High Velocity Impact Research Articles

Modelling dynamic breakage in rock blocks with different elongation and flatness ratios upon impact

AbstractThe two crucial shape factors (elongation ratio and flatness ratio) of brittle particles may influence the dynamic breakage of brittle particles upon impact. Hence, three‐dimensional discrete element method simulations of brittle rock blocks with different shapes upon normal impact were performed. The simulated results indicate that the elongation ratio, that is, ratio of width to length and flatness ratio, that is, ratio of thickness to width can significantly affect the breakage of brittle rock blocks. Three fracture mechanisms, that is, fragmentation, horizontal tensile fracture and vertical tensile fracture, were revealed, which determine the dynamic breakage of rock blocks. The fragmentation results in numerous single‐sphered fragments with velocities even larger than 2 times of the initial velocities. Fragmentation can provide a buffering effect at high impact velocities of larger than 4 m/s. With an increasing elongation ratio or flatness ratio, the phenomenon of fragmentation gradually disappears. The reflection of a compression stress wave results in horizontal tensile fracture. The expansion in the plane perpendicular to the impact velocity results in vertical tensile fracture.

Machine learning accelerated search for the impact limit of the graphene/aluminum alloy whipple structure

This paper proposes a Whipple structure to enhance the impact resistance of graphene/aluminum alloy composites by varying the interlayer spacing between graphene and aluminum alloy. The increased interlayer spacing provides more deformation space for the graphene to absorb more deformation energy, and enables the formation of a debris cloud from the bullet fragments and graphene fragments, significantly reducing the impact energy per unit area of the next material. The impact limit serves as a critical metric for assessing the impact resistance of the Whipple structure. Based on molecular dynamics simulations, we developed a machine learning model to predict the protection of aluminum alloy, and quickly determined the impact limits of velocity, bullet radius, and interlayer spacing by using the machine learning model. An empirical equation for the impact limit of interlayer spacing was established. The results showed that non-zero interlayer spacing can significantly improve the impact resistance of the hybrid structure; to fully exploit the superior impact resistance of this Whipple structure, the number of graphene layers should be at least 3. Furthermore, at high impact velocities and large bullet radii, the impact limit of the interlayer spacing exhibits a substantial correlation with the number of graphene layers. These results provide valuable information for the design of the impact resistance of the graphene/aluminum alloy composites.

Effect of stitch density on the damage inhibition and compression strength after high-velocity impact of UHMWPE fiber composites

This paper investigates the effect of stitch density on the high-velocity impact damage inhibition and CAI (compression after impact) strength of UHMWPE (Ultra-High Molecular Weight Polyethylene) fiber composites. The damage response and compression behavior after impact were quantified and analyzed using CT scanning and DIC (Digital Image Correlation) techniques. The findings reveal that the delamination area of the composite plate with the stitch space of 1 cm reduces by 49.14 % compared to the unstitched sample, and exhibits a 73.05 % higher compressive load than the plate with a 4 cm stitch space. Notably, the 4 cm stitch composite plates demonstrate a significant advantage in energy absorption. However, the sparse stitch structure destroys the original structure inside the composite, resulting in a degradation of CAI performance. The study provides guidance for the practical design of composite materials with enhanced energy absorption and damage resistance.

Estimation of Impact Strength of Kevlar/Basalt and Kevlar/Glass Interwoven Composite Laminate after High-Velocity Bullet Impact

The application of composite materials has increased so drastically in the aerospace industry. The Impact strength signifies the importance of composite materials when exposed to suddenly applied loads. This paper is focused on describing the behavior of interwoven kevlar/glass-epoxy and kevlar/basalt-epoxy composite laminate under high-velocity bullet impact. The composite lamina of kevlar/glass and that of kevlar/basalt are prepared using three different weaving techniques. The composite laminates are prepared using the compression moulding technique. The laminates have been subjected to high-velocity bullet impact. The velocity range is from 220 m/s to 260 m/s. The impact damage area in the laminate has been assessed through ultrasonic pulse echo submerged nondestructive technique. The impact strength has been calculated using the damaged area derived using the impact energy absorbed by the laminate. The results have shown that the maximum impact which found out to be kevlar/basalt (KB 1 × 1) is 28.24 J/cm2.

