Geometric nonlinearity

In a geometrically nonlinear analysis the local material directions may rotate with the deformation in each element. For shell, beam, and truss elements the local material directions always rotate with the deformation. For solid elements the local material directions rotate with the deformation only if the elements refer to nondefault local material directions; otherwise, the default local material directions remain constant throughout the analysis.

Local directions defined at nodes remain fixed throughout the analysis; they do not rotate with the deformation. See Transformed coordinate systems, for further details.

Once you include geometric nonlinearity in a step, it is considered in all subsequent steps. If nonlinear geometric effects are not requested in a subsequent step, Abaqus will issue a warning stating that they are being included in the step anyway.

The large deformations in a model are not the only important effects that are considered when geometric nonlinearity is activated. Abaqus/Standard also includes terms in the element stiffness calculations that are caused by the applied loads, the so-called load stiffness. These terms improve convergence behavior. In addition, the membrane loads in shells and the axial loads in cables and beams contribute much of the stiffness of these structures in response to transverse loads. By including geometric nonlinearity, the membrane stiffness in response to transverse loads is considered as well.