Evolution of rail surface degradation in the tunnel: The role of water on squat growth under service conditions

Abstract Squats on open tracks, as opposed to track inside tunnels, have been reported by railway networks across the world. Theoretical research hypothesised that the hydraulic entrapment of water is critical to crack propagation associated with squat growth. The requirement for a fluid to enable crack propagation provides a rational to why squats vanish as soon as the railway enters a tunnel. However, the metallurgical evidence from the ex-service rails damaged by the presence of water at wheel and rail contact interface is lacking. In the current work, a localised section of rail was found to suffer severe surface damage associated with water dropping from an air-conditioning system located in a tunnel roof. This section of rail represented an ideal controlled location for detailed metallurgical investigation to examine the formation of white etching layers (WELs) under both dry and wet conditions. The location allowed to determine the relationship between WELs and squat initiation; and also to investigate mechanics of water on crack propagation and squat growth of ex-service rail. It was found that the presence of water on the rail surface is not an important condition for WEL formation. White etching layer in dry rails was observed to be associated with a distinguished sub-layer; called brown etching layer (BEL). Brown etching layer is thought to be a development stage of white etching layer. Crack initiation on rails inside the tunnel was confirmed to be caused by ratchetting (severe plastic deformation of the surface layer), with the requirement of the rail top surface to contain WEL. Crack propagation was manly influenced by the presence of water. The metallurgical analysis revealed significant amount of oxides existed along the crack faces. The presence of oxides associated with an absence of shear deformation on the cracks faces revealed that crack growth was driven by Mode I loading (tensile opening) associated with the mechanism of hydraulic entrapment of water. Furthermore, both fracture behaviour of some cracks, and confirmation of the presence of corrosive products inside the cracks by EDS analysis, represent strong evidence that stress corrosion cracking was involved in both crack growth and the observed formation of secondary cracks.

[1]  Sakdirat Kaewunruen,et al.  Wheel/rail conditions and squat development on moderately curved tracks , 2012 .

[2]  Yi Zhu,et al.  Friction Between Wheel and Rail: A Pin-On-Disc Study of Environmental Conditions and Iron Oxides , 2013, Tribology Letters.

[3]  Rolf Dollevoet,et al.  Dutch research results on wheel/rail interface management: 2001–2013 and beyond , 2014 .

[4]  Ulf Olofsson,et al.  Adhesion modeling in the wheel–rail contact under dry and lubricated conditions using measured 3D surfaces , 2013 .

[5]  R. Dollevoet,et al.  On the mechanism of squat formation on train rails – Part II: Growth , 2013 .

[6]  Stephen Marich,et al.  The Development of Squat Defects under High Axle Load Operations , 2002 .

[7]  Makoto Ishida,et al.  Adhesion between rail/wheel under water lubricated contact , 2002 .

[8]  Zili Li,et al.  Rolling–sliding laboratory tests of friction modifiers in dry and wet wheel–rail contacts , 2010 .

[9]  Motohiro Kaneta,et al.  A Possible Mechanism for Rail Dark Spot Defects , 1998 .

[10]  S L Grassie,et al.  Studs: a squat-type defect in rails , 2012 .

[11]  J. F. Santa,et al.  Dry and lubricated wear of rail steel under rolling contact fatigue - Wear mechanisms and crack growth , 2017 .

[12]  G. Krauss.  Steels: Processing, Structure, And Performance , 2005 .

[13]  Zili Li,et al.  Squat growth—Some observations and the validation of numerical predictions , 2011 .

[14]  Andrew Wilson,et al.  The Epidemiology of Squats and Related Defects , 2008 .

[15]  C. Esveld,et al.  An investigation into the causes of squats—Correlation analysis and numerical modeling , 2008 .

[16]  Rolf Dollevoet,et al.  Differential wear and plastic deformation as causes of squat at track local stiffness change combined with other track short defects , 2008 .

[17]  Stanisław Bogdański.  Liquid–solid interaction at opening in rolling contact fatigue cracks , 2005 .

[18]  O. Datsyshyn,et al.  A fracture mechanics approach to prediction of pitting under fretting fatigue conditions , 2006 .

[19]  Yi Zhu,et al.  Adhesion in the wheel-rail contact under contaminated conditions , 2011 .

[20]  L. Kestens,et al.  Volume Expansion of Compacted Graphite Iron Induced by Pearlite Decomposition and the Effect of Oxidation at Elevated Temperature , 2013, Oxidation of Metals.

