welding project report.pdf

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CHAPTER 1

INTRODUCTION

Among the welding typical problems and most important are the residual

stress/strain and the induced distortions in structures of the components. In order to get

better understand the welding process and its effects on structures, engineers and

researchers around the world, covering a large number of industries, have been trying to

create algorithms and methodologies to simulate the complete welding process or just

individual phases (e.g. the cooling phase). In recent years, due to the high expansion of

computer software, computations possibilities, many researchers identified the Finite

Element Analysis (FEA) as a reliable method for this purpose. Hence ANSYS is used for

the welding simulation.

1.1 Need of the Project

The need of the project arises due to the problem of inaccuracies that take place during the

heating or welding process of the production and hence increase partly from the thermal

distortions and partly in the form of dimensional variations due to human factors.

Furthermore, with the increasing use of the automation, it is necessary to quantify and

calculate the thermal distortions by means of mathematical models by using FEA, so that

the required tolerances of the automation process can be achieved as efficient as possible.

In order to improve planning and work scheduling by reducing the rework, to reduce the

production cost significantly by reducing the measurements and rework, and to improve the

quality of the weldment the significance of FEA is studied.

1.2 Scope of the Project

The problem of creation of residual stresses during welding steel plates leads to

dimensional inaccuracies and misalignments of structural members, which can result in

complex tasks or rework when tolerance limits are crossed. Hence cause increase in the

cost of production and leads to loss of time. In fabrication sector, for example, expenses

required for rework such as straightening could have a heavycost. Therefore, the problems

of distortion and residual stresses arealways of great concern in welding sector. In order to

deal with this problem, it is necessary to interpret the extent of distortion resulting from the



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welding operations. One way to interpret the distortion and shrinkage of steel welding is

through numerical analysis such as finite element analysis (FEA). Once the techniques to

predict the distortion and shrinkage are recognised, then the problems can be controlled

accordingly. During the welding process, there are so many factors such as welding process

type, welding process parameters, preheat patterns, welding sequence, level of constraint

and joint details that contribute to the creation of the residual stresses in the welded

structure. By determining which parameters have an effect on the quality of the weld and

which factorswill give the most significant effect on the weld quality are the main aspects

in welding industry.

1.3 Problem Statement

In this project work the direct coupled field transient thermal structural analysis will be

carried out using finite element analysis for arc welding for a butt joint. To carry the FEA

two plates of ASTM 36 were considered to be welded. The dimensions of the plate were

taken as 200 x 100 x 3 mm for each plate. Welding was assumed to be done along 100 mm

length of the plate. The groove angle for welding was taken as 60º.

1.4Methodology of the Project

• The adapted experimental methodology is as follows,

– Collection of data or information for the arc welding simulation using Finite

element analysis software.

– 3D modeling of the weld and ASTM 36 steel plates to be welded using

CAD software

– Finite element model creation by using finite element software

– Carry out thermal analysis to find temperature distribution due to welding

process in the steel plate.

– Structural analysis of weld and welded plate to find residual stresses.

– To find out temperature distribution across the center line of the weld at 100

seconds after completion of welding process



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– residual stress calculation due to welding by using FEA

– To find out strain across the center line of the weld after cooling of the

welded steel plate.

– Comparison of results from experiments with FEA results of residual

stresses observed due to welding

1.5 Objectives of the Project

This report introduces finite element analysis for the modeling of welds and it explains a

brief history of the simulation of welds. Welding is one of the reliable and highly effective

metal fabrication process which is widely used in industries. Localized and excessive

heating during the welding process, followed by rapid cooling causes to generate residual

stress and distortion in the weld and base metal. In the last few years various research

efforts have been directed towards the control of welding process parameters in order to

reduce the residual stress and distortion.

Objectives of the project are to find out -

1. Residual stresses in the welded parts due to phase change due to solidification of

weld with respect to distance from weld.

2. Temperature change with respect to time due to phase change to solidification of

weld with respect to distance from weld.

3. Strain in the welded parts due to phase change to solidification of weld with respect

to distance from weld.

4. Suitability of software to interpret residual stresses.



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1.6 Publications

A paper has been published related to the project work entitled as “Finite Element

Analysis for Residual Stress, Strain and Temperature Characteristics of Butt Welded

Steel Plate” in International Journal of Scientific Research, Volume:2,Issue:6, June 2013,ISSN no. 2277 - 8179.

1.7 Use of Finite Element Analysis

Finite element analysis makes it possible to evaluate a detailed and complex structure with

a very short period of time. The adequate strength of the structure and the possibility of

improving the design during planning could justify the cost included in this analysis work.

FEA has also been known to analyze the structure that were significantly over designed and

built many decades ago.In absence of finite element analysis (or other numerical analysis)

development of structures must be based on manual calculations only. In case of complex

structures, the simplifying assumptions necessary to make any calculation possibly can lead

to a conservative and heavy design. An important factor of ignorance can remain as to

whether the structure will be adequate for all design loads. Considerable changes in designs

involve risk. Design will require prototypes to be built and field tested completely. The

field tests may include expensive strain gauging to evaluate strength and deformation of the

components.



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CHAPTER 2

LITERATURE REVIEW

The research work in welding simulation was initializedmany years ago.Understanding of

the theory of heat flow is essential in order to study the welding processanalytically,numerically or experimentally. Rosenthal (1946) was the first researcher who succeeded in

developing an analytical solution of heat flow during welding based on conduction heat

transfer for determining the shape of the weld pool for two and three-dimensional welds.

By using the Fourier partial differential equation (PDE) of heat conduction, he initialized

the moving coordinate system to develop solutions for the point and line heat sources and

also applied this successfully to apply to a wide range of welding problems. His analytical

solutions for the heat flow made possible for the first time the analysis of the process from

the point of view of the welding parameters namely the voltage, current, welding speed,

and weld geometry. Due to the pioneering work done by Rosenthal,significant interest in

the thermal aspects of welding was developed by many researcherssuch as Goldak (1984)

The most critical and important input data required for welding thermal analysis are the

parametersnecessary to determine the heat input to the weldment by the arc. Goldak et al.

(1984) developeda mathematical model for welding heat sources based on a Gaussian

distribution of powerdensity. They proposed a double ellipsoidal distribution in order to

capture the size and shapeof the heat source of shallow and deeper penetrations.

Some of the researchers have alsodeveloped the thermal finite element simulation to

determine the temperature distribution of ametal.Over the past forty years, finite element

techniques have been used extensively in order topredict distortion and residual stresses due

to welding operations such as the studies byFriedman (1975), Michaleris and Debiccari

(1997) and Taylor et al. (1999). The finiteelement method has already been proven to be a

successful tool for the simulation of the complexwelding process as performed by Friedman

(1975). His 2-D finite element analysis work wasthen used by Taylor et al. (1999) for the

verification of their 3-D computational modeling of weldingphenomena.

The final results of finite element analysis done by Taylor et al. (1999) were inreasonable

agreement with the result obtained by Friedman (1975). Most of the welding research work

in the past was conducted to investigate the distribution and effect ofresidual stress and

distortion of welded metal component. It is possible to estimates the welding shrinkage in a



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welded butt joint by applying amathematical model approach. Michaleris and Debiccari

conducted thermo-elasto-plastic finite element analysis for welding simulation to determine

thewelding distortion. It has been claimed by them that their approaches have been similar

toexperimental and empirical data. Not only the welding residual stress and distortion have

been studied by welding researchers,but also the effects of welding sequence, welding joint

geometry,welding parameter and rootopening has also been studied by several researchers

in the last years.Harwig et al. (1999) for example, studied the effect due to welding

parameters and electrodeclassification on the diffusible hydrogen content of gas shielded

flux cored arc welds.

In 1999,Tsai et al. studied the influence of welding sequence on warping and buckling

behavior of athin-plate panel structure. Tsai et al. (2004) have also investigated the effects

of weldingparameters and joint geometry on the distribution and magnitude of residual

stresses onthick-section butt joints.

As proven by the researchers, residual stress distribution and distortion in a weldedplate are

strongly affected by their interaction and by many parameters. Yet, certain aspects ofthe

welding phenomenon are still subjected to further research specifically the effects of

welding speed, restraint, heatinput, gap on arc welding responses and plate curvature as

appliedto curved steel plate welding.In the recent ten years, there is growing need to

concern about the numerical research on line heatingand welding process. Murakawa et al.

