The Step Manager distinguishes between general nonlinear steps and linear perturbation steps by indenting the names and procedure descriptions of linear perturbation steps. General nonlinear analysis steps define sequential events: the state of the model at the end of one general step provides the initial state for the start of the next general step. Linear perturbation analysis steps provide the linear response of the model about the state reached at the end of the last general nonlinear step. You use the Procedure type field to choose between General and Linear perturbation steps when you select the procedure in the Create Step dialog box.

For each step in the analysis the Step Manager also indicates whether ABAQUS will account for nonlinear effects from large displacements and deformations. If the displacements in a model due to loading are relatively small during a step, the effects may be small enough to be ignored. However, in cases where the loads on a model result in large displacements, nonlinear geometric effects can become important. The Nlgeom setting for a step determines whether ABAQUS will account for geometric nonlinearity in that step.

The Nlgeom setting is turned on by default for ABAQUS/Explicit steps and turned off by default for ABAQUS/Standard steps. The sequence of steps and the current Nlgeom setting determine whether you can change the Nlgeom setting in a particular step. For example, if ABAQUS is already accounting for geometric nonlinearity, the Nlgeom setting is toggled on for all subsequent steps, and you cannot toggle it off. Where permissible, the following methods allow you to change the Nlgeom setting for a step:

For more information, see “Accounting for geometric nonlinearity,” Section 14.9.6, or see “General and linear perturbation procedures,” Section 6.1.2 of the ABAQUS Analysis User's Manual.