PPT: Stress & Strain

 Page 1


TOPICS
• Topic cover
– Stress and strain
• Introduction to stress and strain, stress strain diagram
• Elasticity and plasticity and Hooke’s law
• Shear Stress and Shear strain
• Load and stress limit
• Axial force and deflection of body
– Torsion
• Introduction, round bar torsion, non-uniform torsion.
• Relation between Young’s Modulus E, ? and G
• Power transmission on round bar
Page 2


TOPICS
• Topic cover
– Stress and strain
• Introduction to stress and strain, stress strain diagram
• Elasticity and plasticity and Hooke’s law
• Shear Stress and Shear strain
• Load and stress limit
• Axial force and deflection of body
– Torsion
• Introduction, round bar torsion, non-uniform torsion.
• Relation between Young’s Modulus E, ? and G
• Power transmission on round bar
Stress and strain
DIRECT STRESS
? When a force is applied to an elastic body, the body deforms. The way in 
which the body deforms depends upon the type of force applied to it.
Compression force makes the body shorter.
A tensile force makes the body longer
?
Page 3


TOPICS
• Topic cover
– Stress and strain
• Introduction to stress and strain, stress strain diagram
• Elasticity and plasticity and Hooke’s law
• Shear Stress and Shear strain
• Load and stress limit
• Axial force and deflection of body
– Torsion
• Introduction, round bar torsion, non-uniform torsion.
• Relation between Young’s Modulus E, ? and G
• Power transmission on round bar
Stress and strain
DIRECT STRESS
? When a force is applied to an elastic body, the body deforms. The way in 
which the body deforms depends upon the type of force applied to it.
Compression force makes the body shorter.
A tensile force makes the body longer
?
A
F
Area
Force
Stress ? ? ? ?
2
/m N
Tensile and compressive forces are called DIRECT FORCES
Stress is the force per unit area upon which it acts.
….. Unit is Pascal (Pa) or 
Note: Most of engineering fields used kPa, MPa, GPa.
( Simbol – Sigma)
Page 4


TOPICS
• Topic cover
– Stress and strain
• Introduction to stress and strain, stress strain diagram
• Elasticity and plasticity and Hooke’s law
• Shear Stress and Shear strain
• Load and stress limit
• Axial force and deflection of body
– Torsion
• Introduction, round bar torsion, non-uniform torsion.
• Relation between Young’s Modulus E, ? and G
• Power transmission on round bar
Stress and strain
DIRECT STRESS
? When a force is applied to an elastic body, the body deforms. The way in 
which the body deforms depends upon the type of force applied to it.
Compression force makes the body shorter.
A tensile force makes the body longer
?
A
F
Area
Force
Stress ? ? ? ?
2
/m N
Tensile and compressive forces are called DIRECT FORCES
Stress is the force per unit area upon which it acts.
….. Unit is Pascal (Pa) or 
Note: Most of engineering fields used kPa, MPa, GPa.
( Simbol – Sigma)
?
L
x
Strain ? ? ?
?
DIRECT STRAIN , 
In each case, a force F produces a deformation x. In engineering, we 
usually change this force into stress and the deformation into strain 
and we define these as follows:
Strain is the deformation per unit of the original length.
The 
symbol
Strain has no unit’s since it is a ratio of length to length. Most 
engineering materials do not stretch very mush before they become 
damages, so strain values are very small figures. It is quite normal to 
change small numbers in to the exponent for 10
-6
( micro strain).
called EPSILON
Page 5


TOPICS
• Topic cover
– Stress and strain
• Introduction to stress and strain, stress strain diagram
• Elasticity and plasticity and Hooke’s law
• Shear Stress and Shear strain
• Load and stress limit
• Axial force and deflection of body
– Torsion
• Introduction, round bar torsion, non-uniform torsion.
• Relation between Young’s Modulus E, ? and G
• Power transmission on round bar
Stress and strain
DIRECT STRESS
? When a force is applied to an elastic body, the body deforms. The way in 
which the body deforms depends upon the type of force applied to it.
Compression force makes the body shorter.
A tensile force makes the body longer
?
A
F
Area
Force
Stress ? ? ? ?
2
/m N
Tensile and compressive forces are called DIRECT FORCES
Stress is the force per unit area upon which it acts.
….. Unit is Pascal (Pa) or 
Note: Most of engineering fields used kPa, MPa, GPa.
( Simbol – Sigma)
?
L
x
Strain ? ? ?
?
DIRECT STRAIN , 
In each case, a force F produces a deformation x. In engineering, we 
usually change this force into stress and the deformation into strain 
and we define these as follows:
Strain is the deformation per unit of the original length.
The 
symbol
Strain has no unit’s since it is a ratio of length to length. Most 
engineering materials do not stretch very mush before they become 
damages, so strain values are very small figures. It is quite normal to 
change small numbers in to the exponent for 10
-6
( micro strain).
called EPSILON
MODULUS OF ELASTICITY (E)
•Elastic materials always spring back into shape when released. 
They also obey HOOKE’s LAW. 
•This is the law of spring which states that deformation is directly 
proportional to the force. F/x = stiffness = kN/m
•The stiffness is different for the different material and different sizes of the 
material. We may eliminate the size by using stress and strain instead of 
force and deformation:
•If F and x is refer to the direct stress and strain , then 
A F ? ?
L x ? ?
L
A
x
F
?
?
?
?
?
?
Ax
FL
hence and