(2005) interpreted the hot cracking of a weldment usingtemperature-dependent interface

elements. Mahapatra et al. (2007) modeled the influence of theposition of tack weld

constraints on the angular distortions that were created in one-sided fillet weldingcreated by

SAW.

It is cleared from this literature review that the thermal reactions and the

resultingdistortions in a welded joint are strongly affected by various parameters and their

interactions.A number of finite-element (FE) models used for illustrating the effect of using

differentmodeling strategies for the simulation of the thermo-elasto-plastic stages of the

weldingprocess are applied by Mollicone et al. (2006)Adak and Mandal (2010) studied the

heat sinking as a method of distortion mitigation and usedthe pseudo-linear equivalent

constant rigidity concept for thermo-mechanical analysis of platesundergoing welding with

simultaneous heat sinking. The proposed concept was found to becomputationally more

efficient and simpler to model as compared to FEM for solving similarthermo-elasto-plastic



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nonlinear problems.In 2011, Heinze et al. investigated a single-layer gas metal arc (GMA)

weld of 5 mm thickstructural steel is experimentally and numerically. The numerical

modeling begun with a meshanalysis based on modal analyses. The sensitivity of welding-

induced distortion is examinedrelated to different continuous cooling transformation (CCT)

diagrams.

Fusion welding includes heating by an intense heat source, melting and

solidification of parent metals, and often, addition of filler material in the localized fusion

zone during welding. The heat source causes nonuniform temperature distributions across

the joint and the parent metals. The computational weld pool models have became a

significant route for a priori estimation of weld pool dimensions, peak temperature, cooling

rate, and many other associated aspects of the weld pool and the surrounding heat-affected

zone. Particularly, finite element method-based weld pool models are found very useful to

interpret weld thermal cycle and fluid flow pattern at an early stage of welding process

development and product design. However, the complex geometry of real engineering

components and the complexity of welding processes itself have made the prediction of

weld thermal cycle and corresponding flow field to be a very difficult task. It is further

noticed that the accuracies of these quantitative calculations are largely dependent on the

accuracy of several input parameters in welding. Some of the input parameters are also not

certain in nature, and optimization algorithms are integrated with the numerical process

model to determine the suitable values of these uncertain input parameters for modeling

calculations.

Welding results in very complex thermal cycles which cause irreversible elastic

plastic strain and residual stresses in and around fusion zone and heat affected zone (HAZ).

Residual stresses may be an advantage and disadvantage in structural components

depending on their magnitude and nature. The beneficial effects of compressive stresses

have been widely used in industry as these effects are believed to reduce stress corrosion

cracking and brittle fracture and increase fatigue strength of the component. In large steel

fabrication industries such as marine structures, aero-space industry, shipbuilding, high

speed train guide ways and pressure vessels and piping in chemical and petrochemical

industry; the problem of residual stresses and overall distortion has been observed and

continue to be a major issue. It is well known fact that material response of structural

components is strongly affected by the residual stresses when subjected to structural and



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thermal loads. Due to the presence of these residual stresses produced in and around the

weld zone the strength and life of the component is definitely reduced.

Welds are always an essential part of engineering components. Residual stresses

produced in the welded regions of the metal components, due to the nonlinear thermal

processes during welding, can have detrimental effects, such as hydrogen-induced cracking

,stress corrosion cracking, and reduced fatigue strength. Due to this reason it is pertinent to

simulate the welding process to predict the behavior of welded structures from finite

element residual stress and strain results.

CHAPTER 3



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WELDING TECHNOLOGY

3.1 Introduction to Welding

In general, welding is defined as any process in which two or more pieces of metalare joined together by the application of heat, pressure, or a combination of both. Almostall

the processes may be grouped into two main categories: heat welding, in which the welding

process is achieved by heat; and pressure welding, where the welding process is achieved

by pressure. Heat welding is the welding which is used today. The most important welding

parameters are the welding speed and the arc energy per unit length of the weld.

[Jonsson,M., Karlsson, Lindgren L.E;1985]

During welding process, the weldment is locally heated due to the welding heat source.

Because of the non-uniform temperature distribution during the thermal cycle, incompatible

strains cause to develop thermal stresses in the components. These incompatible strains due

to dimensional changes related with solidification of the welded metal, plastic deformation

and metallurgical transformations are the major sources of residual stresses and

distortion.[M Sundar1, G Nandi, A Bandyopadhyay And S C Roy; 2005]

The parameters of the line heating process have major effect on thermal distribution and the

resulting residual deformation of the heated plate. The thermal transients are generally

dependent on various factors like torch height, gas pressure, torch speed, and nozzle size,

which then controls the residual deformation of the plate. [Biswas, P., Mandal, N.R. & Sha,

O.P. 2007]

Arc welding, which is a heat-type welding, is the most important

manufacturingoperation for the joining of structural components for a wide range of

applications, including ships, bridges, building structures, guide way for trains,

automobiles, and nuclear reactors, to give an example. It is necessary to provide a

continuous supply of either direct or alternating electric current, which is normally used todevelop an electric arc to generate enough heat to melt the metal and form a weld.

The arc welding process is a complex operation involving extremely high

temperatures, which produce high levels of residual stresses and severe distortions .

Theseextreme phenomena results in reduction of the strength of a structure, which becomes

vulnerabletocorrosion, buckling, fracture and other type of failures.



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3.2 Types of Arc Welding

The most widely used types of arc welding processes are gas tungsten arc, gas

metal arc, shielded metal arc and submerged metal arc.

3.2.1 Shielded Metal Arc Welding (SMAW)

In shielded metal-arc welding, a metallic electrode which is used to conductelectricity, is

coated with flux and is connected to a source of electric current. The metal which is to be

welded isconnected to the other end of the same source used to supply current. By having

touch of the tip of theelectrode to the metal and then drawing it away, an electric arc is

developed. The intenseamount of heat of the arc causes to melt both parts to be welded and

alsothe point of the metal electrode. Thispoint of the metal electrode supplies filler metalfor the weld.

3.2.2 Gas Tungsten Arc Welding (GTAW)

In gas tungsten arc welding, a tungsten electrode is used instead of the metal electrode as

used in shielded metal arc welding. A chemically inert gas, such as helium, orhydrogen

,argon, is used to shield the metal from oxidation. The heat produced from the arc

formedbetween the electrode and metal melts the edges of the metal component. Metal used

for the weld may beadded by placing a bare wire in the arc or at the point of the weld. The

GTAW process can be used with almost all metals and produces a high-quality weld

between two joints. Instead of this, therate of welding is considerably slower as compared

to other types of welding processes.

3.2.3 Gas Metal Arc Welding (GMAW)

In this type of arc welding, a bare electrode is shielded from the air by surrounding it with

argon or carbon dioxide gas or by coating the electrode with some type of flux for welding.

The electrode is required tofeedinto the electric arc, and melts off in droplets so as to enter

the liquid metal that forms the weld.



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3.2.4 Submerged Arc Welding (SAW)

This type of arc welding is similar to gas metal arc welding, but in this process no any gas

is used to shield the weld. Instead of gas the arc and tip of the wire are submerged beneath a

layer offusible, granular material formulated to produce a proper weld. This process is very

effective but is only used with steel.

3.3 Types of Welding Joints

Welds are made at the junction of the various pieces that cause to make up the weldment.

The junctionsof parts, or joints, are termed as the location where two or more members are

to be joined. Metal parts being joined to produce the weldment may be in the form of

castings, forgings, rolled plate, sheet, pipes, or billets. The five basic types of welding joints

for plates are explained below.[ Bai-Qiao Chen,2011]

3.3.1 Butt Joint

It is a joint between two members lying approximately in the same plane as shown in

Figure 3.1

Figure 3.1 -Butt Joint Arrangement.



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3.3.2 Corner Joint

It isa joint between two members located nearly at right angles to each other in the form of

an angle as shown in Figure 3.2.

Figure 3.2 -Corner Joint Arrangement.

Figure 3.3 - Edge Joint Arrangement.



