Comparison of laser peening with other potential methods (Shot Peening and Ultrasonic Impact Treatment). Laser shock peening to enhance fatigue performance in presence of Foreign Object Damage. Preliminary peening trials in Gas Tungsten Arc Welding (GTAW).

1. An Experimental Study on Residual
Stress and Material Response to
Laser Shock Peening
By
Suraiya Zabeen, S. Clitheroe, J.A Francis, A. Evans,
M. Turski, M. Preuss, and P. J. Withers
University of Manchester, School of Materials, United Kingdom
First International conference on Laser Peening
Thursday, Dec 16th, 2008
NASA Johnson Space Centre, Houston, Texas, USA

2. 1st International Conference
on Laser Peening, 2008
Stress & Damage
Characterisation Group
Presentation Outline
q Comparison of laser peening with other
potential methods (Shot Peening and
Ultrasonic Impact Treatment).
q Laser shock peening to enhance the fatigue
performance in presence of Foreign Object
Damage.
q Preliminary peening trials in Gas Tungsten
Arc Welding (GTAW).

3. 1st International Conference
on Laser Peening, 2008
Stress & Damage
Characterisation Group
COPYRIGHT
“The copyright of all parts of this
presentation is solely reserved by the
University of Manchester”

4. Comparison of Laser peening with
other potential methods (SP and
UIT)
Material: 304 Austenitic
Stainless Steel

5. 1st International Conference
on Laser Peening, 2008
Stress & Damage
Characterisation Group
Objectives
Compare current peening with other
potential methods
• Shot Peening (SP),
• Laser shock Peening (LSP)
• and Ultrasonic impact treatment (UIT)

6. 1st International Conference
on Laser Peening, 2008
Stress & Damage
Characterisation Group
Measurement Techniques
Effect of Peening
Residual Stress
q Measured via neutron diffraction depth profiling
Work Hardening
Measured via nanoindentation
Microstructure
q Analysed by Scanning Electron Microscope (SEM) in
Back Scattered Electron Diffraction mode.

7. 1st International Conference
on Laser Peening, 2008
Stress & Damage
Characterisation Group
304 Austenitic steel peened coupons
SP UIT
LSP
25 x 25 x
8mm
Yield strength ≈
300 MPa

8. 1st International Conference
on Laser Peening, 2008
Stress & Damage
Characterisation Group
Neutron Diffraction residual stress
depth profile
-700
-600
-500
-400
-300
-200
-100
0
100
200
-8 -7 -6 -5 -4 -3 -2 -1 0
Depth from Peened Surface (mm)
Residualstress(MPa)
UIT In-Plane Parallel
UIT In-Plane Perpendicular
SP In-Plane Parallel
SP In-Plane Perpendicular
LSP In-Plane Parallel
LSP In-Plane Perpendicular
Parallel
Perpendicular
Peened
surface

9. 1st International Conference
on Laser Peening, 2008
Stress & Damage
Characterisation Group
Microstructure
Shot peened layer
174µ
m
100µm
500µm
Shot
200µm
TRIP*
Laser
*Transformation Induced
martensite
100µm
100µm

10. 1st International Conference
on Laser Peening, 2008
Stress & Damage
Characterisation Group
Hardening via Nanoindentation
0
1
2
3
4
5
6
0 1 2 3 4 5 6 7 8 9
Depth profile into sample (mm)
Hardness(GPa)
SP 110
LSP M
UIT M

11. 1st International Conference
on Laser Peening, 2008
Stress & Damage
Characterisation Group
Conclusions
q All methods go above the yield strength of the material.
q Laser peening is a competitive method with respect to
compressive residual stress depths of other treatments.
q Concerning corrosion effects laser peening has a
superior surface finish when compared with other methods
and is also supported by minimal microstructural changes.
q Laser peening also work hardens less which in some
applications may be of benefit.

