Low-velocity Collisions Research Articles

Nonlinear dynamic response of a sandwich plate with negative Poisson’s ratio honeycomb-core layer under low-velocity collision impact

In this paper, a nonlinear analytical model is presented for the low-velocity collision impact of a sandwich plate with auxetic honeycomb-core layer. The auxetic feature of the honeycomb material is realized by mathematically expressing the effective material coefficients in terms of material property and cellular geometric parameters through a homogenization method. The higher order shear deformation theory, the von Kármán nonlinearity theory, and a modified Hertz contact law which accounts for the contact pressure distribution and indentation effect, are employed to establish the kinematic relations. The Newmark time integration scheme in conjunction with the direct iterative method is utilized to establish a solution procedure for the nonlinear dynamic governing equation. The verification of the presented model with the data in published literatures is carried out, followed by a series of numerical analyses for influences of cellular geometric features and impactor’s initial conditions (such as impactor’s initial velocity, mass, and nose curvature radius) on the nonlinear dynamic response. The results of numerical analyses show that the geometric features of the unit cell in the honeycomb-core and impactor’s initial conditions can cause significant influences on the nonlinear collision impact behaviors of the system.

Molecular dynamics simulations of head-on low-velocity collisions between particles.

The particle contact model is important for powder simulations. Although several contact models have been proposed, their validity has not yet been well established. Therefore, we perform molecular dynamics (MD) simulations to clarify the particle interaction. We simulate head-on collisions of two particles with impact velocities less than a few percent of the sound velocity to investigate the dependence of the interparticle force and the coefficient of restitution on the impact velocity and particle radius. In this study, we treat particles with a radius of 10-100nm and perform simulations with up to 0.2 billion atoms. We find that the interparticle force exhibits hysteresis between the loading and unloading phases. Larger impact velocities result in strong hysteresis and plastic deformation. For all impact velocities and particle radii, the coefficient of restitution is smaller than that given by the Johnson-Kendall-Robert theory, which is a contact model that gives the force between elastic spherical particles. A contact model of inelastic particles cannot reproduce our MD simulations. In particular, the coefficient of restitution is significantly reduced when the impact velocity exceeds a certain value. This significant energy dissipation cannot be explained even by the contact models including plastic deformation. We also find that the coefficient of restitution increases with increasing particle radius. We also find that the previous contact models including plastic deformation cannot explain the strong energy dissipation obtained in our MD simulations, although they agree with the MD results for very low impact velocities. Accordingly, we have constructed a new dissipative contact model in which the dissipative force increases with the stress generated by collisions. The new stress-dependent model successfully reproduces our MD results over a wider range of impact velocities than the conventional models do. In addition, we proposed another, simpler, dissipative contact model that can also reproduce the MD results.

Sputnik Planitia as an impactor remnant indicative of an ancient rocky mascon in an oceanless Pluto

Pluto’s surface is dominated by the huge, pear-shaped basin Sputnik Planitia. It appears to be of impact origin, but modelling has not yet explained its peculiar geometry. We propose an impact mechanism that reproduces its topographic shape while also explaining its alignment near the Pluto–Charon axis. Using three-dimensional hydrodynamic simulations to model realistic collisions, we provide a hypothesis that does not rely upon a cold, stiff crust atop a contrarily liquid ocean where a differentiated ~730 km ice–rock impactor collides at low-velocity into a subsolidus Pluto-like target. The result is a new geologic region dominated by impactor material, namely a basin that (in a 30° collision) closely reproduces the morphology of Sputnik Planitia, and a captured rocky impactor core that has penetrated the ice to accrete as a substantial, strength-supported mascon. This provides an alternative explanation for Sputnik Planitia’s equatorial alignment and illustrates a regime in which strength effects, in low-velocity collisions between trans-Neptunian objects, lead to impactor-dominated regions on the surface and at depth.