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3.3.3 Edge Joint

It is a joint between the edges of two or more parallel or mainly parallel members or

components as shown in Figure 3.3

3.3.4 Lap Joint

It isajoint between two overlapping members as shown in Figure 3.4.

Figure3.4 - Lap Joint Arrangement.

3.3.5 T Joint

It is a joint between two members located nearly at right angles with respect to each other

in the form of a T as shown in Figure 3.5.



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Figure 3.5 - T Joint Arrangement.

3.4 Technique of Arc Welding

Thetechnique of arc welding is related with complex physical phenomena

associated with electricity, magnetism, welding including heat, light, and sound. By the

application of intense heat, the metal at the joint between two parts is melted and is

allowed to intermix. In general, itisdescribed by an electric field between the positive

anode and the negative cathode which is surrounded by an ionization gas. In arc welding,

the intense heat required to melt metal is produced by an electric arc. On the surface of

metal, there is a thin layer of surface electrons andwhichare being accelerated in the field

towards the anode. These electrons get collide with the atoms in the gas, resulting in

impact ionization where these atoms are decomposed into electrons and positive ions,

which tend to cause further ionization. The amount of current of electrically charged

particles in the arc and the temperature are related with each other as high temperatures

increases ionization. The temperature rise is due to the released energy. To obtain

suitable welding conditions the temperature or the current must initially be brought up to

a certain level, which is achieved by igniting the arc.

Arcignition is achieved by the short circuit current which is produced as the anode

and the cathode are brought into direct contact. Due to direct contact, the short-circuit

current shortly increases the temperature and the current and subsequently the arc can be

maintained constant in the electric field existing under normal welding conditions when



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applied. The arc is being surrounded by a magnetic field which directs the charged

particles towards the center of the arc, hence causing the arc to localize in the spots on

the anode and the cathode.During the period, when the electrically charged particles get

impacted on the anode and the cathode, the anode and the cathode spots are being heated

to high temperatures. This high temperature of approximately 3000 to 5000 C causes

both theelectrode and the welded metal, both to melt. Because ofthe suction force of the

plasma flow, the droplets of the electrode material are deposited on the metal.

Heat source

Heat affected zone

Melt-pool zone

Basemetal

Figure 3.6 - Illustration of Melt-Pool Zone and Heat Affected Zone (HAZ)

3.5 Heat Affected Zone (HAZ)



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A welded joint normally consists of melt-pool zone (MPZ), heat affected zone (HAZ), and

unaffected base metal portion. The HAZ is generally defined as the portion of the base

metal which has not been melted and whose mechanical properties or microstructures have

been changed by the heat of the welding. The HAZ is crucial and important to the strength

of the weldment since the fracture and cracking occur inside the HAZ region. During

welding process, the temperature at this region is very much severe. As a result, it contains

a different types of microstructures, some of which may have weak toughness and strength

properties.Figure 3.6 shows a melt-pool zone (MPZ) and heat affected zone (HAZ) in the

weldment during welding. The effects of temperature distribution on microstructure of

material in the HAZ have been studied by Weisman (1976).



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3.6 Theory of Welding Strains

Due to its nature, the welding process is one of the complicated transient procedure which

typically occurs in a 3-D (3-dimensional) structure. A typical welding simulation is

considered to be consists of two phases one is a transient heat flow analysis phase and

another is quasistatic plastic structural analysis phase. A reasonably good welding

simulation has requred to have a fine enough mesh in order to accommodate the high

thermal gradients that are developed (in time and in space) during the transient heat flow

analysis phase. At the same time, the mesh is required to be able to solve the plastic-

structural phase of the problem. [Cristian Simion,Corneliu Manu, Saleh Baset and Julian

Millard]

During the period ofthe heating and cooling cycles of a welding process, there are many

factors which affect shrinkage of the metal and therebymaking accurate predictions of

distortion complex and difficult. The mechanical and physical properties of the metal that

affect the degree of distortion change with respect tothe application of the heat. When the

temperature of the weld gets increasedthe modulus of elasticity, the yield strength and the

thermal conductivity of the steel decrease, whereas, the coefficient of thermal expansion and

the specific heat increase.

Thechanges in temperature and stresses during welding process have been studied by

Weisman (1976). To explain the temperature changes during welding, various cross-sections are required to be analyzed as shown in Figure 3.7(a).In some distance apart of the

welding torch i.e. section along A-A, the temperature gradient, ΔT due to the welding is

nearly zero. Along section B-B, which crosses the welding arc, at this section, the

temperature change is very high and the distribution is very uneven. Along section C-C,

having some distance behind the welding arc, the temperature change becomesmore even

and less steep. Finally, along section D-D, which is very much far from the welding arc, at

that section, the temperature change due to welding has reached to nearly zero.



(a) T

(b) Stres

Figure 3.7 – Schematic Rep

The effective distribution of st

and D- D are shown in F

stresses, xy,also exist, but the

thermal stresses due to weldin

section B-B are also nearly zer

heat-affected zone (HAZ) are

restrained by surrounding me

temperature in these regions is

as high due to the yield stre

magnitude of compressive stre

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mperature distribution during welding

σ x distributionduring welding.

resentation of Changes of Temperature and Stre

Welding (Weisman, 1976).

resses x,in the X-direction at cross sections A

gure 3.7(b). Normal stresses in y-directi

y are usually much smaller than x.Along sec

g are nearly zero. Stresses in region below th

o because molten metal cannot support a load.

ormally compressive, because the expansion o

al where the temperature is generally lower.

high and the yield strength of material is low, t

gth of the material at the corresponding tem

ss gets to a maximum value with increasing dis

ses during

-A, B-B, C-C,

n, y,shearing

tion A-A, the

weld pool at

Stresses in the

these areas is

As the metal

e stresses are

erature. The

ance from the



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weld or with decreasing temperature. Stresses in regions which are away from the weld line

tend to tensile to balance with the compressive stresses in areas near the weld.

At section C-C, where the welded metal and heat-affected zone have cooled, the

result is creation of tensile stresses in regions near the weld as they tend to shrink and

compressive stresses at greater distance. Finally, section D-D which represents a region

which is cooled-down and where high- tensile stresses are present in the HAZ zone and

compressive stresses exist in base plate normally away from the weld.

3.7 Types of Welding Strains

Duringwelding process, there are non-uniformheating and cooling cycles in the weld and

adjacent base metal, which produces complex thermal strains. The stresses formed due to

the strains produce internal forces resulting in shrinkage of the material. The stresses that

would exist in weldment after all external loads are removedare called residual stresses.

Depending on the shape of the structure welded and the shrinkage pattern , various strains

such as buckling, bending and rotation take place.

When steel structure parts are connected by welding, they are subjected to not only

welding residual stresses but also distortion. This distortion found in the welded structures

results due to four fundamental dimension changes that occur during welding process.

(Refer fig. 3.8)

1. Transverse shrinkage of butt joints which occurs due to dimensional reduction in the

directionwhich is perpendicular to the welding line.

2. Longitudinal shrinkage of butt joints which occurs due to dimensional reduction in a

direction parallel to the weld line. Themagnitude of the longitudinal shrinkage is

small as compared to the transverse shrinkage, which is about 1/1000 of the weld length

as reported by Weisman (1976).



(a)

(c)

Figure3.8 -Various Types of (b) Angular Change in a B

Distortion in a Fillet Joint.

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(b)

(d)

elding Distortion - (a) Transverse Shrinkage intt-Joint; (c) Angular Change in a T-Joint; (d)

a Butt-Joint;Longitudinal



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3. Angular distortion of butt joints which is caused due to an angular change that occurs due

to a non-uniform thermal contraction through the thickness of the plate. The thermal

contraction which is non-uniform originates from the uneven heating through the thickness

during welding.

4. Similar to the angular distortion of welds in butt joints, there is non-uniform thermal

contraction through the thickness of the flanges creates a moment M about the flange neutral

axes and cause angular distortion of fillet welds.

5. Longitudinal bending distortion is produced by bending stresses induced by the

longitudinal shrinkage forces of the welds which do not coinciding with the neutral axis of

the weldment.

3.8 Residual Stress

Theresidual stress is produced in the weldment primarily because the weld material

that has been melted contracts on cooling down from melting point to roomtemperature.

