Holding A Non Rotating Workpiece

Published Date: 02 Nov 2017

contact with a rotating workpiece under constant or slowly increasing pressure until the interface

reaches the welding temperature, and then the rotation is stopped to complete the weld. The Carbon

Steels are widely used in different industrial applications such as shipbuilding, and automobile

industries due to their good mechanical strength. In this work, friction welding of low carbon steel rods

of 12mm diameter are investigated with an aim to predict the value of tensile properties. Welds are

made with various process parameter combinations which are subjected to tensile tests. Here, the

three factors, five levels, central composite, rotatable design matrix are worn to optimize the required

number of experiments. The empirical relations are established by using Response Surface Method

(RSM). The adequacy of the models have been checked through ANOVA technique. Through using the

developed mathematical models, Yield strength, ultimate tensile strength and % of elongation of the

joints can be predicted by means of 95% confidence level. The integrity of the joints has been

investigated using the optical microscopy. The fracture surface of the tensile test specimens is analyzed

by using Scanning Electron Microscope (SEM) and is presented in details.

Elsevier Editorial System(tm) for Journal of Materials Processing Technology

Manuscript Draft

Manuscript Number: PROTEC-D-13-00237

Title: Mathematical model to predict the tensile properties of Friction welded Low carbon steel rods

Article Type: Research Paper

Keywords: Low Carbon Steel, Friction Welding, Tensile strength, Mathematical model.

Corresponding Author: Prof. K. Palanikumar, Ph.D

Corresponding Author's Institution: Sri Sai Ram Institute of Technology

First Author: S.T Selvamani, M.E

Order of Authors: S.T Selvamani, M.E; K. Palanikumar, Ph.D; K Umanath, M.E

K. Palanikumar

Date: 09/02/2013

To

The Editor-in-Chief,

Journal of Materials Processing technology.

Dear Professor,

Sub: Submission of manuscript-Reg.

Herewith I have enclosed the manuscript titled "Developing a mathematical model to predict

tensile properties of Friction welded Low carbon steel rods" to publish in your esteemed

International Journal. I request you to kindly accept it as a candidate for Publication.

We declare that the submission is original and have not submitted elsewhere for publication.

Thanking you,

Yours sincerely,

All the references are corrected properly and discussed.

Ref. PROTEC-D-13-00237

Title: Developing a mathematical model to predict tensile properties of Friction welded Low

carbon steel rods

Journal of Materials Processing Technology

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Microstructure and fracture surface are studied.

Research Highlights

Highlights











Environmental friendly friction welding is considered.

The influencing parameter rotational speed is considered which is new.

Tensile behavior of friction welded joints is reported.

Empirical relations are established by using RSM

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Mathematical model to predict the tensile properties of

Friction welded Low carbon steel rods

S. T. Selvamani

Research scholar, Department of Mechanical Engineering, Anna University, Chennai,

Tamilnadu, India

Department of Mechanical Engineering, Vel Tech Multi Tech Engineering College,

Chennai 600062, Tamilnadu, India

Tel.: +91 9940540221; E-mail address:

[email protected]

K. Palanikumar

Department of Mechanical Engineering, Sri Sairam Institute of Technology, Chennai-

600044, India

Tel.: +91 44 22512111; Fax: +91 44 22512323; E-mail addresses:

[email protected]

[email protected]

K. Umanath

Research scholar, Department of Mechanical Engineering, Anna University, Chennai,

Tamilnadu, India

Department of Mechanical Engineering, Vel Tech High Tech Engineering College,

Chennai 600062, Tamilnadu, India

Tel.: +91 9840403231; E-mail address:

[email protected]

2

Abstract

The rotary friction welds are prepared by holding a non-rotating workpiece in

contact with a rotating workpiece under constant or slowly increasing pressure until

the interface reaches the welding temperature, and then the rotation is stopped to

complete the weld. The Carbon Steels are widely used in different industrial

applications such as shipbuilding, and automobile industries due to their good

mechanical strength. In this work, friction welding of low carbon steel rods of 12mm

diameter are investigated with an aim to predict the value of tensile properties. Welds

are made with various process parameter combinations which are subjected to tensile

tests. Here, the three factors, five levels, central composite, rotatable design matrix are

worn to optimize the required number of experiments. The empirical relations are

established by using Response Surface Method (RSM). The adequacy of the models

have been checked through ANOVA technique. Through using the developed

mathematical models, Yield strength, ultimate tensile strength and % of elongation of

the joints can be predicted by means of 95% confidence level. The integrity of the

joints has been investigated using the optical microscopy. The fracture surface of the

tensile test specimens is analyzed by using Scanning Electron Microscope (SEM) and

is presented in details.

