Propagation of reactive cracks and characterization of reaction violence in spherical charge under strong confinement
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摘要: 炸药燃烧的高温高压气体产物可以进入基体裂纹中引发炸药表面热传导燃烧，形成所谓的对流燃烧。在一定约束条件下，不断上升的气体压力反过来又使炸药基体产生更多的裂纹，为对流燃烧提供更多的通道和燃烧表面积，快速生成大量产物气体导致高烈度反应现象的产生。本文中设计了一种新型强约束球形装药中心点火实验，针对一种HMX为基的PBX炸药，对高烈度反应条件下燃烧裂纹传播和反应增长过程进行了观测，实验中采用测得的反应压力和壳体速度历程对反应烈度进行了量化表征。在带窗口结构中，早期炸药中的燃烧裂纹不可见；中期燃烧裂纹扩展到药球表面时，先形成4条沿经线方向近似对称的主裂纹，随后环向贯通并扩展到整个药球表面；最后的剧烈反应造成强烈发光。上述反应演化经历低压增长阶段约为100 μs，之后伴随着壳体变形膨胀产生剧烈的反应，此时产物压力在约10 μs时间内超过1 GPa，并形成约20%相对于裸炸药爆轰的超压输出。在全钢结构中，20 mm厚的壳体膨胀速度最大可达到500 m/s，此时壳体完全破裂。Abstract: High temperature gaseous products of conductive burning on explosive surface can penetrate into preformed crack inside explosive bulk under high pressure to form so-called convective burning. The high rising gaseous products pressure resulting from the convective burning in turn will create cracks inside the explosive bulk, leading to the formation of new channels for convective reaction and the more reaction surfaces for burning. In this paper, a new experimental method is designed for a pressed HMX-based PBX, in which a highly confined spherical charge is ignited on center point via non-shock initiation. The propagation of such kind of reactive cracks inside is recorded and evaluated with the total reaction violence growth behavior characterized by reaction pressure and confinement wall velocity profile. In the experiment with a transparent window, the early stage evolution of crack inside explosive sphere is invisible and the crack system after the crack break through to the spherical surface shows a 4 fold symmetric crack pattern which is deduced to be related with outer layer confinement conjunction manner. The violence evolution experiences a sustaining low pressure growing rate stage for 100 μs. Then it is observed that a rapid burst pressure in about 10 μs is up to over 1 GPa during the confinement wall movement stage, which gives to a typical explosion outcome with ～20% of bare explosive detonation calculated by air blast over pressure. In the experiment with a 20 mm steel wall, the velocity of the wall has reached 500 m/s at the moment of confinement wall rupture.
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Key words:
- convective burning /
- brittle PBX /
- reactive crack /
- violent reaction
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图 1 带窗口强约束球形装药实验装置及其测试布局示意图
Figure 1. Schematic representation of experimental setup and diagnostic arrangement of spherical charge under strong confinement with optical window
图 2 全钢结构强约束球形装药实验装置及其测试布局示意图
Figure 2. Schematic representation of experimental setup and diagnostic arrangement of spherical charge under full steel confinement without optical window
图 3 带窗口实验装置反应裂纹完整演化过程高速摄影图像（幅频18 000 s−1）
Figure 3. High-speed photos of full evolution process of reactive crack system in the experiment with PMMA window (frame rate of 18 000 s−1)
图 4 反应裂纹扩展演化早期阶段II高速摄影图像（幅频18 000 s−1）
Figure 4. High-speed photos of the crack propagation at the early half of stage II (frame rate of 18 000 s−1)
图 5 全钢结构实验装置壳体破裂反应发光过程高速摄影图像（幅频18 000 s−1）
Figure 5. High-speed photos of full evolution process of case rupture and reaction illumination in the experiment with steel shell (frame rate of 18 000 s−1)
图 6 带窗口实验装置壳体速度和内部压力历程
Figure 6. Pressure inside confinement and velocity profiles in experiment with window
图 7 全钢结构实验装置壳体速度和内部压力历程
Figure 7. Velocity profiles and pressure inside confinement without window
图 8 全钢结构实验回收壳体碎块残骸
Figure 8. Recovery fragments of full steel confinement in second experiment
图 9 带窗口和全钢结构实验中测得的空气冲击波超压波形
Figure 9. The air blast overpressure measured in the experiment with and without window
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