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Unit 2
Properties of Materials
Material PropertiesMaterial Properties
MechanicalMechanical
Tensile propertiesToughnessDuctilityFatigueHardnessCreep resistance
Tensile propertiesHeat distortionCompression - strengthPV LimitToughness
DimensionalDimensional
Available shapesAvailable sizesAvailable surface-textureManufacturing-tolerances
Manufacturing-tolerancesStabilityAvailable sizes
ChemicalChemical
CompositionMicrostructurePhasesGrain sizeCorrosion resistanceInclusionsCompositionFillersCrystallinityMolecular weightFlammabilitySpatial configurationChemical resistance
Pla
stic
sM
etal
s
PhysicalPhysical
Melting PointThermalMagneticElectricalOpticalAcousticGravimetricColor
Dimensional
Tensile propertiesCompression strengthFracture toughnessHardness
Tensile propertiesCompression strengthFracture toughnessCreep resistance
Available shapesAvailable sizesManufacturing-tolerancesAvailable surface-texture
Available shapesAvailable sizesManufacturing-tolerancesStability
CompositionPorosityGrain SizeCrystal structureCorrosion resistance
Composition(matrix/reinforcement)Matrix/reinforcementbondVolume fraction ofreinforcementReinforcement natureCorrosion resistance
Cer
amic
sC
omp
osit
es
Unit 2
Properties of Materials
Mechanical Properties
A Model of Mechanical Properties
Mechanical Properties
*Slow Force*
Mechanical Force
(Stress)
“INPUT”
Deformation (Strain)
Fracture
“OUTPUT”
STRENGTH
HARDNESS
STIFFNESS
DUCTILITY
Material
Mechanical Properties
Physical properties of material that determine the behaviour of a
material when it is subject to applied forces and loads
Example
• Tensile Strength
• Compressive
Strength
• Shear Strength
• Yield Strength
• Fracture Strength
• Creep
• Fatigue Strength
• Hardness
• Toughness
• Young’s Modulus
When the applied forces tends to increase the length and decrease cross-sectional area of bar.
When the applied forces tends to decrease the length and increase the cross-sectional area of bar.
Produce a rotational motion about the longitudinal axis of one end of the member relative to the other end.
Stress
Tensile Stress Compressive Stress Shear Stress
Torsional Stress
Opposing applied forces tending to cause one part of the material to slip or slide with respect to the other part.
Concept of Stress and Strain
(a) Tensile load produces an
elongation and positive linear
strain, = + ve
(b) Compressive load produces
contraction and a negative linear
strain, = - ve
(c) Shear strain, = tan = x/L
(d) Torsional deformation
produced by an applied torque,
T.
(a)
(d)
(c)
(b)
Engineering StressThe mechanical forces or energy that causes or produces deformation or fracture in a materials.
F Direct stress , = --------
Aowhich
F = load applied perpendicular to the cross section area, (in N)
A0 = original cross-sectional area before any load is applied (in
m2).
= in N/m2
Engineering StrainThe deformation of a materials subjected to mechanical energy forces
• Strain is defined as the change per unit of length in a linear dimension of the material body
0l
l
l
ll
0
0i
which l0 = original length before any load is appliedl1 = Final length l = l1 - l0 (termed as deformation / stretches / change in length).
Unit•is unitless, or you can expressed it as a percentage, in which the strain value is multiplied by 100.
Elastic Region
Plastic Region
Young’s Modulus/Modulus of Elasticity
Fracture
Ultimate Tensile Strength/Tensile Strength
Yield Strength, y
Stress, (N/mm2)
Strain, (%)
Elasticity(Area under the curve)
Proportional Limit
Yield Point(Lower Yield Point)
Upper Yield Point
Typical Stress Strain Curve
Strength
Yield Strength (Y)
Stress at which slip becomes noticeable and significant
Ultimate Tensile Strength / Tensile Strength
Maximum strength the material sustains prior to
fracture
The Effect of Alloys on The Yield Stress
Yield Stress vs the Amount and Size of the
Precipitated Particles of Niobium Carbide
The Effect of Various Solutes on the Yield Stress of
Ferrite
Strength For The Various Categories of MaterialsS
tren
gth
, N/m
2
Shear stress, The shear stress τ is defined as the shear force used to distorted or deform the object.
where
F = load or force imposed parallel to the upper and
lower faces
A0 = area parallel the applied load or force.
Unit
= in N/m2.
OA
Fτ
Modulus of Elasticity / Young Modulus
Is the measurement of stiffness of a material (Ratio of stress within
proportional limit to corresponding strain).
Toughness
A measure of the amount of energy absorbed by a material as it
fractures. Toughness is indicated by the total area under the
material’s tensile stress-strain curve.
Poisson Ratio
z
y
z
x
ε
ε
ε
εv
Axial (z) elongation (positive strain) and lateral (x and y) contractions (negative strains) in response to an imposed tensile stress.
• Poisson’s ratio for isotropic materials should be 0.25
• The maximum value for is 0.50.
• For many metals and other alloys, values of Poisson’s
ratio range between 0.25 and 0.35
• The negative sign is include in the expression so that
will always be positive, since x and y will always be
of opposite sign.
Modulus of Elasticity versus Temperatures(Tungsten, Steel and Aluminium)
Room-Temperature Elastic and Shear Moduli, and Poisson’s Ratio for Various Metal Alloys
Modulus of Elasticity Shear Modulus
Metal Alloy psi x 106 Mpa x 104 Psi x 106 Mpa x 104 Poisson’s Ratio
Aluminium 10.0 6.9 3.8 2.6 0.33Brass 14.6 10.1 5.4 3.7 0.35Copper 16.0 11.0 6.7 4.6 0.35Magnesium 6.5 4.5 2.5 1.7 0.29Nickel 30.0 20.7 11.0 7.6 0.31Steel 30.0 20.7 12.0 8.3 0.27Titanium 15.5 10.7 6.5 4.5 0.36Tungsten 59.0 40.7 23.2 16.0 0.28
Typical Mechanical Properties of Several Metals in an Annealed State, and of Commercial Purity.
