There is however one large difference: using the External Stress, you can also prescribe a stress contribution that only acts as a load on the structure but is not added into the stress tensor. The typical case is when there is a pore pressure in a porous material, a common case in geotechnical engineering. The stress carried by the solid material, excluding the pore pressure, is often called the effective stress. So the load from the pore pressure helps to balance the external loads, while not contributing to the stress tensor of the solid. The contribution to the virtual work of the external stress is then

The External Stress subnode can be added to Linear Elastic Material, Nonlinear Elastic Materials, Piezoelectric Material, or Elastoplastic Soil Models.