How use nodal force (NFORC) to replace the surface stress by an equivalent surface traction.

[aaltuna]

Dear to everyone,

I have a model where I introduce surface residual stress value in 0.4mm. These values is introduced in the integration point of the element (in this case C3D8R).
Now, I would like to replace the surface residual stress by an equivalent surface traction. I mean, I would like to introduce this stress value by means of node force.
I do not if it is possible to define node force (NFORC)in some way. I do not know with subrutine or maybe there is another way.

Any help it would be appreciated.

Regards,

Ane