The effect of impact orientation on the critical velocity needed to initiate a covered explosive charge

Recent studies show that a heavy metal fragment, such as tungsten, could be more effective against a covered target than a conventional steel fragment. To further quantify this, we determined the detonation threshold surface for a tungsten platelet 1.24- x 1.24- x 0.62 cm impacting a steel plate 0.330 cm thick covering an explosive charge. The objectives were to determine the threshold impact speed for detonation as a function of impact orientation; determine if the Jacobs equation applies to this impactor; and, if not to gain insight into developing a similar relation that could be used in vulnerability analysis. Three dimensional simulations of various fragment-target encounters were developed using the Eulerian Hydrocode CTH. We selected the impact geometry and estimated a starting velocity, then CTH was run to determine if a detonation was predicted. From this starting point, fragment velocity was adjusted up or down until the critical velocity was bounded within ± 33m/s. We learned that fragment orientation has a significant effect on the critical velocity needed to initiate a covered charge. The current shape factor provides reasonable results for a range of impact orientations.