Short Notes: Structure and Properties of Engineering Materials | Short Notes for Mechanical Engineering PDF Download

 Page 1


Structure and Properties of Engineering Materials  
Structure of Materials
The structure of materials can be discussed on different levels (scales) ranging 
from the human scale to the atomic scale: •
• Human scale - on the order of 1 meter This is also called macroscopic scale 
because structure on this level is observable with the human eye.
• Mill scale - on the order of 10"3 meter
• Microscale - on the order of 10'6 meter Milliscale and microscale are also 
called microscopic scale because structure on this level is observable with a 
microscope.
• Nanoscale - on the order of 10"9 meter, nowadays, this is also observable 
with a microscope.
• Atomic-scale - on the order of 10"1 0 meter 
Material Properties
• Material properties are the inherent characteristics of a material. These can 
be described qualitatively and quantitatively.
• Material properties fit into six broad categories bases on the type of stimulus:
° Mechanical properties - measures the response to a load (force) (e.g. 
tensile strength, elastic modulus)
° Electrical properties - measures the response to an electric field (e.g. 
conductivity)
° Thermal properties - measures the response to heat (e.g. melting 
temperature)
Page 2


Structure and Properties of Engineering Materials  
Structure of Materials
The structure of materials can be discussed on different levels (scales) ranging 
from the human scale to the atomic scale: •
• Human scale - on the order of 1 meter This is also called macroscopic scale 
because structure on this level is observable with the human eye.
• Mill scale - on the order of 10"3 meter
• Microscale - on the order of 10'6 meter Milliscale and microscale are also 
called microscopic scale because structure on this level is observable with a 
microscope.
• Nanoscale - on the order of 10"9 meter, nowadays, this is also observable 
with a microscope.
• Atomic-scale - on the order of 10"1 0 meter 
Material Properties
• Material properties are the inherent characteristics of a material. These can 
be described qualitatively and quantitatively.
• Material properties fit into six broad categories bases on the type of stimulus:
° Mechanical properties - measures the response to a load (force) (e.g. 
tensile strength, elastic modulus)
° Electrical properties - measures the response to an electric field (e.g. 
conductivity)
° Thermal properties - measures the response to heat (e.g. melting 
temperature)
° Magnetic properties - measures the response to a magnetic field (e.g. 
permeability)
° Optical properties - measures the response to electromagnetic or light 
radiation (e.g. index of refraction)
° Deteriorative properties - measures the response to environmental 
factors including moisture, oxygen, uv radiation.
Crystal Structure of Materials
• The crystal structure is defined as the arrangement of the crystal within 
metals. When metals solidify from molten state, the atoms arrange 
themselves into various orderly configurations called crystal.
There are seven basic crystal structures, they are given below:
Crystal
system
R elation
betw een
prim itives
Interface
A ngles
Exam ples
Cubic a - b= c a= p= y= W f Fe.Al.Cu
Tetragonal a= p= y= 9ff
Sn. SO,
O rthogonal a=^b=^c
a= p= y= 9ff KNOs Ba.S04
Hexagonal a = b^c
a= p= 90" 7=120"
SiO^.AgCI.Zn
Rhombohedral a = b=c
a=p=j?±9 0"
CaS04.CaC03
Monoclinic a ^ b ^ c
a= p= 90" ^ 7
FeSOr NaSOA
Friclinic a ^ b ^ c
90"
CiiSOA . K2 Cr2 01
• There relatively simple crystal structures are found for most of the common 
metals i.e., SSC, BCC and FCC are discussed below.
Simple Cubic Cell (SCC)
• In this arrangement, atoms are present at each corner of the cell and their 
centres coincide with each corner.
Simple cubic cell structure
Page 3


Structure and Properties of Engineering Materials  
Structure of Materials
The structure of materials can be discussed on different levels (scales) ranging 
from the human scale to the atomic scale: •
• Human scale - on the order of 1 meter This is also called macroscopic scale 
because structure on this level is observable with the human eye.
• Mill scale - on the order of 10"3 meter
• Microscale - on the order of 10'6 meter Milliscale and microscale are also 
called microscopic scale because structure on this level is observable with a 
microscope.