Residual stress getsincreases with increase in plate thickness. Arc voltage and welding

current, both have direct effect on the residual stress in the welding process. An increase in

the voltage and current increases heat input rate thus increasing residual stresses. Also,

increase in welding speed cause reduction in residual stresses but at the same time reduces

quality of weld as well.[Gurinder Singh Birar; 2013]Figure3.9shows the deflection of a

welded plate at the moment when a longitudinal edge is heated by amoving welding arc.

The metal which is near the heat sourceisheatedtohighertemperaturesthan the metal which is

away fromthe heat source. The hotter metal gets expands, and the plate firstdeforms as

shown by curve AB. Due to the presence ofplastic strains, when the plate cools to

roomtemperature, the final strain δ remains as shown by curve ABCD.



Figure3.9- Strain of Welded

To understand this phenomen

gap and without a gap. When

expands but the base metal pre

element 1 is in tension wherea

cools down, the opposite phe

base metal stops it to contract.

in tension as shown in Figure

such a way that the top surfac

case of the butt joint welding

is free to expand as it cools do

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late under the Influence of a LongitudinalMovi

n, let’s consider a butt joint welding with tw

the weld material first starts solidifying, the h

vents it to get expand. As can be seen in the F

element 2 is under compression. At the time,

omena can be observed; the weld material co

Consequently, element 1 is in compression an

3.10 (b). As a result of which themetal plates

e is in tension and bottom surface is under co

ithout gap, less strain is expected due to the

n.

gHeat Source.

cases with a

eated material

igure 3.10 (a),

hen the weld

tracts but the

d element 2 is

ill deform in

pression. In

ottom surface



Figure 3.1

23

0- Contraction and Expansion Phenomena.



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3.9 WeldingApplications

Welding application for the followingmaterials are explained below.

A) Steel:-

1. Structural carbon steel welded tostructuralcarbon steel.

2. Concrete reinforcing steel

3. Carbon or low-alloy and high-strength, steels for all types of piping

systems.

4. Rails.

5. Steel castings, carbon or high-strength and low-alloy.

6. Structural carbon steel welded tohigh- strength, low-alloy steel

7. High-strength and low-alloy steel weldedto high-strength andlow-alloy

steel.

B) Stainless steels.

1. Cryogenic vessels and piping materialsusedfor storage and transport of

extremelylow temperature liquids

2. Vacuumchambers.

3. All otheruses.

C) Nickel Steels andnickelalloysare used forcryogenicvessels andpipingsystems.

D) Alloys of Aluminum used for cryogenic vessels, piping systems,andotheruses.

E)Carbon and high-strength and low-alloy steels welded tostainlesssteels. An

exampleofthis useiswhen steel supports or stiffeners areattached to stainless steel

vessels.

3.10 Introduction to ASTM 36

As the material used for welding simulation is ASTM 36, itsvarious properties and

applications are necessary to know.ASTM 36 is the most commonly used mild steel and

hot-rolled steel. This hot rolled steel has excellent welding properties and also it is

suitable for tapping, drilling, grinding, punching and machining processes. The yield

strength of ASTM 36 is less compared to cold roll C1018, hence enablingASTM 36 to

bend more easily than C1018. Normally, larger diameters in ASTM 36 are not

manufactured since C1018 hot roll rounds are used. Steel shapes like channels, angles,



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H-beams and I-beams can also be produced with ASTM 36. [30]

ASTM 36 is usually available in the following three forms:

1. Rectangle bar

2. Square bar

3. Circular rod

Table 3.1shows the Chemical composition, Table 3.2 shows Physical Properties and

Table 3.3 showsMechanical properties of ASTM 36 respectively.

Table 3.1 - Chemical Composition of ASTM 36

Element Content

Carbon, C 0.25 - 0.290 %Copper, Cu 0.20 %

Iron, Fe 98.0 %

Manganese, Mn 1.03 %

Phosphorous, P £ 0.040 %

Silicon, Si 0.280 %

Sulfur, S £ 0.050 %

Table 3.2 - Physical Properties of ASTM 36

Physical Properties Metric Imperial

Density 7.85 g/cc 0.284 lb/in

Table 3.3 - Mechanical Properties of ASTM 36

Mechanical Properties Metric Imperial

Tensile Strength, Ultimate 400 - 550 MPa 58000 - 79800 psi

Tensile Strength, Yield 250 MPa 36300 psi

Elongation at Break (in 200 mm) 20.0 % 20.0 %Elongation at Break (in 50 mm) 23.0 % 23.0 %

Modulus of Elasticity 200 GPa 29000 ksi

Bulk Modulus (typical for steel) 140 GPa 20300 ksi

Poissons Ratio 0.260 0.260

Shear Modulus 79.3 GPa 11500 ksi



26

Machining

The machinability rate of ASTM 36 is estimated to be 72%, and the average surface cutting

feed of ASTM 36 is 120 ft/min. Machining process of ASTM 36 steel is not as easy as AISI

1018 steel.

Welding

ASTM 36 steel is easy to weld by using any type of the welding, and the welds and joints so

formed are of excellent quality.

Heat Treatment

Any standard carburizing and hardening types of AISI 1018 steel is suitable for ASTM 36.

Heat treatment processes for ASIM A36

ASTM 36 is subjected to the following heat treatment processes:

Normalizing at 899°C – 954°C (1650°F-1750°F)

Annealing at 843°C – 871°C(1550°F-1600°F)

Stress relieving at 677°C – 927°C(1250°F-1700°F)

Carburizing at 899°C – 927°C (1650°F-1700°F)

Hardening at 788°C – 816°C(1450°F-1500°F)

Applications of ASTM 36

ASTM 36 steel has the following applications:

It is used for various parts obtained by flame cutting such as in walkways, boat landing

ramps, parking garages and trenches. It is used in bolted, riveted or welded construction of

buildings, bridges and oil rigs. It is also used in forming bins, sprockets, cams, gears, stakes,

bearing plates, base plates, forgings, ornamental works, fixtures, tanks, rings, templates, jigs,

brackets, automotive and agricultural equipment, frames, machinery parts etc.

3.11. TemperatureEffects of Butt Welding on Steel Plate



27

1. The heat affected zone of double-layer weld pass remains togreater extentthan single-layer

weld pass.

2. The changes in temperature gradient are quite small at a certain distance from weld pass

due to heat convection effect.

3. The temperature gradient of vertical weld pass is normally greater than the direction of

weld heat source.

4. With the same number of weld passes, heat affected zones get decreased with the increase

of weld speed.

5. When the heat source has shifted half the size of the parent material, there exists still high

temperature gradient where the heat source has initially caused effects.

3.12 Important Factors to Determine the Welding Quality

A) Strict control over welding proceduresandoperations is necessary in five cases

1. Distress in onemembercan causeatleast partial collapse or failurewith

somehazardto property and life ; applicationofthedesignload mayapproach

10,000 cycles overmanyyears.

2. Some of the welds necessary forstructural integrity are highly

stressed;applicationof thedesign loadmayexceed10,000 cyclesovermanyyears.

3. Empirical design requirementscompensate for overloads, mishandling,

“acts of God,” abuse and similar hazards; applicationof the designload

maybein the range ofnearly about 100,000cycles.

4. Failure of welds or components couldbecatastrophic, as in structures such

as bridges orhigh--pressure gas piping systems; fatigue ofmaterials must be

carefully considered in to account or applicationofdesign load is on the

order of 2 million cycles.

5. Applications require the highest qualityofmaterial and workmanship

throughout, such asfor nuclear, space, and ballistic applications

andforsystems subjected to extreme pressures,hazardous chemicals, or

temperatures.

B)Less control overweldingproceduresandoperations is needed where:



28

1. Stress levelsare toolow.

2. Welds are subjected occasionallyto design loads.

3. The structure is composed ofmanycomponents, and distress in one

memberwill result ininconvenience rather than collapse

orcatastrophicfailure.

