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Final Project Presentation
Measurement of Residual Stress Distribution And
Fatigue Life Assessment of Butt Welded Joint
Pankaj Kumar : (1BG11ME034)
Guide: Co-Guide:
Mr. Harish A. Mr. Karthik N.
Asst. Prof. Asst. Prof.
Mechanical Dept. Mechanical Dept.
B.N.M.I.T B.N.M.I.T

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Aim of the Project
Measurement of Residual Stress Distribution
and Estimation of Fatigue life of a Butt
Welded Joint before and after surface
treatment.

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Introduction
 Welding process induces residual tensile stress that is detrimental to
fatigue life.
 Residual tensile stress act to stretch or pull apart the surface of the
material.
 With enough load cycles and high enough tensile stress, a metal surface
will initiate crack. Residual stress directly affects a components fatigue
life.
 It is well known that when a welded component fails in fatigue the
failure location is usually at the weld. Residual stress directly affects a
components fatigue life.
 Detrimental residual tensile stress decreases the fatigue life while
beneficial residual compressive stress increases the fatigue life.

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 Both types will be thoroughly investigated through the use of X-ray
diffraction in this project work.
 This project work will investigate how detrimental residual stresses
are created through the welding process.
 This paper will explain through theory and residual stress
measurements how welding stresses can be modified by surface
modification process such as shot peening for a more beneficial
condition from a fatigue standpoint.
 To complete the technical study, multiple carbon steel components
were welded and exposed to various manufacturing processes.
Introduction

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Introduction
Figure: Residual Stress Distributions after Welding

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Project Objectives
1] To review the literature on fatigue life of welded joint and on
surface enhancement treatment.
2] Experimental investigation of induced residual stress in butt
welded joint before and after surface modification process of shot
penning method.
3] Estimation of fatigue life in butt welded joint before and after
surface modification process.
4] Analyzing the Effect of residual stress modification on fatigue life
of the welded component.

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Objective 1: To review the literature on fatigue life of welded joint and
on surface enhancement treatment.
Literature Summary:
 Residual stresses are a consequence of the welding process and are an
important consideration in structural assessment.
 The welding process induces residual tensile stress that is detrimental to
fatigue life.
 Tensile stress act to stretch or pull apart the surface of the material .
 With the enough load cycles at a high enough tensile stress a metal surface
will initiate the crack.
 It is commonly observed that complex fabricated structures subject to
fatigue loading fail at the welded connections.
 Some problems can be corrected by improved detail design but fatigue
performance can also be improved using post-weld improvement methods.
Methods and Methodology

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Method and Methodology
RESIDUAL STRESS MODIFICATION:
Residual stress can significantly affect engineering properties of materials and
structural components, notably fatigue life, distortion, dimensional stability,
corrosion resistance etc.
The residual stress analysis is a compulsory stage in the design of structural
elements and in the estimation of their reliability under real service conditions
Significant improvement in the fatigue life can be obtained by modifying the residual
stress levels in the material.
Some of the different methods of residual stress modification methods are
a.) Shot peening
b.) Hammer peening
c.) Ultrasonic method
d.) Heat treatment.

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Shot peening: Shot peening is a cold work process used to finish metal parts
to prevent fatigue and stress corrosion failures and increase product life for
the part. In shot peening, small spherical shot bombards the surface of the
part to be finished. The shot acts like a peen hammer, dimpling the surface
and causing compression stresses under the dimple.
Methods and Methodology

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Figure: Wheel blasting machine for Shot peening
Methods and Methodology

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Objective 2: Experimental investigation of induced residual stress in
butt welded joint before and after surface modification process.
Experimental details :
a.) Material : SS304L and Mild steel
b.) Type of joint : Butt weld joint.
c.) Type of welding : TIG
d.) NDE technique : XRD method
Methods and Methodology

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Figure: XRD equipment setup for measurement of residual stress in
given specimen
Methods and Methodology

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Methods and Methodology
Figure: XRD machine setup

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Objective 3: Estimation of fatigue life in butt welded joint before and
after surface modification process.
Estimation of fatigue life of the butt welded component is carried out
with the help of rotating fatigue testing machine TM7001.
The dumbbell shape specimen of required size is gripped on to a
motor at one end to provide the rotational motion whereas the other end
is attached to a bearing and also subjected to a load or stress.
 When the specimen is rotated about the longitudinal axis, the upper
and the lower parts of the specimen gauge length are subjected to
tensile and compressive stresses respectively.
Therefore, stress varies sinusoidal at any point on the specimen
surface. The test proceeds until specimen failure takes place.
Methods and Methodology

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 The number of cycle for which the specimen withstands without any
failure is noted down.
 This cycle is known as fatigue strength of given specimen. The
revolution counter is used to obtain the number of cycles to failures
corresponding to the stress applied.
 Increasing of the load applied to the fatigue specimen results in a
reduction in number of cycles to failure.
Methods and Methodology

