Exp 3 Tensile Test

7/27/2019 Exp 3 Tensile Test

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Chan Kah Fai 1001025381EE 102 Mechanics and Strength of Materials [Mr. Naveen]16 Feb 2011

ELEMENTS OF MATERIAL SCIENCE LAB REPORT

EXPERIMENT 3: TENSILE TEST

CHAN KAH FAI (GROUP 4)

SCHOOL OF ENGINEERING

FACULTY OF ENGINEERING, ARCHITECTURE & BUILT

ENVIRONMENT

16 FEBRUARY 2011


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Table of Contents

Contents Page Number

1.0 Introduction 3

2.0 Objectives 4

3.0 Material and Methodology 4

4.0 Procedure 5

5.0 Calculations 6

6.0 Results 7

7.0 Discussions 20

8.0 Conclusions 22

9.0 Limitations of the Experiment/ Difficulties Encountered 22

10.0 Reference 22


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3

1.0 Introduction

One of the most common mechanical tests used to evaluate the strength of

materials is tensile test. Tensile tests are performed in order to collect data to be used in

selecting materials for engineering applications. Tensile tests are often used to predict the

behaviour of a material under forms of loading other than unaxial tension. The tests are

carried out by applying a pulling force to the sample in a relatively short time at a

constant rate.

The strength of the material is the primary concern in tensile tests. The strength of

a material can be measured in either the stress required to cause plastic deformation to the

material or the maximum stress the material are able to withstand. The force applied on

the material could be collected and converted into several graphs in order to obtain

certain important values of the materials.

The mechanical properties of materials such as metals and alloys which are very

important for engineering applications in structural designs could be obtained from the

tensile tests are as following:-

1. Modulus of elasticity

2. Yield strength at 0.2% offset

3. Ultimate tensile strength

4. Percent elongation at fracture

5. Percent reduction in area at fracture


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2.0 Objectives

1. To identify the strength of materials, metals and alloys.

2. To identify the materials behaviour under a tensile force.

3. To identify the important parameters through tensile test such as Youngs

Modulus, yield stress, and ultimate tensile stress.

3.0 Materials and Apparatus

Materials : Brass and carbon-steel specimens

Apparatus : Universal testing machine

The types of samples used for the tensile test vary considerably. The specimens

are usually have enlarged ends or shoulders for gripping. The most important part of the

specimens is the gage section. The cross-sectional area of the gage section is reduced to

ensure that deformation and failure will be concentrated in this region.

The gage length is the region over which measurements are made and is centred

within the reduced section. For metals with a thick cross-section such as a plate, a 0.050in

diameter round specimens are commonly used [Figure 3.1 (a)]. For metals with thinner

cross-sections such as sheet, flat specimens are used [Figure 3.2(b)]. A 2-in gage length

within the specimens are the most common used cage length for tensile tests.

Figure 3.1 (a) Figure 3.1 (b)

Standard round tension test Standard rectangular tension

specimen with 2-in gage length. test specimen with 2-in gage length.


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4.0 Procedure

1. The original gage length and the area of the specimen are measured using a

vernier calliper.

2. The tensile test for the specimen is carried out using the Universal testing

machine under the supervision of the lab tutor.

3. After the test is completed, the percent elongation and percent reduction of area

are obtained.

4. From the plot of force versus strain, the graph of engineering stress versus

engineering strain is obtained.

5. The Youngs Modulus, ultimate tensile stress, 0.2% offset yield stress and

fracture stress are obtained for the specimen.


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5.0 Calculations

1. Engineering stress:

2. Engineering strain:

3. Ultimate tensile strength:

4. Percent elongation: % elongation = x 100%

5. Percent reduction in area: % reduction in area =

6. Youngs Modulus or modulus of elasticity can be obtained from the linear

relationship between stress and strain in the elastic region of t he engineering

stress-strain diagram.

