Hemispherical-nosed Projectiles Research Articles

Cratering for Impact of Hypervelocity Projectiles into Granite Targets within a Velocity Range of 1.91–3.99 km/s: Experiments and Analysis

To understand and analyze crater damage of rocks under hypervelocity impact, the hypervelocity impact cratering of 15 shots of hemispherical-nosed cylindrical projectiles into granite targets was studied within the impact velocity range of 1.91–3.99 km/s. The mass of each projectile was 40 g, and the length–diameter ratio was 2. Three types of metal material were adopted for the projectiles, including titanium alloy with a density of 4.44 g/cm3, steel alloy with a density of 7.81 g/cm3, and tungsten alloy with a density of 17.78 g/cm3. The projectile–target density ratio (ρp/ρt) ranged from 1.71 to 6.86. The depth–diameter ratios (H/D) of the craters yielded from the experiments were between 0.14 and 0.24. The effects of ρp/ρt and the impact velocity on the morphologies of the crater were evaluated. According to the experimental results, H/D of craters is negatively correlated with the impact velocity, whereas the correlation between H/D and ρp/ρt is weak positive. The crater parameters were expressed as power law relations of impact parameters by using scaling law analysis. The multiple regression analysis was utilized to obtain the coefficients and the exponents of the relation equations. The predicted values of the regression equations were close to the experimental results.

Effect of Lode angle incorporation into a fracture criterion in predicting the ballistic resistance of 2024-T351 aluminum alloy plates struck by cylindrical projectiles with different nose shapes

The aim of the present paper is to evaluate the effect of Lode angle incorporation into a fracture criterion when predicting the ballistic resistance of 2024-T351 aluminum alloy plates struck by cylindrical projectiles with different nose shapes through finite element (FE) simulations. To this end ballistic tests in the sub-ordnance impact velocity range were firstly conducted on 9.94 mm thick 2024-T351 aluminum alloy plates using cylindrical projectiles with blunt, hemispherical and ogival nose shapes, a nominal diameter of 12.66 mm, and a nominal mass of 50 g. Ballistic limit velocities (BLVs) for different projectile-target pairs considered were calculated using initial vs. residual velocity data obtained in the experiments. Subsequently FE simulations of the conducted experiments were performed with SIMULIA Abaqus software. In those simulations Johnson–Cook yield criterion with a modified strain hardening law was accompanied with either the Lode-independent Johnson–Cook (JC) fracture criterion or the Lode-dependent modified Mohr–Coulomb (MMC) fracture criterion to describe target material properties. Finally, the predicted ballistic resistance and fracture patterns of the targets were compared with those observed in the experiments. It was found that in the simulations with the Lode-independent JC fracture criterion the BLVs of the targets were overestimated by 18.0–35.1% depending on the projectile nose shape. In the simulations with MMC fracture criterion the BLVs predictions were substantially improved, so that the difference with the experimental results did not exceed 9.0%. Targets failure mechanisms obtained in the simulations with MMC fracture criterion also better match the experiments than those predicted with JC fracture criterion. In the simulations with MMC fracture criterion the targets impacted by the projectiles with blunt and hemispherical noses failed through shear plugging, whereas ogive-nosed projectiles caused ductile hole enlargement and target fragmentation due to its rear side radial fracture and bending of formed short petals with their eventual shear fracture. At the same time the simulations with JC fracture criterion predicted shear plugging for the blunt-nosed projectiles, very small conical plug ejection and target fragmentation due to discing for the hemispherical-nosed projectiles, and ductile hole enlargement for the ogive-nosed projectiles. A detailed analysis of the failure process revealed that in the case of the ogive-nosed and hemispherical-nosed projectiles, respectively, the ductile hole enlargement occurs during the initial stage of the impact and subsequent through-thickness fracture develops causing either fragmentation of the target or its shear plugging failure. The Lode-independent JC fracture criterion overestimates a material fracture strain under shear, thus leading to poor prediction of 2024-T351 aluminum alloy targets ballistic performance in the numerical simulations.

Ballistic performance and damage simulation of fiber metal laminates under high-velocity oblique impact

Fiber metal laminates have been successfully applied in military aircrafts, armor vehicles and other modern engineering industries as protective structures due to their outstanding impact resistant properties. Prediction of the ballistic performance and investigation on the damage mechanism of the fiber metal laminates under general oblique impact conditions still remain a very challenging issue. In this study, a nonlinear dynamic finite element model in terms of continuum damage mechanics including intra- and inter-layer failure modes is presented. The accuracy of this model is validated with available experimental data. The damage and ballistic performance of two different structural fiber metal laminates subjected to high-velocity oblique impact by rigid hemispherical nose projectile with angles of 0°, 30°, 45° and 60° are studied. The numerical results show that the projectile deflects when the oblique impact occurs and the deflection angle decreases with increasing the impact velocity. The residual velocity of the projectile and the energy absorption of the target are related to the initial impact velocity and impact angle of the projectile. The proposed simulation approach offers a new proper reference for numerical investigations of common oblique impact problems in other fiber metal laminates.

