How to Troubleshoot Convergence Problems in Nonlinear Implicit LS-DYNA

Tools to help visualize the source of converge problems in implicit LS-DYNA

When convergence issues arise in a nonlinear implicit LS-DYNA analysis, the following keywords and settings are helpful in diagnosing problems:

1. Visualize Newton Iterates

In the *CONTROL_IMPLICIT_SOLUTION card, set D3ITCTL=1, and in the *DATABASE_EXTENT_BINARY card, set RESPLT = 1.  These settings will provide the D3ITER database that provides the ability to visualize the Newton iterates as a contour plot in Ls-PrePost.

2. Use MORTAR Contacts

It is highly recommended to use MORTAR contacts in nonlinear implicit analyses.

3.  Implicit Accuracy

In the *CONTROL_ACCURACY card, set IACC=1 to turn on implicit accuracy.

4. Use Fully Integrated Elements

Implicit analyses are helped by using fully integrated elements as well as higher-order elements.

5. Print Contact Penetrations for Every Force Evaluation

In the *CONTROL_OUTPUT card, set MINFO=2 to print contact penetrations for every force evaluation.  If necessary, adjust the contact stiffness.

6. Run an Eigenvalue Analysis

If convergence issues persist, run an eigenvalue analysis to see if any negative eigenvalues are detected.  If so, check if material properties are valid, if there are any inverted elements from severe distortion, and/or if there are any rigid body modes.  If so, address these issues and re-run until there are no more negative eigenvalue issues.

Another suggestion is to create a load curve to run an eigenvalue analysis at some critical times; refer to the LS-DYNA Manual for further details: