On the deformation of spherical fragment driven by explosion

Spherical fragments deform into a bullet-like shape under detonation. This deformation has a significant effect on the aerodynamic and penetration performance of the fragment. In this work, normalized axial and radial eccentricity ratios are proposed to characterize the features of the deformed spherical fragments. A two-dimensional shockwave propagation theoretical model is established to reveal the deformation mechanism. Numerical simulations supported by fragment recovery experiment are conducted to verify the accuracy of the model. The effects of the simplifying assumptions on the theoretical results are evaluated and discussed. The results show that the radial asymmetric deformation of the fragment is caused by the difference in shockwave velocities inside and outside the fragment. These velocities are controlled by the Hugoniot parameters of the fragment and the binding material. Fragments with lower acoustic impedance have a more pronounced radial asymmetric deformation trend. Spherical fragments experience two phases during deformation: a unilateral compression phase and a bilateral stretching and compression phase. The difference between deformation direction of these two phases leads to the axial asymmetric deformation. The axial eccentricity ratio increases with the relative distance from the initiation end of the warhead. This study provides a reference for material selection and structural design of spherical fragment warheads.