Lab Science of Materis report

Summary

This experiment was designed to investigate the behavior of a number of common engineering materials that were subjected to tensile loading. The materials that were tested were Carbon Steel, Aluminum Alloy, High Conductivity Copper, Brass, Coconut Fibre, Sisal Fibre, Plastic Fibre, Plywood, Teak and White Pine. The following properties were determined: Young’s Modulus, yield stress, yield point Ultimate Tensile Stress (UTS) percentage elongation at the facture and the percentage reduction in the cross-section area. This Tensile Testing experiment is important for determining a material’s properties, limits and its potential application in a wide range of industries. If a material is to be used in an engineering structure it will be subjected to various loads and it is important to know that the material is strong enough to withstand the loads that it will experience during its service life.

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Description of Apparatus

Hounsfield Tensometer(see instruction booklet)

Hounsfield Extensometer (see instruction booklet)

Percentage Elongation Gauge (see instruction booklets)

Specimen: 0.1 Carbon Steel (Long and Short)

Aluminium Alloy H.D.14 annealed at 360oc(short)

High conductivity Copper (short)

70/30 Brass (short)

Coconut Fibre (short)

Sisal fibre

Plastic fibre

Plywood (short)

Teak (short)

White Pine (short)

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Procedure

(i)Test of Fracture

1) The sample was placed in the Hounsfield Exstensometer2) Load was uniformly increased until sample ruptured3) Readings for load and extension were recorded on a graph by the extensometer4) Broken sample was placed in the elongation gauge5) Elongation was measure and recorded.

(ii)Elastic Test

1) the long copper specimen was inserted into the machine chucks and to the extensometer was attached to the specimen.

2) The dail was zeroed3) The load was increased in increments of 1000 with a maximum well below the yield

point of the sample 4) At each incremental increase the extension was recorded. 5) A graph of stress-strain was plotted.

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Theory

Test of Fracture

The Hounsfield extensometer was used to apply a tensile load until the specimens fractured. During the test the loads and their corresponding elongations for each material were recorded and a Load vs Elongation graph was plotted for each material. A stress- percentage elongation graph can be constructed from the load vs Elongation graph by making the required calculation.The relevant formulae are: σ = P/Ao Percentage Elongation = (∆l/lo)*100

σ - Stressɛ - Strain∆l – Elongationlo – Initial Length/gauge lengthP – LoadAo – Original Cross-Sectional Area

Yield point is the stress level at which plastic deformation starts. Below this level the material is said to be elastic which means that the material will return to the gauge length if the loading seizes.

Beyond yielding, continuous increase of the tensile loading leads to an

increase in the stress required to permanently deform the specimen At this stage the specimen is strain hardened. The material is said to be in its plastic region, where deformation is permanent.

If the load is continuously applied, the stress-strain curve will reach the maximum point, which is the Ultimate Tensile Strength (UTS). At this point, the specimen can withstand the highest stress before necking takes place where the load will continuously fall off until fracturing occurs.

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Relevant Formulae: σUTS = Pmax/Ao

σUTS – Ultimate Tensile Strength

Test Within The Elastic Limit

In this experiment the Hounsfield Extensometer meter was used to apply incremental forces to the copper, In order to get more accurate values for necessary calculations.

The Elastic region is the part of the stress strain curves that extends to the yield point. Deformation in this region is recoverable. In order to calculate the stress in this region Hooke’s Law will have to be applied:

σ = Eɛ ɛ = ∆l/lo

E = σ/ɛ

σ – StressE – Modulus of Elasticity or Young’s Modulusɛ – Strain

In the elastic region the stress-strain graph is plotted a as a straight line which means that stress is linearly related to strain. Therefore the linearity constant or the gradient of the stress-strain graph is defined as E – The Modulus of Elasticity/Young’s Modulus. The Young’s Modulus of a material describes speaks to its resistance deformation.  A material with a higher modulus is stiffer and has better resistance to deformation.

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Results

Observations Recorded Data –Fracture Test

Metals

Gauge Length – 25.25 mmCross Section Area – 20 mm^2Test Speed – 10mm/min

Woods

Gauge Length – 80 mmTest Speed – 10mm/min

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Material Reduction Area (%) Elongation (mm)Carbon Steel 55 37High Conductivity Copper 72 1970/30 Brass 15 14Aluminum allow 50 28

Material Length(mm) Width(mm)Plywood 14.95 9.75Teak 13.35 10.3White Pine 13 8.1

Fibres

Gauge Length – 80 mmTest Speed – 10mm/min

Recorded Data –Elastic Test

Material : CopperGauge Length – 90mmCross-Sectional Area – 20mm^2

Calculated Data

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Material Diameter(mm)Sisal Fibre 0.225Coconut Fibre 0.320Plastic Fibre 0.230

Load (N) Elongation(mm)1000 0.1962000 0.343000 0.4684000 0.603

Fracture Test Graphs

0 5 10 15 20 25 30 35 40 450

100

200

300

400

500

600

SteelCopperAluminumBrass

Stre

ss (

N/

mm

2)

Percentage Elongation (%)

Metals

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Material Ultimate tensile Strength Yield StressCarbon Steel 409.375 6812.5High Conductivity Copper 325 319.37570/30 Brass 500.625 400Aluminum allow 326.25 221.875

0 5 10 15 20 25 30 35 40 450

50

100

150

200

250

300

350

400

450

Steel

Steel

0 2 4 6 8 10 12 14 16 180

100

200

300

400

500

600Brass

Brass

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0 2 4 6 8 10 12 14 16 18 200

50

100

150

200

250

300

350

Series2

Percentage Elongation(%)

Str

ess(

N/

mm

2)

