Foam Projectiles Research Articles

Dynamic response of UHMWPE/polyurea composite plates under combined blast and ballistic impact

Combined load caused by blast impulse and fragmentation impact poses a synergetic damage threat to the protective structure. To improve the blast and ballistic impact resistance of Ultra-high molecular weight polyethylene (UHMWPE), polyurea coated Ultra-high molecular weight polyethylene structure was proposed, and the composite structures with different coating thickness and coating position were prepared. Composite projectiles formed by combining foam projectiles and steel projectiles were launched by light gas gun to simulate the combined load of explosion impact and fragmentation. Comparative experimental studies were carried out. The experimental results show that the polyurea layer has good elastic properties, preventing the excessive deformation of the PE layer. The polyurea coating position and the time interval of the combined load show significant influence on the impact resistance of the composite structure. When the load was relatively low, PE plate with polyurea coating on booth face has both the advantages of PE plate with coating on the front and back face, but when the load increased, the impact resistance potential of polyurea layer was not fully developed. With the increase of the combined load, structures with polyurea coating on the back face has a good resistance of combined impact.

Assessment and litigation of ocular injuries by less-lethal weapons.

The main cause of serious ophthalmological injuries, includingviolent eye amputations in the context of so-called less lethalweapons, is the use of blunt objects, such as batons or extendablesticks and the use of kinetic energy projectiles (rubber bullets,pellets, foam projectiles or others). Such injuries in the contextof population control have been considered to constitute cruel,inhuman or degrading treatment or even torture when they arecarried out, intentionally or unintentionally, by State officials(or with their acquiescence or protection) and involve any of thepurposes contemplated in the Convention against Torture. Dueto their special characteristics, they constitute rights violationsthat entail unique difficulties and complexity from both a legaland forensic point of view. This paper addresses some of thesedifficulties with practical legal and forensic recommendations.It is structured in two parts: First, legal, where we considerlegal difficulties and provide suggestions on elements for obtainingevidence are given. Second, medico-psychological andforensic where we review the elements to be considered in theinterview, the medical and ophthalmological evaluation, andthe psychometric, psychological and psychiatric evaluation.

Shakedown of metallic sandwich beams when subjected to repeated impact loadings

When a monolithic metallic beam/plate subjected to repeated dynamic loadings with fixed impact level experiences elastoplastic deformation, its measurable deformations may cease to develop for further repetitions of the same dynamic load: this phenomenon was referred to as “pseudo-shakedown” in previous studies (Jones, 2014; Shen and Jones, 1992). Would pseudo-shakedown occur in a metallic sandwich structure under repeated shock loadings remains elusive. A combined experimental and numerical study was carried out to explore whether dynamic shakedown could occur in all-metallic ultralightweight corrugated core sandwich beams. For repeated impact tests, the sandwich beams were fabricated via the sequential process of cutting-stamping-vacuum brazing. When subjected to repeated impact loads (achieved via aluminum foam projectiles launched from a light gas gun), the dynamic responses of each sandwich specimen - including structural evolutions, beam deflections, and deformation/failure modes - were measured. Experimental results revealed that, depending upon the level of impact momentum applied to the sandwich beam, either dynamic shakedown or progressive failure could occur. The method of finite elements (FE) was subsequently employed to simulate the repeated shock tests, which was validated against experimental measurements, with good agreement achieved. To explore the physical mechanisms underlying the observed dynamic shakedown, the FE results of final plastic energy and effective plastic strain distribution in the sandwich beam were extracted and analyzed. When shakedown occurred, the measurable permanent deformation of the sandwich beam kept a relatively stable state, but its plastic energy remained positive, which is different from its monolithic beam/plate counterpart (i.e., plastic energy dropping to zero during dynamic shakedown). Such difference is mainly attributed to stress concentration occurring at the connecting joint points between the corrugated core and face sheets of sandwich and clamped endings, which produces plastic deformations that are difficult to reflect in overall large deformations of the beam. Consequently, the dynamic shakedown of metallic corrugated core sandwich beam captured in this study appears to be inexhaustive and hence may be termed as the “apparent pseudo-shakedown” (with danger lurking in the welding joints as well as clamped endings). Finally, based on a simplified bi-linear hardening constitutive law, the mechanisms underlying the dynamic shakedown of sandwich beam were further discussed from a purely base material point of view.

Experimental and theoretical study on the response of the X-frame CFRP sandwich beam under the local impulsive loading

The impact resistance of the carbon fibre reinforced X-frame sandwich beam and its foam reinforced structure was investigated experimentally and theoretically. To simulate the blast loading on the composite sandwich beams, the aluminum foam projectiles were utilised to impact the composite specimens. Under the local impulsive loads of the different intensities, the core shear failure, core crushing and skin fracture of the sandwich beams were observed by using a high-speed camera. A theoretical model for the dynamic response of the fibre-reinforced composite sandwich beam under the impact loads was constructed. Three phases, namely the local compression, the propagation of global bending/shearing wave and global stretching were considered in this theory. The theoretical model can provide the reasonable deflection history and failure modes of the sandwich beam compared with the experimental and simulated results. The impact pressure between the foam projectile and the beam were obtained by the theoretical and numerical predictions. The results indicated that the decreasing of the structural density can reduce the transmitted impulse. The optimal design charts were constructed by introducing the normalised variables based on the theoretical model. The minimum weight design revealed that the composite sandwich beams with low-density cores generally had the better specific impact resistance, while the foam-filled sandwich beams with the higher density had the outperformed impact resistance at the low impulse. It is expected that the theoretical model can provide a useful reference for predicting the impact resistance of the fibre-reinforced composite sandwich structures.

Blast response of laminated glass: A gas-gun experimental investigation of the fracture pattern and yield lines observed in full-scale blast tests

The applications of architectural and automotive laminated glass continue to grow. This is largely due to the enhanced safety in extreme events, such as blast. However, the complex interaction between the glass fragments and the polymer interlayer after glass fracture is still only partially understood, with existing analysis methods adopting a semi-empirical approach for the post-fracture response. These include a plastic yield-line analysis based on a failure pattern repeatedly observed during blast tests. In recent research it was demonstrated that yield lines can develop in fractured laminated glass through the composite bending action of the glass fragments, working in compression, together with the interlayer working in tension. This paper investigates the influence of the inertia loading associated with blast response, which has not been explicitly studied previously, with the aim of understanding the pattern of yield lines observed in blast tests. Impact tests are performed on laminated glass specimens using foam projectiles launched from a gas gun, which simulate the loading from a blast pulse. These tests demonstrate that the yield line pattern formed under short-duration dynamic loading depends on the loading intensity, thereby providing further evidence of a dynamic, plastic collapse mechanism in which inertia plays a significant role.

Soft impact of GLARE fiber metal laminates

Dynamic response of fully clamped GLARE fiber metal laminates (FMLs) subjected to closed-cell aluminum foam projectile impact has been investigated experimentally and numerically. FMLs with various layup angles are made of glass fiber prepreg and aluminum alloy with identical thickness among each type of layers. The active failure modes of FMLs, including the global deformation and local denting with cracks of the metals, fiber fracture, delamination and interlayer debonding are observed in the experiments. It is shown that the damage degree and deflections of FMLs decrease with increase of the thickness. FMLs of the oblique angle layups have similar deformation and failure modes as the orthogonal layups. Finite element (FE) simulations are performed and are in good agreement with the experimental results. Most kinetic energy of the metal foam projectiles is dissipated by the deformations of the metal layers, the deformations and fracture of the composite layers, debonding and foam compression. The impact resistance of FMLs can be enhanced by increasing the interlayer bonding strength.

