Similar Impact Conditions Research Articles

INFLUENCE OF BUBBLE GROWTH AND LIQUID FILM INSTABILITIES ON DROPLET IMPACT PHENOMENA UNDER SATURATED BOILING REGIMES

Evaporation and boiling are processes that occur in many industrial applications involving multiphase flows. For liquid films, however, studies are scarce regarding heat and mass transfer mechanisms and require further research. The main objective of this work is to evaluate bubble formation and detachment, followed by the impact phenomena. Therefore, an experimental setup was built and adapted for this purpose. A borosilicate glass impact surface is placed over a heat source, which consists of an aluminum block with four embedded cartridge heaters that heat the liquid film by conduction. Water and n-heptane are the fluids adopted for the experimental study, as the differences in thermophysical properties allow for a wider range of experiments. Study cases include dimensionless temperatures of θ > 0.6 for similar impact conditions. In terms of bubble formation, n-heptane displays smaller bubble diameters and higher release rates, whereas water exhibits larger bubbles and lower rates. Qualitatively, liquid film temperatures close to the saturation temperature do not reveal a direct influence on the crown development and posterior secondary atomization. For later stages of the impact, the central jet height and breakup are influenced by the film temperature, which is associated with the variation of thermophysical properties.

Interfacial dynamics of viscous droplets impacting a superhydrophobic candle soot surface: Overview and comparison

The impact of droplets on textured or rough surfaces has garnered remarkable appreciation due to its multifarious applications such as self-cleaning, anti-icing, and anti-fouling, leading to a plethora of engineered superhydrophobic surfaces (SHPs) exhibiting different interfacial dynamics during impact. However, the prime limiting factors in using these surfaces abundantly arise from their long fabrication time and concurrent high cost. Here, we propose using carbon soot nanoparticle (CSNPs) coated fractal superhydrophobic surfaces prepared from flame deposition as an alternative to overcome the limitations. We establish our claim by exploring the dynamic wetting behavior of the soot-coated surface in terms of key droplet impact parameters such as rebounding, contact time, impalement transition, and splashing dynamics. A systematic investigation is undertaken by considering a vast range of viscosity and impact conditions. One of the significant observations is the absence of the partial rebound regime during the impact of water droplets on the CSNPs surface, unlike most of the existing superhydrophobic surfaces under similar impact conditions. Furthermore, the surface promotes droplet splashing for moderately viscous solutions at high impact velocities, also characterized by unified scaling laws based on different non-dimensional numbers. Finally, a regime map is proposed to elucidate the complete dynamic wetting characteristics of these CSNPs' surfaces for viscous fluids, which further reflects competitive and equal, if not superior, wetting behavior compared to a series of existing non-wetting surfaces. The results are expected to promote CSNPs based surfaces in applications such as self-cleaning, oil-water separation, and thermal management.

Jetting during oblique impacts of spherical impactors

During the early stages of an impact a small amount material may be jetted and ejected at speeds exceeding the impact velocity. Jetting is an important process for producing melt during relatively low velocity impacts. How impact angle affects the jetting process has yet to be fully understood. Here, we simulate jetting during oblique impacts using the iSALE shock physics code. Assuming both the target and impactor have the same composition (dunite), we examine the jetted material which exceeds the impact velocity. Our results show that oblique impacts always produce more jetted ejecta than vertical impacts, except for grazing impacts with impact angles <15°. A 45°impact with an impact velocity of 3 km/s produces jetted material equal to ∼7% of the impactor mass. This is 6 times the jetted mass produced by a vertical impact with similar impact conditions. We also find that the origin of jetted ejecta depends on impact angle; for impact angles less than 45°, most of the jet is composed of impactor material, while at higher impact angles the jet is dominated by target material. Our findings are consistent with previous experimental work. In all cases, jetted materials are preferentially distributed downrange of the impactor.

