vii improving the fatigue life of weldments

AM 11/03 1
VII Improving the fatigue
life of weldments
AM 11/03 2
Outline
n Obvious things to do
n Problems the weld toe
n Fatigue life Improvement Strategies
n Light and heavy industry weldments
n Improving the “bad” weldments
AM 11/03 3
Crude! (bad)
AM 11/03 4
Better
AM 11/03 5
Bad - planar weld discontinuities
AM 11/03 6
Outline
n Obvious things to do
n Problems the weld toe
n Fatigue life Improvement Strategies
n Light and heavy industry weldments
n Improving the “bad” weldments
AM 11/03 7
Weld toe is a stress concentration
AM 11/03 8
Slag entrapments at toe?
Virtually
eliminates
fatigue
crack

initiation
life NI
AM 11/03 9
Welding procedure A
Welding procedure B
Cold-lap defects at weld toe
Cold laps virtually eliminate the
fatigue crack initiation life (NI)
Such weldments may have
an appreciable fatigue crack
initiation life (NI)
“Nominal”
“Perfect”
AM 11/03 10
Cold lap at a weld toe
Loading
Direction
D
Weld Metal
Base Metal
Heat Affected Zone
Weld Toe Location
Without Cold-Lap Defect
Curved Path
Vertical Path
θ
r
φ
AM 11/03 11
Effect of cold lap depth

1
10
0.001 0.01 0.1
D = 0.0 mm, M
K CG
, curved path from
weld toe location
D = 1.0 mm, M
K CG
, curved path from
cold-lap defect
D = 1.0 mm, M
K CG
, vertical path from
cold-lap defect
K
Crack length / main plate thickness, (a/T)
2-D FEM
Weld geometry correction factor, M
K
AM 11/03 12
Effect of flank angle
1
10
0.001 0.01 0.1
θ = 30
o
θ = 45
o
θ = 60

o
K
Crack length / main plate thickness, (a/T)
2-D FEM
D = 1.0 mm
Weld geometry correction factor, M
K
AM 11/03 13
Effect of cold root radius
1
10
0.001 0.01 0.1
D = 0.00 mm, weld toe location
D = 2.00 mm, r
cl
= 0.146 mm
D = 2.00 mm, r
cl
= 0.025 mm
K
Crack length / main plate thickness, (a/T)
Weld geometry correction factor, M
K
AM 11/03 14
Recent study on rail welds
Toe Radius, R
Weld
Reinforcement
Height, H
Base Metal

Thickness, T
b
Weld Collar
Width, W
Flank
Angle, θ
AM 11/03 15
Geometric Parameters
Fin Length, L
f
Cold Lap
Length, L
cl
Fin Thickness,
T
f
Flank
Angle, θ
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Weld with a Fin and a Cold Lap
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Deformed Shape
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Nominal Weld Geometry
1
1.5
2
2.5
3
3.5

4
4.5
0 10 20 30 40 50 60 70 80 90
Flank Angle, θ (Deg.)
R=.5mm
R=1mm
R=3mm
R=6mm
AM 11/03 19
1
2
3
4
5
6
7
0 2 4 6 8 10 12 14
Fin Length, Lf (mm)
Elastic Stress Concentration Factor, Kt (-)
Fin Thickness = .5mm
Fin Thickness=1mm
Fin Thickness=2mm
Fin length
AM 11/03 20
Fins and Cold Laps
1
2
3
4
5

6
7
-4 -2 0 2 4 6 8
Cold Lap Length, L
cl
(mm)
Cold Lap; NO Fin
Cold Lap with Fin 0.5 mm Thick
Cold Lap with Fin 1 mm Thick
Cold Lap with Fin 2 mm Thick
Defect Free
For All Tests
R=3mm and
θ=30°
AM 11/03 21
Trends in “Ideal”
1.0-in plate
thickness, non-load
carrying cruciform
weldments fatigue
strength.
• R = 0
• Welding residual
stresses = 50% of
S
YBM
• S
fab
˜ S
YBM

Predicted effect of S
uBM
0
10
20
30
40
50
60
0 50 100 150 200
Fatigue Strength at 1E+07 cycles, Sa (ksi)
Base Metal Ultimate Strength, Su
BM
(ksi)
As Welded, S
fab
= 0
As Welded, S
fab
= Sy
BM
Over Stressed
Hot Rolled Steel
Q & T Steel
Stress Relieved
AM 11/03 22
Outline
n Obvious things to do
n Problems the weld toe
n Fatigue life Improvement

Strategies
n Light and heavy industry weldments
n Improving the “bad” weldments
AM 11/03 23
Good - grind off reinforcement
AM 11/03 24
Good - burr grind weld toe
AM 11/03 25
Very good - full face grinding