properties of materials

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


Mechanical Properties

A Model of Mechanical Properties


*Slow Force*

Mechanical Force

(Stress)

“INPUT”

Deformation (Strain)

Fracture

“OUTPUT”

STRENGTH

HARDNESS

STIFFNESS

DUCTILITY

Material


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


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


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


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


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

properties of materials

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