Numerical simulation of confined PBX charge under low velocity impact at high temperature
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摘要:
炸药撞击感度和热安全性是评价炸药安全性能的重要指标。为了对高温下炸药撞击敏感性变化规律进行可靠预测，本文中通过数值模拟，研究不同预加热温度下带壳PBX炸药装药在小弹丸低速撞击下的热力学响应，得到炸药点火前至点火阶段局部高温区的位置、形态、温度和应变随时间在炸药中分布的变化。结果显示，炸药发生点火的撞击阈值速度与烤燃温度的关系并非单一随温度升高而降低，而是在加热至348.15 K时达到最高；根据温度和应力应变云图分析可得，随着烤燃温度的提高，炸药强度下降，PBX炸药装药局部高温区快速升温的主导因素由局部剪切变为压缩。热软化对炸药的撞击敏感性起重要作用。
Abstract:Accidental initiations of the explosive subjected to mechanical or thermal loads have caused numerous catastrophic tragedies. The impact sensitivity and thermal safety of explosive is of great importance for the applications. Previous work showed an evident decline on modulus with increasing cook-off temperature, which suggest that Cook-off temperature may affect the deformation process of the impacted PBX, and further affect the critical impact velocities for initiation. In this work, to investigate the mechanical and thermal response of confined PBX charge under low velocity impact of a small projectile during cook-off events, a finite-element model was established to provide reliable prediction of explosive safety performance at high temperature. A thermal-mechanical-combined experiments from literature enabled comparisons between simulated results and measured data for the critical impact velocities of initiation for a HMX-based PBX charge (HMX/TATB/olefin). The simulation results showed that when it was heated up to 348.15 K, the critical impact velocity of initiation for the explosives reached the maximum (360 m/s). With the increase of cook-off temperature, the localized heating regions change from the surface of explosive charge to the center. This phenomenon was caused by the effect of compression overshadows shearing on the initiation because of the strength decreases in the heated PBX, implying that thermal softening plays an important role in the impact sensitivity of the heated PBX charge.
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Key words:
- PBX /
- thermal-mechanical coupling /
- impact /
- sensitivity
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图 1 使用表1参数的应变率-温度-最大流动应力曲面图
Figure 1. Maximum flow stress as a function of temperature and strain rate at selected parameters
图 2 二维轴对称有限元模型及其网格划分示意图
Figure 2. Meshing of two-dimensional axisymmetric finite-element model
图 3 预加热温度为301.15 K时，不同撞击速度下炸药装药的反应过程分数云图
Figure 3. Reaction fractions at different impact velocities and a preheating temperature of 301.15 K
图 4 预加热温度为348.15 K时，不同撞击速度下炸药装药的反应过程分数云图
Figure 4. Reaction fractions at different impact velocities and a preheating temperature of 348.15 K
图 5 预加热温度为378.15 K时，不同撞击速度下炸药装药的反应过程分数云图
Figure 5. Reaction fractions at different impact velocities and a preheating temperature of 378.15 K
图 6 不同预加热温度和撞击速度下炸药装药中的最大反应过程分数
Figure 6. The maximum reaction process fraction at different pre-heating temperatures and impact velocities
图 7 不同预加热温度和撞击速度下PBX炸药装药的平均反应过程分数
Figure 7. The average reaction fractions of the PBX charge at different temperatures and impact velocities
图 8 预加热温度为301.15 K时炸药装药的温度云图
Figure 8. Temperature of the explosive charge at a preheating temperature of 301.15 K
图 9 预加热温度为301.15 K时炸药装药的体积应变云图
Figure 9. Volumetric strain of the explosive charge at a preheating temperature of 301.15 K
图 10 预加热温度为301.15 K炸药装药的等效应变云图
Figure 10. Equivalent strain of the explosive charge at a preheating temperature of 301.15 K
图 11 预加热温度为301.15 K炸药装药的Mises应力云图
Figure 11. Mises stress of the explosive charge at a preheating temperature of 301.15 K
图 12 预加热温度为348.15 K时炸药装药的温度云图
Figure 12. Temperature of the explosive charge at a preheating temperature of 348.15 K
图 13 预加热温度为348.15 K时炸药装药的体积应变云图
Figure 13. Volume strain of the explosive charge at a preheating temperature of 348.15 K
图 14 预加热温度为348.15 K炸药装药的等效应变云图
Figure 14. Equivalent strain of the explosive charge at a preheating temperature of 348.15 K
图 15 预加热温度为348.15 K炸药装药的Mises应力云图
Figure 15. Mises stress of the explosive charge at a preheating temperature of 348.15 K
图 16 预加热温度为378.15 K时炸药装药的温度云图
Figure 16. Temperature of the explosive charge at a preheating temperature of 378.15 K
图 17 预加热温度为378.15 K时炸药装药的体积应变云图
Figure 17. Volumetric strain of the explosive charge at a preheating temperature of 378.15 K
图 18 预加热温度为378.15 K炸药装药的等效应变云图
Figure 18. Equivalent strain of the explosive charge at a preheating temperature of 378.15 K
图 19 预加热温度为378.15 K炸药装药的Mises应力云图
Figure 19. Mises stress of the explosive charge at a preheating temperature of 378.15 K
图 20 局部高温区的位置变化
Figure 20. The change of the locations of localized heating at different preheating temperatures
图 21 不同预加热温度下PBX炸药中局部高温区的温度时间曲线
Figure 21. Temperature as a function of time for the localized heating regions at different preheating temperatures
图 22 不同预加热温度下PBX炸药中局部高温区的塑性功时间曲线
Figure 22. Plastic work as a function of time for the localized heating regions at different preheating temperatures
图 23 不同预加热温度下PBX炸药中局部高温区内能时程曲线
Figure 23. Histories of internal energy for the localized heating regions at different preheating temperatures
表 1 Johnson–Cook强度模型参数
Table 1. Parameters of Johnson–Cook model
A/MPa B/MPa C m n Tref/K Tm/K 15 0 0.2 0.6 1 301.15 540 
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表 2 固体反应物的状态方程参数
Table 2. Equation of the state parameters for solid reactants
pcrush/MPa μcrush K1 K2 K3 Klock μlock 0.689 5 0.125×10−3 0.102 7×1011 0.217 2×1012 0.288 8×1013 0.665 4×1011 0.09
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表 3 气体产物的状态方程参数
Table 3. Equation of the state parameters for gaseous products
R1/GPa R2 R3/GPa R4 ω 166.89 5.9 5.969 2.1 0.45
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表 4 PBX化学动力学参数
Table 4. Chemical kinetic parameters for PBX
No. Zk/s−1 Ea k/(kJ·g−1·mol·K) 1 1.08×1026 148.93 2 1.41×1021 220.64 3 2.60×1016 185.48
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表 5 用于温度计算的参数
Table 5. Parameters for temperature calculation
TCJ/K vCJ/cm3/g R5/GPa CV, s/(J·kg−1·K−1) CV, CJ/(J·kg−1·K−1) 2 500 0.387 3 0.85 1 600 2 000
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