Crater Depth Research Articles

Film cooling effectiveness enhancement on wall surface with crater hole and SDBD plasma actuation

At three blowing ratios ( M = 0.5, 1, and 1.5), film cooling effectiveness on plain wall surface with designed contoured crater cooling hole was numerically investigated. With variable crater depth (0.4 D≤ d≤2.7 D) and crater expansion angle (18°–30°), the optimal crater hole was determined and then combined with SDBD plasma actuation further. Effects of SDBD plasma actuation frequency (0≤ Dθ≤11.25) and actuation strength (0≤ Ds≤100) were analyzed, and the cases of the conventional cylindrical holes (i.e. baseline cases) were also conducted for comparison. The results showed that the wall film cooling effectiveness gradually rises with increased crater depth and remains stable with crater depth up to 2.3 D. Compared to the baseline case, the laterally averaged wall film cooling effectiveness of the contoured crater hole of d = 2.3 D is increased by over 55%, 500%, and 700% near the hole ( X/ D<3), and nearly 45%, 300%, and over 850% downstream region (3< X/ D<10) at M = 0.5, 1 and 1.5 respectively. Increasing the crater expansion angle also improves the wall film cooling effectiveness by expanding the coolant coverage area and strengthening the coolant attachment onto the wall. Compared with the baseline case, the overall laterally averaged wall film cooling effectiveness is improved by nearly 450% for the crater hole with a 30° outward expansion angle at M = 1. As SDBD plasma actuation frequency and intensity increase, the wall film cooling effectiveness increases and remains stable at Dθ = 6.25 and Ds = 60. The benefits of the contoured crater hole configuration and plasma actuation mainly result from the generation of anti-kidney vortex pair, which can effectively suppress the development of the existing kidney vortex pair and restrain the coolant rising. Compared with the baseline case, the optimized contoured crater hole combined with the plasma actuation at Dθ = 6.25 and Ds = 60 increases the laterally averaged wall film cooling effectiveness by nearly 1200% near the hole ( X/ D<3), and over 600% in the downstream region ( X/ D>3) at M =1.

Determination of relative sensitivity factor, sputtering rate, and detection limits of deuterium in deuterium ion‐implanted Zircaloy‐4 using secondary ion mass spectrometer

Zirconium‐based alloys are extensively used in the nuclear industry as materials for reactor core components. These alloys are used in fuel cladding and pressure tubes with 1H2O or 2H2O as the primary heat exchange fluid. Continuous usage of pressure tubes and fuel cladding inside the reactor results in heavy ingress of hydrogen (1H) or deuterium (2H), which gives rise to the formation of hydrogen (or deuterium) precipitates in the host of zirconium matrix. This is called hydrogen (or deuterium) embrittlement phenomenon. Therefore, determination of hydrogen or deuterium concentration periodically in zirconium alloy pressure tubes and cladding are crucial for safe operation of nuclear reactors. Hence, in this work, secondary ion mass spectrometry (SIMS) has been utilized to determine the relative sensitive factor (RSF), sputtering rate, and detection limits of 2H in 2H+ ion‐implanted Zircaloy‐4 sample. SIMS analysis has been carried out using O2+ and Cs+ primary ion beams. Depth profiles of various elemental and molecular secondary ions have been monitored to determine the RSF values and detection limits of 2H in the sample under different primary ion beam analysis conditions. Sputtering rate under different analysis conditions has also been determined from the correlation between the projected range of 2H+ ions in Zircaloy‐4 sample determined from Stopping and Range of Ions in Matter (SRIM) software and the depth of the crater formed by primary ion beam bombardment process. The projected range of 2H+ ions in Zircaloy‐4 was estimated to be ~524.2 nm using the simulation carried out by SRIM software. The projected range, evaluated by SRIM software, was utilized for depth scale calibration of SIMS sputtered time profiles. The SIMS depth profiles were also calibrated by determining the depth of the SIMS crater by using optical depth profilometer. The values of range estimated by SRIM as well as optical profilometer were found to be in good agreement, within instrument uncertainty.