Keywords: Low Carbon Steel; Friction Welding; Tensile strength; Mathematical

model.

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1.

Introduction

Welding is one of the important processes used in the manufacturing industries.

There are various welding methods that have been developed to achieve suitable joints

in various applications. This study, deals with the significance of welding in the

manufacturing methods. However, Mumin Sahin et al. (2007) have investigated the

friction welding, which is an alternative production method and it is also one of the

methods that have been broadly used for more than a few years. As friction welding is

known the heat is generated by the change of mechanical energy into thermal energy at

the interface of the work pieces during rotation under pressure. Generally, friction

welding can be easily used to join the components that have circular or non-circular

cross sections. Vill (1962). The friction welding is known for high material saving,

lower production time and also possible of welding of parts that are made of different

metals or alloys. Friction time, friction force, forging time, forging force and the rotation

speed are the most influencing parameters used in the friction welding methods

Friction welding appears to offer a number of advantages over the arc welding of

steels. Metallurgically, joint of steels can result in hard intermetallic phases that

generally formed by fusion welding (liquid state welding). The formation of these

phases mainly occurs by inter diffusion of the species and is vastly dependent on the

specific time and temperature history of the rotary friction welding process. The

increased thermal cycles (higher temperatures/ longer times) associated with fusion

welding processes generally result in the formation of hard intermetallic compound

layers of the joint interface. The formation of these layers is normally considered as the

root cause of the property degradation seen with these types of joints. Solid state

welding (friction welding) techniques facilitate joint formation at lower temperatures

and often at very short period of times. The use of solid state joining process is

generally associated with the reduced formation of these intermetallic phases, which

minimize the grain growth in the HAZ (heat affected zone) and limit distortion and

residual stress in steels. Additionally, problems with hydrogen cracking in steels are

eliminated by the friction welding because it is a solid state process. Friction welding

has been effectively been used for joining steels in production environments. Properly

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applied, friction welding (and its variant inertia friction welding) allows the joining of

materials at relatively low temperatures with an overall short thermal cycle which have

been discussed by

Fujii et al. (2006)., Marya et al. (2007)., Agudo et al. (2007).,

Yokoyama (2003)., Villars et al. (2007)., and Olson et al. (1993).

Different studies on friction welding have been carried out by various

researchers. Mumin Sahin et al. (2007). Vill (1962)., Tylecote (1968)., Jenning (1971).,

Lucas (1971)., Kinley (1979)., and Fomichev (1980).

Made studies on friction

welding. Ellis (1977) has examined the relationships between "friction time workpiece

diameter", "shortening-upsetting pressure" and "carbon equivalent-hardness variation".

Dunkerton (1986) has investigated the effects of rotation speed, friction pressure and

upsetting pressure in all friction welding methods for steel. Akata et al (2003) have

reported a research on the effect of dimensional differences in the rotary friction

welding of AISI 1040 specimens. Sahin and Sahin (2003) have investigated the joining

of plastically deformed carburising steel with friction welding. An experimental study

on rotary friction welding of medium carbon and austenitic-stainless steel are discussed

by by the same authors. Sahin and Akata (2004); Sahin (2004) have directed the

simulation of friction welding using a developed computer program.

Midling and Grong. (1994), Ananthapadmanaban et al. (2009), Fukumoto et al.

(2000) and Maalekian et al. (2008) have investigated the friction welding process.

From the literature, it is understood that the most of the published information on

continuous drive friction welding of steel has focused on phase formation studies,

microstructure analysis, hardness survey at the interface to evaluate the subsequent

influence on the strength and the processing map to find out the best quality joint.