CHAPTER 4

FINITE ELEMENT ANALYSIS

4.1 Introduction



29

At present the finite element method (FEM) is the most widely used tool for solving this

kind of thermal problems When the aim of the analysis is to determine the mechanical

effects of welding(residual stress and distortions) the simple approach is to consider the

thermal and mechanical relation only, because there is a weak connectionfrom mechanics to

heat flow. Heat generated bydeformation can be neglected) and hence the most used

approach is to carry a sequentially coupled thermal and mechanical analysis, if the structure

deformation during weldingdoes not change significantly. This aspect gives also

thepossibility for the use of general purpose finite element computer codes. [Viorel

Deaconu;2007]

The results obtained by FEA emphasize the ability of this method to give quality results, in

agreement with experimental results and also offer the possibility to a better understanding

of residual stress field characteristics. Despite the limitations related to the need for information related to the welding process and for complex material data and numerical

modeling remains actually the sole method which is able to fully characterize the residual

stress field through the whole structure without any limitations related to his geometry or

shape and size. Once having residual stress distributions information, subsequent

simulations related to stress relief carried by mechanical loading or by post weld heat

treatments can be performed. [Viorel Deaconu;2007]Following are the important aspects of

FEA

4.1.1 Simulationof Butt WeldingProcess

During fabrication of welded components residual stresses are produced as a result of non-

uniform temperature distribution during the welding process and particularly the cooling

processes. The residual stresses have a significant effect on the overall performance of the

components in service, [Pornwasa Wongpanya;2009]To simplify the welding simulation, it

is bettertoperform thermaland mechanicalanalyses separately.

At first, thecomputationof thetemperaturehistory duringweldingand

subsequentcoolingiscompletedand thistemperaturefield isapplied tothemechanicalmodel

asabodyforcetomaketheresidualstressanalysis. Theheatinputrequired duringwelding

ismodeledin commerciallyavailablesoftwareby using theequivalentheat

inputwhichincludesbodyheat flux.

Theamount ofheatinput,QR has been calculated by usingempiricalrelationshowninEq.1.

[M.Jeyakumar; 2011]Arcefficiency isdenotedby η,arcvoltagebyV,arccurrent byI.



30

Heat input = efficiency x voltage xcurrent

QR = η x V x I(1)

By usingequation (1)ofheatinputthe amount of heat input is determined.Bythermal

analysisthetemperature at different pointsarenoted. This

simulatedtemperaturefieldisthenused in analysis step forcalculatingthe residualstresses

andafterthat thevaluesof residual stressesarecalculated by doingstressanalysis.

4.1.2 Use of Finite Element Analysis

Finite element analysis is helpful to make it possible to evaluate a detailed and complex

structure, in a computer, during the planning of that structure. The possibility of improving

the design during planning and the adequate strength of the structure can justify the cost of

the analysis work. FEA has been known to improve the design ofthe structure that were built

many decades ago and significantly over designed.

In absence of finite element analysis (or other numerical analysis) development of structures

depends onlyupon hand calculations only. For complex structures, the simplified

assumptions which are required to make any calculation possible can lead to a conservative

and heavy design. Animportant factor of ignorance can remain as to whether the structure

will be adequate for all design loads. Significant changes in designs involve a lot of risk.

Design will require prototypes to be built and they should be field tested. These field tests

may involve expensive strain gauging to evaluate characteristics like strength and strain.

With the help of finite element analysis, the weight of a design can be optimized and

there could be a reduction in the number of prototypes built. Field-testing is required to

establish loading on structures, which can be used to do future design improvement by using

finite element analysis.

4.1.3 Advantages of FEA

The power of the finite element technique resides principally in its versatility. The

FEA can be applied to various physical problems. The body to be analyzed can be having

arbitrary size and shape, loads and various support conditions. The command mesh can mix

elements of differentphysical properties,types and shapes.



31

Another important feature of finite element method lies in the close physical

resemblance between the actual structure and its finite element model.

4.1.4 Limitations of FEA

1. A computer, a reliable program and intelligent use and software skills are essential.

2. Deep experience and good engineering judgment are needed in order to define a good

finite element model.

3. Different input data are required and voluminous output must be sorted and understood.

4. Specific numerical results are required to be found for specific problem.

5. The finite element analysis does not provide any close form of solution that allows

analytical study of the effects of changing parameters.

4.2 Geometric Modeling

The geometry and the element type are required to be considered together. Shellelement is

typically used for structure where the thickness is almost negligiblecompared to its length

and width. Nevertheless, a plate modeled with solid element would provide similar results.

The disadvantage can be found in the computation time. FEA provides large no. of choices

of elements. Following are the basic aspects of geometric modeling.

4.2.1 Mesh Generation

Mesh generation can be defined as the process of dividing the analysis continuum into a

number of discrete parts or finite elements. The finer the mesh, the better will be the result,

but the longer will be the analysis time. Hence, a compromise between accuracy & solution

speed is usually done. The mesh can be created manually. In the manually created mesh, it

will be noticed that the elements which are at the joint are smaller. This is termed as mesh

refinement, and it helps in allowing the stresses to be captured at the geometric discontinuity

(the junction). Manual meshing is somewhat a long & tedious process for models with any

degree of geometric complication, but providedwith useful tools emerging in pre-processors,

the work is becoming easy. Automatic mesh generators are found to be very useful &

popular. The mesh is being created automatically by a mesh engine; the only requirement is



32

to define the mesh density along the path of the model's edges. Automatic meshing has

limitations as related to mesh quality & solution accuracy. Automatic brick element (hex)

meshers are limited in function, but are getting steadily improving. Any mesh can be usually

applied to the model by simply selecting the mesh command on the preprocessor list

provided in the GUI.

4.2.2 Properties Assignment

Material properties (coefficients of expansion, friction, thermal conductivity, Young’s

modulus, Poisson’s ratio, the density, & if applicable, damping effect, specific heat etc.) are

required to be defined. In addition element properties may be needed to be set. If 2D

elements are going to be used, the thickness property is required. 1D-beam elements require

area, Ixx, Iyy, Ixy, J, & a direction cosine property, that defines the direction of the beam axis

in 3D space. Shell elements like 2D elements in 3D space which are 2½D in nature, require

neutral surface offset parameters to be defined & orientation also. Special elements

likemass, contact, spring, gap, coupling, damper etc. require properties to be defined for

their use and should be specific to the element type. Following properties of ASTM 36 were

considered during analysis by finite element method. Table no 4.1 shows thermal properties

while table no.4.2 shows mechanical properties of ASTM 36.

Table no.- 4.1 Thermal Material Properties

Temp Density Enthalpy Thermal Conductivity Specific

(k) (kg/m³) (J/m³) Expansion(1/k) (W/mk) Heat(J/kgk)

273 8038.7 9.76E+08 2.03E-05 13.29 456.28



33

293 8030.47 1.05E+09 1.99E-05 13.63 464.73

373 7997.02 1.35E+09 1.50E-05 14.99 494.23

473 7954.03 1.75E+09 1.96E-05 16.62 522.74

573 7909.76 2.16E+09 1.93E-05 18.19 543.93

673 7864.18 2.59E+09 2.03E-05 19.72 559.87

773 7817.31 3.03E+09 2.06E-05 21.26 572.69873 7769.13 3.48E+09 2.08E-05 22.81 584.49

973 7719.66 3.94E+09 2.12E-05 24.42 597.38

1073 7668.9 4.41E+09 2.15E-05 26.09 613.45

1173 7616.83 4.90E+09 2.21E-05 27.86 634.82

1273 7563.47 5.40E+09 2.26E-05 29.76 663.58

1373 7508.81 5.93E+09 2.29E-05 31.81 701.85

1473 7452.85 6.49E+09 2.33E-05 34.03 751.72

1573 7395.6 7.09E+09 2.37E-05 36.46 815.30

1673 7354.75 7.54E+09 2.40E-05 38.29 869.09

Table no. - 4.2 Mechanical Material Properties

Temp Yield Tensile Elastic

(k) Strength(N/m²) Strength(N/m²) Modulus(N/m²)

273 3.47E+08 6.45E+08 2.00E+11

293 3.20E+08 6.20E+08 1.96E+11

373 2.11E+08 5.20E+08 1.92E+11

473 1.67E+08 4.60E+08 1.84E+11573 1.45E+08 4.40E+08 1.76E+11

673 1.35E+08 4.20E+08 1.68E+11

773 1.29E+08 4.00E+08 1.60E+11

873 1.23E+08 3.80E+08 1.52E+11

973 1.17E+08 3.60E+08 1.44E+11

1073 1.11E+08 3.40E+08 1.35E+11

1173 1.05E+08 3.20E+08 1.27E+11

1273 9.90E+07 3.00E+08 1.19E+11

1373 6.60E+07 2.54E+08 1.05E+11

1473 2.40E+07 9.80E+07 2.00E+101573 1.05E+07 3.90E+07 7.00E+09

1673 1.00E+07 2.70E+07 5.56E+08



34

Figure4.1 Graph for Thermal Conductivity V/S Temperature

4.2.3 Graphs of Material Properties

For transient thermal structural coupled filed analysis temperature dependent

material properties as shown in fig 4.1, fig.4.2, fig.4.3, fig.4.4 &fig.4.5 areconsidered. The

specific heat of the material goes on increasing with the increase of temperature as shown in

figure 4.2.

