Varying Impact Velocities Research Articles

Ballistic impact response of Fe40Mn20Cr20Ni20 high-entropy alloys

High-entropy alloys (HEAs), recently emerging alloys with numerous excellent mechanical performances, may have a wide application prospect in impact engineering. The ballistic impact response of Fe40Mn20Cr20Ni20 HEA was investigated under various loading conditions. Ballistic impact tests with spherical projectiles and 87 type 5.8 mm small caliber bullets (DBP87 bullets) were conducted on 10 mm thick Fe40Mn20Cr20Ni20 HEA plates with varying impact velocities, compared with 20Mn23AlV steel (high manganese low magnetic steel). The relationship between microstructural details and aspects of ballistic behavior governing performance was established through experimental explorations and theoretical models. According to the findings, dense dislocation structures led to distinguishing work hardening in the HEA, and the strain-hardening capacity of the HEA enhanced dramatically with increasing strain rate under dynamic tension. Meanwhile, under 500 m/s impact velocity, twinning and microbanding had outstanding strain-hardening capabilities for the current HEA, and the cooperation of the dislocation slip and stacking faults was critical for strain hardening in the HEA when the impact velocity was increased to 930±15m/s, whereas only a small amount of dislocation sliding and twinning occurred during the dynamic deformation process of 20Mn23AlV steel at different impact velocities. These findings demonstrated that the outstanding strain-hardening capabilities of Fe40Mn20Cr20Ni20 HEA made it a promising candidate for ballistic impact engineering compared with 20Mn23AlV steel.

Ejecta Pattern of Oblique Impacts on the Moon From Numerical Simulations

AbstractThe commonly adopted ejecta deposit models always assume vertical impacts for simplification. However, most impacts on planetary surfaces are oblique, which produce significantly different ejecta patterns from vertical impacts. Although the asymmetric ejecta patterns from oblique impacts have been studied in laboratory experiments, they cannot be directly applied to large craters on the planetary scale. Here, we use the three‐dimensional shock physics code iSALE‐3D to systematically simulate impact excavation processes under Moon's gravity with varied impact angles (10°–90° with respect to the horizontal), impactor diameters (1–120 km), and impact velocities (10–20 km/s), which produce craters or basins ranging from ∼5 to ∼1,000 km. For each model, we record ejecta launch velocities and angles and calculate their integrated patterns after ballistic sedimentation. Our model results show that as the impact angle departs from the vertical, launch velocities of the uprange ejecta decrease, forming a V‐shaped zone devoid of ejecta. For even lower impact angles, the downrange ejecta thickness significantly decreases due to reduced launch angles and smaller deposit distances, forming a butterfly pattern with most ejecta concentrating in crossrange. In addition, our model results indicate that large impactors tend to produce more asymmetric ejecta patterns and the ejecta patterns are insensitive to typical impact velocities on the Moon. Our modeling results provide a semi‐quantitative relation between the ejecta pattern and impact parameters for oblique impacts on the Moon, which can be used to constrain the possible impact parameters for lunar crater or basins according to the observed ejecta pattern.

Dynamic response of wind turbine blade surface material under water droplet high velocity impact

When a wind turbine blade exposure to some degree of rainfall, water droplets in the atmosphere impact the blade at high velocity will causes erosion damages of the leading edge. The damages have significant influence to the aerodynamic performance of the blade, and also the cost of power generation. In this paper, a high velocity impact dynamics model of water droplet impact on wind turbine blade is develops based on SPH-FEM coupling method, where SPH model is used to model the large deformation region of the fluid domain, and FEM method is used to model the small deformation region of the structure domain. Together with properties of gelcoat material on the blade surface, effects of varying impact velocities and angles on the impact response of the gelcoat material are analysed through numerical simulation. The results show that during a high velocity impact event of water droplet, the contact force history appears two peaks. Also contact forces and strains on the blade material decreases with decreasing droplet impact velocity and impact angle, the total contact duration of the droplet during the impact decreases with increasing droplet impact velocity and angle. The present study is expected to provide theoretical guidance for enhancing the erosive capacity of wind turbine blade gelcoat material.

