Crater Shape Research Articles

Ries crater and suevite revisited—Observations and modeling Part II: Modeling

AbstractWe present the results of numerical modeling of the formation of the Ries crater utilizing the two hydrocodes SOVA and iSALE. These standard models allow us to reproduce crater shape, size, and morphology, and composition and extension of the continuous ejecta blanket. Some of these results cannot, however, be readily reconciled with observations: the impact plume above the crater consists mainly of molten and vaporized sedimentary rocks, containing very little material in comparison with the ejecta curtain; at the end of the modification stage, the crater floor is covered by a thick layer of impact melt with a total volume of 6–11 km3; the thickness of true fallback material from the plume inside the crater does not exceed a couple of meters; ejecta from all stratigraphic units of the target are transported ballistically; no separation of sedimentary and crystalline rocks—as observed between suevites and Bunte Breccia at Ries—is noted. We also present numerical results quantifying the existing geological hypotheses of Ries ejecta emplacement from an impact plume, by melt flow, or by a pyroclastic density current. The results show that none of these mechanisms is consistent with physical constraints and/or observations. Finally, we suggest a new hypothesis of suevite formation and emplacement by postimpact interaction of hot impact melt with water or volatile‐rich sedimentary rocks.

Discrete particle simulation of jet-induced cratering of a granular bed

Abstract Jet-induced catering in a granular bed is an interesting phenomenon observed in nature and in many industries. This paper presents a numerical study of this process by the combined approach of computational fluid dynamics (CFD) for gas phase and discrete element method (DEM) for solid phase. The applicability of the model is verified by comparing the numerical results with experimental measurements of crater depth and crater shape in the cratering regime of Diffusion Driven Flow. The sensitivity of numerical results to model parameters such as restitution coefficient, sliding friction coefficient and Young's modulus is also examined. Then, the effect of jet velocity is quantified, followed by a detailed analysis of flow characteristics and forces between particles, as well as between particles and fluid, to understand the underlying mechanisms. Based on the simulated results, two equations are respectively formulated to estimate the asymptotic crater depth and crater width.

Quantification of lithium in LIB electrodes with glow discharge optical emission spectroscopy (GD-OES)

Glow discharge optical emission spectroscopy (GD-OES) was applied to quantification of Li in both positive and negative electrodes. Depth profiles of Li1.03Ni0.32Co0.33Mn0.32O2 (NCM) and hard carbon based electrodes in the range of state of charge (SOC) 0–100% were measured throughout from the surface to the current collector within a few hours. The flat crater shapes, although slightly concave at the edge for NCM, suggested a good depth resolution in the profiles. The sample surfaces sputtered during the GD-OES measurement were smooth in SEM observation, suggesting that remarkable preferential sputtering of the composite materials did not occur. The Li intensities obtained from GD-OES were correlated with the Li components determined using ICP-MS for both positive and negative electrode samples. The correlation coefficients of the linear relationship were improved by considering intensity ratio of Li to the matrix element, Li/Co and Li/C for NCM and hard carbon electrodes, respectively, to correct the sputtering rate variation of samples. These results confirm that GD-OES is a potential technique for quantitative analysis of Li in the electrodes.

Influence of Mechanical Properties Relevant to Standoff Deflection of Hazardous Asteroids

The National Academy has recently produced reports on the potential hazard and mitigation strategies for near Earth objects (NEO) [1,2]. The NRC reported to Congress that nuclear explosives are the only current technology to protect the Earth from impact of large asteroids. This is mainly due to difficulties in predicting the impact with high confidence leading to a short time to impact. Thus, the velocity deflection required when they are determined to be potentially hazardous asteroids (PHA) can only be achieved with nuclear explosives. A standoff explosion, without direct contact with the Near Earth Object (NEO) is a robust option for a non-destructive push, which offers several advantages. We have investigated the efficiency of energy deposition and its dependence on porosity and strength properties of NEO. An Eulerian hydrocode (GEODYN) with an interface reconstruction algorithm, wide-range equation of states and a flexible constitutive model library was used for numerical studies. The largest difficulties in predicting deflection velocity and fragmentation of asteroids are related to uncertainty in composition and mechanical properties of NEO. To reduce this uncertainty, we performed simulations of normal impact cratering of an NEO surface and related results with observables such as the crater shapes, the critical crater diameter (necessary to remove previous craters) and the maximum crater size (necessary for asteroid break-up). The velocity distribution of the material ejected from the impact crater is also germane to the asteroid deflection problem where the ablated material provides the thrust resulting in a deflection velocity. We performed parametric studies on how porosity and strength of the asteroid would affect these results.