Soft impact behavior of composite I-beams

As the increasing requirement of high-strength and lightweight structure in engineering applications, thin-wall I-section beams made of composite materials have drawn much attention in recent years. This paper made an effort to reveal the dynamic behavior of composite I-beams under soft impact. I-beam specimens were manufactured through resin transfer molding and then struck by aluminum foam projectiles. Numerical models were subsequently built up and verified through comparison of deflection and failure types with test results. After modification of the models with more reasonable construction method, parametric study was carried out and structure with the optimal dimensions was chosen. The I-beam was further optimized through adding polyurethane foam in the web. It was proved that the introduction of foam core with proper thickness will prevent buckling of the web and reduce the damage occurred during soft impacts.

Dynamic response of Nomex honeycomb sandwich panels subjected to aluminum foam projectile impact–An experimental study

AbstractThe impact resistance of the Nomex honeycomb sandwich structure subjected to strong dynamic loading of lightweight and deformable projectiles was studied experimentally. The deformation process and failure modes of the sandwich panels were investigated by using a first‐state gas gun to launch aluminum foam projectiles. 3D‐DIC was presented to investigate the dynamic response in terms of response rate and deflection‐profile history. And the impact resistance of three structures, namely single‐layer sandwich, rubber‐honeycomb sandwich and double‐layer sandwich, was compared in relation to the load intensity. The results show that the dynamic response process of the sandwich panel can be divided into discrete deformation stage, concentrated deformation stage，elastic stage, vibration stage and stabilization stage. As the impulse increases, the maximum deflection of the back face‐sheet continues to increase. Under the strong load of a light and deformable projectile, both rubber‐honeycomb and double‐layer honeycomb sandwich structures can effectively reduce the deflection change of the back face‐sheet and improve the load‐bearing capacity of the structure. Qualitatively analyzing the relationship between structure, loading, and performance can be carried out to provide guidance for structural design.

Experimental investigation into the response of GFRP S-shaped foldcore sandwich panels to impulsive loading

S-shaped foldcore sandwich structures have potential applications as protection structures under impact loading. In this paper, the S-shaped glass fiber composite foldcore sandwich structure was fabricated by hot pressing method and its impact resistance against the aluminum foam projectiles was studied using a one-stage gas gun.The three-dimensional digital image correlation system was used to measure the dynamic deformation of the sandwich panels. During the experiments, the dynamic response of the structure was studied when the projectile impacted the node and base locations of the sandwich structure, where the node location refers to the top platform of the core and the base location refers to the middle position between the nodes. In addition, the influence of the face sheet thickness and core thickness on the impact resistance of the sandwich structure was also investigated. The results show that the sandwich structure is dominated by tensile fracture of the face sheet, crush fracture or extrusion fracture of the core, and debonding failure between the face sheet and the core. The impact resistance of the node location is better than that of the base location for the same configuration. Moreover, the maximum deflection of the rear sheet increases linearly with the increase of the impact loading when impacting the base location. And increasing the face sheet thickness or core thickness can better reduce the structure deflection and improve the impact resistance of the structure.

Introducing students to neural communication: an embodied-learning classroom demonstration

Learning about neural communication can be a dry and challenging undertaking, particularly for students without a background in biology. To enhance learning of this and other STEM material, there has been a call for science educators to embrace the use of active learning techniques. The aim of this Brief Communication is to encourage the use of embodied metaphors in the university classroom by sharing an active learning method for introducing students to a number of key concepts in neural communication. The students work in pairs or small groups, using foam projectiles such as Nerf guns to work through several metaphors for electrical and chemical processes including action potentials, neurotransmission and receptor action, excitatory and inhibitory post-synaptic potentials and neurotransmitter inactivation. The activities are easy to stage and lend themselves well to customisation based on available class size, classroom space, and resources. Student feedback showed that the activities improved self-reported impressions of understanding and ability to convey key concepts to others. The activities thus can serve as a useful method of student engagement and help develop understanding of complex material in a neuroscience classroom.