MetalYield Strength
[psi (MPa)]Tensile Strength
[psi (MPa)]Ductility, % EL
(in 2 in.)Gold Nil 19,000 (130) 45Aluminium 4,000 (28) 10,000 (69) 45Copper 10,000 (69) 29,000 (200) 45Iron 19,000 (130) 38,000 (262) 45Nickel 20,000 (138) 70,000 (480) 40Titanium 35,000 (240) 48,000 (330) 30Molybdenum 82,000 (565) 95,000 (655) 35
Unit 2
Properties of Materials
Electrical Properties
Electrical Conductivity of MaterialElectrical Conductivity of Material
SemiconductorSemiconductor Insulator InsulatorConductorConductor
Example:•Metal
Example:•Silicon•Germanium•GaAs
Example:•Polymer•Ceramic
Electrical Conductivities For The Various Categories Of Materials
Type of Conductor
Conductor
• An excellent conductor of electricity is a metal
• Electrical conductor are metallic solids that have a low
electrical resistivity, ranging from approximately 1.6 x 10-8
to 1.4 x 10-6 -m at room temperature.
Semiconductor
• A substance with electrical conductivity intermediate
between these two extremes is called a semiconductor.
• The electrical resistivity of semiconductors is
intermediate between that of metals and insulators and
ranges from 10 to 10-6 at room temperature.
Insulator
• A very poor conductor of electricity is called an
insulator.
• Insulators have high resistivity, varying from 107 -m to
108 -m at room temperature.
Resistivity
• The resistivity of a material can be determined by
measuring the resistance of a sample having a length l,
and a cross-sectional area A.
• If the resistance of the sample is R, then the resistivity
of material is given by
l
RAρ
Resistivities of Typical Conductors, Semiconductors and Insulators
Material Resistivity (-m) TypeSilver 1.60 x 10-8 Metal
Copper 1.67 x 10-8 MetalGold 2.30 x 10-8 Metal
Aluminium 2.66 x 10-8 MetalGraphite 1.40 x 10-5 Semiconductor
Germanium 4.50 x 10-1 SemiconductorSilicon 2.30 x 103 Semiconductor
Diamond 5.00 x 1012 InsulatorNylon 1.00 x 1014 InsulatorMica 9.00 x 1014 Insulator
Conductivity• The ability of a material to conduct an electric current is
called its conductivity, and it is defined as the inverse of
resistivity.
• The conductivity is given by
where
l = length of wire (m)
= resistivity of wire (.m)
A = cross section area (m2)
R = resistance of wire (, ohms)
RAρ
1σ
l
Unit 2
Properties of Materials
Chemical Properties
Chemical Properties
• Chemical properties are a measure of how a material
interacts with gases, liquid, or solid environment.
Example :
• The ability of iron to resist rusting when exposed to air and
moisture
• The resistance of wood to rotting
• The ability of rubber to withstand sunlight (ultraviolet rays)
without drying and cracking.
Composition
The elemental or chemical components that make up a
material, and the relative proportions of these components.
Microstructure
The structure of polished and etched materials as revealed by
microscope magnifications greater than ten diameters;
structure includes the phases present, the morphology of the
phases, and their volume fractions.
Chemical Properties
e.g: SiO2 and GaAs etc
Crystal Structure
The ordered, repeating arrangement of atoms or molecules in
a material.
Stereospecificity
A tendency for polymers and molecular materials to form
with an ordered, spatial, three-dimensional arrangement of
monomer molecules.
Corrosion Resistance
The ability of a material to resist deterioration by, chemical
or electrochemical reaction with its environment.
Oxidation
The interaction of oxygen with elements in a material to
cause structural changes due to the movement of valence
electrons in the atoms of materials
Unit 2
Properties of Materials
Physical Properties
Physical Properties
Melting Point
The point at which a material liquefies on heating or solidifies
on cooling. Some materials have a melting range rather than
a single melting point.
Density
The mass of a material per unit volume.
Specific Gravity
The ratio of the mass or weight of a solid or liquid to the
mass or weight of an equal volume of water.
Curie Point
The temperature at which ferromagnetic materials can no
longer be magnetized by outside forces.
Unit 2
Properties of Materials
Thermal Properties
Heat TransferHeat may be transferred from one point to another by
Conduction
• The transmission of heat through substance
Convection
• The transfer of heat by the upward flow of hot air
downward flow of cold air
Radiation
• The emission of heat as electromagnetic waves or as
moving particles
Thermal Properties
Thermal Conductivity
The rate of heat flow per unit time in a homogeneous
material under steady-state conditions, per unit area, per
unit temperature gradient in a direction perpendicular to
area.
m.KW 1
T
x
At
Qk
Thermal Expansion (Coefficient of thermal expansion)
The rate at which a material elongates when heated. The
rate is expressed as a unit increase in length per unit rise in
temperature within a specified temperature range.
T
V
V
1
Heat Distortion Temperature
The temperature at which a polymer under a specified load
shows a specified amount of deflection.
Specific Heat
The ratio of the amount of heat required to raise the
temperature of a unit mass of a substance l (Celsius or
Fahrenheit) to the heat required to raise the same mass of
water 1.
Property Comparison of Engineering Materials