**1. Introduction**

24 Will-be-set-by-IN-TECH

232 Mechanical Engineering

can be noticed that the value of angle of attack, at this moment, mostly depends on *q*, since *a*<sup>13</sup> = 1. In this way, every term *Aij* on the right-hand side of Eq.(6) can be analyzed on its impact on the left-hand side of same equations. Analysis of every term *Aij*, brings about a deeper understanding of the physical image of the studied regime. In addition, it enables the determination of terms that have the most effect on such a state, in cases when the aircraft does not fulfill necessary requirements for spin, and by appropriate modifications obtain an

[1] R.H. Barnard; D.R. Philpott; A.C. Kermode (2006). *Mechanics of Flight* (11th Edition),

[4] Barnes W. McCormick (1994). *Aerodynamics, Aeronautics, and Flight Mechanics*, (2nd

[5] John D. Anderson (2001). *Fundamentals of Aerodynamics* (3rd Edition), McGraw-Hill

[6] J. H. Blakelock (1991). *Automatic Control of Aircraft and Missiles*, John Wiley & Sons, Inc.,

[7] Bernard Etkin; Lloyd Duff Reid (1995). *Dynamics of Flight: Stability and Control* (3rd

[8] D. E. Hoak (1975). *USAF Stability and Control DATCOM*, N76-73204, Flight Control Division, Air Force Flight Dynamics Laboratory, Wright-Patterson Air Force Base, Ohio [9] D. Raymer (2006). *Aircraft Design: A Conceptual Approach* (4th Edition), AIAA Education

[10] Roger D. Schaufele (2000). *The Elements of Aircraft Preliminary Design*, Aries Pubns, ISBN:

[11] E. L. Houghton; P. W. Carpenter (2003). *Aerodynamics for Engineering Students* (5th

[2] Warren F. Phillips (2009). *Mechanics of Flight* (2nd Edition), Wiley, ISBN: 0470539755 [3] B. Pamadi (2004). *Performance, Stability, Dynamics, and Control of Airplanes* (2nd Edition),

aircraft with necessary technical characteristics for spin.

Prentice Hall, ISBN: 1405823593

AIAA Education, ISBN: 1563475839

Edition), Wiley, ISBN: 0471575062

Edition), Wiley, ISBN: 0471034185

New York, ISBN: 0471506516

Series, ISBN: 1563478293

0970198604

Science/Engineering/Math, ISBN: 0072373350

Edition), Butterworth-Heinemann, ISBN: 0750651113

**9. References**

Since its early days the development of railway systems has been an important driving force for technological progress. From the 1840s onward a dense railroad network was spread all over the world. Within a few decades railway became the predominant traffic system carrying a steadily increasing volume of goods and number of passengers. This rapid development was accompanied by substantial developments in many areas such as steel production, engine construction, civil engineering, communication, etc (Zerbst et al., 2005). The railway industry worldwide is introducing heavier axle loads, higher vehicle speeds, and larger traffic volumes for economic transportation of goods and passengers. Increasing demands for high-speed services and higher axle loads at the turn of the 21st century account for quite new challenges with respect of material and technology as well as safety issues. The main factors controlling rail degradation are wear and fatigue, which cause rails to become unfit for service due to unacceptable rail profiles, cracking, spalling and rail breaks. Degradation of rail is microstructure and macrostructure sensitive and there is a complicated interaction between wear mechanisms, wear rates, fatigue crack initiation and growth rates, which affect rail life (Eden et al.,2005; Kapoor et al.,2002). Defects such as squats and wheelburns occur even in the most modern and well maintained railway networks and, as a broad general rule, every network develops one such defect each year, every two kilometers. At least one European railway network suffers almost 4000 rail fractures every year. Although such fractures are rarely dangerous when actively managed, they entail a high replacement cost and can be disruptive to the network (Bhadeshia,2002). The replacement of such defects with a short rail section is expensive and not always desirable as it introduces two new discontinuities in the track in the form of two aluminothermic weld that destroy the advantages obtained with long hot-rolled rail.

Given that an average cost per repair or short replacement rail can run into several thousands of euros and that the occurrence of wheel rail interface defects is likely to increase with the evident increase in levels of traffic on most railways, the importance of the surface welding is easy to understand. Growing need for reparation due to large financial demands, have imposed research in this field.

Based on up-to date theoretical grounds and referencial facts, the aim of this paper is to show the possibilities of surface welding of the pearlitic high-carbon steel and the properties of the obtained joint. Discussion of the aquired results and conclusions indicate superior

Surface Welding as a Way of Railway Maintenance 235

Fig. 1. Typical development of a rail crack (schematically) (Ishida &Abe, 1996).

disintegration of the rail (Cannon et al.,2003).

Such damage can be repaired by surface welding, Fig 2b.

today.

Rolling contact fatigue (RCF) is likely to be a major future concern as business demands for higher speed, higher axle loads, higher traffic density and higher tractive forces increase. Head checks, gauge-corner cracks and squats are all names for surface-initiated RCF defects. They are caused by a combination of high normal and tangential stresses between the wheel and rail, which cause severe shearing of the surface layer of the rail and either fatigue or exhaustion of ductility of the material. The microscopic crack produced propagates through the heavily deformed (and orthotropic) surface layers of steel at a shallow angle to the rail running surface (about 10◦) until it reaches a depth where the steel retains its original isotropic properties. At this stage the crack is a few millimetres deep into the rail head. At this point the crack may simply lead to spalling of material from the rail surface. However, for reasons still not clearly understood, isolated cracks can turn down into the rail, and, if not detected, cause the rail to break. These events appear to be rare, but are highly dangerous since RCF cracks tend to form almost continuously at a given site. Fracture at one crack increases stress in the nearby rail, increasing the risk of further breaks and

RCF initiation is not normally associated with any specific metallurgical, mechanical or thermal fault; it is simply a result of the steel's inability to sustain the imposed operating conditions. The problem is known to occur in most of the rail-steel types in common use

While wear has been reduced, rolling contact fatigue defects have become more prominent on busy routes where the rails are highly stressed. Although its wear reserve may not be used up, rail may have to be replaced because such defects quickly become critical for safety (Pointner & Frank, 1999). The relationship between RCF and mechanical wear is not well undersood, as for example zero (or minimal) mechanical wear leads to significant microcrack propagation and thus RCF failure. On the other hand, excessive mechanical

The rate of rail degradation depends also on the location; rail head erosion is at a maximum in regions where the track curves. In Fig.2 is shown damage of the inner edge of rail head, caused by centrifugal force which tends to expel vehicle towards the outside of the track.

wear eliminates RCF but leads to unrealistically short rail life (Kapoor et al., 2001).

properties of reparation welded layers in comparison to base steel. In repaired rail, maximal stresses are induced in newly deposited layer, i.e. new layer becomes area of future crack initiation, that in turn will delay its initiation and provide secure and reliable exploitation. This results open further possibilities for cheaper and reliable rail maintenance in future. Finally, this work shows clearly that repaired rails, due to improved microstructure and crack initiation resistance, have dominant mechanical properties in comparison to the original rails.
