Thin Target Plates Research Articles

Damage of thin target plates impacted by conical projectiles with varying apex angles in ballistic application: experimental, FEA and ANN integrated approach

In the current study, an experimental setup consisting of smoothbore 30-caliber powder gun was employed to launch spherical projectiles (3 g/ϕ9) in the ballistic range of velocities from 500 to 1700 m/s and obliquity (0, 33 and 65°), impacting 2 mm thin Steel 1006 target plates. Crater dimensions (major and minor dia.) obtained from series of FE simulations run for the above configuaration was validated by corresponding experimental data. Subsequently, a fullscale 3D FE model considering 8-noded hexahedral elements was used to discretize SS304 conical projectiles (replacing spherical projectile) with various apex angles viz. 40°, 60°, 80° and 100° impacting on single (3 mm) and double layer (1.5 mm each) steel 1006 targets (replacing 2 mm target) in LS dyna. The material behavior was characterized using J–C strength and damage models, along with Gruneisen Equation of State. An erosion algorithm was used in the explicit FE code LS-DYNA to remove undesirable elements. In the next stage, Adam and Nadam optimizers have been employed in ANN models developed using Python code within the Tensor-Flow framework. The Keras Tuner library in the Tensor-Flow framework was used for hyper parameter tuning. The ANN models trained using simulation data successfully predicted the residual KE of conical projectiles with intermediate apex angles of 90°, 70°, and 50° across twelve different impact scenarios. The models with Adam and Nadam optimizers achieved mean squared error (MSE)/coefficient of determination (R2)/mean absolute percentage error (MAPE) values of 109.44/0.998/6.72 and 91.19/0.998/7.76, respectively.

Comparative study of effect of fragment nose shapes on damage characteristics of thin target plate in ballistic applications

Experimental and numerical investigations in ballistic applications have predominantly focused on determining the ballistic limit of target plates for various projectile shapes. However, limited attention has been given to the influence of projectile nose shapes at high impact velocities. To address this gap, 3D FE simulations were carried out on a 1 mm thin target plate using J-C material model, the Gruneisen equation of state (EOS), an erosion contact algorithm, and the explicit FE code LS-DYNA. The simulations involved impact of fragments of equal mass but different nose shapes. The results revealed a significant influence of fragment shape on both the ballistic limit and overall plastic deformation of the target plate. Particularly, the target plate impacted by a hexagonal pyramid fragment shape exhibited the highest ballistic limit and global plastic deformation. Further, it was also observed that at higher impact velocities, the former fragment shape caused the maximum damage to the target plate, while at lower impact velocities, the cubical fragment shape demonstrated the highest lethality. This difference in target damage is known to be governed by the energy required to erode the target and fragment material. The results from the current study offers valuable insights into how different fragment shapes influence the damage inflicted on target plates in ballistic scenarios. The findings presented in this study also offer guidance on selecting suitable fragment shapes for future use in Fragment Generator Warheads (FGW) in order to maximize the damage or lethality inflicted on targets.

Numerical investigation on effect of different projectile nose shapes on ballistic impact of additively manufactured AlSi10Mg alloy

In the last few years, due to the superior mechanical qualities of Additive Manufacturing (AM) AlSi10Mg alloy to those of traditional casting process AlSi10Mg alloys, the application of AM technology has significantly increased. The ballistic impact research has a wide range of uses, notably in the mining, construction, spacecraft and defence sectors. This work focuses on analyzing the behavior of different projectile nose shapes on the AlSi10Mg alloy fabricated by AM. There are several projectile nose forms to consider, including blunt, hemispherical, conical, and ogive shapes. The impact of various projectile shapes on the ballistic limit of the additively created AlSi10Mg alloy is carefully examined in this study. All numerical simulations were carried out using LS-DYNA software, and the Johnson-Cook material and damage model were considered to assess the ballistic resistance behavior. The ballistic limit for various projectile shapes is computed using the Jonas-Lambert model, which describes the connection between residual velocity and starting projectile velocity. The results showed that, the ogive-shaped Projectile offers the highest ballistic limit, and the blunt projectile shows the lowest ballistic limit for a 5 mm thin target plate. The ballistic impact phenomenon showed plugging failure for the blunt nose projectile, the formation of plug and small fragments were observed in the case of hemispherical nose projectile, fragmenting failure is observed with radial necking in the case of conical nose projectile and petals are formed at the impacted zone in ogive nose shape projectile. Moreover, the ballistic limit of AM AlSi10Mg alloy was slightly higher compared to the ballistic limit of the die-cast AlSi10Mg alloy for the 7.62 mm AP bullet (core). Therefore, AM AlSi10Mg alloy may have equal or good ballistic properties compared to die-cast AlSi10Mg alloy.