12. Laser shock peening to enhance the
fatigue performance in presence of
FOD
Material: Ti-6Al-4V
Fisrt International conference on laser peening

13. 1st International Conference
on Laser Peening, 2008
Stress & Damage
Characterisation Group
Objective
Characterization of laser shock peened Ti-6Al-4V
leading edge airfoil shaped sample.
Analyse the influence of laser shock peening on the
fatigue performance in presence of foreign object
damage (FOD).

14. 1st International Conference
on Laser Peening, 2008
Stress & Damage
Characterisation Group
Measurement Techniques
Effect of Peening
Surface Profilometry
Measured via contour measurement machine (CMM) and laser
Profiler.
Macro and Microstructure
Analysed by Optical and Scanning Electron Microscope (SEM)
in Back Scattered Electron Diffraction mode.
Residual Stress
Measured by laboratory X-ray Diffraction (sin2ψ technique)

15. 1st International Conference
on Laser Peening, 2008
Stress & Damage
Characterisation Group
Laser Profilometry and
Microstructure
-0.1
0
0.1
0.2
0.3
0.4
0 20 40 60 80 100 120 140
DeformationinX(mm)
Distance along Y (mm)
X
Y
Z
-0.2
-0.15
-0.1
-0.05
0
0.05
0.1
0.15
0.2
0 20 40 60 80 100 120 140
Bottom surface
DeformationinX(mm)
Distance along Y (mm)
Roughness values
In the peened region,
Ra=0.67
Outside the peened region,
Ra=0.43
127××
Top surface

16. 1st International Conference
on Laser Peening, 2008
Stress & Damage
Characterisation Group
Residual Stress Profile
q A pre-existed compressive stress of -400 MPa is present in the
sample.
q Maximum compressive stress is about -600 MPa at a distance of
4 mm from the leading edge
-700
-600
-500
-400
-300
-200
-100
0
100
0 5 10 15 20 25 30
Distance from the leading edge (mm)
Stress(MPa)
_ xx _ yy )_yy (Frankel 2007
σyy
σxx
σyy(Frankel 2008)
X
Y
Z

17. 1st International Conference
on Laser Peening, 2008
Stress & Damage
Characterisation Group
Conclusions
q Laser shock peening can induce a maximum
compressive residual stress of -600 Mpa at the
surface which is beneficial from the fatigue
performance standpoint.
q It also gives smooth surface finish and less
microstructural degradation compared to other
existing peening techniques.

18. Preliminary peening trials in GTAW
Material: AISI 304 Stainless
Steel
Fisrt International conference on laser peening

19. 1st International Conference
on Laser Peening, 2008
Stress & Damage
Characterisation Group
• 20 mm thick AISI grade 304 stainless steel plates with 10 mm deep
groove along centreline
• Groove filled in 8 passes by GTAW using AISI grade 308 filler metal.
• Residual strains on weld centreline measured by neutron diffraction
before and after peening treatment on top surface of plate.
• 2 surface treatments used (UIT and LSP)
dimensions of welded plate 10 mm deep groove filled
in 8 weld passes
peened area
ND measurements
down weld centreline

20. 1st International Conference
on Laser Peening, 2008
Stress & Damage
Characterisation Group
Longitudinal Strain on centre-line of welds
Preliminary results for longitudinal strain suggest UIT
and LSP can dramatically alter weld residual stresses,
to depths of several millimeters.Peened
Surface
Surface corrections still to be applied

21. 1st International Conference
on Laser Peening, 2008
Stress & Damage
Characterisation Group
Some other works in relation to the LSP
Andy King
Residual stress and damage characterization in wide chord fan
blades
Alex Evans
Residual stress characterization of peened aerospace materials
Chris Gill
Evaluation of the Evolution of Beneficial Compressive Residual
Stresses in a Gas Turbine Engine Environment”
Philip Frankel
Residual Stresses in Aerospace Components

22. 1st International Conference
on Laser Peening, 2008
Stress & Damage
Characterisation Group
Macro and Microstructure
FOD at 45°
LCF+HCF Loading
X
Y
Z

23. Thank You
Questions?

24. 1st International Conference
on Laser Peening, 2008
Stress & Damage
Characterisation Group
Nasa – Johnson Space Center