Since I upgraded to 4.8 the only destructible actor I use breaks on any impact event, no matter how small. It seems to be disregarding several of it’s properties, changing them doesn’t matter at all. It’s a totally average vase, nothing extreme about it.
Right now it has the following settings:
Yet a fall from 1 cm makes it break apart. Of course it had more reasonable values when it was still working properly.
You need to set a Support Depth of at least 1 for allow the chunks to not break free from each other until they receive enough damage to do so.
If you’re using UE4 to make your Destructible then you only need to set Support Depth to 1. If you’re using Nvidia’s PhysXLab to make your DM and you have more than a single destruction depth you can user higher values to set how your support works.
Oh yes I forgot to mention that I use Unreal’s fracturing. So setting support depth to 1 does help a bit, however even at depth of 10 a few chunks just fall off when the game begins, regardless if the mesh falls 1 cm or not at all. Even when gravity is turned off so no impact occurs on start: I nudge the mesh gently, from any direction, and the same certain chunks float away. According to the preview button the mesh only has 2 levels of depth.
Setting Support depth any higher than 1 will not have any effect since you’ve made your destructible in UE4. You only get two depths. 0 and 1. In PhysXLab you can use up to 5 depths.
Instead of using very high values to try and test, try setting everything back to around defaults.
Damage Threshold: 1
Damage Spread: 0.1 (this directly controls how much damage is spread to surrounding chunks if a impact is detected on a chunk. (ie. If i hit a chunk in the center with a large force it will apply more damage to the chunks directly around and can destroy the entire mesh if enough force is received)
Impact Damage: 0.1
Impact Damage depth: 0 (should be fine for simple setup)
Custom Impact Resistance: use higher values, Start high and then lower it until you get something you like. I typically set it to a point where no damage is received. Then lower it from there by a couple of thousand every time.
Support Depth: 1
To test this. Place the mesh in your scene and set to simulate physics.
If you’re still getting it to fracture, try adjusting the impact CIR or the damage spread. You can test Damage Spread easily by setting it to 0. This means that only the chunks that receive enough damage will break free. No damage will be passed to surrounding chunks.
Instead of using very high values to try and test, try setting everything back to around defaults.
That is exactly what I’ve done with every property: started with the values which worked fine in 4.7.5 and kept increasing/decreasing them hoping to see a change or sense in the behavior.
Now I’m downloading 4.7.5 in order to create a clear “4.7 vs 4.8” bug showcase.
These are the settings I’m using. I’m on 4.8.2 and I’ve not enabled anything else to get this working. I’m using the basic cube mesh as a test asset. I’ve set the fractures to 250 chunks.
Testing 4.7 for Custom Impact Resistance is futile. It didn’t work until 4.8.
Try setting up a basic cube destructible and see if you’re seeing the same result using the settings I have in the picture. If you’re using a custom mesh we can at least rule out if that may be the source of the issue or not.
for Damage Spread. Use this as the starting point for testing the Support Depth as well. Set it to 0 initially and you should see that only a few chunks break free if you drop the mesh from a height when it is simulating physics and PIE. Probably helps to rotate it so that a corner hits the ground first to better apply damage to those chunks. Then if that only breaks away a few chunks then try resetting it to the default value of 0.1 and go from there.
It seems that reimporting the mesh and re-slicing it helped. Maybe the mesh topology was the problem as I could not reproduce the issue with other, simpler meshes. The object in question is a tube with a square cross section twisted around the main axis. My best guess is that two of the generated chunks had overlapping collisions so when the simulation started the interpenetration was fixed by forcing the chunks apart hence the instant breaking.
I’d like to add my thoughts after encountering something similar to this.
I’d grab destructible meshes and some would instantly break and other would not even though they were all using the same Destructible mesh with the same really high damage threshold. The ones I could pick up were fine and would not break, the ones that did instantly did so the moment I grabbed them.
What I did to resolve my issue was just lift up the objects slightly and use the “End” key to have unreal place them back down. My guess is my manual placement clipped through the floor a bit causing the destructible mesh to spawn inside another collision leading to this absurd behavior.
EDIT: So my comment above doesn’t really seem to be accurate. After a few tries it would occur again. I ended up disabling the “Accumulate Damage” tick box and this does seem to address the problem for me but obviously at the cost of no damage accumulation. This makes me think that something is causing damage either randomly on start, within mesh itself or something small but periodic but whatever it is, it is not consistent. Personally I’m ok with just breaking it after a threshold is breached.