Evaluation of Absorbed Energy in High-Velocity Particle Impact for Aero-Engine Materials

A single particle impact testing system was developed to estimate an absorbed energy in particle perforation process of aero-engine materials. Thin target plates of 0.1-1 mm thickness were impacted by a 3 mm diameter spherical particle. A wide range of impact velocities from 50-375 m/s was covered using a compressed gas gun. First, particle impact tests were conducted on aluminum and copper plates to evaluate the validity of the experimental system. The experimental results show that there is no significant difference in the effect of the particle impact velocity on the absorbed energy of aluminum and copper, and the ballistic limit can be reasonably estimated based on a simple energy balance equation. Second, impact tests were conducted on TiAl alloys and Ni-based alloys. There was no clear ballistic limit for the TiAl alloys, and the absorbed energy tended to increase as the particle impact velocity increased. The absorbed energy of the TiAl alloy was half that of the Ni-based alloy for specimens of the same thickness. Radial and petal-shaped cracks were observed in the Ni-based alloys after impact tests, while brittle cracks, fractures, and scattering of debris were observed at the periphery of the penetration hole in the TiAl alloys.

Status of the MUonE experiment

The MUonE experiment has been proposed to measure the differential cross section of μe elastic scattering, by colliding the 160 GeV muons of the CERN M2 beam with atomic electrons of thin target plates. From a very precise measurement of the shape one can achieve a competitive determination of the leading hadronic contribution to the muon magnetic moment, independent from the other existing ones. In preparation for the Test Run with a reduced setup the detector geometry has been optimised. Expected yields for a first physics run with limited statistics are discussed, together with prospects for the assessment of the main systematic uncertainties.

Hypersonic impact flash characteristics of a long-rod projectile collision with a thin plate target

Impact flash occurs when objects collide at supersonic speeds and can be used for real-time damage assessment when weapons rely on kinetic energy to destroy targets. However, the mechanism of impact flash remains unclear. A series of impact flash experiments of flat-head long-rod projectiles impacting thin target plates were performed with a two-stage light gas gun. The impact flash spectra for 6061 aluminum at 1.3–3.2 km/s collision speeds were recorded with a high-speed camera, a photoelectric sensor, and a time-resolved spectrometer. The intensity of the impact flash exhibited a pulse characteristic with time. The intensity (I) increased with impact velocity (V0) according to I∝V0n , where n = 4.41 for V0 > 2 km/s. However, for V0 < 2 km/s, n = 2.21, and the intense flash duration is an order of magnitude less than that of higher V0. When V0 > 2 km/s, a continuous spectrum (thermal radiation background) was observed and increased in intensity with V0. However, for V0 < 2 km/s, only atomic line spectra were detected. There was no aluminum spectral lines for V0 < 2 km/s, which indicated that it had not been vaporized. The initial intense flash was emission from excited and ionized ambient gases near the impact surface, and had little relationship with shock temperature rise, indicating a new mechanism of impact flash.

Fragmentation Behaviour of Radial Layered PELE Impacting Thin Metal Target Plates

The fragmentation mechanism of the penetrator with lateral effect (PELE) after perforating a thin target plate has been summarised and analysed firstly. Then the fragmentation of radial layered PELE was analysed qualitatively and verified by experiment. In the experiment, the target plates were made of 45# steel and 2A12 aluminium respectively. Qualitative analysis and experimental results show that: for normal PELE without layered, after perforating the thin metal target plate, from the bottom to the head of the projectile, the number of fragments formed by the jacket gradually increases, and the mass of the fragment decreases correspondingly. Compared with the normal PELE without layered, the radial layered PELE is less likely to break into fragments, when impacting the thin metal target plate with the same material and thickness under the same impact velocity. However, from the mechanism of the PELE, when the resistance of the target plate is large enough, and the duration of pressure is long enough, the radial layered PELE also can break into fragments with transverse velocity component. The resistance of the target plate plays an important role in the fragmentation of radial layered PELE. The radial layered PELE produced massive fragments with transverse velocity component when impacting the 45# steel plate with5 mm thickness under the impact velocity of 657.2 m/s.

Influence of Target Span and Boundary Conditions on Ballistic Limit of Thin Aluminum Plate

A collective study was performed to probe the influence of projectile nose shape, target span and target boundary condition on ballistic limit of thin aluminium plates. 1 mm thick 1100-H12 aluminium target plates were normally impacted by ogive and blunt nosed projectiles of 19 mm diameter and 50.8 mm length. The target span was varied as 95, 190, 285, 380, 475, 570, 665 and 760 mm whereas the target boundary condition was studied by varying the fixity at the target circumference region as 100%, 75%, 50% and 25%. ABAQUS/Explicit finite element code using Johnson-Cook elasto-viscoplastic material model were employed to carry out the numerical simulation. To validity of numerical results are revealed by experiments performed on pressure gun in the sub-ordnance velocity regime.The numerical as well as experimental study revealed that the ballistic limit of thin target plate was significantly affected by target span as well as target circumference fixity. The ballistic limit increases with increase in target span diameter while opposite trend was observed with increase in the region of fixity.

