Available online at: A Thesis Report On ... · ABAQUS/Explicit. This approach provides control of mesh distortion which is again very much possible at the time of necking during tensile

International Journal of Advance Research, Ideas and Innovations in Technology

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ISSN: 2454-132X

Impact factor: 4.295 (Volume 4, Issue 3)

Available online at: www.ijariit.com

A Thesis Report

On

FINITE ELEMENT ANALYSIS OF UTM TESTING OF

ALUMINIUM ALLOY AA6082

BY

Jay Kalamkar

2012ABTS458H

Under the supervision of

DR. AMRITA PRIYADARSHINI

SUBMITTED IN PARTIAL FULLFILLMENT OF THE REQUIREMENTS OF

BITS F421T/422T Thesis

BIRLA INSTITUTE OF TECHNOLOGY AND SCIENCE PILANI (RAJASTHAN)

HYDERABAD CAMPUS

(DECEMBER 2015)

https://www.ijariit.com/?utm_source=pdf&utm_medium=edition&utm_campaign=OmAkSols&utm_term=V4I3-1206


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ACKNOWLEDGEMENT

I would like to take this opportunity to express my profound gratitude and indebtedness to

Dr. Amrita Priyadarshani, Assistant Professor, Department of Mechanical and Manufacturing Engineering, BITS Pilani

Hyderabad Campus for her inspiration, guidance constructive criticism and valuable suggestions throughout this project.

I would also like to thank Prof. Y.V. Daseswara Rao, Head of Department, Department of Mechanical and Manufacturing

Engineering, BITS Pilani Hyderabad Campus, for his constant support and motivation.

A special acknowledgement to Prof. N. Suresh Kumar Reddy, Assistant Professor, Department of Mechanical and

Manufacturing Engineering and In-charge, Workshop, BITS Pilani Hyderabad Campus and to Prof. C.P. Kiran, Assistant

Professor, Department of Mechanical and Manufacturing Engineering and In-charge, Material Testing Lab, BITS Pilani

Hyderabad Campus for allowing me to use the institute workshop facilities for my work.

A note of thanks also goes to the workshop instructors and my colleagues Chirag Sancheti and Shrivani Pandiya for their

consistent assistance and help in carrying out experiments.

Last but not the least, my sincere thanks to all my friends who have extended all types of help to accomplish my targets.

Jay Kalamkar


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Birla Institute of Technology and Science-Pilani,

Hyderabad Campus

Certificate

This is to certify that the Thesis report entitled “FINITE ELEMNT ANALYSIS OF UTM TESTINGOF ALUMINIUM

ALLOY AA6082” submitted by Mr. Jay Kalamkar (2012ABTS458H), in partial fulfillment of the requirements of the course

BITS F421T/422T Thesis, embodies the work done by them under my supervision and guidance.

Date: 7th December 2015(Dr. Amrita Priyadarshini)

BITS- Pilani, Hyderabad Campus


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LIST OF SYMBOLS AND ABBREVIATIONS USED:

1. UTM : Ultimate Tensile Machine

2. FEM : Finite Element Method

3. ALE: Arbitrary Lagrangian Eulerian

4. EDM : Electronic Discharge Machine

5. ux, uy, uz : Displacements in X, Y and Z directions.

6. vx, vy, vz : Velocities in X, Y and Z directions.

7. 𝜀𝑒 : Strain Rate

8. : Original Length of the Specimen.

ABSTRACT

Aluminum alloy AA6082 is one of the stronger alloys in its series and has high corrosion resistance properties. These properties combined

with its light weight make it extremely useful in the aerospace and automotive industries. It is, hence, essential to test the given grade of

aluminum and find out its mechanical properties and failure criteria for further applications in the industry. One of the major sources for

testing the mechanical characteristics of a material is the Ultimate Tensile testing Machine (UTM). Tensile testing helps us to ensure a safe

and high quality material and to reduce the chances of failure in the respective field. The various mechanical characteristics provided as an

output to the tensile testing experiment along with the interpretation of the flow curves obtained are necessary for the predicting the tensile

behavior of the material (including necking and deformation homogeneity).

Finite Element Method is a powerful tool used today for the simulation of such experiments and software using this are widely used to

predict the mechanical properties of different materials, after validating a particular model. Another advantage is that it reduces the amount

of material wastage as the validated model can then be used to find the mechanical properties of the given material under different boundary

conditions, thus eliminating the need for those experiments.

