MACROSCOPIC PROPERTIES MATERIALS

MACROSCOPIC AND STRUCTURAL PROPERTIES:

Generally a material property is a measure of its response to imposed stimuli and constraints. Response
of material can be qualitative (how the material respond) or quantitative (the magnitude of the
response). Thus material property can be re-defined as the factor which affects the response of a given
material to imposed stimuli or constrain. The elasticity, opacity, transparency, viscosity, electrical and
thermal conductivity are materials properties, these on their own are various measures of response of
different materials to stimuli in the form of stress/force, shear, and temperature gradient. A structural
property is dependent on the atomic and crystal structure of the material and is applicable to material in
which the position of the elementary particle is practically fixed.

ELASTIC AND PLASTIC DEFORMATION:

The behavior (response) of a material to applied force/stress takes the form of varying deformation.
These deformations which are due to disturbances (stresses) set up in the material are of two types:-
Elastic and plastic deformations.

A) Elastic Deformation: This is a reversible (recoverable) deformation in which the original dimensions
are recovered after externally applied stresses are removed. Elastic deformation occurs
instantaneously with the application of external stress.
B) Plastic deformation: Plastic deformation is an irreversible deformation in crystals that is caused by a
permanent set of strains macroscopically.

STRESS AND STRAIN

 Stress: The intensity of the internal force, which is the magnitude of the total force within a
section, is divided by the area of the cross-section is defined as the stress. It is given as δ= F/A
N/m2
 Strain: The change in the dimension(s) of a material in a state of stress is defined as the strain.

The mechanical behavior of materials is described by their mechanical properties which are the results
of idealized simple tests. These tests are designed to represent different types of loading condition. The
stress and strain relationship of a material under tensile loading condition is best demonstrated by
tensile test that describe the resistance of a material to slowly applied stress. The parameters that are
mostly used to describe tensile behaviors are:

Field strength, tensile strength, ductility, and the modulus of elasticity to measure stiffness of the
material.
 NORMAL STRESS AND STRAIN

A simple stress is said to be normal when the direction of the force producing the tress is
perpendicular (i.e normal) to the cross sectional area of the stressed body. Simple stresses are tensile or
compressive stress.

Tensile load causes increase in length (δ1) but decrease in cross sectional area: while
compressive load causes decrease in length but increase in cross sectional area. The ratio of the increase
or decrease in length to the original length is referred to as strain.

Mathematically, strain is expressed as

Δ = δ1

Where, δ=strain (epsilon); δ1 = change in length; 1 = original length.

Strain is a dimensionless parameter. Nevertheless, tensile strain is considered positive while

compressive strain is negative.

MODULUS OF ELASTICITY

Young’s modulus is also known as modulus of elasticity and is defined as:

The mechanical property of a material to withstand the compression or the elongation with
respect to its length

It is denoted as E or Y.

Young’s Modulus (also referred to as the Elastic Modulus or Tensile Modulus), is a measure of
mechanical properties of linear elastic solids like rods, wires, and such. Other numbers measure the
elastic properties of a material, like Bulk modulus and shear modulus, but the value of Young’s Modulus
is most commonly used. This is because it gives us information about the tensile elasticity of a material
(ability to deform along an axis).

Young’s modulus describes the relationship between stress (force per unit area) and strain
(proportional deformation in an object). The Young’s modulus is named after the British scientist
Thomas Young. A solid object deforms when a particular load is applied to it. The body regains its
original shape when the pressure is removed if the object is elastic. Many materials are not linear and
elastic beyond a small amount of deformation. The constant Young’s modulus applies only to linear
elastic substances.
 CONDUCTORS

Conductors are the materials or substances which allow electricity to flow through them. They
conduct electricity because they allow electrons to flow easily inside them from atom to atom. Also,
conductors allow the transmission of heat or light from one source to another.

Metals, humans, earth, and animals are all conductors. This is the reason we get electric shocks!
Moreover, the human body is a good conductor. So it provides a resistance-free path for the current to
flow from wire to body.

Conductors have free electrons on its surface which allow current to pass through easily. This is the
reason why conductors are able to conduct electricity.

EXAMPLES OF CONDUCTORS

 Material such as silver is the best conductor of electricity. But, it is costly and so, we don’t use
silver in industries and transmission of electricity.

 Copper, Brass, Steel, Gold, and Aluminum are good conductors of electricity. We use them
in electric circuits and systems in the form of wires.

 Mercury is an excellent liquid conductor. Thus, this material finds use in many instruments.

 Gases are not good conductors of electricity because the atoms are quite far away. Thus, they
are unable to conduct electrons.

APPLICATIONS OF CONDUCTORS:

 Mercury is a common material in thermometer to check the temperature of the body.

 Aluminum finds its use in making foils to store food. It is also used in the production of fry pans
to store heat quickly.
 Iron is a common material used in vehicle engine manufacturing to conduct heat.
 The plate of iron is made up of steel to absorb heat briskly.
 Conductors find their use in car radiators to eradicate heat away from the engine.

INSULATORS

Insulators are the materials or substances which resist or don’t allow the current to flow through them.
In general, they are solid in nature. Also, insulators are finding use in a variety of systems. As they don’t
allow the flow of heat, the property which makes insulators different from conductors is its resistivity.

Wood, cloth, glass, mica, and quartz are some good examples of insulators. Also, insulators are
protectors. They give protection against heat, sound and of course passage of electricity. Furthermore,
insulators don’t have any free electrons. It is the main reason why they don’t conduct electricity.
 EXAMPLES OF INSULATORS

 Glass is the best insulator as it has the highest resistivity.

 Plastic is a good insulator and it finds its use in making a number of things.
 Rubber is a common material used in making tyres, fire-resistant clothes and slippers. This is
because it is a very good insulator.

DIFFRENCE BETWEEN CONDUCTORS AND INSULATOR

CONDUCTORS INSULATORS
A conductor allows current to flow easily Insulators don’t allow current to flow through it.
through it
Electric charge exists on the surface of Electric charges are absent in insulator
conductors
Conductors don’t store energy when kept in a Insulators store energy when kept in a
magnetic field magnetic field
Thermal conductivity ( heat allowance) of a Thermal conductivity of an insulator is very low
conductor is very high
The resistance of a conductor is very low The resistance of insulator is very high
Copper, Aluminums, and Mercury are some Wood, paper and ceramic are some insulators
conductors
Conductors are used in making electrical Insulators are used in insulating electrical
equipment. equipment for safety purpose