Name of the experiment:

Determination of tensile strength, elongation at break and modulus of elasticity.

Abstract:
Tensile strength is a measure of the ability of a material to withstand a longitudinal
stress, expressed as the greatest stress that the material can stand without breaking . [1] Tensile
strength is important in the use of brittle materials more than ductile materials. [2] They are
tabulated for common materials such as alloys, composite materials, ceramics, plastics, and
wood.[3] Elongation at break, also known as fracture strain, is the ratio between changed length
and initial length after breakage of the test specimen . The elongation at break is determined by
tensile testing in accordance with EN ISO 527. [4] Modulus of elasticity is the ratio of the stress
applied to a body or substance to the resulting strain within the elastic limit. [5] A stiffer material
will have a higher elastic modulus. [6ASTM D638 is the standard test method for tensile testing.
The supplied test specimen made of pure polypropylene breaks under a uniaxial load of 71N
without elongation giving a tensile strength of 2.37 N/mm2 and an infinite modulus of elasticity
ad proves it to be highly rigid material.

Introduction:

The tensile strength of a material is the maximum amount of tensile stress that it can
take before failure, such as breaking or permanent deformation. Tensile strength specifies the
point when a material goes from elastic to plastic deformation. It is expressed as the minimum
tensile stress (force per unit area) needed to split the material apart. [2 It is usually found by
performing a tensile test and recording the engineering stress versus strain. It is a destructive
test process that provides information about the tensile strength, yield strength and ductility of
a material.

There are three types of tensile strength:

 Yield strength- The stress a material can withstand without permanent deformation. For
a stable component, the yield strength of the material must be high enough to remain in
elastic deformation. When a component is made by changing its shape, then the applied
stress must be higher than the yield strength of the material.
 Ultimate strength- The maximum stress a material can withstand. The highest point of
the stress–strain curve is the ultimate strength .It is an intensive property.
 Breaking strength -The stress coordinate on the stress-strain curve at the point of
rupture . [2]

Elongation at break expresses the capability of a material to resist changes of shape

Figure: stress- strain diagram[4]

Young’s modulus or modulus of elasticity is a number that measures an object or

The procedure for measuring the static modulus of elasticity in compression is described in
ASTM C469.[9]

Ductility: Ductility is the ability of material, such as steel, to be drawn out into thin wires
or flat sheets without pulling apart or breaking. Materials that are extremely ductile can be
stretched thin without cracking and losing their strength. To measure a material's ductility, the
tester typically takes a measurement of the material's tensile strength.[10]

Stiffness: A quantitative measure of the elastic deformation is produced in a material. A

Toughness: toughness is the amount of energy that a material can absorb before
fracturing. It is the area contained in the true stress-strain curve.
Universal testing machine is used to test the tensile strength and compressive strength of

materials.

Figure: universal testing machine

Materials:
1. Test specimen
2. Universal testing machine (UTM)
3. Extensometer(if provided with UTM)
4. Slide calipers
5. Computer connection

Procedure:
1. The thickness and width of the specimen is measured by using a slide calipers.
2. The test sample is securely held by top and bottom grips attached to the tensile or
universal testing machine.
3. The grips are moved apart at a constant rate to strength the specimen.
4. The force on the specimen and its displacement is continuously monitored and plotted on
a stress-strain curve until failure. If there is a computer connections, the graph can be done
automatically.
5. The test sample is put back together after breaking to measure the final length and obtain
elongation.
6. The final area is measured by slide calipers.
 7. The tensile strength, yield strength, ductility are calculated after the specimen has broken.
8. The breaking strength can be calculated simply by observing counter for applied force at
the point of breaking.
9. Tensile and yield strength are obtained from the stress-strain curve.

Results and discussion:

Thickness of the specimen = 0.3 cm = 3 mm

So the original cross-sectional area of the specimen = (10×3) mm2

The test specimen broke suddenly without any elongation at an applied stress of 71 N.

The experiment is not done so correctly for error in equipment. For this specimen broke
without elongation.

In time of experiment some safety and precaution is maintained:

 Apron, safety goggles and shoes should be used at the time of testing, since the loose
particle may spread during the breaking specimen.
 It should be assured that the sample is held tightly by grips.
 Test machine alignment should be checked and after test electric supply should be
turned off.

Conclusion:
Tensile strength, along with elastic modulus and corrosion resistance, is an important
parameter of engineering materials that are used in structures and mechanical devices. It is also
vital for construction safety and personal safety, both during and after the building is
completed. In this experiment, the pure polyprolylene specimen breaks without any elongation
giving a breaking strength, tensile strength and yield strength of 2.37 N/mm 2. As the modulus of
elasticity is infinitive, the specimen is highly rigid. By compounding it with another material
ductility, toughness can be imparted to the material.

References:
[1] http://www.thefreedictionary.com/tensile+strength

[2] https://www.corrosionpedia.com/definition/1072/tensile-strength

[3]https://en.wikipedia.org/wiki/Ultimate_tensile_strength
 [4] http://www.ensinger-online.com/en/technical-information/properties-of-
plastics/mechanical- properties/elongation-at-break/

[5] http://www.thefreedictionary.com/modulus+of+elasticity

[6]https://en.wikipedia.org/wiki/Elastic-modulus

[7] http://composite.about.com/library/glossary/e/bldef-e1955.htm

[8]Askeland, Donald R.; Phulé, Pradeep P. (2006). The science and engineering of
materials(5th ed.). Cengage Learning. p. 198. ISBN978-0-534-55396-8.

[9]http://www.hpcbridgeviews.com/i64/Article4.asp

[10]http://www.wisegeek.org/what-is-ductility.htm