Molecular dynamics (MD) simulations have been performed to investigate AP (ammonium perchlorate)/HMX (octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine) composites at various concentrations and temperatures in NVT ensemble using the modified PCFF force field. The binding energies and the average and maximum bond lengths of pyrogenation trigger bond N—NO2 in the AP/HMX composites were obtained. It was shown that with the mass ratio of AP/HMX increasing the binding energy changed according to a complex mode, but the maximum bond length of N—NO2 changed according to a parabola mode, which means that the bond length increased first and then decreased, and the peak of the parabola was at the AP/HMX ratio of 1∶1. This agreed well with experimental fact that the sensitivity value was highest at this ratio. The maximum bond lengths of the N—NO2 trigger bonds of 1∶1 AP/HMX system were calculated and found to increase with increasing temperatures, which was consistent with the experimental fact of sensitivity increase with temperature increasing. Thus it was suggested that the maximum trigger bond length of the most sensitive component in energetic composites could be used as a theoretical criterion of thermal or impact sensitivity to judge or predict the relative safety of energetic composites.

Key words: energetic composite, ammonium perchlorate (AP), octahydro-1,3,5,7-tetranitro-1,3,5,7-tetra- zocine (HMX), molecular dynamics, trigger bond, binding energy, sensitivity