Materials testing of railway wheelset components

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Lecture: Materials Testing of Railway
Wheelset Components by Dr. Ingo Poschmann.

> About werkstoff-service
> Wheel Set Components - Duties
> Wheel Set Components – Service Conditions
> Requirements on the Materials (Static Properties)
> Product Design and Materials Testing
> Steel Making and Materials Testing
> Hot Forming and Materials Testing
> Heat Treatment and Materials Testing (Microstructure)
> Heat Treatment and Materials Testing (Mechanical Properties)
> Machining / Finishing and Materials Testing
> Testing During Service

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Materials testing of railway wheelset components

  1. 1. Materials Testing of Railway Wheelset Components Ingo Poschmann W.S. Werkstoff Service GmbH, Essen Essen – World Heritage „Zeche Zollverein“I. Poschmann, „Materials Testing of Railway Wheelset Components“, www.werkstoff-service.de 1 / 15
  2. 2. About UsCompany www.werkstoff-service.deLocation Essen (Ruhr Area), World Heritage „Zeche Zollverein“Business Fields:Materials Testing • Accredited testing lab (EN17025) → Testing of wheels, axles, rails, …Consulting • Accredited inspection body (EN17020) → Failure analysis of railway components → Technical approval of railway NDT processes → Appointed expert of the German federal railway authorityTraining • Certified and approved training facility (ISO 9001, DGZfP) → Destructive testing, non destructive testing → Heat treatment, materials engineeringI. Poschmann, „Materials Testing of Railway Wheelset Components“, www.werkstoff-service.de 2 / 15
  3. 3. Wheel Set Components - Duties • Carrying the load of the vehicle • Guiding the vehicle on track → Straight track and curves • Transmission of acceleration forces Finished railway axles • Transmission of deceleration forces • Wheels part of braking system → Tread of freight waggon wheels • Assuring high running comfort → Passenger traffic Finished railway wheelsI. Poschmann, „Materials Testing of Railway Wheelset Components“, www.werkstoff-service.de 3 / 15
  4. 4. Wheel Set Components - DutiesWheel hub RimAxle-wheel interference fit assembly FlangeWheel centre CentreFlexible hub-rim connectionWheel rim HubRunning surface, rail-wheel contactWheel flangeGuidance of the wheel set on the rails Functional elements of a wheelSummaryDifferent functional elements need different properties!Manufacturing and testing have to address that!I. Poschmann, „Materials Testing of Railway Wheelset Components“, www.werkstoff-service.de 4 / 15
  5. 5. Wheel Set Components – Service Conditions• Static axle loads → Wheelset loads up to 25 to (and more)• Dynamic loads → Speeds partly far beyond 300 km/h → Load cycles far beyond 107 (one trip from Hamburg to Munich and back: 5,5*105 cycles• Fatigue – depending on the wheelset type → Rolling contact fatigue → Bending fatigue („basic“ fatigue process) → Torsional fatigue (driven wheelsets) High speed wheelset → Thermal fatigue (braking of the treads)• Wear due to rail wheel contact → Tread: running comfort → Flange: safe guidance• Corrosion and surface damages during service• Temperatures between -50° and +50°C CI. Poschmann, „Materials Testing of Railway Wheelset Components“, www.werkstoff-service.de 5 / 15
  6. 6. Requirements on the Materials (Static Properties) Residual stresses → Requirement: compressive circumferential stress Ultimate strength → To be tested per batch → To be tested in different areas of the components → Values restricted to a min.-max. range → Typical values: 600 – 1000 MPa Yield strength → To be tested in different areas of the components → Minimum values required Tensile test on railway steels → Typical values: 400 – 600 MPa Hardness → Wheel surface: 100% → Cross section: to be tested per batch → Minimum values required – depending on speed Toughness / elongation / reduction of area → To be tested in different areas of the components → Typical impact „toughness“: starting from 5 J → Typical elongation 15 – 20% Typical tensile sampleI. Poschmann, „Materials Testing of Railway Wheelset Components“, www.werkstoff-service.de 6 / 15
  7. 7. Requirements on the Materials (Dynamic Properties) Fatigue strength → Values and testing conditions defined by railway standards → Especially important for axles (fatigue endurable design) → Typical values: 200 – 450 MPa Crack propagation rate → Not defined by standards → Increasingly important to define NDT testing intervals Fatigue failure of an axle Fracture toughness → Relevant for freight waggon wheels → Defined by railway standards → Result: KQ-values (due to sample geometry) → Typical values: 80 – 100 MPa·√m → Two-step testing: pre-cracking and tensile test (rupture) Compact tension fracture toughness samplesI. Poschmann, „Materials Testing of Railway Wheelset Components“, www.werkstoff-service.de 7 / 15
