Theoretical Model of Metal Gap Ejection under Strong Impact Loading and Its Verification

Metal plates containing penetrating gap may eject high velocity material outward from the gap opening under strong impact loading. Experiments have observed that some facts significantly affect the gap ejection behavior, such as metal properties, gap size, and loading method. Since the shape of the gap is the strip with a much greater depth than width, the mature instability theory is hard to apply, and it is difficult to accurately predict the mass and the velocity of the ejecta under this situation. In this paper, we develop a model for this case based on the shaped charge jet theory. The modeling is divided into two parts: the approximately steady jet formed by the long distance closure of gap in the depth direction, and the overturning of the interface after the gap closure reaches the surface. The theoretical model can precisely predict the total mass and maximum velocity of the ejecta. Thereafter, the verification of the theoretical model is carried out with the experiments and the simulation of the detonation-driven lead and copper metal plates containing penetration gaps. The total mass and maximum velocity of the ejecta obtained from the theoretical model agree well with the experimental and simulation results. The experimental phenomenon of the needle-like and mushroom-like ejecta formation is interpreted by the jet incoherence theory, and we proposed a method to determine the ejection coefficient of the theoretical model from this. Finally, a theoretical estimate model for metal gap ejection under sliding detonation loading is presented. The model in this paper can also be applied to the metal gap ejection phenomena formed by non-penetrating elongated gaps closure that satisfying the conditions of steady jet formation.