LIBS Protocol for the Assessment of Depth Profile, Homogeneity, and Quantification of Fe/Co - based Bilayer Ribbon

The present work explores the applicability of a single spectroscopic technique, Laser-induced breakdown spectroscopy (LIBS), for the rapid quality assessment and quantification of individual layers of an amorphous bilayer ribbon (thickness ~ 35 μm). This kind of materials (ribbon) offer a convolution of the two sets of unique properties of individual layer, in a single ribbon, in contrast to the layered systems prepared by thin film technologies, and are useful and applicable for sensing and actuating in different experimental conditions. The sample was prepared by rapid quenching using the modified double-nozzle technique. One side of the ribbon is a layer of iron (Fe) - silicon (Si) - boron (B) and other side of the ribbon consists of cobalt (Co) - silicon (Si) - boron (B). Owing to its versatility and advantages, LIBS has been used for assessing the elemental distribution on the surface of the investigated matrices and across the layer interface. After optimizing the experimental parameters, the LIBS measurements have been performed using a Q-switched Nd:YAG laser working at its second harmonic wavelength (532 nm) with the 30 mJ/pulse energy under ambient air and atmospheric pressure conditions. Following the LIBS spectral analysis, a chemometric approach, principal component analysis (PCA), has been used for the visualization of the spectra from the two layers and to observe dominant spectral lines responsible for the discrimination of both layers. The depth profile analysis of the layers has been carried out using LIBS and the number of pulses corresponding to the individual layers have been correlated with the depth of the ablation craters obtained using the 3D-optical profilometry in order to estimate the thickness of the individual layers and the ablation rates. Furthermore, the homogeneity of the sample has been examined by measuring the intensity of selected spectral lines corresponding to the composition of the sample. Calibration-free (CF) - LIBS analysis has been performed for the compositional quantification of both layers of the sample and found in a good agreement with the production ratio. This work paves the way towards the investigation and control of the properties of such intelligent materials.

Experimental study of the oblique impact and ricochet characteristics of cylindrical fragments

When the casing charge exploded near or inside a steel installation such as a ship or plant, part of the fragments would impact the target plate and ricochet. Plastic deformation occurs on both the fragment and target plate during the oblique impact, in which the direction and velocity of fragments change. The ricochet of fragments would change the damage range, which cannot be predicted by previous theories. In our experiment, cylindrical fragments were used to impact target plates under different impact velocities and angles, and the target plates are made of marine steel 921A and commonly used Q345B, which are the two most commonly used steels for ships and steel installations. The empirical formulae of ricochet velocity and angle for two target plates were obtained, which were applicable to the positive ricochet. The ricochet velocity increased with the increase in impact velocity and angle, but the ricochet angle only increased with the increase in impact angle. In addition, the ricochet velocity increased with the increase in the hardness of target plate when the impact angle was less than 40° due to the deformation of the target plate, the ricochet angle increased with the increase in the hardness of target plate since the pile-up effect would increase the deflection, causing the ricochet angle decreased. The fragment mass loss model was obtained based on the experimental data, which is a strong function of impact velocity but a weak function of impact angle. With the increase in impact angle, the plastic deformation of fragments gradually decreased, the target plate changed from plastic compression deformation to shear deformation, the deformation energy of target plate changed from volumetric energy to more shear strain energy, and the impact crater became shallower. With the increase in impact velocity, the plastic deformation of fragments increased, the inertial resistance of target plate increased, the impact crater on the target surface became larger and deeper, and then only the depth of impact crater increased when the impact velocity reached a certain extent. The plastic deformation of target plate decreased with the increase in the hardness. The proposed formulae and model can provide guidance for the fragment damage range evaluation and equipment protection.