Crater morphology in sandstone targets: The MEMIN impact parameter study

Abstract– Hypervelocity (2.5–7.8 km s−1) impact experiments into sandstone were carried out to investigate the influence of projectile velocity and mass, target pore space saturation, target‐projectile density contrast, and target layer orientation on crater size and shape. Crater size increases with increasing projectile velocity and mass as well as with increasing target pore space saturation. Craters in water‐saturated porous targets are generally shallower and larger in volume and in diameter than craters from equivalent impacts into dry porous sandstone. Morphometric analyses of the resultant craters, 5–40 cm in diameter, reveal features that are characteristic of all of our experimental craters regardless of impact conditions (I) a large central depression within a fragile, light‐colored central part, and (II) an outer spallation zone with areas of incipient spallation. Two different mechanical processes, grain fragmentation and intergranular tensile fracturing, are recorded within these crater morphologies. Zone (I) approximates the shape of the transient crater formed by material compression, displacement, comminution, and excavation flow, whereas (II) is the result of intergranular tensile fracturing and spallation. The transient crater dimensions are reconstructed by fitting quadric parabolas to crater profiles from digital elevation models. The dimensions of this transient and of the final crater show the same trends: both increase in volume with increasing impact energy, and with increasing water saturation of the target pore space. The relative size of the transient crater (in percent of the final crater volume) decreases with increasing projectile mass and velocity, signifying a greater contribution of spallation on the final crater size when projectile mass and velocity are increased.

Automatic Detection of Lunar Elliptical Craters from Apollo Image

Impact crater is the major geomorphologic unit of the lunar surface.Its shape and distribution characteristics can provide a large amount of information about the impact history and the lunar evolution process.In this paper,based on the real shape of craters,the authors proposed an automatic extraction method of elliptical craters.The method consists of three steps: image preprocessing,edge detection and ellipse fitting.The last step uses principal component analysis(PCA) of local interesting parameters and Hough transform to derive multiple ellipses.The total accuracy based on a comparison with manually-derived result is over 76%,with the result of larger craters even in excess of 83%.Statistics of the size-frequency distributions of the craters show that,when the length of the long half axis(D) is smaller than 160 meters,the crater number N and D-3.8 has a significant linear relationship.

Geological and geophysical investigation of Kamil crater, Egypt

Abstract– We detail the Kamil crater (Egypt) structure and refine the impact scenario, based on the geological and geophysical data collected during our first expedition in February 2010. Kamil Crater is a model for terrestrial small‐scale hypervelocity impact craters. It is an exceptionally well‐preserved, simple crater with a diameter of 45 m, depth of 10 m, and rayed pattern of bright ejecta. It occurs in a simple geological context: flat, rocky desert surface, and target rocks comprising subhorizontally layered sandstones. The high depth‐to‐diameter ratio of the transient crater, its concave, yet asymmetric, bottom, and the fact that Kamil Crater is not part of a crater field confirm that it formed by the impact of a single iron mass (or a tight cluster of fragments) that fragmented upon hypervelocity impact with the ground. The circular crater shape and asymmetries in ejecta and shrapnel distributions coherently indicate a direction of incidence from the NW and an impact angle of approximately 30 to 45°. Newly identified asymmetries, including the off‐center bottom of the transient crater floor downrange, maximum overturning of target rocks along the impact direction, and lower crater rim elevation downrange, may be diagnostic of oblique impacts in well‐preserved craters. Geomagnetic data reveal no buried individual impactor masses >100 kg and suggest that the total mass of the buried shrapnel >100 g is approximately 1050–1700 kg. Based on this mass value plus that of shrapnel >10 g identified earlier on the surface during systematic search, the new estimate of the minimum projectile mass is approximately 5 t.

