Unstable Contact
Contact problems are the most common cause of convergence failures in assemblies.
Contact problems are the most common cause of convergence failures in multi-body assemblies.
Symptoms
- Solver aborts with a contact-related message
- Parts visually penetrate each other in the result
- Unrealistic deformations in the contact zone
Contact stiffness
Too high a contact stiffness → poor convergence. Too low → excessive penetration. Start with the default values and adjust incrementally if needed.
Initial penetration
Check whether contact surfaces already overlap in the undeformed state. Initial penetration can immediately cause instability as the solver tries to enforce contact constraints that are already violated.
Start with bonded (tied) contact instead of frictional contact. Bonded contact is much more stable and will tell you whether the basic model setup is correct before you introduce the added complexity of sliding contact.
Diagnostic steps
- Switch to bonded contact and check if the solver converges — if yes, the problem is specific to the frictional contact settings
- Inspect the geometry for initial penetrations
- Reduce contact stiffness by a factor of 10 and retry
- Increase the number of load steps so contact is established gradually