Physical Properties of Materials

8/4/2019 Physical Properties of Materials

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PHYSICAL PROPERTIES OF

MATERIALS

STRUCTUREAtom is the smallest particle of an element which may or may

not have independent existence. If they are not independent, then two or

more atoms make a building block of the material, named as molecules.

Solids on the basis of the arrangement of the atoms or

molecules, are being classified mainly into two types:

Crystalline Solids

Amorphous Solids

CRYSTALLINE SOLIDS

Solids, in which atoms or molecules are arranged in a

definite 3-D pattern, are called crystalline solids.

AMORPHOUS SOLIDS

In these solids, atoms do not have any regular

arrangement.

ENGINEERING MANUFACTURING

MATERIALS

From crystalline solids, mainly we are concerned with;

1. METALS

From amorphous solids,

GLASS, PLASTICS, RUBBER, POLYMERS AND CERAMICS are most of concern.

IMPORTANCE

Every material has its own importance according to the

manufacturing requirement as metals are very soft, usually when are in pure

form but can be hardened according to the requirement by mixing the other


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metals, making alloys. Ceramics are highly electrical insulators and highly

resistive to heat conduction. Polymers are flexible and highly resistive to

corrosion. They are also good in their strength.

2. STRUCTURE AND SHAPE

Structure of a material depends that which kind of solid that. If the

material is crystalline, then their shape will be definite. And if solids will be of

type amorphous, arrangement of atoms or molecules will not be regular in

the structure and consequently shape would not be regular.

IMPORTANCE

Crystalline solids have sharp melting points and they do

break along definite planes. While amorphous solids do not have sharp

melting points. That is why glass can be soften over a range of temperature.

So according to the requirement we select a material for our purpose.

3. DENSITY

Mass of the material divided by its volume is called Density of the

material.

Solids have more density than to the liquids and liquids have more

density to the gases.

4. MELTING POINTThe temperature at which a substance starts deforming

(structural failure) at 1 atm pressure is called the melting point of that

material.

IMPORTANCE

With this information, one can estimate the environment with

which the material can with stand.

5. BOILING POINT

The temperature at which a material (liquid) starts

converting into gaseous state at sea level (1 atm) pressure is called Boiling

point of that material (liquid).

IMPORTANCE


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This factor is important in determining the fluidity of a fluid

which is an important feature in manufacturing processes. OR

Temperature at which the vapour pressure of a liquid

becomes equal to the external pressure, is called Boiling point of the liquid.

CHEMICAL AND ELECTRICAL

PROPERTIES

1. METALS

Elements which have a tendency to form +ve ions by loosing

electrons are termed as metals.

Here we will discuss some chemical properties of metals.

2.ATOMIC RADIUS

The half of the distance between the centers of two

adjacent atoms, is termed as Atomic Radius.

3.ATOMIC NUMBER

Number of electrons in the valence shell or number of

protons in the nucleus is termed as Atomic Number.

4.ATOMIC WEIGHT

Total number of all protons and electrons in the

nucleus is called the Atomic Weight of the element.

5.METALLIC CONDUCTION

Most metals are of conductors of electricity

because of the availability of free electrons through out the metallic lattice.

This property is called Metallic Conduction.

6.BOND ENERGY

Energy required to break all bonds in one mole of the

substance.


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7. VALENCY

Tendency of a substance to attract shared pair of electrons

towards itself.

8. IONIZATION ENERGY

Minimum energy required to remove most loosely bound

electron from gaseous atom.

9. VAPOUR PRESSURE

Pressure exerted by the vapors of a liquid in

equilibrium with the liquid at a given temperature.

THERMAL PROPERTIES

Definition

These are the properties of the material, depends upon the

temperature of the environment in which the material is being placed.

Some of the basic thermal properties of the materials are

discussed as follows:

a. Specific Heat

b. Thermal Conductivity

c. Thermal Expansion

1.SPECIFIC HEAT

The specific heat or heat capacity of a material is a

amount of energy that must be given or extracted to produce a change of 1

degree in temperature.

IMPORTANCE

The change in temperature is an important property for the

processes in which heating or cooling take place such as casting, molding

etc. Also we control the brittleness of the material by increasing or

decreasing the time of cooling after melting the metal for molding.


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2. THERMAL CONDUCTIVITY

It measures the rate at which heat can be

transported or conducted through a material.

IMPORTANCE

Thermal conductivity is directly proportional to the electrical

conductivity. So with the help of this property we can tell that which elements

(materials) are good conductors to electricity by seeing their thermal

conductivity.

3. THERMAL EXPANSION

Materials mostly expand on heating and contract on cooling.

But how much a material will expand or contract on heating or cooling,depends on the type of material.

IMPORTANCE

Usually there is a difference between environment where a

part of machine is developed and the environment where it has to be used.

So by the information about the thermal expansion of the materials, we will

choose such a material which will be suitable for the place where it has to be

used.

MECHNICAL PROPERTIES OF

MATERIALS

1. STRENGTH

Strength of a material can be defined as the resistance of the

material to the maximum amount of various loads which the material can be

sustained.