Copper

0 5 10 15 20 25 300

50

100

150

200

250

300

350

Series2

Aluminum

10

0 50 100 150 200 250 300 3500

1000

2000

3000

4000

5000

6000

PlasticSisalCoconut

Percentage Elongation(%)

Stre

ss(N

/mm

2 )

Fibres

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Material Ultimate Tensile Stress Yield StressPlastic Fibre 5655.434813 5655.434813Sisal Fibre 2640.450763 2288.390661Coconut Fibre 1460.80323 1305.398631

0 2 4 6 8 10 12 140

500

1000

1500

2000

2500

3000Sisal

Sisal

0 5 10 15 20 25 30 35 40 450

200

400

600

800

1000

1200

1400

1600

Coconut

Coconut

12

0 50 100 150 200 250 300 3500

1000

2000

3000

4000

5000

6000Plastic

Plastic

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0 5 10 15 20 250

10

20

30

40

50

60

70

80

TeakPlywoodWhite Pine

Precentage Elongation (%)

Stre

ss (

N/m

m2

)

WOODS

Materials Ultimate Tenisle Stress Yield StressTeak 72.06065947 45.89850922White Pine 22.31718898 9.021842355Plywood 21.95352028 20.58142526

14

0 5 10 15 20 250

10

20

30

40

50

60

70

80 Teak

Teak

Percentage Elongation(%)

Stre

ss(N

/mm

2)

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 50

5

10

15

20

25White Pine

White Pine

15

0 0.5 1 1.5 2 2.5 3 3.5 40

5

10

15

20

25

Plywood

Plywood

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Elastic Test

0 0.002 0.004 0.006 0.0080

50

100

150

200

250

Stress VS Strain - Copper

Stress VS Strain - Copper

Strain

E = σ/ɛ = (153-100.5)/(0.0052-0.00378) = 36971.83 N/mm2

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Discussion:

The Stress-Percentage Elongation graph shows that the Steel sample experienced more plastic deformation that the copper, brass and aluminum sample, and this is reflected by the higher Percentage Elongation. The steel sample also displayed a higher Toughness and durability than the other metal samples, which is represented by the larger area beneath the stress percentage elongation graph. As shown in the graph the Steel a showed a gradual transition from strain hardening to failure which is the property called necking. Necking is a property of ductile material. Steel exhibits more ductile properties. It has large strains and stress before it fails. Thus making steel the material of choice for structural members. Though Brass as shown by the graphs can reach strengths greater than steel, it does not absorb nearly as much energy before it fails, making it a less suitable material for structures.

The copper sample has a very small strain hardening section and almost immediately begins to exhibit a decrease in strength after yielding, which is evident by the fairly steady decline in the plastic section. This shows that the copper is not as ductile as steel, but, holds a certain level of ductility.Brass has the highest yield point and Ultimate Tensile Stress of all the metals tested, but also has the smallest elastic section. This signifies that if brass is loaded pass its yield point; it would likely fail before steel and aluminum.

When comparing Aluminum and copper it is shown that aluminum will yield earlier than copper but will strain harden to strength comparable with copper’s Ultimate Tensile Stress. This speaks to the material’s toughness, durability and ductility.

The plastic fiber is able to withstand very high stresses before yielding, and then the strength falls off rapidly before fracturing. In comparison with plastic, the coconut and sisal fibers withstand low stresses before yielding. The sisal and coconut are brittle materials and as such have no plastic region because they fail after yielding. Making both materials not very suitable for construction. Sisal would be more effectively used as agricultural twine because of its ability to stretch and it durability. Of the three wood samples tested Teak is by far the strongest. It is one of the hardest, strongest and most durable of all natural woods. It exhibits some ductile properties though it’s not considered ductile. It has high yield stresses, high

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Ultimate Tensile stresses relative to the plywood and white pine and is also shown to strain harden before fracturing teak ideal for bearing loads though not as ideal as any of metals. An effective use for teak would be building wooden huts of furniture. However teak is one of the most expensive natural woods which may influence it’s uses. White pine is a soft and weak wood that breaks soon after yielding making it more or less a brittle material. White Pine can be a good choice for flooring. Plywood which is a slightly weaker material than white pine fails shortly after yielding making an un-suitable material for construction. More fitting uses of plywood are shelving, framing, and formwork.

The Hounsfield tensometer has an advantage over other tensile machines as it gives data at incremental values allowing more decisive values to be recorded, thus making calculations more accurate.

Young’s modulus calculated using the data from the Tensometer was found to be 36.97183 KN/mm2, while Young’s Modulus calculated from the data obtained from the Extensometer was calculated to be 7.9 KN/mm2 both of which differs significantly from the known value of 117 KN//mm2 . The tensometer is much more accurate than the extensometer though not accurate. Factors that could have altered the values during the test are human error and machine error.

Conclusion

In conclusion a lot of the engineering properties of common materials can determined from examining how the stresses and strains of the material differ under loading. The conclusion can be drawn that steel is the ideal metal for bearing loads, plastic is ideal for rope fibers because of its ability to stretch and teak is ideal structural timber.

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Appendix

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The University of The West IndiesCVNG-1005 – Science of Material

Experiment 1

Tensile Testing of Different Material

Instructor: Dr Mwasha

Table of Contents

Summary……………………………………………………………………………………………………………………1

Description of Apparatus…………………………………………………………………………………………..2

Procedure………………………………………………………………………………………………………………….3

Theory……………………………………………………………………………………………………………………….4 Results……………………………………………………………………………………………………………………….6 (a) Observations…………………………………………………………………………………………….……..6 (b) Calculated Results……………………………………………………………………………………………8

Discussion………………………………………………………………………………………………………………….18

Conclusion……………………………………………………………………………………………………………..….19

Appendix*………………………………………………………………………………………………………………….20