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Protective shields are used to protect the technical devices from the impacts of high-speed objects, for example, the space systems from orbital garbage. This problem is so important that special spacecrafts are designed to clean up the trash. Ceramic-polymer composite panels have some advantages. However, the characteristics of such panel components have not been studied sufficiently yet. The finite element analysis is an efficient method for the composite characteristics improvement. Obviously, such improvement necessitates searching for a rich variety of composites characteristic. Each option requires creating a brick elements mesh. Adequate FE models have to be developed for penetrators (metal cones, for example) as well as for panels. Voxel based micro modeling makes it possible to develop a composite structure parametrical model. Further on, it is easy to transform this model to FE one. Developing a material model is an important problem of the impact simulation. To study the ceramic-polymer composite behavior using a traditional Johnson-Holmquist model and the most recent Toughened Adhesive Polymer model is suggested. The calculations using LS-DYNA give initial adequate results for impact modeling and thus the suggested approaches of geometrical and of FE modeling are rather effective. [ABSTRACT FROM AUTHOR]

One of the primary design considerations of earth-orbiting spacecraft is the mitigation of the damage that might occur from an on-orbit MMOD impact. Traditional damage-resistant design consists of a ‘bumper’ that is placed a small distance away from a spacecraft component or from the wall of the element in which it is housed. The performance of such a multi-wall structural element is typically characterized by its ballistic limit equation (BLE), which defines the threshold particle size that results in a failure of the spacecraft element. BLEs are also key components of any micro-meteoroid/orbital debris (MMOD) risk assessment calculations. However, these assessments often call for BLEs to predict impact response for projectiles made of materials not used in the development of those BLEs. The question naturally arises regarding how close are the predictions of such BLEs when used in impact scenarios involving projectiles made of materials not necessarily considered in their development. In an effort to address this issue, a study was performed with the objective of assessing the validity of the NNO BLE for non-aluminum particles. Particle materials considered included steel, copper, and Al 2 O 3 (i.e. particles that are made of materials that are more dense than aluminum). Comparisons are made between actual test results involving these non-aluminum projectiles and the predictions of the NNO BLE. In nearly all cases, the NNO BLE was found not to work very well in the predicting failure / no failure response of these non-aluminum projectiles. A new NNO-type BLE is then developed that can be used to more reliably predict the response of dual-wall systems under the hypervelocity impact of such “heavier” non-aluminum projectiles. [ABSTRACT FROM AUTHOR]

Cold Metal Transfer (CMT) is a proven type of welding method using Metal Inert Gas (MIG). It is a welding technique which can be employed for marine fabrications too. Plates of AA5086-H111 and AA6061-T6 with AA4043 filler is welded by CMT. Parameters like current, voltage, arc length, shield gas pressure etc. are varied to obtain a continuous weld without any crack. Welded thin plates are subjected to a tensile test as per American Welding Society (AWS B4.0:2007) and thereafter impact loads are applied. The plates subjected to impact loads in the range of sub-ordinance level velocities, the feasibility of ordinance and ultra-ordinance can be scaled and compared. Responses and terminal ballistics limit are determined for plate thickness of 1.2 mm and 3 mm. Present work consists of simulation using Abaqus Software and experiments using Laboratory prepared gun. It was observed that, there was petaling in very thin plates and in some plates it was perforated by plugging for lower ballistic loads and thinner plates. The work gives new insights into the application of CMT in joining plates of different materials with varied thickness values. The material property of plates joined by this welding method was found to be new resource information to the permanent literature of material technology. [ABSTRACT FROM AUTHOR]

The ballistic optimization of the L1-L2 and L2-L1 missions in the Earth-Moon system using electric propulsion is considered. The motion control is studied using the Fedorenko's successful linearization method to estimate the derivatives and the gradient method to optimize the control laws. The transfers are designed in frames of the restricted circular three-body problem. The mathematical model of the missions is described within the barycentric system of coordinates. The perturbation from the Earth, the Moon and the Sun are taking into account. The impact factor of the shaded areas, produced by the Earth and the Moon, is also accounted for. As for the results, the optimization of the optimal control laws and corresponding trajectories were obtained. [ABSTRACT FROM AUTHOR]