RF-pulsed glow discharge time-of-flight mass spectrometry for glass analysis: Investigation of the ion source design

Radiofrequency (RF) millisecond pulsed glow discharge (PGD) coupled to time-of-flight mass spectrometry (TOFMS) was investigated for direct elemental analysis of glass samples. Aiming at achieving highest elemental sensitivity, appropriate discrimination from polyatomics, and good crater shapes on glasses, a new Grimm-type GD chamber (termed from now “UNIOVI GD”, designed and constructed in our laboratory) was coupled to TOFMS, and the results compared with those obtained with the former GD design (here denominated as “GD.1”) of the initial RF-PGD-TOFMS prototype. The critical differences distinguishing the two GDs under scrutiny are the GD chamber thickness (15.5mm for the GD.1 and 7mm for the UNIOVI GD) and the “flow tube” which is inserted in the GD.1 and inexistent in UNIOVI GD.A pulse period of 4ms and a duty cycle of 50% were selected for the PGD studies. In order to characterizing the UNIOVI GD, the effect of RF-PGD experimental conditions (pressure and power) on signal shapes along the pulse was first investigated. Then, the analytical performance achieved was compared with results obtained using the GD.1 chamber. Results show that the UNIOVI GD source induced less thermal stress on the glass specimens. Consequently higher GD power can be applied to the UNIOVI GD (up to at least 130W), as compared to the GD.1 (maximum of 60W), without glass sample breakdown. Also, better crater shapes on samples were obtained using the UNIOVI GD. Moreover, the detection limits attained with the UNIOVI GD (in the range of μgg−1) were in most cases about one order of magnitude better for the analytes investigated (B, Na, Al, Si, Mn, Ni, Co, Cu, Zn, As, Sr, Ag, In, Sn, Sb, Ba, Pb and Bi), than those observed using the GD.1.

Micro-Structuring on Cylindrical Inner Surface Using Whirling Electrical Discharge Texturing

The authors developed Whirling Electrical Discharge Texturing (WEDT) in order to reduce friction coefficient of cylinder-shaped parts. In previous research, the authors verified fundamental characteristics of WEDT by observation of textured surface. It was found that a crater shape and texture-area ratio can be controlled by WEDT. The texture-area ratio depends on feed speed of tool electrode. In this research, crater depth, crater diameter, texture area ratio and total removal volume of craters were investigated to confirm characteristics of WEDT in detail. In addition, tungsten wire was used as a whirling shaft in order to improve stability of whirling phenomenon. Moreover, a textured surface was finished by lapping-film in order to remove protrusions around craters and reduce friction coefficient. As a result, it was verified that the texture-area ratio slightly increased with decreasing feed speed and it was confirmed that crater depth, crater diameter, and total removal volume of craters were also related to feed speed.

The collapse of a cylindrical cavity in a granular medium

A cylindrical cavity in a noncohesive granular medium will collapse under gravity, leaving a circular crater in the surface of the material. We study this process through experiment and numerical modeling. Experimentally, we determine the shape and dimensions of craters formed by the collapse of a cylindrical cavity in a bed of small glass beads. Using a depth-averaged continuum model with cylindrical symmetry, we calculate the shape of the free surface both during and after the collapse. We use the model to study the energetics of the collapse process and investigate the dependence of the final crater on the initial shape of the cavity and the initial velocity field. While the shapes of the final craters are not identical in model and experiment, we find good qualitative agreement in aspect ratio and slope.

Bubble pinch-off and scaling during liquid drop impact on liquid pool

Simulations are performed to show entrapment of air bubble accompanied by high speed upward and downward water jets when a water drop impacts a pool of water surface. A new bubble entrapment zone characterised by small bubble pinch-off and long thick jet is found. Depending on the bubble and jet behaviour, the bubble entrapment zone is subdivided into three sub-regimes. The entrapped bubble size and jet height depends on the crater shape and its maximum depth. During the bubble formation, bubble neck develops an almost singular shape as it pinches off. The final pinch-off shape and the power law governing the pinching, rneck ∝ A(t0 − t)αvaries with the Weber number. Weber dependence of the function describing the radius of the bubble during the pinch-off only affects the coefficient A and not the power exponent α.

Laser‐induced breakdown spectroscopy of metals covered by water droplets

LIBS analyses of deep metallic layers were performed by dual-pulse excitation, where the first laser pulse efficiently ablates material covered by poly-dispersed water aerosol and water droplets, and the second laser pulse generates the analytical plasma on the crater's bottom. Enhancement of ablation rate in presence of water confinement was studied on various pure metals, namely Sn, Pb, Zn, Al, Cu, Fe, W, Ti and Mo. Crater depths and shapes were measured comparatively for dry surfaces and the same covered with water aerosol and water droplets of various volumes, and at different laser energies. With wet ablation using water droplet the mass removal efficiency was increased up to 20 times with respect to a dry process. The correlation between ablated mass and the thermal and mechanical properties of the examined metals was also studied.