0

5

10

15

20

25

30

35

40

45

2 2 9

3 5 9 1 0

1 1

1 2

1 1 6

C o n d u c t i v i t y ( W / m K )

Temp (K)

Conductivity

Conductivity



35

Figure 4.2 Graph for Specific Heat

Inverse to the specific heat property the density of ASTM 36 decreases with increase in

temperature as shown in fig.4.3

Figure 4.3 Graph for Density

0.00

100.00

200.00

300.00

400.00

500.00

600.00

700.00

800.00

900.00

1000.00

2 3 6 8 9 1 1

1 2

1 1 6

S p e c i f i c H e a t ( J / K g

K )

Temp (K)

Specific Heat

Specific Heat

7000

7200

7400

7600

7800

8000

8200

D e n s i t y K g / m 3

Temp (K)

Density

Density



36

Figure 4.4 Graph for Elastic Modulus

The elastic modulus of the material goes on decreasing with temperature as shown in

fig.4.4.When the material attains a temperature which is equal to 1373 K, the value of elastic

modulus begins to decrease drastically. Fig 4.5 shows Graph for Thermal Expansion against

various values of temperatures.

0.00E+00

5.00E+10

1.00E+11

1.50E+11

2.00E+11

2.50E+11

E l a

s t i c M o d u l u s ( N / m 2 )

Temp (K)

Elastic Modulus

Elastic Modulus



37

Figure 4.5 - Graph for Thermal Expansion

4.3 Applied Loads

Some specific type of load is usually applied to the analysis model. The loading may be in the form

of a pressure, a point load or a displacement in a stress (displacement) analysis, a heat flux or a

temperature in a thermal analysis & a fluid pressure or velocity in a fluid analysis. The loads may be

applied to an edge, a surface, a point, or even a complete body. The various loads should be in the

same units as used in the model geometry & material properties are to be specified. In the cases of

buckling analyses & modal (vibration) , a load is not required to have to be specified for the analysis

to run.

In this project analysis, load due to increase in temperature i.e. load due to heat flux was

considered.At first, thecomputationof thetemperaturehistory duringweldingand

subsequentcoolingiscompletedand thistemperaturefield isapplied tothemechanicalmodel

asabodyforcetomaketheresidualstressanalysis. Theheatinput required duringwelding

0.00E+00

5.00E-06

1.00E-05

1.50E-05

2.00E-05

2.50E-05

3.00E-05

2 2 9

3 8 9 1 0

1 1

1 2

1 3

1

T

h e r m a l E x p a n s i o n ( m / m

K )

Temp (K)

Thermal Expansion

Thermal Expansion



38

ismodeledin commerciallyavailablesoftwareby using theequivalentheat

inputwhichincludesbodyheat flux.

Theamount ofheatinput,QR has been calculated by

usingstandardrelationshowninEq.1.Arcefficiency isdenotedby η,arcvoltagebyV,arccurrent byI.Typicalweldingparameterstaken in thisstudy are,arcvoltage is considered30 volts,

arccurrent to be as 200 amp and arc efficiency70%.

Heat input = efficiency x voltage xcurrent

QR = η x V x I (1)

By usingequation (1)ofheatinputthe amount of heat input is determined. Bythermal

analysisthetemperature at different pointsarenoted. This

simulatedtemperaturefieldisthenused in analysis step forcalculatingthe residual

stressesandafterthat thevaluesof residual stressesarecalculated bymeans of stressanalysis.

4.4 BoundaryConditions

If a load is applied to the model, in that case in order to stop it accelerating infinitely through the

computer's virtual ether (which is mathematically alsoknown as a zero pivot),it is necessary that at

least one constraint or boundary condition must be applied. The structural boundary conditions areusually taken in the form of zero displacements, thermal boundary conditions such as temperatures

ranges are usually specified, fluid BCs are usually specified by pressures. A boundary condition may

be specified in order to act in all directions (x, y, z), or in some cases to certain directions only. They

can be placed or applied on key points, nodes, and areas or on lines. Boundry conditions's on lines

can be represented in the form of symmetric or anti-symmetric type boundary conditions, one

allowing in plane rotations &out of plane translations, whereas the other allowing in plane

translations & out of plane rotations for a given line. The applications of correct boundary conditions

are critical related to the accurate solution of the design problem. At least one boundary condition is

required to be applied to every model, in case when even buckling & modal analyses with no loads

applied.

The welding process simulation was carried out in three different steps. As the welding

process is time dependent the transient thermal structural coupled field analysis is carried out

by using following boundary conditions,



39

Stage I - Welding

a) Weld temperature of 1200º C applied on weld volume

b) Room temperature 20º C applied on plate volume

c) Weld time defined as 10 secStage II – Phase Change

a) Convection applied on surfaces subjected to air

b) Phase change time defined as 100 sec

Stage III – Solidification

a) Convection applied on surfaces subjected to air

4.5 Finite Element Analysis

The Finite Element solver may be logically divided into three main parts i.e. the pre-

solver, the post-solver and the mathematical-engine. The pre-solver is able to read in the

model created by the pre-processor and also formulates the mathematical representation of

the model. All important parameters defined in the pre-processing stage are going to be used

to do this, so if something is left out, chances are the pre-solver will complain & cancel the

call to the mathematical-engine. If the model is correct then the solver proceeds to form theelement-stiffness matrix for the problem & calls the mathematical-engine which calculates

the result (temperatures, pressures, displacement etc.) The results are then returned to the

solver & the post-solver is used to calculate heat fluxes, velocities, strains and stresses etc.)

for each and every node within the component or continuum. Finally all these results are

sent to a result file, which may be read by the post-processor.

During finite element analysis of welding process, a transient heat transfer analysis is

carried out by determining the temperature distribution in all nodes. After that a static

mechanical analysis is performed. Each step of the mechanical analysis represents a time

step in the thermal analysis. Finally, at the last step, when temperatures attain their initial

values and the residual stress field is obtained as result of all intermediary analysis

steps.[Viorel Deaconu; 2007]



40

4.6 Simulation

During simulation of welding process, the results of the analysis are read & interpreted.

They can be represented in the form of a contour plot, a table, deformed shape of the

component or the mode shapes and natural frequencies in case if frequency analysis isinvolved. Other results are also available for thermal, fluids and electrical analysis types.

Most of the post-processors provide an animation service, which is able to produce

animation & hence brings your model to life. Contour plots are generally the most effective

way of viewing results for structural type problems. Slices maybe made through 3D models

to facilitate the viewing of internal stress patterns. All post-processors nowadays include the

calculation of stress & strains in any of the x, y or z directions, or if requred in a direction at

an angle to the coordinate axes. The principal stresses and strains can also be plotted and if

required the yield stresses and strains can also be plotted according to the main theories of

failure (Von mises, St. Venant, Tresca etc.). Other necessary information such as plastic

strain, the strain energy, and creep strain may be obtained for certain types of analyses.



41

CHAPTER- 5

COUPLED FIELD ANALYSIS

5.1 Coupled Field Analysis

When the input of one of the field analysis depends on the results from another

analysis, the analyses are said to be coupled. A coupled-field analysis is defined as a

combination of analyses from different engineering disciplines (physics fields) that interact

to solve a global engineering problem; due to this, we often refer to a coupled-field analysis

as a multiphysics analysis.