Effects of sand filling on the dynamic response of corrugated core sandwich beams under foam projectile impact

How sand filling affects the dynamic response of metallic corrugated sandwich beams under shock loading was characterized, both experimentally and numerically, with shock loading simulated by high-speed impact of aluminum foam projectiles at beam mid-span. To facilitate evaluating the effects of sand filling, both empty and sand-filled corrugated core sandwich beams were assessed and compared for shock resistance. Representative deformation processes, deformation and failure modes, and beam deflections were experimentally obtained and analyzed. Sand-filled sandwich beams exhibited much higher shock resistance than the empty ones. Numerical simulations were subsequently conducted using a coupled discrete particle/finite element approach that takes into account the coupling interaction between the sand grains and corrugation members. The simulations predicted reasonably well the primary features (permanent mid-span deflections and deformation modes) of both the empty and sand-filled sandwich beams observed experimentally. The validated numerical model was employed to evaluate how the properties of the filling sand and other granular filling materials, e.g., density, stiffness, friction and damping, affect the shock resistance of sandwich beams. The results indicated that the shock resistance was sensitive to, firstly, the density and stiffness of sand and, secondly, the friction between sand particles. In contrast, the damping between sand particles had little effect.

Ocular Trauma From Toy Guns With Foam Projectiles in 4 Children

Ocular Trauma From Toy Guns With Foam Projectiles in 4 Children

Shock loading simulation using density-graded metallic foam projectiles

Density-graded metallic foam projectiles are proposed for shock loading simulation, with special focus placed upon designing pressure pulses having specific shapes. Experiments are performed to explore the potential of density-graded foam projectiles in generating shock loadings of various pulse shapes. Subsequently, three-dimensional Voronoi foam models with varying gradient profiles along the length direction are constructed for finite element (FE) simulations, which are validated against the experimental data. Then, FE simulations of density-graded foam projectiles impacting a stationary rigid wall are conducted to quantify the effect of density gradient on the shape of the pressure pulse generated and explore the physical mechanisms underlying such effect. It is demonstrated that density gradient affects significantly local crushing stress and local density within the shock front when it propagates from the impact end to the other end of the foam projectile. Inspired by the FE simulation results and the classical Taylor impact model, one-dimensional theoretical model for density-graded foam projectiles is developed to predict the contact force between the projectile and the fixed rigid wall. Finally, the theoretical model is employed to determine the geometry, density gradient, and firing velocity of foam projectiles needed to generate shock loadings with prescribed pulse shapes.

The response of clamped sandwich panels with layered-gradient aluminum foam cores to foam projectile impact

ABSTRACTThe dynamic response of clamped square sandwich panels with layered-gradient closed-cell aluminum foam cores under the impact of metallic foam projectiles is investigated. The present solutions are compared to those results of monolithic solid plates and non-graded monolithic core sandwich panels. The resistance performance of specimens to projectile impact is estimated by the maximum transient central-point deflection of back face-sheet. Results indicate that all the sandwich panels have a better shock resistance performance than the monolithic solid plate with the equivalent mass, and the resistance of sandwich panels to shock loading could be improved by utilizing the layered-gradient cores. The sandwich configuration is demonstrated to be able to effectively contribute to energy absorption and material efficiency, and the positive gradient-core configuration is the best choice in term of specific energy absorption. The strain-rate effect of face-sheet and core materials can mitigate the deformation of the back face-sheet of specimens due to its hardening effect.

The Response of Clamped Shallow Sandwich Arches with Metallic Foam Cores to Projectile Impact Loading