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Objective 4: Analyzing the Effect of residual stress modification on
fatigue life of the welded component.
 Residual stress directly affects a components fatigue life.
Detrimental residual tensile stress decreases the fatigue life while
beneficial residual compressive stress increases the fatigue life.
 Surface modification process such as shot peening reduces the
residual tensile stress and induces residual compressive stress in the
welded component.
 Hence the hardness and fatigue life of the welded component
increases with the decrease of detrimental tensile stress.
Methods and Methodology

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Literature Review
 Sylvain Chataingner et al: Steel structures are mainly prone to two types of
degradation: corrosion and fatigue particularly in the case of welded structures.
The presented work aims at investigating two treatment methods to increase the
fatigue life expectancy of welded steel joints. It includes both numerical and
experimental investigations and is interested in the use of shot peening. As far as
experimental investigations are concerned, for both treatment methods and for
untreated samples, the stress concentration coefficients are determined, surface
residual stresses are measured using X-ray diffraction and fatigue tests are
conducted. The results allow explaining for both methods the observed
improvements in fatigue behaviour. Numerical investigations are concerned and
this allows the determination of residual stresses due to welding operation and
their comparison with the former experimental measures.

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 M Hasegawa et al: The shot peening method, which requires simple equipment and
treatment, is extensively employed as a method to improve fatigue strength.
However, conventional steel ball shot material has a low specific gravity, so high
speed projection is required in order to improve fatigue strength; thus, the
accompanying noise and high air flow are problems. Accordingly, in order to
improve these aspects, high hardness and high specific gravity shot material has
been developed with 1.7 times the hardness (HV1400) and approximately 1.9 times
the specific gravity (approximately 14) compared with a conventional steel ball.
 Mark S. Molzen et al: The welding process induces residual tensile stress that is
detrimental to fatigue life. Tensile stresses act to stretch or pull apart the surface of
the material. With enough load cycles at a high enough tensile stress, a metal
surface will initiate a crack. Significant improvements in fatigue life can be obtained
by modifying the residual stress levels in the material. Two methods of performing
this are through heat treating and shot peening. Both will be thoroughly analyzed in
this paper through the use of x-ray diffraction. X-ray diffraction is the most accurate
and best-developed method to characterize the residual stress in polycrystalline
material.
Literature Review

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 Manoj Saini et al: Dissimilar metal joints between austenitic stainless steels
and carbon steels containing low amounts of carbon are being extensively
utilized in many high-temperature applications in energy conversion systems. In
steam generating power stations, the parts of boilers that are subjected to lower
temperatures as in the primary boiler tubes and heat exchangers are made of
ferritic steel(mild steel) for economic reasons. Other parts, such as the final
stages of the super heaters and repeaters operating at higher temperatures where
increased creep strength and resistance to oxidation are required, are
constructed with austenitic stainless steels. Therefore, transition welds are
needed between the two classes of materials.Dissimilar metal weld is also used
to anlysis of strength of joint.Beacause due to residual stress induces in the
weld.We can find the amount of residual stress in two different metal.
Literature Review

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Work Carried Out
 Literature survey is carried out on fatigue life of welded joint and on surface
enhancement treatment process.
 Selection of material and specification required according to ASTM standard.
 Mild steel and stainless steel plates are machined to the required shape and size.
 Machined MS and SS304L materials are joined by butt welding process and
specimens of MS to MS and MS to SS are prepared according to ASTM standard.
 Shot peening is done on the specimens surface to reduces tensile stress and to
induces compressive stress in the specimens.
 Residual stress on the specimen is measured before and after shot peening
operation.
 Fatigue strength is measured for both shot peened and without shot peened
specimen and compared.
 Hardness of the specimen near the welding zone is measured before and after shot
peening process.

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Results and Discussion
Sl. No Specimen Stress before shot peening(Psi) Stress after shot peening(Psi)
1. MS to MS 4 -186.9
2. MS to SS 3.75 -910.8
Table 1] Experimental result of residual stress of the specimens before and after shot
peening
Sl. No Specimen Load(N) Speed(rpm) Number of cycles to
failure before shot
peening
Number of cycles to
failure after shot
peening
1. MS to MS 25 2500 35,475 49,942
2. MS to SS 25 2500 45,372 61,266
Table 2] Experimental result of fatigue life of the specimens before and after shot
peening

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Results and Discussion
Sl. No Specimen Load (kgf) Hardness before shot
peening(HRC)
Hardness after shot
peening(HRC)
1. MS to MS 60 52 63
2. MS to SS 60 57 65
Table 3] Experimental result of hardness on the heat affected zone in the specimens
before and after shot peening

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Results and Discussion
Discussion:
The obtained results of all the specimens were tabulated.
It is observed that (from table 1) the residual stress in the specimen before shot
peening is positive i.e. tensile but it becomes negative i.e. compressive after shot
peening. This indicates that the shot peening reduces the residual tensile stress and
induce residual compressive stress.
Table 2 shows that the fatigue life of component increases after the shot peening
process. Also the fatigue life of MS to SS specimen is greater than that of MS to MS
specimen before and after shot peening process.
Table 3 shows the hardness value of two specimens at the heat affected zone. It is
observed that the shot peening process increases the hardness of material. Also the
hardness of the MS to SS specimen is greater than that of MS to MS specimen before
and after shot peening.