Modeling of Electrostatic and Contact Interaction between Low-Velocity Lunar Dust and Spacecraft

The accumulation of highly adhesive dust on spacecraft presents a serious issue to hinder long-term extravehicular activity and the establishment of a permanent station on lunar surface. In contrast to the immediate physical damage caused by hypervelocity (>1.0 km/s) impacts, this adhesion observed at low-velocity (0.01 to 100 m/s) collisions can more unobtrusively and mortally degenerate the performance of equipment. This paper proposes a theoretical model aimed at comprehensively analyzing the dynamics of adhesion and escape phenomena occurring during low-velocity impacts between charged dust particles and spacecrafts enveloped by a plasma sheath. The electrostatic force is modeled using the image multipole method, and contact force is calculated based on the adhesive–elastic–plastic theory. The results reveal that the implementation of a dielectric coating possessing both low permittivity and low interface energy can substantially reduce energy dissipation during collisions. However, the ultimate adhesion on the surface or escape from the sheath for low-velocity charged dust is dominated by the long-range electrostatic interaction rather than short-range contact interaction. Positively charged particles of smaller sizes demonstrate a greater propensity for surface adhesion in comparison to negatively charged particles of larger sizes. Counterintuitively, without additional dust removal techniques, modifying the properties of the dielectric coating does not effectively reduce the accumulation of dust, which can be merely accomplished by decreasing the spacecraft’s potential. The model presented in this study serves as a crucial step toward understanding the mechanism of lunar dust pollution.

Formulation of a similarity law for static and low-velocity collision experiments for beam in gravitational field

Scaled testing offers a financially viable and pragmatic methodology for ascertaining the performance attributes of full-scale civil engineering structures. While the necessity for a similarity law to guide scaled experiments is well-understood, few studies has been directed toward formulating a similarity law that comprehensively addresses both geometrical and mechanical equivalences in experiments where material properties and gravitational factors remain constant between the scaled and full-scale tests. Our prior work has introduced a similarity law tailored for scaled experiments conducted within gravitational fields, utilising materials that bear a resemblance to those used in full-scale structures; however, the scope of applicability was restricted to elastic responses. This study introduces a method for approximating the elasto-plastic displacement in full-scale beams based on data gathered from scaled tests, utilising an integrated approach that combines the principles of similarity and equal-energy laws as formulated by Veletsos et al. Validation of this innovative method was achieved through static three-point bending tests using circular cross-sectional steel beams, with tests conducted at six varying similarity ratios, ranging from 0.26 to 1.00. The empirical results demonstrated that the estimated displacement for the full-scale structure exhibited an error margin of approximately 10 %. When an impact analysis involving a steel ball was carried out on a steel cantilever beam, the residual displacement estimates were found to be significantly imprecise when plastic deformations occurred at multiple locations within the structure. In conclusion, this research contributes to foundational advancements in the field of structural modelling through the introduction of a new methodological approach.

Frequency of the dark matter subhalo collisions and bifurcation sequence arising formation of dwarf galaxies

ABSTRACT The cold dark matter model predicts galaxies have 100 times more dark matter mass than stars. Nevertheless, recent observations report the existence of dark-matter-deficient galaxies with less dark matter than expected. To solve this problem, we investigate the physical processes of galaxy formation in head-on collisions between gas-containing dark matter subhaloes (DMSHs). Analytical estimation of the collision frequency between DMSHs associated with a massive host halo indicates that collisions frequently occur within one-tenth of the virial radius of the host halo, with a collision time-scale of about $10\, \mathrm{Myr}$, and the most frequent relative velocity increases with increasing radius. Using analytical models and numerical simulations, we show the bifurcation channel of the formation of dark-matter-dominated and dark-matter-deficient galaxies. In the case of low-velocity collisions, a dark-matter-dominated galaxy is formed by the merging of two DMSHs. In the case of moderate-velocity collisions, the two DMSHs penetrate each other. However, the gas medium collides, and star formation begins as the gas density increases, forming a dwarf galaxy without dark matter at the collision surface. In the case of high-velocity collisions, shock-breakout occurs due to the shock waves generated at the collision surface reaching the gas surface, and no galaxy forms. For example, the simulation demonstrates that a pair of DMSHs with a mass of $10^9\, \mathrm{M_\odot }$ containing gas of 0.1 solar metallicity forms a dark-matter-deficient galaxy with a stellar mass of $10^7\, \mathrm{M_\odot }$ for a relative velocity of $200\, \mathrm{km\, s^{-1}}$.

