Shear Stresses: With shear stress components, the single subscript notation is not practical, because such stresses are in direction parallel to the surfaces on which they act. We therefore have two directions to specify, that of normal to the surface and the stress itself. To do this, we stress itself. To do this, we attach two subscripts to the symbol ' t' , for shear stresses. In cartesian and polar co-ordinates, we have the stress components as shown in the figures.
txy , tyx , tyz , tzy , tzx , txz
trq , tqr , tqz , tzq ,tzr , trz
So as shown above, the normal stresses and shear stress components indicated on a small element of material seperately has been combined and depicted on a single element. Similarly for a cylindrical co-ordinate system let us shown the normal and shear stresses components separately.
Now let us combine the normal and shear stress components as shown below :
Now let us define the state of stress at a point formally.