-over from the two dimensional structures of the past to three dimensional space system, we are now on the eve of a great architectural revolution. This remakable trend towards greater use of space structures, resulting from architectural preference and imaginations, is partly due, no doubt, to reaction from the“column-beam”system of the previous decades, but it is also due to the realization of the advantages of space structures. Engineers realized many years ego that space structures require less material than ordinary linear systems and that, if properly designed, they can be highly economical in cost. Since 1950, space truss structures have been used widely, especially at roofs or similar parts of constructions on which there is no effective live loads. The cause of this choise, using space truss structures, can be as; - lightness of weight, - stiffness, - high degree of mdeterminancy, - almost no bending element so, using minimum quantity of materials, - freedom of drawing and forming, - great facility in erection, in disassemble and in changing the truss members. vinAlso in Türkiye, space truss structures have been used widely smde 1985. The using ratio of space truss structures in Türkiye, has increased continously every year. Approximately, fifteen construction companies, manufacture products on this subject in Türkiye and, %85 of these companies, choose a joint type similar to Mero joint type, in their manufactures. This kind of joint type is made up of a sphere in which there are eighteen screwed holes at theree directions perpendicular to each other and at their bisectors, and member of space truss structures have been connected to this spehere, with high-strength bolts, at the joints. The high-strength bolts used to connect the members to the joints, or spheres, include a transverse brad hole, on their shanks. Bolts, which are used to connect the members to the joints, screwed into the sphere with a brad. The Usefulness of Stainless Steel Stainless steels do not rust in the atmosphre as most other steels do. The term stainless implies a resistance to staining, rusting, and pitting m the air, moist and polluted as it is, and generally defines a chromium content in excess of 1 1% but less than 30%. And the fact that the stuff is steell means that base is iron. With spesific restrictions in certain types, the stainless steels can be shaped in conventional ways. They can be produced and used in the ast cast condıtıons;shapes can be produced by the powder-metallurgy techniques ; cast ignots can be railed and forged (and this accounts for greatest tonnage by far). The rolled product can be drawn, bent, extruded, or spun. Stainless steel can be further can be shaped by machining, and can be joined by soldering, brazing, and welding. It can be used as an integral cladding on plain carbon or low alloy steels. The generic term“stainless steell”covers scores of standard compositions as well as variations bearing company trade names and special alloys made for particular aplications. Stainless steels vary in their composition from a fairly simple alloy of, essentially, iron with ll%chromium, to complex alloys that include 30%chromium, substantial quantities of nickel and half adozen other effective elements. At the chromium, high-nickel and of the range they merge into other groups of heat-resisting alloys, and one has to be arbitrary about a cut off point. If the alloy content is so high that the iron content is less than 50%, however, the alloy falls outside the stainless family. Even with this imposet restrictions on compositions, the range is great and naturally, the properties that affect fabrications and use vary enormously. It is obviously not enough to specify simply a“stainless steel”. IXClassification of Stainless Steels The varms specifying bodies categorize stainless steels according to chemical compositions and other properties. For example, the American Iron and Steel Instituted (AISI) lists more than 40 approved wrought stainless steel compositions; The American Society for Testing and Materials(ASTM) calls for specifications that may conform to AISI compositions but additionally require certain mechanical properties and dimensional tolerances; the Alloy Casting Institute(ACI) specifies compositions for cast stainless steels within the categories of corrosion-and heat-resisting alloys; the Society of Automotive Engineers (SAE) has adopted AISI and ACI compositional specifications. In addition federal and military specifications and manifacturers' specifications are laid down for special purposes and sometimes acquire a general acceptance. However, all the stainless steels, whatever specifications they conform to, can be conveniently classified into five major classes that represent three distinct types of alloy constitution, or structure. This classes are ferrıtıc, martensıtıc, austenitic, manganese-substituted austenitic, and preıpıtatıon-hardenıng. Ferritic Stainless Steels. This class is so named because the crystal structure of the steel is the same as that of iron at room temperature. The alloys in the class are magnetic at room temperature and up to their Curie temperature (about 1400F). Common alloys in the ferritic class contain between 11 and 27% chromium, no nickel, and 0.2% maximum carbon in the wrought condition. The low-chromium alloys of the class are the cheapest stainless steel, and therefore, where strength requirements can be met and the corrosion problem demands nothing more elaborate, they have an economic appeal. However, limitations to their use are associated with fabrication difficulties. Hence we find that while a prodution-line operation may be designed to accomodate a ferritic stainless steel (as may be the case with automotive trim), the more casual user of stainless steel seems to avoid them, even when their properties would be adequate for the