Hard Projectile Research Articles

Local damage characteristics of reinforced concrete slabs subjected to hard/deformable projectile impact

This study aims to investigate the local failure mechanism of reinforced concrete slabs subjected to hard and deformable projectile impacts. This is done by conducting impact tests and numerical simulations. In a series of impact tests, a hard/deformable steel projectile (8.3–8.4 kg) collided with a reinforced concrete slab with a thickness of 10–30 cm at an impact velocity of 64–90 m/s, and the impact and reaction forces were measured. The numerical simulation demonstrated that the failure of the reinforced concrete slab was affected by the rigidity of the projectile in terms of the maximum impact force and impulse.

Analytical Model Formulation of Steel Plate Reinforced Concrete Walls against Hard Projectile Impact

Steel plate reinforced concrete (SC) walls can effectively resist projectile impact by preventing the rear concrete fragments flying away, thus attracting much attention in defence technology. This work numerically and analytically investigated the hard projectile perforation of steel plate reinforced concrete walls. Impact resistance theories, including cavity expansion analysis as well as the petaling theory of thin steel plates were used to describe the cratering, tunneling and plugging phases of SC walls perforation. Numerical modeling of SC walls perforation was performed to estimate projectile residual velocity and target destructive form, which were validated against the test results. An analytical model for SC wall perforation was established to describe the penetration resistance featuring five stages, i.e., cratering, tunneling and plugging, petaling with plugging and solely petaling. Analytical model predictions matched numerical results well with respect to projectile deceleration evolution as well as residual velocity. From a structural absorbed energy perspective, the effect of front concrete panel and rear steel plate thickness combinations was also studied and analyzed. Finally, equivalent concrete slab thickness was derived with respect to the ballistic limit of SC walls, which may be helpful in the design of a protective strategy.

Advanced computer algorithms to simulation of transient dynamics in solids and structures

The new approach of designing computation algorithms for simulation of transient dynamics in solids and structures is proposed. The algorithms are based on explicit finite-difference scheme built under special conditions imposed on the values of difference mesh parameters. The designed calculation devices possess a minimal influence of spurious effects of numerical dispersion that allows discontinuities and high-gradient components caused by wave fronts and fracture events to be accurately computed. A set of advanced computer algorithms and calculation examples of 1D/2D model and engineering problems are presented: (a) longitudinal impact onto a rod embedded into an elastic medium, (b) propagation of cylindrical and spherical waves with front discontinuities, (c) stress concentrations near a head surface of hard projectile indented into elastic solids and (d) transient wave dynamics and delamination in fiber reinforced composites.

An investigation of ballistic response of reinforced and sandwich concrete panels using computational techniques

Structural performance of nuclear containment structures and power plant facilities is of critical importance for public safety. The performance of concrete in a high-speed hard projectile impact is a complex problem due to a combination of multiple failure modes including brittle tensile fracture, crushing, and spalling. In this study, reinforced concrete (RC) and steel-concrete-steel sandwich (SCSS) panels are investigated under high-speed hard projectile impact. Two modeling techniques, smoothed particle hydrodynamics (SPH) and conventional finite element (FE) analysis with element erosion are used. Penetration depth and global deformation are compared between doubly RC and SCSS panels in order to identify the advantages of the presence of steel plates over the reinforcement layers. A parametric analysis of the front and rear plate thicknesses of the SCSS configuration showed that the SCSS panel with a thick front plate has the best performance in controlling the hard projectile. While a thick rear plate is effective in the case of a large and soft projectile as the plate reduces the rear deformation. The effects of the impact angle and impact velocity are also considered. It was observed that the impact angle for the flat nose missile is critical and the front steel plate is effective in minimizing penetration depth.

