In this report I explain a recent experiment aimed at ...rpowelldesign.co.uk/.../Youngs-Modulus-Lab-Report.pdf · experiment aims to test the young’s modulus of a ... tensile strength

Robbie Powell – i7624400 (Youngs Modulus Lab Report) Page 1

Abstract

In this report I explain a recent experiment aimed at finding out the Youngs Modulus, Ultimate tensile

strength and elastic limit, total elongation and total reduction section in cross section of two materials:

- Steel and Aluminium. I discuss the atom structure of materials as well as the cause of the yield point

phenomenon seen in steel. Finally I calculate values for the various properties discuss the results and

explore applications for the different properties as well as the materials.


Introduction:

All products undergo stress and strain caused by forces on an object, whether big or small they must

always be accounted for to avoid failure in a given design. In most cases, materials will have

undergone rigorous testing in order to confirm whether they are fit for function. One such

experiment aims to test the young’s modulus of a given material. “Young’s modulus is a measure of

the ability of a material to withstand changes in length when under lengthwise tension or

compression” (The Editors of Encyclopædia Britannica)

Figure 1: Stress/Strain Equation

A Young’s modulus experiment is where a material’s tensile strength is tested by being slowly

stretched to find the elastic limit and finally see the breaking point. This information is then used

later in accordance with other factors such as a cost and aesthetics to see if it suits the purpose.

Apparatus and procedure:

Equipment used

- Hounsfield H20K-W*

Two different materials underwent this experiment

- 0.1% Carbon Steel normalised at 900 °C

- Pure Aluminium

Diameter: 5mm

Length: 27mm

Test Speed: 5mm/min

Experiments undertaken on 05/01/2015

Both materials were individually tested by clamping the test pieces into the machine* and beginning

the stretching process. The machine* would slowly pull the test pieces apart until it found breaking

point and then stop.

Figure 2: Hounsfield Picture One Figure 3: Hounsfield Picture Two


Results

The experiment was only undertaken once so the results cannot be checked for precision.

Measurements of materials after test:

Steel

- Cross section of break: 2.79mm

- Longitudinal Extension: 10.88mm

Aluminium

- Cross section of break: 1.26mm

- Longitudinal Extension: 11.23mm

Figure 4: Steel Graph Figure 5: Steel Results

Figure 6: Aluminium Graph Figure 7: Aluminium Results


Figure 8: Steel Material Figure 9: Aluminium Material

Results Analysis

“Load: The force applied to a material during testing

Yield point: Beyond the yield point, plastic deformation occurs.

Ultimate tensile strength: This is the maximum load/force the specimen withstood.

Failure (Breaking Point): This is the point where the specimen failed/fractured.

Elastic deformation: Within this blue region the material will return to its original shape if the load is removed.

Plastic deformation: Within the red region the material will show a permanent change if the load is removed.”

(State of New South Wales, Department of Education and Training 2009)

Figure 10: Load extension Graph


Figure 11: Steel Stress/Strain Graph

Figure 12: Aluminium Stress/Strain Graph

Results for steel

Ultimate tensile strength (Maximum force/Original Area)

7350(N)/19.63x10^-6(mm) = 374.43 (MPa)

Elastic Limit (Can be seen on graph)

6600 (N)

Elastic Modulus (Using stress/strain graphs gradients – Stress/Strain)

(254.7122-20.37697)/((0.02963x10^-6)-(0.018519x10^-6) = 21.09 GPa

Total Elongation (Extension/Original length x 100)

10.88(mm)/27(mm)x100=40.30%

Total reduction in cross section (100-(Cross section at break/original cross section x100)

100-(2.79(mm)/5(mm) x100)=44.2%

-50

0

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400

0 0.1 0.2 0.3 0.4 0.5

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ss

Strain

Steel

Stress

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Figure 14: Dislocations

Results for Aluminium

Ultimate tensile strength (Maximum force/Original Area)

1440(N)/19.63x10^-6(mm) = 73.36 (MPa)

Elastic Limit (Can be seen on graph)

580 (N)

Elastic Modulus (Using stress/strain graphs – Stress/Strain)

