Dr Stephen Marich - Marich Consulting Services - Module 1: Wheel rail dynamics

• 1. Wheel/Rail Interface Forum Brisbane, May 2014 The Basics of Wheel/Rail Interaction The Wheel/Rail Interface

2. Wheel/Rail Interface Forum Brisbane, May 2014 The Basics The Applied Loads/Forces @ The Wheel/Rail Interface and the Contact Area xy z zx Contact area Pressure distribution over contact area 3. Wheel/Rail Interface Forum Brisbane, May 2014 Loads/Stresses - Contact Lateral Creep Creep Stresses are critical for development of surface defects on both wheels and rails Contact Patch Contact Stress Zone Longitudinal Creep Vertical Load/ Force Lateral Load/ Force The Basics Contact Patch 5mm wide x 12mm long x 8mm deep 4. Wheel/Rail Interface Forum Brisbane, May 2014 The Basics Creep Forces/Stresses Creep forces/stresses are generated at the wheel/rail contact patch, by the very localised action of the wheel rolling on the rail. Creep forces in the longitudinal direction are generally obtained when the wheels apply some traction to the rail, or when the solid wheelset tries to engage a sharp curve and compensate for the different wheel diameters contacting the rails. Creep forces in the lateral or transverse direction are generally obtained when the wheelset oscillates laterally on the rail, or when wheelset/bogie steering occurs. Often, both longitudinal and lateral creep forces are produced, for example: when a wheelset attempts to engage a curve in a misaligned mode, ie crabbing, causing a high angle of attack of the wheel on the rail. 5. Wheel/Rail Interface Forum Brisbane, May 2014 The Basics Longitudinal Creep For coned wheels and canted rails, as wheelset moves towards one rail (High), DH > DL In a solid wheelset, when DH > DL the differential is compensated for by Longitudinal Creep Forces Produced when traction is applied to the rails by the wheelsets Also 6. Wheel/Rail Interface Forum Brisbane, May 2014 Lateral Creep The Basics When DH > DL the wheelset tries to move back to equilibrium position (D = 0) Wheelset Steering (Lateral Creep Forces) Produced when wheelset oscillates from side to side in tangent track and shallow curves Also 7. Wheel/Rail Interface Forum Brisbane, May 2014 The Basics Combined Longitudinal and Lateral Creep Produced when wheelset has high angle of attack on the rail 8. Wheel/Rail Interface Forum Brisbane, May 2014 The Basics Spin Creep Produced when 2 point contact occurs on the high rails which leads to R on the same rail Rrs Rrs Rgf 9. Wheel/Rail Interface Forum Brisbane, May 2014 Adhesion/Microslip at Contact Patch Direction of rolling Adhesion Traction Distribution Microslip The Basics 10. Wheel/Rail Interface Forum Brisbane, May 2014 Shear Stresses The main stresses that are produced within the contact patch are shear in nature (ie they act at an angle to the loading direction), and depend on a range of factors, in particular: The vertical wheel load The radii of the contacting surfaces, including the wheel tread radius and the rail crown radius The creep (or traction) forces Load Shear Stress The Basics 11. Wheel/Rail Interface Forum Brisbane, May 2014 Shear Stresses Pure Rolling (Tangent Track) Notes: With no/small traction, maximum occurs at 2-4mm from contact surface Maximum shear stress increases as wheel load increases and rail crown radius decreases Wheel Load and Contact Shear Stresses 0 100 200 300 400 500 600 700 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 Depth Below the Wheel/Rail Contact Surface (mm) 150 kN 187.5 kN 225 kN ShearStresses Rail Crown Radius and Contact Shear Stress 0 100 200 300 400 500 600 700 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 Depth Below the Wheel/Rail Contact Surface (mm) 150 mm 200 mm 250 mm 300 mm ShearStresses The Basics 12. Wheel/Rail Interface Forum Brisbane, May 2014 Notes: At higher traction (higher T/N), the maximum increases substantially and moves closer to the contact surface Shear Stresses Traction/Creep Traction and Contact Shear Stress 0 100 200 300 400 500 600 700 800 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 Depth Below the Wheel/Rail Contact Surface (mm) T/N=0 T/N=0.1 T/N=0.2 T/N=0.3 T/N=0.4 ShearStresses The Basics 13. Wheel/Rail Interface Forum Brisbane, May 2014 The Basics Material Performance Johnson et al Shakedown Limit b a c b a c Y-axis is P0 (load) divided by shear yield strength , k X-axis is traction coefficient (Tangential/normal force) Point a: always elastic no damage Point b: initially plastic, then shakes down (work hardens) to elastic no damage if maintained Point c: always plastic, always damage Higher T/N reduces the shakedown zone 14. Wheel/Rail Interface Forum Brisbane, May 2014 The Basics Beneficial work hardening can occur near the rail/wheel surface due to material deformation. The depth of the beneficial compressive/work hardened layer increases: As the wheel loads increase (more deformation). As the rail hardness decreases (more deformation). 