The problem of the choice of optimal ballistic schemes for a transfer to a geostationary orbit (GEO) with low and high thrust propulsion is considered. A bi-criteria optimization problem is solved by outputting a set of Pareto-optimal solutions. Results of the numerical modeling of combined insertion schemes, their ballistic optimization, and calculations of design parameters for a spacecraft with a combined propulsion unit are given. To insert a satellite into a given orbital plane, semi-major axis and eccentricity deviations are reduced by solving a terminal control problem. An approximately-optimal control and an expression for characteristic velocity expense as a function of initial boundary conditions with insertion of an electric propulsion (EP) powered spacecraft into a given station with the control are obtained. [ABSTRACT FROM AUTHOR]

Energy absorption behavior of flexible armour materials treated with Shear Thickening Fluids (STF) was studied. Five different structures were prepared with varying thread densities of p-aramid yarns, followed by treatment with 60% w/w STF. In untreated condition, plain woven fabrics show highest impact resistance in low velocity impacts, followed by 3/1 twill, 2/2 twill, 5-end satin and 2/2 matt weaves. Ballistic impact mitigation behavior improves with increase in thread density in case of plain woven fabrics. Addition of STF significantly improves both low and high velocity impact behavior of the panels. Low velocity behavior of STF treated fabrics have been published previously [12]. This paper brings together both low and high velocity impact behavior of various geometries of fabrics. It was seen that both primary and secondary yarns are engaged during impact which improves impact mitigation behavior of STF treated fabrics. However, fabrics get jammed at thread densities beyond 32×32 per inch. As was observed earlier in low velocity impact conditions, addition of STF did not enhance performance of fabrics with high thread density in high velocity impact as well. [ABSTRACT FROM AUTHOR]

Effect of heat treatment on mechanical properties and ballistic resistance of AA-7017 aluminium alloy plates has been investigated. The stress-strain behaviour of AA-7017 plates subjected to different heat treatment schedules namely under-aging, peak aging and over-aging, is evaluated from quasi-static tension tests. The heat-treated plates display large differences in static mechanical properties in terms of strength and ductility. The peak-aged plate shows the highest strength and hardness followed by the under-aged and over-aged materials. The ballistic resistance of these plates are evaluated by impacting deformable projectiles at a velocity of 830±10 m/s at a normal angle of attack. The peak-aged plate exhibits the best ballistic penetration resistance. The changes in the mechanical properties with different heat treatments have been correlated with ballistic performance of the AA-7017 alloy. Both the post ballistic micro-structural observations and micro-hardness measurements adjacent to the impacted crater walls have been carried out to understand the change in material deformation behaviour with heat treatment. [ABSTRACT FROM AUTHOR]

Numerical investigations were carried out on 1.27, 3.18, 6.35, 12.7and 19.05 mm thick 2024-O aluminum target against blunt nose steel projectiles of 12.7 mm diameter and 37.7 gram mass. Three-dimensional numerical simulations of the problem are carried out using finite element code ABAQUS. The ABAQUS/Explicit finite element code in conjunction with Johnson-Cook elasto-viscoplastic material model proposed by Leuser[1] was employed to perform the simulations. The present studyis concerned with the measurement of ballistic limit of deformable projectiles. The results obtained were compared with the experimental results conducted by [3,4] and a close correlation between the two was found. The failure mode of the target was also found in good agreement. The results obtained showed a consistent increase in the ballistic resistance of target with an increase in the target thickness. [ABSTRACT FROM AUTHOR]