High‐velocity impact behavior and quasi‐static indentation of new elastomeric nanocomposites reinforced with cellulose nanofibers and lignin powder

AbstractThe present study investigates the indentation resistance of elastomeric nanocomposites based on natural rubber with different amounts of cellulose nanofibers (CNFs) under quasi‐static indentation (QSI) and high‐velocity impact (HVI) tests. At first, the baking characteristics and hardness of the samples were checked. The results showed that with the increase in CNFs content, the hardness of the samples increases, and the optimal baking time decreases. A high‐quality final product is produced through good dispersion and acceptable physical bonding between the CNF filler and the rubber chain. Further, the results of quasi‐static indentation showed that the amount of energy absorption for optimal loading of 6 phr increased by 43% compared to a control sample (0 phr). Similarly, from the high‐speed impact results for optimal loading (6 phr), the ballistic limit and energy absorption values increased by 23.6 and 52.7%, respectively, compared to the control sample (0 phr). It was also observed for higher values (9,12 phr) that the glass transition temperature, Tg, effect significantly affected the fracture behavior of the samples due to the high‐speed impact. Finally, CNFs provide better bonding with polymer chains to improve properties through good interaction with natural rubber, making them suitable for energy absorption applications.Highlights New elastomeric nanocomposites reinforced with cellulose nanofibers were made. Increasing the amount of CNFs decreases the optimum curing temperature. The hardness of elastomeric nanocomposites is increased by cellulose nanofibers. The indentation properties of nanocomposites have increased significantly. The optimum value of 6‐phr increased the impact resistance of nanocomposites.

Experimental study on the damage characteristics of the stepped repaired fiber reinforced composites

Stepped repair, scarf patch repair, and patch repair are important in terms of repair techniques. The composite plate repair process starts after damage zone determination either by the unaided eye or nondestructive testing (NDT) techniques. This study investigates design cases for the stepped repairs of damaged fiber-reinforced composite materials. Before preparing steps for repair, the material around the damage zone is removed. In the stepped repair, it needs extra care to ensure that the repair plies overlap each other properly in the cut. Different cases are performed considering different step sizes. 5, 10, and 15 mm step sizes are used. The damages are given to the produced fiber-reinforced composite laminates using the Quasi-static indentation (QSI) method. Using QSI high-velocity impact simulation can be done. To get damage characteristics well-known damage test method is issued. Different span-to-punch diameter ratio (SPR) values were also used to compare different damage sizes. As a result, High ratio strength recovery was obtained using the longer step size. Maximum penetration force was reduced by nearly % 6-7 and maximum stress reduction was obtained by nearly % 8-9 for the 15 mm step size repaired composites. Among the all cases, case-1 has the highest strength recovery and case-5 has the lowest. For SPR 2, The average ultimate force value of specimens repaired with case-1 was maintained at nearly 94%. For SPR 4, repairs carried out using case-1 maintain more than 95% of damage resistance.

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%.

On strain rate effect and high-velocity impact behavior of carbon fiber reinforced laminated composites

In this paper, the tensile and in-plane shear behaviors of carbon fiber reinforced laminated composites (CFRLCs) under high strain rate loading were experimentally investigated. The strain and damage processes of the specimens were obtained using the Digital Image Correlation (DIC) method and a high-velocity camera. Quasi-static test results were used as the control group for obtaining the dynamic correction factors of the material system under high strain rate conditions. In addition, high-velocity impact (HVI) tests with different impact velocities and angles were conducted on CFRLCs. The dynamic correction factors were used in HVI simulations to consider the effect of strain rate. The energy absorption mechanisms and failure modes of laminates under different impact conditions were analyzed using testing and simulated results. It is found that during the HVI, matrix tension and fiber tension failures are the main failure modes. The energy absorbed by the laminate in oblique impact is larger than the one in normal impact. The possible reason is that the increase rate of the damage area with the four failure modes in oblique impact is larger than the one in normal impact.

High-Velocity Projectile Impact Behaviour of Friction Stir Welded AA7075 Thick Plates

High-Velocity Projectile Impact Behaviour of Friction Stir Welded AA7075 Thick Plates

The Behaviour of Thin-Walled Cylinders with Reinforcing Inner Walls Subjected to High-Velocity Impact

Thin cylindrical tubes as impact energy absorbers have been widely used in various fields. Previous researchers have proposed many methods to increase the ability to absorb energy by modifying the geometry or using different materials. This study discusses using reinforcing walls in the cylinder to increase energy absorption capability. We make thin cylindrical specimens made of aluminium alloy with a length of 150 mm, a diameter of 50 mm, and a thickness of 1 mm. Reinforcing walls are fitted in the cylinder with a vertical position of 1, 2, 3, and without supporting walls. An impactor moving at high velocity hits the up-end cylinder in the axial direction. The finite element method modelling results show that installing reinforcing walls in thin-walled cylinders increase the maximum impact force, decreases the maximum deformation, changes the deformation mode, and increases the energy absorption capability. The amount of wall added to the thin wall will affect the impact behaviour of the specimen. However, in this study, the presence of a wall will have an effect when the deformation reaches the location of the wall. Nevertheless, using this reinforcing wall also makes the manufacturing process more complex. Therefore, this study’s results are recommendations for the design of the impact energy absorption structural system.

