Topic 3 - Material Science
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Transcript of Topic 3 - Material Science
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TOPIC 3: MATERIAL
PROPERTIES & BEHAVIOR
PREPARED BY :
NORSHEILA BINTI BUYAMIN
PENSYARAH POLITEKNIK UNGKU OMAR
DJJ3213 MATERIAL SCIENCE
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MATERIAL PROPERTIES
(A) Physical Properties
is a characteristic that can be observed or measured without changingThe composition of the substance
Physical properties describe the substance itself Examples:
i. Changes of states
ii.Colour
iii.Mass, shape, length
iv.Magnetic properties
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(B) Thermal Properties
(C) Mechanical Properties
Thermal Conductivity A property of the material (the materials ability to transfer heat)
Thermal diffusivity The ratio of thermal conductivity to the volumetric heat capacity
of material (the ration of the materials ability to transfer heat to
its capacity to store that)
Specific heat Melting point Thermal expansion
Mechanical properties determine a materials behavior when subjected to mechanical stresses
Properties include elastic modulus, ductility, hardness, toughness, brittleness and various measures of strength.
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(D) Electrical Properties
It is well known that one of the subatomic particles of an atom is the Electron.
The electrons carry a negative charge and under certain conditions canMove from atom to atom
Examples of electrical of properties:i.Electrical conductivity measure of how well a material accommodates
the movement of an electric charge
ii. Electrical resistivity the opposition of a body or substance to the
flow of electrical current through it
iii. Temperature Coefficient of Resistivity
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MECHANICAL PROPERTIES
Strength (Kekuatan)
Is the ability of a material to withstand an applied stress without
failure or deformation.
Tensile & Compressive Strength (kN), Shear & Bending Strength, Proof Stress, etc.
^High strength double girder overhead crane having lifting capacity
up to 500ton.
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Hardness (Kekerasan) Ability of resistance to localized plastic deformation or
penetration (e.g., a small dent, wear or a scratch).
Anti scratch sapphire glass
Turning a metal rod it in a lathe by tool
bit (harder than workpiece).
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Elasticity (Keanjalan)
Elastic deformation is nonpermanent, which means that
when the applied load is released, the piece returns to its
original shape.
Modulus of elasticity (Youngs modulus, E [GN/m2])
^ Elastic bow pushes the arrow
forward.
v Fishing rods or poles
^ Elastic chest expander
^ Rat trap
> Car suspension
springs
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Plasticity (Keplastikan)
Is a permanent deformation; the object does not return to
its original shape when the stress is removed.
Plaster have highly plastic
deformations and ductile fracture.
1981 50 sen Malaysia double striking Error coin
The stamping images on coins and ornamental work
show plasticity of metal.
Permanent plastic deformation after
tube bending
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Ductility (Kemuluran)
Ability to deform plastically (elongation or bending) before
fracture under tensile force.
This property important in drawing and pressing process.
Bending a ductiles mild steel
Tensile test of an
AlMgSi alloy. The
local necking & the
cup and cone
fracture surfaces
are typical for
ductile metals.
Tensile test of a
nodular cast iron
with very low
ductility.
Aluminium Wire are made by
drawing out through a die hole.
Handmade aluminium wire
bicycle, art scale model.
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Toughness (Keliatan)
Ability of a material to prevent impact load without
fracture.
Automobiles Bumpers are designed
to allow car to sustain an impact
without damage to the vehicle's
safety systems
Motocycle helmet able to reduce impact force to
prevent injury to the occupant.
High toughness torque wrench is
used to torque the bolts/nuts during
installing wheels.
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Brittleness (Kerapuhan)
The ability of the materials to break/fracture without a
permanent deformed when a tension force is applied.
Brittle fracture of metal
Brittle fracture of glass
brittle fracture and stress-
corrosion cracking of
steel pipe.
Brittle fracture of a hollow stone sculpture.
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MATERIAL BEHAVIOURS
(A) Creep When a metal or an alloy is under a constant load or stress, it may
undergo progressive
plastic deformation over a period of time. This time dependent strain
called creep.
For example, an engineer selecting an alloy for the turbine blades of a gas turbine engine must choose an alloy with a very low creep rate
so that the blades can remain for in service for a long period of time
before having of replaced.
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A typical creep curve for a metal. The curve represents the time versus strain
behavior of a metal or alloy under a constant load at constant temperature.
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(B) Fatigue
In many types of service applications metal parts subjected to repetitive or cyclic stresses will fail due to fatigue loading at a much
lower stress than that which the part can withstand under the
application of a single static stress.
These failures that occur under repeated or cyclic stressing are called fatigue failure.
Example: machine parts in which fatigue failures are moving parts such as shafts, connecting rods and gears.
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Schematic diagram of an R.R. Moore reversed-bending fatigue machine
Stress versus number of cycles (SN) curve for fatigue failure
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(C) Fracture
One of the important and practical aspects of materials selection in the design, development and production of the new components is
the possibility of failure of the component under normal operation.
Failure can defined as the inability of the material or a component to: Perform the intended function Meet performance criteria although it may still be operational Perform safely and reliably even after deterioration
Yielding, wear, buckling (elastic instability), corrosion and fracture are examples of situations in which a component has failed.
Fracture is separation of a solid under stress into two or more parts. In general metal fractures can be classified as ductile or brittle, but a
fracture can be a mixture of the two.
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i. Ductile Fracture
Occur after extensive plastic deformation and is characterized by slow crack propagation
i. Brittle Fracture
Proceed along characterized by crystallographic planes called cleavage planes and has rapid crack propagation