240 260 280 300 320 340 360 380 400 420 440 460 0 2 4 6 8 10 12 14 16 Depth from Contact Surface (mm) After 50 MGT After 200 MGT After 400 MGT After 800 MGT After 1000 MGT Base Hardness Work Hardened Region Hardness Controlled deformation/ work hardening improves the rail properties and hence performance. Uncontrolled deformation leads to rail corrugations, mushrooming of the head, loss of profiles, etc. The Work Hardened Layer 15. Wheel/Rail Interface Forum Brisbane, May 2014 The Basics The Interface Layer Lubrication Friction Modification Influence the actual traction at the wheel/rail interface Also Iron oxides From environment (leaves, dust, etc) From traffic (brakeshoe debris, sand, mineral dust, etc) = 0.1 (gauge face lubricated) to 0.6 (running surface dry) 16. Wheel/Rail Interface Forum Brisbane, May 2014 Corrugations The Consequences Short pitch - about 30mm to 90mm in wavelength Long pitch - about 150mm to 450mm in wavelength 17. Wheel/Rail Interface Forum Brisbane, May 2014 The Consequences Corrugations Contributing Factors Short Pitch (lower axle loads) Differential wear associated with stick/slip of wheels in solid wheelset + excitation of the torsional resonance of the wheelset. Wheelset geometry characteristics Running surface friction Long Pitch (higher axle loads) Plastic flow + combined vertical resonance of the vehicles unsprung mass and the track stiffness All factors that influence the dynamic wheel loads All factors that influence wheel/rail contact stresses All factors that influence the creep/traction forces All factors that enhance the material deformation 18. Wheel/Rail Interface Forum Brisbane, May 2014 The Consequences Wear Major longer term deterioration mode Particularly on gauge face of high rails in sharp curves and wheel flanges 19. Wheel/Rail Interface Forum Brisbane, May 2014 The Consequences Wear Contributing Factors High lateral forces. Insufficient material hardness. Poor wheel and rail profiles. Inefficient lubrication: Wrong lubricator location. Wrong lubricant. Poor lubricator maintenance. Poor wheelset/bogie curving performance: Poor bogie maintenance. Higher stiffness bogies. 20. Wheel/Rail Interface Forum Brisbane, May 2014 The Consequences Rolling Contact Fatigue Defects (RCF) Gauge Corner Checking Running Surface Checking Shelling Transverse Defects 21. Wheel/Rail Interface Forum Brisbane, May 2014 The Consequences Rolling Contact Fatigue Defects (RCF) Squats from Gauge Corner RCF RCF Defects in Wheels 22. Wheel/Rail Interface Forum Brisbane, May 2014 The Consequences RCF Defects Contributing Factors All factors that influence the resultant wheel/rail contact shear stresses and the ability of the material to withstand such stresses, including: The nominal, dynamic and impact wheel loadings, and all factors that influence such loadings. The wheel and rail profile characteristics. The resultant traction/creep forces at the contact zone. The cleanliness of the older rail (and wheel) materials, in the case of shelling defects. The strength of the rail (and wheel) materials. + Enhancement of growth by contamination of contact surfaces. + Increased development if rail wear rate is minimal. 23. Wheel/Rail Interface Forum Brisbane, May 2014 The Consequences Thermal/Traction Defects Wheel Burns (Both Rails) Squats (One Rail) 24. Wheel/Rail Interface Forum Brisbane, May 2014 The Consequences Thermal/Traction Defects Skids/Squats Wheel Flats 25. Wheel/Rail Interface Forum Brisbane, May 2014 The Consequences Thermal/Traction Defects Contributing Factors All factors that enhance partial/continuous slipping of wheels on rails and material transformation, including: Excessive track grades. Poor train driving procedures, such as rapid acceleration/ deceleration. Insufficient locomotive/traction power. Contamination of the running surface of the rails. Higher tractive effort units. The traction/creep forces at the wheel/rail contact zone. The wheel and rail profile characteristics. Controlled slip power units. Torsional build up/release in axles? 26. Wheel/Rail Interface Forum Brisbane, May 2014 The Consequences Noise/Vibration From: Corrugations. Surface irregularities: Wheel burns. Squats. Wheel flats. Wheel/rail flanging. Wheel squeal. 40 50 60 70 80 90 100 110 120 0 10 20 30 40 50 60 70 80 90 100 110 120 130 Time (seconds) [email protected](dBA) Standard Lubrication No Friction Modification Modified Lubrication Friction Modification 27. Wheel/Rail Interface Forum Brisbane, May 2014 The Consequences Noise/Vibration Attenuation Reduced development of surface defects. Improved gauge face lubrication. Appropriate rail surface maintenance. Control of running surface friction. Improved wheelset bogie monitoring and maintenance. 28. Wheel/Rail Interface Forum Brisbane, May 2014 The Consequences Others (covered in other units) Allowable wear limits Wheelset/bogie dynamics High Conicity Contact Increased Risk of Hunting Gauge Side 29. Wheel/Rail Interface Forum Brisbane, May 2014 Concluding Remarks Wheel/Rail Interface Wheel/Rail Interaction Vehicle/Track Dynamics Material Properties and Performance Maintenance Practices Operating Practices Wheel/Rail DesignVehicle/Track Design Performance Monitoring 30. Wheel/Rail Interface Forum Brisbane, May 2014 Concluding Remarks A Major Future Problem The Fathers Johann Klingel Heinrich Hertz Frederick Carter Joost Kalker Ken Johnson Charles Frederick The Sons Stuart Grassie Joseph Kalousek Stephen Marich Paul Clayton Harry Tournay Anders Ekberg Claus Epp Yoshihiko Sato The Grandsons Robert Frohling Darrien Welsby ??????????????????????????????????? Need to develop people with both a strong and (varied) scientific background and also a strong first hand connection to the actual railway operations (you have to see and do things yourself) Need to reduce barriers between Academia and Industry (not much has changed!!!)