Benchmarking iSALE and CTH Shock Physics Codes to In Situ High‐Velocity Impact Experiments Into Fe‐Ni Targets

AbstractCratering is a prominent evolutionary process on asteroids. Crater morphologies, regolith generation, bulk fracturing and projectile implantation are all examples of asteroidal surface evolution resulting from impact processes. The characterization of these processes on metal‐rich bodies has become a priority due to the upcoming NASA Psyche mission, poised to study the likely metal‐rich 225‐km main belt asteroid, (16) Psyche. Small‐scale impact experiments into metals (e.g., iron, aluminum, copper, steel) have shown that crater morphologies into these materials are different than rocky targets—exhibiting notable distinctive features such as raised, sharp rims, and deeper cavities. In this work, we determine strength constants for different metals used in prior impact experiments, namely manufactured Fe‐Ni materials and the Gibeon iron meteorite at 77 K. These parameters have been used as inputs for the Johnson and Cook (1983) strength model in a suite of numerical simulations reproducing impact experiments. Using the Johnson and Cook strength model and our laboratory‐derived material constants, we find that it is possible to closely match small‐scale experimental crater diameters and depths using iSALE and CTH shock physics codes.

Seismic Reflection Data Reveal the 3D Subsurface Structure of Pit Craters

AbstractPit craters are quasi‐circular depressions observed on rocky and icy planetary bodies, as well as numerous asteroids. Pit craters are thought to form by overburden collapse into a subsurface cavity or volumetrically depleted zone. Importantly, the surface size and distribution of pit craters may provide an important record of otherwise inaccessible subsurface processes. However, because we cannot access the subsurface of many planetary bodies, we rely on physical and numerical models to infer processes linked to pit crater formation. Here, we use 3D seismic reflection data to quantify the palaeosurface and subsurface geometry of 59 Late Jurassic pit craters buried to depths of ∼3 km within a sedimentary basin, offshore NW Australia. The pit craters are typically funnel‐like, with an inverted conical upper section underlain by a pipe. Pit crater depths, that is, the height of inverted cone sections, correlate with their plan‐view length, consistent with observations of pit craters elsewhere; this trend is rendered less apparent by later sediment‐infilling. For the first time, we show some pit crater pipes connect to underlying igneous dikes or steeply dipping, likely dilatational portions of normal faults. Although some pit craters seemed to have formed due to faulting and others to dyking, they cannot be differentiated based on their surface expression. Our data also suggest pit crater size may not relate to the mechanical properties of the host material. Overall, we conclude that the surface expression of pit craters on Earth and other planetary bodies may not be diagnostic of subsurface processes or properties.

Analysis of Particle Size and Concentration in Die Sinking Electric Discharge Machining.

Electric discharge machining with a powder mix dielectric is a promising technique to harden a work piece’s surface using electricity with a high energy density. The quality of the electrical discharge-machined surface is related to its surface integrity in which the surface’s roughness, residual stresses, micro hardness and surface micro cracks are some of the major factors. In this research, graphite powder was mixed in a dielectric with a particle size of 20 µm, 30 µm, and 40 µm, with the concentration of the graphite powder ranging from 2 g/L to 4 g/L. Moreover, the peak current and pulse time on were also coupled with an additive of graphite powder to investigate the effect on the surface quality, i.e., the recast layer thickness, micro hardness and crater depth as well as the material removal rate (MRR) and tool wear rate (TWR). A Box–Behnken design was employed to design the experiments and the experimental results revealed that the graphite powder size and concentration coupled with the electrical parameters (peak current and pulse time on) significantly influenced the recast layer thickness, micro hardness, crater size, MRR and TWR. The crater depth and micro hardness were maximized at a higher concentration and particle size, while the recast layer thickness was reduced with a higher gain size.

An in-depth investigation into high fluence femtosecond laser percussion drilling of titanium alloy

High fluence femtosecond laser percussion drilling has a potential to produce micro holes for cooling purpose in turbine blades made of titanium alloys due to its short interaction time with the material. For an in-depth investigation, numerical simulation is carried out using 2D axi-symmetric two-temperature and heat conduction models in tandem, mimicking the laser percussion drilling. Moving mesh approach in finite element based COMSOL Multiphysics software is used to arrive at the crater geometry during the ablation process. The heat conduction model provides the value of surface temperature after each pulse. Taking temperature-dependent thermo-physical and optical properties with intraband absorption effect, the simulations are carried out on a 2 mm thick Ti6Al4V plate for 1–15 pulses with fluence in the range of 0.84 to 8.4 J cm−2. For comparison, the simulation results based on room temperature properties are also included. Validation experiments are carried out and the crater morphology is measured using laser scanning confocal microscope. The overall average absolute deviations of the results for crater diameter and depth are within 20% and 40% respectively. The proposed simulation approach is robust and can be used to investigate multi pulses laser ablation process in any other applications.

