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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 impact experiment of penetrator with enhanced lateral efficiency (PELE) penetrating the metal target plate was carried out to study the fragmentation characteristics of PELE shell made of tungs...

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.

A smooth particle hydrodynamics (SPH) model was used to simulate the fragmentation process of the jacket during penetrator with lateral efficiency (PELE) penetrating the metal target plate to study the fragmentation characteristics of PELE jacket made of tungsten alloy. The validity of the SPH model was verified by experimental results. Then the SPH model was used to simulate the jacket fragmentation under different impact velocity and thickness of target plate. The influence of impact velocity and thickness of target plate on the jacket fragmentation was obtained by analysing the mass distribution and quantity distribution of the fragments formed by the jacket. The results show that the dynamic fragmentation of tungsten alloy can be simulated effectively using the SPH model, Johnson-Cook strength model, maximum tensile stress failure criterion and stochastic failure model. When the thickness of target plate is fixed, the greater the impact velocity, the greater the pressure produced by the projectile impacting the target plate; with the increase of impact velocity, the mass of residual projectile decreases, the number of fragments formed by fragmentation of jacket increases linearly, and the average mass of fragments decreases exponentially. When the impact velocity is constant, the greater the thickness of the target plate, the longer the pressure duration by the projectile impacting the target plate; with the increase of the thickness of target plate, the mass of residual projectile decreases, the number of fragments formed by fragmentation of jacket increases linearly, and the average mass of fragments decreases exponentially. The numerical calculation model and research method adopted in this paper can be used to study the impact fragmentation of solid materials effectively.

In addition to its usage as a top attack ammunition in the battle field against troops, 120 mm mortar bomblethas been recently used in the terror attacks against military shelters and civil constructions. This research studiesthe protection of vehicle and personnel military shelters against mortar fragmentation warhead projectile and it’sdestroying effects. The mortar warhead threat combines both blast load and ballistic fragment penetration effects. Composite structure layers are proposed herein to be integrated with concertina walls to achieve full protection against the mortar projectile destroying effects. The current paper investigates the ability of the proposed layers to stop the mortar’s fragments and to mitigate its blast load. The velocity and the mass distribution of the produced projectile fragments were estimated using Split-X software. Besides, the ability of the proposed protection layers to stop the fragments and mitigate the blast wave was evaluated using AUTODYN hydrocode. A static firing test was then performed to validate the theoretical results and verify the effectiveness of the proposed protection added layers. The current study showed that the proposed composite layers are sufficient to protect the military shelters from the mortar’s destroying ballistic effects.

The investigation of the fragmentation properties along the axis of a metal shell under explosive loading is valuable for understanding the fragment formation principles of a warhead. To investigate the axial fragmentation distribution of a metal shell, herein the fragmentation from different axial positions of a metal shell under single-end detonation conditions was analyzed based on the microelement method. Moreover, a corresponding simplified model for the average fragment mass was established. The fragment distribution characteristics at different axial positions and the internal features from the metal shell fragmentation was analyzed by designing an experiment for fragment segmented recovery and fragment perforation occurring in the fragmentation of a 1045 metal steel cylinder shell filled internally with 8701 high explosives. The similarity between the fragment perforation contour and the projected contour of fragments was applied to verify the accuracy of the simplified model of the fragmentation along the axial direction, which can provide an important reference for the design of warheads and the performance of protective architecture.

