Microscale impact response characteristics of ε-CL-20: A multiscale simulation study with coupled force fields

Exploring the microscopic mechanism of critical initiation conditions is a challenging task in shock research on energetic materials. Herein, a multiscale impact simulation of hexanitrohexaazaisowurtzitane (ε-CL-20) was conducted within a velocity range of 8.0∼10.0 km/s by coupling the NNP-SHOCK force field with the ReaxFF-lg force field. Using peak pressure as a stage division indicator, the impact initiation process was quantitatively divided into two stages: impact compression and intense reaction. Among the large variety of ε-CL-20 decomposition products, CO₂ content was identified as a key metric to reflect the initial reaction process of ε-CL-20, rather than the initial product NO₂. The correlation between the change in CO₂ quantity and the change in unit cell pressure is particularly high when the shock wave velocity is below the critical shock initiation velocity (9.1 km/s) of CL-20. Correspondingly, the calculated critical decomposition rate of CL-20 reaches 9.451 ps^-1 when subjected to a critical detonation velocity. In addition, reaction network diagrams of ε-CL-20 and its typical final products (CO₂, H₂O, and N₂) were drawn to clarify the initial transformation pathways of ε-CL-20 and to determine the intrinsic relationships among the chemical reactions of CO₂, H₂O, and N₂.