Formation of the Figge Maar Seafloor Crater During the 1964 B1 Blowout in the German North Sea

In 1964, exploration drilling in the German Sector of the North Sea hit a gas pocket at ∼2900 m depth below the seafloor and triggered a blowout, which formed a 550 m-wide and up to 38 m deep seafloor crater now known as Figge Maar. Although seafloor craters formed by fluid flow are very common structures, little is known about their formation dynamics. Here, we present 2D reflection seismic, sediment echosounder, and multibeam echosounder data from three geoscientific surveys of the Figge Maar blowout crater, which are used to reconstruct its formation. Reflection seismic data support a scenario in which overpressured gas ascended first through the lower part of the borehole and then migrated along steeply inclined strata and faults towards the seafloor. The focused discharge of gas at the seafloor removed up to 4.8 Mt of sediments in the following weeks of vigorous venting. Eyewitness accounts document that the initial phase of crater formation was characterized by the eruptive expulsion of fluids and sediments cutting deep into the substrate. This was followed by a prolonged phase of sediment fluidization and redistribution widening the crater. After fluid discharge ceased, the Figge Maar acted as a sediment trap reducing the crater depth to ∼12 m relative to the surrounding seafloor in 2018, which corresponds to an average sedimentation rate of ∼22,000 m3/yr between 1995 and 2018. Hydroacoustic and geochemical data indicate that the Figge Maar nowadays emits primarily biogenic methane, predominantly during low tide. The formation of Figge Maar illustrates hazards related to the formation of secondary fluid pathways, which can bypass safety measures at the wellhead and are thus difficult to control.

Morphometric Analysis of Scoria Cones to Define the ‘Volcano-Type’ of the Campo de Calatrava Volcanic Region (Central Spain)

The Campo de Calatrava Volcanic Region is the largest volcanic field in the Iberian Peninsula and presents a complex volcanic history, with more than 360 monogenetic basaltic volcanoes developed in effusive, Strombolian, and hydromagmatic eruptions. The large number of scoria cones, compared to the other existing types of volcanic morphologies, indicates that these landforms represent the most common eruptive events that occurred during Calatrava’s geological past. In this work, a morphometric analysis of the scoria cones was carried out, based on statistical analysis of the main morphological parameters of these volcanoes (height, cone width, crater width, crater depth, slope, area, etc.). The results were used to identify the most frequent scoria cone by means of statistical analysis of its main morphological features. To do this, a methodology based on statistical correlations of the morphological and morphometric parameters that best define the morphology of these volcanoes was applied. The number of cones and their distribution correspond to platform volcanic fields. The most frequent identified monogenetic volcano corresponds to a scoria cone developed in Strombolian dynamics with lava flows, with mean dimensions of 36.54 m height, 0.008113 km3 volume and an area of 0.454 km2.

Experimental study on the dynamics and parameters of nanosecond laser-induced aluminum plasma

In this paper, impulse measurement, spectral diagnostics, temporal evolution images and target ablation are employed to investigate the dynamic behaviors and parameters of Nd:YAG nanosecond laser-induced aluminum plasma at different pressures and laser fluences. The impulses and coupling coefficients generated by laser ablation increase firstly and then reduce with the decrease in pressure for the laser fluences of 17.22 J cm−2 and 20.94 J cm−2, but they only drop at 0.5 Torr for a laser fluence of 6.19 J cm−2. The fast exposure images captured by the high-speed camera and ICCD show that the plasma plumes present the separation at atmospheric pressure and expansion near vacuum, but last longer time at pressures of 150 Torr and 22 Torr. The duration and dynamic property of plasma are responsible for the impulse, as well as are mainly dependent on the characteristics of plasma parameters. Therefore, the electron density and electron temperature are obtained by Stark broadening method and Boltzmann plot, respectively. The change in the electron density is proportional to pressure and laser fluence. The variation trend of the crater depth and ablative mass with pressure is opposite to that of the electron density, which is ascribed to the plasma shielding effect caused by the inverse bremsstrahlung absorption mechanism. Besides, the electron temperature varies inversely with pressure in the detection range due to various recombination processes. This study provides an insight for clarifying the energy conversion mechanism and improving the laser propulsion performance.