Ballistic performance of bioinspired nacre-like aluminium composite plates

Inspired by the hierarchical structure of nacre, an aluminium alloy (AA) 7075-T651 based composite plate is developed for ballistic applications. The proposed nacre-like composite plates are made of 5, 7 or 9 layers consisting of many ~1 mm thick AA7075-T651 tablets bonded together with toughened epoxy adhesive. Experimental ballistic tests on these composite plates, using a hemispherical nosed steel projectile at impact velocities in the range of 340–450 m/s, were performed. Both the 5-layer and 7-layer plates exhibited a better ballistic performance than their bulk counterparts based on the observation that the measured residual velocity of the projectile through the composite plate was lower than that through the corresponding bulk plate with similar areal density. However, the performance improvement is reduced as the composite plate thickness increases (from 5 to 9 layers) due to the increased likelihood of ductile failure occurring prior to perforation in the thicker bulk plates. The failure pattern analysis of the impacted specimens confirmed that the impact performance enhancement of the nacre-like composite plates can be attributed to the hierarchical structure facilitating both localized energy absorption (by tablet deformation and interlocking) and more globalized energy absorption (by inter-layer delamination and friction).

Numerical and Experimental Investigation of Supercavitating Flow Development Over Different Nose Shape Projectiles

Recently, the interest for new technologies to speed up underwater vehicles has increased. In this work, one of these technologies is investigated by creating a gaseous cavity, in which the high-speed underwater vehicles flow, to reduce the drag forces acting on these vehicles. A supercavitating flow over different nose projectile shapes is studied numerically and experimentally to understand the effect of the projectile nose shape on the supercavitating flow behavior. The numerical simulations are accomplished by using a commercial code named ESI-CFD through an unstructured mesh. Also, supercavity flow characteristics are investigated experimentally over the projectile body by using a high-speed camera. The numerical results are validated with other experimental results, where the stages of growth of the cavity over the different shapes projectiles are distinguished briefly and the existence of wake vortex is observed. The cavitator shape controls the time of cavity appearance and the drag coefficient value. The hemispherical nose projectile has the lowest drag coefficient value among all the tested projectiles. So, the cavitating flow behavior is investigated for the hemispherical nose projectile at different cavitation numbers ranging from 0.065 to 1.0. A new correlation is deduced to investigate the drag coefficient for the hemispherical projectile. Good agreement is obtained from the result of this correlation and previous data. Also, a new cavitator shape (a modified conical cavitator projectile) is examined, which is a modification of previously used one. The supercavity has not been formed using the modified conical cavitator projectile but it moves faster than any other examined projectile because it takes longer time before the cavity begins to decay.

Low-velocity penetration of a rigid, hemispherical nose projectile in incompressible, elastoplastic, strain-hardening Mises media

A core-cavity model for steady, low-velocity penetration of a rigid, hemispherical nose projectile in elastoplastic, strain-hardening Mises media is presented. The target response is modelled by two distinct regions. The first region is an incompressible, elastoplastic flow field core around the projectile nose. The second region, outside the plastic core, is an incompressible, elastoplastic material response, which is induced by an internally pressurized spherical cavity. The analytical analysis has led to a closed-form expression for the penetration resisting pressure, for an arbitrary target material stress-strain curve with a definite yield point, which depends on the extent of the plastic core. This expression reduces to the quasi-static spherical cavitation pressure when a plastic core does not exist and it matches with well-known results for the resisting pressure of a perfectly-plastic Mises solid. The strain hardening effect on the penetration resisting pressure is found to be significant when compared to elastic/perfectly-plastic target response. Comparison with available numerical results has revealed that a relatively large flow field core, with the outer boundary at the elastic region, should exist around the hemispherical nose. By further comparison to penetration depth experiments, the core outer boundary location is found to be identical to the elastic/plastic interface location of a quasi-static cylindrical cavitation in incompressible Mises media under plane-strain conditions.