  8. 8. Product Design and Materials Testing Residual stresses → Product qualification: by strain gauge, X-ray diffraction or ultrasonic measurement → Production: saw cut → Typical value: -100 MPa or 1mm (wheel rim) Fatigue strength → During design and product qualification In-production measurement of residual stresses → Testing of wheels and axles → Supported by FEM calculations → Main test system in Germany: resonance pulsator Brake test → For freight waggon wheels (1:1 Test) → Testing for geometric stability and crack resistance (thermal stresses) Fatigue test (source: www.sincotec.de)I. Poschmann, „Materials Testing of Railway Wheelset Components“, www.werkstoff-service.de 8 / 15
  9. 9. Steel Making and Materials Testing → Unalloyed (wheels) or low-alloyed (axles) steels → High quality steel with high degree of purity (important for fatigue behaviour) → Minimised S- and P-content → H-content below 1,5 - 2 ppm → Main difference in steel grades: C-content (0,25 – 0.65 % carbon) High quality steel making → Narrow tolerances of the main alloying elements (e.g.: C-content of the cast/product analysis within range of 0,04%) → Testing by optical emission spectrometry and metallography → „Ordinary“ steels, but very well done! Blue brittleness test for non-metallic inclusionsI. Poschmann, „Materials Testing of Railway Wheelset Components“, www.werkstoff-service.de 9 / 15
  10. 10. Hot Forming and Materials Testing Primary material → Ingot casting → Continuous casting Objectives of hot forming → Removal of defects such as pores and shrinkages cavities (degree of deformation - reduction of cross section - up to 5x) Forging of axles → Optimising the grain flow towards geometry (benifical for fatigue behaviour) → shaping Controll of hot forming by → Ultrasonic testing → Laser based measurement of geometry → Metallography (hot etched slices) Rolling of wheelsI. Poschmann, „Materials Testing of Railway Wheelset Components“, www.werkstoff-service.de 10 / 15
  11. 11. Heat Treatment and Materials Testing (Microstructure) Desired microstructure → Axle: Quenched and Tempered → Wheel: Pearlite-Ferrite → Fine grained (class 6 and better) Targets of microstructural design → Axle: strength and fatigue strength → Wheel: strength and optimised wear → Wheel: homogeneous structure in circumferential direction Heat treatment of wheels → Wheel: minimal changes of structure / properties along rim cross section Testing methodes → Metallography → Hardness profiles Pearlitic-ferritic microstructure of a wheel steelI. Poschmann, „Materials Testing of Railway Wheelset Components“, www.werkstoff-service.de 11 / 15
  12. 12. Heat Treatment and Materials Testing (Mechanical Properties) Microstructure defines mechanical properties! Typical amount of testing → Hardness (100% of the batch) → Residual stress (per batch) → Hardness (cross section) → Tensile samples from different locations (ultimate strength, yield strength, elongation) → Impact toughness samples from different locations and Impact toughness test at different temperatures → Fracture toughness → Microstructure → Phase composition → Grain size → Cleanliness → Testing frequently on-site-monitored by state-owned railway operators / classification societies Impact samples (Charpy-U)I. Poschmann, „Materials Testing of Railway Wheelset Components“, www.werkstoff-service.de 12 / 15
  13. 13. Machining / Finishing and Materials Testing Dimensional control → Accuracy to 1/1000 mm (axle journals, seats) → Out of roundness less than 5/100 mm for wheel diameters of up to 1250 mm Roughness → Ra less than 1,6 µm (for fatigue reasons) → Problem: fatigue improvement vs. adhesion of paint Roughness measurement Non destructive testing → Carried out by certified staff → 100% visual inspection (VT) of the components → 100% surface crack detection by magnetic particle testing (MT), acceptance criterion can be as low as 1mm → 100% ultrasonic volume testing – partly up to 4x per piece Non destructive testing of an axleI. Poschmann, „Materials Testing of Railway Wheelset Components“, www.werkstoff-service.de 13 / 15
  14. 14. Testing During Service Conditions of components are intensively monitored during service and maintenance Testing is mandatory and defined by standards Testing intervalls ranging from several 10.000 km to several 100.000 km (depending on type of vehicle and service conditions) Ultrasonic testing of a railway wheel Extent of testing → Visual testing (surface damages and corrosion ) of wheels and axles (e.g. EVIC catalogue) → Magnetic particle testing of wheels and axles (surface defects) → Ultrasonic testing of wheels and axles (surface defects) → Residual stress measurements In-service residual stress measurementI. Poschmann, „Materials Testing of Railway Wheelset Components“, www.werkstoff-service.de 14 / 15
  15. 15. Materials Testing of Railway Wheelset Components Ingo Poschmann W.S. Werkstoff Service GmbH, Essen Thank You for Your Attention!I. Poschmann, „Materials Testing of Railway Wheelset Components“, www.werkstoff-service.de 15 / 15

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