Influence of the Gas Preheating Temperature on the Microstructure and Electrical Resistivity of Copper Thin Films Prepared via Vacuum Cold Spraying

Vacuum cold spraying (VCS) has emerged as an environmentally sustainable method for fabricating ceramic and metal films. A high particle impact velocity is a critical factor in the deposition of metal particles during the VCS process, which can be significantly enhanced through gas preheating. This study employs Computational Fluid Dynamics (CFD) simulations to investigate the substantial impact of gas preheating temperature on particle impact velocity and temperature. Elevating the gas temperature leads to higher particle impact velocity, resulting in severe deformation and the formation of dense copper films. The experimental results indicate improvements in both film compactness and electrical properties with gas preheating. Remarkably, the electrical resistivity of the copper film deposited at a gas preheating temperature of 350 °C was measured at 4.4 × 10−8 Ω·m. This study also examines the evolution of cone-shaped pits on the surface of copper films prepared on rough substrates. VCS demonstrates a self-adaptive repair mechanism when depositing metal films onto rough ceramic substrates, making it a promising method for ceramic surface metallization.

Numerical investigation on the high-velocity impact resistance of textile reinforced composite mesh designs inspired by spider web

The need for thin and highly deformable textile reinforcements is constant in sectors like thin composites, catching nets, and complex construction designs (like dome-shape). The conventional rectangular-patterned meshed wovens are used in thin composite structures as reinforcement at the commercial level. These woven textiles are bidirectional and exhibit approximately the same strength along both axes. However, these conventional rectangular-patterned mesh designs show poor impact stress distribution capacity. Interestingly, very thin and fine mesh designs are available in nature. One such example is the spider web structure. These structures have evolved with time and optimised their mesh pattern design for better impact damage resistance and load transfer. In this study, the basalt fibre reinforced mortar textile composites are considered for the investigation due to their growing interest in civil and construction applications. To demonstrate how the mesh geometry in textiles significantly influences the stress transfer, energy absorption, and deformation of reinforcements under various impact situations, three different geometries, (a) square shape mesh, (b) diamond-shaped mesh, and (c) bio-inspired spider web mesh, are modelled and meshed based on the reference geometry’s meshing pattern and dimensions. The results of numerical simulations show that a meshed reinforcement design inspired by spider-orb-web has improved mechanical features compared to conventional square and diamond shape mesh designs under high velocity impact loading.

On in-plane crushing behavior of a combined re-entrant double-arrow honeycomb

A novel re-entrant double-arrow honeycomb (RDAH) has been proposed and investigated by combining re-entrant hexagonal honeycomb and double-arrow honeycomb. Quasi-static compression experiments of 3D printed samples in different loading directions were carried out. Deformation modes and stress–strain response have been explored and identified. The corresponding finite element (FE) models were established and verified, and the dynamic crushing behaviors of RDAH were further investigated by FE simulations. The results show that RDAH has three typical deformation modes under different impact velocities. When subjected to quasi-static loading and low-velocity impact along the horizontal wall, two stress plateau regions of the stress–strain curves can be observed, while there is only one stress plateau when loaded perpendicular to the horizontal wall. Based on deformation modes, theoretical models of plateau stresses of RDAH under low-velocity and high-velocity impact were further established. The theoretical results of the plateau stresses agree well with the FE simulation results. The effects of impact velocity and geometric parameters on densification strain, Poisson's ratio and energy absorption were also discussed. The results show that the RDAH exhibits obvious negative Poisson's ratio effect in both directions. The energy absorption of RDAH is higher when loaded along the horizontal wall and can be 29.45 % higher than the traditional RH structure. The energy absorption of RDAH increases with the decrease of inclined wall l1, the decrease of inclined angle θ (perpendicular the horizontal wall), and the increase of inclined angle θ (along the horizontal wall).

