Fatigue Design of Railway Vehicle Structures

Alois Starlinger Stadler Rail,

Structural Analysis, Testing and Authorization, Altenrhein, Switzerland

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Contents • Introduction • Requirements for the structural

assessment of railway vehicles: – Car Bodies – Bogies

• Acceptance program • Structural analysis • Laboratory Testing • On Track Testing • Conclusions

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Stadler‘s Sites in Europe Stadler Rail Group: • Fast growth over 20 years • Turnover: 1,5 Billion CHF • 4’700 employees

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Stadler Altenrhein: • Center of Structural

Development • Structural Analysis of Car

Bodies and of Bogies • Authorization

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Introduction into Railway Vehicles : • Small series business:

– From two to 100 vehicles per order – Adjustments for each customer – Time between contract signature and start of passenger service:

• 24 months (until now) • 36 – 48 months if TSI requirements have to be met • Design release requirement: four months after contract signature • Tight delivery schedule (with penalties for delay or for missing authorization)

– Usually no prototypes • No excessive service testing before series production • On track testing with first series vehicle high commercial risk Numerical analyses must capture structural behavior in detail Numerical fatigue assessment must deliver reliable results

– Operational lifetime up to 40 years • Typical costs per unit:

– City tram vehicle (5 wagons): 3 million Euros – Regional train (four wagons): 5 million Euros – High speed train (10 wagons): 15 million Euros

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Acceptance Program for Car Bodies (EN 12663-1): • Structural analysis:

– Static compressive loads: 1500 kN – Fatigue loads:

• P-II: ax = 1,5 - 2,0 m/s2, ay = 1,5 m/s2, az = 1,5 m/s2 • Static testing • Measurements on track followed by fatigue evaluation for

low floor tram vehicles

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Acceptance Program for Bogies (EN 13749): • Structural analysis • Static testing • Endurance test: 10 million load cycles • Measurements on track followed by fatigue evaluation

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Structural Analysis - Modeling: • Finite element analyses of all structural components • Finite element meshes have become extremely fine:

– Car body structures: 12 million degrees of freedom up to 3 million elements

– Bogie frames: 400.000 elements – Shell elements (70%) and Solid elements (30%): linear shape functions

– Local stress gradients have to be captured: • Structural notches (sharp edges, corners, ...) • Large stiffness changes, ...

– 50 single load cases for bogies & 50 combinations

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Fatigue Assessment - Nominal Stress Approach: • most common in railway design:

– simple, proven praxis – based on section forces and moments analytical method – not appropriate for finite element modeling, since local geometry

effects are captured corresponding stress peaks might be overrated – Strength standards:

IIW recommendations, FKM guideline, DVS 1608, DVS 1612

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Nominal stress evaluation point

Evaluation of FE Results for Nominal Stress Concept According to DVS 1608 Guideline

• Definition of evaluation point: – Enables direct comparison of FE results with test data – Evaluation point positioned into the center of the strain gauge

used in testing – Analogy to ERRI B12 RP17:

• Butt weld: e = 5 (mm) + strain gauge length / 2 • T-type weld: e = 5 (mm) + strain gauge length / 2

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• Based on IIW-Recommendation XIII-2240-08/XV-1289-08 • According to Seeger / Radaj: Radius r = 1 mm for all materials and

notch details • Notch factors derived for normal stresses transverse to the weld

direction (starting from a sheet thickness of t ≥ 6 mm) • Strength standards: IIW recommendations, FKM guideline, DVS 1608

Fatigue Assessment – Notch Stress Concept for Welds

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• Weld seams identified in FE model by Visualizer • Evaluation according to standard DVS 1608 guideline /

IIW recommendations • Stadler database for notch factors of weld types typical for

railway design • More exact method than nominal stress concept

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Fatigue Analysis – Notch Stress Concept for Welds

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Fatigue Analysis - Notch Stress Concept • Automated fatigue stress assessment with FEMFAT • Fatigue stress assessment extrapolation to notch location • Mesh strategy: integration point is located 5 mm away from

weld transition comparison with test results (same location as strain gauges)

• Results: utilization for all welds and all load combinations

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FEMFAT Weld –Bogie Frame – Utilization:

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Z04/Z05

Z09 Z08

SX1

SX2

Z14

SY1 SY2

SZ4

V1 (SZ1)

SZ3

SZ2

Z02

Z06

Z07

Z11

Z12

Z10

Z13

Q1/ Achs-verwindung

Z03a

Z03

Z1

Z16

Z01Z19

Q2

Q3Q4

Laboratory Testing of Bogie Frames (EN 13749): • 10 - 28 hydraulic cylinders for fatigue testing • 10 million load cycles - three phases 100%, 120% and 140%

Load run 100% loads complete

IMA-pr.no.: C041/08-1

-125

-100

-75

-50

-25

0

25

50

75

100

0 10 20 30 40 50 60 70

load cycles

load

[kN

] axl

e to

rsio

n [m

m]

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• Around 100 strain gauges channels • Comparison with analytical results

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Laboratory Testing of Bogie Frames (EN 13749):

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Laboratory Testing of Bogies (EN 13749):

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Testing of Variobahn bogie frame at IMA, Dresden: • 10 million

load cycles

• Criterion: no cracks

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On Track Testing • Requirement in EN 13749 for bogie frames • German Guideline developed by DIN working group with clear definitions for

on track testing: – Measurement length: at least 1/10000 of overall lifetime mileage – Strain gauges per bogie frame type: 30 positions with highest degree of

utilization in numerical analysis – Loading: 2/3 of maximum passenger load – Rain flow counting and classification – Damage accumulation according to Miner rule

• Stadler approach:

– Miner Elementar with„cut off“ at the 50% value of the fatigue strength at 5 million load cycles of S-N-curve

– Allowable damage sum Dm = 1,0

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© Stadler Altenrhein AG

On track testing - Stadler tram vehicles:

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Length Vehicle Year

• Successful on-track testing of Stadler tram vehicles • Measurements followed damage accumulation

On track testing:

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Conclusions: • The structural design of railway vehicles requires special

procedures: – Small series – Individual adjustments for each customer – Short development time – No prototypes

• Sophisticated methods for fatigue assessment are necessary: – Notch stress concept – Database with notch stress factors – Successful application of FEMFAT – Numerical results have been verified by laboratory testing and by on-

track-testing: • Tram car bodies • Bogie frames

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Thank you for your attention!