Reliability Assessment of HFRC Slabs Against Projectile Impact

In the present study, a probabilistic procedure is presented for estimating the reliability of hybrid fiber reinforced concrete (HFRC) slabs against the impact of hemispherical nose projectiles considering uncertainties involved in the material, geometric and impact parameters. The influence of hybrid fibers in improving the safety level of reinforced concrete slabs against impact loads has also been studied on a parametric basis. The failure of the HFRC slabs was assumed to occur when the impact velocity of the projectile exceeds the ballistic limit of the slab i.e. perforates the slab. To illustrate the procedure, a probabilistic analysis was carried out on the impact test results of HFRC slabs containing different proportions of hooked-end steel, polypropylene and Kevlar fibers, recently published by the authors. Reliability assessment was performed for a range of applied nominal impact loads by varying the impact velocity of the given projectile. Reliability analysis yields the safety level of all the HFRC slabs against the impact of the above projectile. Effect of fibers, especially steel fibers, and slab thickness on the reliability of HFRC slabs are also investigated on a parametric basis.

Influence of metal layer distribution on the projectiles impact response of glass fiber reinforced aluminum laminates

The effect of the distribution of aluminum layer through the thickness of fiber metal laminates (FMLs) on their projectiles impact response is studied using high speed 3D digital image correlation technique (DIC). The FMLs consisting of aluminum alloy 2024-T3 sheets of thicknesses 0.3 mm, 0.4 mm, and 0.6 mm and glass fiber reinforced epoxy layers (two layers with each of 0° and 90°) were prepared by the hand layup process followed by vacuum bagging. The metallic layers are placed at different locations through the thickness of four different layups while keeping the total metal layer thickness constant. The hemispherical and conical nose projectiles of the same mass are impacted normal to the FMLs plate using nitrogen gas gun. The performance of the FMLs is evaluated using different parameters such as the deformation history, residual deformation and also the surface and internal damages. FML 4/3–0.3 in which the two adjacent composite layers with different fiber orientations separating by an aluminum layer exhibited the highest deformation with hemispherical projectile impact for the same impact energy level. The deformation was found to be lower and nearly same for the other three FMLs. This observation is also noticed in the case of drop weight impact (low velocity impact). The FML 2/1–0.6 in which the composite layers were stacked together exhibited a comparatively higher lateral spread of delamination and interlayer opening with hemispherical projectile impact when compared to FML 4/3–0.3, indicating that the lateral spread of damage within the FML can be decreased by distributing the aluminum layers in the FML. This is also observed in the case of drop weight impact.

Experimental study of ballistic resistance of sandwich targets with aluminum face-sheet and graded foam core

In this research, we have investigated the ballistic resistance of sandwich structures with aluminum face-sheet and graded polyurethane foam core with different densities. The effects of graded changes of core foam density and the effect of the sequence of foam layers with different densities on energy absorption and ballistic limit of sandwich structures under the impact of hemispherical nose projectiles at high speeds (160 to 300 m/s) are studied. The results of this study showed that increasing the density and thickness of the foam core leads to increase in the ballistic limit and energy absorption; also, the ballistic limit of sandwich structures with the same mass with graded foam core for three- and five-layer panels is, respectively, 10.37 and 5.57% more than single-layer foam core with the average density in case the foam layer with less density is placed in the impact side. By using the graded foam core (laminate), the core resistance is increased and the damaged zone shape is changed, and the energy absorption of back face-sheet is increased.

A new analytical model for the low-velocity perforation of thin steel plates by hemispherical-nosed projectiles

Abstract Ballistic experiments were conducted on thin steel plates that are normally impacted by hemispherical-nosed projectiles at velocities higher than their ballistic limits. The deformation and failure modes of the thin steel plates were analyzed. A new method was proposed according to the experimental results and the perforation phenomenon of the thin steel plates to determine the radius of the bulging region. In establishing this new method, a dynamic method combined with the plastic wave propagation concept based on the rigid plastic assumption was adopted. The whole perforation process was divided into four consecutive stages, namely, bulging deformation, dishing deformation, ductile hole enlargement, and projectile exit. On the basis of the energy conservation principle, a new model was developed to predict the residual velocities of hemispherical-nosed projectiles that perforate thin steel plates at low velocities. The results obtained from the theoretical calculations by the present model were compared with the experimental results. Theoretical predictions were in good agreement with the experimental results in terms of both the radius of the bulging region and the residual velocity of the projectile when the strain rate effects of the target material during each stage were considered.

