University of Technology, JamaicaFaculty of Engineering

Material Science Lab 1

Lab # 4: Tensile Testing

Name: Ovrian Campbell

Id No. 0905141

Lab session: Friday 8-11 pm

Lab Tutor: Mr. Lindsay

October 19, 2012

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Abstract

The aim of the experiment was to carry out a uniaxial tensile test on a material to determine its

mechanical properties (yield strength, ultimate tensile strength, % elongation, ductility, modulus

of elasticity). The tensile test was carried out using the dension testing machine where force was

applied at both end of the material to determine the specifications of the Material. The

engineering strain calculated for the specimen after testing was 0.033 and the calculated stress

was 110.3 MPa.

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Table of Content

Nomenclature……………………………………………………….…………………4

Objective……………………………………………………………………………….5

Introduction/Theory…………………………………………………………………..5

Apparatus……………………………………………………………………………...7

Procedure……………………………………………………………………………...8

Results……………………………...…………………………………………………..9

Discussion……………………………………………………………………………..11

Conclusion and recommendation…………………………………………………….12

References……………………………………………………………………………..12

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Nomenclature

Tensile Strength - A material's ability to resist forces that attempt to pull it apart or stretch it

Tensile Stress - A force that attempts to pull apart or stretch a material

E modulus of elasticity (Young's modulus) n Poisson's ratio G modulus of rigidity (shear modulus

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Aim/Objective:

To carry out a uniaxial tensile test on a material to determine its mechanical properties (yield strength, ultimate tensile strength, % elongation, ductility, modulus of elasticity)

Introduction/Theory

Tensile testing, also known as tension testing is a fundamental materials science test in which a sample is subjected to uniaxial tension until failure. The results from the test are commonly used to select a material for an application, for quality control, and to predict how a material will react under other types of forces. Properties that are directly measured via a tensile test are ultimate tensile strength, maximum elongation and reduction in area. From these measurements the following properties can also be determined: Young's modulus, Poisson's ratio, yield strength, and strain-hardening characteristics

Stress Strain curve

Elastic Region

In the context of material behavior, a structural component is said to behave elastically if during loading/unloading the deformation is reversible. In other words, when the loads are released the specimen will return to its original, undeformed configuration.

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Plastic Region An area of the stress-strain graph in which permanent changes to a metal begin to occur.

True elastic limit is a very low value and is related to the motion of a few hundred dislocations. Micro strain measurements are required to detect strain on order of 2 x 10 -6 in/in.

Proportional limit is the highest stress at which stress is directly proportional to strain. It is obtained by observing the deviation from the straight-line portion of the stress-strain curve.

Elastic limit is the greatest stress the material can withstand without any measurable permanent strain remaining on the complete release of load. It is determined using a tedious incremental loading-unloading test procedure. With the sensitivity of strain measurements usually employed in engineering studies (10 -4in/in), the elastic limit is greater than the proportional limit. With increasing sensitivity of strain measurement, the value of the elastic limit decreases until it eventually equals the true elastic limit determined from micro strain measurements.

Yield strength is the stress required to produce a small-specified amount of plastic deformation. The yield strength obtained by an offset method is commonly used for engineering purposes because it avoids the practical difficulties of measuring the elastic limit or proportional limit.

Ultimate Tensile StrengthThe ultimate tensile strength (UTS) or, more simply, the tensile strength, is the maximum engineering stress level reached in a tension test. The strength of a material is its ability to withstand external forces without breaking. In brittle materials, the UTS will at the end of the linear-elastic portion of the stress-strain curve or close to the elastic limit. In ductile materials, the UTS will be well outside of the elastic portion into the plastic portion of the stress-strain curve.

The ductility of a material is a measure of the extent to which a material will deform before fracture. The amount of ductility is an important factor when considering forming operations such as rolling and extrusion. It also provides an indication of how visible overload damage to a component might become before the component fractures. Ductility is also used a quality control measure to assess the level of impurities and proper processing of a material.

