[Solved] Hyperelastic material – spurious stress after rigid-to-deformable switch

Solver Version:

Version : smp s R14                           
Revision: R14.1.1-8-g2ef819c24f 
AnLicVer: 2025 R1 (20241030+dl-67-g73b144a) 

Description:

I've encountered an issue where hyperelastic materials develop strange initial stresses (solver: SMP single precision, double precision solver will crash the simulation immediately) when a part is switched from rigid to deformable using *DEFORMABLE_TO_RIGID_AUTOMATIC. The same setup works perfectly with elastic materials.

Summary of behavior:

1. A part with hyperelastic material is initially rigid, then automatically switched to deformable at t=10.0

2. Immediately after the switch, the part shows spurious stresses

3. If I replace the hyperelastic material with an elastic material, the problem disappears

4. The same issue occurs whether using full restart with *STRESS_INITIALIZATION to add a new hyperelastic part, or within a single continuous simulation using *DEFORMABLE_TO_RIGID_AUTOMATIC

Attached test case:
A minimal working example demonstrating the issue. One single element uses *DEFORMABLE_TO_RIGID_AUTOMATIC to switch from rigid to deformable at t=10.0 with hyperelastic rubber material. Simply swap the material to elastic (*MAT_ELASTIC) to see the problem disappear.

Questions:

1. Is this a known limitation/bug in R14?

Any insights would be greatly appreciated.

Key file to reproduce the issue is attached