  The inclusion of a fragmentation mechanism in population balance equations
introduces complex interactions that make the analytical or even computational
treatment much more difficult than for the pure aggregation case. This is
specially true when variable sized fragments are allowed, because of the
exponential growth in fragments size combinations with the number of monomers
in the exchanges. In this contribution we present a new model that incorporates
an instability threshold in the clusters, which induces arbitrary losses or
gains of particles by fracture with a substantial simplification of the
combinatorics of the process. The model exhibits two different regimes.