Size Dependence of the Bouncing Barrier in Protoplanetary Dust Growth

Understanding the collisional behavior of dust aggregates is essential in the context of planet formation. It is known that low-velocity collisions of dust aggregates result in bouncing rather than sticking when the filling factor of colliding dust aggregates is higher than a threshold value. However, a large discrepancy between numerical and experimental results on the threshold filling factor was reported so far. In this study, we perform numerical simulations using soft-sphere discrete element methods and demonstrate that the sticking probability decreases with increasing aggregate radius. Our results suggest that the large discrepancy in the threshold filling factor may reflect the difference in the size of dust aggregates in earlier numerical simulations and laboratory experiments.

Charged Atmospheric Aerosols from Charged Saltating Dust Aggregates

Grain collisions in aeolian events, e.g., due to saltation, result in atmospheric aerosols. They may regularly be electrically charged, but individual charge balances in collisions including small grains are not easily obtained on the ground. We therefore approach this problem in terms of microgravity, which allows for the observation of collisions and the determination of small charges. In a drop tower experiment, ∼1 mm dust aggregates are traced before and after a collision within the electric field of a plate capacitor. The sum of the electric charge of two particles (total charge) before and after the collision often strongly deviates from charge conservation. Due to the average low collision velocities of 0.2 m/s, there is no large scale fragmentation. However, we do observe small charged particles emerging from collisions. The smallest of these particles are as small as the current resolution limit of the optical system, i.e., they are at least as small as tens of µm. In the given setting, these small fragments may carry 1 nC/m2–1 µC/m2 which is between 1% and ten times the surface charge density of the large aggregates. These first experiments indicate that collisions of charged aggregates regularly shed charged grains into the atmosphere, likely down to the suspendable aerosol size.

A Theory about a Hidden Evander-Size Impact and the Renewal of the Intermediate Cratered Terrain on Dione

The study introduces a theory about an Evander-size impact on the surface of Dione. Our study suspects a relatively low-velocity (≤5 km/s) collision between a ca. 50–80 km diameter object and Dione, which might have resulted in the resurfacing of one of the satellite’s intermediate cratered terrains in various ways, such as surface planing by “plowing” by ricocheting ejectiles, ejecta blanket covering, partial melting, and impact-triggered diapir formation associated with cryotectonism and effusive cryo-slurry outflows. Modeling the parameters of an impact of such a size and mapping the potential secondary crater distribution in the target location may function as the first test of plausibility to reveal the location of such a collision, which may be hidden by younger impact marks formed during, e.g., the Antenor, Dido, Romulus, and Remus collision events. The source of the impactor might have been Saturn-specific planetocentric debris, a unique impactor population suspected in the Saturnian system. Other possible candidates are asteroid(s) appearing during the outer Solar System’s heavy bombardment period, or a collision, which might have happened during the “giant impact phase” in the early Saturnian system.

Chondrule formation via impact jetting in the icy outer solar system

Impact jetting during planetesimal collisions is a process that ejects small amounts of highly shocked material during the earliest stages of an impact. Jetting can produce melted and vaporized material during relatively low velocity collisions and has previously been presented as a mechanism for producing chondrules in the inner solar system during impacts between rocky planetesimals. However, chondrules are observed in both non‑carbonaceous and carbonaceous chondrites, which are thought to have formed in the inner and outer solar system, respectively. In this work, we use the iSALE2D hydrocode to investigate the viability of jetting for producing chondrules in the outer solar system, where ice-rich bodies begin to be incorporated into the planetesimal population. We create mixed material equations of state for ice mass fractions of 10–50% intimately combined with dunite to emulate the compositions of ice-rich outer solar system planetesimals. We account for collisions between a sphere and flat target at 2–7 km/s. Our results indicate that the presence of ice lowers the total mass of chondrule forming material jetting can produce, but a significant mass of chondrules is likely to form nonetheless even through collisions of bodies with relatively high ice concentrations. For example, for collisions at 4 km/s, pure dunite bodies create ~1% the mass of a 10-km-diameter projectile of chondrules, while bodies that include 50% ice by mass produce ~0.004% the mass of an impactor of chondrules. The presence of ice results in water vapor in the jet plume which may generate an oxidizing environment that favors the production of chondrules relatively enriched in 17O and 18O due to 16O-poor composition of water ice in the outer solar system.

