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CCB 231 Material Science For Engineers Specimen Until Deformation Causes University of Botswana

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University of Botswana

CCB 231 Material Science For Engineers Specimen Until Deformation Causes University of Botswana

This experiment was conducted so as compare the mechanical properties of aluminium and mild steel. The basics
on the operation of universal testing machine were also learnt during this experiment. The Universal Testing
Machine can be used to determine the tensile strengths of many engineering materials. The design of many
engineering structures is based on the tensile properties of the materials used. The stress- strain relationship of
various metals can be used to predict the characteristics of materials when subjected to different types of loadings.
From this experiment, it can be seen that mild steel have higher tensile and yield strength than aluminium. This
explains the wide applications of mild steel in many constructions and other engineering applications that require
high strength.
I. INTRODUCTION
For safe design of structural components in bridges, railway lines, marines ships, aircrafts, pressure vessels
etc, the tensile properties of materials used should be analyzed. Hence the tensile strength of the materials should
meet the strength requirements of the structural applications. The mechanical properties of the metals determine the
kind of engineering application to be used for. Experiments on tensile tests can be used to predict the tensile
properties and they are conducted by application of axial or longitudinal forces to a specimen with known
dimensions. [ CITATION Dav04 \l 1033 ]. These forces are applied on the specimen until deformation causes
failure. The tensile load and corresponding extensions are then recorded for calculations and determination of stressstrain relationship of the material specimen. The tensile test experiment can be used to determine other mechanical
characteristics of the specimen like yield strength, percentage elongation, and ultimate strength among others. The
original gauge lengthLo
, diameter Do
or cross sectional area also used in calculations hence should be recorded.
[ CITATION Mic13 \l 1033 ]
Aim
 To compare and contrast the tensile strengths of mild steel and aluminium specimens
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lOMoARcPSD|5960618Objectives
 To study the deformation and fracture characteristics of mild steel and aluminium when they are subjected
to uniaxial loading
 To observe the load extension and stress – strain relationships in both aluminium and mild steel
 To study the basics of uniaxial tensile testing.
A. Stress- strain relationship
Tensile loading on material causes the material to undergo deformations. The kind of deformation can either be
elastic or plastic deformation. The elastic deformation is characterised by linear relationship between the extension
and applied load. Engineering stress σ is given by the ratio of load applied to the original cross sectional area, while
engineering strain ε is given by change in length (extension) ∆ L over the original length L.[ CITATION GJa12 \l
1033 ]
Hence;
σ=
P
Ao
and (1)
ε=
∆ L
Lo
(2)
Where,
σ is engineering stress
P is the applied axial load
Ao
is the original cross sectional area
ε is the engineering strain
∆ L is the extension
Lo
is the original length
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lOMoARcPSD|5960618B. Young’s modulus
The engineering stress- strain relationship for elastic deformation is based on Hooke’s law. The gradient on
this curve gives a modulus of elasticity called The Young’s Modulus E.
E=
σ
ε
, (3)
Where:
E is Youngs modulus
σ is engineering stress and ε is the engineering strain.
In engineering applications of materials/ metals that are subjected to deflections, Young’s modulus is of critical
importance. [ CITATION Ric14 \l 1033 ]
Figure 1: stress- strain relationship under uniaxial loading. Source [ CITATION Ric14 \l 1033 ]

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CCB 231 Material Science For Engineers Specimen Until Deformation Causes University of Botswana

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