INEGI, FEUP

1
Fatigue Crack Growthof Rails for Railways

• Lucas F M da Silva, Fernando M F de Oliveira
• and Paulo M S T de Castro
• INEGI and Universidade do Porto,
• Portugal

2
Introduction

• european project SMT4-CT98-2240
• current limits for qualifying rails unacceptable
  (too much scatter due to test technique)
• objective effect of R and RH, and measure
  scatter in 6 laboratories to optimise test
  procedure
• da/dN vs. DK of 5 specimens

3
Contents

• test procedure
• data analysis
• results and discussion
• conclusions

4
Test procedure
Test rig
5
Test procedure
Specimens geometry W45, B20, L230, M10, n4,
L190, L290
6
Test procedure
Factor settings
7
Data analysis
(a)
(b)
7 point incremental polynomial technique
Secant method
8
Results and discussion
Test details
Note Specimen 1B4 smaller
9
Results and discussion
da/dN C (DK)m (da/dN in m/cycle and DK in
MPam1/2) constants of Paris law for each
specimen (7 point incremental polynomial
technique)
10
Results and discussion
comparison of da/dN vs DK curves
11
Results and discussion
1- Fatigue test
2- Static Test
2B9, 3B14 and 4B19
3- Fracture surface
12
Results and discussion
Tensile curve and microstructure (4B19)
13
Results and discussion
Toughness estimation based on KQ (BS 7448-11991)
and UT (area under stress-strain curve)
14
Results and discussion
Statistical analysis by University of Newcastle

• low scatter between 6 laboratories
• interaction between humidity and our laboratory
• optical method ? interruptions

15
Conclusions

• rails from 4 manufacturers similar
• m?4 (R0.5)
• toughness
• 76 lt UT lt 90 (MPa)
• 42 lt KQ lt 53 (MPa m1/2)
• 6 laboratories ? similar results
• interruptions should be avoided