Improving the resistance of concrete panels to hard projectile impact

In this article, the response of nine plain concrete panels to an impact of hard projectiles was examined in an experimental study. The tests were planned with an aim to observe the influence of compressive strength on the performance of concrete under impact loading. Concrete panels with compressive strengths within the range of 26 to 92 MPa subjected to impact by 23 mm hard projectile at velocities within the range of 270 to 348 m/s were studied. Also, using a glass fiber reinforced polymer sheet, as a liner on the rear face of the plain concrete panel, to strengthen the panel was examined. The experimental results indicate that strengthening concrete panel with a rear glass fiber reinforced polymer sheet showed more satisfactory performance under the impact load than increasing compressive strength of concrete. Also, the use of glass fiber reinforced polymer sheets as rear liners in addition to increasing the concrete strength showed superior performance of concrete panels against impact; it is recommended to be used in protective structures.

INTERNAL BALLISTICS OF CLASSIC GUN WITH COMPOSITE CHARGE

The paper presents a lumped parameter mathematical model considering the changes of thermodynamic properties for combustion products of a composite propelling charge, and of a burning cartridge casing or shell as well, when shot with classic guns. In addition a method was proposed for considering not coincidental instants of ignition for particular components of the charge and also for powder grains of each component, and the heat flow into the walls containing the space with combustion products. Some results of numerical computations are shown for 125 mm 2A46 tank gun firing a hard core projectile. Moreover an evaluation of accuracy of the results is given on the basis of experimental data. Maximum pressure and muzzle velocity were basic criteria at the verification of the model. Analysis of accuracy for solutions of model equations allows a conclusion that the proposed mathematical model may be useful at the designing process of ammunition and guns.

Numerical study on the hard projectile perforation on RC panels with LDPM

This paper numerically investigates the medium-caliber hard projectile perforation of steel rebar reinforced concrete panels by using the recently developed Lattice Discrete Particles Model (LDPM). With mesoscale constitutive laws governing cohesive fracture, strain hardening in compression and compaction due to pore collapse, LDPM naturally captures the failure mechanisms at the length scale of coarse aggregate of concrete. A constant area and shape partition method for circular cross-section is employed to determine the Gauss integration points distribution for beam elements. The sliding friction model for rebar-concrete interaction, in conjunction with LDPM for concrete are utilized for RC panel perforation modeling. Simulations of normal and high strength concrete panel perforation tests are carried out to validate the numerical model whereby agreement with the experimental data is achieved in terms of projectile residual velocity as well as damage contour. Extensive simulations are further performed to investigate the effect of projectile impact location and reinforcement on high strength concrete (HSC) panel perforation responses. Comparative numerical studies indicate that the projectile residual velocity is significantly reduced when the projectile hits the reinforced rebars. Furthermore, the reinforcement can considerably limit the damage area, crack openings and prevent the concrete shelter from structural failure. Finally, the LDPM simulations of HSC panel perforation are combined with cavity expansion analysis to achieve the RC perforation analytical model whereas the target resistance parameter R (Forrestal et al., 2003) is determined a672 MPa while the shear plugging thickness value is estimated as 33 mm for the cases of interest.

Simulation of rock dynamic failure using discontinuous numerical approach

In this paper, an improved DDA method proposed by the authors is used to simulate the rock failure process under dynamic loading, and several SHPB tests on Brazilian discs with different angle pre-cracks are conducted for verification. The simulated main crack paths of different specimens agree well with the observations in the SHPB tests. In addition, the perforation process of a hard projectile into rock is also simulated, and some heavily discontinuous phenomena in impact failure are captured. It shows that the improved DDA method is able to simulate the failure behavior of rock under dynamic loading.

