Shock-Induced Microstructural Evolution, Phase Transformation, Sintering of Al-Ni Dissimilar Nanoparticles: A Molecular Dynamics Study.

Molecular dynamic simulations have been performed to explore contact behavior, microstructure evolution and sintering mechanism of Al-Ni dissimilar nanoparticles under high-velocity impact. We confirmed that the simulated contact stress, contact radius, and contact force under low-velocity impact are in good agreement with the predicted results of the Hertz model. However, with increasing the impact velocity, the simulated results gradually deviate from the predicted results of the Hertz model due to the elastic-plastic transition and atomic discrete structure. The normalized contact radius versus strain exhibits a weak dependence on nanosphere diameter. Below a critical velocity, there are very few HCP atoms in the nanospheres after thermal equilibrium. There are two different sintering mechanisms: under low-velocity impact, the sintering process relies mainly on the dislocation slip of Al nanospheres, while the dislocation slip of Ni nanospheres and the atomic diffusion of Al nanospheres predominate under high-velocity impact.

Dynamics of rebounding Bacillus subtilis spores determined using image-charge detection.

A novel image-charge detection technique was used to investigate the mechanical elasticity of bare bacterial spores during high-velocity impact. Spores of Bacillus subtilis introduced to vacuum using electrospray and aerodynamic acceleration impacted and rebounded off of a glass plate. A dual-stage, asymmetric image-charge detector measured the velocity and direction of each spore both before and after impact with the glass surface. Two ranges of impact velocity were investigated, with average initial velocities of 197 ± 17 and 145 ± 12 m/s. Impacts were strongly inelastic, with most of the translational kinetic energy lost upon impact, similar to polystyrene particles of similar size under similar impact velocities. Specifically, 69% (± 16%) and 74% (± 11%) of initial kinetic energy was lost in impacts at the two velocity ranges, respectively. The average coefficients of restitution for the two velocity regimes were 0.53 ± 0.15 and 0.49 ± 0.12. There was no statistically significant difference in the fractional kinetic energy loss between these two populations. The variance of these results is much larger than experiments using polystyrene spheres of comparable size. These results imply significant plastic deformation of the spore-a striking result given that spores of this strain of B. subtilis are known to survive impacts on glass at these velocities. Triboelectric charge transfer during impact was also observed. Although much is known about spore elasticity from static measurements, this is the first study to investigate the elastic properties of bacterial spores in a dynamic scenario, as well as the first demonstration of an image charge detector for measurements of rebounding particles.

Comparative Performance of Kevlar, Glass and Basalt Epoxy- and Elium-Based Composites under Static-, Low- and High-Velocity Loading Scenarios-Introduction to an Effective Recyclable and Eco-Friendly Composite.

In general, the majority of fiber-reinforced polymer composites (FRPs) used in structural applications comprise carbon, glass, and aramid fibers reinforced with epoxy resin, with the occasional utilization of polyester and vinyl ester resins. This study aims to assess the feasibility of utilizing recyclable and sustainable materials to create a resilient composite suitable for structural applications, particularly in scenarios involving low-velocity and high-velocity impact (LVI, HVI) loading. The paper presents a comparative analysis of the performance of E-glass, aramid, and eco-friendly basalt-reinforcing fabrics as reinforcement fibers in both thermosetting (epoxy) and recyclable thermoplastic (Elium©) resins. Given the limited research on Elium composites, especially those incorporating basalt-reinforcing fiber, there is an urgent need to expand the databases of fundamental mechanical properties for these diverse composites. This necessity is exacerbated by the scarcity of the literature regarding their performance under low- and high-velocity impact loadings. The results of this study will demonstrate the potential of basalt-reinforced Elium composite as an effective recyclable and environmentally friendly structural material system for both static and dynamic loading conditions.

Characterization of Low- and High-Velocity Responses of Basalt-Epoxy and Basalt-Elium Composites.