Yield Strength is the point on the stress-strain curve where there is a sudden increase in strain, but no increase in stress. It is at this point that a metal is about to permanently deform.

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Apparatus

Test Specimen

Dension testing machine

Extensometer

Vernier caliper

A pair of divider

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Procedure

Students got familiar with the operation of the testing machine. The gauge length and the

diameter of the specimen were measured. The extensometer was used to place gauge marks on

the specimen. Testing parameters were imputed. Specimen was mounted in the draw of the

machine. The extensometer was attached and the load on it was zeroed. Machine drive keyboard

was pressed to begin tensile testing. A graph was simultaneously drawn ass the testing proceeds.

The extensometer was removed before the elastic limit was exceeded. Measurements were taken.

Specimen was strain until fracture. The specimen was observed.

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Results

Diagram 1 showing specimen after testing

Table 1and 2 showing values of stress and strain values for aluminum and mild steel respectivelyTable 1 Table 2

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Aluminumstress (N/mm^2) strain

27779603 0.012579866310 0.02501.18E+08 0.03501.37E+08 0.05001.41E+08 0.06251.46E+08 0.07501.48E+08 0.08751.5E+08 0.10001.53E+08 0.11251.53E+08 0.12501.5E+08 0.13751.39E+08 0.15001.23E+08 0.17001.13E+08 0.18001.02E+08 0.190081023682 0.207518517953 0.230032408964 0.247539353196 0.257548612172 0.270048612172 0.2775

Mild Steel

stress (N/mm^2) strain80213903.74 0.0264249554367.2 0.0528319073083.8 0.0647319073083.8 0.0792319073083.8 0.1000374331550.8 0.1264401069518.7 0.1528418894830.7 0.1792427807486.6 0.2198436720142.6 0.2462441176470.6 0.2726447415329.8 0.3264454545454.5 0.3528454545454.5 0.3792454545454.5 0.4064454545454.5 0.4128454545454.5 0.4792436720142.6 0.5264409982174.7 0.5528383244206.8 0.5792294117647.1 0.6198

170613700 0.6462106951871.7 0.6660

0 0.05 0.1 0.15 0.2 0.25 0.30

20000000

40000000

60000000

80000000

100000000

120000000

140000000

160000000

180000000

f(x) = NaN xGraph plot of Engineering Stress, (N/m^2) against

Engineering Strain (Aluminium)

Engineering Strain

En

gin

eeri

ng

Str

ess

0 0.1 0.2 0.3 0.4 0.5 0.6 0.70

50000000100000000150000000200000000250000000300000000350000000400000000450000000500000000

f(x) = NaN xGraph plot of Engineering Stress, N(mm^2) against En-

gineering Strain (Mild Steel)

Engineering Strain

En

gin

eeri

ng

Str

ess

Discussion

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The aim of the experiment was to carry out a uniaxial tensile test on a material to determine its

mechanical properties (yield strength, ultimate tensile strength, % elongation, ductility, modulus

of elasticity). The tensile test was carried out using the dension testing machine Before the test a

gage marks was placed on the specimen the initial gage length and diameter was measured. A

load scale to deform and fracture the specimen was selected. During the test he load was

measured and test was conducted until fracture. A tensile test, also known as a tension test, tests

a material's strength. It's a mechanical test where a pulling force is applied to a material from

both sides until the sample changes its shape or breaks. It's is a common and important test that

provides a variety of information about the material being tested, including the elongation, yield

point, tensile strength, and ultimate strength of the material. A tensile test in this experiment was

performed on a metal. The tensile strength of a sample of material describes how it reacts when

tension is applied to it. By measuring the changes in the material as tension is applied, engineers

can determine a variety of things about the material, which is helpful in determining whether the

material is a suitable choice for the application they have in mind. In addition to whether a

material changes in shape, a tensile test will also show a material's ultimate strength. The

ultimate strength refers to the maximum tensile load that the material can stand. A tension test