Lattice discrete particle modeling of plain concrete perforation responses

This paper numerically investigates the large-caliber hard projectile perforation of plain concrete slab with steel culvert confinement by using the recently developed Lattice Discrete Particles Model (LDPM). With mesoscale constitutive laws governing the interaction between adjacent particles, LDPM simulates concrete features like cohesive fracture, strain hardening in compression and compaction due to pore collapse. The perforation simulation model is established with LDPM for concrete, elastoplastic model for steel culvert and penalty contact for projectile-concrete interaction. Simulation of 5 shots concrete perforation tests are carried out to validate the numerical model, and the numerical results are in good agreement with the experimental data in terms of residual velocities as well as target damage mode. Extensive simulations are further performed to investigate the effects of aggregate discretization, steel culvert confinement and diameter size on perforation responses. Comparative numerical study indicates that with culvert confinement, the projectile residual velocity is significantly reduced except for perforation case with 0.3 m thickness target. Meanwhile, crack fills the 0.6 m diameter target which poses less resistance to projectile impact.

An experimental study on the temperature and structural behavior of a concrete wall exposed to fire after a high-velocity impact by a hard projectile

Projectiles, such as turbine blades, can be released in an accident and impact structures. Airplanes and other flying objects can also become impact projectiles. These impacts occasionally cause fire when fire loads, such as oil, fuel, and other combustible materials, are present. This study examines the thermal insulation performance of concrete plates and the structural fire behavior of load-bearing reinforced concrete walls that are exposed to fire after a high-velocity impact by a hard projectile. Impact and fire tests were carried out using small-scale concrete plates and reinforced concrete walls. The results show the influence of local damage and the advantage of short-fiber reinforced concrete subjected to impact loads and fire.

Retraction Note to: All-Atom Molecular-Level Analysis of the Ballistic-Impact-Induced Densification and Devitrification of Fused Silica

All-atom molecular-level computations are carried out to infer the dynamic response and material microstructure/topology changes of fused silica subjected to ballistic impact by a hard projectile. The analysis was focused on the investigation of specific aspects of the dynamic response and of the microstructural changes such as the deformation of highly sheared and densified regions and the conversion of amorphous fused silica to SiO2 crystalline allotropic modifications (in particular, α-quartz and stishovite). The microstructural changes in question were determined by carrying out a post-processing atom-coordination procedure. This procedure suggested the formation of stishovite (and perhaps α-quartz) within fused silica during ballistic impact. To rationalize the findings obtained, the all-atom molecular-level computational analysis is complemented by a series of quantum-mechanics density functional theory (DFT) computations. The latter computations enable determination of the relative potential energies of the fused silica, α-quartz, and stishovite under ambient pressure (i.e., under their natural densities) as well as under imposed (as high as 50 GPa) pressures (i.e., under higher densities) and shear strains. In addition, the transition states associated with various fused-silica devitrification processes were identified. The results obtained are found to be in good agreement with their respective experimental counterparts.

Trajectory instability and convergence of the curvilinear motion of a hard projectile in deep penetration

This paper studies the trajectory instability and convergence of the curvilinear motion of a hard projectile in deep penetration, based on rigid body dynamics and the differential area force law. It is observed that both sudden (instable) and gradual (curvilinear) changes of the projectile trajectory may happen under certain conditions depending on projectile geometry, target property, impact velocity and other striking parameters. A criterion is introduced to determine the occurrence of trajectory instability. Two characteristic velocities are identified, i.e. (a) the critical impact velocity for the occurrence of trajectory instability, and (b) the characteristic convergent velocity, at which the projectile trajectory turns to a straight line (linear motion) from the curvilinear motion, which is supported by experimental evidence. It is shown that both the critical impact velocity and the characteristic convergent velocity depend linearly on the relative location of projectile's centre of mass. However, the characteristic convergent velocity is independent of the non-axisymmetrical disturbance and impact velocity.

