FATIGUE PROPERTIES OF MACHINED SPECIMENS FROM CAST AND FORGED RAILROAD WHEELS
Queiroz, Syme R. S. 1, Guimarães, V.2, and Ferreira, I.3 1,3
FEM, Universidade Estadual de Campinas (Unicamp), Campinas, SP, Brazil 1
DCC, Instituto Federal do Pará (IFPA), Belém, PA, Brazil 3
FEG, Universidade Estadual Paulista, Guaratinguetá, SP, Brazil
ABSTRACT
The worldwide tendency of railways is the high load per wagon in cargo transport and high speed in the passenger sector. In both situation the wheel is strongly required, especially in respect of fatigue, which have being the mainly cause in accidents having wheel failure or bring the wheel out of service before end of its life. This research shows the comparison between the fatigue properties of forged and cast wheels. The research indicates what type of wheel is more resistant to fatigue taking account the test conditions.
Keywords: Wheel, fatigue, mechanical properties, fatigue properties
INTRODUCTION
The failures caused by fatigue in railway wheels are the mainly cause of wheels removal before the end of its life, as well as, accidents involving derailment of wagons. This research analyzed specimens of forged and cast wheels having similar chemical composition in the same class of material (class C) from AAR (Association of American Railroads) (1). The fatigue properties were analyzed in samples taken from the rim of the wheel (2, 3). The wheels were divided as follow:
Wheel 1: Cast wheel
Wheel 2: Forged wheel with no degassing steel Wheel 3: Forged wheel with degassing steel
Fatigue tests were performed in three point bending specimens of rectangular section, with 7x14x63 mm, machined from three railway wheels, two forged (one with degassing of the steel and other without desgassing) and a cast, by using tests with load ratio 0.1, maximum load of 15kN (specimens from cast wheel) and 18kN (specimens from forged wheels), sine waves, and in neutral environment (2, 3, 7, 9).
MATERIALS AND METHODS
The phenomenon of fatigue occurs in railway wheels due to the nature of the request component, This phenomenon is the cycle high fatigue. Fatigue can reduce the tensile strength limit of martensitic carbon steels on average 75%, which can lead to fracture of the same. Cracks openings in railway wheels can lead to loss of part of the wheel by scaling or an extension by radial opening with release consequent of accessories exist between the wheel and the axle. Fatigue tests contribute with caution and defects minimizing in cast and forged railway wheels (4, 7, 8). Most fractures of wheels originate from a fatigue crack on the outer circumference of the wheel tread. Cracks that lead to failure are often associated with some type of mechanical or metallurgical damage (4, 5, 6, 7). The figure 1 gives an overview of the damaged wheel and the resulted final crack, which grew radial towards the axle. The crack origin was at the outer surface of the rim and the critical crack size, which led to the fracture, was only 25 mm in length.
position in all wheels. The following specimens were extracted from each wheel type: 12 specimens. The specimens dimension used on this research are showed on follow picture (Figure 2a). The Figures 2b show the localization of each specimen.
According to the introduction, the research analyzed wheels from the same chemical composition class of AAR. The wheel chemical composition is on Table 1:
TABLE 1 – Wheels chemical composition
Chemical Composition Wheel 1 Wheel 2 Wheel 3
Carbon 0.744 0.73 0.73 Manganese 0.643 0.72 0.75 Phosphorus 0.016 0.009 0.013 Sulfur 0.008 0.014 0.019 Silicon 0.593 0.32 0.31 Nickel 0.02 0.07 0.014 Chromium 0.287 0.011 0.015 Molybdenum 0.007 0.024 0.031 Vanadium 0.002 0.002 0.003 Cupper 0.21 0.13 0.12 Aluminum 0.01 0.01 0.017 Titanium 0.002 0.009 0.001 Niobium 0.001 0.0012 0.0026 Gases (ppm) Nitrogen 58.17 60.31 26.36 Hydrogen - 5.8 0.5
The railroad wheels are manufactured by forging or casting process. The forged wheels have no restriction application, while cast wheels are restricted for freight transportation. The following flow charts describe the difference between these processes:
Figure 2 - (a) Fatigue specimen. (b) Fatigue specimen on wheel rim.
- Cast Wheel
- Forged Wheel
Tests were performed on a machine of the type servo-hydraulic MTS (Figure 4.a), model TestStar II, and load capacity of 10 tons. Fatigue tests were performed at three points of bending specimens (Figura 4.b) and temperature of 25º C.
RESULTS
The results are basically the same for three wheels in terms of the Weibull distribution. Table 2 shows the results of fatigue tests for the three wheels, the Ingot cut operation in blocks Steel
manufacture
Ingot teeming
Blocks heating
Wheel machining
Forging + Rolling mill
Final Inspection Heat treatment
Shipping Cast - Molding Heat Treatment
Bore machining Shipping Final Inspection
Steel manufacture
Figure 3 – (a) Photo MTS machine used in the fatigue test. (b) Photo of three points of a railway cast wheel specimen during the bending fatigue test.
lives were 104,454, 117,453 and 98,801 cycles, respectively for cast and forged wheels, and the correlation coefficient of about 0.9 for the three samples. Figures 5 and 6 shows test results (fatigue tests and fractography).
