Issues with Linear Force-Displacement Curve and Tunneling in PhysX 5 Deformable Body Simulation

Omniverse Isaac Sim
1

Isaac Sim Version

5.1.0

Operating System

Ubuntu 22.04

GPU Information

  • Model: NVIDIA GeForce RTX 5060
  • Driver Version: 580.126.09

Topic Description

Detailed Description

I am using Isaac Sim 5.1.0 to generate a synthetic dataset for soft body deformation research. My goal is to simulate a rigid sphere probe pressing into a deformable cube to capture the non-linear Force-Displacement (f-d) relationship caused by changing contact area (Hertzian contact) or shear force. However, the f-d curves are always linear after many turns of adjustments. Is my configuration wrong or it is just a PhysX 5 bug?

Steps to Reproduce

  1. Create a Deformable Body cube using deformableUtils.add_physx_deformable_body.

  2. Set simulation_hexahedral_resolution to 50 and collision_simplification=True.

  3. Create a rigid sphere and attach it to a kinematic base via a D6 Joint (Spring drive) to act as a force sensor.

  4. Move the sphere into the cube and record the displacement vs. the spring force.

  5. Change collision_simplification to False and run the simulation again.

Screenshots or Videos

(If applicable, add screenshots or links to videos that demonstrate the issue)

Additional Information

What I’ve Tried

  • I adjusted the sensor spring stiffness to ensure the linearity was not caused by the sensor deformation itself.
  • I adjusted the mesh resolution and increased simulation substepping, but the non-linear force response did not improve.
  • I modified the contactOffset and restOffset in the PhysxDeformableBodyAPI to mitigate the tunneling issue when simplification was disabled.

Related Issues

  • I searched existing forums and found that tunneling after disabling collision_simplification seems a known stability issue with no clear fix.
  • I compared results with other FEA solvers where Hertzian contact is a standard feature, highlighting the limitation in the default Isaac Sim setup.

Additional Context

  • The experimental setup uses a kinematically controlled rigid sphere to indent a 1x1x1 hexahedral deformable body.
  • This simulation is intended to generate high-fidelity synthetic datasets for research, making the physical accuracy of the f-d curve critical.


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3

Hi @henrysun579, thank you for posting this issue. I am working on reproducing your setup and will get back to you. I am assuming that the deformable object simulated through Particle Based Dynamics should approximate Hertzian contact as the mesh resolution increases, but I may not fully know the limitations of the physx implementation.

4

Following up on this — I reproduced your setup and the linear F-D curve is a real limitation of how PhysX 5 FEM resolves rigid-on-deformable contact, not a configuration mistake. Across hex resolutions 30→50, skin densities 8→20, with collision_simplification on and off, contact offsets 0.005→0.010, and iteration counts 20→60, the power-law fit stays in F ≈ C · d^[0.7…1.2] — never close to the d^1.5 you’d expect from Hertzian theory. The per-vertex contact penalty dominates over bulk elasticity, so the curve doesn’t enter the area-growth-dominated regime.

For the tunneling at collision_simplification=False: it goes away with PHYSICS_DT=1/480, solver_position_iteration_count≥60, and a slow approach (≤ 0.03 m/s).

If you actually need a non-linear F-D for your Hertzian-contact dataset, switching to a particle-based soft body (ParticleSystem + cluster constraints, GPU) can help — the contact pipeline should resolve growing contact area more faithfully.

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repro.py (10.2 KB)

5

Hello!

We noticed that this topic hasn’t received any recent updates from anyone reporting this issue, so we are closing it for now to help keep the forum organized.

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