Steel containing 0.65 wt % nitrogen has been investigated for armour applications by subjecting it to different percentages of hot rolling. The effect of percentage reduction during hot rolling on microstructures, mechanical properties and ballistic performance has been studied. The ballistic performance of 6.5 mm, 7.5 mm thick plates against 7.62 ball and 16 mm, 17 mm thickness against 7.62AP projectiles were assessed. The nature of damage has been studied by varying percentage reduction during hot rolling of these plates for providing full protection. [ABSTRACT FROM AUTHOR]

The ballistic resistance of 12 mm thick mild steel plates has been studied against 7.62 API projectiles through numerical simulations carried out using ABAQUS/Explicit finite element code. The incidence angle was varied as 0°, 15°, 30°, 45°, 57° and 59°. The material parameters for the JC model proposed by the Authors were employed to predict the material behavior of the target, while the material behavior of the projectile was incorporated from the available literature. The numerical results thus obtained have been compared with the experiments reported in earlier study, wherein the incidence velocities of the projectile were considered close to 820 m/s. The experimental and numerical results with respect to failure mechanism, residual projectile velocity and critical angle of ricochet have been compared. A close correlation between the experimental findings and the predicted results has been found. In general, the resistance of the target has been found to increase with increase in target obliquity. [ABSTRACT FROM AUTHOR]

In this study, bubbled- armour forms are assessed for ballistic penetration resistance. A key component is optimization of the bubble shape to maximize its fundamental modal frequency. A ‘large- plastic- regime’ automotive steel alloy is adopted for the bubble and the penetration process simulated by LS- DYNA for a ‘rigid’ projectile. Three forms: - a flat-, spherical and the shape- optimized one, of identical planform dimensions and mass, are studied for their penetration resistance characteristics under a common impact speed. The optimum form is found to be the most superior, causing a momentum loss of as much as 140%, implying a total reversal of the projectile, post- impact. This is more than the 111% for the spherical form and far above the 30% for the flat form. Modal response also correlates well with impact- induced bubble- response acceleration in wavelet decomposition. We conclude that with the fundamental modal frequency maximized, shape- optimized bubbled- armour forms can have much higher penetration resistance than a traditional plate armour's. [ABSTRACT FROM AUTHOR]

Conical aluminium projectiles of apex angle 34 degrees were made to impact thin aluminium targets inclined at an angle of 60 degrees at low subordnance velocities where material strength effects are still valid. Thin targets of thickness 1.5 mm and 2 mm underwent failure by reverse petalling as the projectiles penetrated the targets. Projectiles underwent ricochet while impacting 2.5 mm targets causing severe dents and visible contact marks on the target. While the projectile nose tips were separated in the 1.5 mm and 2 mm cases, the projectiles impacting 2.5 mm targets underwent substantial nose deformation. Numerical simulation performed using ABAQUS/Explicit was able to capture the projectile deformation and target deformation quite well phenomenologically. [ABSTRACT FROM AUTHOR]

The objective of this study is to investigate the effect of multi walled carbon nanotube (MWCNT) inclusion on the fracture toughness and the ballistic resistance properties in terms of energy absorption. The determination of fracture toughness of the epoxy/MWCNT matrix was carried out by using a single edge notch bending (SENB) method according to the ASTM D5045-99. Four different weight percentage (wt %) of multi-walled carbon nanotubes (MWCNTs) contents were used, which were 0 wt.%, 0.1 wt.%, 0.55 wt.% and 1.0 wt.%. Epoxy binder and MWCNTs were mixed by using a mechanical stirrer for 10 minutes at 1500 rpm speed and was further sonicated for 30 minutes at 30 Hz amplitude in order to enhance the homogeneity of MWCNTs in the matrix. The compositepanel comprised of Twaron fabrics with epoxy resin filled with MWCNTs was fabricated using hand layup and vacuum bagging assist method. The Twaron/epoxy/MWCNT composite panels weresubjected toa ballistic test using 9 mm Full Metal Jacket bullet at different impacting velocities. From the SENB results, it can be reported that MWCNT inclusion up to 1.0% w.t content shows significantinfluence towards increment of fracture toughness value.MWCNT also improves the ballistic resistance capability of the composite panel where it was found that the impact energy absorption value was proportionally increasewith theepoxy/MWCNT matrix's fracture toughness properties. [ABSTRACT FROM AUTHOR]

