Use the Boundary Stress node to define the total surface (boundary) stress through a stress tensor, a traction force, or a pressure. Add this node from the
Mechanical submenu. The stress condition reads
where Ftr is the surface traction force. The pressure condition reads
where pbnd is the pressure applied to the boundary (acting in the normal direction).
Select a Stress type —
Stress tensor, Traction (the default), or
Pressure. For
Stress tensor enter the (symmetric)
Stress tensor 
(SI unit: N/m
2) components, for
Traction enter the traction force
Ftr (SI unit: N/m
2) components, and for
Pressure enter the boundary pressure
pbnd (SI unit: Pa).
is a symmetric stress tensor, the product 
defines a traction force. The traction condition reads