Laser Shock Peening Process and Current Application

Laser Shock PeeningProcess and Current Applications

Goran Iveti¢

May 10, 2010

Laser Shock PeeningCurrent state of LSP technology

Conclusions

Contents

1 Laser Shock PeeningProcess OverviewExperimental ActivityNumerical Activity

2 Current state of LSP technologyApplications of LSPLSP technology di�usion

3 ConclusionsSetting up LSP technology

Goran Iveti¢ Laser Shock Peening 2 / 48


Conclusions

Contents






Conclusions

Contents





Laser Shock Peening


Conclusions

Process OverviewExperimental ActivityNumerical Activity

History of LSP

1960s - First theoretical bases for LSP

1970s - First demonstrations of practical use of LSP

1980s and 90s - Expansion and further development of themethod

2000s - Industrial level applications of the method



Conclusions


History of LSP







Conclusions


History of LSP







Conclusions


History of LSP







Conclusions


Physics of LSP



Conclusions


Physics of LSP



Conclusions


Physics of LSP



Conclusions


Physics of LSP



Conclusions


Physics of LSP



Conclusions


Physics of LSP



Conclusions


Physics of LSP



Conclusions


Physics of LSP



Conclusions


Physics of LSP



Conclusions


Applications of LSP on aeronautical structures

Fatigue prone locations of an aircraft

Fuselage skin (riveted joints)

Highly stressed areas of an aircraft structure



Conclusions


Thin Sheets 2024-T351

Examining the e�ects of Laser Peening on the fatigue life ofthin sheets of 2024-T351 Aluminium Alloy

Experimental tests that have been de�ned in order to evaluatee�ects of di�erent LSP process parameters on the obtaineddistributions of residual stress

The specimens in clad and unclad condition with 2 mmthickness



Conclusions








Conclusions








Conclusions



E�ect of LSP parameters on the distribution of residual stresses

Investigated parameter E�ect on compressive residual stresses

Laser power density Compressive stresses increase with the increaseof laser power

Number of layers Increasing the number of layers increases thevalue of compressive residual stresses until satu-ration

Peen size Super�cial residual stresses increase with the sizeof the impact and decrease with the plasticallya�ected depth

Pulse Duration Reducing the pulse duration should reducethe depth of the compressive residual stressesthrough the thickness



Conclusions



Laser Shock Peening of clad and unclad sheets

Process settings: laser power density (GW/cm2) - pulseduration (ns) - number of layers

Evaluated settings: 0.5-18-2, 0.5-18-4, 1-18-2, 1-18-4 for cladand unclad specimens (RS measurements by Open University)



Conclusions








Conclusions








Conclusions


Thin Sheets 2024-T351 - Residual stresses

Clad specimen



Conclusions


Thin Sheets 2024-T351 - Residual stresses

Unclad specimen



Conclusions



Fatigue tests on clad specimens (results by Cran�eld University)

LSPIntensity

DefectDepth

Test 1 Test 2 Average BaselineResults

Di�.

(GW/cm2) (µm) (cycles) (cycles) (cycles) (cycles) %

1 50 91121 91899 91510 62328 47

1 150 22198 21311 21755 18666 17

3 50 69925 81363 75644 62328 21

3 150 15903 17855 16879 18666 -10



Conclusions


Thick plates 7050-T7451

Examining the e�ects of Laser Peening on the fatigue life ofthick aluminium plates made of a high strength Al alloy, 7050in T7451 condition.

Experimental tests have been de�ned in order to evaluatee�ects of di�erent LSP process parameters on the obtaineddistributions of residual stress

The measurement of residual stresses has been performed byEADS Innovation Works



Conclusions








Conclusions








Conclusions



As in the case of thin aluminium sheets, the LSP processparameters of interest are the same:

laser power densitynumber of layerspeen sizepulse duration



Conclusions



As in the case of thin aluminium sheets, the LSP processparameters of interest are the same:

laser power densitynumber of layerspeen sizepulse duration



Conclusions



Residual Stresses - Borehole Method



Conclusions



Fatigue Tests, R=0.1



Conclusions



Fatigue Tests, R=-1



Conclusions



Fatigue Tests, R=-3



Conclusions


Shock wave creation and propagation

When a shock wave is created in a solid material, one has totake into account the elastic-plastic properties of the target

Di�erent analytic and numerical models exist that describe theplastic behaviour of metallic materials under high strain loads

The two models found in the literature that are mostcommonly used:

Hugoniot elastic limit (HEL) modelJohnson-Cook �ow stress model



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Conclusions









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Conclusions


Material Models

HEL model

Hugoniot's elastic limit of a material is the compressive yieldstrength of the material under a shock condition that takesinto consideration the increase of the material's yield strengthwith the increase of strain rate

Assuming that the yielding occurs when the stress in the directionof the wave propagation reaches the HEL, the dynamic yieldstrength under uniaxial strain conditions can be de�ned in terms ofthe Hugoniot's elastic limit by:

σy ,dynamic = HEL1− 2ν

1− ν



Conclusions


Material Models

Johnson-Cook �ow stress model

Used for stress-strain dependences at high strain rates (strainrates of up to 106/s)

This material model is purely empirical, the material constants needto be obtained experimentally for each case observed

σ = (A+ Bεneq)

[1 + C ln

( .ε.ε0

)] [1−

(T − T0

Tm − T0

)m]



Conclusions


FEM of LSP

Material models are de�ned

Known input parameters for loading de�nition

Laser intensity (in terms of GW/cm2)Con�ning mediumLaser impulse duration and temporal distributionSpot size