Thick AA7020-T651 plates under ballistic impact of fragment-simulating projectiles

The ballistic performance of an Al alloy AA7020-T651 (AlZn4.5Mg1, 3.4335) against fragment-simulating projectiles (FSPs) is investigated at impact velocities between 900 m/s and 1500 m/s. The target plates are considered as thick regarding the ratio between the specimen thickness (40 mm) and the projectile diameter (20 mm). With increasing impact velocities, the observed failure modes of the target plates change from plugging to discing. The stress state leading to the discing formation has been described and numerically modeled by the Lagrangian approach. In order to understand the mechanisms that occur in the material under highly dynamic loadings, its mechanical, thermal and micro-structural properties are discussed. The experimental conditions (thick target, penetrator of a specific shape, high-velocity impacts) allow the authors to draw conclusions, which are complementary to those that resulted from investigations of semi-thick and thin target plates under ballistic impacts in a lower velocity range.

Analytical and numerical description of the PELE fragmentation upon impact with thin target plates

The PELE ammunition is characterized by a low-density filling material surrounded by a high-density brittle jacket material. An analytical model describing the fragmentation of this ammunition behind a target plate is presented. This model assumes uniaxial strain in the filling and uses the Ranking–Hugoniot relations to calculate the material state. In addition, shock and rarefaction wave interactions at the target free surface and the filling/target interface are accounted for, as well as the radial rarefaction originating from the jacket outer surface. This allows the calculation of the pressure evolution in the filling and the radial acceleration of the jacket at any axial position along the projectile. This model aims at improving previously published analytical models where the acoustic wave approximation was used and the wave interactions were neglected. Experimental results (Paulus and Schirm, 2006) are used to validate the analytical model for different target materials (aluminum and steel), target thicknesses (3 mm and 8 mm), filling materials (polyethylene and aluminum) and impact velocities (900 m/s to 3000 m/s). A qualitative comparison based on X-ray photographs reveals similar features between the model and the experiments, such as smaller and lighter fragments with a greater radial velocity at the front of the projectile compared to the fragment characteristics at the back of the projectile. A quantitative comparison based on the maximum radial velocity of the fragments shows on average a 20% difference between the analytical and experimental results for all impact conditions considered. Despite this difference, the analytical trend follows more closely the experimental one compared to the acoustic approximation especially at high impact velocities. In addition, the acoustic approximation fails to reproduce the jacket fragmentation pattern since the fragmentation length of the jacket is significantly under-predicted. A numerical simulation is also presented using the ANSYS Autodyn 14.0 software. The results show that the numerical and analytical pressure evolution in the filling and the radial velocity of the jacket are in very good agreement, verifying the uniaxial strain assumption. This agreement (together with the experimental agreement) thus suggests that the Rankine–Hugoniot relations, the wave interactions and the radial rarefaction wave must all be included in the model to adequately describe the fragmentation of the PELE ammunition behind a thin target plate.

Revisiting the perforation of ductile plates by sharp-nosed rigid projectiles

The process of ductile plate perforation by sharp-nosed rigid projectiles is further examined in this work through 2D numerical simulations. We highlight various features concerning the effective resisting stress ( σ r ) which a finite thickness plate, with a flow stress of Y t , exerts on the projectile during perforation. In particular, we show that the normalized resisting stress ( σ r / Y t ) can be represented as a unique function of the normalized thickness of the plate ( H/ D, where H is plate thickness and D is projectile diameter), for a large range of normalized thicknesses. Our simulations for very thin target plates show that the penetration process is achieved through the well-known dishing mechanism, where the target material is pushed forward by the projectile’s nose. An important observation, which emerges from our simulations, is that the transition between the dishing and the hole enlargement mechanisms takes place at a normalized thickness of about H/ D = 1/3. We also find that the normalized resistive stress for intermediate plate thicknesses, 1/3 < H/ D < 1.0, is relatively constant at a value of σ r / Y t = 2.0. This range of thicknesses conforms to a state of quasi plane stress in the plates. For thicker plates ( H/ D > 1) the σ r / Y t ratio increases monotonically to values which represent the resistance to penetration of semi-infinite targets, where the stress state is characterized by plane strain conditions. Using a simple model, which is based on energy conservation, we can predict the values of the ballistic limit velocities for many projectile/target combinations, provided the perforation is done through the ductile hole enlargement mechanism. Good agreement is demonstrated between predictions from our model and experimental data from different sources, strongly enhancing the confidence in both the validity and usefulness of our model.

