Influence of Void Configurations on Hot Spot Temperature in PBXs under Impact Loading

Abstract

In this study, similarity analysis and mesoscale simulations were performed to investigate hot spot temperatures in triangular voids inside polymer-bonded explosives (PBXs). We found that there are two different void collapse modes, namely single and double hydrodynamic jet modes. The hot spot temperatures achieved in the double hydrodynamic jet mode are much higher than previous predictions, such as predictions based on circular voids, which agrees with recent experimental observations. Additionally, we verified that void configuration (position and shape) plays a significant role in increasing hot spot tem-peratures, implying that when establishing a mesoscale reaction rate model, it is insufficient to use void volume alone to characterize the impact sensitivity of PBXs. Finally, two semi-empirical analytical expressions are proposed to represent the dependence of hot spot temperature on both the void configuration and shock intensity. The resulting theoretical predictions are in good agreement with the numerically simulated results. Such mesoscale analytical expressions can be used for establishing theoretical mesoscale hot spot ignition rate models in the future.

Ubiquitiform Hotspot Ignition Model of PBX for Shock Initiation

“…To obtain the upper and lower limits of the hotspot ignition reaction rate, two extreme cases of voids in explosives are considered: 1) The voids generating the maximum hotspot energy with the same volume; 2) The voids generating the minimum hotspot energy with the same volume. For these two kinds of voids, the hotspot temperatures generated by their collapse under dynamic loading are respectively as [19, 20]: …”

“…In the previous analysis [19, 20], we have obtained that, under the same shock strength P s and the same void area S , the hotspot temperature generated by the elliptical void (the elongated state λ =4 and the inclination angle θ =90°) is the smallest, so it can be used as the position parameter T 0 , which can be expressed as: …”

“…Many studies show a clear correlation between internal defects and initiation sensitivity [8–20]. These studies mainly involve the influence of void size and shape on the formation of hotspots.…”

“…On the one hand, void size has a strong influence on sensitivity, where larger voids require lower shock pressures to form hotspots [8–14]. On the other hand, void shape and orientation can also have strong effects on initiation sensitivity [15–20], which indicates that the void volume alone does not seem reasonable to characterize the impact sensitivity of PBXs well.…”