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Conclusions
Conclusions are drawn based on the results obtained from experimental methods are
summarized as follows:-
Welding process creates residual tensile stress which is detrimental to fatigue life
and is required to be removed or compensated.
The similar (MS to MS) and dissimilar (MS to SS304L) butt welded joints were
prepared according to the ASTM (American Society for Testing and Materials)
standard and the induced tensile stresses were measured by X-Ray diffraction method.
Shot peening method which is employed for surface modification, uses S330 shot
balls of diameter ranges between 0.7mm to 1.20mm to strike the surface of the
specimen for duration of 25 seconds. This Surface modification process induces
compressive residual stresses.
After shot peening process the induced compressive residual stresses in the
specimen measured by using X-Ray diffraction method.

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 The fatigue test was carried out for both the specimens before and after shot
peening process for load 25N, numbers of cycles to failure were noted down.
 The effect of surface enhancement method has improved the fatigue life of the
welded specimen by 28.97% in the case of M.S-M.S welded joint and by 12.31 %
in the case of MS-SS304L.
 The effect of surface enhancement method on the surface hardness of the welded
specimen are found to be increased by 17.46 % in the case of M.S-M.S welded
joint and by 35.03% in the case of MS-SS304L
Conclusions

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Scope for future work
Here, there are few research work are projecting as scope for future
researches to improve welded joint fatigue life.
Improvement of fatigue strength of welded joint by using other
surface enhancement process like burnishing process, surface grindings
process, heat treatment process can be carried out and compare the
fatigue strength obtained from the above mention process.
Improvement of the surface hardness and fatigue strength of welded
joints by surface modification process such as shot peening process by
using different shot material by varying peening condition.

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References
1. Mark S. Molzen and Doug Hornbach, Evaluation of Welding Residual Stress
Levels Through Shot Peening and Heat Treating.
2. Sylvain Chataigner, Lamine Dieng, Kevin Guit and Michel Grasset,
Improving welded joint fatigue life using shot peening or grinding, France, Jan
2013.
3. M Hasegawa and H Suzuki, Improvement of the fatigue strength of aluminium
alloy welded joints by high hardness and large specific gravity shot peening,
Welding International, Volume 19, 2010.
4. Manoj Saini, Navneet Arora, Chandan Pandey and Husain Mehdi,
Mechanical properties of bimetallic weld joint between sa 516 grade 65 carbon
steel and SS 304 l for steam generator application, 2014.
5. Xiaohua Cheng1, Henry J. Prask, Thomas Gnaeupel Herold, Vladimir
Luzin4, and John W. Fisher, Neutron Diffraction Measurements for Residual
Stresses in AL-6XN Stainless Steel Welded Beams.
6. M.H. (Johnny) Johnson, Fatigue life improvement Techniques for welds, Process
Barron Alabama.
7. Vinod M. Bansode and N. D. Misal, Fatigue life estimation of a butt welded joint
by s-n approach, College of Engineering, Pandharpur, India, 2012.

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References
8. Baptista R., Infante V., and Branco C.M., Experimental and Numerical
Analysis of Fatigue Life Improvement Techniques in Welded Joints of Stainless
Steels, Lisbon, Portugal.
9. B. Mvola, P. Kah and J. Martikainen, Dissimilar ferrous metal welding using
advanced gas metal arc welding processes, Finland, 2014.
10. N. S. Rossini, M. Dassisti, K. Y. Benyounis and A. G. Olabi, Methods of
Measuring Residual Stresses in Components, Ireland.
11. Rafailov G., Sariel J., Dahan I., Reuven R., and Szanto M., Prediction and
XRD measuring of residual stress in Machined welded parts, Beer-Sheva.
12. Y. Kudryavtsev and J. Kleiman, Fatigue of Welded Elements: Residual
Stresses and Improvement Treatments, Canada.

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Acknowledgements
The journey of this research endeavour has been a great learning experience. We feel truly
blessed to have had the support of many people, who have made this journey of research
meaningful and worthwhile. We take this opportunity to express our gratitude to all those who
helped us during the course of this work.
We have extremely thankful to Prof. T.J. Ramamurthy, Director and Dr. K. Ranga, Dean,
for constantly encouraging us to do our best.
We express our heartfelt thanks to our beloved principal, Dr. M.S. Suresh for his
encouragement all through our graduation life and providing us with the necessary infrastructure,
without which we could not have demonstrated this project.
We express our deep sense of gratitude to Dr. N.C. Mahendra Babu, Head of the
Department, Dept. of Mechanical for his constant guidance and cooperation which consequently
resulted in getting the project work completed successfully.
We are thankful to Dr. Mukesh Patil, Project Coordinator, for his valuable guidance and
support leading to the successful completion of the project.
We are thankful to our project guide Mr. Harish A., Asst. Professor, Dept. of Mechanical,
for extending his valuable insight and suggestions offered during the course of this project. He
had a very important role in the successful completion of the project.
We are indebted to the staff of the Department of Mechanical Engineering, BNM Institute of
Technology for their sincere cooperation, encouragement and constructive criticism. We would
also like to thank our non-teaching staff for their efforts to support us in our venture.

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Thank You