application. Martensitic Stainless Steels. Just as iron-carbon alloys are heat treatable, so alloys with a properly adjusted composition of iron, chromium and carbon (and other elements) can be quenched for maximum hardness and subsequently tempered to improve ductility. We recall that the hardenability of alloy steels is greater than that of plain carbon steels; that is, as the alloy content increases, so will a greater thickness be hardened undergiven quenching conditions. The martensitic stainless steels, which necessarily contain more than 11% chromium, have such a great hardenability that substantial thicknesses will harden during air cooling, and nothing more drastic than oil quenching is ever required. The hardness of the as-quenchedmartensiyic stainless steel depends upon its carbon content. However, as we shall se, the development of mechanical properties through quenching and tempering is inevitably associated with increased susceptibility to corrosion. Austenitic Stainles Steel. The high temprature form of iron (between 1670 and 2250 f) is known austemte. (strickly speaking the term austenite also implies carbon in solid solıtıon.). The structure is none magnetic and can be retained at room temprature by appropriate alloying. The most common austenite retainer is nickel. Hence, the traditional and familiar austenitic stainless steels have acomposition that contains sufficient chromium to offer corrosion resitence, together with nickel to ensure austenite at room temprature and below. The basic austenite composition is the familiar 18% chromium, 8% nickel alloy. Both chromium and nickel contents can be increased to improve corrosion resistance, and additional elements (most commonly molybdenum ) can be added to futher enhace corrosion resistance. While the ferntic stainless steels can be strength to some extent by cold working, this effect is not great, and its extent is limited by the rather low ductulity of the grade. However, the austenitic grades are much more ductile: they can surfer more cold work without breaking, and, further, during cold work, many members of the group undergo a transformation that is, in fact, martensitic.Thus we should expect to find substantial strengthening in many austenitic steels during cold working. The austenitic stainless grades are easier to weld than the ferritic. Sensitization can be reasonably overcome ; the problem of grain growth is not nearly so critical ; there are fewer problems of lack of weld ductility. This, with the comparative ease of forming, makes the austenitic stainless steel a reasonable one to handle in the shop. Manganese-Subsititued austenitic stainless steels The austenitic structure can be encoureged by elements other than nickel, and the subsitituion of mangenese and nitrogen produces aclass that we belive is sufficiently different in its properties to be separeted from the chromium- nickel austelitic class just descirebed The most important difference lies rhe higher strength of the mangenese-subsituted alloys. Precipitatio-Hardening Stainless Steels. Just as the familiar aluminum age- herdening alloys can be heat trated to improve their strength through a process that is associated with the formation of a precipitate, so stainless steels can be designed so that their composition is amenable to precipitation hardening. This class cuts across two of the other classes, to give us martensitic and austenitic presipitation-hardening stainless steels, in this class we find stainless steels with the greates useful strength as well as the highest useful operating temperature. XIBasic 18-8 Steels: AISI 301,302 and 304. These steells accounts for more than half of austenitic stainless steel production. 304 contains a maximum of 0.08% carbon, and the chromium range is increased by 1 or 2% (which may not show in the particular shipment ). However, the lower carbon reduces susceptibility to sensitization ( although a more complete remedy must lie in the selection of an extra carbon or a stabilized grade) and also reduces the extent of work hardening, particularly at moderrate amounts of cold work. Stabilized Steels : AISI 321, 347 and 348 Sensitization can be reduced by the addition of strong carbide formers to the basic stainless steei composition. The composition of 321 is similar to 304, but titanium is added to a minimum of five times the carbon content. The room-temperature mechanical properties of the stabilized grades are similar to those of 304. Differences arises, of course, in corrosion performance and, as we will see, in some aspects of fabricabilitry. High-temperature properties of the stabilized grades show improved resistance to creep and rupture over 304. This study has two goals. One is to investigate problems that may emerge as a result of the use of stainless steel material in space frames. The other one is to compare theoretical strength value of stainless steel with strength value of stainless steel obtained from experiment. To achive these goals, six experiments have been implemented. In experiments, there have been two different diameters and three experiments have been implemented for each diameters. As a result of these experiments, in all samples, yield signs were seen first in the pipe. Therefore, when allowable load capacity of bar each type, which form up space frame, is being calculated, pipes' theoretical yield stress can be used. In this case, experimental load capacity which is calculated according to experimental yield stress, is in safer side than theoretical load capacity. This extra safety coefficient is 1.42 times in 1 1/4“ pipes and 1.80 times in 3”pipes. When same comparison is done according to experimental load capacity that is based on the proportional limit stress, then safety coefficient is 1.18 in 1 1/4“ pipe and 1.42 in 3”pipes. Xll
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