• Nanoscale - on the order of 10"9 meter, nowadays, this is also observable 
with a microscope.
• Atomic-scale - on the order of 10"1 0 meter 
Material Properties
• Material properties are the inherent characteristics of a material. These can 
be described qualitatively and quantitatively.
• Material properties fit into six broad categories bases on the type of stimulus:
° Mechanical properties - measures the response to a load (force) (e.g. 
tensile strength, elastic modulus)
° Electrical properties - measures the response to an electric field (e.g. 
conductivity)
° Thermal properties - measures the response to heat (e.g. melting 
temperature)
° Magnetic properties - measures the response to a magnetic field (e.g. 
permeability)
° Optical properties - measures the response to electromagnetic or light 
radiation (e.g. index of refraction)
° Deteriorative properties - measures the response to environmental 
factors including moisture, oxygen, uv radiation.
Crystal Structure of Materials
• The crystal structure is defined as the arrangement of the crystal within 
metals. When metals solidify from molten state, the atoms arrange 
themselves into various orderly configurations called crystal.
There are seven basic crystal structures, they are given below:
Crystal
system
R elation
betw een
prim itives
Interface
A ngles
Exam ples
Cubic a - b= c a= p= y= W f Fe.Al.Cu
Tetragonal a= p= y= 9ff
Sn. SO,
O rthogonal a=^b=^c
a= p= y= 9ff KNOs Ba.S04
Hexagonal a = b^c
a= p= 90" 7=120"
SiO^.AgCI.Zn
Rhombohedral a = b=c
a=p=j?±9 0"
CaS04.CaC03
Monoclinic a ^ b ^ c
a= p= 90" ^ 7
FeSOr NaSOA
Friclinic a ^ b ^ c
90"
CiiSOA . K2 Cr2 01
• There relatively simple crystal structures are found for most of the common 
metals i.e., SSC, BCC and FCC are discussed below.
Simple Cubic Cell (SCC)
• In this arrangement, atoms are present at each corner of the cell and their 
centres coincide with each corner.
Simple cubic cell structure
Atomic radius of SCC 
So,
- th
S
part of the atom is present in the atom,
r + r = a
Where r = Atomic radius 
a = Lattice constant.
The total number of atoms present in crystal structure,
n = - x 8 = 1 
8
Atomic Packing Factor (APF):
_ Volume of atomsinacell * •
Volume of unit cell
4-ntf
8 x 3 x c r5 
7T_ 3.14 
~ 6 ~ 6 
= 0.52
• Percentage APF = 52%
• Percentage of voids = 100 - 52 = 48%
° In the crystal structure, the arrangement of the atoms in the crystal is 
called crystalline structure.
° The lattice structure of a particular metal is shown by the smallest group 
of atoms and known as a unit cell.
Body-Centered Cubic (BCC) Structure
• In this, arrangement, an atom is present at the centre of the crystal and each 
corner is a centre of an atom. Total effective number of atoms present in the 
crystal
= 1- 8 x -
8
= 1 + 1 = 2
Page 4


Structure and Properties of Engineering Materials  
Structure of Materials
The structure of materials can be discussed on different levels (scales) ranging 
from the human scale to the atomic scale: •
• Human scale - on the order of 1 meter This is also called macroscopic scale 
because structure on this level is observable with the human eye.
• Mill scale - on the order of 10"3 meter
• Microscale - on the order of 10'6 meter Milliscale and microscale are also 
called microscopic scale because structure on this level is observable with a 
microscope.
• Nanoscale - on the order of 10"9 meter, nowadays, this is also observable 
with a microscope.
• Atomic-scale - on the order of 10"1 0 meter 
Material Properties
• Material properties are the inherent characteristics of a material. These can 
be described qualitatively and quantitatively.
• Material properties fit into six broad categories bases on the type of stimulus:
° Mechanical properties - measures the response to a load (force) (e.g. 
tensile strength, elastic modulus)
° Electrical properties - measures the response to an electric field (e.g. 
conductivity)
° Thermal properties - measures the response to heat (e.g. melting 
temperature)
° Magnetic properties - measures the response to a magnetic field (e.g. 
permeability)
° Optical properties - measures the response to electromagnetic or light 
radiation (e.g. index of refraction)
° Deteriorative properties - measures the response to environmental 
factors including moisture, oxygen, uv radiation.