Microscale Modeling of Particle Impact on Thermal Protection System Materials During High-Speed Entry

Micron-sized particles suspended in planetary atmospheres can damage thermal protection systems (TPS) during entry of space capsules into planetary bodies. TPS materials are complex heterogeneous carbon composites, where the microstructure of the composite can play a pivotal role in the propagation of damage caused by the impact. Here, we present the application of a novel computational technique called the lattice particle method to understand the initiation and growth of craters formed on TPS materials upon impact by particles. The simulations are initially compared against experiments that used borosilicate as the impacting particle and fused silica as the target surface. The simulations reproduce the damage profiles, diameters, and depths of the craters being formed on the target silica surface. A parametric study is then performed by varying the fracture strength of the target surface and the impacting particle. It is found that the profiles of the damaged region on the silica surface primarily depend on the fracture strength of the silica surface, and not the impacting particle. The simulations are extended to model the damage of porous carbon composites that are used as TPS materials. Microstructures of carbon composites are generated using an in-house code that has been shown to reproduce features of the real material in past studies. While the crater depth on the fused silica surface was within 38% irrespective of the fracture strength of the particle, the damaged depth changes by at least an order of magnitude when a carbon composite surface is used and the fracture strength of the impacting particle is varied. Finally, the influence of damage on the effective permeability is computed using the direct simulation Monte Carlo technique. The maximum increase in the permeability force for the damaged microstructures is found to be 22%, which is within the statistical variability of the material properties observed for the TPS material that is under investigation.

Ballistic impact experiments and modeling on impact cratering, deformation and damage of 2024-T4 aluminum alloy

Single-shot ballistic impact experiments are conducted on a 2024-T4 aluminum alloy (2024Al-T4) using spherical projectiles, to investigate the effects of impact velocities (∼100 to 2000 ms−1) on impact cratering, deformation and damage. High-speed photography is applied to capture the impact processes. Impact-recovered targets are characterized using optical imaging, three-dimensional laser scanning, metallography, scanning electron microscopy and electron backscatter diffraction. With increasing impact velocity, the normalized crater depth follows the Poncelet model, and the normalized crater volume, a power-law relation, over the entire impact velocity range. Meanwhile, deformation and damage mechanisms undergo changes sequentially from micro deformation banding, shear banding, macroscopic deformation twining, microcracking, to melting. Macroscopic deformation twins are observed for the first time in high stacking-fault-energy materials including Al alloys under single-shot impact. Compared to multiple-shot impact cases, equivalent single-shot impact cases with the same total impact energy show similar crater parameters, but different microstructures (shear bands, cracks and deformation twins). Numerical simulations based on the Johnson–Cook model are established for impact penetration of 2024Al-T4 alloys, and simulations with this model are consistent with the experimental observations.

Ex Vivo Exposure to Soft Biological Tissues by the 2-μm All-Fiber Ultrafast Holmium Laser System

We present the results of ex vivo exposure by an ultrafast all-fiber Holmium laser system to porcine longissimus muscle tissues. A simple Ho-doped laser system generated ultrashort pulsed radiation with less than 1 ps pulse width and a repetition rate of 20 MHz at a central wavelength of 2.06 μm. Single-spot ex vivo experiments were performed at an average power of 0.3 W and different exposure times of 5, 30 and 60 s, varying the total applied energy in the range of 1.5–18 J. Evaluation of laser radiation exposure was performed according to the depth and diameter of coagulation zones, ablation craters and thermal damage zones during the morphological study. Exposure by ultrashort pulsed radiation with an average power of 0.3 W showed destructive changes in the muscle tissue after 5 s and nucleation of an ablative crater. The maximum ablation efficiency was about 28% at the ablation depth and diameter of 180 μm and 500 μm, respectively. The continuous-wave radiation impact at the same parameters resulted only in heating of the near-muscular tissue, without ablation and coagulation traces. Exposure to tissue with an average power at 0.3 W of ultrashort pulsed radiation led, within 30 and 60 s, to similar results as caused by 0.5 W of continuous-wave radiation, although with less carbonization formation.