Modeling of GFRP-reinforced concrete slabs under various impact masses and velocities

Fiber-reinforced polymer (FRP) bar is increasingly employed, due to their advantages in higher tensile strength, light weight and corrosion resistance than steel bars. A numerical model was created and verified using existing testing data to explore the impact behavior of concrete slabs reinforced with Glass FRP (GFRP) under varied impact masses and velocities. The damage process was determined using calibrated model that depicted the failures of concrete slabs reinforced with GFRP bars when subjected to impact loading. Moreover, the influence of the impact velocity and impact mass on the impact behavior of the slabs was systematically examined. It is found that the characteristic of the time histories of central displacement and impact force has a certain functional relationship with impact velocity or impact mass. From the viewpoint of impact energy, the maximum central displacement grows linearly as impact energy increases, while the peak impact force and energy satisfy the quadratic function. In addition, as the impact velocity or mass increases, the response of the slabs transforms from global dominant to local dominant. Under the impact loads, the concrete dissipates most of the impact energy. Finally, both the normalized peak and residual displacements of the slabs vary in a practically linear form concerning the change of their natural frequency.

Experimental and numerical investigation on slurry erosion performance of hybrid glass/steel fiber reinforced polymer composites for marine applications

AbstractThe accelerating growth in the utilization of industrial waste to prepare sustainable material is gaining interest of researchers globally owing to their synergistic effect with enhanced performance and cost‐effective approach. This study mainly discussed the development of hybrid polymer composites by partial replacement of steel fiber in place of synthetic glass fiber to investigate the slurry erosion performance in an erosive environment. Initially, fabrication of hybrid glass/steel fiber reinforced polymer composites with different weight percentages (38, 37, 36, 35 wt%) glass fiber and (11, 12, 13, 14 wt%) steel fiber are fabricated through vacuum assisted resin transfer modeling (VARTM) technique. After that, steady‐state slurry erosion performance analysis is carried out by varying impact velocity (10–40 m/s), fiber loading (4:1 to 10:4), impingement angle (30°–90°), and slurry concentration (160–265 g/min) respectively in the slurry erosive environment. The observation indicates that at steady‐state conditions the maximum erosion rate lies within the range of 45°–75° by varying the impingement angle whereas the other factors remain constant. The experimental results are validated with different theoretical models as well as a numerical simulation model using computational fluid dynamics approach. Finally, Taguchi's design of experimental analysis (L16 orthogonal array design) is studied by varying all the four factors at‐a‐time to get the erosion rate of the hybrid composites. At the end, the simulated results depicted a clear picture of erodent particle trajectories, eroded surface, and streamlines, and all are in good agreement with the experimental results.

Low-velocity impact behavior of carbon woven laminates after exposure to varying temperatures

The present study reports the low-velocity impact (LVI) performance of carbon woven reinforced polymer (CWRP) composites with varying temperatures. The fabrication of carbon woven lamina and carbon woven reinforced two-layered laminate (named CWRP-1 and CWRP-2) was done using a vacuum-assisted resin transfer molding (VARTM) process. CWRP-1 samples were tested at varying impact velocities of 1, 2, 3, and 4 m/s at −25, 25, and 50 °C for each incident velocity. CWRP-2 samples were tested at room temperature at varying incident velocities to determine the effect of multiple woven layers. The impact resistance of the first-crack load, peak impact load, and absorbed energies were recorded and evaluated under different loading conditions. In addition, the Weibull probability method is adapted to forecast failure behavior as a function of load. Visual inspection, optical microscopy, and scanning electron microscope (SEM) images were used to assess the damage pattern and failure morphologies in forecasting the failure phases during LVI. The low-velocity impact behavior of CWRP-1 at −25 °C with various velocities was shown to be random due to the polymer matrix freezing condition. The softening of the resin matrix at 50 °C is responsible for the difference in damage tolerance. The relevance of multiple layered composites for better impact resistance characteristics was demonstrated during testing of CWRP-2 at room temperature. Overall, the results of this experiment showed that CWRP lamina and laminates are highly sensitive to the impact velocities and external temperatures.

