Laser shock peening produces a compressive residual stress in the surface of metallic materials, which significantly increases fatigue life in applications where failure is caused by surface-initi ated cracks. Laser shock peening is applied by using a high energy pulsed laser to create a high amplitude stress wave or shock wave on the surface to be treated. This stress wave propagates into the material, causing the surface layer to yield and plastically deform, and thereby, develop a residual compressive stress. Where comparisons have been made to shot peening, the magnitude of the residual stresses at the surface are similar, but the compressive stresses from laser peening extend much deeper below the surface than those from shot peening. The resulting fatigue life enhancement is often greater for laser peering than it is for shot peening. In addition to fatigue strength improvement, laser peering can also locally strain harden thin sections of parts or strain harden a surface
2. CONTENTS
Introduction
Literature Review
Experimental Setup
Working Process
What are residual stresses
Incremental hole drilling method
Factors influencing residual stresses
Advantages
Conclusion
References
3. INTRODUCTION
Peening is the process of working a metals‘ s
surface to improve its material properties
It is a cold working process.
Mechanical working processes
1. Hammers
2. Shots
3. Laser
4. WHAT IS LASER PEENING?
Laser peening is a surface enhancement method
for extending the life of metal components
Laser peening improves fatigue life
residual stresses generated by LSP typically
extend 5to 10 times deeper than those produced
by shot peening.
longer service lifetimes
5. RESIDUAL STRESS ANALYSIS ON
TITANIUM ALLOY TC4 BY LASER
SHOCK PEENING
This test was performed by jun hong li ,he is
from china.
He is done LSP test on TC4 material
the residual stresses using x-ray stress analyser
Results indicates that there was large residual
stresses are induced on the surface of material.
6. PARAMETRIC STUDY ON SINGLE SHOT
AND OVERLAPPING LASER SHOCK
PEENING ON VARIOUS METALS VIA
MODELLING AND EXPERIMENTS
This paper is written by yunfeng cao and yung
c.shin.
this experiment performed on 4140 steel and TI-
6AL-4V materials
These are underwater confinement process
And he used 3-d finite element for analyse
residual stresses in the materials
7. AN ANALYTICAL MODEL TO PREDICT
RESIDUAL STRESS FIELD INDUCED BY
LASER SHOCK PEENING
This paper was published by yongxiang hu and
zheqiang yao and jun hu
He proposed a complete analytical model of LSP
He used FEM to calculate residual stresses in the
material
8. EXPERIMENTAL AND NUMERICAL
INVESTIGATION OF RESIDUAL
STRESSES IN LASER PEENED AA2198
This paper was published by s.keller,s.chupakhin,
p.staron,e.maawad,n.kashaev
Lsp is done on AA2198 material
Experimental and numerical investigation are done
using different investigating models
Using hole drilling method and x-ray diffraction test
9. FINITE ELEMENT ANALYSIS OF
VARIATION IN RESIDUAL STRESS
DISTRIBUTION IN LASER SHOCK
PEENING OF STEELS
This paper was published rohit voothaluru and
c.Richard liu gary j.cheng
This experiment was done on 1053STEEL &
52100 AISI STEELS
By using ansys software he compared residual
stresses of 1053 STEEL and 52100 AISI
STEELS
11. EXPERIMENTAL DETAILS
Laser characteristics
1. Neodymium glass (Nd) laser (1054 nm wavelength)
2. 0.6 - 5 J energy per pulse
3. 1 - 3mm spot diameter
4. 2.78- 25GW/cm2 power density
Opaque used
1. Paint
2. Tape
Coolant used
1. water
12. • Specimen used
1. AA2198-T3, AA2198-T5
2. Specimen thickness : 3.2 mm
• Base layer used:
1. Steel plate
2. Air
13. •PROCEDURE
A high-energy, short-duration laser pulse
produces a rapidly expanding plasma burst on
the part surface
The rapid rise of pressure generates a powerful
compressive shockwave that propagates into the
material.
14. TYPICAL LSP PROCESSING PARAMETERS FROM THE LITERATURE USED FOR
DIFFERENT MATERIALS WITH CONCLUDING REMARKS.
15. WHAT ARE RESIDUAL STRESSES?
Residual stresses are stresses that remain in a
solid material after the original cause of the
stresses has been removed
Residual stress may be desirable or undesirable
Undesirable residual stresses cause premature
failures
16. WHY ARE RESIDUAL STRESSES
BENEFICIAL?
When a component is enhanced with
compressive residual stresses, it can withstand
greater tensile forces before cracking and failure
occur.
buffer against tensile strain,
deeper compressive stresses inhibit crack
initiation
17. METHODS TO FIND RESIDUAL
STRESSES
Nano-indentation,
X-ray diffraction,
metallographic microscope,
SEM,
TEM
Incremental hole drilling method
Fem
18. INCREMENTAL HOLE DRILLING
METHOD
Residual stresses were determined by the
measurement system Prism from Stress-tech by
1. electronic speckle pattern interferometry
(ESPI) or Strain gauges.
1. Drilling a hole incrementally.
2. Measurement of the surface deformation after
each increment using ESPI or Strain gauges
3. Calculation of the residual stresses from surface
deformations(Integral method)
23. FOCAL SIZE
• Low focus size
1. high overlapping stresses
2. spherical wavefront
• High focus size
1. high depth of penetration
2. linear wave front
Laser power density
1. Higher power density leads to high pressure pulse
irrespective of pulse energy
24.
25. Influence of base layer
Base layer is placed at the back of the work
piece as a support.
This will reflect back the wave into material to
increase residual stresses.
26. Influence of specimen thickness
1. Increase in the thickness the shock wave
intensity decreases at the end of plate
2. Reflected shock wave intensity also decreases
27. X-RAY DIFFRACTIONS TEST
The photon energy: 87.1 kev
Wave length:0.1419 Aº
Pixel size :200μm
Beam is 1.5 mt from work-piece
31. APPLICATIONS
Engine components
Turbine, fan, and compressor blades
Bulkheads, wing attachments, flight control
mechanisms, wheels
Brakes, landing gear
Welded titanium and aluminum components for
improved reliability
Welded aging aircraft parts for improved
reliability
32. CONCLUSION
As the LSP power density increased, the residual
compressive stresses on the surface were also
increased.
fatigue resistance of material would be greatly
improved
Laser shock processing can make high residual
compressive stress on the surface and deep
inside of the material.
Compressive stresses decreased gradually with
the depth increased,