Miscibility and wettability: how interfacial tension influences droplet impact onto thin wall films

Abstract

Water entry impact dynamics of diving birds

Some seabirds (such as northern gannets and brown boobies) can dive from heights as high as 30 m reaching speeds of up to 24 m s−1 as they impact the water surface. The physical geometry of plunge diving birds, particularly of the beak, allows them to limit high impact forces compared to non-diving birds. Numerically simulated data for one species (northern gannet) provides some insight into the impact forces experienced during diving, however, no reliable experimental data with real bird geometries exist for comparison purposes. This study utilizes eleven 3D printed diving bird models of three types of birds: plunge-diving (five), surface-diving (five) and dipper (one), with embedded accelerometers to measure water-entry impact accelerations for impact velocities ranging between 4.4–23.2 m s−1. Impact forces for all bird types are found to be comparable under similar impact conditions and well within the safe zone characterized by neck strength as found in recent studies. However, the time that each bird requires to reach maximum impact acceleration from impact is different based on its beak and head shape and so is its effect, represented here by its derivative (i.e. jerk). We show that surface diving birds have high non-dimensional jerk, which exceed a safe limit estimated from human impact analysis, whereas those by plunge divers do not.

Experimental study on the high-speed impact of a sand particle on Ti–6Al–4V

When sand is ingested by a helicopter engine, it collides with the compressor blades at a high relative speed, causing severe erosion damage. A test was conducted on the high-speed impact of sand particles on the target of Ti–6Al–4 V alloy to enhance the understanding of high-speed impact damage mechanism. The test apparatus was used to create supersonic airflow, which was produced by normal temperature air flowing through a special Laval nozzle. The supersonic airflow produced the drag force to increase the velocity of sand particles up to about 400 m/s. The experiment demonstrated that fractured sand particle caused less damage than nonfractured particle under similar impact conditions. The nonfractured particle directly cut the target more easily than the fractured at a relatively low impact velocity. When the impact speed exceeded 300 m/s, the crater depth increased exponentially with the increase of velocity. Impact angle determined the mode of material failure.

Highly Flexible Mechanical Energy Harvester Based on Nylon 11 Ferroelectric Nanocomposites

We report here a flexible piezoelectric energy harvester using castor-oil-derived nylon 11 and biomass-derived cellulose nanocrystals (CNC). Using a simple solution casting process, we were able to fabricate flexible large area nylon 11 and composite films. Neat nylon 11 films crystallized predominantly in the α- phase. Incorporation of CNC at a low concentration of 2–5 wt % resulted in almost complete transition of α-phase to polar γ-phase, which could be attributed to strong hydrogen bonding interactions between CNC and amide groups in nylon 11. This remarkable shift in crystallization behavior also led to enhanced piezoelectric performance. We also found that the addition of 5 wt % glycerol (on the dry weight of nylon 11 or composite) enhanced the flexibility of the film. Energy harvesting devices made from 5 wt % nylon 11/CNC films showed about 2.6 times higher output voltage as compared to neat nylon 11 devices under similar impact conditions, and the effect was durable over 800 cycles. These devices were also used to charge a 10 μF polarized capacitor, and we found that the 5 wt % nylon 11/CNC devices charged up to 3.78 V in 90 s, which is 2.8 times higher than nylon 11 devices. To the best of our knowledge, this is the first report on nylon 11 nanocomposites, where cellulose nanocrystals have been used to enhance the electroactive γ phase in nylon 11 and yield such high piezoelectric performance.

An experimental and computational study of high speed two-particle impacts of Ag nanoparticles

The laser ablation of the microparticle aerosol process utilizes high velocity (∼1000 m/s) impact of nanoparticles to produce thick films. Transmission electron microscopy was used to study the final morphologies of several particle-to-particle impact events in an effort to understand the film's microstructure and morphology that develop following high-speed impact. A range of particle morphologies and defect structures were observed, even under nominally similar impact conditions. In some instances, grain boundaries were observed within the impacted particles, whereas in other cases, the impacted particles were free of grain boundaries (i.e., epitaxial deposition). To understand the reasons for these ranges in grain morphologies, molecular dynamics simulations were conducted using conditions that were similar to typical experimental conditions. The simulations revealed that the final states of the impacted particles are not only sensitive to impact velocity but that particle crystallographic orientations also strongly influence the final states. The implications of these findings on the ability to control film microstructures are discussed.

Experimental investigation of non-Newtonian droplet collisions: the role of extensional viscosity

We investigate the collision behaviour of a shear thinning non-Newtonian fluid xanthan, by binary droplet collision experiments. Droplet collisions of non-Newtonian fluids are more complex than their Newtonian counterpart as the viscosity no longer remains constant during the collision process. Despite the complex collision dynamics, we are able to present a complete regime map based on non-dimensional Weber (We) number and impact parameter (B). We compare the collision outcomes of xanthan, glycerol and a milk concentrate at similar impact conditions. These experiments reveal very rich and complex collision morphologies for shear thinning xanthan solution, strikingly different from Newtonian droplet collisions. Unlike glycerol and milk, xanthan collisions show no reflexive separation even at very high We number. Instead of breakup, we observe disc-like shapes with an oscillating behaviour of the colliding droplets. A detailed analysis reveals that this outcome is related to increased viscous energy dissipation and extensional effects.