The Coupled field analysis may be carried out using following two methods,

1. Direct Method

2. Sequential Method

5.1.1 Introduction to Direct Coupled Field Analysis

The direct method for doing a coupled-field analysis includes a single analysis that

uses a coupled-field element. There are different types of coupled filed analyses which are

available according to different engineering streams. For this dissertation work thermal

structural direct coupled field analysis is used for simulation of the welding process.

5.1.2 Objective of Direct Coupled Field Analysis

The aim of thermal structural direct coupled filed analysis is to simulate welding

process using finite element analysis and thereby find the residual stresses due to phase

change.



42

5.2 Steps for Coupled Field Analysis

Coupled field analysis consists of the following steps

1. Preprocessing:-

Create the model geometry.

Define Material Properties

Mesh generation.

2. Solution:-

Boundary conditions (loads & constraints)

Solve.

3. Post Processing:-

Review results

5.3 Modeling Geometry

The ultimate purpose of finite element analysis is to re-produce mathematically the

behavior of an actual engineering system. In other words, modeling geometry is used to

create an accurate mathematical model of a physical prototype. In the broadest sense, thismodel can comprises material properties, real constants, all the nodes, elements, boundary

conditions and other features that may be used to represent the physical system.

In terminology, the term model generation usually takes on the narrower meaning

which includes generating nodes & elements that can represent the spatial volumes &

connectivity of the actual system.

In thepresentstudy, thebutt-weldjointof twoASTM 36stainless steel plates is modeled

using a commerciallyavailable finite elementsoftware. Thetwo semi-

infiniteplatesofthejointare3mm thickand100mmwide(alongthewelding direction).Theweld-

grooveangleis 60°.3Dview oftheASTM 36steel plateisshowninFigure 5.1.



43

Figure5.1.-3D Model of the Plate to be Welded



44

Figure5.2 Geometry of the Plate to be Welded

Fig.5.2 showstheGeometry of the platetobebuttwelded.Meshcontrolisappliedtothe

weldmentarea.Plates arefixedattheends andheat convectionwasallowed atthetop surface

oftwo plates.

ASTM A 36steelmaterial can beweldedby using

differentmethodslikeelectricarcwelding,resistance andinductionweldingorby

meansofradiationprocess. Fromallthesetypestheanalysisofstainlesssteelinthis project is

beingperformed bymanual metalarc welding,or also known as MMAW.

5.4 Material Properties

Thetemperaturedependantthermalmaterialproperties forthe plates,thefillerweld material and

heataffectedzone (HAZ) were assumedto be thesame,see Table 1.Forthe mechanicalmaterial

properties, samematerial models were usedforthe



45

weldbeadsandthebasematerialsaccordingto theyieldstrength. The plasticitymaterialmodel

usedwas vonMisses rate-independentisotropicbilinearhardening.

Table 5.1.MaterialProperties [Dragi Stamenkovic; 2009]

Specific

heat

(J/kg°C)

Yield

stress

(MPa)

Thermal

expansion

coefficient

(10-5/°C)

Young΄s

modulus

(GPa)

Temperature Conductivity DensityPoisson΄s

ratio

(°C) (W/m°C) (kgm-3)

0 480 60 7880 380 1.15 210 0.3

100 500 50 7880 340 1.2 200 0.3

200 520 45 7800 315 1.3 200 0.3

400 650 38 7760 230 1.42 170 0.3

600 750 30 7600 110 1.45 80 0.3

800 1000 25 7520 30 1.45 35 0.3

1000 1200 26 7390 25 1.45 20 0.3

1200 1400 28 7300 20 1.45 15 0.3

1400 1600 37 7250 18 1.45 10 0.3

1550 1700 37 7180 15 1.45 10 0.3

5.5 Meshing Geometry

Meshing the geometry is creation of finite element model, which consists of nodes

and elements. Fig 5.3 shows the meshed model of the plate that is to be welded. Meshing is

done through following three important steps as

a) Set element attributes.

b) Set meshing controls.

c) Generate mesh



46

a) Element attributes: -

Before starting generation of a mesh appropriate elements must be defined. The

Solid70 element type is being used for meshing the plate using ET command. The material

properties for analysis are appliedwith thehelp of MP command.

Figure5.3 - Meshed Model

b) Meshing controls: -

After setting the element attributes, the element density is required to be defined for

meshing the model. The element or mesh density is set by using ESIZE, ESHAPE, KESIZE

and LESIZE command.

Type of elements : Solid 45

No. of Nodes : 12393

No. of elements : 8250



47

c) Mesh generation: -

There are two main types of meshing as free & mapped mesh. Meshing can be made

by using AMESH, VMESH commands. But 3-D model must be meshed with only VMESH

command only. The plate is meshed by using VMESH (mapped) command. Then the solidmodel is meshed by using solid 70 element by creating the FEA model having no. of nodes

12393 and no. of elements 8250 as shown in fig.5.3 and is used for further processing then

in FEA solution the FEM model created is analysed for coupled field analysis (also termed

as coupled field analysis).After completion of simulation the results are read and tabulated

by using post-processing stage.

5.6 Boundary Conditions

The welding process simulation was carried out in three different steps. As the

welding process is time dependent the transient thermal structural coupled field analysis is

carried out by using boundary conditions as mentioned earlier [Cristian Simion, Corneliu

Manu, Saleh Baset and Julian Millard],

5.7 Solution

This is the one of the important stage in FE analysis. With the help of ANTYPEcommand the type of the solution is specified as transient. Then by using SOLVE command

program solves the analysis using numerical methods for three different stages.

5.8 Post Processing

In post processing section, the results of stress analysis were reviewed. There are two types

of post processing methods viz. /POST1 & /POST26. With /POST1 only static analysis

results can be viewed and with /POST26 mainly time dependent analysis results are seen.

/POST26 is also termed as time history post processing.



48

CHAPTER 6

RESULTS AND DISCUSSION

Depending upon the simulation results, shrinkage or distortion of the weldment can be

predicted. In this way, the experimental analysis, which is costly, can be avoided. The

temperature near the region of weld bead and the HAZ decreases rapidly proportional to the

distance from the centre of the heat source. The different results obtained by using FEA are

studied as follows.

6.1. Temperatureat Different Distances from Center Line of Weld with FEA.

During study of welding process, it has been found that the magnitude and distribution of

Figure 6.1. Temperature Distribution in Steel Plate after Welding at T = 100 Sec



49

residual stresses is strongly influenced by temperature distribution through the various

crossections of the plates and mechanical properties of material at elevated temperatures.

As the welding process progresses, both the weld metal and the base metal experience an

increase in temperature. At the solidus temperature, the material within the fusion zone

begins to liquefy. Upon cooling, a reverse process occurs and the fusion zone solidifies to

complete the joining process

A 3 D model showing the relation between temperature and distance from weld at 100

seconds after the completion of welding process is shown in fig. 6.1. The relation between

temperature and distance from weld can be predicted by getting tabular data from the graph

as shown in table no.6.1.From graph as shown in fig. 6.2, we can see that temperature of

Figure6.2 - Graphbetween Temperature and Distance from Center Line of the Weld at100 Sec

welded plate goes on decreasing drastically from weld center line from 0 to 85 mm and after

85 mm it becomes almost constant up to 100 mm. The temperature distribution as a

consequence of thermal load was employed to calculate equivalent shrinkage forces. 3D

finite element elastic structural analysis was conducted to estimate the deformations and

0

50

100

150

200

250

300

350

400

450

500

0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 100

FEA

FEA



50

residual stresses.The variation in temperature profile and the distribution of thermal stresses

was simulated with different welding parameters, e.g. the number of welding layer during

the butt welding and the welding speed.[Chun-Ho Yin , Chao-Ming Hsu and Jao-Hwa

Kuang; 2013] The distributions and the peak magnitude of residual stress with different

welding parameter were also simulated.

