A substructure is formed from a one-element truss model constructed of an elastic-plastic material. The substructure will be subjected to a preload (axial force) that causes inelastic strains. The substructure stiffness matrix is then formed about this base state. Additional loads are applied during global usage through a perturbation step and a general step.

Two substructures are created from single-element truss models, one made of a pure elastic material and the other made of an elastic-plastic material. Young's modulus is 3.0E5 in both models, and both structures are subject to a preload (prescribed displacement). The effects of the nonlinearities are incorporated into the static analysis by using the NLGEOM parameter. The magnitude of the applied load is high enough to ensure plastic deformation in the elastic-plastic material. The tangent stiffness value, , obtained for each case is compared to the corresponding value obtained by the analysis of an analogous global model without substructures.

A substructure is formed from a one-element model constructed of an elastic material. A rigid surface consisting of R2D2 elements is moved down to compress the element in the first step. In the second step the element is moved across the rigid surface to generate frictional forces at the contact interface. The substructure stiffness matrix is then formed about this base state. Additional loads are applied during global usage through a perturbation step.