Table 2 - Results of fatigue tests of the specimens from the cast and forged wheels
Wheels Specimens Average degree* Failure probability (F) (%) Fatigue life (N) (cycles) Cast (Wheel 1) Maximun load of fatigue 15kN e R=0,1 1-3 6,697 83297 1-4 16,226 84268 1-5 25,857 85346 1-6 35,510 88716 1-7 45,169 90384 1-8 54,831 101153 1-9 64,490 108464 1-10 74,142 109783 1-11 83,774 115277 1-12 93,303 116213 Average 98290 Standard deviation 13319 Forged (Wheel 2) Maximun load of fatigue 18kN e R=0,1 2-3 6,697 77644 2-4 16,226 80795 2-5 25,857 81387 2-6 35,510 83766 2-7 45,169 91036 2-8 54,831 91279 2-9 64,490 113166 2-10 74,142 132007 2-11 83,774 139598 2-12 93,303 163797 Average 105448 Standard deviation 30137 Forged (Wheel 3) Maximun load of fatigue 18kN e R=0,1 3-3 6,697 75221 3-4 16,226 76982 3-5 25,857 78293 3-6 35,510 83060 3-7 45,169 89379 3-8 54,831 90012 3-9 64,490 94136 3-10 74,142 95543 3-11 83,774 104507 3-12 93,303 134370 Average 92150 Standard deviation 17493
Figure 4 - Results of the fatigue tests of the specimens machined from cast and forged wheels in terms of the Weibull statistical distribution. F is the failure probability and N is the life (number of cicles to fracture). The maximum load is 15kN for cast specimens and 18kN for the forged. NBR 6752, 1987
(a) Specimens 1-7. Fatigue zone. (b) Specimens 1-11. Fatigue zone.
Figure 5. Fractography of specimens 1-7 and 1-11 of the cast wheel.
CONCLUSION
The results obtained from the Weibull distribution showed a behavior similar to the three wheels. However, as the maximum load in the case of the cast wheel is 20% smaller, it can be concluded that fatigue life of specimens machined from the forged wheels is around 20% higher than specimens from the cast wheel.
ACKNOWLEDGMENTS
The authors gratefully acknowledge the funding by MWL Brasil, UNICAMP (Universidade Estadual de Campinas), UNESP (Universidade do Estado de São Paulo) and IFPA (Instituto Federal de Educação, Ciência e Tecnologia do Pará).
REFERENCES
1. ASSOCIATION OF AMERICAN RAILROAD. Manual of Standards and Recommended Practices Wheels and Axles, "section G", A.A.R. M-107. USA, 2007. 34p.
2. AMERICAN SOCIETY FOR TESTING AND MATERIALS. Standard terminology relating to fatigue and fracture testing. ASTM E 1823-10. USA, 2010. 23p.
3. ASSOCIAÇÃO BRASILEIRA DE NORMAS TÉCNICAS. Weibull distribution applied to fatigue analysis. NBR 6742. 1987. (in Portuguese). 18p
4. FERREIRA, I., Propriedades Mecânicas dos Materiais e Mecanismos de Fratura- parte B. Campinas: FEM, UNICAMP, 2009.
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8. SIVAPRASAD, S.; TARAFDER, S.; RANGANATH, V. R.; PARIDA, N. Fatigue and fracture behaviour of forged and cast railway wheels. National metallurgical laboratory Jamshedper. India. 6p. 831007. 2007.
9. TARAFDER S., SIVAPRASAD S., RANGANATH V. R. Comparative assessment of fatigue end fracture behaviour of cast and forged railway wheels. National metallurgical laboratory. Jamshedpur. India. National Aerospace Laboratories. Bangalore 560017, 14p. 2007.
FATIGUE PROPERTIES OF MACHINED SPECIMENS FROM CAST AND FORGED RAILROAD WHEELS
Queiroz, Syme R. S. 1, Guimarães, V.2, and Ferreira, I.3 1,3
FEM, Universidade Estadual de Campinas (Unicamp), Campinas, SP, Brazil 1
DCC, Instituto Federal do Pará (IFPA), Belém, PA, Brazil 3
FEG, Universidade Estadual Paulista, Guaratinguetá, SP, Brazil
ABSTRACT
The worldwide tendency of railways is the high load per wagon in cargo transport and high speed in the passenger sector. In both situation the wheel is strongly required, especially in respect of fatigue, which have being the mainly cause in accidents having wheel failure or bring the wheel out of service before end of its life. This research shows the comparison between the fatigue properties of forged and cast wheels. The research indicates what type of wheel is more resistant to fatigue taking account the test conditions.