Expansion and fragmentation of metallic cylinders is an important area of study both for designing munitions and mitigation techniques against fragments as well as in the failure of pressurised pipes in industry. Most of the reported studies on fragmentation have been carried out by detonating explosively filled metallic cylinders. However, this approach has inherent limitations in terms of both safety and repeatability – not least due to packing issues with explosive fills. Fragmentation studies on hollow metallic cylinders of both mild and stainless steel of various thicknesses (2–4 mm) were carried out by firing a polycarbonate projectile from a single-stage light gas gun. Strain rates of the order of 2 × 104 s−1 were observed at cylinder expansion velocities of 400–450 m s−1, calculated from flash X-ray radiographs. The differences in fragmentation behaviour of both materials was observed, attributed to their different response to high strain-rate loadings. Microscopic analysis of mild steel fragments showed interesting alignment of ferrite and pearlite grains, similar to reported effects of explosive loading. This suggests the potential to employ this technique to simulate explosive cylinder expansion in a non-explosive laboratory environment enabling a convenient recovery of fragments. Numerical modelling with using ANSYS AUTODYN® allowed for a better understanding of the various parameters controlling expansion and fragmentation. Analysis of recovered fragments by a Fragment Weight Distribution Map (FWDM), a method generally used for characterising pipe bombs, could clearly demonstrate the effect of casing material and thickness.

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.

This paper presents an innovative explosive welding technology, namely Universal Substitutive Explosive Welding technique, which was recently developed by Australian Defence Science and Technology Group to improve the survivability and mobility of military vehicles. The new technique is superior to the existing industrial explosive welding ones in terms of integrity, quality and stability. It is able to significantly upgrade the hardness upper limit of target material and ensure the perfect welding bond between the flyer (soft) and target (hard) panels without size limitation of target panel. Experimental results show that using the new technique raised the ballistic velocity limit (V50) of the explosively welded panel by up to 20% and reduced the bulge depth (related to dynamic plasticity) significantly without any rupture or fragmentation issues. Charpy impact test on the sample fabricated by the new technique showed strong recovery effects with time with no transition temperature. Keywords: Explosive welding, Armour materials, Ballistic velocity limit, Bulge depth, Charpy impact test

Oil shale is a kind of high-combustion heat mineral; in the process of exploitation, storage, and utilization, oil shale dust has the risk of explosion. The explosion characteristics and flame propagation behavior of oil shale dust are worth studying. The difference between the multiple explosion behaviors of oil shale dust was investigated with the use of a 20 L explosive spherical tank and a dust MIE experimental device. The explosion characteristics and microstructure changes of the explosive products in multiple explosions were examined. The experimental results show that the maximum explosion pressure (Pmax) dropped, and simultaneously, the minimum ignition energy (MIE), the explosion time (t), and the maximum rate of pressure rise (dp/dtmax) increased as the explosions continued. Furthermore, the oil shale continued exploding until the third explosion. Some original oil shale dust (OOSD) and explosive residues were analyzed using a scanning electron microscope (SEM) and Fourier transform infrared (FT-IR) spectrometer. The SEM images of the explosive residues indicate a high fragmentation degree and well-developed pore structure during the entire multiexplosion process. Oxygen-containing functional groups, the aliphatic C-H bond, and the aromatic C-H bond in oil shale dust all participated in the oil shale dust explosion process.

The damage pattern of rear wall/witness plate could express the fragmentation features of projectile relatively, in the ground-based tests of Whipple shield and its improved structure. In this paper, the damages of rear wall for 20 Whipple shield tests are statistically analyzed, and the linkage between the damages with impact conditions (impact velocity and plate-thickness-to-sphere-diameter ratio) are obtained. The damage pattern of rear wall, or the fragmentation pattern of sphere is defined as Intact, Ruptured and Smashed. The perforation hole on rear wall is described quantitatively. The fragmentation patterns under different impact conditions are analyzed based on the propagation and evolution of shock waves. A series of SPH simulations prove and extend the analytical and experimental works, and clearly reveal the normalized relationship between fragmentation pattern and impact condition.

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.