7. Yield strength is the strength at which a metal or alloy shows significant plastic

deformation. Because there is no definite point on the stress-strain curve where

elastic strain ends and plastic begins, the yield strength is chosen to be the

strength when a definite amount of plastic strain has occurred, for example, 0.2%

offset yield strength.

where, F= average uniaxial tensile force

Ao = original cross-sectional area

l = new length of specimen after being extended by uniaxial tensil force

lo = original length of specien

Fmax = maximum tensile force

Af = final cross-sectional area


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6.0 Results

Brass 60% Copper/40% Zinc [Wed Batch 1]

Diameter : 0.005 m Max Force : 2752.0 N

Ultimate Tensile Strength :140.158 Mpa Elongation : 22.28 %

Graph of Force against Extension

y = -5.3253x6

+ 94.633x5

- 658.43x4

+ 2342.9x3

- 4762.9x2

+ 5154.1x + 360.81

R2

= 0.9748

0.0

250.0

500.0

750.0

1000.0

1250.0

1500.0

1750.0

2000.0

2250.0

2500.0

2750.0

3000.0

0.0 0.3 0.5 0.8 1.0 1.3 1.5 1.8 2.0 2.3 2.5 2.8 3.0 3.3 3.5 3.8 4.0 4.3 4.5 4.8 5.0 5.3 5.5 5.8 6.0

Extension (mm)

Force(N)


2. Engineering strain: Extension of Specimen

0.00253. Ultimate tensile stress : 2752.0

1.96E-5

= 140.158 Mpa

4. Percent elongation: 0.0307 0.0250 x 100

0.0250 = 22.8%


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5. Youngs Modulus :

Graph of Stress against Strain

y = -7E+13x6

+ 5E+13x5

- 1E+13x4

+ 2E+12x3

- 2E+11x2

+ 7E+09x + 2E+07

R2

= 0.9748

0.0

10000000.0

20000000.0

30000000.0

40000000.0

50000000.0

60000000.0

70000000.0

80000000.0

90000000.0

100000000.0

110000000.0

120000000.0

130000000.0

140000000.0

150000000.0

0.00 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 0.10 0.11 0.12 0.13 0.14 0.15 0.16 0.17 0.18 0.19 0.20 0.21 0.22 0.23 0.24

Strain ()

S

tress()

From the graph above, Youngs Modulus:

= 110.0 MPa

0.023

= 4.783GPa

Yield Strength: 110.0 MPa


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Ultimate Tensile Strength : 120.321 MPa Elongation : 17.46%


y = -24.403x6

+ 322.39x5

- 1634.9x4

+ 4094x3

- 5712.2x2

+ 4641.7x + 491.05

R2

= 0.9741

0

250

500

750

1000

1250

1500

1750

2000

2250

2500

2750

3000

0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 2.6 2.8 3.0 3.2 3.4 3.6 3.8 4.0 4.2 4.4 4.6

Extension (mm)

Force(N)



0.00253. Ultimate tensile stress : 2362.5

1.96E-5

= 120.321 Mpa


0.0250 = 17.46%


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5. Youngs Modulus :


y = -3E+14x6

+ 2E+14x5

- 3E+13x4

+ 3E+12x3

- 2E+11x2

+ 6E+09x + 3E+07

R2

= 0.9741

0.0

10000000.0

20000000.0

30000000.0

40000000.0

50000000.0

60000000.0

70000000.0

80000000.0

90000000.0

100000000.0

110000000.0

120000000.0

130000000.0

0.00 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 0.10 0.11 0.12 0.13 0.14 0.15 0.16 0.17 0.18 0.19

Strain ()

S

tress()


= 70.0 MPa

0.08

= 0.875 GPa



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y = -7.7714x6

+ 152.63x5

- 975.76x4

+ 2899.3x3

- 5008.8x2

+ 5515.6x - 301.72

R2

= 0.9905

-500.0

-250.0

0.0

250.0

500.0

750.0

1000.0

1250.0

1500.0

1750.0

2000.0

2250.0

2500.0

2750.0

3000.0

0.00 0.25 0.50 0.75 1.00 1.25 1.50 1.75 2.00 2.25 2.50 2.75 3.00 3.25 3.50 3.75 4.00

Extension (mm)

Force(N)



0.0025

3. Ultimate tensile stress : 2808.01.96E-5

= 143.01 Mpa


0.0250 = 14.832%


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5. Youngs Modulus:


y = -1E+14x6

+ 8E+13x5

- 2E+13x4

+ 2E+12x3

- 2E+11x2

+ 7E+09x - 2E+07R

2= 0.9905

-30000000.0

-20000000.0

-10000000.0

0.0

10000000.0

20000000.0

30000000.0

40000000.0

50000000.0

60000000.0

70000000.0

80000000.0

90000000.0

100000000.0

110000000.0

120000000.0

130000000.0

140000000.0

150000000.0

160000000.0

0.00 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 0.10 0.11 0.12 0.13 0.14 0.15 0.16