Impact behaviour of PELE projectiles perforating thin target plates

The first experiments with a penetrator with enhanced lateral efficiency (PELE) were carried out in 1996. The unusual behaviour of the penetrator as it perforates a target can generally be described in three main stages. In the first stage the different kinetic energies of the jacket and the filling lead to the enclosure of the filling material. This induces a pressure rise in the filling, which dilates the surrounding jacket in the second stage. During the last stage the high-density jacket breaks into pieces. When a thin target, as in our case, is perforated, a fourth stage must be added to the other three. This new stage describes the interaction between the filling and the plug, which is produced during the impact. For the lateral efficiency of the PELE, the second stage is the important one. The behaviour in this stage (pressure build-up and radial expansion of the jacket) is dominated by only a few physical parameters. For weak shock waves, these parameters are determined by theoretical consideration. A number of experiments were carried out in the velocity range between 900 and 3000 m/s in order to obtain an experimental database. In the last section a comparison between the physical model and experimental data gives a short outline of the complex impact behaviour of the PELE projectile. The physical model and the experimental data are in good agreement for impact velocities under 1400 m/s. For higher velocities causing stronger shock waves, the theory has to be modified; but the set of physical parameters influencing the terminal ballistic behaviour of PELE remains valid.

Debris Cloud Material Characterization for Hypervelocity Impacts of Single- and Multimaterial Projectiles on Thin Target Plates

The key to conducting an accurate damage assessment of a target impacted by a high speed projectile is the use of a robust assessment methodology. To accurately determine total target damage, a damage assessment methodology must include the effects of discrete impacts by solid debris cloud fragments as well as impulsive loadings due to molten and vaporous debris cloud material. As a result, the amount of debris cloud material in each of the three states of matter must be known to accurately assess total target damage and break-up due to a high speed impact. This article presents a first-principles based method to calculate: the amount of material in a debris cloud created by a perforating hypervelocity impact that is solid, molten, and vaporous; the debris cloud leading edge, trailing edge, center-of-mass, and expansion velocities; and the angular spread of the debris cloud material. The predictions of this methodology are compared against those of empirically based lethality assessment schemes as well as numerical and empirical results obtained in previous studies of debris cloud formation.

Debris Cloud Material Characterization for Hypervelocity Impacts of Single- and Multi-Material Projectiles on Thin Target Plates

The key to conducting an accurate damage assessment of a target impacted by a high speed projectile is the use of a robust assessment methodology. To accurately determine total target damage, a damage assessment methodology must include the effects of discrete impacts by solid debris cloud fragments as well as impulsive loadings due to molten and vaporous debris cloud material. As a result, the amount of debris cloud material in each of the three states of matter must be known to accurately assess total target damage and break-up due to a high speed impact. This article presents a first-principles based method to calculate: the amount of material in a debris cloud created by a perforating hypervelocity impact that is solid, molten, and vaporous; the debris cloud leading edge, trailing edge, center-of-mass, and expansion velocities; and the angular spread of the debris cloud material. The predictions of this methodology are compared against those of empirically based lethality assessment schemes as well as numerical and empirical results obtained in previous studies of debris cloud formation.

Experimental and numerical investigation of shock-induced full vaporization of zinc

A systematic computational and experimental study is presented on shock-induced full vaporization of zinc resulting from record-high impact speeds recently achieved on the Sandia Hyper-Velocity Launcher. In these experiments, a thin target plate of zinc is impacted by a tantalum flier plate at speeds ranging from 8 to 10.1 km/s, producing pressures from 3 Mbar to over 5.5 Mbar and temperatures as high as 39000 K (∼ 3.4 eV). Such high pressures produce essentially full vaporization of the zinc because the thermodynamic release isentropes pass into the vapor dome near the critical point. To characterize vapor flow, the velocity history produced by stagnation of the zinc expansion products against a witness plate is measured with velocity interferometry. For each experiment, the time-resolved experimental interferometer record is compared with wavecode calculations using an analytical equation of state, called ANEOS, that is known to have performed well at lower impact speeds (less than ∼7 km/s) where vaporization is negligible. Significant discrepancies between experiment and calculation are shown to exist under conditions of the more recent higher impact speeds in excess of 7 km/s. Numerical predictions underestimate witness-plate velocity for impact speeds up to about 9 km/s but overestimate witness-plate velocity for impact speeds exceeding 9 km/s. This qualitative change in the character of the discrepancy is conjectured to occur when the temperature on the release isentrope at the critical density lies above the critical temperature. These experiments can be used to develop and refine models representing the dynamics of the shock-induced vaporization process.