Evaluation of low-velocity impact responses of flexible protective materials with a novel, visible approach

Due to occurrences of human injury induced by external low-velocity impact (LVI), the development of flexible protective materials (FPM) with superior properties is critical. However, the damage appearance of FPM under LVI is unintuitive, which brings extra challenges in evaluating their protective effects. Herein, a novel damage evaluation approach was designed by using homogeneous glass slides and wood boards, and responses of six protective fabric materials subjected to LVI were evaluated. According to visible damage morphologies and related quantitative values of the glass slides and wood boards on the back of specimens after LVI, it was clearly revealed that the protective effects of specimens with various types or parameters were different under the same condition of LVI. In addition, visible damage effects at varied impact velocities in this approach could distinguish the protective mechanisms of various specimens. Compared with the results of impact parameters outputted by universal impact testing machine, this approach was verified to be feasible and effective. Consequently, this paper was establishing a simple and visible approach for the purpose of promoting the research and development of flexible protective equipment for the human body to some extent.

Spreading and freezing of supercooled water droplets impacting an ice surface

The present study conducts supercooled droplet impact experiments on flat ice surfaces with varied impact velocities, initial diameters, droplet supercoolings, and ice surface temperatures. Droplet spreading at room temperature can be described by equating the inertial force to capillary and viscous forces. A universal scaling on maximum spreading can be obtained by interpolating between the laws in the capillary and viscous regimes where the dominant forces are capillary and viscous, respectively. During supercooled droplet spreading on ice surfaces, dendritic solidification occurs, forming a moving ice–water interface and leading to new droplet spreading mechanisms. The maximum spreading factor is sensitive to droplet supercooling, whereas surface temperature has a minor influence on spreading. A new dimensionless number, the icing number, is proposed to scale icing effects on a flow field, refining the law in the viscous regime for supercooled droplets. Nevertheless, icing does not affect the scaling in the capillary regime. The total influence of icing is related to the magnitude of the icing number and the competition between capillary and viscous forces. The icing number can then form a simple criterion for determining whether icing is negligible. The newly derived scaling performs well when modeling the present experimental results.

Impact velocity-dependent bonding mechanisms in metal cold spray

In this paper, we probe the bonding mechanisms for an impacting particle on a substrate, as in the cold spray process, over a range of impact velocities using molecular dynamics simulations. For the model copper/copper system, we find that grain boundary-like amorphous phase interlocking and metallurgical bonding are dominant at low and medium impact velocities, respectively, while metallurgical bonding and mechanical interlocking are dominant at high impact velocities. In particular, features including substrate crater depth, particle flattening ratio, and jetting area are tracked with varying impact velocities to further enhance our understanding of the underlying bonding mechanisms and the grain refinement in and around the interface. Because our findings are based only on small particle simulations allowable in MD, size effects can preclude extrapolating the results to physical micron-sized particles used in actual cold spray.

Oblique pancake bouncing

Despite extensive efforts in approaching the theoretical limit of solid-liquid contact time, the vertical bouncing droplet eventually lands on the impact spot of horizontally placed surfaces, which makes the liquid removal inefficient and thus limits its practical applications. To address this challenge, we use superhydrophobic surfaces consisting of regularly patterned pillars with an inclined Janus structure and report a phenomenon that involves synergistic effects of both pancake rebound and directional transport in one bouncing cycle, contributing to the reduction of contact time and the lateral removal of impacting droplets simultaneously. We generalize this particular regime to a broad range of working environments with various thermal conditions and impact velocities, demonstrating the robustness of water repellency and the directionality of liquid motion. The unusual bouncing performance, generality, and practicability of our work may provide useful insights into various applications, including electricity generation, self-cleaning, defogging, and anti-icing. • Contact time reduction and droplet directional transport are achieved simultaneously • Flexibility to manipulate oblique pancake bouncing behavior by varying impact velocity • Robust water repellency and liquid motion directionality under various conditions Tao et al. report a strategy to achieve the oblique pancake bouncing of droplets, allowing for a synchronized solid-liquid contact time reduction and the directional transport. Furthermore, the remarkable bouncing performance is applicable to a broad range of working environments with various thermal conditions and impact velocities.