Crashworthiness and dimensional stability analysis of zero Poisson's ratio Fish Cells lattice structures

The present article introduces Zero Poisson's Ratio (ZPR) Fish Cells metamaterial and investigates the effects of Poisson's ratio on the crashworthiness of Positive (PPR), Negative (NPR), and Zero Poisson's ratio lattice structures. High-fidelity Finite Element (FE) models of the proposed sandwich structures are built, based on identical domains for unit cells. Impact performances of lattice structures are addressed for low (2 m/s) and high (5 m/s) impact velocities in three orthogonal directions. The parameters investigated for crashworthiness include impactor's penetration depth, von Mises stress distribution, edges deformation and dimensional stability. Numerical results demonstrate that, unlike PPR and NPR models, the Fish Cells ZPR model possesses greater lateral stability and structural integrity with minimal edge deformations in all three directions. This leads to reduced lateral impact transfer to adjacent components and localised damaged zones, increasing the life span of structural components while reducing maintenance and repair downtime. Experimental analyses are conducted on the Fish Cells metamaterial through a drop tower test for demonstrating agreement with simulations and validation of the proposed modelling approach.

Fiber metal laminates for high strain rate applications with layerwise shock impedance tuning

Novel materials such as fiber-metal laminates (FMLs) have demonstrated significant potential in a variety of applications. They must contend with problems such fatigue, creep, high-speed projectile impact, and deformation at high strain rates while in use. When employed as structural materials in aircraft, especially when exposed to shock wave impact and high velocity impact, fiber-metal laminates’ high strain rate characteristics become crucial. Shock impedance matching is a revolutionary approach used for shock-tuning the separate layers. The novelty of the current work is in developing custom shielding laminates, with in-depth analysis on the response of the shock impedance tuning of individual layers on the laminate behaviour at high strain rates. In the current study, five stackups of FMLs comprising metallic (AA 6061-T6) and fiber-reinforced polymer (FRP) plies, were formulated, incorporating shock impedance matching. The fiber-polymer plies used in the FMLs include ultra-high molecular weight polyethylene (UHMWPE), p-aramid for supplementing the impact resistance. Transmission loss functions (TL) estimated from the impedance tube experiments were used to indicate the shock tuning of the various laminates. The laminates underwent testing using a Split Hopkinson Pressure Bar (SHPB) apparatus to determine their properties at high strain rates (350, textrm{s}^{-1} to 460, textrm{s}^{-1}). The variation in the Shock Energy (SE) absorbed by the laminates at various strain rates was analyzed as a function of the corresponding Transmission Loss employing regression. The dynamic stress-strain curves showed an increase in shock energy absorption at higher strain rates. The sequence SSP-IV and SSP-II showed the highest values of energy absorption as well as Transmission Loss.

Frequency domain analyses of low-velocity impact loading of elastomeric foams

Frequency analyses can reveal spectral features otherwise concealed within the time domain data. Such analyses are imperative to gain more insights into the undergoing dynamics in structures and materials, especially those with strong time dependence, such as elastomeric foams. This study aims to extend the applicability to data analysis from low-velocity impact scenarios by transforming into the frequency-domain, concurrently reporting crucial attributes of the dynamic loading and materials properties. Elastomeric polyurea foams with different densities were impacted at four different energies, ranging from 1.71 J to 7.09 J, to simulate low-velocity impact scenarios relevant to dynamic loading at different strain rates. In each impact test, a flattop drop mass was released from a preset height to control the impact velocity and energy while recording the impact and transmitted forces using impactor-mounted and base-mounted force sensors. The time-domain data of the primary impact was transformed into the frequency-domain using fast Fourier analysis. In the transformed domain, impact scenario characteristics, including acceleration and strain rate, and viscoelastic properties, i.e., storage and loss moduli, were extracted and benchmarked to time domain results. The impact characteristics agreed with previous reports based on time domain analysis while revealing the frequency-dependence of the acceleration and strain rate on the foam density and impact energy. The extracted viscoelastic properties were also in reasonable agreement with previously reported properties while consistent with linear viscoelastic principles. The robustness of the demonstrated method unlocks the potential for more in-depth data analysis from other dynamic mechanical experimental setups, including high-velocity impact and shock loading.

Structural Performance of Ferrocement Panels under Low- and High-Velocity Impact Load.

