Rayların aşınma analizi ve aşınmayla ilgili formülasyon çalışması

Arslan, Mehmet
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Fen Bilimleri Enstitüsü
Raylar üzerilerinden geçen dinamik tesirler altında bulunduklarından, sonunda kullanılma özelliklerini yitirirler ve bu nedenle değiştirilmeleri gerekir. Bu zararlı etkiler gittikçe rayların yuvarlanma yüz eğlerini aşındırmaya başlar ve rayların mukavemet ve geometrik karakteristikleri değişir. Hiç şüphe yok ki rayların mukavemeti de düşer. Rayların mukavemetleri devamlı aşınmadan dolayı değişeceğinden kontrol altında tutulmalı ve sınır mukavemet değerini aşmamalıdır. Bu çalışmada, rayların aşınma analizi yapılmış ve aşınan rayların tekrar kullanılıp kullanılamayacağı konusunda bizlere ipuçları verecek bir yaklaşım getirilmiştir. Bu yaklaşımın esası ise, geometrik yapılarının kompleks olması nedeniyle mukavemet karakteristikleri kolayca hesaplanamayan rayların, başka temsili ray kesitleri tarafından temsil edilebilmesine dayanmaktadır. Bu çalışmada, standart rayları temsil edecek ray kesitleri oluşturulmuş ve daha sonra bu temsili ray kesitleri üzerinde aşınma analizi yapılmıştır. Raylarda oluşan düşey, yanal ve her iki aşınma şeklinin olduğu aşınma durumları ayrı ayrı ele alınmış ve aşınma miktarlarına göre mukavemet karakteristiklerinin nasıl değiştiği incelenmiştir. Daha önce düşey aşınma ile ilgili olarak SHRAMM tarafından geliştirilen aşınma formülü ile yapılan çalışmada ele alınan yaklaşım sonuçları karşılaştırılmış ve yapıtlar çalışma sonunda bulunan değerlerle SHRAMM'ın aşınma formülüyle hesaplanan değerlerin birbirine yakın değerler verdiği görülmüştür. Ayrıca bu çalışmada ele alınan standart ray tiplerinin yanal ve düşey aşınma miktarlarına göre mukavemet momentindeki değişimi gösteren abaklar oluşturulmuştur. Ayrıca bu çalışmada oluşturulan abakların, abakları oluşturulan standart ray tiplerinin geometrik karakteristiklerine yakın değerlerde olan ray tipleri için de kullanılabileceği dile getirilmiştir.
Today, we can probably agree that railroads are important to themselves and to their owners; but just how important are they to the people and the land they serve ? Today, when there is a widespread network of highways, airways, waterways, and pipelines, we can not say that railroads are the most important part of the country's transportation system. Nevertheless, railroads must continue for any foreseeable future to constitute the backbone of the transportation system. More recently new location and construction have been limited, generally, to line improvements and the building of branch or independent lines for access to raw materials and new industrial locations. Most recently the trend has been toward rationalizing the network, that is, retrenchment, with an emphasis on system mergers, abandoning unprofitable mileage, and rehabilitating system segments that have experianced deferred maintenance, or upgrading for higher speeds, axle loads, or traffic densities. Access to energy sources, especially coal, is causing a flurry of construction activity, as is the need to meet the passenger demands of certain highly populated and congested corridors. While the need for profit is still a dominant element, other factors are influencing the decisions to build, upgrade, or retire railroad mileage. Foremost is the recognation that the railroads' service function is essential to the nation's economy and security. Services that may not in themselves earn a profit are supported by public funds because those services make possible the conduct of other necessary and highly profitable economic activities. In general, the life of railroad is expressed by the life of the rails. In railroads maintenance, it is important to take the life of rails under the control. Rail life is usually expressed in millions of gross tons carried. The service life of rail will vary with traffic ( tonnage, axle loads, speed ), the amount of curvature, gradient, subgrade and ballast support, and the standart of maintenance. A heavier rail normally outlasts a light rail, other conditions being equal. Rail may be removed early from main track for use in secondary track. The T section rail of today has a girderlike shape. Its height is usually greater than its base, and the head is deep and narrow. Rails are designated by weight and section. A rail section must fulfil the following requirements: 1-The running surface of the rail should be sufficiently wide and designed so that the contact between wheel and rail is the most efficient possible and the surface pressures the smallest possible. 2- To assure long life of the rail, the head of the rail should be deep enough for sufficient material to be available to take the wear expected. XI 3- To ensure the required bearing capacity and bending resistance, the web must be sufficiently thick to make reasonable allowance for corrosion. 4- To ensure stability and, at the same time, providing an adequate bearing area for the sleeper or bearing plate, the base of the rail should be as wide as possible. 5- To ensure sufficient rigidity, and to provide against loss of material by corrosion, the base of the rail must be sufficiently thick. 6- The moment of resistance of the rail under vertical pressure should be as high as possible, i.e. the height of the rail must be as great as possible; the same applies to the head and base cross-sections in proportion to the cross-section of the web. 7- The resistance moment of a rail subject to horizontal forces should be as great as possible in order to obtain a sufficient lateral rigidity, i.e. the head and the base of the rails should be as wide as possible. 