Ballistic tests with plate and stiffened targets impacted by cylindrical and blade-like projectiles were conducted using compressed gas gun to investigate the perforation-resistance performance of aero-engine fan casing during a blade-out event. It was observed that for the plate target impacted by the blade-like projectile, fragmentation on the projectile nose occurred and the targets were failed by petaling; but for the other combinations, the main failure mode of the targets was plugging and the projectiles were intact except in cases when the blade-like projectile hit the stiffeners. Due to the distinct failure mode, ballistic limit for the plate target impacted by the blade-like projectile was much higher. To analyze the perforation resistance of the target, the energy absorption modes were classified and described with analytical models. A new dishing energy calculating method was proposed for a plate normally impacted by an arbitrary cross-section projectile. The energy absorbed by each mode and the ballistic limits for the plate target were calculated using these analytical models. It was found that fragmentation of the projectile led to a larger amount of dishing energy. The formation conditions of the fragmentation on projectile nose were theoretically analyzed, and the influencing factors for the fragmentation such as the critical thickness of the target and the critical impact velocity of the projectile were derived with established formulas. The theoretical analysis agreed well with the test results. It is argued that if the target is thicker than the critical thickness and the initial velocity of the projectile is larger than the critical impact velocity, fragmentation on projectile nose will occur, failure mode of the target will change to petaling, and the perforation resistance of the target will be significantly enhanced.

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.

A High-velocity Impact-ignition Testing System (HITS) was developed to study the dynamic response of intermetallic projectiles penetrating through two aluminum plates at impact velocities up to 1300 m/s. The intermetallic projectiles are contained in a 0.410 caliber shot gun shell and launched from a propellant driven gun into a catch chamber equipped with view ports and imaging diagnostics. Penetration, impact, and reaction are monitored using high-speed cameras that provide macroscopic and localized perspectives of projectile and target interaction. Several key results include the following. The first-plate penetration of the projectile follows well established ballistic curve fits. Subsequent plate penetration shows significant deviations attributed to projectile damage resulting from the first plate impact. The damage imparted to the projectile transitions from significant plastic deformation to severe fragmentation as impact velocity increases. Penetration of the aluminum target plate is significantly affected by the fragmentation field and show a 45% increase in rupture size at the highest impact velocity case. Combustion within the fragmented projectile is observed starting at 850 m/s. These results show the transition in dynamic interaction between multiple target plates at increasing projectile impact velocity.

The sphere impacting on the thin wall is simulated with node-separation finite element method, and investigations of the projectile fragmentation initiation threshold are processed based on the numerical results. The bumper-thickness-to-projectile-diameter ratio ( t/ D) is found to be the main determinant of the velocity threshold. The simulation cases contain the t/ D ranging from 0.008 to 0.424 and impact velocity ranging from 2 km/s to 7 km/s. The numerical results are in good agreement with the tests in sphere fragmentation initiation threshold, inner spall of the sphere, debris cloud pattern. The simulations reproduce the fragmentation initiation threshold curve that is obtained by the tests. That shows the feasibility of node-separation finite element method for hypervelocity impact simulation. The shock wave analyses show that the propagation/reflection process of shock wave in the thin wall cases is very different from that in thick wall cases. That inherently results in the different variations of the threshold in the low and high intervals of t/ D. The extreme thin plate case shows that when t/ D is further reduced, a thick layer of debris cloud would form at the rear of the plate. Compared to the projectile residual, the debris cloud from the plate would induce wider destruction in the inner structure.

Understanding the mechanical properties of different piping material under various conditions is important to predicting the behavior of pipe bombs. In this study, the effect of temperature on pipe bomb containers (i.e., PVC, black steel and galvanized steel) containing low explosive fillers (i.e., Pyrodex and double-base smokeless powder (DBSP)) was investigated. Measurements of fragment velocity and mass were compared for similar devices exploded in the spring (low/high temperature was 8°C/21°C) and winter (low/high temperature range was -9°C/-3°C). The explosions were captured using high speed filmography and fragment velocities were plotted as particle vector velocity maps (PVVM). The time that elapsed between the initiation of the winter devices containing double-base smokeless powder (DBSP) and the failure of their pipe containers ranged from 5.4 to 8.1 ms. The maximum fragment velocities for these devices ranged from 332 to 567 m/s. The steel devices ruptured and exploded more quickly than the PVC device. The steel devices also generated fragments with higher top speeds. Distributions of fragment masses were plotted as histograms and fragment weight distribution maps (FWDM). As expected, steel devices generated fewer, larger fragments than did the PVC devices. Comparison to devices exploded in the spring revealed several pieces of evidence for temperature effects on pipe bombs. For example, the mean fragment velocities for the winter devices were at or above those observed in the spring. The maximum fragment velocity was also higher for the winter steel devices. Although there were no significant differences in mean relative fragment mass, the fragment weight distribution maps (FWDMs) for two winter devices had anomalous slopes, where lower energy filler caused more severe fragmentation than higher energy filler.