Ballistic resistance and energy absorption of honeycomb structures filled with reactive powder concrete prisms

Two kinds of innovative re-entrant and hexagonal cell honeycomb sandwich structures filled with reactive powder concrete were proposed, and the ballistic resistance and energy absorption of the sandwich structures were investigated by numerical simulations. The deformation and failure modes of the different structures were analyzed and evaluated in detail. The honeycomb sandwich structures filled with reactive powder concrete prisms improved the capacity of ballistic resistance and energy absorption significantly, compared to the normal reactive powder concrete plates and sandwich structures without reactive powder concrete prisms. The analysis shows that the auxetic re-entrant cell honeycomb sandwich structures have a better ballistic performance than the hexagonal cell honeycomb sandwich structures. The sandwich structures were subjected to impact by three kinds of projectiles: flat, hemispherical and conical nosed. The ballistic limit of the flat nosed projectile is the highest, while the impact performance of the conical and hemispherical nosed projectiles is obviously different from the flat nosed projectile, especially in a relative high velocity range. The sharper nose leads to a higher value of exit velocity and mass loss. In addition, effects of different design parameters on ballistic resistance were also studied by changing the thickness of honeycomb cell and face plates. Results indicate that the thickness of honeycomb walls and face plates have significant effect on the ballistic resistance and energy absorption in a relative low velocity range, while there are no big differences when the initial impact velocity exceeds 400 m/s.

Numerical simulation of high-speed water-entry for hemispherical-nosed projectile

Aiming at the lack research of high-speed water-entry for large projectile, this paper studied the high-speed water-entry for hemispherical-nosed projectile in the method of fluid-solid coupling. Good agreements were obtained compared with the theoretical results. The modalities of water were calculated such as cavity, uplift and pressure. The velocity and deceleration curves of water-entry were gained. Numerical research shows that there is heavy shock pressure on the projectile and pressure waves in water by a projectile impacting into water at high speed, the pressure at the apex and the vicinity is much higher than the rest of area. The projectile’s peak acceleration is in linear correlation with the square of impact velocity. The simulation affords bases for impact-resistant design of the airdropped projectile, and of certain value to investigation of other correlative bodies’ high-speed water-entry.

Energy absorption characteristics of thin aluminium plate against hemispherical nosed projectile impact

The energy absorption characteristics of monolithic and layered aluminium plates made of aluminium 1100-H12 were investigated against hemispherical nosed projectile impact both experimentally and numerically. The span diameter of 1mm thick monolithic plates were varied as 68, 100, 150, 200, 255, 350, 450, 550, 650 and 750mm whereas the effect of target configuration were studied for monolithic (1mm), layered in contact (0.5+0.5) and spaced target (0.5+0.5) of 150mm free span diameter. The spacing between thin layers was varied as 4.5, 10, 20, 30, 40, 50 and 60mm. Each target was impacted normally by 19mm diameter hemispherical nosed projectile. Some of numerical results were validated with experimental results with varying target span diameter (68, 100, 150, 200 and 255mm), layered in contact target and the target with 4.5mm spacing. Numerical results were found to be quite close with experimental results. A pressure gun was employed to carry out the experiments while the numerical simulations were performed on ABAQUS/Explicit finite element code. Further numerical simulation results were used to calculate the energy dissipation in plastic deformation. The energy was further disintegrated in stretching in radial, circumferential, axial and tangential directions. Both the ballistic performance and energy absorption characteristics were significantly influenced by target span and configuration. The ballistic limit has been found to be significantly increased with an increase in the span diameter of the target. The monolithic target was found to be superior followed by layered in contact and spaced target.

Ballistic resistance of 2024 aluminium plates against hemispherical, sphere and blunt nose projectiles

Numerical investigation has been carried out on 2024 aluminium plate targets against 12.7mm diameter hardened steel projectiles. The ballistic resistance of 1.27mm thick target was studied against a spherical ball as well as the hemispherical and blunt nosed cylindrical projectiles. The simulations were performed on ABAQUS/Explicit finite element code by modelling the target as deformable and the projectiles as rigid three dimensional surface. The Johnson-Cook (JC) elasto-viscoplastic material model was employed to predict the flow and fracture behaviour of the target. The objective of the study was to investigate the efficiency of the JC model to numerically reproduce the maximum target deflection and peak impact force caused by three distinct shaped projectiles during target perforation. Three different sets of JC parameters calibrated by different authors [20,21] for 2024 aluminium alloy were considered to simulate the performance of the target against each projectile and the results thus obtained were compared and validated through available experiments [24]. The failure mode, deflection and impact force obtained have been noticed to have significant influence of the material models. The ballistic limit of 1.27mm thick target was numerically computed against each of the three projectiles and validated through the Recht-Ipson model. The effective span and target thickness were also varied to investigate the influence on the maximum deflection and peak impact force.