also uncovers the material's yield point which is the amount of tension that causes the sample to

break or fail. Tensile testing is vitally important in a number of industries, including mechanical

engineering, structural engineering and architecture. During the planning stage of a building

project, for example, these professionals normally calculate the stresses to which a building

might be subjected. To ensure a stable construction, it is then necessary to select appropriate

building materials, which will be able to withstand those stresses without breaking. The

engineering strain calculated for the specimen after testing was 0.033. The type of experiment

done does not support the constructions of a graph could not be constructed and completion of

additional calculation was not possible therefore the objective of the experiment was no met the

calculated stress was 110.3 MPa.

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Conclusion and Recommendation

In concluding the tensile test was carried out using the dension testing machine. The engineering

strain calculated for the specimen after testing was 0.033 and the calculated strain was 110.3

MPa. It is recommended that when conducting a tensile test one should get all parameters

possible to calculate the characters of the specimen. Tesile testing in summary can be used to test

specification of materials for the it to be used for suitable applications.

Reference

Czichos, Horst (2006). Springer Handbook of Materials Measurement Methods. Berlin: Springer. pp. 303–304. ISBN 978-3-540-20785-6.

John, Vernon, “Introduction to Engineering materials”, 4th ed., Palgrave Macmillan 2003

John, Vernon. Introduction to Engineering Materials, 3rd ed.(?) New York: Industrial Press,

1992. ISBN 0-8311-3043-1.

Van Vlack, L. H., Elements of Materials Science and Engineering, Addison-Wesley

Pub. Co., (Mass:1994)

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Sample Calculations

Details ALUMINUM SPECIMEN SI UNITSGauge length, l0 50.00 mm 0.050 mFinal length, l 56.00 mm 0.056 mInitial cross-sectional area, A0 78.54 mm2 0.00007854 m2

Final cross-sectional area, A 19.63 mm2 0.00001963Breaking force, L 11.92 kNYoung’s Modulus 38.5 kN/mm2

Reduction in Area 75 %Elongation 12 %

Aluminum SpecimenThe engineering stress at maximum load is:n = L / A0

Where A0: initial arean = 11920 N/0.00007854 m2 n = 151769799 Pa

The engineering strain at fracture point is:εn = (l ─ l0)/ l0

Where l: current lengthl0: initial length

εn = (0.056 ─ 0.05)/ 0.05εn = 0.12

The Young’s Modulus, En

En = Δn/(Δ εn) = Gradient from graph 1.0 (elastic region) = En = 3228 N/mm2

En = 3.288 GPa

The percentage elongation, % EL;% Elongation = [(l ─ l0)/ l0] × 100% EL = [(0.056 ─ 0.05)/ 0.05] × 100% EL = 12 %

The Percentage Reduction in Area, %RA % RA = [(A0 ─ A)/ A0] × 100% RA = [(0.00007854 ─ 0.00001963)/ 0.00007854] × 100% RA = 75.006 %

Mild Steel SpecimenThe nominal (engineering) stress at maximum load is:n = L / A0

Where A0: initial area

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n = 32680 N/0.00007854 m2 n = 416093710.21 Pa

The engineering strain at fracture point is:εn = (l ─ l0)/ l0

Where l: current lengthl0: initial length

εn = (0.0684 ─ 0.05)/ 0.05εn = 0.368

The Young’s Modulus, En

En = Δn/(Δ εn) =Gradient from Graph 1.1 (elastic region) = En = 4685.8 N/mm2

En = 4.686 GPa

The percentage elongation, % EL;% Elongation = [(l ─ l0)/ l0] × 100% EL = [(0.0684 ─ 0.05)/ 0.05] × 100% EL = 36 %

The Percentage Reduction in Area, %RA % RA = [(A0 ─ A)/ A0] × 100% RA = [(0.00007854 ─ 0.00002678)/ 0.00007854] × 100% RA = 65.902 %

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