In this paper, the perforation resistance of 20 mm thick aluminum plates subjected to moderate velocity impacts is examined experimentally and numerically. Plates made of four different tempers of aluminum alloy AA6070 were struck by ogive-nosed and blunt-nosed cylindrical projectiles with a diameter of 20 mm. We show that for this alloy material strength is not the decisive factor for the plates' resistance against perforation, but that a combination of ductility and strength, which inhibits fragmentation of the target plate, might be more important. Interpreting the results with previously obtained experimental data in mind sheds new light upon the role fragmentation plays for the capacity of metal plates undergoing impact loading. Increasing the material strength increases the probability of fragment ejection, which is unfavorable for the capacity. A novel 3D node-splitting technique which is available in the finite element code IMPETUS Afea Solver was employed to describe possible fragmentation and debris ejection in the numerical simulations. By using the node-splitting approach instead of element erosion, an improvement in the qualitative description of fracture for the least ductile tempers can be obtained without compromising the predicted component behavior for the more ductile tempers. © 2015. This is the authors’ accepted and refereed manuscript to the article. LOCKED until 2017-09-10 due to copyright restrictions. This manuscript version is made available under the CC-BY-NC-ND 4.0 license http://creativecommons.org/licenses/by-nc-nd/4.0/

A better understanding of the detonation performance of an explosive charge can be gained by directly measuring pressure, temperature and velocity of detonation (VOD). This is particularly important with explosives used in the mining industry because their performance is directly influenced by the degree of confinement given by the borehole diameter and the surrounding rock mass. A project funded by the Australian Coal Association Research Program (ACARP) was initiated in early 2009 with the view to design and build cost effective prototype instrumentation to measure the relative differences in detonation pressures and temperatures of commercial mining explosives. The project’s primary focus was on low density explosives. Low density (also referred to as low shock) explosives have been available in various forms for nearly 20 years. There have been significant advances in the availability, reliability and flexibility of these explosives which now offer a range of densities and degrees of water resistance. Their detonation performance is not well understood and cannot be accurately predicted with current ideal and non-ideal detonation codes. It was therefore viewed as important to be able to directly measure pressure and temperature during the detonation process of these complex mixtures in production blastholes. Identifying the pressure release patterns of both conventional and low density explosives under different geotechnical conditions should provide the necessary information to both validate detonation codes and better define input parameters for breakage and fragmentation models. This paper gives a general description of the prototype instrumentation developed and reports on the results obtained to date in both laboratory and full scale conditions.

One-dimensional symmetrical explosive loadings are applied to expand structural components: tubular cylinders, spherical shells and rings of 304 stainless steel and double and single walled cylinders of an aluminum alloy, A5052 to fragmentation, and the effects of wall thicknesses, explosive driver diameters and the constant proportionality of the in-plane biaxial stretching rates are investigated on the deformation and fracture behavior of three types of single walled structures and shatterproof behavior for double walled cylinders experimentally and numerically. In the cylinder tests, the driver is a column of high explosive PETN, inserted coaxially into the bore of a cylinder and initiated by exploding a fine wire bundle at the column axis using a discharge current. In case of the ring tests, ring specimens are placed onto a cylinder charged with the PETN as an expansion driver, and for sphere tests, a specimen filled with the PETN is also initiated by exploding a fine copper wire line with small length located at the central point. Observation results of deformation have shown the final maximum in-plane stretching rate order of , and fracture evaluations on recovered fragments are discussed indicating the need of modified fragmentation model for the structural components. In the double walled cylinder tests, only for lowermost amount of the explosive the outer cylinder has almost caught the fragments of inner cylinder, revealing that the damage phenomena are much different from those for single walled ones.

