Impact overview

Impact simulates breaking and colliding rigid pieces: demolition, fracture and joints. It uses Extended Position Based Dynamics (XPBD) on the GPU. A mesh is cut into Voronoi shards, the shards are glued together with breakable bonds, and the solver breaks the bonds when loads pass a threshold.

The quickest start is Quick Demolition on a mesh, or an Impact template: Mortar Wall, Staged Demolition, Reinforced Pillar or Demolition Dust.

The workflow

1. Fracture a mesh into shards with Fracture Selected Mesh. The shards go into a BLUX fracture collection, and a graph is set up for them.
2. Add colliders and forces (ground plane, a projectile, gravity, an explosion).
3. Decide how the structure holds together with bonds and rebar, and when parts wake up with groups, activation and triggers.
4. Press Run, or Bake. You can bake the result to object keyframes (location and rotation) from the Solver panel’s Keyframes section.

The graph

Node	Purpose
Impact Source (RBD Source)	The fractured collection or object to simulate.
Forces	Gravity, wind, drag, explosion, vortex, turbulence, attractor, curve.
Colliders	Object Collider and Ground Plane. Kill Volumes are not part of the rigid solver.
Impact Constraint	The glue bonds between pieces.
Impact Rebar	Reinforcement that holds broken concrete together.
Impact Debris	Chips and dust spawned when pieces break.
Impact Joint	A hinge, slider, ball, spring or weld between pieces.
Impact Group, Group Combine	Select sets of pieces.
Impact Activation	When groups wake up.
Impact Trigger	Volumes and frame ranges that act on pieces.
Impact Solver	Runs the simulation.

Impact Solver settings

Setting	Default	What it does
Auto-Fit Domain	on	Computes the domain from the fractured asset’s bounding box plus a clearance margin.
Debris Clearance Margin	2.5	Multiplier around the asset that lets debris fly freely.
Substeps	10	More is more accurate for stacks and glued chunks, and slower.
Solver Iterations	4	Constraint passes per substep. More makes glue and contacts stiffer.
Bond Stiffness	1,000,000	Stiffness of the glue bonds.
Breaking Force	45	The threshold that snaps glue bonds.
Chunk Friction	0.6	Friction for chunk-ground and chunk-chunk contact.
Chunk Restitution	0.25	Bounciness.
Restitution Threshold	0.2 m/s	Impacts slower than this do not bounce, so resting stacks settle without jitter.
CCD Speed	3 m/s	Chunks faster than this are swept with continuous collision detection to stop tunnelling. 0 keeps it always on.
Sound Speed	0	Speed of the stress wave through glued chunks. Bonds crack only once the wave reaches them. Concrete is about 3,400 m/s, steel about 5,100. 0 is instant.
Linear / Angular Sleep Speed	0.04, 0.06	Below these, chunks begin to sleep.
Sleep Delay Frames	12	Frames at rest before freezing.
Dynamic Re-Fracture	on	Shards re-fracture in flight on high-energy impacts.

Dynamic re-fracture

Setting	Default	What it does
Shatter Speed	7.5 m/s	Minimum approach speed that triggers shattering.
Shatter Energy	25 J/kg	Minimum impact energy per kilogram (0.5v²; 25 is about 7 m/s). Each doubling above it adds a piece.
Max Fracture Depth	2	How many times a shard can be re-fractured.
Max Pieces	4	Most pieces one impact breaks a shard into.
Eject Speed	1 m/s	Speed the new pieces fly apart at.
Min Shard Volume	0.0005 m³	Shards below this do not fracture further.

Friction and bounce

Static Friction gives shards a separate friction that holds a resting contact. Friction Combine and Bounce Combine decide how the friction and restitution of two different surfaces combine.

Every setting is in the Solver reference.

Requirements

Rigid-body bonding and fracture use SciPy. See Dependencies.