Currently, fiber-reinforced polymer composites (FRPs) used for demanding structural applications predominantly utilize carbon, glass, and aramid fibers embedded in epoxy resin, albeit occasionally polyester and vinyl ester resins are also used. This study investigates the feasibility of employing recyclable and sustainable materials to formulate a composite suitable for load-bearing structural applications, particularly in scenarios involving low-velocity and high-velocity impacts (LVIs and HVIs, respectively). The paper presents a comparative analysis of the performance of basalt-Elium, a fully recyclable, sustainable, and environmentally friendly composite, with an epoxy-based counterpart. Moreover, an accurate and reliable numerical model has been developed and introduced through which the response of these composites can be examined efficiently and accurately under various loading states. The results of this investigation demonstrate the viability of the basalt-elium composite as a fully recyclable and sustainable material for crafting efficient and lightweight composites. Additionally, the accurately developed finite element model presented here can be used to assess the influence of several parameters on the composite, thereby optimizing it for a given situation.

On exploiting nonparametric kernel-based probabilistic machine learning over the large compositional space of high entropy alloys for optimal nanoscale ballistics.

The large compositional space of high entropy alloys (HEA) often presents significant challenges in comprehensively deducing the critical influence of atomic composition on their mechanical responses. We propose an efficient nonparametric kernel-based probabilistic computational mapping to obtain the optimal composition of HEAs under ballistic conditions by exploiting the emerging capabilities of machine learning (ML) coupled with molecular-level simulations. Compared to conventional ML models, the present Gaussian approach is a Bayesian paradigm that can have several advantages, including small training datasets concerning computationally intensive simulations and the ability to provide uncertainty measurements of molecular dynamics simulations therein. The data-driven analysis reveals that a lower concentration of Ni with a higher concentration of Al leads to higher dissipation of kinetic energy and lower residual velocity, but with higher penetration depth of the projectile. To deal with such conflicting computationally intensive functional objectives, the ML-based simulation framework is further extended in conjunction with multi-objective genetic algorithm for identifying the critical elemental compositions to enhance kinetic energy dissipation with minimal penetration depth and residual velocity of the projectile simultaneously. The computational framework proposed here is generic in nature, and it can be extended to other HEAs with a range of non-aligned multi-physical property demands.

Study on High-Velocity Impact Perforation Performance of CFRP Laminates for Rail Vehicles: Experiment and Simulation.

To study the perforation performance of CFRP laminates for rail vehicles under high-velocity impact from foreign objects, impact tests on CFRP laminates at a velocity of 163 m/s were carried out, and a corresponding finite element model was established using ABAQUS and verified. The user-defined material subroutine combined the material strain rate hardening effect and the 3D-Hashin damage criterion. The effects of impact velocity, impact object shape, and oblique angle on the perforation performance of CFRP laminates are discussed. Results show that impact velocity positively correlates with impact peak force and residual velocity. Laminates can be perforated by projectiles with a velocity above 120 m/s, and impact velocity greatly influences delamination below 140 m/s. Three shapes of projectile impacting laminates are considered: spherical, cylindrical, and conical. The conical projectile penetrates the laminate most easily, with the largest delamination area. The cylindrical projectile with a flat end suffers the most resistance, and the delaminated area is between the impact conditions of the conical and spherical projectiles. Increasing the angle of inclination increases the impacted area of the laminate and the extent of damage, thus dissipating more energy. The projectile fails to penetrate the laminate when the oblique angle reaches 60°. CFRP composite structures penetrated by high-speed impacts pose a significant threat to the safety of train operations, providing an opportunity for the application of bio-inspired composite structures.

Experimental and Numerical Study on the Perforation Behavior of an Aluminum 6061-T6 Cylindrical Shell.

