Impact Velocity Research Articles

Outcomes of Sub-Neptune Collisions

Observed high multiplicity planetary systems are often tightly packed. Numerical studies indicate that such systems are susceptible to dynamical instabilities. Dynamical instabilities in close-in tightly packed systems, similar to those found in abundance by Kepler, often lead to planet–planet collisions. For sub-Neptunes, the dominant type of observed exoplanets, the planetary mass is concentrated in a rocky core, but the volume is dominated by a low-density gaseous envelope. For these, using the traditional perfect merger assumption (also known as the “sticky-sphere” approximation) to resolve collisions is questionable. Using both N-body integration and smoothed-particle hydrodynamics, we have simulated sub-Neptune collisions for a wide range in realistic kinematic properties such as impact parameters ( b′ ) and impact velocities ( vim ) to study the possible outcomes in detail. We find that the majority of the collisions with kinematic properties similar to what is expected from dynamical instabilities in multiplanet systems may not lead to mergers of sub-Neptunes. Instead, both sub-Neptunes survive the encounter, often with significant atmosphere loss. When mergers do occur, they can involve significant mass loss and can sometimes lead to complete disruption of one or both planets. Sub-Neptunes merge or disrupt if b′<bc′ , a critical value dependent on vim /v esc, where v esc is the escape velocity from the surface of the hypothetical merged planet assuming perfect merger. For vim/vesc≲2.5 , bc′∝(vim/vesc)−2 , and collisions with b′<bc′ typically leads to mergers. On the other hand, for vim/vesc≳2.5 , bc′ ∝ vim /v esc, and the collisions with b′<bc′ can result in complete destruction of one or both sub-Neptunes.

Spreading of graphene oxide suspensions droplets on smooth surfaces

Understanding and predicting the spreading of droplets on solid surfaces is crucial in many applications such as printed electronics and spray coating where the fluid is a suspension and in general non-Newtonian. However, many models that predict the maximum spreading diameter usually only apply to Newtonian fluids. Here, we study experimentally and theoretically the maximum spreading diameter of graphene oxide suspension droplets impacting on a smooth surface for a wide range of concentrations and impact velocities (5≤We≤700, 30≤Re≤2000). As the particle concentration increases the rheological behavior changes from a viscous fluid to a shear-thinning yield stress fluid and the maximum spreading diameter decreases. The rheology for all concentrations is well described by a Herschel–Bulkley model that allows us to determine the characteristic viscosity and corresponding Reynolds number Re during spreading. Analogous to Newtonian fluids, the spreading ratio follows the Re1/5 scaling in the viscous spreading regime. Furthermore, we use this characteristic viscosity to develop an energy balance model that takes into account the viscous dissipation and change in surface energies to find the maximum spread diameter for a given impact velocity. The model contains one non-dimensional parameter α that encodes both the dynamic contact angle during spreading and the droplet shape at maximum spread. Our model is in good agreement with our data at all concentrations and agrees well with literature data on Newtonian fluids. Furthermore, the model gives the correct limits in the viscous and capillary regime and can be solved analytically for Newtonian fluids.

New insights into impact-induced removal of the deposited droplet

This paper presents a comprehensive investigation into the collision dynamics of equal and unequal-sized nanodroplets on a flat surface using molecular dynamics simulations, revealing new insights into scaling laws and energy dissipation mechanisms. The simulations, conducted with the Large-Scale Atomic/Molecular Massively Parallel Simulator software, involved an initially stationary droplet on the surface and a suspended droplet with varying diameter ratios (λ) and impact velocities. The results show that at low Weber numbers (We &amp;lt; 24.15), the droplets tend to deposit after impact, while at higher Weber numbers (We ≥ 24.15), they undergo spreading and retraction, ultimately rebounding. The study reveals that the dimensionless contact time (t*) and maximum spreading factor (βmax*) in collisions between droplets of different sizes do not follow the same scaling relationship observed in single nanodroplet impacts. By redefining the Weber and Reynolds numbers (Re), the new scaling relationships t* ∼ We2/3Re−1/3λ−1/3 and βmax* ∼ We2/3Re−1/3λ−1/3 are proposed and validated. This work represents a further in-depth study of previous research on single nanodroplet impact, introducing for the first time the diameter ratio in unequal droplet impacts into the variation patterns of contact time and maximum spreading diameter. Moreover, these findings highlight the importance of revisiting and potentially revising classical theories to accommodate the unique physical phenomena that emerge at smaller scales.