Strain ()

Stress()


= 110.0 MPa

0.032

= 3.438 GPa



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Brass 60% Copper/40% Zinc [Thurs Batch 1]




y = -1.123x6

+ 20.492x5

- 135.32x4

+ 422.58x3

- 979.72x2

+ 2182.6x - 333.64

R2

= 0.9784

-500.0

-250.0

0.0

250.0

500.0

750.0

1000.0

1250.0

1500.0

1750.0

2000.0

2250.0

0.0 0.3 0.5 0.8 1.0 1.3 1.5 1.8 2.0 2.3 2.5 2.8 3.0 3.3 3.5 3.8 4.0 4.3 4.5 4.8 5.0 5.3 5.5 5.8 6.0

Extension (mm)

Force(N)



0.0025

3. Ultimate tensile stress : 2127.51.96E-5

= 108.352 Mpa

4. Percent elongation: 0.0306925 0.0250 x 1000.0250 = 22.77%


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Brass 60% Copper/40% Zinc [Thurs Batch 2]




y = -0.2523x6

+ 9.1882x5

- 126.63x4

+ 795.82x3

- 2281.9x2

+ 4057.6x - 814.06

R2

= 0.9972

-2000.0

-1000.0

0.0

1000.0

2000.0

3000.0

4000.0

5000.0

6000.0

7000.0

8000.0

9000.0

10000.0

0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0 6.5 7.0 7.5 8.0 8.5 9.0 9.5 10.0

Extension (mm)

Force(N)



0.0025

3. Ultimate tensile stress : 9360.0

1.96E-5

= 476.7 Mpa


0.0250 = 37.52%


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5. Youngs Modulus:

Graph of Stress against Stress

y = -3E+12x6

+ 5E+12x5

- 3E+12x4

+ 6E+11x3

- 7E+10x2

+ 5E+09x - 4E+07

R2

= 0.9972

-100000000.0

-50000000.0

0.0

50000000.0

100000000.0

150000000.0

200000000.0

250000000.0

300000000.0

350000000.0

400000000.0

450000000.0

500000000.0

550000000.0

0 0.025 0.05 0.075 0.1 0.125 0.15 0.175 0.2 0.225 0.25 0.275 0.3 0.325 0.35 0.375 0.4

Strain ()

St

ress()


= 470.0 MPa

0.252

= 1.865 GPa



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Copper Steel [Wed Batch 1]




y = -0.1616x6

+ 8.7988x5

- 153.96x4

+ 1102.8x3

- 3128.3x2

+ 3815.6x - 458.63

R2

= 0.9965

-2000.0

-1000.0

0.0

1000.0

2000.0

3000.0

4000.0

5000.0

6000.0

7000.0

8000.0

9000.0

10000.0

11000.0

12000.0

0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0 6.5 7.0 7.5 8.0 8.5 9.0 9.5 10.0 10.5

Extension (mm)

Force(N)



0.0025

3. Ultimate tensile stress : 10337.5

1.96E-5

= 526.484 Mpa


0.0250 = 39.85%


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5. Youngs Modulus:


y = -2E+18x6

+ 4E+17x5

- 3E+16x4

+ 9E+14x3

- 1E+13x2

+ 5E+10x - 2E+07

R2

= 0.9965

-50000000.0

0.0

50000000.0

100000000.0

150000000.0

200000000.0

250000000.0

300000000.0

350000000.0

400000000.0

450000000.0

500000000.0

550000000.0

600000000.0

0.000 0.003 0.005 0.008 0.010 0.013 0.015 0.018 0.020 0.023 0.025 0.028 0.030 0.033 0.035 0.038 0.040 0.043

Strain ()

Stress(

)


= 520.0 MPa

0.028

= 18.57 GPa



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Overall Results for All Experiments

Brass

60% Copper/40% Zinc

Day/

Group

Diameter,

d (m)

Ultimate

Tensile

Strength,

ult (MPa)

Maximum

Force,

Fmax (N)

Percent

Elongation

(%)

Youngs

Modulus,

E (GPa)

Yield

Strength,

(Mpa)