Many investigations are carried out on a trial basis to attain optimum bonding

conditions. Only a few research works have been reported to optimize the friction

welding parameters to attain the tensile strength of steel joints. But they have not

considered the other tensile properties such as yield strength and % of elongation.

The reported earlier works considered the rotational speed as only the fixed

process parameter. Normally, the rotational speed is one of the important process

parameter which influence the tensile properties. In the present study, the various

rotational speeds are considered as a process parameter and its effect is discussed.

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To obtain the maximum strength, it is essential to have complete control over the

relevant process parameters. It has been proved by some researchers that efficient use

of statistical design of experimental methods allows to the development of an empirical

methodology to incorporate a scientific approach in solid state procedures such as

friction and friction stir welding which have been presented by Babu et al. (2009) and

Rajakumar et al. (2010)

In the present study, an experimental friction welding setup, which is a

continuous drive friction welding set-uphas been in the experiments. To develop the

empirical relationships between process parameters and tensile strength, Yield strength

and % of elongation are obtained to join parts having an equal diameter.

2 Experimental work and analysis

In order to achieve the desired results, the investigation has been designed in the

sequence as defined by Palanikumar et al. (2006)., Palanikumar (2007)., Palanikumar

and Karthikeyan (2007). The low carbon steel of AISI1035 Steel round extruded rod is

used for this research. Its applications include levers, studs, bolts, nuts, and similar

parts which are headed and or extruded.

2.1 Identification of important parameters

From the literature provided by Mumin Sahin (2007) and the previous work

carried out by the researchers of this paper, among many independently controllable

primary and secondary process parameters affecting the tensile strength, the primary

process parameters via friction time, friction force, forging time, forging force and

rotation speed are selected as process parameters for this study. The friction time,

friction force, forging time, forging force and rotation speed are the primary

parameters contributing to the heat input and subsequently influencing the tensile

strength variations in the friction welded steel joints.

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2.2 Finding working limits of the parameters

A large number of trial runs have been carried out using the 12 mm diameter

extruded rod of low carbon steel (AISI1035 steel round) to find out the feasible

working limits of FW process parameters. The chemical composition and mechanical

properties of low carbon steel are presented in Tables 1 and 2. Different combinations

of process parameters are used to carry out the trial runs. This is carried out by varying

one of the factors while keeping the rest of them at constant values. The working range

of each process parameter is decided upon by inspecting the macrostructure (cross

section of the weld) for a smooth appearance without any visible defects. The Friction

welding machine setup is shown in Fig.1, which has been used to fabricate the joints.

The chosen levels of the selected process parameters with their units and notations are

presented in Table 3.

2.3 Conducting the experiments

The extruded rods of 12 mm in diameter (AISI1035 steel round) are cut into the

required sizes (100 mm length) by power hacksaw cutting machine. The design matrix

chosen to conduct the experiments is a central composite Rotatable (k<6) design,

which is listed in Table 4. An indigenously designed and developed machine of

continuous drive Servo controlled Friction welding machine (Model: Rexroth, R. V.

Machine tools, Cap.20kN Tools) is used to fabricate the joints. The photographs of the

before and after friction welded specimens are shown in Fig.2.

The welded joints are turned by using a CNC lathe to the required dimensions as

shown in Fig.3. American Society for Testing of Materials (ASTM E8M-04) guiding

principles are followed in preparing the test specimens. Three tensile specimens are

prepared from each joint to evaluate the transverse tensile strength. Tensile test is

carried out on a 100 kN Electromechanical controlled universal testing machine (FIE-

Blue Star, India; Capacity: 0-100KN, Model: Instron-UNITEK-94100). The specimen

is loaded at the rate of 1.5 kN/min according to the ASTM specification and the

average of the three results is presented in Table 4. The photographs of before and after

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tensile tested specimens are shown in Fig.4. The various zones of optical micrographs

of friction welded Low Carbon Steel are shown in Fig.5.

3.