The shapes of improvised explosive devices (IEDs) used in conflicts are complex and take many forms. As device fragmentation and soil interaction must be included to provide accurate system physics, modelling unique IED device, artillery shell, and high explosive (HE) shapes is critical for the successful evaluation of protective structures for soldiers and civilians. Finite element and discrete particle method (DPM) techniques using the explicit non-linear transient finite element software IMPETUS Afea Solver® are documented for a series of studies ranging from a simple cylinder explosion to a complex full vehicle blast. Explored in detail are detonation results of a soil buried M795 artillery shell and its ejecta interaction with the TARDEC Generic Vehicle Hull containing a seated IMPETUS Afea hybrid III 50th percentile dummy. These studies also evaluate sensitivity to nine design variables and structure fragmentation response resulting from element type and the use of a node splitting algorithm.

Experimental evidence from a wide range of sources shows that the expanding cloud of explosively disseminated material comprises “particles” or fragments which have different dimensions from those associated with the original material. Powders and liquids have often been used to surround explosives to act as blast mitigants, and this is the main driver for our research. There are also many other areas of interest where an initially intact material surrounding an explosive charge is dynamically fragmented into a distribution of fragment sizes. Examples of such areas include fuel air explosives and enhanced blast explosives as well as quasi-static pressure mitigation systems, and our studies are thus also relevant to these applications. In this paper, we consider the processes occurring as an explosive interacts with a surrounding layer of liquid or powder and identify why it is important to model these processes as a multiphase material problem as opposed to a single phase, single material velocity problem. We shall present results from this class of numerical modelling. In this paper we shall explore what determines the particle or fragment size distribution resulting from explosive dissemination of a layer of material and discuss reasons why clouds from disseminated liquids and powders look similar. We shall support our analysis with results from recent explosives trials and introduce early results from some ongoing small scale explosive mitigation experiments.

Fragmentation of metal casings is an important issue in a variety of problems like weapon effectiveness, safety distances or collateral damage. To be able to describe the intended or unintended effects of naturally fragmenting shells, one needs to know the mass distribution of the fragments produced after detonation of the explosive charge. In the present study the fragmentation behavior of very light and heavier casings has been investigated. The data collection method is outlined and applied to the fragment mass distribution of four different shells. The results are given in diagrams. It was found that an existing fragmentation model adequately predicts the dependence of circumferential fragment size on material strength. Fracture in axial direction should also be considered to predict correct fragment masses, but currently a suitable model for this purpose is not available.

A technique for predicting performance of explosive fragmentation munitions presented in this work is based on integrating three-dimensional axisymmetric hydrocode analyses with analyses from a newly developed fragmentation computer code PAFRAG. The validation of the PAFRAG code fragmentation model was accomplished using the existing munition arena test data. After having established the crucial parameters of the model, a new explosive fragmentation munition was designed and optimized. Upon fabrication of the developed munition, the performance of the new charge was tested in a series of small-scale experiments including the flash radiography, the high-speed photography, and the sawdust fragment recovery. Considering relative simplicity of the model, the accuracy of the PAFRAG code predictions is rather remarkable.

The dynamic fragmentation of a 2-mm steel spherical projectile at normal impact velocities ranging from 2.5 to 7.3 km/s impacting 1-mm bumper plates has been studied. The duralumin bumper and the porous bumper made from low-pressed fine copper powder with a density from 2.2 to 4 g/cc have been used. High-porous bumper is applied to decrease the effect of bumper fragments. The areas and the effective diameters for all craters have been measured in the witness plate. The threshold impact velocities for failure of the steel sphere at impact upon the duralumin and porous plates, and the number-size distributions for debris craters have been obtained. The main result of experiments is as follows: at decreasing of linear dimension of fine fragments of steel projectile, the density of number-size distribution is an increasing function. For statistical interpretation of data the Grady-Kipp and the Gilvarry exponential distributions were used. It is shown that the superposition of the above distributions allows to describe the statistical results on fragmentation of steel spherical projectile in the wide range of impact velocities.