Wed

Batch 10.005 140.158 2752.0 22.8 4.783 110.0

Wed

Batch 20.005 120.321 2362.5 17.46 0.875 70.0

Wed

Batch 30.005 143.010 2808.0 14.83 3.348 110.0

ThurBatch 1

0.005 108.352 2127.5 22.77 1.120 103.0

Thur

Batch 20.005 476.7 9630.0 37.52 1.865 470.0

Carbon-Steel

Day/

Group

Diameter,

d (m)

Ultimate

Tensile

Strength,

ult (MPa)

Maximum

Force,

Fmax (N)

Percent

Elongation

(%)

Youngs

Modulus,

E (GPa)

Yield

Strength,

(Mpa)

Wed

Batch 10.005 526.484 10337.5 39.5 1.857 520.0


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6.0 Discussions

1. Describe what you observe about the specimen after failure.

Ans: Upon the specimen fail, the shapes of the specimen is observed carefully. It is

found that both specimens experienced ductile failure by identifying the cup-

and-cone fracture. However, from the data recorded, it is clearly see that carbon-

steel has higher ductility compare to brass with its higher percentage of elongation.

2. Compare the stress-strain graph that you have obtained for the specimen with that

of an aluminium specimen.

Ans: From the aluminium stress-strain graph obtained, it is clearly seen that the

Youngs Modulus of aluminium is so much lower than brass and carbon-steel.

From the value of Youngs Modulus, we can assume that the ultimate tensile

strength, maximum force, and the yield strength would be lower than brass and

copper-steel provided all specimens are with same area and length in comparisons.


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3. What are some of the factors that may affect the precision of your results in

carrying out this test?

Ans: As we know, there are no materials in this world in perfect, the specimens

themselves might contains flaws such as imperfections arrangement of atoms in

the specimens, voids in the specimens, irregular shape of the specimens and

presence of impurities in the specimens which are almost impossible to be

avoided in materials. These flaws might strongly affect the precisions of the

results when experiment is carried out with the specimens.

With all datas recorded from the Universal testing machine, we are able to

measure the extensions of the specimens and the forces applied to the specimens

precisely and accurately at each points. By carrying out tensile testing on brass and

carbon-steel, the universal testing machine could measure a range of parameters such as

forces applied and extension of specimens until the specimens fail.

Although there are severals failures of the experiments conducted, the datas are

still recoreded as a comparison to the complete experiment. By converting all the datas

recorded into graphs, we are able to calculate a range of parameters to identify thebehaviour and properties such as the engineering stress, engineering strain, ultimate

tensile strength, percentage of elongation, yield strength and Youngs Modulus of each

specimens.

From the overall results of the experiments with is tabulated in a table, it is shown

that Thursday Batch 2 obtained the best results for brass experiment and Wednesday

Batch 1 for Carbon-steel among all other groups. This might due to some limitations or

difficulties occurred when experiment is carried out.


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Chan Kah Fai 1001025381EE 102 M h i d St th f M t i l [M N ]

7.0 Conclusions

As for the conclusions, we are able to identify the strength of each type of

materials, in this experiment, brass and carbon-steel specimens are used. Using universal

testing machine to carry out the experiment, we are able to observe the behaviour and

properties of the specimens when tensile force is applied.

Upon completing the experiment, with a set of data recorded, all the necessary

steps are calculated and converted to graphs which are graph of force against extension

and engineering stress against engineering strain. By obtaining both types of graphs for

each specimen tested, all important parameters regarding the properties of the materials

could be found. For instant, Youngs modulus which tells us how much force required to

separate the atoms of the materials and cause the material to stretch easily or in other

words, the stiffness of the materials.

8.0 Limitations of the Experiment/ Difficulties Encountered:

1. We are unable to place the specimen firmly to the grip of the universal testing

machine resulting the specimen to slip when the experiment is carried out

2. Specimens that we used in this experiments are not the exactly same for each

specimens due to natural flaws such as imperfections of arrangements of atoms in

the metal.

3. We have difficulties to operate the universal testing machine as we do not

understand well about the functions of the machine.

9.0 Reference

1. Beer, Ferdinand P.; Johnston, E. Russell; Dewolf, John T. (2001).Mechanics of

Materials (3rd ed.). McGraw-Hill.

2. No ownership. Retrieved on 23 Feb 2011. From

http://en.wikipedia.org/wiki/Yield_(engineering)

3. No ownership. Retrieved on 23 Feb 2011. From

http://web.mit.edu/course/3/3.11/www/modules/ss.pdf

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