Crystal Structure of Materials
• The crystal structure is defined as the arrangement of the crystal within 
metals. When metals solidify from molten state, the atoms arrange 
themselves into various orderly configurations called crystal.
There are seven basic crystal structures, they are given below:
Crystal
system
R elation
betw een
prim itives
Interface
A ngles
Exam ples
Cubic a - b= c a= p= y= W f Fe.Al.Cu
Tetragonal a= p= y= 9ff
Sn. SO,
O rthogonal a=^b=^c
a= p= y= 9ff KNOs Ba.S04
Hexagonal a = b^c
a= p= 90" 7=120"
SiO^.AgCI.Zn
Rhombohedral a = b=c
a=p=j?±9 0"
CaS04.CaC03
Monoclinic a ^ b ^ c
a= p= 90" ^ 7
FeSOr NaSOA
Friclinic a ^ b ^ c
90"
CiiSOA . K2 Cr2 01
• There relatively simple crystal structures are found for most of the common 
metals i.e., SSC, BCC and FCC are discussed below.
Simple Cubic Cell (SCC)
• In this arrangement, atoms are present at each corner of the cell and their 
centres coincide with each corner.
Simple cubic cell structure
Atomic radius of SCC 
So,
- th
S
part of the atom is present in the atom,
r + r = a
Where r = Atomic radius 
a = Lattice constant.
The total number of atoms present in crystal structure,
n = - x 8 = 1 
8
Atomic Packing Factor (APF):
_ Volume of atomsinacell * •
Volume of unit cell
4-ntf
8 x 3 x c r5 
7T_ 3.14 
~ 6 ~ 6 
= 0.52
• Percentage APF = 52%
• Percentage of voids = 100 - 52 = 48%
° In the crystal structure, the arrangement of the atoms in the crystal is 
called crystalline structure.
° The lattice structure of a particular metal is shown by the smallest group 
of atoms and known as a unit cell.
Body-Centered Cubic (BCC) Structure
• In this, arrangement, an atom is present at the centre of the crystal and each 
corner is a centre of an atom. Total effective number of atoms present in the 
crystal
= 1- 8 x -
8
= 1 + 1 = 2
I
Body centred cubic 
structure
• Atomic Packing Factor (APF)
7 :^ 3 3.14x1.732
= 0.68 V r =
• Percentage APF = 68%
• Percentage of voids = 100 - 68 = 32%
Face Centred Crystal (FCC): In this arrangement, each face has an atom and 
corners are also occupied by atoms.
• Total effective number of atoms in cell
= 8 x - + 6 x - + 1 + 3 = 4 
8 2
a
• Atomic Packing Factor (APF)
4 ,
n x — - r 
3
ct
_ 1 6 t t 
~ 16 x 3^2 
3.14
~ 3 x 1.414 
= 0.74
Page 5


Structure and Properties of Engineering Materials  
Structure of Materials
The structure of materials can be discussed on different levels (scales) ranging 
from the human scale to the atomic scale: •
• Human scale - on the order of 1 meter This is also called macroscopic scale 
because structure on this level is observable with the human eye.
• Mill scale - on the order of 10"3 meter
• Microscale - on the order of 10'6 meter Milliscale and microscale are also 
called microscopic scale because structure on this level is observable with a 
microscope.
• Nanoscale - on the order of 10"9 meter, nowadays, this is also observable 
with a microscope.
• Atomic-scale - on the order of 10"1 0 meter 
Material Properties
• Material properties are the inherent characteristics of a material. These can 
be described qualitatively and quantitatively.
• Material properties fit into six broad categories bases on the type of stimulus:
° Mechanical properties - measures the response to a load (force) (e.g. 
tensile strength, elastic modulus)
° Electrical properties - measures the response to an electric field (e.g. 
conductivity)
° Thermal properties - measures the response to heat (e.g. melting 
temperature)
° Magnetic properties - measures the response to a magnetic field (e.g. 
permeability)
° Optical properties - measures the response to electromagnetic or light 
radiation (e.g. index of refraction)
° Deteriorative properties - measures the response to environmental 
factors including moisture, oxygen, uv radiation.
