When we apply an external force on a body, it tends to
undergo deformation. The body will resist the force. The
internal resisting force is equal and opposite of the
external applied force. This internal resistance is known as
stress. So a stress can be defined as
The internal resistance offered by a body per unit area of
the cross section is known as stress.
Stress, σ = P/A
Where P
represents the applied force and A represents the externally
applied force.
In SI
units the stress is expressed as N/mm^{2} or N/m^{2}.
N/m^{2
}is also called Pascal (pa).
Types
of stresses
1.
Direct stress
2.
Shear stress or Tangential stress
3.
Bending stress
4.
Torsional stress
5.
Thermal stress
Direct
Stress:
The
direct stress acts perpendicular to the cross section of a
body. It can be either Tensile or Compressive.
Tensile
stress – When two equal and opposite forces are applied to a
body and the body tends to increase in length is known as
tensile stress.
σ_{tensile}
= P/A
Compressive stress – When two equal and opposite forces are
applied to a body and the body tends to decrease in length
is known as compressive stress.
σ_{compressive
}= P/A
Shear
Stress or Tangential stress:
Shear
stress is similar to the direct except that the forces are
applied tangentially and the body sheared or twisted.
Shear
Stress, ζ = Shear stress/Shear area = P/A
Bending
Stress:
It is a
compressive or/and tensile stress due to the nonaxial forces
acting on a beam. It tends to bend or deflect the beam.
Torsional Stress:
Shear
stress produced when we apply the twisting moment to the end
of a shaft about its axis is known as Torsional stress.
Thermal
Stress:
Due to
the change in the material temperature, the dimensions of
the material also changes. But some of the parts are not
free to expand. The stress set up when the parts are not
free is expand due to the change in body temperature is
known as thermal stress.