Evaluating a transparent coating on a face shield for repelling airborne respiratory droplets.

A face shield is an important personal protective equipment to avoid the airborne transmission of COVID-19. We assess a transparent coating on a face shield that repels airborne respiratory droplets to mitigate the spread of COVID-19. The surface of the available face shield is hydrophilic and exhibits high contact angle hysteresis. The impacting droplets stick on it, resulting in an enhanced risk of fomite transmission of the disease. Further, it may get wetted in the rain, and moisture may condense on it in the presence of large humidity, which may blur the user's vision. Therefore, the present study aims to improve the effectiveness of a face shield. Our measurements demonstrate that the face shield, coated by silica nanoparticles solution, becomes superhydrophobic and results in a nominal hysteresis to the underlying surface. We employ high-speed visualization to record the impact dynamics of microliter droplets with a varying impact velocity and angle of attack on coated and non-coated surfaces. While the droplet on non-coated surface sticks to it, in the coated surface the droplets bounce off and roll down the surface, for a wide range of Weber number. We develop an analytical model and present a regime map of the bouncing and non-bouncing events, parametrized with respect to the wettability, hysteresis of the surface, and the Weber number. The present measurements provide the fundamental insights of the bouncing droplet impact dynamics and show that the coated face shield is potentially more effective in suppressing the airborne and fomite transmission.

FINITE ELEMENT BEHAVIOR OF AA7075 UNDER SQUARE SHAPE OF STRIKER OF SPLIT HOPKINSON PRESSURE BAR WITH VARYING LOADS

To know the high strain rate behavior of aluminum alloy 7075 (AA7075) is very significant due to its vital uses in aviation, buildings, and automobile industries. Taylor impact test, projectile tests and split Hopkinson pressure bar are usually utilized to know the behavior of materials under high strain rate conditions. But due to lack of availabilities and very costly setups, various types of changes can’t be done easily. However, numerical simulation gives opportunity to observe the phenomena of materials under different conditions without much cost. This paper investigated the behavior of square shaped specimens of AA7075 under varying impact velocities of impact velocities of 20m/s-50m/s of square striker bar of SHPB using Abaqus. To understand the importance of shape, striker bar and specimen shape are varying from square to circular under dynamic conditions. Results obtained under varying conditions indicated that the material behavior strongly dependent to the strain rates, striker shapes and specimen shapes.

A finite element-guided mathematical surrogate modeling approach for assessing occupant injury trends across variations in simplified vehicular impact conditions.

A finite element (FE)-guided mathematical surrogate modeling methodology is presented for evaluating relative injury trends across varied vehicular impact conditions. The prevalence of crash-induced injuries necessitates the quantification of the human body's response to impacts. FE modeling is often used for crash analyses but requires time and computational cost. However, surrogate modeling can predict injury trends between the FE data, requiring fewer FE simulations to evaluate the complete testing range. To determine the viability of this methodology for injury assessment, crash-induced occupant headinjury criterion (HIC15)trends were predicted from Kriging models across varied impact velocities (10-45 mph; 16.1-72.4 km/h), locations (near side, far side, front, and rear), and angles (-45 to 45°) and compared to previously published data. These response trends were analyzed to locate high-risk target regions. Impact velocity and location were the most influential factors, with HIC15 increasing alongside the velocity and proximity to the driver. The impact angle was dependent on the location andwas minimally influential, often producing greater HIC15 under oblique angles. These model-based head injury trends were consistent with previously published data, demonstrating great promise for the proposed methodology, which provides effective and efficient quantification of human response across a wide variety of car crash scenarios, simultaneously. This study presents a finite element-guided mathematical surrogate modeling methodology to evaluate occupant injury response trends for a wide range of impact velocities (10-45 mph), locations, and angles (-45 to 45°). Head injury response trends were predicted and compared to previously published data to assess the efficacy of the methodology for assessing occupant response to variations in impact conditions. Velocity and location were the most influential factors on the head injury response, with the risk increasing alongside greater impact velocity and locational proximity to the driver. Additionally, the angle of impact variable was dependent on the location and, thus, had minimal independent influence on the head injury risk.