8- The rail must be as rigid as possible to prevent tilting, i.e. the height must not be too great in comparison to the width of the base. 9- For static reasons, the centre of gravity of the section should be as near as possible to a point at half the height of the rait. 10-The top and bottom planes of the fishing surface must be so designed as to conform with the design of the fishplate which will be used. 11- For rolling ease, and to ensure a favourable distribution of stresses within the rail cross-section, all angles, especially those in the fishing surface, should be rounded off to the greatest possible radius. Rail life may be determined by wear-abrasion, rail-end batter, curve wear. It can olso be determined by fatigue-extended repetition of flexture combined with the formation of contact-and shearing-stress -related defects such a detailed fractures. When wheel loads seldom exceeded 12000 kg and with jointed track, tangent rail was removed primarily because of head wear and rail and batter. Curve rail was usually removed because of abrasion ( curve wear). Following the advent of curve oilers, fatigure-related defects became an increasingly frequent cause for rail removal from curves. Today, where high-capacity cars and unit trains predominate, fatigue has become a major rail life factor in tangent track, where new rail is subject to heavy loading before acquiring a work-hardened running surface. But on curves abrasion wears the rail so rapidly that fatigue stresses do not have time to develop, so it acts as a prime limit on rail life. Rail life will be considered first in terms of conventional traffic, that is, jointed track carrying light ( 15000 kg ) wheel loads or a mixture of heavy and light wheel loads predominating. On tangents and on curves up to 4 degrees of curve direct wear ( abrasion ) has no practical effect in reducing rail life. Joint and surface deterioration usually do not set in until after the passage of 100 million gross tons. Above 100 million gross tons, abrasion then becomes more significant especially as curvature increases from 4 to 7 degrees. Curve wear is limiting rail life factor for curves over 7 degrees. We can can say that rail life is limited by rail-end batter and running surface abrasion, which varry with traffic. Abrasive wear varies more or less as the degree of curve, with the actual amount depending on the traffic volume and characteristics and xit whether or not curve oilers are in use. In addition, gradient has also an effect on rail life. Excessive wear and abrasion come from the use of sand and heavy brake application. Reduced speed may reduce curve wear and the greater rate of wear on low-density lines may represent less work hardening, more surface corrosion ( from less frequent wheel passage ), and a lower standart of maintenance. Vertical head alone is an inadequate measure of rail dterioration, especially on curves where excessive side wear can weaken a rail. The limit of wear on a rail is often taken as 25 % of the head area. This amount of wear may be produced by 300-600 million gross tons of traffic, but rail is often removed long before this, improper maintenance may, from a false sense of economy, destroy the salutary effects of laying new rail. Inadequate maintenance causes bent rail, chipped rail ends, and worn and battered rail ends and joints. In this study, wear of rail is analyzed and the question of can worn rail be used again or not' is answered by developing an approach for worn rails. SHRAMM's are investigations given briefly and Shramm's wear formula is compered with method proposed in this thesis. In this study, both vertical and horizontal wear are considered. At the end of this study, for several type of rails, depending on vertical and horizantal wear,the strength moment valve of worn rails are calculated and shown both in tables and in diagrams. This thesis consists of 4 chapters. The first chapter explains requirements and importance of this thesis subject. The second chapter gives general information about rails and wear. In that information, especially elements of rail are explained and detailed information on rail and its function, is given. The second chapter also gives general information about rail wear and types of wear. Chapter 3 deals with investigations. In this thesis desired results are obtained by using 3 approaches. Five different standard rail type are idealized as cross section, in the first approach. As shown in the Tablel, standard rail type and idealized rail section's resistance characteristics are mismatched. Then, the second approach is required. Table 1. Resistance Characterises Of Idealized Rail Sections According to The First Approach. XIII By using the second approach, standard rail type is idealized as T section rail. As shown in the Table 2, at the end of assumptions made, the decision which is standard rail can not be modelized by idealized rail type, is taken. In other words, at the end of the second approach, standard rail type and idealized rail section's resistance characteristics are also mismatched. The First and the second approach did not give reasonable result. Therefore, a third approach is required. By using the third approach ; W, = W- idealized- »Vstandafd is achieved. Consequently, standard rails are modelized as T section rail types. Asshown in theTable3, WideaHzed3 Wstandard is achieved. In the study of wear analysis, T section rail type which is obtained from the third approach is used instead of standard rails. Table 3 Resistance Characterictics Of Idealized Rail Sections According to The Third Approach. In wear study.the geometric characteristics of T rail, which is used instead of standard rail section, are also calculeted and given in Table 4. xrv Table 4. Geometric and Resistance Characteristics of T Section Rails Which Finally, both vertical and horizontal wear are considered. For the types of rails, depending on vertical and horizontal wear, the strength moment valve of worn rails is calculated and shown both in tables and diagrams.
Tez (Yüksek Lisans) -- İstanbul Teknik Üniversitesi, Fen Bilimleri Enstitüsü, 1996
Anahtar kelimeler
Aşınma, Raylı sistemler, Ulaşım sistemleri, Wear, Railway systems, Transportation systems