Hi mattias, thanks.
There is the ParticleContainer.disappear and ParticleContainer.reappear function (http://woodem.eu/doc/woo.dem.html#woo.dem.ParticleContainer.disappear
) which will hide particle (makes invisible, deletes contacts, avoids all further interactions). I looked at the now and it will not prevent the internal force from being computed and applied, so there would have to be a flag saying that internal forces can be disregarded.
Another approach would be to remove the particle, simply by using ParticleContainer.remove (http://woodem.eu/doc/woo.dem.html#woo.dem.ParticleContainer.remove),
as in S.dem.par.remove(id) or S.dem.par.remove([id1,id2,...]). I now see the documentation of that function is lacking. It will internally correctly remove the particle also from DemData.parRef, and will remove the node from S.dem.nodes if it no longer belongs to any particle.
Damaging material model (using something like the isotropic damage model - http://www.oofem.org/resources/doc/matlibmanual/html/node32.html
) for membrane is something I would like to implement at some point as well. But let's keep it simple for now. Just remove the particle, that will work. Let me know if not.