An Abaqus model uses the following two types of steps to describe the environmental actions on a system:
The initial step
Abaqus creates a special initial step at the beginning of the Simulation History and names it Initialization. Only one initial step is created for each model. You can rename the initial step, but you cannot edit, replace, copy, or delete it.
The initial step allows you to define interactions that are applicable at the very beginning of the analysis. For example, if a connection or field is applied throughout the analysis, it is usually convenient to apply such conditions in the initial step. Likewise, when the first analysis step is a linear perturbation or frequency step, conditions applied in the initial step form part of the base state for the procedure.
Analysis steps
The initialization step is followed by one or more analysis steps. Each analysis step represents a period of time in the simulation history and is associated with a specific analysis procedure, such as a static stress analysis or a transient heat transfer analysis. You can change the analysis procedure from step to step. Since the state of the model (stresses, strains, temperatures, etc.) is updated throughout all general analysis steps, the effects of previous history are always included in the response for each new analysis step.
There is no limit to the number of analysis steps you can define, but there are restrictions on the step sequence. (For more information, see Step Sequence Restrictions.)
For example, consider the following structural analysis of a section of a piping system:
Initialization Step:
No changes are needed in the default initial step.
Step 1: Compress
Apply boundary conditions to fix the left end of the pipe and to allow only axial movement at the right end. Apply a compressive force to the right end of the pipe. This step is a general static step.
Step 2: Twist
Calculate the stresses and strains in the pipe in its compressed state. This step is a static linear perturbation step.
When you create or edit an analysis step (as discussed in Structural Analysis Steps or Thermal Analysis Steps), it becomes the current step. All analysis step operations you perform, such as defining loads or boundary conditions, act on the current step. To set a different analysis step to be current, right-click on the step in the specification tree and select Set As Current Step from the menu that appears.