Table no.6.1-Temp.(k)(results from FEA) v/s Distance From Weld(mm)

Sr. no.Distance From

Weld(mm)Temp.(k)(results from FEA)

1 0 450

2 5 446

3 10 446

4 15 442

5 20 441

6 25 433

7 30 421

8 35 418

9 40 415

10 45 40811 50 380

12 55 370

13 60 368

14 65 366

15 70 362

16 75 346

17 80 344

18 85 332

19 90 332

20 95 33121 100 331



51

6.2 Strain Calculation with FEA

Anundesirable result of the induced nonlinear thermal cycles associated with the welding

processisthedevelopmentofresidualstresses. Thefluidmaterial in the fusion zone is

Table no.6.2- strain (results from FEA) v/s Distance fromWeld (mm)

Sr. no. Distance From Weld(mm)Strain x10

-3(from

FEA)

10 67.2

2 1 46.08

3 2 43.2

4 3 40.325 4 19.2

6 5 6.72

7 6 4.8

8 8 4.8

9 10 2.88

10 15 1.92

11 20 1.92

12 25 1.728

13 30 1.53614 35 1.248

15 40 0.96

16 45 0.864

17 50 0.768

18 55 0.672

19 60 0.576

20 65 0.48

21 70 0.192

22 75 0.105623 80 0.1056

24 85 0.1056

25 90 0.0864

26 95 0.0864

27 100 0



52

bounded by the solid HAZ material & unaffected base metal. The solid material adjacent to

the fusion zone acts as a mechanical constraint which results in inelastic strains being

produced as the fusion zone material gets solidified. As the fusion zone gets solidified, the

grain growth progresses from the heat affected zone toward the center of the weld. The

elastic strains tend to result in tensile residual thermal stresses in the fusion zone. From the

graph as shown in fig.6.3, the values of strains at different distances from center line of the

Distance From Weld(mm)

Figure6.3 -Graph between Strain at Mid Section Perpendicular to the Weld of theASTM36 Steel Plate along its Length Direction

weld can be obtained. The value of strain for different distances from center line of the weld

is shown in table 6.2. It can be seen from the table that the value of strain goes on decreasing

0

10

20

30

40

50

60

70

80

0 2 4 6 10 20 30 40 50 60 70 80 90 100

Strain (from FEA)

Strain (from FEA)



as the distance from the cente

strain the value of stress gets

observed in the parts due to we

6.3 StressCalculation with F

Fig. 6.4shows the von moises

in axial direction formanualme

in welded plate of single V-butt

zone.Table no.6.3givesthevalu

weldcentre whenplatethicknes

53

r of weld gets increased. As stress is directly

varied according to the value of stress. The m

lding process is 67.3 x10-3

mm.

A

lot in FEASoftware. Fig.6.5 showsthe graph o

talarcwelding obtained by FEA. The highest resi

joints has been observed in the weld metal adjace

es of residualstresses distributionagainstthed

is 3 mm.Itis clearfromthe plotthatheat

Figure 6.4 - Von Mises Plots

roportional to

aximum strain

residualstress

dual stress level

nt to the fusion

stance from



54

affectedzone extendsupto 38mm onbothsidesoftheweldment.Itisseenthatthe residual stress in

the transverse direction for butt weldingof3mmthick platescomesoutto bemaximum

(320Mpa)in thecentre ofweldment. Simulated results are in a good agreement with

experimental results, which shows the reliability of FEA or equivalent load method. Von

mises residual stress goes on decreasing rapidly in transverse direction in areas near the weld

region. In contrast to this, welding deformation shows a smooth continuous increasing

behavior. The residual stress distribution is ununiform through the thickness of plate with

maximum value at the top surface of plate and decreases gradually to minimum at the

bottom. Every mode of deformation has greater value in case when thickness is very small.

Figure 6.5 - Graph between residual stress at mid section perpendicular to weld of the

ASTM36 steel plate along its length direction

An increase in plate thickness causes reduction of residual stresses in areas adjacent to fusion

zone. Weld induced stresses are the one which are major contributors to the overall stress

states in welded structural components. Residual stresses may be determinable to the

performance of component assemblies and can be induced, in addition to distortions failures

through stress corrosion cracking, brittle fracture and can cause to the detoriation of fatigue

life.

-300

-200

-100

0

100

200

300

400

1 1 2 3 6 6 8 8 9 9 1 0

FEA Stress

FEA Stress



55

Table No.6.3- Stress (in Mpa)Results from FEA V/S Distance from Weld (mm)

Sr. no. Distance From Weld(mm) FEA Stress(Mpa)

1 0 270

2 5 320

3 10 290

4 15 150

5 20 -110

6 25 -180

7 30 -220

8 35 -80

9 40 -55

10 45 -30

11 50 -10

12 55 -5

13 60 10

14 65 20

15 70 20

16 75 30

17 80 30

18 85 35

19 90 40

20 95 40

21 100 40

6.4 ComparisonoftheFEMwithExperimentalResultsforAxial ResidualStresses

The values ofaxialresidualstresses calculatedbythe finite element method are compared

withthe experimental results[M.Jeyakumar; 2011]with the help of tabular data as shown in

table no.6.4. The results from these tables are obtained from the graph as shown in figure6.6.



56

Table no.6.4-comparison of experimental stress v/s FEA stress

Sr. no.Distance From

Weld(mm)

Experimental

Stress(Mpa)FEA Stress

1 0 350 270

2 5 390 320

3 10 300 290

4 15 100 150

5 20 -120 -110

6 25 -200 -180

7 30 -125 -220

8 35 -100 -80

9 40 -50 -55

10 45 -25 -30

11 50 -5 -10

12 55 0 -513 60 5 10

14 65 10 20

15 70 15 20

16 75 18 30

17 80 20 30

18 85 22 35

19 90 25 40

20 95 28 40

21 100 30 40

These results are obtained by reading the results at various nodes and elements at various

distances of the plate along x axis and across y-z plane. These results show that

thecomputatedfinite element resultsarevery closeto the experimentalresults.There is a little

variation between the two results because in actual practice there are different types of heat

losses and error in manual welding process which causes ununiform distribution of heat

through welding path. The results emphasize the ability of this method to create quality

results which are in agreement with experimental data and to offer the possibility to a better

calculation of residual stress field characteristics as well as to reduce the conservatism its

components quantification according to the current integrity assessment procedures. Despite

the shortcomings in relation to the need for information related to the welding process and



57

Figure 6.6 -ComparisonoftheFEA ResultswithExperimentalResultsforAxial ResidualStresses

For complex material data, numerical modeling is practically the only method able to fully

characterize the residual stress field over the whole structure without imposing any

limitations related to his geometry or size. After having residual stress distributions data,

subsequent simulations of stress relief by mechanical loading or by post weld heat

treatments can be performed. Validated by experiments, FE modeling techniques can be an

effective support for integrity assessments of structures containing welds.

CHAPTER 7

-300

-200

-100

0

100

200

300

400

500

0 10 20 30 40 50 60 70 80 90 100

Experimental Stress(Mpa)

FEA Stress



58

CONCLUSIONS

From the present study the following major conclusions are drawn -

1) In case of experimental stress analysis it will require the prototype of the structure to be

analyzed while analysis by FEA software eliminates that and so the cost & time of product

design also gets reduced. With the help of FEA software the behavior of the structure can be

studied for any number of welds. By using different mesh densities the results can be

obtained with great accuracy. Thus FEA is one of the important tool for thermal and

structural analysis which gives results very fast. Thetime and cost required to find residual

stress in the parts due to welding process using FEA software is very less as compared to the

experimental method. Calculation of Residual stress for any complicated welding process as

well any complicated structure is possible by using finite element methods without altering

the physics of the problem.

2) Themaximum strain observed in the butt welded steel plate is found to be 67.2 x10-3

at the

region of weld.The maximum temperature at 100 seconds after completion of welding

process, observed in the butt welded steel plate is found to be 450 K at the region of weld

and it goes on decreasing along the length of plate. Finally the temperature at 100 seconds at

a distance of 100 mm from the center line of the weld after completion of welding process is

found to be 331 K which is the minimum temperature along the length of the butt welded

steel plate. Distribution of temperature, strain and residual stresses with respect to distancefrom weld are showed in tabulated form as well as by using graph for better understanding

of the welding process. The maximum residual stress observed in the butt welded steel plate

is found to be 320 Mpa at a distance of 5mm from the center line of the weld.

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