Hello,
I’m quite new to blender.
I already searched the forum, but couldn’t find an answer.
If there is already an answer to this, just let me know.
What I want to do is just break a stone into two pieces.
I don’t need any real physics, like explosions or any other objects smashing the stone…
Thanks a lot for telling me your ideas on how to do this.
DeuxPierre
What do you mean by “breaking a stone”?
Do you mean an animation of a stone breaking?
Or have you modeled a stone and can’t figure out how to separate both pieces of it?
It’s the second - I can’t figure out, how to make 2 pieces out of one.
(By
animation of a stone breaking
do you mean I already know how separate the pieces and then want to know on how to make them fall apart?)
Basically you select the vertices of one part and press [P] - you might need to fill up/create the surface fo the connection area (the one that is created when splitting something)
See also the FAQ (especially FAQ/Modelling/Mesh)
EDIT: Another thing - you can use knife subdsivision ([Shift][K]->Exact Line) or Loop Subdivision ([Ctrl][R]) before doing the above.
EDIT: And one more … there is also the possibility to use booleans ([W] in ObjectMode) to e.g subtract one object from another , but this produces strange results most if the time - use this with care since it’ll mess up your geometry.
Werner
Well, making an animation of a stone breaking would require some skill 
At least if you want it to be realistic.
Hoehrer’s suggestions should be good for what you want to do.
Do note that you’ll have to arrange the vertices of the two surfaces which were once glued together in the stone in such a way that it looks like a piece of it broke of. How that looks like greatly depends on your type of stone, so I suggest you do some research.
Thanks for your help.
Isn’t there anything like Softbodies but for Hardbodies?
How would you animate a cup that falls on the floor and breaks into pieces?
And I do have problems to create the two new surfaces - to create the stone I used icosphere and to make the outside smooth I used subsurf and set smooth.
When I do create the new surface it gets automatically “smoothend” and “subsurfed” and even when I try correct that with “shift” + “e” the two halfs won’t fit together anymore.
Any suggestions on that?
(by the way I want to animate the whole thing - but it does not have to look very realistic
well I already figured out how to animate a lightning, so I think a breaking stone should be possible somehow)
Naw, shattering hard-bodies is for those losers with their $20,000 in-house, home-built wonder systems. 
EDIT: Re: shift+e, you can’t just do the rim edges, you have to do corner edges, too. Try shift+e-ing the inside connecting edges as well.
I saw a demo of a plug-in for some other 3D system, might have been Maya, that did breaking glass, exploding buildings, planes crashing into the ground and realistically shattering into pieces. The plug in was fairly expensive, and looked like it was a bear to set up. Whatever was supposed to be broken was built out of “pre-broken” parts, with some options: shards, chunks or linear pieces of different sizes. The plug in smoothed everything out and made it look whole, then when the thing crashed, smashed or exploded, it calculated the direction and amount of force on the piece to send it flying off in a physically accurate direction. I suppose you could do something similar in Blender.
Start with the pieces. Parent the pieces to each other (or to an empty) so they look like an unbroken rock. When the rock gets hit by the lightning bolt, animate the pieces moving away from the center. Maybe put it in the game engine and give everything a little force bump to see how the chunks would fly out and bounce.
There used to be a beta modifier in Blender several versions back to handle shattering, but hold on, because I think that in the next version or two will be a particle re-factor that will do this. (Can someone verify this??)
Actually the Particle Rewrite project will hopefully bring us some nice things such as breaking hardbodies (see e.g the suzanne_explode.avi), but don’t expect wonders (i.e don’t expect that it always looks like you want it to 
)
I dunno when/if it’s planned to implement it into Blender, so for more information you might want to read the whole page
EDIT: to quote the page (bottom)
Basic general particle system code (not yet read/write) and basic code with Emitter type system is coded. Completion of the rewrite is not yet in the near future as the sheer amount of code to write is quite large. Hopefully I will have some subset of planned functionality working in few weeks time if I find the time to code from my studies.
Werner
OK, This is an inspired hack. I haven’t tried it, but it’s so crazy it might just work…
Make your rock in several pieces and give each piece the same point of origin. (ie, stick the 3D cursor in the middle of them and click “center Cursor” in the mesh editing buttons for each rock bit). Make an empty at this location too.
Now comes the fun bit that i’m not certain about, so look for tutorials…
Use the Physics Engine and record to IPO function to record the animation of all the bits breaking up and going everywhere.
Now go back… Remember the empty? At the beginning of the animation, set a key-frame for it’s location. Now go forward to the frame where the rock just touches the ground, move the empty to about the middle of the rock and set another key-frame. on the empty.
OK - For the magic… For each rock bit, set a “Copy Location” constraint pointing to the empty. At the first frame, set the influence to 1 and create a key-frame (Press I-key while pointer is over the constraint window to set a constraint keyframe1)
Move to the frame where the rock touches the ground. Set another constraint keyframe at 1
Move forward about 5 frames, set the influence to 0 and keyframe it.
Go back to the beginning and hit alt-A with the pointer in the 3D window to see the result.
Hey Ammusionist,
in the game engine the pieces of the rock are just doing what ever they want - but that has nothing to do with “real physics”,
so I’m afraid that this doesn’t really work…
(if you like I can send you the .blender file to try it out).
I finished this thing more or less - if you’re interested I can put the video online somewhere.
Maybe you have some ideas about what to change or on how to make it look better.
Well here’s the link to the video
(on my Mac the vid is quite dark, while not on my PC - so maybe you have to try to change brightness)
I think for my very first 3D animation it’s not that bad - I hope you like it…
If you have any ideas, comments or what ever - please let me know!