The influence of gravity on granular impacts

Context. Slow interactions on small body surfaces occur both naturally and through human intervention. The resettling of grains and boulders following a cratering event, as well as observations made during small body missions, can provide clues regarding the material properties and the physical evolution of a surface. In order to analyze such events, it is necessary to understand how gravity influences granular behavior. Aims. In this work, we study slow impacts into granular materials for different collision velocities and gravity levels. Our objectives are to develop a model that describes the penetration depth in terms of the dimensionless Froude number and to use this model to understand the relationship between collision behavior, collision velocity, and gravity. Methods. We used the soft-sphere discrete element method to simulate impacts into glass beads under gravitational accelerations ranging from 9.81 m s−2 to 0.001 m s−2. We quantified collision behavior using the peak acceleration, the penetration depth, and the collision duration of the projectile, and we compared the collision behavior for impacts within a Froude number range of 0–10. Results. The measured penetration depth and collision duration for low-velocity collisions are comparable when the impact parameters are scaled by the Froude number, and the presented model predicts the collision behavior well within the tested Froude number range. If the impact Froude number is low (0 < Fr < 1.5), the collision occurs in a regime that is dominated by a depth-dependent quasi-static friction force. If the impact Froude number is high enough (1.5 < Fr < 10), the collision enters a second regime that is dominated by inertial drag. Conclusions. The presented collision model can be used to constrain the properties of a granular surface material using the penetration depth measurement from a single impact event. If the projectile size, the collision velocity, the gravity level, and the final penetration depth are known and if the material density is estimated, then the internal friction angle of the material can be deduced.

The acoustic resonant drag instability with a spectrum of grain sizes

ABSTRACT We study the linear growth and non-linear saturation of the ‘acoustic Resonant Drag Instability’ (RDI) when the dust grains, which drive the instability, have a wide, continuous spectrum of different sizes. This physics is generally applicable to dusty winds driven by radiation pressure, such as occurs around red-giant stars, star-forming regions, or active galactic nuclei. Depending on the physical size of the grains compared to the wavelength of the radiation field that drives the wind, two qualitatively different regimes emerge. In the case of grains that are larger than the radiation’s wavelength – termed the constant-drift regime – the grain’s equilibrium drift velocity through the gas is approximately independent of grain size, leading to strong correlations between differently sized grains that persist well into the saturated non-linear turbulence. For grains that are smaller than the radiation’s wavelength – termed the non-constant-drift regime – the linear instability grows more slowly than the single-grain-size RDI and only the larger grains exhibit RDI-like behaviour in the saturated state. A detailed study of grain clumping and grain–grain collisions shows that outflows in the constant-drift regime may be effective sites for grain growth through collisions, with large collision rates but low collision velocities.

Granular mechanics simulations of collisions between chondritic aggregates

Context. Collisions of dust aggregates are relevant for the evolution of protoplanetary disks. Aims. While in the past interest focused on aggregates composed of monodisperse grains, here we study the collision of chondritic aggregates, in which – besides a majority of dust grains – larger chondrules are embedded. Methods. We use granular-mechanics simulations to study collisions of chondritic aggregates. Results. Low-velocity collisions lead to pancake-shaped deformations of the fused cluster accompanied by a compaction of the dust grains. Higher collision velocities fragment the aggregates. While some chondrules are almost laid bare after the collision, we find that the largest fragments typically contain chondrules; large fragments thus capture chondrules. Grain compaction is accompanied by an increase in grain – chondrule contacts and is maximum for intermediate velocities, just before aggregates start fragmenting. Conclusions. The presence of chondrules considerably influences the fragmentation behavior of dust aggregates.

Constraining the Regolith Composition of Asteroid (16) Psyche via Laboratory Visible Near-infrared Spectroscopy

Abstract (16) Psyche is the largest M-type asteroid in the main belt and the target of the NASA Discovery-class Psyche mission. Despite gaining considerable interest in the scientific community, Psyche's composition and formation remain unconstrained. Originally, Psyche was considered to be almost entirely composed of metal due to its high radar albedo and spectral similarities to iron meteorites. More recent telescopic observations suggest the additional presence of low-Fe pyroxene and exogenic carbonaceous chondrites on the asteroid's surface. To better understand the abundances of these additional materials, we investigated visible near-infrared (0.35–2.5 μm) spectral properties of three-component laboratory mixtures of metal, low-Fe pyroxene, and carbonaceous chondrite. We compared the band depths and spectral slopes of these mixtures to the telescopic spectrum of (16) Psyche to constrain material abundances. We find that the best matching mixture to Psyche consists of 82.5% metal, 7% low-Fe pyroxene, and 10.5% carbonaceous chondrite by weight, suggesting that the asteroid is less metallic than originally estimated (∼94%). The relatively high abundance of carbonaceous chondrite material estimated from our laboratory experiments implies the delivery of this exogenic material through low velocity collisions to Psyche's surface. Assuming that Psyche's surface is representative of its bulk material content, our results suggest a porosity of 35% to match recent density estimates.