Exploring mechanisms of asymmetric droplet impact dynamics on roughness gradient surface

Droplet impact on surfaces with varying roughness and wettability is a common phenomenon in both natural and industrial environments. While previous studies have primarily examined asymmetric droplet rebound driven by impact velocity or Weber number, the influence of surface structure and associated impact mode transitions has received less attention. In this study, molecular dynamics simulations and detailed analyses are employed to investigate the mechanisms governing droplet rebound on nanopillar arrays with gradient distributions. Results reveal that nanopillar height significantly influences rebound direction, with two distinct directional transitions occurring as the height increases. Additionally, the effects of surface structure and Weber number on impact patterns, rebound velocity, and contact time are systematically evaluated, with contact angle calculations shedding light on the underlying force mechanisms. A phase diagram is developed to illustrate the relationship between rebound direction, Weber number, and nanopillar height. The study further extends the analysis to substrates with bidirectional gradient distributions, demonstrating consistency with single-directional gradient results and validating the broader applicability of the findings. This research provides critical insights into droplet dynamics on roughness gradient surfaces, emphasizing the role of nanopillar height and impact mode in controlling droplet behavior and highlighting potential applications in the design of structured array surfaces.

Self-driven transport and heat transfer characteristics of a droplet on a wettability-gradient surface by front-tracking method

Droplet manipulation is a multidisciplinary field with broad applications across various industries. It holds significant potential in areas such as microfluidics, oil–water separation, water harvesting, and heat transfer. However, there is still a lack of comprehensive knowledge regarding droplet migration on restricted surfaces. In this study, we conducted a numerical simulation using the front-tracking method to investigate the heat transfer associated with droplet migration on a cold plate with a wettability gradient. We examined the effects of relative temperature differences, surface wettability, low initial impact velocities (We≤10), and wettability constraints (the width of the wettability stripe capable of driving droplet movement) on various droplet-related heat transfer characteristics and the resulting temperature field distribution. Our key findings indicate that as the temperature difference between the droplet and the surface increases, the heat flux experienced by the droplet after deposition also increases. Additionally, the decline in the heat flux curve during the descending phase becomes more significant. The surface contact angle plays a crucial role in the heat transfer dynamics during droplet migration. Droplets reach thermal equilibrium more quickly on hydrophilic surfaces with smaller contact angles. Higher initial impact velocities initially cause droplets to rebound on the surface, leading to more pronounced fluctuations in transient heat flux during the impact phase. However, as droplets transition from the rebound phase to the migration phase, the impact velocity's influence diminishes. Additionally, the restricted wettability (W*) affects the droplet-surface heat transfer through variations in the wetting area. We observed a fourfold difference in the relative wetting area between W*=0.4 and W*=2.5 in the final stage.

The Influence of Impact Velocity on Stresses and Failure of S355j2 Steel Under Slurry Erosion Conditions

The Influence of Impact Velocity on Stresses and Failure of S355j2 Steel Under Slurry Erosion Conditions

The rebound law of micro-particle on amorphous alloys under high impact velocities

Compared to their crystalline counterparts, amorphous alloys due to disordered structures are expected to have higher elasticity of deformation. However, in this work, we use the micro-ballistic impact technique to show a smaller dynamic redound of micro-particles on a Zr-based amorphous alloy than that on its corresponding polycrystalline target. We find that the two alloys follow the same rebound law of micro-particle under low impact velocities, but with increasing impact velocity the amorphous alloy exhibits a faster decrease in rebound velocity of micro-particle. This lower rebound results from the easier activations of shear banding in glassy structures, thus contributing to more significant energy dissipation during the micro-particle impact. Further analyses imply that the amorphous alloys and their crystalline counterparts are more favorable in shock wave and projectile protection, respectively. This work is useful in the understanding of the dynamic elasticity and shock energy dissipation of amorphous alloys under micro-particle impacts.