The primary objective of this experimental study is to examine the response and energy absorption capacity of ferrocement panels exposed to low- and high-velocity impact loads. The panels are reinforced with two different types of mesh layers, namely, welded wire grid (WWG) and expanded wire grid (EWG), with varying percentages of steel fibers (SF). The ferrocement panel system is made up of cement mortar reinforced with 0-2% SF with an increment of 1% and wire grid layers arranged in three different layers 1, 2, and 3. A consistent water-cement ratio (w/c) of 0.4 is maintained during mortar preparation, and all panels are subjected to a 28-day curing process in water. The study utilized square-shaped ferrocement panels measuring 290 mm × 290 mm × 50 mm. The panels are exposed to repeated impact blows from a 2.5 kg falling mass dropped from a height of 0.80 m. The count of blows necessary to commence the first crack formation and the cause of ultimate failure are recorded for each panel. The study reports that an increase in SF content and the number of wire grid layers increased the number of blows needed for both the first crack and the ultimate failure. In the high-velocity impact test, 7.62 mm bullets are fired at the panels from a distance of 10 m with a striking velocity of 715 m/s. The study observed and analyzed the extent of spalling, scabbing, and perforation. The results showed that an increase in fiber content and the number of wire grid layers led to a decrease in the area of scabbing and spalling compared with the control specimens. It was also possible to see the mode of failure and crack pattern for impacts with low and high velocities.

A numerical study on high-velocity impact behaviour of ceramic composite laminates

Currently, silicon carbide (SiC) is of enormous concern because of its high compressive strength,high thermal conductivity, high thermal shock resistance and small coefficient of thermal expansion. SiC has its applicability in armored vehicles, hypersonic armaments, and bullet-resistant armours in the future. The current focus is on understanding the behavior of SiC as used in laminated ceramic armours during the ballistic impact for its profound use in armoured vehicles. To achieve these objectives, computational simulations have been performed for the aforementioned materials using ANSYS/AUTODYN. It was concluded that when SiC was used as a front layer in laminated armours, it significantly increased the strength of the material against the hitting projectiles. The aforementioned composite material was even successful against the sniper gun projectile. The optimized thickness for the given configuration was found to be 41 mm with the consideration of approximately 50% depth of penetration. The modeled configuration was found to be approximately nine times stronger than the conventional laminated armours. The current study was compared with the previous experimental studies and the results were in good agreement. This agreement solely pertains to the pattern observed and not to individual values. It indicated the difference in % age DOP for the present research and previous studies with the increasing thickness of laminated armour. The trend observed was nearly similar to previous experimental studies. This showed that the DOP was reduced, as the thickness increased. Moreover, the previous studies showed that only ALON (aluminium-oxynitride) and sapphire had the required strength to act as a hard front-faced layer in laminated glass, but the current study improvised it to a Silicon carbide hard front-faced layer also.

Investigating fracture behavior and energy absorption of flexible hybrid biocomposites with soft–hard rubber/biofiller layers and fabric impregnated with matrix under high-velocity impact

Investigating fracture behavior and energy absorption of flexible hybrid biocomposites with soft–hard rubber/biofiller layers and fabric impregnated with matrix under high-velocity impact

Development and ballistic impact study on environment friendly sustainable jute reinforced carbon black/lignin-based elastomeric flexible composites

This study compares the behaviour of jute/elastomer bio-composites based on lignin and carbon black under high-velocity impact using experimental methods. Compared to carbon black, SEM data showed that lignin was more evenly distributed across the yarns. The space between the threads was filled by the good interaction of lignin and rubber. Additionally, the findings of the tensile and dynamic compression tests demonstrate that adding lignin to a matrix enhances the tensile strength of rubber samples and composites. On single-layer and three-layer composites made of lignin and carbon black, experimental tests were conducted utilizing a gas gun apparatus with a flat projectile travelling between 100 and 180 m/s. The damage behaviour of the proposed composites is analyzed. The findings demonstrate that the composites' energy absorption and ballistic velocity have enhanced due to the jute-woven fabric cover and the diluted rubber matrix. The results reveal that single and three-layer lignin-based composites exhibit better ballistic limits with an increase of 12.5% and 23.8% over composites based on single and three-layer carbon black composites. Lignin-based composites outperform carbon black composites in terms of energy absorption with single and three-layered lignin-based composites absorbing 23.5% and 25.86% more energy compared to single and three-layered carbon black-based composites. Additionally, the analysis of energy absorption at the ballistic limit for single-layer and three-layer lignin-based composites reveals an increase of 26.56% and 53.35%, respectively, compared to carbon black-based composites.