Ice Shell Structure of Ganymede and Callisto Based on Impact Crater Morphology

AbstractUnderstanding the thermal structure of the ice shells around Ganymede and Callisto remains a critical step in unraveling the geologic histories of the moons. The depth‐diameter (d‐D) trends of pristine craters on each surface have an inflection point in crater morphology at approximately 26 km diameter, at which point observed crater depths transition from craters deepening with increasing crater diameter to craters shallowing with increasing crater diameter. In this work, we use iSALE‐2D to simulate impact crater formation in ice shells. We test conductive thermal gradients between 5 and 15 K/km and convective ice temperatures between 240 and 260 K in a modeled ice shell to determine if these observed d‐D trends correlate to specific thermal parameters. We find that the conductive thermal gradient has a more pronounced effect than the temperature of the underlying convective ice on reproducing the d‐D trends of craters up to 100 km in diameter, and that the inflection point in the observed crater depth trend on both Ganymede and Callisto is replicated in ice shells with a conductive thermal gradient of ∼10 K/km. With this conductive thermal gradient, the conductive ice was approximately 12–14 km thick on each body at the time they accrued these unmodified craters. The similar thermal constraints for both moons suggest that there are other differences between Ganymede and Callisto responsible for their divergent evolutionary paths, such as an increased proportion of strong impurities in Callisto's ice shell.

Воздействие лазера среднего инфракрасного диапазона на ткани глаза

Purpose. To study the effect of mid-infrared laser radiation on eye tissues. Material and methods. As a laser, an experimental laser device “Laser scalpel in the middle infrared range 2-8µm for precision surgery” developed at the Vavilov State Optical Institute. The experiment was carried out at a laser radiation wavelength of 3µm, which coincides with the peak of the spectral absorption of water. The retina, choroid, and sclera of pig eyes were used as biological tissue. The effect of laser radiation on tissue was carried out in air. The impact of laser radiation on eye tissues was assessed using an EVO LS10 scanning electron microscope from Zeiss (Germany). After obtaining an image on an electron microscope using the GNU Image Manipulation Program, the depth and diameter of the crater and the width of the collateral damage were calculated. Results and discussion. When exposed to a single laser pulse with an energy of 1 MJ, a through retinal defect was observed. With continuous exposure to laser radiation on the choroid with an energy from 1 to 3 MJ, the crater depth was 128–150 microns, the crater width was 87–110 microns, the collateral damage zone was 50–71 microns. With continuous exposure to laser radiation with similar parameters on the sclera, the depth of the crater, the width of the crater and the area of collateral damage were larger. Conclusions. The depth, width of the crater, the zone of collateral damage when exposed to laser radiation are directly proportional to the time, frequency and energy of the radiation. This laser can be useful in ophthalmic surgery, in particular in vitreoretinal surgery. However, further studies are needed to optimize the parameters of laser radiation. Keywords: vitrectomy, laser vitrectomy, photovitrectomy, Er:YAG laser, mid-infrared spectrum, laser ablation, precision surgery.

Numerical analysis of oblique hypervelocity impact damage to space structural materials by ice particles in cryogenic environment

A phase-aware constitutive model is developed and integrated with the meshfree simulations to study the failure mechanisms of space structural materials under the oblique hypervelocity impact of ice. The proposed constitutive model covers material’s dynamic behavior in a wide range of temperature, pressure, and strain rates. The numerical analysis combines the Hot Optimal Transportation Meshfree method with the EigenErosion algorithm to explicitly account for large deformation, brittle and ductile failure, phase transition, and debris cloud formation in the target materials and ice projectile. Specifically, the surface erosion and crater formation in the target under different impact speeds and angles are characterized by the damage’s shapes, depth, and length. The predicted crater depths in the Al6061 targets are validated by the Cour-Palais empirical model. It is evident that the damage to the space structural material by ice particles results from the competition between fracture, plasticity, and phase transition in the materials. The impact angle and velocity determine the crater deformation and the potential thread of the ejected debris.