Developing the empirical relationship for friction welding parameters

In the present investigation, RSM has been applied for developing the

mathematical model in the form of multiple regression equations for the quality

characteristic of the friction welded low carbon steel. In applying the response surface

methodology, the independent variable is viewed as a surface to which a mathematical

model is fitted. The second order polynomial equation used to represent the response

surface Y is given by Balasubramanian (2008).

As the range of individual factor is wide, a central composite rotatable three-

factor, five-level factorial design matrix has been selected. The experimental design

matrix (Table 4), consisting of 20 sets of coded conditions and comprising a full

replication Three-factor factorial design of 8 points, 6 star points, and 6 center points,

is used. The upper and lower limits of the parameters are coded as +1.68 and −1. 68

respectively. The coded values for intermediate levels can be calculated by:

Xi=2 [2X− (Xmax+Xmin)] /(Xmax−Xmin)

(1)

Where Xi is the required coded value of a variable X and X is any value of the

variable from Xmin to Xmax. The friction welds were made under every condition

dictated by the design matrix in random order so as to avoid the noise creeping output

response. As prescribed by the design matrix, 60 joints have been fabricated.

The tensile strength (σ) of the friction welded low carbon steel joint is a function

of the friction welding parameters such as a friction force/time (FRt), forging

Force/time (FOt ) and Rotational Speed (N) which can be expressed as:

σ =f {FRt, FOt, N}

(2)

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The second-order polynomial (regression) equation used to represent the response

surface σ is given by:

σ = b0+ΣbiXi+ΣbiiXi2+ΣbijXiXj

For three factors, the chosen polynomial could be expressed as:

σ = b0 + b1(FRt) + b2(FOt) + b3(N) + b12(FRt*FOt) + b13(FRt*N) + b23(FOt*N)

+b11(FRt 2)+b22(FOt 2) + b33(N2)

(4)

(3)

Where b0 is the average of the responses, and b1, b2, b3, …, b33 are regression

coefficients that depend on the respective linear, interactive, and squared terms of

factors (Murti and Sunderesan; 1986). The values of the coefficient are calculated by

using the Design Expert Software. The significance of each coefficient is determined

by Student‟s t test and p values, which are listed in Table 5. The values of "Prob>F"

less than 0.05 indicate that the model terms are significant. In this case, FRt, FOt, N,

FRt FOt,FRt N, FOt N ,FRt 2, FOt 2, and N2 are significant model terms. The values

greater than 0.05 indicate that the model terms are not significant. The results of

multiple linear regression coefficients for the second- order response surface model are

given in Table 6. The final empirical relationship is constructed using only these

coefficients and the developed final empirical relationship for ultimate tensile strength

(σ), yield strength (σy) and % of elongation are given below:

σ in Mpa = +547.03+1.17FRt+1.96FOt+8.48N-2.37FRt FOt - 6.37 FRt N- 1.37 FOt N

-25.14 FRt2 - 1.25 FOt2 - 13.11

σy in Mpa = + 547.03 + 1.17 FRt + 1.96 FOt + 8.48 N - 2.37 FRt FOt - 6.37 FRt N-

1.37 FOt N - 25.14 FRt2 - 21.25 FOt2 - 13.11N2

% of Elongation = + 1.3103 - 0.214 FRt - 0.267 FOt - 0.803 N+ 0.113 FRt FOt +

0.7125FRt N + 0.1125 FOt N + 1.347 FRt2 + 0.727 FOt2 + 0.0513 N2 (7)

(6)

(5)

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Analysis of variance (ANOVA) technique is used to check the adequacy of the

developing empirical relationship. In this investigation, the desired level of confidence is

considered to be 95%. The relationship may be considered to be adequate, which

provides that 1) the calculated F value of the model developed should not exceed the

standard tabulated F value and 2) the calculated R value of the developed relationship

should exceed the standard tabulated R value for a desired level of confidence. It is

found that the above model is adequate. Normal probability plot of residuals for tensile

strength, yield strength and % of elongation is shown in Fig.5. Shew and Kwong (2002)

have given that the normal probability plot is used to validate the normality assumption.

