Subject: Seeking help with Contact Penetration issue in General Static Analysis (Valve/Piston Assembly)

Hi everyone,

I am facing a strange contact issue in Abaqus/Standard. Previously, the simulation worked perfectly with a Full model, and the contact interaction was recognized without any issues.

However, to improve computational efficiency, I switched to a Quarter model and added Symmetry boundary conditions. Since this change, the valve now completely penetrates the piston, even though no other contact settings were altered. I checked all load, BC, interaction conditions, but didn't find clear cause.

1. Model & Simulation Setup:

• Model: 1/4 symmetry valve and piston assembly.
• Changes: Switched from Full to Quarter model; added Symmetry BCs for X and Y planes.
• Step: Static, General (Nlgeom ON).
• Loading: 1.39 MPa Pressure load.
• Contact Property: Hard contact.

2. The Problem: The contact interaction, which was robust in the full model, is no longer functioning. The valve passes right through the piston surface as if the interaction doesn't exist.

3. Questions:

• Why would a working contact interaction fail just by switching to a quarter model and adding symmetry conditions?
• Is it possible that symmetry BCs interfere with the surface normals or the contact tracking algorithm?
• etc.

I would appreciate any insights into why this model transition is causing contact failure. Thank you!