低压长脉冲载荷下β-HMX单晶滑移系的微观物理化学响应

采用基于ReaxFF反应力场的分子动力学方法, 从炸药弹塑性微观机制出发, 研究了在低压长脉冲载荷下β-1,3,5,7-四硝基-1,3,5,7-四氮杂环辛烷(β-HMX)炸药单晶中最有可能的七组滑移系的微观物理化学响应.模拟结果表明沿着垂直于(001)、(101)、(100)、(011)、(111)、(110)、(010)晶面的长脉冲作用方向, 这七组滑移系呈现不同的物理化学响应. 体系的剪切应力、能量、温度以及化学反应与长脉冲作用方向存在明显的依赖性: 对(010)晶面, 体系的剪切应力位垒高, 能量和温度升高得快, 化学反应很快发生, 反应敏感度最高; 对(001)晶面,体系的剪切应力位垒低, 能量和温度变化缓慢, 化学反应很难发生, 因此反应敏感度低. 滑移系的反应敏感度与滑移面两侧的分子间接触程度(即空间位阻)以及接触原子或基团间的反应活性紧密相关. 对空间位阻大且相互接触的原子或基团容易发生反应的方向, 滑移系的反应敏感度就高; 对空间位阻小或相互接触的原子或基团不容易发生反应的方向, 滑移系的反应敏感度就低. 具有较高化学反应敏感度的滑移系被认为与单晶炸药中的“热点”起源有关. 本研究为进一步发展更加合理和可靠的感度评价方法提供了理论支撑.

Microscopic Physical and Chemical Responses of Slip Systems in the β-HMX Single Crystal under Low Pressure and Long Pulse Loading

From the viewpoint of the elastic-plastic microscopic mechanisms of explosives, we investigated the microscopic physical and chemical responses of seven dominant slip systems in the β-octahydro-1,3,5,7- tetranitro-1,3,5,7-tetrazocine (β-HMX) single crystal under low pressure and long pulse loading using the ReaxFFforce- field-based molecular dynamics method. The simulation results suggest that the seven slip systems exhibit different physical and chemical responses for loading orientations normal to the (001), (101), (100), (011), (111), (110), and (010) crystal planes. The shear stress, energy, temperature, and chemical reaction strongly depend on the loading direction. For the (010) plane, the shear stress barrier is very high, which leads to fast energy accumulation and temperature increment that contribute to the early bond-breaking process, making it the most sensitive direction. For the (001) plane, the small shear stress barrier results in slow energy accumulation and temperature increase, and thus little bond dissociation, making it the least sensitive direction. The reaction sensitivity of the slip system is suggested to be significantly related to the intermolecular contacts on the two sides of the slip plane (i.e., steric hindrance) and the reaction activity of contacted atoms or groups. Directions with large steric hindrance and high reaction activity lead to high reaction sensitivity, whereas directions with small steric hindrance or low reaction activity result in low reaction sensitivity. The slip system with relatively high chemical reaction sensitivity is suggested to be associated with the origin of“hot spots”in energetic single crystals. This study provides theoretical support for developing a more reasonable and reliable sensitivity evaluation method for high explosives.