(28.52057-18.33465/(0.002778x10^-6)-(0.00083x10^-6) = 5.23 GPa Total Elongation (Extension/Original length x 100)

11.23(mm)/27(mm)x100=41.59%

Total reduction in cross section (100-(Cross section at break/original cross section x100)

100-(1.26(mm)/5(mm)x100)=74.8%

Material Ultimate Tensile Strength

Elastic Limit Elastic Modulus

Total Elongation

Total Reduction in cross section

Steel 374.43 (MPa) 6600(N) 21.09 (GPa) 40.30% 44.2%

Aluminium 73.36 (MPa) 580(N) 5.23 (GPa) 41.59% 74.8% Figure 13: Final Results Table

Discussion

As can be seen from figure 13 the two materials tested gave very different results. Steels Ultimate

tensile strength and Elastic Modulus are both over 4 times of that of Aluminium’s. This clearly

suggests that Steel would be much better suited in load bearing scenarios than aluminium.

These results amongst others aren’t necessarily 100% accurate. Although the machine* used was

calibrated previously, only one test was carried out for each material which could cause the

precision of the results to be questioned.

Other factors could include the technician’s skill that carried out the test as well as fatigue and

impurities in the material.

Impurities can play a major part in testing and failure in a

material and could refer to a few different things.

Point defects are where an atom is missing or irregularly

placed.

Dislocations are where groups of atoms are arranged

awkwardly weakening the structure.

Impurities weaken a material as gaps are left and bonds

cannot connect atoms together. If there is an impurity in a

certain section of a material it could cause that area to fail

unexpectedly. As this test was only carried out once, the


precision of results cannot be known.

As can be seen from the information displayed on figure 13, Steel has a very high Elastic Modulus

and Ultimate tensile strength making it very useful for high load structures such as bridges, vehicle

frames and building supports. When looking at figure 11, we can see that after enough force is

applied so that it passes the elastic limit, the stress drops and rises – faltering as it goes. This is called

the yield point phenomenon and is a result of strain aging as well as dislocations in the material.

This is because as the metal is stretched before the elastic limit, the atom structure will not

permanently change. However, after the elastic limit has been passed dislocations start to occur and

while the molecules are rearranging; the stress drops. However once the bonds have attached once

again, the stress will rise. The higher the dislocation density, the longer this will continue for until

finally the graph should show a more fluid curve up to the Ultimate tensile strength. After this point

is achieved, the cross sectional area will begin to decrease at a rapid rate, causing the stress to drop

considerably until the breaking point.

Compared to Steel, the aluminium can be seen to be weaker due to its low ultimate tensile strength

and elastic modulus. As demonstrated in figure 12, the stress has a much gentle curve as the atoms

are able to rearrange more effectively in the structure. This is why aluminium is more suited to less

load bearing applications such as tin cans. The total elongation is roughly the same as steels however

the reduction in cross section is significantly more, as is displayed in figure 13. This is ultimately due

to the strength of the material in which materials with higher elastic modulus’s can resist lateral

stress more effectively. Aluminium, just like rubber (although an extreme example) will reduce in

width as it’s stretched, reducing the force and therefor the stress needed to pull it apart.

Applications

- Crane Wire

An application in which the properties of this experiment would

have needed to be measured could be a crane wire. A crane wire is

made up of a huge amount of wires used together to create one -

but for sake of this example, ill think of it as one large part. Cranes

are capable of picking up extreme amounts of weight - often as

much as 20 tons. The result of failure could be catastrophic so

huge amounts of testing would have to be undergone before it could be cleared for use. Obviously a

material with high, ultimate tensile strength, elastic modulus and elastic limit would be needed as

the wire cannot be allowed to plastically deform and a factor of safety must be added in case the

maximum limit is exceeded. For example of the maximum mass allowed is 20 tons (18143.7 kg) then

we can work out the minimum elastic limit.

- Minimum elastic limit = 18143.7 x 9.81 = 177989.697 N

This means that if any more than this weight is put on the wire then it will plastically deform. The

ultimate tensile strength would have to be much higher than the elastic limit to avoid dramatic

failure in the case of far too much weight being put on the wire.