This project aims at developing and validating the uniaxial tensile test models of the proposed material, varying the strain rates, temperatures

and material models, using the commercial FE software ABAQUS 6.14.


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CONTENTS

Title page…………………………………………….………………..…….1

Acknowledgement…………………………………………….……..….......2

Certificate……………….………………………….…………………….....3

List of Symbols and Abbreviations ……………….……………………......4

Abstract………………….…………………………………………….........4

Contents.........................................................................................................5

List of Figures................................................................................................6

List of Tables.................................................................................................6

CHAPTER 1: INTRODUCTION…...…………….…………………..........7

CHAPTER 2: MATERIAL AND SAM…………………………….………8

CHAPTER 3: FINITE ELEMENT SIMULATIONS…….……………........9

i. Experimental Procedure……………………………………….........9

ii. Methodology……………………………………………………......10

iii. Work Done………………………………………………………… 15

CHAPTER 4: RESULTS…………………………..…………………….....16

CONCLUSION……….…………………………………………….............24

References…………………………………………………………….…....25


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List of Figures

Figure no. Figures Pg .no.

1 Image of Dog bone Specimen 8

2 Image of the broken specimen in Universal Testing Machine 9

3 Geometric Representation of the cross section of the specimen 10

4 The part created for the simulation 10

5 The boundary conditions 11

6 Meshed part 12

7 The meshed part consisting of 1280 small block elements. 13

8(a) Graph showing Stress Vs Strain with different strain rates of Experimental data 16

8(b) Graph showing True Stress Vs Strain with different strain rates of Experimental

data

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8(c) to 8(f) Specimen after the tensile testing 17

9 Show the necking and the failure of the work piece at the strain rate of 0.3 when

simulated with a course mesh

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10 Show the necking and the failure of the work piece at the strain rate of 0.3 when

simulated with a medium fine mesh.

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11(a) and 11(b) show the necking and the failure of the work piece at the strain rate of 0.3 when

simulated with a fine mesh.

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11(c) Specimen after undergoing the tensile test at 0.3 strain rate 20

12 Shows the stress vs. strain plots of the simulations with the three different

types of meshing used.

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13 Shows the stress strain curves of various strain rate values simulated, also

indicating the type of mesh used in each simulation.

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14 Shows the values of the above curve as obtained from the software 23

List of Tables

Table no. Tables Pg .no.

1 6082-T6 aluminium alloy chemical composition 8

2 6082-T6 aluminium alloy mechanical properties 8

3 Properties of the material used. 14

4 CPU Time.(in sec) obtained by monitoring the simulations 21


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CHAPTER 1: INTRODUCTION

The aluminium alloy 6082 has many highly stressed structural applications such as cranes, trusses, bridges, ore skips, etc., as a result of its

strength, light weight and corrosion resistance. Also, due to its good machinability and weldibility, it is used in applications such as

packaging containers, foils, radiator tubes, collapsible tubes, wide jar closures, etc. These large numbers of applications make it necessary

for the manufacturer to know the exact mechanical properties and characteristics of the material for ensuring the best quality of the product

and for providing customer satisfaction by reducing any possible chance of failure that might occur when the product is under actual loading.

Tensile testing is one of the well-established and most effective ways of testing material properties and for finding its failure criteria. It

yields data sufficient for determining the mechanical properties of ductile materials such as ultimate tensile strength, modulus of elasticity

and yield strength and the relation between stress and strain. Compression testing is not required in the case of ductile materials as the yield

limits are the same under tension and compression. However, in materials which are brittle or fibrous, there is a considerable difference

between the tensile strength and the compressive strength. Hence, the two experiments should be performed separately in such cases. The

material used for this project is a ductile material and does not require a separate compression test.

For our project, we will conduct experiments at different combinations of strain rates and temperatures, taking three principle values in

each case. Finite Element Method is the most widely used and also a very powerful tool for the visual delineation of field variables such as

stress, strain, temperature, complicated deformation behaviour etc. A model will be simulated using FEM under the same boundary

conditions on the commercially available software, ABAQUS 6.14. The experimental data obtained will be used to validate our model so

that it can be used for further variations in boundary conditions without actually performing the experiments.

CHAPTER 2: MATERIAL AND SAMPLE

Experiments were carried out on 6082 Aluminum. Its chemical properties and mechanical properties are shown in Table 1 and Table 2

respectively. The typical rectangular cross-section sample was used under all strain rates, with the gauge length of 25 mm, thickness of 3


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mm, and width of 6.4 mm; the clamping segment length on both ends is 25.7 mm. (Machine Specification – to be mentioned here). The

experimental sample is shown in Figure 1.