Oblique impact cratering experiments in brittle targets: Implications for elliptical craters on the Moon

Most impact craters observed on planetary bodies are the results of oblique impacts of meteoroids. To date, however, there have only been very few laboratory oblique impact experiments for analogue targets relevant to the surfaces of extraterrestrial bodies. In particular, there is a lack of laboratory oblique impact experiments into brittle targets with a material strength on the order of 1MPa, with the exception of ice. A strength on the order of 1MPa is considered to be the corresponding material strength for the formation of craters in the 100m size range on the Moon. Impact craters are elliptical if the meteoroid's trajectory is below a certain threshold angle of incidence, and it is known that the threshold angle depends largely on the material strength. Therefore, we examined the threshold angle required to produce elliptical craters in laboratory impact experiments into brittle targets. This work aims to constrain current interpretations of lunar elliptical craters and pit craters with sizes below a hundred meters. We produced mortar targets with compressive strength of 3.2MPa. A spherical nylon projectile (diameter 7.14mm) was shot into the target surface at a nominal velocity of 2.3km/s, with an impact angle of 5°‐90° from horizontal. The threshold angle of this experiment ranges from 15° to 20°. We confirmed that our experimental data agree with previous empirical equations in terms of the cratering efficiency and the threshold impact angle. In addition, in order to simulate the relatively large lunar pit craters related to underground cavities, we conducted a second series of experiments under similar impact conditions using targets with an underground rectangular cavity. Size and outline of craters that created a hole are similar to those of craters without a hole. Moreover, when observed from an oblique angle, a crater with a hole has a topography that resembles the lunar pit craters. The relation between the impact velocity of meteoroids on the Moon and the probability of elliptical crater formation was investigated based on our experimental results and an existing empirical equation. The results suggest a distinct possibility that most craters in the 100m size range on the Moon, given their elliptical shape, originated as secondary craters.

An experimental study for impact of a drop onto a particle in mid-air: The influence of particle wettability

Drop impact onto a particle in mid-air is a fundamental physical phenomena relevant to many applications involving a fluidized bed, for example, refining of heavy oil or coating of drug particles for pharmaceutical industry. A literature analysis shows that previous studies were focused on collisions of drops with static particles of either spherical or non-spherical shapes. This paper reports on experiments conducted at similar impact conditions with water drops and particles made of hydrophobic (polystyrene) and hydrophilic (soda-lime glass) materials. It was observed that at similar Weber numbers, wettability of the particle plays a key role in transition between collision outcomes with formation of a liquid lamella and ligaments. Present investigation is one of the first which reveals quantitative aspects for dynamics of the lamella and liquid ligaments in a particular case of mid-air collisions.

Survivability and reactivity of glycine and alanine in early oceans: effects of meteorite impacts.

Prebiotic oceans might have contained abundant amino acids, and were subjected to meteorite impacts, especially during the late heavy bombardment. It is so far unknown how meteorite impacts affected amino acids in the early oceans. Impact experiments were performed under the conditions where glycine was synthesized from carbon, ammonia, and water, using aqueous solutions containing (13)C-labeled glycine and alanine. Selected amino acids and amines in samples were analyzed with liquid chromatography-mass spectrometry (LC/MS). In particular, the (13)C-labeled reaction products were analyzed to distinguish between run products and contaminants. The results revealed that both amino acids survived partially in the early ocean through meteorite impacts, that part of glycine changed into alanine, and that large amounts of methylamine and ethylamine were formed. Fast decarboxylation was confirmed to occur during such impact processes. Furthermore, the formation of n-butylamine, detected only in the samples recovered from the solutions with additional nitrogen and carbon sources of ammonia and benzene, suggests that chemical reactions to form new biomolecules can proceed through marine impacts. Methylamine and ethylamine from glycine and alanine increased considerably in the presence of hematite rather than olivine under similar impact conditions. These results also suggest that amino acids present in early oceans can contribute further to impact-induced reactions, implying that impact energy plays a potential role in the prebiotic formation of various biomolecules, although the reactions are complicated and depend upon the chemical environments as well.

