- Principal stresses :
Principal stresses may be defined as
” The extreme values of the normal stresses possible in the material.”
These are the maximum normal stress and the minimum normal stress. Maximum normal stress is called major principal stress while minimum normal stress is called minor principal stress.
- Principal plane :
Principal plane may be defined as
” The plane on which normal stress attains its maximum and minimum value.”
So these planes are also called as major principal plane and minor principal plane. The shear stress on principal plane is zero.
- Principal Axis :
Principal axis may be defined as
” The axis where moment of inertia is maximum or minimum and product of inertia is zero.”
- Principal plane is the property of stress whereas principal axis is the property of moment of inertia. There is no relation between principal axis and principal plane.