Soil deformation after one water-drop impact – The effect of texture and soil moisture content

The splash phenomenon (being the first stage of water erosion) is caused by the drops’ impact on the soil surface, resulting in the displacement of soil particles and the creation of a deformation – a small-sized crater. The aim of this research was to analyse the effect of the drops' impact energy, the initial moisture content, and the texture of the soils used (loamy sand, sandy loam, silty loam) on the size of the formed craters. Measurements were made using a 3D surface scanner to determine the depth and volume of craters along with the equivalent diameter and circularity of their top cross-sections. In each of the experiment variants, the impact of the drops resulted in changes on the soil surface. Moisture content was the factor with the highest influence on crater formation (increase in moisture resulted in an increase in the size of the craters). The highest circularity was observed in craters formed on silty loam, which had the largest amount of silt content among the investigated soils. Increasing the drop energy resulted in an increase in the average values of the measured quantities, but only in a few cases were these changes statistically significant. The conducted research demonstrates the utility of surface scanners in accurately measuring soil deformation after drop impact. In addition, the acquired results can support the development of erosion models, increase the knowledge regarding the splash phenomenon, and help to make further steps in linking the splash to subsequent stages of water erosion.

Experimental and Analytical Study on the Penetration Depth of Mortar Targets Subjected to Projectile Impact in the Hypervelocity Regime

A projectile may be deformed and eroded due to the high pressure generated by hypervelocity penetration, which makes it difficult to describe the penetration mechanism for protection engineering by existing theories at such high velocities. To analyze the penetration depth of concrete-like targets subjected to hypervelocity impact by kinetic energy weapons, experiments with ogive-nosed steel projectiles penetrating mortar targets are conducted, where the average uniaxial compressive strength of the mortar targets is 41.8[Formula: see text]MPa and the impact velocities range from 1[Formula: see text]225[Formula: see text]m/s to 2[Formula: see text]392[Formula: see text]m/s. The experimental results show that the crater diameter and crater depth have a linear relationship with the striking velocity. The depth of penetration (DOP) increases linearly first and then decreases sharply and increases slowly again. Three penetration regimes are observed in turn with increasing velocity, i.e. rigid projectile penetration, abrasive projectile penetration and semifluid projectile penetration. Furthermore, based on a study of the dynamic compression behavior and penetration resistance function of concrete, a hydroelastoplastic-frictional penetration model is established. The velocity range is divided into solid penetration, semifluid penetration and fluid penetration, which correspond to [Formula: see text], [Formula: see text] and [Formula: see text], respectively. Then, the rigid and abrasive projectile penetration models, which consider the projectile mass loss, are verified by the present test data. Finally, the semifluid projectile penetration model is evaluated with the existing test data. These results can provide support for research on the damage effect of hypervelocity kinetic energy weapons and the design of underground strategic protection engineering.

Methane-saturated Layers Limit the Observability of Impact Craters on Titan

Abstract As the only icy satellite with a thick atmosphere and liquids on its surface, Titan represents a unique end-member to study the impact cratering process. Unlike craters on other Saturnian satellites, Titan’s craters are preferentially located in high-elevation regions near the equator. This led to the hypothesis that the presence of liquid methane in Titan’s lowlands affects crater morphology, making it difficult to identify. This is because surfaces covered by weak fluid-saturated sediment limit the topographic expression of impact craters, as sediment moves into the crater cavity shortly after formation. Here we simulate crater-forming impacts on Titan’s surface, exploring how a methane-saturated layer overlying a methane-clathrate layer affects crater formation. Our numerical results show that impacts form smaller craters in a methane-clathrate basement than a water-ice basement due to the differences in strength. We find that the addition of a methane-saturated layer atop this basement reduces crater depths and influences crater morphology. The morphology of impact craters formed in a thin methane-saturated layer is similar to that in a “dry” target, but a thick saturated layer produces an impact structure with little to no topography. A thick methane-saturated layer (thicker than 40% of the impactor diameter) could explain the dearth of craters in the low-elevation regions on Titan.