A Novel Spring-Actuated Low-Velocity Impact Testing Setup

Evaluating the behavior of materials and their response under low-velocity dynamic impact (less than 30 m/s) is a challenging task in various industries. It requires customized test methods to replicate real-world impact scenarios and capture important material responses accurately. This study introduces a novel spring-actuated testing setup for low-velocity impact (LVI) scenarios, addressing the limitations of existing methods. The setup provides tunable parameters, including adjustable impactor mass (1 to 250 kg), velocity (0.1 to 32 m/s), and spring stiffness (100 N/m to 100 kN/m), allowing for flexible simulation of dynamic impact conditions. Validation experiments on steel plates with a support span of 800 mm and thickness of 5 mm demonstrated the system’s satisfactory accuracy in measuring impact forces (up to 714.2 N), displacements (up to 40.5 mm), and velocities. A calibration procedure is also explored to estimate energy loss using numerical modeling, further enhancing the test setup’s precision and utility. The results underline the effectiveness of the proposed experimental setup in capturing material responses during low-velocity impact events.

Numerical investigation of droplet impacting, spreading and penetration on porous substrates

The behavior of droplets impacting porous surfaces, including spreading and penetration, plays a critical role in various engineering applications, yet the underlying mechanisms governing the interaction between these processes remain unclear. In this study, the complex interplay between droplet spreading and penetration on porous media was comprehensively investigated using the Level Set method. The droplet evolutions outside and inside the porous substrate influenced by droplet size, impact velocity, porosity, particle diameter, surface tension, and dynamic viscosity were explored. The results indicate that increases in droplet size and velocity lead to a simultaneous increase in both spreading factor and penetration depth. Higher values of porosity, particle diameter, and surface tension facilitated droplet penetration, despite at the expense of impeding droplet spreading on porous surfaces. Droplet size and surface tension exhibited less pronounced effects on penetration depth, particularly during the early stages. The spreading factor exhibited a non-monotonic trend with viscosity, initially increasing and subsequently decreasing, while the penetration depth decreased accordingly. Moreover, a larger spreading diameter corresponds to an expanded penetration width. A correlation was proposed to predict the maximum spreading factor based on Weber number, Reynolds number, and Darcy number, which can predict 83 % data in literature with deviations within ±20 %. This study provides new insights into the droplet dynamics on porous media and offers practical guidance for optimizing relevant engineering applications.

Determine deformation energy in side impact by incorporating contact area in crash algorithm

This research paper explores potential enhancements to the CRASH algorithm by proposing a hypothesis that relates deformation to applied stress instead of force. By incorporating stress instead of force, the calculation can account for the contact area, leading to a more precise estimation of impact velocity, particularly in side impacts. An initial evaluation of this energy absorption calculation formula is presented, focusing on side impacts in vehicle "2022 Hyundai Ion." Two side impact reports for the vehicle from the National Highway Traffic Safety Administration (NHTSA) database were utilized. One report involved the vehicle tilted at a 45-degree angle against a fixed pole with a 254 mm diameter, while the other examined the vehicle colliding with a moving deformable barrier (MDB) at various speeds. Additionally, a Monte Carlo simulation was conducted to validate the model's applicability. The verification process involved estimating stiffness coefficients from the first report and employing them to calculate energy absorption during the crash against the moving deformable barrier. The analysis demonstrates promising improvements in accurately calculating deformation energy absorbed during impacts.

Study on the Dynamic Crushing Behaviors of Hourglass Honeycomb Sandwich Panels

In response to the problem of enclosed internal spaces in existing honeycomb sandwich panels, the concept of an hourglass honeycomb sandwich panel model is proposed for the first time, which provides a breakthrough approach for achieving the multifunctional integration of honeycomb sandwich panels. Numerical simulation methods are employed to investigate the dynamic performance of the hourglass honeycomb sandwich panels. The focus is on discussing the influences of the geometric parameters on the deformation mode, dynamic response, load uniformity, and energy absorption capacity of the hourglass honeycomb sandwich panel under different impact velocity conditions. The research results indicate that under low-velocity-impact conditions, the influence of the geometric parameters is predominant. In contrast, under high-velocity-impact conditions, the influence of the impact velocity conditions is predominant. Hourglass honeycomb sandwich panels with low density, a large inclination angle of the honeycomb wall, and small contact distances between the hourglass honeycomb cell and the panel have excellent load uniformity, and the distances between the contact points of the hourglass honeycomb cell and the panel have a great influence on the energy absorption capacity of the sandwich panels. This study provides a theoretical basis for the application of honeycombs in aerospace and other engineering areas.