Table 1: 6082-T6 aluminium alloy chemical composition [1]

Si Mg Fe Cu Mn Cr Zn Ti Other Al

0.7-1.3 0.6-1.2 ≤0.5 ≤0.1 0.4-1 ≤0.25 0.2 ≤0.1 0.15 Balance

Table 2: 6082-T6 aluminium alloy mechanical properties [1]

Alloy Density Young's Modulus Poisson's Ratio

6082-T6 2700 70 GPA 0.3

Figure 1 Image of Dog bone Specimen

CHAPTER 3: FINTE ELEMENT SIMULATIONS

FE software ABAQUS/Explicit version 6.13-1 was used for developing a 3 Dimensional FE model for uniaxial tensile tests. As the thickness

value of the specimen is very less compared to its length a plain strain condition is considered. The dynamic explicit analysis has been used


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because it is computationally efficient for the analysis of uniaxial tensile tests which involve very large deformations and fracture

conditions. Moreover, Arbitrary Lagrangian Eulerian (ALE) adaptive meshing technique is more generally applicable in

ABAQUS/Explicit. This approach provides control of mesh distortion which is again very much possible at the time of necking during

tensile tests.

(i) Experimental Procedure

The specimen of 6082 Aluminum was first cut out using EDM (Electronic Discharge Machine) wire cut to achieve required dimensional

accuracy. The original cross sectional area of the specimen at its smallest point is recorded. Use ink and a scribe or punch to place gage

marks on the test specimen at the appropriate gaze length. The distance between the gage marks after the specimen is broken is used to

determine the percentage elongation. The original cross section measurement is also compared to the final cross section to obtain reduction

in area.

The test sample was securely held by top and bottom grips attached to the universal testing machine. Vertical alignment of the specimen

is an important factor to avoid side loading or bending moments created in the specimen. During the tension test, the grips are moved apart

at a constant strain rate to stretch the specimen. The force on the specimen and its displacement is continuously monitored and plotted on

a stress-strain curve until failure.

12 tensile test specimens were prepared from the aluminum 6082 sheet. These specimens were mounted to the universal testing machine

separately to conduct uniaxial tensile test at different strain rates. Strain rates used were 0.005, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.08, 0.1,

0.3, 0.5 and 0.75.

Figure 2 Image of the broken specimen in Universal Testing Machine

(ii)Methodology

(a)Geometric modelling:

The cross-section of the 3 dimensional model for the analysis consists of a rectangular section representing the gage length of the specimen

in order to make the model simple and computationally faster. The dimensions taken are as follows: length = 30 mm, width 6 mm and

thickness = 3 mm. All the values are in millimetres for convenience in the simulation.


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Figure 3: Geometric Representation of the cross section of the specimen.

Figure 4: The part created for the simulation

(b)Boundary Conditions:

In FE modelling, proper type of boundary conditions should be imposed. For the simulation of the tensile test, one side of the specimen

was fixed while the opposite side was made to move in one specific direction.

Hence, the boundary conditions taken on the face with the smallest cross-section, i.e. face A (see figure 3) of the specimen are

ux=0, uy= 0 and uz=0

Such that ux, uy and uz are the displacements in X, Y and Z directions.

While boundary conditions on the face opposite to face A i.e. face B are:

uy= 0, uz=0 and vx= velocity in X direction

Such that vx is the deformation rate i.e. the speed at which the loading takes place.

Deformation rate can be calculated based on the given strain rate which is given as follows:


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��=��.��

stands for the strain rate while Lo denotes the original length of the specimen.

Figure 5: The boundary conditions

(c)Meshing:-

The model was seeded choosing each edge individually. Both the vertical sides to which the boundary conditions were assigned were

seeded in 12 divisions while the horizontal sides were seeded in 60 divisions. The model was meshed using this seeding which created a

total of 4320 elements (4320 finite elements). In this paper, ALE modelling approach is used to conduct the FEM simulation. In the ALE

approach, the explicit dynamics procedure performs a large number of small time increments efficiently. The general governing equations

are solved both Lagrangian boundaries and Eulerian boundary approaches in same fashion. The adaptive meshing technique does not alter

elements and connectivity of the mesh. This technique combines the features of pure Lagrangian analysis in which the mesh follows the

material, and Eulerian analysis in which the mesh is fixed spatially and the material flows through the mesh. Explicit dynamic ALE

formulation allows flow boundary conditions whereby only a small part of the work piece in the vicinity of the tool tip needs to be modelled.