A similitude approach towards the understanding of low velocity impact characteristics of bi-layered hybrid composite structures

This article discusses the impact behavioral responses of opaque bi-layered metal bonded hybrid composites from geometrically equivalent transparent plastic specimens. Low velocity drop weight impact experiments were conducted on bi-material laminated plates made of brittle acrylic sheet adhesively bonded with ductile polycarbonate layer by a compatible room temperature cure epoxy. Depending on the nature of impact face (brittle or ductile) battered by the impactor, the induced impact damage are characterized either as partial or complete interface failure that leads to formation of radial cracks or spalling fracture in the acrylic layer. The influence of relative constituent thickness towards impact damage resistance and the resultant structural integrity are extensively discussed. The obtained results from similitude study made it possible to understand the behavior of geometrically equivalent bi-layered fibre metal laminates under similar impact conditions. In addition through numerical simulations, the energy dissipated via plastic work by the ductile layers was found to be dominant and the only source that create significant difference in energy absorption between hard and soft side impact samples.

Scaling of sub-surface deformation in hypervelocity impact experiments on porous sandstone

Two hypervelocity impact experiments into dry sandstone (Seeberger Sandstein, ~23% porosity), performed under similar impact conditions but with different projectile sizes, have been analyzed to investigate the size scaling of impact damage. For one experiment a 2.5mm steel projectile was impacted at 4.8kms−1 onto a sandstone cube of 20cm side length. For the other experiment a 10mm iron meteorite projectile was impacted at 4.6kms−1 onto a sandstone cube of 50cm side length. The resulting kinetic impact energies of 773 and 42,627J led to crater cavities of 7600 and 612,000mm3. Investigation of thin sections along cross-sections through both craters revealed that the same deformation microstructures are present in both experiments. The occurrence of different microstructural patterns was mapped and zones of characteristic deformation were defined. This mapping was used to calculate the volumes of material deformed by specific mechanisms. Comparing the results, normalized to the size of the projectile, showed that the sub-surface damage is very similar in size, volume and geometry for both experiments. Analysis of deformation bands found in both experiments regarding their long axes orientation showed that these features are developed under shear deformation. Particle size distributions (PSD), expressed as power-law fits, were measured to quantify the impact damage. Comparison showed that the decay of the power-law exponents with increasing distance from the impact point source is similar for both experiments. Reconstruction of the loading path allowed to infer the stresses under which distinct deformation microstructures are developed.

Penetration and cratering experiments of graphite by 0.5-mm diameter steel spheres at various impact velocities

Cratering experiments have been conducted with 0.5-mm diameter AISI 52100 steel spherical projectiles and 30-mm diameter, 15-mm long graphite targets. The latter were made of a commercial grade of polycrystalline and porous graphite named EDM3 whose behavior is known as macroscopically isotropic. A two-stage light-gas gun launched the steel projectiles at velocities between 1.1 and 4.5 km s−1. In most cases, post-mortem tomographies revealed that the projectile was trapped, fragmented or not, inside the target. It showed that the apparent crater size and depth increase with the impact velocity. This is also the case of the crater volume which appears to follow a power law significantly different from those constructed in previous works for similar impact conditions and materials. Meanwhile, the projectile depth of penetration starts to decrease at velocities beyond 2.2 km s−1. This is firstly because of its plastic deformation and then, beyond 3.2 km s−1, because of its fragmentation. In addition to these three regimes of penetration behavior already described by a few authors, we suggest a fourth regime in which the projectile melting plays a significant role at velocities above 4.1 km s−1. A discussion of these four regimes is provided and indicates that each phenomenon may account for the local evolution of the depth of penetration.

Mechanistic aspects of impact initiated reactions in explosively consolidated metal+aluminum powder mixtures

The mechanisms influencing impact initiation of reactions in structural energetic materials formed by explosive compaction of pure Ni, Ta, or W powders mixed with Al powder are investigated in this work. High speed images of rod-on-anvil impact tests indicate that the energy requirements for initiating reaction in Ta+Al compacts are lower than those in W+Al, while no reaction at all is observed in Ni+Al under the tested conditions. Mesoscale simulations performed on actual microstructures reveal differences in the deformation behavior of the Ni+Al, Ta+Al, and W+Al compacts under similar impact conditions. In the Ni+Al and W+Al systems, the impact induced deformation is localized primarily in the Al constituent, while significant plastic deformation of both constituents is observed in Ta+Al, making it a more reactive system.