Crystal Structure of Materials
• The crystal structure is defined as the arrangement of the crystal within 
metals. When metals solidify from molten state, the atoms arrange 
themselves into various orderly configurations called crystal.
There are seven basic crystal structures, they are given below:
Crystal
system
R elation
betw een
prim itives
Interface
A ngles
Exam ples
Cubic a - b= c a= p= y= W f Fe.Al.Cu
Tetragonal a= p= y= 9ff
Sn. SO,
O rthogonal a=^b=^c
a= p= y= 9ff KNOs Ba.S04
Hexagonal a = b^c
a= p= 90" 7=120"
SiO^.AgCI.Zn
Rhombohedral a = b=c
a=p=j?±9 0"
CaS04.CaC03
Monoclinic a ^ b ^ c
a= p= 90" ^ 7
FeSOr NaSOA
Friclinic a ^ b ^ c
90"
CiiSOA . K2 Cr2 01
• There relatively simple crystal structures are found for most of the common 
metals i.e., SSC, BCC and FCC are discussed below.
Simple Cubic Cell (SCC)
• In this arrangement, atoms are present at each corner of the cell and their 
centres coincide with each corner.
Simple cubic cell structure
Atomic radius of SCC 
So,
- th
S
part of the atom is present in the atom,
r + r = a
Where r = Atomic radius 
a = Lattice constant.
The total number of atoms present in crystal structure,
n = - x 8 = 1 
8
Atomic Packing Factor (APF):
_ Volume of atomsinacell * •
Volume of unit cell
4-ntf
8 x 3 x c r5 
7T_ 3.14 
~ 6 ~ 6 
= 0.52
• Percentage APF = 52%
• Percentage of voids = 100 - 52 = 48%
° In the crystal structure, the arrangement of the atoms in the crystal is 
called crystalline structure.
° The lattice structure of a particular metal is shown by the smallest group 
of atoms and known as a unit cell.
Body-Centered Cubic (BCC) Structure
• In this, arrangement, an atom is present at the centre of the crystal and each 
corner is a centre of an atom. Total effective number of atoms present in the 
crystal
= 1- 8 x -
8
= 1 + 1 = 2
I
Body centred cubic 
structure
• Atomic Packing Factor (APF)
7 :^ 3 3.14x1.732
= 0.68 V r =
• Percentage APF = 68%
• Percentage of voids = 100 - 68 = 32%
Face Centred Crystal (FCC): In this arrangement, each face has an atom and 
corners are also occupied by atoms.
• Total effective number of atoms in cell
= 8 x - + 6 x - + 1 + 3 = 4 
8 2
a
• Atomic Packing Factor (APF)
4 ,
n x — - r 
3
ct
_ 1 6 t t 
~ 16 x 3^2 
3.14
~ 3 x 1.414 
= 0.74
Atomic Packing Factor 
(APF) calculation
Percentage APF = 74%
Percentage of voids = 100 -7 4 = 26%
Material Properties:
• Poisson's Ratio
° When a material is stretched in one direction it contracts in the lateral 
directions. The resulting longitudinal and lateral strains occur in a fixed 
ratio known as Poisson's ratio.
The value of Poisson's ratio for a given material may be determined from 
a simple tension test as:
p
., _ _ lo u r a :
p
o The minus sign recognizes that the two strains always have opposite 
signs.
° This simple definition can be used to calculate the value of Poisson’s 
ratio only for a uniaxial stress state with the material still in the linear 
region where a = E e. In multidimensional stress states both strains are 
effected by stress induced strains in the other direction.
• Generalized Hooke's Law: Three-dimensional stress state.
These relationships are valid within the linear region of the materials stress-strain 
response.
G is the modulus of rigidity (shearing modulus of elasticity)
G , E , and v are related by the formula:
G =
E
2(1 + 1 /)
Plane stress state: oz = tx z = T yz = 0
*x= 2 \ a * - v* , i
o . =
1 1 - , -
+ » « , )
*.V= £( " M
a. =
1- v
tt( ef + vsx)