Inactivation of MS-2 virus in water by rotational generator of hydraulic shock

This study investigates the effect of hydraulic shock waves on inactivation of MS-2 bacteriophage, a norovirus surrogate. A falling circular jet of water spiked with the MS-2 (∼1000 PFU/mL) was repeatedly impacted by a rotating blade, resulting in occurrence of hydraulic shock waves within the liquid region adjacent to the impact. The proof-of-concept rotational generator of hydraulic shock treating 9 L of water spiked with viruses was able to achieve 3 logs reduction of viral plaque count within 80–100 liquid passes at moderate blade impact velocities (namely, 70 and 88 m/s) despite the water temperature not exceeding 40 °C and no detectible cavitation. Within the first 20 liquid passes, most MS-2 capsid proteins were degraded, with their concentration reduced from 22 μg/mL to only 7.3 μg/mL. Due to the lack of further capsid protein destruction, additional reduction in MS-2 plaque count in subsequent 80 passes is indicative of damage inflicted to the viral recognition receptors. All this suggests that shockwaves of moderate amplitude (few tens of MPa) alone are sufficient for effective viral inactivation. Considering this and the device's good scalability potential, rotational hydraulic shock generators could prove effective in treating virus-contaminated waters.

Investigation of Low Velocity Impact Behavior of Aluminum Honeycomb Sandwich Structures with GFRP Face Sheets by Finite Element Method

The aim of this study is to examine the low velocity impact behavior of aluminum honeycomb sandwich structures with glass fiber reinforced plastic (GFRP) face sheets with the help of finite element method. In the study, low velocity impact tests were carried out in the LS DYNA finite element program to examine the effects of face sheets thickness, core number, wall thickness, impact location and impact velocity on maximum contact force, absorbed energy efficiency and damage mode. Progressive damage analysis based on the Hashin damage criterion and the combination of Cohesive Zone Model (CZM) and the bilinear traction-separation law was performed using the MAT-54 material model. At the end of the study, it was determined that the face sheets thickness in sandwich structures had a significant effect on the impact resistance up to a certain impact energy. It has been observed that as the impact velocity gradually increases, there is a decrease in the contact force after a certain threshold value. As the impactor velocity increases, the energy absorption efficiency also increases. It has been determined that the location of the impact is very effective on peak force and energy absorption efficiency. The effect of the number of core layers depends on the face sheets thickness. When the face sheets thickness was not damaged at first contact, the peak force value increased in parallel with the number of layers. It was determined that the dominant damage mode after impact was matrix damage. It has been observed that as the energy level of the impactor increases, damage also occurs on the back surfaces.

Solidification process of hollow metal droplets impacting a substrate

Recently, there has been a renewed interest in hollow droplet impact, as the internal bubble makes a difference in the spreading morphology during thermal spraying and three-dimensional printing. This paper is dedicated to the solidification process of a hollow metal droplet impacting a cold substrate. The influence of initial impact velocity and substrate temperature on the spreading process is numerically investigated by employing a phase-field method coupled with a solidification model. Solidification was shown to strongly alter droplet spreading and the flow state of the center liquid column. To describe the flow state of the center liquid column, three patterns, namely ‘no-jet’, ‘transition region’, and ‘counter-jet’ are defined. The simulation results show that the formation of the center counter-jet is inhibited by the solidification layer when Péclet number Pe<357, where Pe is the ratio of convection rate to diffusion rate. In addition, the critical Pe at which the phenomenon of counter-jet occurs gradually rises with the substrate temperature falling. Finally, a quantitative analysis of the maximum spreading diameter is proposed by establishing an energy conservation equation. The predicted diameters are in good agreement with the simulated results. It allows us to provide a general expression for the hollow droplets' maximum spreading diameter, using the impact and temperature parameters.

