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When considering the bomb explosion damage effect, the air shock wave and high-speed fragments of the bomb case are two major threats. In experiments, the air shock wave was studied by the bare explosives superseding the real cased bomb; in contrast, the bomb case influence was ignored to reduce risk. The air explosion simulations of the MK84 warhead with and without the case were conducted. The numerical simulation results showed that the bomb case significantly influenced the shock wave generated by the bomb: the spatial distribution of shock wave in the near field changed, and the peak value of shock wave was reduced. Breakage of the case and kinetic energy of the fragmentation consumed 3 and 38% of the explosion energy, respectively. The increasing factors of the peak overpressure induced by the bare explosive on the ground and in the air were 1.43–3.04 and 1.37–1.57, respectively. Four typical stages of case breakage were defined. The mass distribution of the fragments follows the Mott distribution. The initial velocity distribution of the fragments agreed well with the Gurney equation.

The Gurney method is widely used in the conceptual design stage of explosive fragmentation warheads employed in various weapons systems. This method states that the peak fragment velocity ( V 0 ) is a function of the Gurney velocity ( 2 E G ) and the charge-to-metal weight ratio ( C / M ). The current study is concerned with finding a practical approach for computing the Gurney velocity of pure and mixed high explosives which will eventually help warhead designers to select the best explosive to fulfill the needs of a particular mission. Using multiple regression analysis technique, a four-variable model was derived and used thereafter to estimate the Gurney velocity of aluminized and non-aluminized explosive formulations. The results show that the new model is particularly accurate in predicting the Gurney velocity of combined effects explosives, which are relatively a new class of high blast, high metal acceleration capability explosive compositions.

With the technical development of new warhead designs and improvised explosive device protection, irregular casing filled with explosive has been paid more attention recently. In this paper, we studied the fragmentation of a type of D-shaped casing, which is a common asymmetric casing in the field of warhead design. Based on the radiograph technique, static explosive experiments were conducted with D-shaped casings under four different eccentric initiation ratios to explore their fragmentation. A numerical model was then established to simulate the dynamic response of D-shaped casing filled with explosive. The results of numerical simulation were found to agree well with the experimental data. According to the results of numerical simulation and experimental data, the dynamic responses of D-shaped casing were analyzed. The results of the current work pave way for the innovative design of new warhead and for further studying the dynamic response of asymmetric casing. Keywords: D-shaped casing, Eccentric initiation, X-ray radiograph technique, Fragmentation, Numerical simulation

New advanced numerical computer model enabling accurate simulation of fragmentation parameters of large Length over Diameter (L/D) explosively driven metal shells has been developed and validated. The newly developed large L/D multi-region model links three-dimensional axisymmetric high strain high strain-rate hydrocode analyses with the conventional set of Picatinny Arsenal FRAGmentation (PAFRAG) simulation routines. The standard PAFRAG modeling technique is based on the Mott's theory of break-up of idealized cylindrical “ring-bombs”, in which the length of the average fragment is a function of the radius and velocity of the shell at the moment of break-up, and the mechanical properties of the metal. In the newly developed multi-region model, each of the shell region, the break-up is assumed to occur instantaneously, whereas the entire shell is modeled to fragment at multiple times, according to the number of the regions considered. According to PAFRAG methodology, the required input for both the natural and the controlled fragmentation models including the geometry and the velocity of the shell at moment of break-up had been provided from the hydrocode analyses and validated with available experimental data. The newly developed large L/D multi-region PAFRAG model has been shown to accurately reproduce available experimental fragmentation data.

The tuneable effects concept is aimed at achieving selectable blast and fragmentation output, to enable one charge to be used in different scenarios requiring different levels of blast and fragmentation lethality. It is a concept QinetiQ has been developing for an energetic fill consisting of three principal components arranged in co-axial layers, two explosive layers separated by a mitigating but reactive layer. The concept was originally designed to operate in two modes, a low output mode which only detonates the central core of high explosive and a high output mode which detonated both the central core and outer layer of the explosive. Two charge case designs where manufactured and tested; one of these designs showed a reduction in blast and fragment velocities of ~33% and ~20%, respectively, in the low output mode.

Natural fragmentation of warheads that detonates causes the casing of the warhead to split into various sized fragments through shear or radial fractures depending on the toughness, density, and grain size of the material. The best known formula for the prediction of the size distribution is the Mott formulae, which is further examined by Grady and Kipp by investigating more carefully the statistical most random way of portioning a given area into a number of entities. We examine the fragmentation behavior of radially expanding steel rings cut from a 25 mm warhead by using an in house smooth particle hydrodynamic (SPH) simulation code called REGULUS. Experimental results were compared with numerical results applying varying particle size and stochastic fracture strain. The numerically obtained number of fragments was consistent with experimental results. Increasing expansion velocity of the rings increases the number of fragments. Statistical variation of the material parameters influences the fragment characteristics, especially for low expansion velocities. A least square regression fit to the cumulative number of fragments by applying a generalized Mott distribution shows that the shape parameter is around 4 for the rings, which is in contrast to the Mott distribution with a shape parameter of ½. For initially polar distributed particles, we see signs of a bimodal cumulative fragment distribution. Adding statistical variation in material parameters of the fracture model causes the velocity numerical solutions to become less sensitive to changes in resolution for Cartesian distributed particles.