Finite Spherical Cavity Expansion Method for Layering Effect

A decay function for the layering effect during the projectile penetrating into layered targets is constructed, which is obtained via the theoretical solution of a dynamically expanding layered spherical cavity with finite radius in the layered targets that are assumed to be incompressible Mohr-Coulomb materials. By multiplying the decay function with the semi-empirical forcing functions that account for all the constitutive behavior of the targets, the forcing functions for the layered targets are obtained. Then, the forcing functions are used to represent the targets and are applied on the projectile surface as the pressure boundary condition where the projectile is modeled by an explicit transient dynamic finite element code. This methodology is implemented into ABAQUS explicit solver via the user subroutine VDLOAD, which eliminates the need for discretizing the targets and the need for the complex contact algorithm. In order to verify the proposed layering effect model, depth-of-penetration experiments of the 37 mm hard core projectile penetrating into three sets of fiber concrete and soil layered targets are conducted. The predicted depths of penetration show good agreement with the experimental data. Furthermore, the influence of layering effect on projectile trajectory during earth penetration is investigated. It is found that the layering effect should be taken into account if the final position and trajectory of the projectile are the main concern.

Commotio cordis during prolonged cardiac ventricular repolarization due to exercise-induced hypokalemia: A case report

Abstract Background Commotio cordis is ventricular fibrillation after a direct precordial blow without mechanical damage to organs. Early recognition and prompt cardiopulmonary resuscitation with defibrillation save lives. According to previous reports, the major determinants of commotio cordis include location and timing of the blow. Other risk factors are young age, a thin and undeveloped chest cage, and a small hard spherical projectile. The pathophysiology of commotion cordis remains uncertain, such as individual susceptibility to prolonged repolarization and long QT. Case report A 32-year-old man suddenly collapsed after a direct blow to the anterior chest from an elbow during a basketball game. A bystander called an ambulance and activated the emergency medical service immediately. Dispatch assisted the bystander with cardiopulmonary resuscitation via telephone. An automated external defibrillator was applied when emergency medical technicians arrived, which showed ventricular fibrillation. The patient regained a pulse after the first electrical shock and five-cycle-chest compression. Further examinations revealed a long QT on electrocardiogram and hypokalemia. The QT interval was within normal limits without any ventricular arrhythmia after the potassium level had been normalized. Conclusion This case reminds physicians of the risk of commotio cordis associated with exercise-induced hypokalemia. An electrocardiogram should be checked for QT prolongation immediately after return of spontaneous circulation in patients of sudden cardiac arrest. Supplying adequate potassium for hypokalemia related QT prolongation should be considered as treatment and primary prevention in such case.

A fundamental study of impact response of concrete slabs subjected to medium velocity impact by a hard projectile

A fundamental study of impact response of concrete slabs subjected to medium velocity impact by a hard projectile

A dynamic material model for rock materials under conditions of high confining pressures and high strain rates

A dynamic material model is presented to characterize the mechanical behavior of rock materials under high confining pressures and high strain rates. The yield surface is defined based on the extended Drucker–Prager strength criterion and the Johnson–Cook material model. Two internal damage variables are introduced to represent, respectively, the tensile and compressive damage of rock materials. The proposed dynamic material model of rocks is incorporated into the nonlinear dynamic analysis code LS-DYNA through a user-defined material interface. Its reliability and accuracy are verified by the simulation of various basic experiments with different loading conditions. The present rock model is also applied to simulate the penetration of granite target plate by hard projectile. The typical damage and failure on the granite targets predicated by the proposed dynamic material model of rocks agree well with the experimental results. It demonstrates that the proposed model is capable of capturing the failure of rock materials.

RETRACTED ARTICLE: All-Atom Molecular-Level Analysis of the Ballistic-Impact-Induced Densification and Devitrification of Fused Silica