An Advanced DEM-FEM Method for Herringbone Gear in Shot Peening

Introduction: The complex geometry of herringbone gear can lead to uneven surface strengthening, which affects the overall effect of treatment. Methods: A discrete element model (DEM) of shot peening for herringbone gears was developed, incorporating accurate gear surface parameters to study impact characteristics along the tooth profile. A finite element model (FEM) was created for small local units of the gear surface to calculate the residual stress and roughness. Results: There are a large number of low-velocity shots at the root of the gear, and the closer to the top of the gear, the higher the impact velocity of the shots, but the number of impacts also decreases. The surface roughness Sa near the root of the tooth is the smallest, the Sa at the pitch circle is the largest, and the Sa at the top of the tooth is intermediate. However, the residual stress levels at different positions of the tooth surface are not significantly different. Conclusion: The difference in tooth surface roughness of herringbone gear is the synergistic effect of shot impact velocity and shot frequency, but this synergistic effect has no significant effect on the stress after shot peening.

Influence of Binding Energies on Required Process Conditions in Aerosol Deposition

AbstractWith the high interest in aerosol deposition in order to form high-quality coatings by solid-state impact, there is an increasing demand for developing general guidelines to estimate needed particle velocities and thus process parameter sets for successful deposition of ceramic materials. By using modeling approaches, rather different material properties in first instance can be expressed in terms of binding energies. Needed velocities for possible bonding can then derived by impact simulations and compared to experimental results from the literature. In order to study the role of binding energy on the impact behavior of ceramic particles in aerosol deposition, a molecular dynamics study is presented. Single-particle impacts are simulated for a range of binding energies, particle sizes and impact velocities. The results show that increasing the binding energy from 0.22 to 0.96 eV results in up to three times higher characteristic velocities corresponding to the threshold of bonding or grain size-dependent fragmentation of the particles. However, regardless of the binding energy, exceeding the characteristic velocities results in a similar deformation and fragmentation pattern. This allows for a general representation of the impact behavior as a function of normalized impact velocity for different ceramic materials. Apart from dealing with prerequisites for bonding of different materials by aerosol deposition, this study could also be generally relevant to the high-velocity deformation behavior of ceramics with different grain sizes.

Effect of Primary/Artificial Interface on Dynamic Failure Behavior of Combined Coal and Rock: Monitoring by High-Speed Imaging and Scanning Electron Microscopy.

The instability of the primary coal and rock structure significantly impacts the safety of coal mining and construction. The complex coal-rock interface cannot be simplified as a smooth surface. To investigate the dynamic response of primary composite coal and rock (primary-CCR), we studied the impact of load, hydrostatic pressure, and interface type on the mechanical behavior and macro/micro failure characteristics using a separate Hopkinson bar, a high-speed camera, and a scanning electron microscope. The results indicate a linear relationship between the composite strength, impact toughness, and impact velocity of the two types of composite coal and rock. The mechanical behavior of the primary-CCR initially increases and then decreases with the rise of hydrostatic pressure (turning point: 10 MPa). There is a positive correlation between artificial combined coal-rock (artificial-CCR) and hydrostatic pressure. The dissipative energy of combined coal and rock increases linearly with impact velocity. Initially, the dissipative energy per unit fracture area increases with hydrostatic pressure, then decreases as pressure continues to rise. Additionally, an increase in impact load causes the energy dissipation inflection point to shift forward. The primary interface significantly reduces the energy threshold for instability failure, resulting in a transition from energy transfer to energy dissipation in rock components. This transition manifests as the failure of artificial combined coal and rock cracks, which develop into rock fragments at an impact velocity of 14 m/s. Furthermore, the change in section roughness of coal and rock correlates with the degree of macroscopic crack growth, following the order: coal > primary-CCR > artificial-CCR > rock.

