[en] Nucleus-nucleus collisions in the energy range from 10 MeV/u to 150 MeV/u are investigated in the framework of the Wigner transformed von-Neumann equation on the level of the one-body density matrix. Two-body collisions permitted by the Pauli principle are described by a collision term of the Uehling-Uhlenbeck type. Central collisions of ⁴⁰Ca + ⁴⁰Ca are studied with respect to time dependent distortions of the momentum density in a mean field description. A significant enhancement for subthreshold pion production due to nucleon-nucleon collisions is found. The competition between one-body and two-body effects is investigated via the evaluation of decay times for primary distorted momentum distributions. Double differential preequilibrium neutron spectra d²N/dTHETAdE in coincidence with central collisions of ⁴⁰Ca + ⁴⁰Ca at 20 MeV/u are calculated for primary and secondary emission processes. (orig.)