The values are spread roughly along the straight line as shown in Fig. 5. Therefore, it

can be concluded that, the data are normally distributed . Residuals against the observed

order of data for tensile strength, yield strength and % of elongation are shown in Fig.6.

These are the states which have the runs of negative and positive residuals indicates the

subsistence of a certain correlation. Also the graph shows that the residuals are dispersed

evenly in both negative and positive along the run order. Therefore, the value can be

believed to be independent. Each predicted value matches well with its experimental

value, as shown in Fig. 7.

4.

Result and discussion

Friction welding is one of the important joint method and is environment

friendly. Ananthapadmanaban et al. (2009) have stated that further studies are required

to characterize the heat affected zone and recrystallized zone and also to optimize the

friction welding process parameters. Duffin and Bahrani (1973) have investigated with

the same material like low carbon steel. The results obtained designate that, the

frictional behavior of low carbon steel under these particular conditions is greatly

influenced by the rubbing speed and to a lesser extent of the value of force which is

normal to the rubbing surfaces. In the present work the mathematical models are

developed for the process parameters. The adequacy of the models are checked by using

analysis of variance. The microsturcture analysis and the influence of process

parameters are analyzed and are discussed below:

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4.1

Microstructure of welded parts

Micro and macro structure analysis of the friction welding of the low carbon

steel is carried out for analyzing the behavior of the parent metal and interface region of

the friction welded joints. The specimens are prepared and etched by using picral and are

shown in Fig. 8. The figures indicate the various zones clearly for analyzing the micro

structures. The various zones are heat affected zones (HAZ), interface zone (IFZ),

downward flow metal (DFM), upwards flow metals (UFM), and weld interface. (WI)

Fig.8 (a) shows the macro structure of the welded interface in which the burr

formation is clearly indicated during the friction welding. Due to the application of

pressure and heat the burr formation occur in between the two parent metal. The result

indicates that the revolving side has more proper burr than the stationary side. The

reason being due to the application of pressure and revolving nature of the material. The

burr formation is shown in figure. The figure also indicates the different zones. Fig. 8 (b)

shows the micro structure of the weld interface which clearly indicates the the interface

between the stationary and revolving work pieces. The micro structure is comparatively

dense than the parent metal due to the application of the pressure heat in the interface

zone. Figs. 8 (c) and (d) show the upper and downward metal flow in the welded region

which indicates that the flow of material is like quarter circle and the elongated grain

structure is observed in the upper and downward regions. The figure also indicates that

the upper metal flow is more uniform than the downward metal flow. Figs. 8 (b) and (f)

show the weld zone and interface zone taken at 100x magnification. The weld zone

indicates the dense structure due to the application of pressure during the friction

welding process. The grains are not uniform and have elongated due to the application

of pressure and heat. The heat affected zone, interface zone and welding zone are clearly

presented in the Fig. 8 (f). The grains are different at various zones due to the variation

of pressure and temperature distribution. The Fig. 8 (g) shows the heat affected zone,

this figure has been taken at high magnification to show the micro structural change.

The heat effected zones shows the elongated ferrite, less amount of pearlite and less

quantity of ferrous carbide particles. Fig.8 (h) show the micro structure of the base metal

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taken at high magnification (200X). The figure indicates the presence of ferrite, pearlite

and Fe3C.The micro graphs indicate the different region of the friction welding low

carbon steels.

Fig. 9 shows the scanning electron microscope (SEM) image of the fracture

surface of the tensile specimens. Fig. 9 (a) shows that the structure of the grain is

elongated at the fracture zone. The fracture takes place at weld zone. The nature of the

fracture surface is indicated as shown. The fracture obtained is both brittle and ductile

fractures. Fig. 9 (b) shows the SEM micro structure of fracture specimen. The micro

structure at high magnification considering the small quantity of metal (2μm). This

figure indicates the detailed view of the fracture surface in which the structural

elongation and delocation of material from one region to another region is evident. Fig.

9 (c) shows the base metalFracture surface of the tensile specimen (Base metal)

4.2

Influence of process parameter on friction welding of low carbon steel

The relationships of the friction force/ time, tensile strength and yield strength

has been plotted in the Fig. 10 (a) and Fig. 10 (b). In the graph, as the friction force/ time

for the joints are increased, the tensile strength and yield strength of the joints increases.

