dark fragments on character (Blender 2.76)

Hello everyone!
Maybe somebody here knows how I could possibly solve this issue. I already posted this on the blenderartists forum, but I’m not quite sure if someone can actually help.

So here is the problem:
When rotating a limb of the character too much, I will get dark fragments:







Someone on blenderartists suggested it could be z-fighting, which I considered myself, but even when the faces don’t seem to be coplanar, this is still happening:



Many thanks for any ideas,
Greetings,
Shu

 

In my opinion the edgeloops are too close each other and this is problem maybe try to make bigger distance beetwen edgeloops

 

Thank you for your reply! Yes, that would most likely have been the better way of doing this.
The thing is, I already rendered quite an amount of frames of the animation and changing geometry would have resulted in a different appearance.
In this case, I was able to do something "hacky" to get rid of the problem: I rotated one of the parts of each limb for more than 90°, which made the fragments disappear.
It's not easy to animate now because some bones point into directions they are not supposed to, but it's still better than going through the whole rendering process again.

 

Yes - im not a blender artist but have seen this with improper skinning before.
It happens when verts cross and cause the triangle edges to cross causing terrible shading.
If you want a permanent fix the inner (bend) verts should be weighted correctly to the upper and lower bones so farther verts wont receive a stronger weight influence than nearer verts - and vis versa.

 

Thanks a lot for the detailed answer! I see! I didn't know that crossing edges could be causing harm, too! I thought problems only come up with polygons actually being coplanar. Good thing to know!