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

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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

Topic Description

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

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)

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).

Screenshots or Videos

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

  • (Optional) short video showing “no deformation”

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.

3

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
4

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.

5

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:

  • :white_check_mark: Volume Deformable :left_right_arrow: Rigid Body: Supported (requires tetrahedral mesh)
  • :x: Surface Deformable :left_right_arrow: Rigid Body: Not fully supported/unreliable
  • :white_check_mark: Surface Deformable :left_right_arrow: 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
6

Hi — thanks for the explanation. I want to confirm my understanding and ask a few specific questions about intended use and limits.

Summary of what I think you meant:

  • Surface Deformable is primarily designed as a boundary-surface solver (e.g., cloth or a thin membrane attached to a rigid frame), not as a free-falling volumetric deformable object.

  • It is mainly intended to simulate deformation of the surface itself (often with anchors/attachments), rather than full dynamic rigid ⇄ deformable contact/force transmission for thin zero-thickness meshes.

Questions (please clarify):

  1. Intended use: Is Surface Deformable explicitly intended for “surface attached to a rigid frame” (e.g., cloth/membrane fixed to a support) and not for free thin parts that must fall and be hit by rigid bodies to produce bending/denting?

  2. Rigid ↔ Surface collisions: If a thin surface region is attached to a rigid body (the rigid frame), can a separate rigid object collide with that surface and cause visible deformation via contact forces in the current implementation? If supported, are there known limits (e.g., limited force transfer, impulse-only, unreliable behavior)?

  3. Attachment pattern: Recommended pattern to model “thin deformable region attached to a rigid part” — should we parent the surface to the rigid prim, use anchors/constraints, or use a joint? Any example snippet or recommended API to attach/anchor?

  4. Recommended workflow: For “a thin region attached to a stiff structure that locally bends/dents when impacted by a rigid body”, do you recommend (A) Surface Deformable attached to a rigid frame, or (B) convert the thin region to a volume tetrahedral mesh and use Volume Deformable for correct force transmission? Which is more reliable today?

  5. Examples / references: Are there sample scenes, USD examples, or documentation that demonstrate rigid object colliding with a Surface Deformable attached to a rigid frame, or recommended anchoring/attachment patterns?

I can share a small USD repro. Please let me know what minimal files/details are most helpful (USD, mesh stats, applied schema settings, logs).

Thank you.

7

Hi, you can find more info on Surface Deformable in Omni Physics doc. If you still have questions, I suggest you to ask in the Omniverse platform forum to get better answers there.