Radiation defect formation and effect on mechanical property in octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine investigated by molecular dynamics method

•Irradiation can cause bond breaking, formation of free radicals, new gas molecules, interstitial and vacancy clusters in energetic materials.•The free radicals generated during irradiation can cause further chemical reactions in energetic materials.•The change of color and release of gas of HMX after irradiation as reported in experiments can be explained by formation of different defects, free radicals and new gas molecules.•The strong stress gradient is observed around the defect formation region, resulting in lower external stress needed to deform the system. Energetic materials (EMs) are generally used in various conditions including under the neutron irradiation environment. To understand the radiation damages and related effects on mechanical property of EMs is important and necessary for their further applications under radiation conditions. In this paper, the displacement cascades are firstly simulated with molecular dynamics method in an octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) with the maximum energy of a primary knock-on atom (PKA) up to around 5 keV. The bond breaking, formation of free radicals, new gas molecules and interstitial and vacancy clusters, are all observed after displacement cascades, which can be used to explain the change of color and release of gas after irradiation as reported in experiments. Furthermore, the effect of above defect formation on mechanical property is calculated based on tensile stress simulations on damaged HMX. The results clearly show the appearance of strong stress gradient around defect formation region, resulting in lower external stress needed to deform the system. Thus, the radiation softening can be explored according to these results, same to experimental reports. Therefore, all these results indicate the radiation damages induced by energetic particles should be considered seriously for further application of energetic materials in nuclear conditions. The mechanism of molecular damage and mechanical property degradation of energetic materials after irradiation [Display omitted]