Behavior of Polymeric Substrates and Sintered Silver Printed Hybrid Electronic Assemblies Subject to Extreme Acceleration Levels and Elevated Temperatures

Abstract This paper focuses on the response of printed hybrid electronic (PHE) assemblies with polymeric substrates and additively manufactured sintered silver electrical traces subject to extreme mechanical shocks (up to 100,000 g) and high temperatures (up to 150 °C). The substrates are hemispherical domes of injection-molded polycarbonate and polysulfone thermoplastics. Trace deposition onto the domes is accomplished by a novel process that combines conventional milling with extrusion printing to recess silver traces and dielectric insulation within the surface of the substrate. Mechanical shock testing is performed using an accelerated-fall drop tower equipped with a dual mass shock amplifier (DMSA) able to generate accelerations from 10,000 g up to 100,000 g with pulse durations of ∼0.05–0.1 ms and impact velocities of 6.5–20.5 m/s. Specimen performance is characterized by electrical and physical testing before and after testing. While polycarbonate domes survive multiple drops at all acceleration levels and temperatures, they are sensitive to heat and susceptible to warping and structural deformation at 150 °C which can compromise trace performance. Polysulfone domes can survive these temperatures without issue, but are less shock resistant and only survive 3–4 drops at 100,000 g (compared to 30+ for polycarbonate domes). Trace resistance is used as a metric to assess trace performance. All traces exhibit progressive long-term degradation over the course of multiple shocks, followed by instantaneous discontinuity during the final shock event. Trace failure (defined as the doubling of static trace resistance) occurs at ∼105–106 J/kg cumulative impact energy for all acceleration levels.

Dynamic response of pile–slab retaining wall structure under rockfall impact

Abstract. Pile–slab retaining walls, as innovative rockfall protection structures, have been extensively utilized in the western mountainous regions of China. With their characteristics of a small footprint, high interception height, and ease of construction, these structures demonstrate promising potential for application in mountainous regions worldwide, such as the Himalayas, Andes, and Alps. However, their dynamic response upon impact and impact resistance energy remain ambiguous due to the intricate composite nature of the structures. To elucidate this, an exhaustive dynamic analysis of a four-span pile–slab retaining wall with a cantilever section of 6 m under various impact scenarios was conducted utilizing the finite-element numerical simulation method. The rationality of the selected material constitutive models and the numerical algorithm was validated by reproducing two physical model tests. The simulation results reveal the following. (1) The lateral displacement of the pile at the ground surface and the concrete damage under the pile at the impact center are greater than those under the slab at the impact center, implying that the impact location has a significant influence on the stability of the structure. (2) There is a positive correlation between the response indexes (impact force, interaction force, lateral deformation of pile and slab, concrete damage) and the impact velocities. (3) The rockfall peak impact force, the ratio of the peak impact force to the peak interaction force, and lateral displacement of the pile at the ground surface had strong linear relationships with rockfall energy. (4) Relative to the bending moment, shear force, and damage degree, the lateral displacement of the pile at the ground surface is the first to reach its limit value. Taking the lateral displacement of the pile at the ground surface as the controlling factor, the estimated maximum impact energy that the pile–slab retaining wall can withstand is 905 kJ in this study when the structure top is taken as the impact point. In cases where the impact energy of falling rocks exceeds 905 kJ, it is recommended to optimize the mechanical properties of the cushion layer, improve the elastic modulus of concrete, increase the reinforcement ratio of longitudinal tension bars, enlarge the section size of piles at ground level, or add anchoring measures to enhance the bending resistance of the retaining structure.

Research on the mechanism of electromechanical coupling response of pulse power multilayer ceramic capacitors under high impact and high voltage discharge composite environment

Pulse power multilayer ceramic capacitors (pulse power-MLCC) are commonly used in complex composite environments with high overload and high voltage due to their large size and capacitance. In order to study the electromechanical coupling response characteristics of pulse power-MLCC in high-impact and high-voltage composite environments, a split Hopkinson pressure bar (SHPB) testing system was used to simulate high impact. The mechanical and electrical parameters of pulse power-MLCC were collected under high-impact and voltage environments, and the capacitance changes at different impact velocities were obtained. The stress wave transmission characteristics of pulse power-MLCC were studied by combining numerical simulation and theoretical analysis, and the structural deformation of ceramic dielectric under impact stress was analyzed. The relationship between the capacitance and DC bias of the capacitor was analyzed. A capacitance calculation model for pulse power-MLCC in an electromechanical coupling environment was established, revealing the electromechanical coupling mechanism of pulse power-MLCC.