The modified Johnson-Cook (MJC) material model is widely used in simulation under high-velocity impact. There was a need to estimate a strain rate parameter for the application to the impact analysis, where the method typically used is the Split Hopkinson bar. However, this method had a limit to the experiment of strain rate. This study proposed to estimate the strain rate parameter of the MJC model based on the impact energy and obtained a parameter. The proposed method of strain rate parameter calculation uses strain parameters to estimate from the drop weight impact and high-velocity impact experiments. Then, the ballistic experiment and analysis were carried out with the target of the plate and cylindrical shape. These analysis results were then compared with those obtained from the experiment. The penetration velocities of plates could be predicted with an error of a maximum of approximately 3.7%. The penetration shape of the cylindrical target has a similar result shape according to impact velocity and had an error of approximately 6%.

Microparticle Impact Testing at High Precision, Higher Temperatures, and with Lithographically Patterned Projectiles.

In the first decade of high-velocity microparticle impact research, hardly any modification of the original experimental setup has been necessary. However, future avenues for the field require advancements of the experimental method to expand both the impact variables that can be quantitatively assessed and the materials and phenomena that can be studied. This work explores new design concepts for the launch pad (the assembly that launches microparticles upon laser ablation) that can address the root causes of many experimental challenges that may limit the technique in the future. Among the design changes contemplated, the substitution of a stiff glass launch layer for the standard elastomeric polymer layer offers a number of improvements. First, it facilitates a reduction of the gap between launch pad and target from hundreds to tens of micrometers and thus unlocks a reproducibility in targeting a specific impact location better than the diameter of the test particle itself (±1.75 µm for SiO2 particles 7.38 µm in diameter). Second, the inert glass surface enables experiments at higher temperatures than previously possible. Finally-as demonstrated by the launch of thin-film Au disks-a launch pad made of materials standard in microfabrication paves the way to facile microfabrication of advanced impactors.

Structure of Shock Wave in Nanoscale Porous Nickel at Pressures up to 7 GPa.

The structure of shock waves in pressed porous samples of nickel nanoparticles was investigated in a series of uniaxial planar plate impact experiments in the pressure range of 1.6-7.1 GPa. The initial porosity of the samples was about 50%. Wave profiles were obtained using laser velocimetry techniques. The nanomaterial demonstrated a complex response to shock loading including the development of a two-wave structure associated with precursor and compaction waves. The effect on profiles and measurements of the observed precursor reverberations propagating between the front of a compaction wave and a monitored sample surface was described. The obtained wave profiles were used to estimate the thicknesses of precursor and compaction wave fronts.

High-Velocity Impacts of Pyrophoric Alloy Fragments on Thin Armour Steel Plates.

The terminal ballistics effects of Intermetallic Reactive Materials (IRM) fragments have been the object of intense research in recent years. IRM fragments flying at velocities up to 2000 m/s represent a realistic threat in modern warfare scenarios as these materials are substituting conventional solutions in defense applications. The IRM add Impact Induced Energy Release (IIER) to the mechanical interaction with a target. Therefore, the necessity of investigations on IIER to quantify potential threats to existing protection systems. In this study, Mixed Rare Earths (MRE) fragments were used due to the mechanical and pyrophoric affinity with IRM, the commercial availability and cost-effectiveness. High-Velocity Impacts (HVI) of MRE were performed at velocities ranging from 800 to 1600 m/s and recorded using a high-speed camera. 70 MREs cylindrical fragments and 24 steel fragments were shot on armour steel plates with thicknesses ranging from 2 mm to 3 mm. The influence of the impact pitch angle (α) on HVI outcomes was assessed, defining a threshold value at α of 20°. The influence of the failure modes of MRE and steel fragments on the critical impact velocities (CIV) and critical kinetic energy (Ekin crit) was evaluated. An energy-based model was developed and fitted with sufficient accuracy the Normalised EKin crit (E˜kincrit) determined from the experiments. IIER was observed in all the experiments involving MRE. From the analyses, it was observed that the IIER spreads behind the targets with velocities comparable to the residual velocities of plugs and shattered fragment.

Investigation of the Ballistic Performance of GFRP Laminate under 150 m/s High-Velocity Impact: Simulation and Experiment.