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Figure 6: Meshed part

(d)Boundary Conditions and Loadings

The 2D FE specimen is given two boundary conditions. One face of the model was encastred and the opposite face was given velocity

according to the strain rate.The velocity was given according to the formula:-

v = ė*lo (1)

Where v is the deformation velocity

ė is engineering strain rate

lo is the gauge length of the specimen

So, the given velocities were 0.125, 0.25, 0.50, 0.75, 1.00, 1.25, 1.50, 2.00, 2.50, 7.50, 12.50, 18.75 for the strain rates of 0.005, 0.01,

0.02, 0.03, 0.04, 0.05, 0.06, 0.08, 0.1, 0.3, 0.5, 0.75 per seconds respectively.

(e)Element deletion

The element deletion option was ON in the meshing so that the element are seen as fractured once they pass the fracture point. Also these

commands were given separately in the input files for the simulation.

(f)Meshing:

Eight-node linear brick (C3D8R) elements with reduced integration scheme are used for the discretization of the given specimen. The C3D8

element is a general purpose linear brick element, fully integrated (2x2x2 integration points)(). The specimen is meshed with 1280

(3/4*3/4*3/4 blocks) structured elements of C3D8R type. Finite element formulation of this type of element is based on the iso-parametric

procedure i.e., the element geometry and the displacements are interpolated in the same way.


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Figure 7: The meshed part consisting of 1280 small block elements.

(g)Material Model:

The elastic response of AA6082 was modelled with linear elasticity model. The properties given to the material were as follows.

S.R. No. Mechanical Property Value

1 Density 2700 kg/m3

2 Young's Modulus 70GPA

3 Poisson's Ratio 0.33

Table 3: Properties of the material used.

(h)Solution Method:

The dynamics explicit procedure performs a large number of small time increments efficiently. An explicit central-difference time

integration rule is used. In an explicit dynamic analysis displacements and velocities are calculated in terms of quantities that are known at

the beginning of an increment. An ALE approach is incorporated to conduct the FEM simulations.


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(iii)WORK DONE

The material model presented has been tested for a particular strain rate at room temperature. Further we have:

1. Developed 2 similar models at 2 different values of strain rates.

2. Developed a model by introducing strain rate as the input criteria such that it formulates a relationship with the corresponding

plastic strain and yield stress. We can now vary the boundary conditions, i.e., the deformation rate according to a predefined strain

rate.

3. This was to validate our model which can interpolate the output curve for the intermediate strain rate and its corresponding

deformation rate values.


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CHAPTER 4: RESULTS

(i)Experimental Values

Figure 8(a): Graph showing Stress Vs Strain with different strain rates of Experimental data

Figure 8(b): Graph showing True Stress Vs Strain with different strain rates of Experimental data

-50000000

0

50000000

100000000

150000000

200000000

250000000

-0.02 0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18

Stre

ss (

Pa)

Strain

Stress Vs Strain

0.5 strain rate 0.3 strain rate 0.1 strain rate 0.75 strain rate

-50000000

0

50000000

100000000

150000000

200000000

250000000

300000000

-0.02 0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16

Str

ess

(Pa)

Strain

True stress Vs True Strain

0.5 strain Rate 0.3 strain rate 0.1 strain rate 0.75 strain rate


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Figure 8(c) Figure 8(c)

Figure 8(e) Figure 8(f)

Figure 8(f)

The figure shown above are the specimens after undergoing the tensile testing at different strain rates for example 0.1, 0.3, 0.5, 0.75 .

(ii)THE SIMULATION:


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Figure 9(a)

Figure 9(b)

The figures 9(a) and 9(b) show the necking and the failure of the work piece at the strain rate of 0.3 when simulated with a

course mesh.


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Figure 10(a)

Figure 10(b)


medium fine mesh.

Figure 11(a)


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Figure 11(b)

Figure 11(c)


fine mesh. Figure 11(c) shows the specimen after undergoing the tensile test at 0.3 strain rate.

CPU Time Chart

Meshing

Coarse Medium Fine

Strain Rates

0.3 8.8 11.1 53

0.5 9 54.1 94.8

0.75 25.8 102.5 965.7

Table 4: CPU Time.(in sec) obtained by monitoring the simulations


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Figure 12 shows the stress vs. strain plots of the simulations with the three different types of meshing used.

From the graphs obtained, we observe that:

1. The ultimate tensile strength of the sample remains the same in all three simulations for the same strain rate.

2. The graph travels from the values for coarse meshing to that of the fine meshing indicating more refinement and accuracy as it

goes along the medium meshing for the simulation.