Characterization of Shock Wave Damages in Explosion Welded Mo/Cu Clads

The shock wave damage during explosive welding has not been reported in a flyer Mo plate of the Mo/Cu clads. However, it would be an inevitable problem in group VI elements. This study was aimed to characterize the shock wave damage in the Mo plate, that is less brittle than a W plate, of explosive welded Mo/Cu clads. Cladding at low horizontal collision velocities leading to high collision angles was expected to enhance the shock wave damage, and the clads resulted in less elongation in bending tests. On the other hand, in the clads obtained at high horizontal collision velocities (HCVs) with low collision angles, their bending elongation increased significantly. The shock wave damage penetrated from the surface of a Mo plate to the Mo/Cu interface, and thus reducing thickness of a Mo plate of bending specimens increased bending plastic strain. The shock wave damage is associated with kinetic energy imparted to the flyer Mo plate, and thus loss of kinetic energy due to formation of an intermediate layer at the interface and reducing thickness of a flyer Mo plate would be very helpful for decrease of shock wave damage.

Low-velocity impacts into granular material: application to small-body landing

ABSTRACT With the flourishing number of small body missions that involve surface interactions, understanding the mechanics of spacecraft – surface interactions is crucial for improving our knowledge about the landing phases of space missions, for preparing spacecraft operations, and for interpreting the results of measurements made during the surface interactions. Given their regolith-covered surfaces, the process of landing on a small body can be considered as an impact at low-velocity on to a granular material in reduced-gravity. In order to study the influence of the surface material, projectile shape, and gravity on the collision dynamics, we used two experimental configurations (one for terrestrial gravity experiments and one for reduced-gravity experiments) to perform low-velocity collisions into different types of granular materials: quartz sand, and two different sizes of glass beads (1.5 and 5 mm diameter). Both a spherical and a cubic projectile (with varying impact orientation) were used. The experimental data support a drag model for the impact dynamics composed of both a hydrodynamic drag force and quasi-static resistance force. The hydrodynamic and quasi-static contributions are related to the material frictional properties, the projectile geometry, and the gravity. The transition from a quasi-static to a hydrodynamical regime is shown to occur at lower impact velocities in reduced-gravity trials than in terrestrial gravity trials, indicating that regolith has a more fluid-like behaviour in low-gravity. The reduced quasi-static regime of a granular material under low-gravity conditions leads to a reduction in the strength, resulting in a decreased resistance to penetration and larger penetration depths.

Constraining velocity-dependent self-interacting dark matter with the Milky Way’s dwarf spheroidal galaxies

ABSTRACT The observed anticorrelation between the central dark matter (DM) densities of the bright Milky Way (MW) dwarf spheroidal galaxies (dSphs) and their orbital pericentre distances poses a potential signature of self-interacting dark matter (SIDM). In this work, we investigate this possibility by analysing the range of SIDM scattering cross-section per unit mass, σ/mχ, able to explain such anticorrelation. We simulate the orbital evolution of dSphs subhaloes around the MW assuming an analytical form for the gravitational potential, adopting the proper motions from the Gaia mission and including a consistent characterization of gravitational tidal stripping. The evolution of subhalo density profiles is modelled using the gravothermal fluid formalism, where DM particle collisions induce thermal conduction that depends on σ/mχ. We find that models of dSphs, such as Carina and Fornax, reproduce the observed central DM densities with fixed σ/mχ ranging between 30 and 50 cm2 g−1, whereas other dSphs prefer larger values ranging between 70 and 100 cm2 g−1. These cross-sections correlate with the average collision velocity of DM particles within each subhalo’s core, so that systems modelled with large cross-sections have lower collision velocities. We fit the cross-section–velocity correlation with a SIDM particle model, where a DM particle of mass mχ = 53.93 ± 9.81 GeV interacts under the exchange of a light mediator of mass mϕ = 6.6 ± 0.43 MeV, with the self-interactions being described by a Yukawa potential. The outcome is a cross-section–velocity relation that explains the diverse DM profiles of MW dSph satellites and is consistent with observational constraints on larger scales.