Perforation resistance of aluminum/polyethylene sandwich structure

Ballistic tests were performed on two types of polyethylene core sandwich structures (AA6082/LDPE/AA6082 and AA6082/UHMWPE/AA6082) to investigate their perforation resistance. Bulging and dishing deformation of layered plates were compared under low-velocity impact by hemispherical-nosed projectiles. Different impact failure mechanisms leading to perforation were revealed for laminates composed of a pair of aluminum alloy face sheets separated by a polyethylene interlayer. Using the finite element code Abaqus/Explicit, the perforation behavior and distribution of energy dissipation of each layer during penetration were simulated and analysed. The deformation resistance and anti-penetration properties of polyethylene core sandwich structures were compared with those of monolithic AA6082-T6 plates that had the same areal density. Although the polyethylene interlayer enlarged the plastic deformation zone of the back face, the polyethylene core sandwich structure was a little less effective than the monolithic Al alloy target at resisting hemispherical-nosed projectile impact.

Effect of CFRP strengthening on the response of RC slabs to hard projectile impact

In this paper impact response of CFRP-strengthened RC panels under the impact of non-deformable projectiles has been presented. The control and CFRP-strengthened RC slab panels were tested under the strike of hemispherical nosed steel projectiles at varying impact velocities. The response of these panels was investigated experimentally as well as numerically. The damage of the slab panels was measured in terms of the penetration depth, formation of cracks, spalling and scabbing areas and fracture of CFRP sheet. This study presents a practical and efficient numerical method for analyzing the impact response of CFRP-strengthened RC structures using LS-DYNA. The CFRP strengthening was found to increase the ballistic limit velocity by 18%, perforation energy of RC slabs by 56.7%, reduce the front crater damage and contains the flying of concrete fragments from the rear face. The maximum impact force occurs at almost same penetration depth for the control and CFRP-strengthened slabs but the restraint provided by CFRP increased the penetration depth by about 1/19.3 of the thickness of slab.

An experimental study on the ballistic performance of FRP-steel plates completely penetrated by a hemispherical-nosed projectile

Experiments were carried out to investigate the ballistic performance of fiber reinforced plastic(FRP)-steel plates completely penetrated by hemispherical-nosed projectiles at sub-ordnance velocities greater than their ballistic limits. The FRP-steel plate consists of a front FRP laminate and a steel backing plate. Failure mechanisms and impact energy absorptions of FRP-steel plates were analyzed and compared with FRP laminates and single steel plates. The effects of relative thickness, manufacturing method and fabric type of front composite armors as well as the joining style between front composite armors and steel backing plates on the total perforation resistance of FRP-steel plates were explored. It is found that in the case of FRP-steel plates completely penetrated by hemispherical-nosed projectiles at low velocities, the failure modes of front composite armors are slightly changed while for steel backing plates, the dominate failure modes are greatly changed due to the influence of front composite armors. The relative thickness and fabric type of front composite armors as well as the joining style of FRP-steel plates have large effects whereas the manufacturing method of front composite armors has slight effect on the total perforation resistance of FRP-steel plates.

Numerical studies on perforation of multi-layered targets by hemispherical-nosed projectiles

Numerical studies on perforation of multi-layered targets by hemispherical-nosed projectiles

Depth of penetration prediction for closed-cell aluminum foam experiencing impact of different shape projectiles

In this study, we combined dynamic cavity expansion theory and the Poncelet resistance formula to investigate varying penetration depth of closed-cell aluminum foam impacted by ogival-nose, truncated-ogive nose, and hemispherical-nose projectiles. We employed the explicit finite element program LS-DYNA to predict the penetration depth of projectiles at normal impact. A high-pressure air gun was also used to propel the projectiles. Finally, we compared the results of the theoretical model, experiments, and numerical simulation.

Analytical models versus experimental results for composites containing nanoclay as secondary reinforcement under high velocity impact

This study compares some analytical models on high velocity impact behaviour of composite materials with that of experimental results from high velocity impact of hemispherical nose projectiles on nanoclay-filled composite plates in particular, assessing current models to account for the presence of nanoclay in polymer composites under such loading. Nanocomposites were prepared in 0, 1.5 and 3 wt%. The nanoclay-filled polyester resin was then utilised to manufacture laminated composite panels in four, eight and 12 layers using 400 g/m2 glass fibre woven roving via hand lay-up method. Transmission electron microscopy and X-ray diffraction confirmed intercalation and exfoliation of the nanoclay in the polyester resin system. Five models were selected for assessment. Comparison of predicted ballistic limit velocity (velocity at which the projectile remains in the composite target) with that of experimental results showed close correlation in all thickness for models that incorporated projectile nose geometry. A simple empirical equation is derived as a function of polymer laminate thickness and flexural modulus of polymer nanocomposite laminates, which varies with nanoclay content in polymer composite laminates for predicting ballistic limit velocity.