低压长脉冲刺激下含缺陷HMX晶体的剪切点火行为研究

As one of main mechanisms of non-shock initiation, shear ignition is a frontier issue in the research of explosive safety. As a key ingredient of plastic bonded explosives in modern weapons, HMX crystals probably experience low-pressure and long-pulse loadings in accident scenarios. Under low-pressure and long-pulse loadings, the natural defects in HMX crystals, such as microvoids and microcracks, can cause the shear stress concentration and the formation of shear bands, which may lead to the shear ignition. However, the published research works on the shear ignition of defective HMX crystals under low-pressure and long-pulse loadings are only based on numerical simulations, which severely lack experimental data. Furthermore, there is no clear understanding of the ignition caused by defects in HMX crystals. In this project, the HMX crystals with prefabricated defects are chosen as the experimental samples, and a comprehensive experimental method that includes low-pressure and long-pulse loading, low-to-medium-level temperature-rise measurement, high spatial-temporal resolution imaging and surface velocity measurement is established. In addition, the meso-numerical simulations are also executed. The purpose of this project is to study the rule of defect evolution, defect-induced shear band formation and shear ignition in defective HMX crystals under low-pressure and long-pulse loadings. Besides, the physical images of the temperature rise process around the defect and inside the shear bands are needed. The internal relationship among local-temperature-rise ignition, defect evolution and shear band formation is deeply analyzed, which provides further understandings of shear ignition behaviors of defective HMX crystals.

剪切点火作为非冲击点火的主要机制之一，是炸药安全性领域所关注的前沿问题。HMX晶体作为武器装药中的关键做功介质，其在撞击类事故场景下容易受到低压长脉冲力学载荷刺激。由于HMX晶体内普遍存在一定的微缺陷，在低压长脉冲下微缺陷可能引发剪切点火。然而目前对低压长脉冲刺激下含缺陷HMX晶体剪切点火行为的研究还停留于理论计算层面，缺乏实验数据支撑，对晶体中由缺陷演化引起的剪切温升点火规律尚未形成清晰的认识。因此本项目以含预制缺陷形貌可控的HMX晶体为研究对象，建立集低压长脉冲加载、中低温测量、高时空分辨成像、速度剖面测量等于一体的综合实验技术，并结合细观数值模拟，旨在研究低压长脉冲刺激下含缺陷HMX晶体中的缺陷演化规律、缺陷诱发的剪切带形成规律以及局域温升点火规律，获得缺陷周围及剪切带内部温升历程的物理图像，剖析局域温升点火与缺陷演化、剪切带形成之间的内在联系，为深入认识剪切点火行为提供有力支撑。

首先，针对HMX晶体机械加工难度大、易发生脆性断裂的特点，利用自主搭建的飞秒激光微加工平台，开展了HMX晶体中微缺陷的预制工作，研究了飞秒激光作用下HMX晶体的损伤阈值及飞秒激光脉冲能量和焦斑大小对损伤区形貌的影响，获得了最佳出光条件，在HMX晶体中成功构造了100μm量级形状可控的单一缺陷。其次，利用空间分辨率不低于10μm量级、时间分辨率不低于10μs量级的显微成像技术，开展了低压长脉冲加载下预制缺陷演化、剪切带形成及温升点火行为的研究工作，获得了由预制缺陷诱发剪切带形成及裂纹起裂扩展的特征规律，明确了潜在点火位置为剪切带所在区域。最后，结合数值模拟程序对含缺陷HMX晶体的温度场进行了计算，结果表明剪切带内温升显著高于基体温升。