Research on the Pressure Relief Structure of JEO Shaped Charge Warhead during Cook-off

doi:10.12382/bgxb.2022.0435

Abstract

Abstract:

A pressure relief structure of JEO shaped charge warhead during cook-off is studied to improve the thermal safety of JEO shaped charge warhead. A multiphase flow component transport model of explosive cook-off is established, in which the effect of thermal decomposition pressure on the cook-off process is considered. A multi-point temperature and pressure measurement experiment is designed to study the temperature and pressure change characteristics of JEO explosive during the cook-off process and check the relevant parameters of the model. The thermal decomposition process of JEO explosive in the shaped charge structure is numerically simulated to obtain the change laws of temperature and solid volume fraction of the explosive under different heating rates, and determine the ignition position and pressure of the explosive in the structure. In view of the combustion process of JEO explosive after ignition, the pressure relief delay time is introduced, and an explosive pressure growth model considering the pressure relief structure is established. The critical pressure relief area of JEO explosive in this structure is determined. The influence law of different charge ignition positions on the internal pressure change of the explosive is calculated and obtained by taking the ignition position and ignition pressure obtained in the thermal decomposition numerical simulation as initial conditions. According to the critical pressure relief area, ignition position and pressure growth in the explosive, the area of pressure relief hole on side wall and the pressure screw size of the end liner are determined, and a combined pressure relief structure of pressure relief hole and liner push-out suitable for JEO explosive in this structure is designed. Fast and slow cook-off experiments were carried out on JEO shaped charge warhead with the pressure relief structure, and the effectiveness of the pressure relief structure was verified. The research results indicate that as the heating rate decreases, the ignition time of JEO charge shaped charge warhead is prolonged, and the ignition position moves from the surface of the charge to the center of the charge. As the distance between the ignition position and the pressure relief structure increases, the ignition delay time increases, the peak pressure inside the shaped charge warhead increases, and the reaction intensity of the warhead also increases.

Key words: shaped charge, cook-off, thermal safety, numerical simulation

CLC Number:

O389
TJ5

WANG Xinyu, JIANG Chunlan, WANG Zaicheng, FANG Yuande. Research on the Pressure Relief Structure of JEO Shaped Charge Warhead during Cook-off[J]. Acta Armamentarii, 2024, 45(1): 1-14.

Figures/Tables 29

Table 1 The properties of JEO explosives

参数	取值
NTO/%	45.5
HMX/%	45.5
化学式	C_3.045H_4.600N_5.000O_4.660
密度ρ/(g·cm^-3)	1.78
生成焓ΔH/(kJ·kg^-1)	-259.81
爆速D_C-J/(m·s^-1)	8262
爆压p_C-J/(GPa)	29.25
粘结剂/%	8
钝感剂/%	1
爆热Q_P/(kJ·kg^-1)	4739
冲击感度P_I/%	18
摩擦感度P_F/%)	15
比热容C_p/(Jg·℃^-1)	1.05
热导系数λ/(W·m^-1·K^-1)	0.7562

Fig.1 Test device

Fig.2 Upper and lower shells and bolts after reacting

Fig.3 Temperature/pressure-time curve

Table 2 Chemical reaction kinetic parameters[22]

参数	数值
指前因子A/s^-1	1.97×10¹⁴
活化能E/(J·mol^-1)	117360
摩尔质量MW/(g·mol^-1)	185.7
温度指数m	0
压力指数δ	0.7
参考温度T₀/K	262
参考压力p₀/Pa	101325

Table 3 Thermodynamic parameters

结构	密度/ (g·cm^-3)	热导率/ (W·m^-1·K^-1)	比热容/ (J·kg^-1·K^-1)
壳体	2.72	202.4	871
装药	1.78	0.7562	1050

Fig.4 Comparison of calculated and test results

Table 4 Comparison of calculated and test results (1K/min)

参数	计算值	实验数据	误差/%
点火时间/s	10690	10692	0.01
点火温度/K	492	495	0.6
压力峰值/MPa	1.67	1.59	5

Table 5 Mesh and time step independence verification

网格尺寸/mm	时间步长/s	点火时间/s	误差/%
	1.0	10762	0.6
1.0	0.5	10732	0.3
	0.1	10732	0.3
	1.0	10742	0.40
0.5	0.5	10690	0.01
	0.1	10690	0.01
	1.0	10730	0.30
0.1	0.5	10689	0.02
	0.1	10689	0.02

Fig.5 Simplified structure of shaped charge structure

Fig.6 Structure calculation model and typical gauge points

Table 6 Thermodynamic parameters of each part of shaped charge structure

结构	材料	密度/ (kg·m^-3)	热导率/ (W·m^-1·K^-1)	比热容/ (J·kg^-1·K^-1)
药型罩	Al/PTFE	2420	0.49	436
下部壳体	45号钢	7850	49.8	502.48
上部壳体	铝	2719	202.4	871
引信	等效材料	7300	49.8	502.48
引信传爆药	惰性等效材料	1765	0.75	1050
压螺	45号钢	7850	49.8	502.48

Fig.7 Temperature distribution at typical time of charging under the condition of rapid heating

Fig.8 Temperature/pressure-time curves of typical gauge point inside the charge under the condition of rapid heating

Fig.9 Volume fraction-time curve of solid charge/gaseous product under the condition of rapid heating

Fig.10 Temperature distribution at typical time of charging under the condition of slow heating

Fig.11 Temperature/pressure-time curves of typical gauge point inside the charge under the condition of slow heating

Fig.12 Volume fraction-time curve of solid charge/gaseous product under the condition of slow heating

Fig.13 Explosive combustion crack network model

Fig.14 Simplified model of structure crack propagation(left: warhead, and right: simplified cylindrical structure)

Table 7 Parameters used in the pressure growth model

参数	数值
ρ_e0/(g·cm^-3)	1.78
V_e0/cm³	1561.3
α	0.28
β	0.924
p_IG/MPa	0.32(3K/s)
	2.9(3.3K/h)
S_max/(cm²·g^-1)	208.3
m	1.43
C_D	0.78
a^/*(m·s^-1)	725
G/MPa	2570
ν	0.3
M/MPa	3375

Fig.15 Pressure growth curves of explosives at different positions of ignition

Fig.16 Pressure relief structure

Fig.17 Layout of fast cook-off test

Fig.18 Flame versus time during fast cook-off

Fig.19 Fast cook-off results

Fig.20 Layout of slow cook-off test168600s

Fig.21 Overpressure curves during slow cook-off

Fig.22 Slow cook-off results

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