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kpt_dzban

Two-step fracture driven by animation

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Hi! 

First post here. After months of lurking and picking up tips from other users topics I need more direct help. I'm quite new to Houdini and I hope you share some ideas.

With given FBX meshes, I have to simulate a gate being rammed out from a wall. Chunks of portal around the gate are supposed to be pulled out with it, hit the ground and crumble into bricks while the rest collapses. Gate itself is animated with bones, not physics-driven. After many experiments, I couldn't achieve that two-step fracture (big pieces falling on impact and then crumbling). This is what I've already tried:

1. I've split all wall FBX into bricks using Voronoi fracture fed with array of points (four pieces total: the portal, left, right and top parts of the wall).
2. I've divided the portal into chunks by grouping fractured elements with separate glue constraints. 
3. I've created set of constraints for each piece.).
4. I've constrained all parts of the portal to the animated gate.
5. I've imported gate and wall as RDB Packed Objects to a DOP and fed it to bullet solver.
6. I've set up constraints networks for each piece with SOP solvers connected.

The idea was that the portal is connected to the gate by glue constraint with infinite strength (-1) and pulled that way out of the wall. After few frames the constraint is severed by deleting lines in SOP solver. Constraints for individual chunks remain until they are broken by impact with ground. Meanwhile the result is that: when portal-gate constraint is removed while the portal is still in the wall, it's being abruptly shot upward. It looks like the animation (which I can't alter) forces meshes to overlap, so they pop when it loses control over them. When the constraint is removed few frames later when the portal doesn't collide with anything, it gains such high acceleration already, that bricks spray all around as if it has been an explosion. I suspect that my pipeline my be noobish, but I couldn't find any resources on similar cases. Unfortunately I can't share screenshots nor files as they are part of a commission.  

I'll appreciate your help.

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