This work describes the analysis and ballistic range testing to evaluate the performance of rod-like Kill Enhancement Device (KED) penetrators on of multi-layered targets covering large range of densities including high-density material. Tests showed that (1) high-density material can be penetrated at oblique angles of incidence without projectile fragmentation and (2) high explosive within the target can be initiated. Test data from experiments was compared to predictive analyses generated by hydrocodes and found to be in excellent agreement.

Results of an experimental study of fragmentation effects in the explosion and the piercing power of the fragments of inert masses in the form of hemispherical aluminum and soft–steel shells enclosing the spherical charge of a high explosive under their action on flat steel, aluminum, steel–net, and claydite—concrete barriers are given. A design of the lightest spherical explosion–proof container with a load–carrying steel or glass–reinforced plastic shell protected by a splinter–proof layer capable of withstanding an explosion of a high–explosive charge (with a twofold safety factor) with an inert steel shell is proposed.

The purpose of this paper is to verify the applicability of innovative technologies for manufacturing controlled fragmentation warheads, with particular attention paid to guided ammunition. Several studies were conducted by the authors during the warhead development of DART and Vulcano family munitions. The lethality of the guided munitions can be considerably increased with controlled fragmentation warheads. This increase can compensate a lower payload of the guided munitions. After introducing the concept of warhead and its natural fragmentation, the paper describes both the elements of fracture mechanics related to the fragmentation and the state of the art of controlled fragmentation. A preliminary evaluation of controlled fragmentation technologies is illustrated along with the numerical models developed for predicting the natural and controlled fragmentations. The most promising technologies are presented in detail and the features of the warheads used for the experiments are defined. A description of the entire experimental phase is provided, including results of arena tests, data analysis and revision of numerical models. The applicability of some innovative technologies for controlled fragmentation warheads is fully demonstrated. Two technologies in particular, the laser microdrilling and the double casing solution, provide a high increase of the reference warhead lethality.

Summary Experiments in which both confined and unconfined ceramic targets are perforated by pointed and blunt projectiles are described, and a correlation is established between increased degree of fragmentation and reduced ceramic toughness. Front confinement of the ceramic results in greater overall fragmentation, however fewer, very fine fragments are produced for confined targets compared to unconfined targets. By attributing the fine fragments principally to crushing ahead of the impacting projectile, and coarse fragmentation to the interaction of stress relief waves, the effects of confinement can be qualitatively explained in terms of a simple model for loading and stress relief during perforation. The use of blunt projectiles increases the degree of fragmentation in those cases where the ceramic strength itself is insufficient to fracture the tip on impact. Measurements of fractured ceramic surface area and calculations of fracture work demonstrate that very little of the projectile kinetic energy is consumed in creating new ceramic fracture surface, and it is shown that a high proportion of the projectile impact kinetic energy is redistributed to residual kinetic energy of ejected ceramic debris. For cases where the projectile does not deform during penetration it is possible to derive a value for the average pressure resisting the penetrator. The ballistic efficiency of the ceramic increases with hardness for the lower strength ceramics, however, for the hard ceramics, where the principal influence of the ceramic is to destroy the projectile nose and create an inefficient penetrator, it is found in these tests that the residual penetration depths are similar, and ballistic efficiency is then unrelated to ceramic strength.

The article of record as published may be found at http://dx.doi.org/10.1115/1.4001713 A general methodology for estimating the requirements for defeating an explosive containing mortar threat by an intercepting array of explosively generated natural and controlled fragments is discussed along with the experimental data supporting quantitative interpretation. The target response of covered TNT impacted by single fragments is predicted through numerically determined shock-to-detonation thresholds as well as empirical penetration equations. Included in the methodology is a comprehensive, deterministic endgame model that consists of an intercept model, a static and dynamic fragment model, and a hit model generating the number of effective hits for arbitrary intercept situations. Experimental data supporting the assumptions of the models are reported. The model is also useful in establishing interceptor requirements. Federal Office of Defense and Technology (BWB)

