Fast Cook-off Thermal Protection Effects of Inner and Outer Heat-insulating Composite Structures of Explosive Charge

doi:10.12382/bgxb.2023.0065

Abstract

Abstract:

In order to study the thermal protection effects of the inner and outer heat-insulating composite structures (inner heat-insulating material/outer combustion-insulating material) of explosive charges under the condition of fast cook-off (burning), the multi-point temperature measurement fast cook-off experiments are carried out on explosive charges with various forms of inner and outer heat-insulating composite structures. The temperature-time curves of flame and each measuring point of explosive charge and the ignition response time of the charge are obtained. The fast cook-off ignition of explosive charges with different inner and outer heat-insulating composite structures is numerically simulated to obtain the influence law of inner and outer heat-insulating composite structures on the ignition response time of charge under fast cook-off. The results show that the thermal conductivity of the outer combustion-insulating material is increased and its thermal insulation is weakened due to the burning and denaturation of the material during the process of fast cook-off experiment. This effect should be considered in numerical simulation. The ignition response time of explosive charge is delayed with the increase in the coating thickness of both heat-insulating and combustion-insulating materials, whether using separate insulating/combustion-insulating materials or inner and outer heat-insulating composite structures. The inner and outer heat-insulating composite structures have better thermal protection ability and can significantly delay the ignition response time of the charge. The ignition position all occurs at the corner of the end face of the charge, and the reaction intensity after ignition is not affected by the inner and outer heat-insulating composite structures and is always the deflagration. For insulating/combustion-insulating materials within a certainprotection performance range, the composite structure has the best heat-insulating effect when the coating material on the outer surface of the shell is HGN and the coating material on the inner surface of the shell is GXTI, and when the required heat-insulating effect is given, it is possible to consider increasing the coating thickness of the outer surface coating of the shell first to achieve the optimal thermal protection effect of inner and outer heat-insulating composite structures with minimum coating thickness. The research results provide reference for improving ammunition thermal safety design.

Key words: explosive charge, fast cook-off, inner and outer heat-insulating composite structures, thermal protection effect, ignition delay

CLC Number:

TJ55

BAI Mengjing, DUAN Zhuoping, BAI Zhiling, ZHANG Yulong, LIU Ruifeng, ZHANG Liansheng, HUANG Fenglei. Fast Cook-off Thermal Protection Effects of Inner and Outer Heat-insulating Composite Structures of Explosive Charge[J]. Acta Armamentarii, 2024, 45(5): 1555-1563.

Figures/Tables 13

Fig.1 Diagram of the fast cook-off experimental system

Fig.2 Diagram of temperature measuring point

Table1 Inner and outer heat-insulating composite structures of four cook-off bombs

弹体序号	壳体内表面材料		壳体外表面材料
弹体序号	涂覆厚度/mm	材料	涂覆厚度/mm	材料
1	1.00	HGN
2	1.33	GXTI
3	0.78	GXTI	0.87	HGN
4	1.32	GXTI	1.00	HGN

Table 2 Experimental results

弹体序号	响应时间/s	测点温度/K					响应等级
弹体序号	响应时间/s	测点1	测点2	测点3	测点4	测点5	响应等级
1	150	-	-	-	-	-
2	195	379.85	-	368.55	322.85	299.15	爆燃
3	288	455.45	-	404.45	-	306.25
4	329	497.75	-	403.25	-	299.7

Fig.3 Recovered shells and residual explosives

Fig.4 Computation model for fast cook-off experiment

Table 3 Physical parameters of shell, heat-insulating material and air

材料	ρ/(kg·m^-3)	C_v/(J·kg^-1·K^-1)	λ/(W·m^-1·K^-1)
钢壳体^[18]	8030	502.48	16.27
GXTI	700	1400	0.065
HGN	450	900	0.035
空气^[18]	1.225	1 006.43	0.0242

Fig.5 Comparison of calculated and experimental temperature-time curves for the second cook-off bomb

Fig.6 Comparison of calculated and experimental temperature-time curves for the third cook-off bomb

Fig.7 Comparison of calculated and experimental temperature-time curves for the fourth cook-off bomb

Fig.8 Temperature field at the ignition moment of explosive

Fig.9 Calculated results of fast cook-off response time of cook-off bombs with different inner and outer heat-insulating composite structures

Fig.10 Calculated results of fast cook-off response time of cook-off bombs with different thickness inner or outer heat-insulating HGN coating

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