Dissipation and adhesion in collisions between amorphous FeO nanoparticles

How dust grains aggregate into planetesimals is still an open question. It is experimentally observed that binary collisions between micron-sized dust grains result in adhesion for collisions up to ∼1 ms−1. However, aggregates at scales ∼1 mm and above have been shown to exhibit fragmentation or bouncing at relevant collision velocities, resulting in a barrier preventing the formation of larger aggregates. One key factor is the weak adhesion observed between dust particles in aggregates leading to ruptures even in low-velocity collisions. To better understand the structure and strength of the adhered interface resulting from collisions, we performed molecular-dynamics simulations of head-on collisions between amorphous FeO nanoparticles. The results demonstrate several important phenomena which indicate how bonding between aggregates might become stronger than is often observed in experiments. For nanograins, it is shown that strong attractive interactions result in a minimum relative collision speed vc determined just before impact. The values of vc for particle radii 7 nm and below are computed to be in the range 40–100 ms−1. This high collision speed is shown to result in strong bond reordering at the interface. Moreover, increasing the incident collision speed vrel is shown to increase the work of adhesion Wadh, which is correlated to substantial bond rearrangement. Specifically, for values of vrel in the range between 10–90 ms−1, the interface between adhered grains is structured very closely to perfectly coordinated FeO amorphous solid. The reported results suggest stronger bonding results from collisions between particles with unpassivated surfaces, especially when particles are small, have amorphous surface structures, or when collisions occur at higher relative speeds. These factors should generate aggregates with stronger bonds that are less easily broken in subsequent collisions, and hence might be responsible for aggregates less likely to fragment at larger length scales.

Experimental and Numerical Analysis of Hollow and Solid Reinforced Concrete Piers under Static and Impact Loadings

Collision on reinforced concrete (RC) piers by moving vessels or vehicles is a significant issue. This paper presents the static and impact behavior of RC piers with different hollow ratios. Three specimens were statically tested to obtain the load‐displacement response. Low‐velocity collision on eleven RC piers was conducted under the same velocity of 2.42 m/s. The damage process, failure mode, and force response were comprehensively analyzed. The experimental results indicate that the hollow ratio plays a significant role in the failure mode and ultimate load of RC piers under static and impact loadings. For RC piers with a hollow ratio of 0 and 0.4, the global failure dominated the damage process. However, failure of piers with a hollow ratio of 0.6 was governed by the local damage near the loading point. The static load capacities of the RC piers with a hollow ratio of 0.4 and 0.6 were 1.27% and 60.5% smaller than that of the solid pier, respectively. RC piers with a higher hollow ratio or lighter drop weight suffer smaller peak impact force. The increase of the longitudinal reinforcements leads to a promotion of the peak and mean impact force. Furthermore, the numerically predicted failure modes and impact load response show satisfactory agreement with the experimental results.

Quantifying parameters of the seat-occupant interface during simulated low speed rear-impact collisions

The influence of supplemental lumbar support on automobile seat surface pressures was measured during simulated rear impact collisions with human volunteers. Men and women (age = 25.4 ± 3.4 years; BMI = 25.2 ± 3.9; stature = 1.73 ± 0.06 m) experienced two low-velocity rear impact collisions. Simulated collisions with and without a lumbar support were conducted in random sequence. Using a pressure sensing mat that contained 2288 ferroresistive sensors, seatback pressure was recorded at a rate of 500 Hz. These data were used to compute the total seatback force, area of force concentration, and centre-of-force (CoF). Total seatback force was not significantly different from body mass for either men or women (≈1.2 × body mass). Average contact area of the occupant's back with the seatback (i.e., area of force concentration) was approximately 221.3 cm2 and 100.1 cm2 greater without supplemental lumbar support for men and women, respectively. With respect to the L4 spinal level, the CoF had a greater vertical distance without lumbar support and a greater horizontal distance with lumbar support. In conclusion, the lumbar support used in this study altered the location and distribution of seatback forces applied to the occupant's back.