Further, On increasing the friction force/ time at the peak point of 548MPa at 0.33 ton/

sec and 438.303MPa at 0.33ton/ sec respectively, the tensile strength and yield strength

of the joints decreases. Also Fig. 10 (c) shows that the increase of friction force/ time

increases the % of elongation of the joints and it decrease from the maximum point of

5.65% at 0.16 ton/sec.

The relationship of the forging force/ time, tensile strength, yield strength has

been plotted in the Fig. 11 (a) and Fig. 11 (b). In the graph, as the forging force/ time for

the joints are increased, the tensile strength and yield strength of the joints increases.

Further, On increasing the forging force/ time at the peak point of 548MPa at 0.33 ton/

Sec and 438.303MPa at 0.33ton/sec respectively, the tensile strength and yield strength

of the joints decreases. Also Fig. 11 (c) shows the forging force/ time increases the % of

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elongation of the joints which decrease from the maximum point of 5.65% at 0.16

ton/sec.

The relationship of the Rotational speed, tensile strength, and yield strength have

been plotted in the Fig. 12 (a) and Fig. 12 (b). In the graph, as the Rotational speed for

the joints are increased, the tensile strength and yield strength of the joints increases.

Further, an increasing of Rotational speed at the peak point of 548MPa at 1465.22 r/min

and 438.303MPa at 1452.97 r/min respectively, the tensile strength and yield strength of

the joints decreases. Also Fig. 12 (c) shows the friction force/ time increases the % of

elongation of the joints which decrease from the maximum point of 5.65% at 1200

r/min.

Conclusions

The following important conclusions are obtained from this investigation:

Continuous drive friction welding method can suitably be adapted for mass

production of steels and metals. Optimum welding process parameters should be

properly selected in Continuous drive friction welding of parts. However, the

experimental procedure is limited to the range of factors considered for analysis.

Empirical relationships are developed to predict the Tensile strength, yield

strength and % of elongation of the friction welded low carbon steel rods

incorporating friction welding process parameters.

Developing relationship can be successfully used to predict the tensile strength,

yield strength and % of elongation of friction welded joints at 95% confidence

level.

In macro and microstructure examinations, on low-carbon steel after welding, its

heat- affected zone structure is elongated ferrite, least amount of pearlite and

few carbide particles is found and also the high amount of pearlite is found in the

weld zone is well matched with the base metal structure.

A Predicted maximum tensile strength of the friction welded specimen is

548MPa

is attained under the welding conditions of 125MPa of Friction

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Pressure and Forging pressure and 1465.22r/min of rotational speed at a constant

friction and forging time of 3 sec.

Predicted maximum yield strength of the friction welded specimen is

438.303MPa has been attained under the welding conditions of 125MPa of

Friction Pressure and Forging pressure and 1465.97r/min of rotational speed at a

constant friction and forging time of 3 sec.

A Predicted maximum % of elongation of the friction welded specimen is 5.65%,

which could be attained under the welding conditions of 125MPa of Friction

Pressure and Forging pressure and 1200r/min of rotational speed at a constant

friction and forging time of 6 sec.

As the ratio of friction force and friction time is minimized (0.16 ton/ sec) or

maximum (0.6), the Tensile strength and Yield strength are minimal but the % of

elongation is at peak. If the ratio is optimum of 0.33, the Tensile strength and

Yield strength are of high peak but the % of elongation is obtained at a minimum

level.

Acknowledgement

The authors are grateful to the Vel Shree Dr. R. Rangarajan, Chanceller, Mr. K. D.

Kishore, Director, and

Mrs. R. Mahalakshmi Managing Trusty. Vel Tech Dr.RR and

Dr.SR Technical University, Avadi, Chennai, Tamilnadu, India. For the support and

facilities provided for the preparation of this paper. Also wish to thank the Center for

Materials Joining and Research (CEMAJOR), Department of Manufacturing

Engineering, Annamalai University, Annamalai Nagar, India for extending the facilities

of metal joining and material testing to carry out this investigation.

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