PPT: Mechanical Properties of Solids

 Page 1


Mechanical 
Properties of 
Solids
Page 2


Mechanical 
Properties of 
Solids
I n t r o d u c t i o n
Solids have definite shape and size but can deform 
when force is applied
Elasticity: property of solids to return to original 
shape after force removal
Plastic deformation: when deformation becomes 
permanent
Understanding solid behavior under forces is crucial 
for engineering applications:
Applications include bridges, skyscrapers, 
machines, and prosthetic limbs
Page 3


Mechanical 
Properties of 
Solids
I n t r o d u c t i o n
Solids have definite shape and size but can deform 
when force is applied
Elasticity: property of solids to return to original 
shape after force removal
Plastic deformation: when deformation becomes 
permanent
Understanding solid behavior under forces is crucial 
for engineering applications:
Applications include bridges, skyscrapers, 
machines, and prosthetic limbs
Stress and Strain
When a solid is deformed, it develops an internal restoring force per unit area called 
stress.
Stress = Force / Area SI unit: Pascal (Pa)
There are different types of stress:
Types of Stress
Tensile/Compressive Stress: 
Causes a change in length.
à = F/A
Shearing Stress: Causes surfaces to 
slide relative to each other.
Ä = F/A
Hydraulic Stress: Acts equally in all 
directions (like in liquids).
p = F/A
Types of Strain
Strain is the relative deformation 
produced in a body. It is a 
dimensionless quantity.
Longitudinal Strain: Change in 
length/original length.
· = ?L/L
Shearing Strain: Relative 
displacement/original length.
³ = ?x/y
Volumetric Strain: Change in 
volume/original volume.
» = ?V/V
Page 4


Mechanical 
Properties of 
Solids
I n t r o d u c t i o n
Solids have definite shape and size but can deform 
when force is applied
Elasticity: property of solids to return to original 
shape after force removal
Plastic deformation: when deformation becomes 
permanent
Understanding solid behavior under forces is crucial 
for engineering applications:
Applications include bridges, skyscrapers, 
machines, and prosthetic limbs
Stress and Strain
When a solid is deformed, it develops an internal restoring force per unit area called 
stress.
Stress = Force / Area SI unit: Pascal (Pa)
There are different types of stress:
Types of Stress
Tensile/Compressive Stress: 
Causes a change in length.
à = F/A
Shearing Stress: Causes surfaces to 
slide relative to each other.
Ä = F/A
Hydraulic Stress: Acts equally in all 
directions (like in liquids).
p = F/A
Types of Strain
Strain is the relative deformation 
produced in a body. It is a 
dimensionless quantity.
Longitudinal Strain: Change in 
length/original length.
· = ?L/L
Shearing Strain: Relative 
displacement/original length.
³ = ?x/y
Volumetric Strain: Change in 
volume/original volume.
» = ?V/V
Hooke's Law
Hooke's law states that for small deformations, the stress in a material is directly proportional to 
the strain produced in it.
Stress ? Strain  or
 Stress = Modulus of Elasticity × Strain
This proportionality holds only within the elastic limit of the material. The constant of 
proportionality is called the modulus of elasticity.
Page 5


Mechanical 
Properties of 
Solids
I n t r o d u c t i o n
Solids have definite shape and size but can deform 
when force is applied
Elasticity: property of solids to return to original 
shape after force removal
Plastic deformation: when deformation becomes 
permanent
Understanding solid behavior under forces is crucial 
for engineering applications:
Applications include bridges, skyscrapers, 
machines, and prosthetic limbs
Stress and Strain
When a solid is deformed, it develops an internal restoring force per unit area called 
stress.
Stress = Force / Area SI unit: Pascal (Pa)
There are different types of stress:
Types of Stress
Tensile/Compressive Stress: 
Causes a change in length.
à = F/A
Shearing Stress: Causes surfaces to 
slide relative to each other.
Ä = F/A
Hydraulic Stress: Acts equally in all 
directions (like in liquids).
p = F/A
Types of Strain
Strain is the relative deformation 
produced in a body. It is a 
dimensionless quantity.
Longitudinal Strain: Change in 
length/original length.
· = ?L/L
Shearing Strain: Relative 
displacement/original length.
³ = ?x/y
Volumetric Strain: Change in 
volume/original volume.
» = ?V/V
Hooke's Law
Hooke's law states that for small deformations, the stress in a material is directly proportional to 
the strain produced in it.
Stress ? Strain  or
 Stress = Modulus of Elasticity × Strain
This proportionality holds only within the elastic limit of the material. The constant of 
proportionality is called the modulus of elasticity.
Stress-Strain Curve
When a wire is stretched, a graph of stress versus strain gives important 
information about the material's behaviour.
Hooke's Law Region (O to A): Stress is proportional to strain.
Non-linear Elastic Region (A to B): Elastic behaviour continues, but 
stress is no longer proportional to strain.
Yield Point (Point B): The elastic limit; beyond this, permanent 
deformation begins.
Plastic Region (B to D): Strain increases without much increase in 
stress.
Ultimate Tensile Strength (Point D): Maximum stress the material can 
bear.
Fracture Point (Point E): Where the material breaks.
Ductile materials like copper have a large plastic region, while brittle 
materials like glass break just after the elastic limit.