THE DYNAMIC RESPONSE AND ENERGY ABSORPTION CAPABILITIES OF CLAMPED SHALLOW SANDWICH ARCHES WITH ALUMINUM FOAM CORE WERE NUMERICALLY INVESTIGATED BY IMPACTING THE ARCHES AT MID-SPAN WITH METALLIC FOAM PROJECTILES. THE TYPICAL DEFORMATION MODES, DEFLECTION RESPONSE, AND CORE COMPRESSION OF SANDWICH ARCHES OBTAINED FROM THE TESTS WERE USED TO VALIDATE THE COMPUTATION MODEL. THE RESISTANCE TO IMPACT LOADING WAS QUANTIFIED BY THE PERMANENT TRANSVERSE DEFLECTION AT MID-SPAN OF THE ARCHES AS A FUNCTION OF PROJECTILE MOMENTUM. THE SANDWICH ARCHES HAVE A HIGHER SHOCK RESISTANCE THAN THE MONOLITHIC ARCHES OF EQUAL MASS, AND SHOCK RESISTANCE COULD BE SIGNIFICANTLY ENHANCED BY OPTIMIZING GEOMETRICAL CONFIGURATIONS. MEANWHILE, DECREASING THE FACE-SHEET THICKNESS AND CURVATURE RADIUS COULD ENHANCE THE ENERGY ABSORPTION CAPABILITY OF THE SANDWICH ARCHES. FINITE ELEMENT CALCULATIONS INDICATED THAT THE RATIO OF LOADING TIME TO STRUCTURAL RESPONSE TIME RANGED FROM 0.1 TO 0.4. THE PROJECTILE MOMENTUM, WHICH WAS SOLELY USED TO QUANTIFY THE STRUCTURAL RESPONSE OF SANDWICH ARCHES, WAS INSUFFICIENT. THESE FINDINGS COULD PROVIDE GUIDANCE IN CONDUCTING FURTHER THEORETICAL STUDIES AND PRODUCING THE OPTIMAL DESIGN OF METALLIC SANDWICH STRUCTURES SUBJECTED TO IMPACT LOADING.

Dynamic Response of Orthogonal Three-Dimensional Woven Carbon Composite Beams Under Soft Impact

This paper presents an experimental and numerical investigation into the dynamic response of three-dimensional (3D) orthogonal woven carbon composites undergoing soft impact. Composite beams of two different fiber architectures, varying only by the density of through-thickness reinforcement, were centrally impacted by metallic foam projectiles. Using high-speed photography, the center-point back-face deflection was measured as a function of projectile impulse. Qualitative comparisons are made with a similar unidirectional (UD) laminate material. No visible delamination occurred in orthogonal 3D woven samples, and beam failure was caused by tensile fiber fracture at the gripped ends. This contrasts with UD carbon-fiber laminates, which exhibit a combination of widespread delamination and tensile fracture. Post impact clamped–clamped beam bending tests were undertaken across the range of impact velocities tested to investigate any internal damage within the material. Increasing impact velocity caused a reduction of beam stiffness: this phenomenon was more pronounced in composites with a higher density of through-thickness reinforcement. A three-dimensional finite-element modeling strategy is presented and validated, showing excellent agreement with the experiment in terms of back-face deflection and damage mechanisms. The numerical analyses confirm negligible influence from through-thickness reinforcement in regard to back-face deflection, but show significant reductions in delamination damage propagation. Finite-element modeling was used to demonstrate the significant structural enhancements provided by the through-the-thickness (TTT) weave. The contributions to the field made by this research include the characterization of 3D woven composite materials under high-speed soft impact, and the demonstration of how established finite-element modeling methodologies can be applied to the simulation of orthogonal woven textile composite materials undergoing soft-impact loading.

Shear-dominated plastic behavior of a cross-ply Dyneema® composite

Dyneema® composites derive some of their performance attributes from their elastic and plastic anisotropy. The principal objective of the present study is to develop a finite element framework for predicting the large-strain deformation response of these composites in a [0°/90°] configuration. We employ a binary model comprising a series of line elements to represent the axial fiber properties and a 3D effective medium to represent all off-axis properties. The model is assessed through comparisons with the results of two types of tests: (i) quasi-static punch tests and (ii) dynamic tests performed by firing (crushable) foam projectiles at high velocities. The measured load–displacement response in the punch tests and the evolution of the back-face deflection in the dynamic tests as well as the final shapes of the test specimens are represented well by the numerical simulations. Discrepancies occur only at the highest levels of displacements, wherein material damage becomes a significant factor.