EXPLANATION:

Materials or metals behave differently under different load

conditions. Load can be compressive, tensile or torsion. Strength can be

measured by different tests. Every material has different atomic structure

that is why behavior towards different loads is different.


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IMPORTANCE:

For a mechanical purpose, we examine the strength of a

material before selecting it to make it in our use for a particular purpose. For

engineering application point of view, firstly we see the part which is to be

produced, where it has to be used, what the stresses which it has to bear are

and what the conditions of environment (e.g. temperature) are where it has

to be fitted. Then accordingly we see and select the suitable material.

2. ELASTICITY

It defines the limit of the stress till which if we applied

force(stress) and then if we remove the stress, material will come to its

original condition.

EXPLANATION:The maximum amount of load which if we applied and later

removed without leaving the material permanently deformed is known as

Elastic Limit. In this way the elements having high value of elastic limit can

be chosen for the areas where tensile loads are applied. So by looking the

environmental conditions we choose a material for a specific purpose.

3. PLASTICITY

After the elastic limit, the graph of Stress Vs Strain never

remains straight. Here what happens is, after removing the load, strains are

not completely recoverable and some of the permanent deformation

developed in the material, although the strain is being produced by applying

stress by Hooks Law is not satisfied anymore. This behavior of the material is

called Plasticity.

IMPORTANCE:

In some of the materials, it is useful because it helps to

shape the required product with the raw materials, such as plastic products.

Also plasticity helps us to predict the max allowable stress for a materialbecause after that elastic limit will finish and a permanent deformation will

occur in the material.

4. DUCTILITY


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After the lower yielding point, strain increases remarkably even

with a minor increase in the stress. This ability of a material to produce large

strain (plasticity) or plastic deformation is called Ductility.

Materials having high ductility are called ductile materials.

IMPORTANCE:

Ductile materials are chosen where flexibility is required.

Machines where shocks are continuous, if machine bed will not be flexible,

then it will be broken.

5. MALLEABILITY

Materials ability to be hammered out into thin sheets is

called Malleability.

EXAMPLE:

Lead is a good example of malleable material.

IMPORTANCE:

Malleable materials are important where metal covering is

required on a comparatively larger area. So there we use metal sheets. Also

corners and joints are produced with malleable materials.

6. BRITTLENESS

Brittle materials are those which show comparatively small

extensions to fracture in such a way that plastic region of graph (stress Vs

strain) becomes very small.

EXPLANATION:

In brittle materials, in the tensile test curve, the partially

plastic behavior of the materials is very less. So they reach to the fracture

point very soon. These types of materials are used where no flexibility is

required.

7. STIFFNESS

Stiffness of a material defines its resistance to deformation

below the elastic limit


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EXPLANATION:

Here important point which to be noted is that ,stiffness is

being measured just in the elastic region where Hooks Law is applicable .

Here stiffness E is the slope of the line

E=stress/strain

Steeper will be the line, the more will be slope and hence

stiffness will be more.

8. TOUGHNESS

When a metal combines a high elastic limit with good

ductility, the metal is said to be tough.

EXPLANATION:

From definition, we can check that toughness is

accompanying good elastic limit with a high value of ductility. It means the

materials having good yield strength (e.g) cold worked steel alone or having

good ductility (lead) alone are not tough. Just those materials having both

characteristics called tough.

EXAMPLE: Low-Carbon Steel

IMPORTANCE:

Toughness can also be defined as the ability of a material to

withstand cracks. Means the ductility of the material bears the stress and

avoid the transfer of cracks due to stresses.

10. HARDNESS

Hardness of a material is the ability of the material to resist

indentation, scratch and nick on the surface.

EXPLANATION:

As hardness is also an ability to resist stresses producing

indentation so it is closely associated with stiffness and so with the elastic

limit of a metal.


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11. CREEP

It is a long term effect of elevated temperature on a material.

OR

Defects or changing produced in a material due to its placement

for a long time in an elevated temperature environment is called CREEP.

EXPLANATION:

Let if we apply a tensile load with an object in an elevated

temperature for a long time, the object will elongate continuously until

rupture occurs. Although the applied tensile load is less than the yield

strength of the material at the temperature of testing.

IMPORTANCE:

The rate of elongation is although very small, but this

consideration is very important in designing turbines, power plants and

pressure vessels which have to be operated under high temperatures for a

long period; and mostly these types of failures produce in turbine blades,

nuclear reactors, furnaces, rocket motors etc.

12. FATIGUE:

Fatigue is the failure of a material under fluctuating stresses or

forces.

EXPLANATION:

Fatigue is the structural failure causes due to the fluctuating

force each of which is considered to produce a little amount of plastic

deformation. Fatigue is a very important phenomenon for the components

subjected to repeating and rapidly fluctuating loads.

EXAMPLES:


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Examples of the components facing fatigue are air craft

components, turbine blades and vehicle suspensions.

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Physical Properties of Materials