[21]  Stanisław Bogdański.  A rolling contact fatigue crack driven by squeeze fluid film , 2002 .

[22]  Rolf Dollevoet,et al.  The vertical and the longitudinal dynamic responses of the vehicle–track system to squat-type short wavelength irregularity , 2013 .

[23]  Yi Zhu,et al.  Wear between wheel and rail:A pin-on-disc study of environmental conditions and iron oxides , 2015 .

[24]  R. Carroll.  Surface metallurgy and rolling contact fatigue of rail , 2006 .

[25]  Y. Berthier,et al.  Tribological characterization of rail squat defects , 2013 .

[26]  A. Kapoor.  Wear by plastic ratchetting , 1997 .

[27]  Stanisław Bogdański,et al.  Numerical modelling of a 3D rail RCF 'squat'-type crack under operating load , 1998 .

[28]  W. Daniel,et al.  Stress intensity factors around a 3D squat form crack and prediction of crack growth direction considering water entrapment and elastic foundation , 2012 .

[29]  S. Godet,et al.  Micro and Nanoscale Characterization of Complex Multilayer-Structured White Etching Layer in Rails , 2018, Metals.

[30]  Ajay Kapoor,et al.  Modelling and full-scale trials to investigate fluid pressurisation of rolling contact fatigue cracks , 2008 .

[31]  Huayong Yang,et al.  Twin-disc tests of iron oxides in dry and wet wheel−rail contacts , 2016 .

[32]  J. Beynon,et al.  The influence of lubricant type on rolling contact fatigue of pearlitic rail steel , 1999 .

[33]  A. Bower.  The influence of crack face friction and trapped fluid on surface initiated rolling contact fatigue cracks , 1988 .

[34]  A. Kapoor.  A re-evaluation of the life to rupture of ductile metals by cyclic plastic strain , 1994 .

[35]  David Fletcher,et al.  Simulation study of thermally initiated rail defects , 2014 .

[36]  M. Olzak,et al.  Investigation of crack propagation during contact by a finite element method , 1991 .

[37]  S. Bogdański,et al.  Experimental and theoretical investigation of the phenomenon of filling the RCF crack with liquid , 2005 .

[38]  Zili Li,et al.  “Brown etching layer”: A possible new insight into the crack initiation of rolling contact fatigue in rail steels? , 2016 .

[39]  S. Bogdański,et al.  3D model of liquid entrapment mechanism for rolling contact fatigue cracks in rails , 2008 .

[40]  Zili Li,et al.  Laboratory simulation of martensite formation of white etching layer in rail steel , 2016 .

[41]  Zili Li,et al.  A laboratory investigation on the influence of the particle size and slip during sanding on the adhesion and wear in the wheel–rail contact , 2011 .

[42]  O. P. Datsyshyn,et al.  Service life and fracture of solid bodies under the conditions of cyclic contact interaction , 2005 .

[43]  K. Six,et al.  Development of white etching layers on rails: simulations and experiments , 2016 .

[45]  S. Bogdański.  Quasi-static and dynamic liquid solid interaction in 3D squat-type cracks , 2014 .

[46]  Rolf Dollevoet,et al.  On the mechanism of squat formation on train rails – Part I: Origination , 2013 .

[47]  S L Grassie,et al.  Squats and squat-type defects in rails: the understanding to date , 2012 .

[48]  Ajay Kapoor,et al.  The current status of theory and practice on rail integrity in Japanese railways—rolling contact fatigue and corrugations , 2003 .

[49]  P. Clayton,et al.  Metallurgical Aspects of Surface Damage Problems in Rails , 1982 .

[50]  Zili Li,et al.  Influence of the Fastening Modeling on the Vehicle-Track Interaction at Singular Rail Surface Defects , 2014 .

[51]  J. Song,et al.  Experimental study on adhesion behavior of wheel/rail under dry and water conditions , 2011 .

[52]  W. R. Tyfour,et al.  Deterioration of rolling contact fatigue life of pearlitic rail steel due to dry-wet rolling-sliding line contact , 1996 .

[53]  D. Wexler,et al.  Squat formation and the occurrence of two distinct classes of white etching layer on the surface of rail steel , 2017 .

[54]  Kunihiro Kondo,et al.  Cause, increase, diagnosis, countermeasures and elimination of Shinkansen shelling , 1996 .

[55]  John H. Beynon,et al.  The effect of intermittent lubrication on the fatigue life of pearlitic rail steel in rolling-sliding contact , 2000 .