Figure 15: Crane


- Diving Board

Another application would be a diving board. The most important

properties for function in a diving board are the elastic modulus

and the elastic limit, although ultimate tensile strength will

ultimately control failure and fracture of a material. A diving board

is an interesting one as the design of the board will also change the

minimum properties required in the design. For instance, the

length of the board will effect the strain, and therefor the elastic

modulus. Because of this we can presume the longer the board, the lower the resistance to bending

it will hold. However, it still needs to hold its shape and be able to create an upwards force after

bending so a middle ground must be found.

In terms of the elastic limit, a high yielding material must be found as if to much force is applied to

the board for it to pass this point, the board will not spring back. For this example let’s presume the

maximum mass allowed on the board for safety and function is 150kg. Let’s also presume that a user

will fall at a constant rate after jumping relative to gravity.

- Minimum elastic limit = 150 x 9.81 = 1471.5 N

Finally, the ultimate tensile strength would be important in terms of avoiding fracture so again; a

factor of safety must be considered with this property.

Conclusion

In conclusion this experiment can be extremely important in testing materials so that dramatic

failure is avoided once the product has been made. The two different materials tested both

exhibited very different results in the tests showing their purpose for certain functions in industry,

although steel proved to be the stronger material of the two with results showing as much as five

times of that of aluminium. I’ve found that dislocation densities can effect results from a material

dramatically and must be tested for thoroughly. I’ve also seen that the properties explored in this

report generally rise together, although as shown in applications; particular properties of materials

in given products will need to go against this theory in order to function. This would be achieved by a

variety of different material altering techniques or by incorporating informed design of the product.

References

The Editors of Encyclopædia Britannica. Youngs Modulus. Available:

http://www.britannica.com/EBchecked/topic/654186/Youngs-modulus. Last accessed

17th February 2015.

Figure 1:

Anon. Stress/Strain Equation. Available:

https://papercrete.files.wordpress.com/2010/09/e.jpg. Last accessed 17th February

2015.

Figure 2: Hounsfield Picture One

Wood, Adam. Lab Report 1 and 2 - Photos. [Pictures] Bournemouth

Figure 16: Diving Board


Figure 3: Hounsfield Picture Two


Figure 4: Steel Graph

Bournemouth University. Lab Report Experiment (05/01/2015)

Figure 5: Steel Results


Figure 6: Aluminium Graph


Figure 7: Aluminium Results


Figure 8:


Figure 9:


Figure 10: Load/extension Graph

State of New South Wales, Department of Education and Training 2009.

(2009). Load/extension Graph. Available:

http://lrrpublic.cli.det.nsw.edu.au/lrrSecure/Sites/Web/tensile_testing/lo/03_what_does

_it_mean/applets/highlighter_load_ext_text.htm. Last accessed 17th February 2015.

State of New South Wales, Department of Education and Training 2009

Load/extension Graph labels. Available:

http://lrrpublic.cli.det.nsw.edu.au/lrrSecure/Sites/Web/tensile_testing/lo/03_what_does

_it_mean/applets/highlighter_load_ext_text.htm. Last accessed 17th February 2015.

Figure 12: Aluminium Stress/Strain Graph

Qi, Zang. Lab Report Graph. Bournemouth

Figure 14: Spaceflight Editors. Dislocations. Available:

http://www.spaceflight.esa.int/impress/text/education/Images/Glossary/GlossaryImage0

20.jpg. Last accessed 17th February 2015.

Figure 15: Anon. Crane. Available: http://www.constructionmachineryme.com/wp-

content/uploads/2012/08/liebherr-crane-turkey.jpg. Last accessed 25 February 2015.

Figure 16: SRS Smith. Diving Board. Available:

http://www.srsmith.com/media/14884/cantilever__3_.jpg. SRS Smith. Last accessed 25

February 2015.

Bibliography

https://www.nde-ed.org/EducationResources/CommunityCollege/Materials/cc_mat_index.htm

Documents

In this report I explain a recent experiment aimed at ...rpowelldesign.co.uk/.../Youngs-Modulus-Lab-Report.pdf · experiment aims to test the young’s modulus of a ... tensile strength