The ballistic resistance of GFRP laminates subjected to high-velocity impact was studied. Based on the damage situation of GFRP laminate observed from the single-stage gas gun testing, the three-dimensional (3D) model combining strain rate effect and Hashin failure criterion was established, and the result presented good agreement between the simulation and experiment. Three factors, including layer angle, stacking sequence and proportion of different layer angles, were taken into consideration in the models. An orthogonal test method was used for the analysis, which can reduce the number of simulations effectively without sacrificing the accuracy of the result. The result indicated a correlation between the ballistic resistance and layouts of GFRP laminates, on which the stacking sequence contributed stronger influence. What was more, the laminate with layer angles 0°/90° and ±45° presented greater ballistic resistance than the other angle pairs, and adopting an equal proportion of different layer angles is helpful for GFRP laminates to resist impact as well.

The Influence of Temperature in the Al 2024-T3 Aluminum Plates Subjected to Impact: Experimental and Numerical Approaches.

In this paper, perforation experiments were carried out and numerically modelled in order to analyze the response of 2024-T3 aluminum alloy plates under different initial temperatures T0. This alloy has a particular relevance since it is widely used as a structural component in aircrafts, but it is also interesting for other sectors of industry. A gas gun projectile launcher was used to perform impacts within initial velocities V0 from 40 m/s to 120 m/s and at temperatures varying from 293 K to 573 K. A temperature softening of the material was observed which was manifested in the reduction in the ballistic limit by 10% within the temperature range studied. Changes in the material failure mode were also observed at different test conditions. Additionally, a finite element model was developed to predict the material response at high velocities and to confirm the temperature softening that was observed experimentally. An optimization of the failure criterion resulted in a reliable model for such mild aluminum alloys. The results reported here may be used for different applications in the automotive and military sectors.

Experimental and Numerical Investigation on the Perforation Resistance of Double-Layered Metal Shield under High-Velocity Impact of Armor-Piercing Projectiles.

In the case of protection of transportation systems, the optimization of the shield is of practical interest to reduce the weight of such components and thus increase the payload or reduce the fuel consumption. As far as metal shields are concerned, some investigations based on numerical simulations showed that a multi-layered configuration made of layers of different metals could be a promising solution to reduce the weight of the shield. However, only a few experimental studies on this subject are available. The aim of this study is therefore to discuss whether or not a monolithic shield can be substituted by a double-layered configuration manufactured from two different metals and if such a configuration can guarantee the same perforation resistance at a lower weight. In order to answer this question, the performance of a ballistic shield constituted of a layer of high-strength steel and a layer of an aluminum alloy impacted by an armor piercing projectile was investigated in experimental tests. Furthermore, an axisymmetric finite element model was developed. The effect of the strain rate hardening parameter C and the thermal softening parameter m of the Johnson-Cook constitutive model was investigated. The numerical model was used to understand the perforation process and the energy dissipation mechanism inside the target. It was found that if the high-strength steel plate is used as a front layer, the specific ballistic energy increases by 54% with respect to the monolithic high-strength steel plate. On the other hand, the specific ballistic energy decreases if the aluminum plate is used as the front layer.

Influence of Interfacial Bonding on the Mechanical and Impact Properties Ring-Opening Metathesis Polymer (ROMP) Silica Composites.

Polymers formed by ring-opening metathesis polymerization (ROMP) such as poly(dicyclopentadiene) (pDCPD) exhibit a technologically desirable combination of high toughness, high glass transition temperature, and outstanding low-temperature performance. However, because of their nonpolar molecular structure, they tend to suffer from relatively low elastic moduli and poor adhesion to common fillers, fibers, and substrates, limiting their utility as adhesives and composite binders without specialized bonding agents. Here, we investigate the mechanical properties of a pDCPD-based copolymer filled with well-defined spherical microparticles having four distinct surface chemistries capable of strong, moderate, or weak bonding to the matrix with surfaces ranging from polar to nonpolar. Measurements in uniaxial tension, quasi-static fracture, and high-velocity impact are complemented by digital image correlation (DIC), scanning electron microscopy (SEM) fractography, and X-ray computed tomography (X-µCT) of subcritically loaded crack tips, yielding insight into the complex roles played by interfacial bonding in strength, stiffness, and toughening mechanisms of an already tough polymer. Analysis using quantitative fracture and impact mechanism models provided valuable guidelines for designing heterogeneous systems that combine structural and tough performance.