Scale-up procedure of parameter estimation in selection and breakage functions for impact pin milling

This paper presents a scale-up procedure of parameter estimation in the selection function and breakage function from single particle impact breakage to inform the predictions at the process scale of an impact pin mill. The selection and breakage functions used in population balance model (PBM) for particle breakage in the literature are briefly reviewed. Single particle breakage tests are conducted in a vertical impact tester subject to varying impact velocities. The single particle breakage results further serve to provide the database for the parameter estimation in Vogel and Peukert model (Vogel and Peukert, 2005). The estimated parameters in the particle level are upscaled in an impact pin mill using the population balance model, which is implemented in the software gPROMS (Process Systems Enterprise, UK) (gPROMS® 4.1 Release Notes, 2016). The impact milling tests were carried out in an impact pin mill UPZ100 subject to four feed rates, providing the dataset for model validation. The sensitivity analysis of the PBM parameters was conducted to help identify their leverage on the particle size distribution. The scale-up procedure by specifying the parameters from single particle level to the process level of PBM demonstrates an approach to help predict the size reduction process subject to the prevailing mechanism in an impact pin mill and other milling processes alike.

Low-Velocity Impact Induced Damage Evaluation and Its Influence on the Residual Flexural Behavior of Glass/Epoxy Laminates Hybridized with Glass Fillers

This research work investigates the low-velocity impact induced damage behavior and its influence on the residual flexural response of glass/epoxy composites improved with milled glass fillers. The low-velocity impact damage employing varying impact velocities (3 m/s, 3.5 m/s, and 4 m/s) was induced on baseline and filler loaded samples with different fiber orientations. The residual performance and their damage modes were characterized using post impact flexural (FAI) test and acoustic emission (AE) monitoring. In all fiber orientations, the filler modified glass/epoxy samples showed improved impact strength and stiffness properties. A substantial improvement in impact damage tolerance, especially for samples impacted at 3.5 m/s and 4 m/s was observed. The presence of filler at the interlaminar zone contributed to improved energy dissipation through filler debonding and pull-out. This further contributed in arresting the crack growth, showing reduced damaged area. The inclusion of milled fibers on glass/epoxy laminates enhanced the impact toughness and residual flexural behavior.

High Velocity Impact Testing of Intermetallic Projectiles

A high-velocity impact-ignition testing system (HITS) was developed to study the dynamic response of intermetallic projectiles impacting an inert steel target plate at speeds up to 1500 m/s. The intermetallic projectile is a binary composite of powders consolidated into a 3 g projectile contained in a 0.410 inch (10.5 mm) caliber shot gun case. The projectiles are launched from a propellant driven gun into a catch chamber equipped with view ports and imaging diagnostics. The impact events are monitored using high-speed cameras that provide local and macroscopic perspectives of fragmentation. Results demonstrate the range of visual data that can be captured including fragment count, cone angle, and velocity. A computational solid dynamics model is used to interpret the phenomenology of the experimental impact events. The model assumes an ideal case of plastic projectile and two limiting cases for the target: plastic and elastic and predicts fragmentation behavior based on brittle tension damage at lower impact velocities with increasingly severe fragmentation and smaller fragments at higher impact velocities. Results reveal that the material properties of the target have a strong influence on the trajectory of the fragments. This study provides a fundamental understanding of impact events at varied impact velocities and shows the phenomenological behavior of fragmentation.