Lunar-forming impacts: High-resolution SPH and AMR-CTH simulations

We present results of the highest-resolution simulations to date of potential Moon-forming impacts using a Lagrangian, particle-based method (smooth particle hydrodynamics, or SPH) and an Eulerian, grid-based method with adaptive mesh refinement (AMR-CTH). We consider a few candidate impacts advocated by recent works, directly comparing simulations performed at varying resolutions and with both numerical methods and their predictions for the properties of resulting protolunar disks. For a fixed set of impact conditions, simulations with either method and with different resolutions yield very similar results for the initial impact and the first few hours of the post-impact period. The subsequent disk properties in the ∼5–20h time period can vary substantially from case-to-case, depending on the orbits of and mutual interactions between large bound clumps of ejecta that often form after the initial impact. After such clumps have completed at least one orbit (which typically requires ∼25–50h), the predicted protolunar disk mass and its angular momentum converge to within about 10% for simulations of very similar impact conditions using different resolutions or methods. The disks produced by the CTH simulations are consistently about 10% less massive than those produced by SPH simulations, due presumably to inherent differences between the codes. The two methods predict broadly similar values for the fraction of the protolunar disk that originates from the target vs. the impactor, and for the initial disk radial surface density and temperature profiles.

Computational and experimental models of the human torso for non-penetrating ballistic impact

Both computational finite element and experimental models of the human torso have been developed for ballistic impact testing. The human torso finite element model (HTFEM), including the thoracic skeletal structure and organs, was created in the finite element code LS-DYNA. The skeletal structure was assumed to be linear-elastic while all internal organs were modeled as viscoelastic. A physical human surrogate torso model (HSTM) was developed using biosimulant materials and the same anthropometry as the HTFEM. The HSTM response to impact was recorded with piezoresistive pressure sensors molded into the heart, liver and stomach and an accelerometer attached to the sternum. For experimentation, the HSTM was outfitted with National Institute of Justice (NIJ) Level I, IIa, II and IIIa soft armor vests. Twenty-six ballistic tests targeting the HSTM heart and liver were conducted with 22 caliber ammunition at a velocity of 329 m/s and 9 mm ammunition at velocities of 332, 358 and 430 m/s. The HSTM pressure response repeatability was found to vary by less than 10% for similar impact conditions. A comparison of the HSTM and HTFEM response showed similar pressure profiles and less than 35% peak pressure difference for organs near the ballistic impact point. Furthermore, the peak sternum accelerations of the HSTM and HTFEM varied by less than 10% for impacts over the sternum. These models provide comparative tools for determining the thoracic response to ballistic impact and could be used to evaluate soft body armor design and efficacy, determine thoracic injury mechanisms and assist with injury prevention.

Regimes of drop morphology in oblique impact on deep fluids

Oblique impact of single drops on deep fluids at various impact angles , in the rear part of the impact crater. The spreading patterns of the drop fluid are visualized with dyed drop fluid once it has come to rest after impact. In many cases, patterns of high complexity and strong sensitivity to the impact conditions can be seen which are very reproducible for similar impact conditions. The mechanisms underlying capillary wave or lamella formation and the partial immersions of drop fluid are discussed and their relevance for pattern formation is taken into account.

Compatibility between passenger vehicles and road barriers during oblique collisions

In the European and US testing procedures for road barriers, vehicles are specified for the tests essentially by their mass properties. However, vehicles with similar mass can behave quite differently during a crash event. For the specific crash situation with the roadside restraint systems, e.g. W-beam guardrail, cable barriers, etc., the vehicle structure has to be compatible with the road restraint systems in geometry and crash stiffness to ensure safe operation during the interactions of vehicles and road barriers. The goal of this paper is to make a parametric investigation for the geometric compatibility between the compact passenger vehicles and the road barriers. The Finite Element model Ford Festiva and a weak-post W-beam guardrail were used for analyzing the oblique impact situation with a high impact speed and a small angle. For this specific situation the dynamic responses of the vehicle and the guardrail during impacts were investigated to study their structural interactions. The simulation results of the modified vehicle model and guardrail model were reasonable in comparison with the crash test data under the similar impact conditions.