Response of aluminium honeycomb sandwich panels subjected to foam projectile impact – An experimental study

Aluminium honeycomb sandwich panels have potential applications as a protective mechanism that can be used to prevent failure of an important structure subjected to impact loading. Therefore it is important to fully understand the resistance of the sandwich panels subjected to impact loading conditions. The main objective of this work was to study the resistance of sandwich panels with different aluminium honeycomb cores, air sandwich panels (no core between the two face sheets) and monolithic plates of equivalent mass subjected to impact from foam projectiles. The deformation and the elastic spring-back of the honeycomb sandwich panels and the monolithic plates have been compared and discussed. The resistance of the panels and plates has been quantified by their back-face deflection with respect to the projectile impulse. Five different types of aluminium honeycombs have been used as the core material. The front-face sheet and the back-face sheet of the honeycomb sandwich panels are made of aluminium plate with 1 mm thickness. Cylindrical ALPORAS aluminium foams with a relative density between 9% and 11% are employed as the metal foam projectiles. They are fired at several hundred metres per second towards the centre of the panels and plates using a gas gun. The deflection histories of the back-face have been measured using a laser displacement sensor. From the deflection histories, the maximum deflection and the final deflection of the back-face can be distinguished. Deformation modes and failure modes of the individual component have been observed and classified into several categories. Moreover, the deflections of the honeycomb sandwich panels have been compared with deflections from air sandwich panels. It is found that the honeycomb sandwich panels outperform both the air sandwich panels and the monolithic plates within an impulse range of 2.25 kNsm−2 ～ 4.70 kNsm−2. Outside this operational range, the advantages associated with employing the honeycomb sandwich panels as a protective structure upon impact of foam projectiles diminishes.

Selection of Densification Strain to Predict Dynamic Crushing Stress at High Impact Velocity of ALPORAS Aluminium Foam

Cellular material such as aluminium foam has been considered as a potential material for energy absorption upon impact and blast loadings. One of the most important properties that contribute to this feature is the densification strain. At high impact velocity, prediction of the densification strain from quasi-static engineering stress-strain curve has been found inadequate. Furthermore, theoretical prediction using the equation proposed by Reid et al. always over-predicts the dynamic crushing stress. Formation of the shock wave at high impact velocity is believed to further increase the densification level of the foam. However, this effect is disregarded when determining the densification strain quasi-statically. The present study aims to address this issue by determining the densification strain experimentally from impact tests. Forty cylindrical aluminium foams with three different lengths were used as projectiles and were fired towards a rigid load cell by using a gas gun. The peak forces generated from the impact were recorded and analysed. The experimental densification strains were determined physically by measuring the deformation of the foam projectiles after the tests. It is concluded that, at high impact velocity, the densification strain varies with the initial impact velocity. Therefore an appropriate value of densification strain needs to be used in the equation of dynamic crushing stress for a better approximation.

Response of clamped sandwich beams subjected to high-velocity impact by sand slugs

The dynamic response of end-clamped sandwich and monolithic beams of equal areal mass subjected to loading via high-velocity slugs of dry and water-saturated sand is measured using a novel laboratory-based method. The sandwich beams comprise aluminium face sheets and an aluminium honeycomb core: the effect of sandwich core strength and beam thickness on the dynamic beam deflection is investigated by varying the orientation and height of the anisotropic aluminium honeycomb core material. High-speed imaging is used to measure the transient transverse deflection of the beams and to record the dynamic modes of deformation. The measurements show that sandwich beams with thick, strong cores are optimal and that these beams significantly outperform monolithic beams of equal mass. The water-saturated sand slugs cause significantly higher deflections compared to the dry sand slugs having the same mean slug velocity and we demonstrate that this enhanced deflection is due to the larger mass of the water-saturated slugs. Finally, we show that the impact of sand slugs is equivalent to the impact of a crushable foam projectile. The experiments using foam projectiles are significantly simpler to perform and thus represent a more convenient laboratory technique.