Effects of different types of defects on ignition mechanisms in shocked β-cyclotetramethylene tetranitramine crystals : A molecular dynamics study based on ReaxFF-lg force field

Microscopic defects affect shock sensitivity remarkably. We exhibit a molecular dynamics study of defective β-cyclotetramethylene tetranitramine (HMX) crystals with void (VH), entrained oxygen (OH), and entrained amorphous carbon (CH), as well as a perfect HMX crystal (PH) for contrast. The crystals were shocked with 9 km/s shock velocity perpendicular to the (010) plane for 50 ps using a ReaxFF-lg force field. The results demonstrate that the shock sensitivity of HMX crystals with different defects is enhanced to different degrees. OH has the highest shock sensitivity, which is slightly higher than that in VH; both OH and VH crystals have much higher shock sensitivity than that in CH. Obvious local high temperature areas are found in defective systems, which are not found in PH. The initial reaction is N-NO₂ bond cleavage in PH and is N-NO₂ and N-O bond cleavages in defective systems. More products are found in defective HMX crystals during shock simulations, while fewer immediate products and no final product are found in PH. The average temperature, pressure, and decrement of potential energy during simulation are much higher in defective systems compared to the perfect ones.