A numerical investigation on explosive fragmentation of metal casing using Smoothed Particle Hydrodynamic method

Explosively driven fragmentation of ductile metals is a highly complex phenomenon. It is an important issue in a variety of circumstances like structure protection, weapon effectiveness and safety distance. Simulations of the fragmentation of metal casing are characterized by a number of interesting and challenging behaviors. These include the volume expansion of the solid charge and its transformation into highly pressurized products. This rapid pressurization of the metal case leads to large deformations at high strain rates and eventual casing rupture. Once the metal casing breaks apart, the highly pressurized product escapes from the gap of the failing casing and generates a shock wave. In addition, the fragments from the metal casing scatter with high velocities in set directions. In the conditions of near field explosion, the spatial distribution of fragments with powerful penetrability has considerable influence on the failure pattern of the target. In the present study, the finite difference engineering package AUTODYN combined with Smoothed Particle Hydrodynamics (SPH) method is used to investigate numerically the fragmentation process of a cylindrical metal casing with ends. After applying the numerical method to predict the propagation of detonation wave, the expansion and rupture process, the expansion velocity of metal casing, the leakage of detonation products and the fragment distribution, the fragment mass distribution is validated by comparing the numerical results with experimental data in the literature. Additionally, an experiment was conducted with the same explosive fragmentation geometry as modeled. The characteristics of the observed fragment distributions and fragment velocities are compared with the numerical simulation. The results reveal that the path of detonation wave is directly related to the expansion velocity of the casing. The fragment sizes depend on the axial position on the casing when the charge is detonated at endpoint, and they are related to the relative axial strain rate. The relatively low axial strain rate, especially in the central and further region of the detonating cylindrical casing, is probably the quantity responsible for the larger fragments. The end far away from the initiation point produces more massive fragments with maximum kinetic energy. It has been demonstrated that the numerical method presented here is capable of simulating the explosive fragmentation of a metal casing with ends.