TEFO3
INTRODUCTION TO
TECHNOLOGY B
Mechanical Testing
Lecture 3
Recap – lecture 2
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Materials classification; and
Engineering properties :
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Mechanical
Physical
Electrical
Thermal
Chemical
Optical
Why do Mechanical Tests?
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provide
limiting
values that
a structure
can
withstand
without
failure.
Types of Mechanical Tests
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Tensile test
Hardness test
 Brinell Hardness Test
 Rockwell Hardness
Test
 Vickers Hardness Test
 Scleroscope Hardness
Test
Bend Test
Shear Test
Cupping Test
Fatigue Test
What is Tensile Testing?
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By pulling on
something, you will very
quickly determine how
the material will react to
forces being applied in
tension.
As the material is being
pulled, you will find its
strength along with how
much it will elongate.
Tensile testing
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The test is made by
gripping the ends of a
suitably prepared
standardized test
piece in a tensile test
machine and then
applying a continually
increasing uni-axial
load until such time
as failure occurs.
Standard shape tensile
specimens
Tensile curve
Tensile strength
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Tensile strength, also known as the
ultimate tensile strength, the load at
failure divided by the original cross
sectional area
Yield point
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Yield point (YP), the stress at which
deformation changes from elastic to
plastic behaviour i.e. below the yield
point unloading the specimen means
that it returns to its original length,
above the yield point permanent plastic
deformation has occurred.
Strain
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You will also be able to find the amount
of stretch or elongation the specimen
undergoes during tensile testing.
This can be expressed as an absolute
measurement in the change in length or
as a relative measurement called
"strain".
STRESS
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Stress has units of a force measure
divided by the square of a length
measure, and the average stress on a
cross-section in the tensile test is the
applied force divided by the crosssectional area.
Yield Strength
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A value called "yield strength" of a
material is defined as the stress applied
to the material at which plastic
deformation starts to occur while the
material is loaded.
Ultimate Tensile Strength
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the ultimate tensile strength (UTS) is
the maximum load the specimen
sustains during the test.
Necking
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Localized reduction of cross-sectional
area of a specimen under tensile load.
A Tensile Curve showing all
the important points.
Tensile curve
HARDNESS TESTING
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Hardness is the property of a material
that enables it to resist plastic
deformation, usually by penetration.
However, the term hardness may also
refer to resistance to bending,
scratching, abrasion or cutting.
Brinell Hardness Test
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The Brinell hardness test method consists of indenting the test material
then calculating the hardness from the diameter of the indent.
BHN = Brinell Hardness Number
F = load in kilogram force units
D = diameter of ball in mm
Di = average diameter of impression (indentation) in mm
Rockwell Hardness Test
The Rockwell hardness test method consists of indenting the test
material with a diamond cone or hardened steel ball indenter.
Vickers Hardness Test
F = Load in kgf
d = Arithmetic mean of the two
diagonals, d1 and d2 in mm
HV = Vickers hardness
When the mean diagonal of the indentation has
been determined the Vickers hardness may be
calculated from the formula, but is more convenient
to use conversion tables. The Vickers hardness
should be reported like 800 HV/10, which means a
Vickers hardness of 800, was obtained using a 10
kgf force.
The Scleroscope Hardness
Test
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The Scleroscope test consists of dropping a diamond tipped
hammer, which falls inside a glass tube under the force of its
own weight from a fixed height, onto the test specimen. The
height of the rebound travel of the hammer is measured on a
graduated scale.
The Shore Scleroscope measures hardness in terms of the
elasticity of the material and the hardness number depends on
the height to which the hammer rebounds, the harder the
material, the higher the rebound.
Advantages of this method are portability and non-marking of
the test surface.
The Scleroscope Hardness
Test
The Durometer
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The Durometer is an
instrument for measuring the
indentation hardness of rubber
and rubber-like materials.
The material is subjected to a
definite pressure applied by a
calibrated spring to an
indenter that is either a cone
or sphere and an indicating
device measures the depth of
indentation.
Bend Tests
In a bend test, a flat strap of metal is bent into a U-shape,
stretching the material on the outer surface of the "U," while
compressing the material on the inside surface. Bend testing
measures the ductility of materials.
Notches that are
perpendicular to stress
fields create localized
stress concentrations
where cracks may occur.
Shear Tests
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Shear strength testing is used to
determine the load at which a plastic or
film will yield when sheared between
two metal edges.
Shear Tests
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Shear strength testing is used to
determine the load at which a plastic or
film will yield when sheared between
two metal edges.
Creep Test
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To determine creep properties, a
material is subjected to prolonged
constant tension or compression loading
at constant elevated temperature.
Deformation is recorded at specified
time intervals and a creep vs. time
diagram is plotted.
Cupping Test
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This is a ductility
test which
provides a useful
indication of the
quality of the
sheet metals used
for deep drawing.
Cupping Test
Turn the handle
counter-clockwise
until the digital
indicator reads zero
or less.
Turn the handle
clockwise at an even
speed and observe the
coating on the test
panel, either with the
naked eye or through
the magnifier
At the first sight of
cracks in the coating,
stop turning the
handle
Read the cupping
depth of the
digital gauge
Tutorial questions
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Do Activity 3.1 in your course book for
Thursday’s tutorial.
Do Activity 3.2 in your course book for
Monday’s tutorial.