Evaluation of breach behavior due to plate fragment impact

This paper presents modifications to existing relationships that analyze the breach potential of concrete elements subjected to impact by plate fragments. Experimental data associated with a previous study that evaluated plate fragment impacts were analyzed to determine the impactor kinetic energy required to cause reinforced concrete to present a breached condition. This value was compared to the energy that the existing contact charge relationships indicate is required to breach a wall of the same thickness. Modifications were made to existing contact charge equations to account for the difference between the contact charge energy required to cause a breach condition and that required from fragment impact to produce a breach condition. A numerical model that simulates concrete slab breach response was also created and utilized to further evaluate the breach relationships. These modified relationships provide the ability to determine the thickness of wall required to prevent a breach due to impact from a plate fragment at varying impact velocities; however, they appear to be less reliable for thinner slabs and are not recommended for low aspect ratio projectiles.

A strain rate-dependent enhanced continuum model for elastic-plastic impact response of metal-ceramic functionally graded composites

An enhanced continuum model considering the strengthening of strain rate is developed to explore the particle size-dependent responses of the metal-ceramic functionally graded composite plates subjected to a drop-weight impact. The continuum model explicitly accounts for the effects of geometrically necessary dislocations and strain rate by combining Taylor dislocation model and Johnson–Cook model. The plastic constitutive relation of metal-ceramic FGM is derived from the Tamura–Tomota–Ozowa model subjected to different strain rates. The elastic-plastic impact responses of SiC/Al functionally graded plates with the micron-scale particle sizes and compositional gradient exponents are studied under varied impact velocities. The comparison at the numerical results for the particle size effects in the SiC/Al functionally graded plates and the experimental data reported in references demonstrates validity of the proposed continuum model.

Characterizing drip patterns in bloodstain pattern analysis: An investigation of the influence of droplet impact velocity and number of droplets on static pattern features

This work characterizes fundamental features of static drip patterns simulated for forensic bloodstain pattern analysis. The purpose of this study was to determine if and how two independent variables, impact velocity and droplet number, influence the parent stain size, shape and satellite spatter distribution of drip patterns created with whole ovine blood. To do this, 500 drip patterns were created in a controlled environment at five varying impact velocities and ten different droplet numbers on a hard paper surface. Digital images of the dried patterns were processed and analyzed using Fiji (ImageJ). The data collected from each pattern support the hypotheses that drip patterns contain predictable and reproducible elements based on impact velocity and droplet number. Basic fluid dynamic principles demonstrate that the size of the parent stains, as well as the number and distribution of satellite stains increase with increasing Weber number. A decrease in the circularity of the parent stains was also noted. This study provides fundamental qualitative and quantitative data on observable elements of drip patterns that can be used practically by bloodstain pattern analysts for pattern identification and classification.

Low Velocity Impact Behavior of Aluminum Cenosphere Syntactic Foam

Abstract Free fall drop weight impact testing is an optimum option for studying the impact behavior of various materials under low to medium strain rates because of its applicability in these ranges of strain rates. Herein, drop weight impact test is simulated using non-linear finite element code LS-DYNA®. The material, considered herein for test simulation, is aluminum cenosphere syntactic foam. Three different impact velocities with three different foam models, available in LS-DYNA®, are used to understand the effect of impact velocities and material model on the impact behavior of the considered foam. In the present study, FE model is developed using LS-DYNA® for drop weight impact test wherein, a bilinear material model is used for hammer and three material models i.e. crushable foam, Deshpande-Fleck foam, piecewise linear plasticity are used to model the foam. Based on simulation, force-displacement relation is developed for studying the energy absorption under varying impact velocities and foam models.