Convergence Issues with ABAQUS

Convergence issues are probably the most unpleasant experience of the users. Almost all ABAQUS users have experienced them. To solve such error, first you need to know what has caused it, and then you can take proper strategies. To be honest, convergence is usually one of the most challenging topics in an numerical modeling. Based on my own experience, some of motivated students get disappointed after facing a convergence problem and even stop using Abaqus forever!!! Here is a simple check list that helps you to find the source of convergence error.

1. Check Out ‘Job Diagnostics’: Open the odb file, and follow the bellow path to see a complete report of analysis.

2. Always Pay Attention to Warnings: However warnings are not usually problematic, but they are very informative and can give you a report about analysis difficulties. Never turn a blind eye to warning, instead learn from them.

3. Check the Boundary Conditions: Assigning wrong or inappropriate boundary conditions is one of the most frequent sources of the error. Where the boundary conditions are applied excessively (which makes the problem statically-indeterminate) or Inadequate (which causes instability) the convergence is not achieved.

4. Check the Interactions: There is two important thing about interaction. First, you need to define the interaction realistically, which means you must not apply excessive interactions. Second, you need to know in which step the interaction should be assigned. If you are dealing with an interaction which is provide the stability of the structure, you must activate it in initial step. Otherwise convergence problem happens. On the other hand, if you forget define one of interactions, the solver gets confused and stops the analysis with an error!!

5. Check out the Material Properties: A material must be defined exactly like its real nature. If you forget to assign the stiffness of the material, it deforms without bearing the load. As a result equilibrium is not achieved under an condition, consequently convergence is impossible

6. Last Resort: as the last resort, if you have done all of above items and you are still facing the convergence problem, you can use Explicit solver, instead of using Implicit solver. WHY? Click on this link to find out what their differences are and how explicit solver helps to solve the convergence problem.