Helping Abaqus Find a Converged Solution

Understand the physics of the problem:

• It is vital to understand the physics behind any problem. For example:

·         How does the actual structure behave for the applied loading

·         How is the structure constrained at different locations

·         How are the different components connected to each other

·         What is the nature of the loads acting on the structure

• We make many assumptions and approximations in any analysis, which have to be reasonable and justifiable. For example:

·         Is the chosen material model appropriate?

·         Are the element types properly chosen

·         Is the mesh size appropriate

·         Is contact properly defined (choice sliding algorithm, friction coefficient, surface behavior etc.)

Build up the model slowly:

•  The most important way to help Abaqus find a converged solution is to build up the model piece by piece

·         Do not put every complexity and detail directly in the first attempt-it probably will not work

• Start with the simplest model possible-perhaps one with contact but no plasticity, friction, or nonlinear geometry-this would give valuable insight into how the model behaves

• Add complexities (friction or plasticity) one at a time. Doing this will limit the number of questions to consider if a convergence problem arises.

• Although it might seem as if this process will increase the time needed to perform the analysis, in fact it often reduces the time because debugging a large model with convergence problems can take days or weeks.

Provide reasonable values:

•  Make sure that the units of the material properties (especially density) are consistent with the geometry and loads in the model.

• Make sure that the material properties provide sufficient stiffness to resist the applied loads, or plan accordingly and use the appropriate analysis techniques.

• Give reasonable values for the minimum increment size and the maximum increment size (or use the defaults).

• Use the message file or job diagnostics to identify the proper cause(s) for nonconvergence