Wanted output parameters used in FEM analysis

Peak pressure (in terms of GPa)Pressure impulse duration and temporal distribution

The FEM analysis is divided in two separate steps

Explicit dynamic analysis of laser impactEquilibrium analysis for springback deformation analysis



Conclusions


FEM of LSP










Conclusions


FEM of LSP










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FEM of LSP










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FEM of LSP










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FEM of LSP










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FEM of LSP










Conclusions


FEM Analysis of Thin Sheets 2024-T351



Conclusions



Experimental vs. FEM results clad

Experimental vs. FEM results unclad



Conclusions



Experimental vs. FEM results clad

Experimental vs. FEM results unclad



Conclusions



Alternative process settings - peen depth

Alternative process settings - peen line



Conclusions



Alternative process settings - peen depth

Alternative process settings - peen line



Conclusions


FEM Analysis of Thick Plates 7050-T7451

Experimental vs. FEM results - peen depth

FEM results - peen line



Conclusions



Experimental vs. FEM results - peen depth

FEM results - peen line



Conclusions



FEM Model for Radius E�ect Evaluation

Radius E�ect



Conclusions



FEM Model for Radius E�ect Evaluation

Radius E�ect



Conclusions



Alternative pulse durations - single shot

Alternative pulse durations - three shots



Conclusions



Alternative pulse durations - single shot

Alternative pulse durations - three shots


Applications of LSP


Conclusions

Applications of LSPLSP technology di�usion

Applications of LSP

Jet engine blades

GE (engines for F-16, A320), RR (Trent engines for A340,Boeing 777, 787), P&W (FOD of F119 engines of F22)

For non-aeronautical applications as well - Power GenerationSteam Turbine Blades



Conclusions


Applications of LSP

LSP at General Electric



Conclusions


Applications of LSP

Stress corrosion cracking in nuclear reactors

LPwC approach developed by Toshiba

Portable LSP systems developed



Conclusions


Portable LPwC system



Conclusions


Applications of LSP

Wing attach lugs F-22



Conclusions


Applications of LSP

Helicopter Components



Conclusions


Applications of LSP

Helicopter Components



Conclusions


Applications of LSP

LSP Forming

MIC laser shock peening is forming the wing skins for the new747-8Laser peen forming can produce compression driven curvaturesin panels with minimal surface roughening not achievable withconventional shot peen forming



Conclusions


LSP forming



Conclusions


Presence of LSP capacities


Conclusions


ConclusionsSetting up LSP technology

Conclusions

Laser Shock Peening

Experimental analyses performed on thin panels have shown greatsensibility on LSP settings, as well as on boundary conditions

Experimental analyses performed on thick plates have shown promisingresults, obtaining compressive residual stresses on the surface of thespecimen that were extended up to ten times more in the depth,compared to shot peened specimen

Developed numerical models showed reasonably good correspondencewith experimental data, qualifying itself for analysis and veri�cation ofLSP processing of thin and aluminium sheets and thick aluminium plates

Alternative process settings proposed for both thin and thick aluminiumplates




Future Work

Further investigations are necessary in order to determine with moreaccuracy the material constants for Johnson-Cook model (A, B, C, n andm) for materials under shock loading, for all the materials which wereanalysed (2024-T351, 7050-T7451, Aluminium clad)

More research e�orts are necessary in order to improve the LSP of thinsheets, which have shown great sensibility on shock wave re�ections


What do we need to start in-house LSP?



Necessary equipment

Appropriate laser system

Residual stress measurement capabilities

Fatigue testing capabilities

Metallography capabilities




Laser Systems

For industrial applications - more than 0.5 kW, 50-100 J, 7-10mm spotsLALP France system: Nd:YAG, 1064 nm, 10 ns, 10 Hz, 3 J(1.5 J, 10 ns, 10 Hz, 532 nm (2 mm impacts))Thales France system: 24 J, 8/15 ns, 5 Hz, 1064 nm, 5-6 mmimpacts (14 J, 532 nm)University of Madrid laser system: Nd:YAG, 1064 nm , 9 ns,10 Hz,2 J, spot 1.5 mm, no coatingToshiba laser system: Nd:YAG, 532 nm, 8 ns, 70-200 mJ, spot0.60.8 mm, up to 100 pulses/mm2




Residual stress measurement and testing

Hole drilling method

X-ray di�raction

Slitting (crack compliance)

Testing machines

Metallographic analysis




What can we do?

Assesment of in-house capabilities to meet industry requirements

Research on LSP gives a great opportunity for scienti�c publishing




LSP Publications

G. Ivetic, I. Meneghin, E. Troiani, Applications and numerical analysis ofLaser Shock Peening as a process for generation of compressive residualstresses, Accepted for presentation at ECRS-8, Riva del Garda, Italy, June26-28 2010.

G. Ivetic, A. Lanciotti, Finite Element analysis of Laser Shock Peening ofAluminium alloy 7050-T7451 thick plates, Presented at the 2nd

International Congress on Laser Peening, San Francisco, USA, April18-21, 2010.

G. Ivetic, A. Lanciotti, Numerical analysis and comparison of ShotPeening and Laser Shock Peening processes, Presented at the 2nd

International Congress on Laser Peening, San Francisco, USA, April18-21, 2010.

G. Ivetic, 3-D FEM Analysis of Laser Shock Peening of Aluminium Alloy2024-T351 Thin Sheets, Accepted for publishing in Surface Engineering,July 26, 2009.

G. Ivetic, A. Lanciotti, FEM Modelling of LSP Process, Laser ShockPeening for Fatigue Life Enhancement Workshop, Airbus UK, June 92009.


Documents

Laser Shock Peening Process and Current Application