Isaac Sim 5.1 (Ubuntu) Thin sheet Deformable (beta/deprecated) behaves like rigid (little/no visible deformation)

[sho2125]

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Isaac Sim Version

• 5.1.0 (standalone)

Operating System

• Ubuntu 22.04

GPU Information

• Model: NVIDIA L40S

• Driver Version: 580.95.05

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Topic Description

PhysX Deformable on a thin sheet mesh behaves almost like rigid (little/no visible deformation) in Isaac Sim 5.1 on Ubuntu.

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Detailed Description

I am trying to simulate deformation of a thin sheet metal part in Isaac Sim 5.1 (Ubuntu) using PhysX Deformable. The target object is a thin sheet (open surface / very small thickness). I create a ground plane and drop a rigid cube/sphere onto the sheet to observe bending/denting.

However, the sheet behaves almost like a rigid body and shows little to no visible deformation. I tested both Deformable workflows:

• (beta) Surface Deformable Body + Surface Deformable Material

• (deprecated) Deformable Body (deprecated) + Deformable Body Material (deprecated)

Both produce similar “rigid-like” behavior. I would like to know whether this is a known limitation/bug in Isaac Sim 5.1 or if my mesh/setup is incorrect.

Asset pipeline:

1. Siemens NX: load STEP (TOP_ASSY_ALLCATPART), isolate the work part only

2. Export OBJ from NX

3. Convert OBJ → USD using HOOPS Converter in Isaac Sim

4. Load the USD in a new stage

Important note: to apply Deformable schema, I had to disable instancing on the imported prim:

pythonCopyimport omni.usd
stage = omni.usd.get_context().get_stage()
p = "/World/..."
prim = stage.GetPrimAtPath(p)
prim.SetInstanceable(False)

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Steps to Reproduce

1. Start a new stage in Isaac Sim 5.1

2. Convert OBJ → USD via HOOPS Converter and load it into the stage

   • Target mesh path: /World/.../Mesh

3. Create a ground plane (Create → Physics → Ground Plane)

4. Apply Deformable to the sheet:

   • Option A: Surface Deformable Body (beta) + Surface Deformable Material (beta)

   • Option B: Deformable Body (deprecated) + Deformable Body Material (deprecated)

5. Create a rigid cube/sphere:

   • Rigid Body + Collider (Box/Sphere)

6. Press Play

Error Messages

• No critical errors, but behavior is unexpected (rigid-like / no deformation).

• Previously saw instancing/proxy related errors when applying schema, resolved by SetInstanceable(False).

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Screenshots or Videos

• (Attach screenshots of the applied Deformable schemas/material settings and the rigid body drop test)

• (Optional) short video showing “no deformation”

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Additional Information

What I’ve Tried

• Tested both beta and deprecated Deformable workflows

• Lowered Young’s modulus and increased rigid body mass / drop height

• Increased substeps to reduce tunneling

• Confirmed the rigid body has Collider + Rigid Body

Additional Context

Questions:

1. For thin sheet metal assets, is Surface Deformable Body (beta) the correct approach, or is PhysX Deformable mainly intended for volume/tetrahedral meshes?

2. Is there any known issue in Isaac Sim 5.1 where deformables behave rigid or material parameters have little effect?

3. Are there recommended settings (substeps/iterations, material ranges, simulation mesh generation) for visible bending/denting?

4. If the mesh is the issue, what are the required mesh conditions (scale, triangulation, manifold/closed surface requirements, thickness, etc.)?

I can provide a minimal USD reproduction stage if needed.

[PeterNV]

Hi, Your thin sheet metal is behaving like a rigid body might be caused by:

1. Wrong material properties - Default Young’s modulus/stiffness values are too high for visible deformation
2. Insufficient mesh resolution - Thin sheets need adequate tessellation for FEM simulation
3. Missing surface deformable material - Thin sheets need SurfaceDeformableMaterial, not VolumeDeformableMaterial

Here’s an example settings for metal sheet bending/denting:

_Material_ properties (adjust these for more/less deformation)
youngs_moduli = 1e5      # Lower = softer (try 1e4 to 1e7)
bending_stiffness = 0.05  # Lower = easier to bend (0.01 to 1.0)
vertex_damping = 0.005    # Lower = more oscillation

_Solver settings_
solver_iterations = 20    # Higher = more accurate but slower

[sho2125]

Hi, thanks for the suggestions.

I rebuilt the asset and re-tested with the beta Surface Deformable Body + Surface Deformable Material workflow. However, I’m now seeing a different issue:

• When I apply Surface Deformable Body (beta), the sheet does not fall under gravity (it stays in place).

• Also, it seems to have no collision/contact with other rigid bodies: a rigid cube/sphere dropped onto it passes through as if there is no collider/contact generation.

I’m wondering if this is caused by the fact that the model is thin , or if there are additional requirements for collisions with surface deformables in Isaac Sim 5.1.

Could you clarify:

1. Does Surface Deformable Body (beta) require the mesh to be closed/manifold or have a minimum thickness?

2. Are collisions between rigid bodies and surface deformables supported in 5.1, and if so, what collider/contact settings are required?

3. Is there a recommended way to model/import thin sheet metal so that it both deforms and collides properly (e.g., add thickness, remesh/tessellate, convert to volume/tetra, etc.)?

If needed, I can share a minimal USD stage that reproduces this behavior.

[PeterNV]

Hi, your issues stem from fundamental limitations of PhysX Surface Deformables (beta) in Isaac Sim:

No Gravity Response:

• Surface Deformable Bodies are kinematic by default - they don’t respond to gravity or external forces unless explicitly driven
• They’re designed for *boundary surfaces• (like cloth attached to rigid frames), not free-falling objects
• The PhysX deformable solver treats surface meshes as constraint surfaces rather than dynamic objects

No Collision with Rigid Bodies:

• Surface deformables have limited collision support - they primarily collide with themselves (self-collision) and other deformables
• Rigid body → Surface deformable collision is NOT fully supported in the current PhysX implementation
• Collision requires volume - thin surfaces lack the 3D geometry needed for PhysX contact generation

Manifold/Thickness Requirements

Yes, surface deformables have strict requirements:

• Mesh must be watertight/manifold (no holes, open edges, or non-manifold vertices)
• For collision to work, you need volume-based deformables (tetrahedral meshes), not surface meshes
• Thin sheets with “zero thickness” cannot generate collision contacts - PhysX requires volumetric representation

Rigid-Deformable Collision Support

Current Status in Isaac Sim:

• Volume Deformable Rigid Body: Supported (requires tetrahedral mesh)
• Surface Deformable Rigid Body: Not fully supported/unreliable
• Surface Deformable Surface Deformable: Supported (self-collision)

What’s Required for Collisions:

• Must use Volume Deformable Body (not Surface)
• Mesh must be tetrahedral (volume elements), not just surface triangles
• Apply PhysxDeformableBodyAPI + collision settings