Warm spraying-a novel coating process based on high-velocity impact of solid particles.

In recent years, coating processes based on the impact of high-velocity solid particles such as cold spraying and aerosol deposition have been developed and attracting much industrial attention. A novel coating process called 'warm spraying' has been developed, in which coatings are formed by the high-velocity impact of solid powder particles heated to appropriate temperatures below the melting point of the powder material. The advantages of such process are as follows: (1) the critical velocity needed to form a coating can be significantly lowered by heating, (2) the degradation of feedstock powder such as oxidation can be significantly controlled compared with conventional thermal spraying where powder is molten, and (3) various coating structures can be realized from porous to dense ones by controlling the temperature and velocity of the particles. The principles and characteristics of this new process are discussed in light of other existing spray processes such as high-velocity oxy-fuel spraying and cold spraying. The gas dynamics of particle heating and acceleration by the spraying apparatus as well as the high-velocity impact phenomena of powder particles are discussed in detail. Several examples of depositing heat sensitive materials such as titanium, metallic glass, WC-Co cermet and polymers are described with potential industrial applications.

High-velocity micro-particle impact on gelatin and synthetic hydrogel.

The high-velocity impact response of gelatin and synthetic hydrogel samples is investigated using a laser-based microballistic platform for launching and imaging supersonic micro-particles. The micro-particles are monitored during impact and penetration into the gels using a high-speed multi-frame camera that can record up to 16 images with nanosecond time resolution. The trajectories are compared with a Poncelet model for particle penetration, demonstrating good agreement between experiments and the model for impact in gelatin. The model is further validated on a synthetic hydrogel and the applicability of the results is discussed. We find the strength resistance parameter in the Poncelet model to be two orders of magnitude higher than in macroscopic experiments at comparable impact velocities. The results open prospects for testing high-rate behavior of soft materials on the microscale and for guiding the design of drug delivery methods using accelerated microparticles.

A Stress-Induced Martensitic Transformation in Aged Ti49Ni51 Alloy after High-Velocity Impact.

The effects of a high-velocity impact on the microstructure, phase transformation and mechanical property of aged Ti49Ni51 alloy are investigated. The transformation behavior and microstructure along the impact direction after impact emerge with regionalization characteristics, including a deformed region near the crater (0-4 mm) and an un-deformed region of the distal crater (5-6 mm). Stress-induced martensite is the main deformation mechanism in the deforming region of aged Ti49Ni51 alloy under high-velocity impact.

Scanning electron microscope analysis of gunshot defects to bone: an underutilized source of information on ballistic trauma.

Recent years have seen increasing involvement by forensic anthropologists in the interpretation of skeletal trauma. With regard to ballistic injuries, there is now a large literature detailing gross features of such trauma; however, less attention has been given to microscopic characteristics. This article presents analysis of experimentally induced gunshot trauma in animal bone (Bos taurus scapulae) using full metal jacket (FMJ), soft point (SP), and captive bolt projectiles. The results were examined using scanning electron microscopy (SEM). Additional analysis was conducted on a purported parietal gunshot lesion in a human cranial specimen. A range of features was observed in these samples suggesting that fibrolamellar bone response to projectile impact is analogous to that observed in synthetic composite laminates. The results indicate that direction of bullet travel can be discerned microscopically even when it is ambiguous on gross examination. It was also possible to distinguish SP from FMJ lesions. SEM analysis is therefore recommended as a previously underexploited tool in the analysis of ballistic trauma.