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Figure 13 shows the stress strain curves of various strain rate values simulated, also indicating the type of mesh used in each

simulation.

Figure 14 shows the values of the above curve as obtained from the software.


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CONCLUSION

1. This analysis and simulation lead to the conclusions that the type of mesh does not affect the stress strain graphs at low strain rates.

The values of these simulations as well as experiments are same and hence can be assumed to be right.

2. In simulations, the strains rates and type of meshing plays a major role in determining the nature of curve after yield point.

3. We conducted experiments at different combinations of strain rates and temperatures, taking three principle values in each case.

4. Finite Element Method is the most widely used and also a very powerful tool for the visual delineation of field variables such as

stress, strain, temperature, complicated deformation behavior etc.

5. A model will be simulated using FEM under the same boundary conditions on the commercially available software, ABAQUS

6.14.

6. The experimental data obtained was used to validate our model so that it can be used for further variations in boundary conditions

without actually performing the experiments.

REFERENCES

[1] H. S. Kim, S. H. Kim, W-S. Ryu, “Finite element analysis of the onset of necking and the post-necking behaviour during uniaxial

tensile testing,” materials transactions, Vol. 46, No. 10, pp. 2159–2163, 2005.

[2] G. Partheepan, D. K. Sehgal, and R. K. Pandey, “Finite element application to estimate in-service material properties using miniature

specimen”, World Academy of Science, Engineering and Technology Vol.14, pp. 02–23, 2008.

[3] L.F. Menezes, J.V. Fernandes, D.M. Rodrigues, “Numerical simulation of tensile tests of pre-strained sheets”, Materials Science and

Engineering A264 130–138, 1999.

[4] R. C. Dorward, K. R. Hasse, “Strain rate effects on tensile deformation of 2024-0 and 7075-0 aluminium alloy sheet”, Journal of

Materials Engineering and Performance, April, Volume 4, Issue 2, pp. 216–220, 1995.

[5] M. H. Osman, A. B. Adnan, A. F. Nejad, R. Hodjati, M. Azimi, I. Faridmehr, “Correlation between engineering stress-strain and true

stress-strain curve ” American Journal of Civil Engineering and Architecture, Vol. 2, No. 1, pp. 53–59, 2014.


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[6] J. W. Kim, T. S. Byun, “Analysis of necking deformation and fracture characteristics of irradiated A533B RPV steel”, Nuclear

Engineering and Technology, Vol. 44 (8), 2012.

[7] X. Q. Shi, W. Zhou, H. L. J. Pang, and Z. P. Wang, “Effect of Temperature and Strain Rate on Mechanical Properties of 63Sn/37Pb

Solder Alloy”, ASME Journal of Electronic Packaging, ASME, USA, Vol. 121, No. 3, pp. 179-185, 1999.

[8] L. Noradila, Z. Sajuri, J. Syarif, Y. Miyashita, Y. Mutoh, “Effect of strain rates on tensile and work hardening properties for Al-Zn

magnesium alloys”, IOP Conf. Series: Materials Science and Engineering 46, 2013.

[9] S. A. Bansal, M. Singh, G. Vohra, Parveen, “Numerical Simulation of UniAxial Tensile Testing for Standard Mild Steel Specimen

Over Elastic and Plastic Region”, International Journal of Mechanical Science and Civil Engineering, IJMSCE Special issue on Emerging

Trends in Engineering & Management, ICETE, 2013.

[10] “Material property data—MATWEB. Mechanical properties of AA6082 T6 aluminium alloy,” http://www.matweb.com/

search/DataSheet.aspx?MatGUID=fad29be6e64d4e95a24169- 0f1f6e1eb7

[11] Y. Chen, A.H. Clausen, O.S. Hopperstad, M. Langseth, “Stress–strain behaviour of aluminium alloys at a wide range of strain rates”,

International Journal of Solids and Structures, vol. 46, pp. 3825–3835, 2009.

[12] S. Kalpakjian, S. R. Schmid, Manufacturing processes for engineering materials, Upper Saddle River, N.J: Prentice Hall, 2003.

[13] ABAQUS Analysis User’s Manual version 6.13, Hibbitt, Karlsson and Sorensen Inc., Pawtucket, USA.

Documents

Available online at: A Thesis Report On ... · ABAQUS/Explicit. This approach provides control of mesh distortion which is again very much possible at the time of necking during tensile