Summary This paper is the third of a series concerned with the effects of projectile impact on a simulated explosive or propellant, called Propergol. Experiments were conducted to study the fragmentation and perforation response of disks of this material when subjected to impact by blunt and cylindro-conical strikers. Similar tests were conducted on layered targets of Propergol and steel, and also for a simulated warhead that was struck by armor-piercing projectiles. Data were obtained by velocity measurement, high-speed photography and post-mortem target examination including collected fragments. A fragmentation oriented penetration code, AUTODYN(frag) was developed from the interfacing of a two-dimensional commercial finite difference code, AUTODYN, with a fragmentation subroutine, BFRACT, developed by other investigators. This program was utilized to study the microfracture and fragmentation processes in both monolithic and composite Propergol plates during their penetration by projectiles. In addition, numerical evaluations of the effects of simulated warhead penetration by armor-piercing bullets were conducted using the publicly available finite-element code DYNA2D. The numerical results were compared with corresponding experimental data and also with the predictions of an analytical representation of the phenomenon, described in the second paper of the series. Reasonable agreement was obtained in the domain where the hypotheses concerning the structure of the analysis and of the computations were applicable.

The modeling of fragmentation has historically been linked to the weapons industry where the main goal is to optimize a bomb or to design effective blast shields. Numerical modeling of fragmentation from dynamic loading has traditionally been modeled by legacy finite element solvers that rely on element erosion to model material failure. However this method results in the removal of too much material. This is not realistic as retaining the mass of the structure is critical to modeling the event correctly. We propose a new approach implemented in the IMPETUS AFEA SOLVER ® based on the following: New High Order Finite Elements that can easily deal with very large deformations; Stochastic distribution of initial damage that allows for a non homogeneous distribution of fragments; and a Node Splitting Algorithm that allows for material fracture without element erosion that is mesh independent. The approach is evaluated for various materials and scenarios: -Titanium ring electromagnetic compression; Hard steel Taylor bar impact, Fused silica Taylor bar impact, Steel cylinder explosion, The results obtained from the simulations are representative of the failure mechanisms observed experimentally. The main benefit of this approach is good energy conservation (no loss of mass) and numerical robustness even in complex situations.

When the Magnitogorsk Metallurgical Combine began to make cast-iron rolls with a chill layer, it became necessary to break up the rolls after they had been removed from service. The rolls had to be divided into pieces no larger than 600 • 800 mm in order to be used as a component of the metallic charge for the production of alloyed cast iron in arc furnaces or induction furnaces. The combine conducted an experiment in which the rolls were broken up by two technologies already in use at the combine explosive fragmentation, with the blastholes for the explosive charges being perpendicular to the axis of the roll; breakup of the rolls on an impact breaker. The first method posed the danger of having fragments of the chill layer fly off as the blastholes were being drilled. In the second method, the body of the roll could not be broken up into pieces of the required dimensions, and the ball-weight of the impact breaker would itself be broken due to the high hardness of the body. Thus, two new technologies were proposed and tried out for breaking up two-layer cast-iron rolls explosive fragmentation in which the blastholes are located along the body of the roll; the use of an impact breaker after the roll body has been heated by a powerful mechanical cutter in the area where the roll is supposed to be divided. Explosive fragmentation with axial blastholes was chosen as the main technology after tests (two opposing blastholes are used). To perform a comparative analysis, nine rolls were broken up by the proposed fragmentation technology (A) and one was broken up by the existing technology (B). The results (in terms of one roll) are shown below

An analysis of the fragmentation process for hollow spheres of different materials containing a spherical explosive charge is presented. The condition for complete fracture is found to be similar to that obtained by Taylor for tubular bombs. The analysis is used to predict fragmentation velocity and the radius at which complete fracture occurs. The influence of the radius of the explosive charge, the tensile strength and the wall thickness of a sphere on the fragmentation velocity and the fracture strain is investigated. The results are in good agreement with recent experimental work.

This note is intended to contribute to a clearer understanding of the fragmentation mechanism for tubular bombs and as an introduction to further work on this and related topics which will be published shortly.