All-atom molecular-level computations are carried out to infer the dynamic response and material microstructure/topology changes of fused silica subjected to ballistic impact by a hard projectile. The analysis was focused on the investigation of specific aspects of the dynamic response and of the microstructural changes such as the deformation of highly sheared and densified regions and the conversion of amorphous fused silica to SiO2 crystalline allotropic modifications (in particular, α-quartz and stishovite). The microstructural changes in question were determined by carrying out a post-processing atom-coordination procedure. This procedure suggested the formation of stishovite (and perhaps α-quartz) within fused silica during ballistic impact. To rationalize the findings obtained, the all-atom molecular-level computational analysis is complemented by a series of quantum-mechanics density functional theory (DFT) computations. The latter computations enable determination of the relative potential energies of the fused silica, α-quartz, and stishovite under ambient pressure (i.e., under their natural densities) as well as under imposed (as high as 50 GPa) pressures (i.e., under higher densities) and shear strains. In addition, the transition states associated with various fused-silica devitrification processes were identified. The results obtained are found to be in good agreement with their respective experimental counterparts.

Densification and Devitrification of Fused Silica Induced by Ballistic Impact: A Computational Investigation

A molecular‐level computational investigation is carried out to determine the dynamic response and material topology changes of fused silica subjected to ballistic impact by a hard projectile. The analysis was focused on the investigation of specific aspects of the dynamic response and of the topological changes such as the deformation of highly sheared and densified regions, and the conversion of amorphous fused silica to SiO2 crystalline polymorphs (in particular, α‐quartz and stishovite). The topological changes in question were determined by carrying out a postprocessing atom‐coordination procedure. This procedure suggested the formation of stishovite (and perhaps α‐quartz) within fused silica during ballistic impact. To rationalize the findings obtained, the all‐atom molecular‐level computational analysis is complemented by a series of quantum‐mechanics density functional theory (DFT) computations. The latter computations enable determination of the relative potential energies of the fused silica, α‐quartz and stishovite, under ambient pressure (i.e., under their natural densities) as well as under imposed (as high as 50 GPa) pressures (i.e., under higher densities) and shear strains. In addition, the transition states associated with various fused‐silica devitrification processes were identified. The results obtained are found to be in good agreement with their respective experimental counterparts.

Hard projectile perforation on the monolithic and segmented RC panels with a rear steel liner

Twenty-five shots of reduce-scaled projectiles perforation test on five configurations of monolithic and segmented RC panels with a rear steel liner were conducted. The impact resistances of layered bare RC and RC/steel composite targets were analyzed quantitatively based on the obtained striking and residual velocities of the projectiles, and the accuracy of the newly developed small-caliber accelerometer in recording the high-amplitude accelerations of the projectile is validated. The main conclusions are: (1) With the same overall thickness and projectile striking velocity, the stacked segmented targets have higher impact resistance than the spaced segmented targets. (2) For the spaced segmented targets with the same total thickness (i) the impact resistance of the monolithic RC plate is better than that of the segmented target, which is not dependent on the impact velocity as well as the rear steel liner is attached or not; (ii) the more the layers of the segmented target, the more inferiority of the segmented target has; (iii) while the number of the layers is fixed, e.g. double layers in the present test, the impact resistance of the segmented target is dependent on the order of the slabs, which is enhanced with the thickness of the later RC plate increasing. (3) An explicit dimensionless expression for predicting the terminal ballistic parameters of the projectile perforating the RC slab was proposed and well validated. (4) The newly proposed equivalent approach for predicting the ballistic limit of the projectile perforating RC/steel composite target was evaluated with the present tests.

Critical Impact Energy of Flat Nose Hard Projectile Causing Early Scabbing in Concrete Slab

In this paper, 2D numerical simulation finite element analysis has been carried out for critical impact energy of flat nose hard projectile causing early scabbing in concrete slab, based on reflected stress wave propagation with elastic assumption of the classic wave equation, using ABAQUS software. Numerical simulation predictions were compared with experimental data and with the well established UMIST, NDRC, Li and Reid formulae and found comparable and reliable. The influence of hard projectile diameter with flat nose, and concrete wall thickness on critical impact energy was also investigated. It was found that the effect of critical impact energy is directly proportional to the thickness of concrete target and inversely proportional to the diameter of flat nose hard projectile.