The asymmetric radial crack patterns that occur in brittle targets when impacted by high velocity projectiles are explained using a Phenomenological Mechanochemistry of Damage (PMD) engineering model. The developed model, which constitutes a simplification of the generalized PMD framework, reveals an energy instability during failure of brittle materials configured in a purely symmetric geometry and impact configuration. The underlying cause of the instability is due to the competition between stored elastic energy and the energy associated with new surface creation through broken chemical bonds. The instability manifests itself in the form of asymmetric radial cracking in the brittle target. The model is built upon the general PMD framework and assumes the target material is sufficiently brittle that strains are small and linear elasticity is applicable. Furthermore, the impact geometry is assumed to be purely symmetric, which leads to a reduction of the geometry to a one-dimensional radial configuration. The model is not restricted to any ballistic impact speed regime, provided the target material remains in the solid phase. [ABSTRACT FROM AUTHOR]

At present, the use of refined numerical simulation is gaining more and more importance, especially in extreme load cases where large experimental test programmes are not feasible. A validated numerical methodology can be exploited to investigate critical behaviour as a “virtual test”. According to this premise, a numerical investigation is presented in this work to study the ballistic resistance of Kevlar29-Epoxy fabric plates subjected to impacts of small calibre projectiles, armour piercing (AP), ball type, and a blunt shaped projectile (BSP), all with a 7.62 mm diameter. The numerical models were developed using the explicit finite element code LS - DYNA. The composite plate is 5 mm thick, made up of 12 layers. The fabric is impregnated in Epoxy matrix, to guarantee both structural and ballistic resistance, and is a 2D plain-weave. The mechanical properties of the projectiles’ deformable materials were modelled by means of the Johnson-Cook plasticity model, which also includes the failure criterion. The composite plate is modelled using a mixed Macro-homogenous / Meso-heterogeneous approach. In particular, the area around the impact adopts the Meso-heterogeneous modelling, in which the woven yarns and the matrix are separate parts able to interact, to increase the efficiency of the numerical methodology, allowing the modelling of the friction between the yarns, the delamination and the fibre-matrix debonding. This method needs to assign separately the mechanical properties to the fabric and the matrix as well as the damage criteria for the yarns, the matrix and the delamination. In the Macro-homogenous approach, which models the remainder of the composite plate, the yarns and the matrix are considered as a unique homogenous mean, to which equivalent orthotropic mechanical properties of the impregnated fabric are assigned. The numerical investigation mainly focuses on the residual velocity of the impacting projectiles, identifying the ballistic limit of each couple projectile-target. [ABSTRACT FROM AUTHOR]

In this paper some experimental results of a bullet impact on composite armor are discussed together with numerical modeling approaches. The development of high-quality composite sandwiches for ballistic protection is the target of a grant project in terms of which the research is being conducted. Traditionally, a vehicle ballistic protection is mainly achieved using metal-based armor which is heavy and thus negatively affects other vehicle parameters, such as maneuverability. These days, composite or hybrid sandwiches are becoming more and more popular. Numerical simulations allow for a reduction of the number and variability of experiments needed to obtain appropriate design of ballistic protection, but they require verified modeling approaches and reliable material data. Therefore, different modelling approaches have been tested and possibilities to adjust these models to experimental data were investigated. [ABSTRACT FROM AUTHOR]

An empirical model to estimate the ballistic velocity limit (BLV) for ceramic/metal bi-layer armour materials is proposed by considering momentum and energy balance during impact process. Impact simulations of different combinations of various thicknesses and materials for front ceramic and backing metallic layers and different projectile lengths, chosen based on orthogonal array approach, are performed. Three ceramic materials as front layer, namely: alumina (Al2O3 AD96), boron carbide (B4C) and silicon carbide (SiC) and three materials as backing metallic layer, namely: aluminum alloy (Al 5083H116), steel 4340 and titanium alloy (Ti6Al4 V) are used in the parametric study. Empirical constants in the proposed model are obtained using least square fitting to the BLV data obtained from simulations. Comparison between proposed model results, for BLV of ceramic/metal armour impacted by flat-ended projectiles with available limited experimental data is carried out. [ABSTRACT FROM AUTHOR]

Abstract: The results of 28 hypervelocity impact tests performed using a full-scale and two subscale versions of a simple Whipple shield and aluminum spheres are presented. “Pass/Fail” lines were developed for each subscale shield for impact velocities ranging from 6.90 to 9.77km/s. These lines were compared to one another and to a scale-appropriate ballistic limit curve generated using Ballistic Limit Equations (BLE) from Christiansen. Both subscale shields exhibited similar performance capabilities when the impact velocity was near 7km/s. The Christiansen BLE closely described the capability of a 0.46-scale shield but underpredicted the capability of a 0.25-scale shield, which improved when compared to the ballistic limit curve, as the impact velocity was increased. The performance of the full- scale shield was significantly below its predicted capability when the impact velocity was 7km/s. [Copyright &y& Elsevier]

Abstract: Porous-ceramic, thermal protection systems were used heavily on the Orbiter, and they are currently being used on the next generation of US manned spacecraft, Orion. These systems insulate reentry critical components of a spacecraft against the intense thermal environments of atmospheric reentry. Additionally, these materials are highly exposed to space environment hazards like solid particle impacts. This paper discusses impact studies up to 10km/s on nominally 8 lb/ft3 alumina-fiber-enhanced-thermal-barrier (AETB8) tiles coated with a toughened-unipiece-fibrous-insulation/reaction-cured-glass layer (TUFI/RCG). A first principles impact model that describes projectile dispersion is described that provides excellent agreement with observations over a broad range of impact velocities, obliquities and projectile materials. [Copyright &y& Elsevier]

Abstract: Development and testing of a novel armor system that defeats high-velocity projectiles and penetrators is described, from a phenomenological perspective. The process is covered where fundamental principles of shock mechanics and high fidelity computational physics (HFCP) simulations are used to create the armor system, from concept to proof testing. This armor development effort started with a “clean sheet,” which allowed for the basic ideas of penetration mechanics and advanced simulation to be brought to bear. Particular attention was paid to the nature of the two threats the armor was intended to stop: (1) three .50 caliber armor piercing (AP) projectiles at 850 meters per second, fired one at a time and grouped within a 5 centimeter diameter circle, and (2) an 18.6 gram mild steel projectile at 2,500 meters per second. The impact response of each threat is fundamentally different, and thus requires different mechanisms to defeat. Primary constraints on the armor system were minimal cost, no ceramic components, and minimal weight. There was freedom to make the system relatively thick, which allowed for the use of spaced components to progressively defeat each threat. Simulation was applied to determine geometries and materials that break up and yaw the AP threat, while maintaining multi-hit robustness. Simulation was also used to adapt the design to produce shattering shock pressures in the higher velocity mild steel, and then arrest of the resulting debris cloud. Simulations were performed using an in-house developed Lagrangian hydrocode having smooth particle hydrodynamic (SPH) capabilities. Outlined items include the material and failure models used, benefits of Lagrange-to-SPH conversion, and advantages of massive parallel processing capabilities which enabled the HFCP simulations. Also outlined is a design process that relies on the simulation capability to achieve minimal prototyping and testing. Results from proof tests are shown. Comparisons are made to show that simulations match well with the test data. [Copyright &y& Elsevier]