An ion source for radiofrequency-pulsed glow discharge time-of-flight mass spectrometry

A Grimm-type glow discharge (GD) has been designed and constructed as an ion source for pulsed radiofrequency GD spectrometry when coupled to an orthogonal time of flight mass spectrometer. Pulse shapes of argon species and analytes were studied as a function of the discharge conditions using a new in-house ion source (UNIOVI GD) and results have been compared with a previous design (PROTOTYPE GD). Different behavior and shapes of the pulse profiles have been observed for the two sources evaluated, particularly for the plasma gas ionic species detected. In the more analytically relevant region (afterglow), signals for 40Ar+ with this new design were negligible, while maximum intensity was reached earlier in time for 41(ArH)+ than when using the PROTOTYPE GD. Moreover, while maximum 40Ar+ signals measured along the pulse period were similar in both sources, 41(ArH)+ and 80(Ar2)+ signals tend to be noticeable higher using the PROTOTYPE chamber.The UNIOVI GD design was shown to be adequate for sensitive direct analysis of solid samples, offering linear calibration graphs and good crater shapes. Limits of detection (LODs) are in the same order of magnitude for both sources, although the UNIOVI source provides slightly better LODs for those analytes with masses slightly higher than 41(ArH)+.

Pulse-Duration-Dependent Mid-Infrared Laser Ablation for Biological Applications

There are significant benefits to medical laser surgeries performed with mid-infrared wavelengths, including the ability to select laser parameters in order to minimize photochemical and thermal collateral damage. It has been shown that a wavelength of 6.1 μm is optimal when high ablation efficiency and minimal collateral damage is desired in biological soft tissues. Historically, free electron lasers were the only option for ablating tissue at this wavelength due to their ample pulse energy and average power. In recent years, new sources are being developed for this wavelength that can successfully ablate tissue. These alternative sources have different pulse structures and pulse durations than free electron lasers, motivating investigation of how these parameters affect the ablation process. Here, we present the pulse duration dependence for mid-IR laser ablation of biological tissues at a wavelength of 6.1 μm on a tissue phantom of cooked egg white. The crater shape, depth, and volume all changed in a significant, nonmonotonic manner as the laser pulse duration was increased from 100 ns to 5 μs.

STEPWISE EROSION AS A METHOD FOR INVESTIGATING THE WEAR MECHANISMS AT DIFFERENT IMPACT ANGLES IN SLURRY EROSION

In the present work, stepwise erosion technique was carried out to investigate in detail the influence of impact angle on the erosion process of AISI 5117 steel. The impact sites number and their morphology at different impact angles were investigated using SEM examination and image analysis. In addition, the SEM images of eroded surface using stepwise technique were used presented for better understanding of material removal at different angles. The tests were carried out with particle concentration of 1 wt %, and the impact velocity of slurry stream was 15 m/s. Silica sand has a nominal size range of 250 – 355 µm was used as an erodent, using whirling-arm test rig. The results showed that the number of craters as expected increases with the increase in the mass of erodent for all impact angles and that this number decreases with the increase of the impact angle. In addition, the counted number of craters is larger than the calculated number of particles for all impact angles and at any stage. The effect of impact angle based on the impact crater shape can be divided into two regions; the first region for θ ≤ 60o and the second region for θ ≥ 75o. In the first region the length of the tracks decreases with the increase of impact angle. The calculated size ranges from few micrometers to 100 micrometer for the first region and to 50 micrometers in the second region. Chipping of the former impact sites by subsequent impact particles plays important role in developing erosion.

Sputter crater formation in the case of microsecond pulsed glow discharge in a Grimm-type source. Comparison of direct current and radio frequency modes

Depth profiling with pulsed glow discharge is a promising technique. The application of pulsed voltage for sputtering reduces the sputtering rate and thermal stress and hereby improves the analysis of thin layered and thermally fragile samples. However pulsed glow discharge is not well studied and this limits its practical use. The current work deals with the questions which usually arise when the pulsed mode is applied: Which duty cycle, frequency and pulse length must be chosen to get the optimal sputtering rate and crater shape? Are the well-known sputtering effects of the continuous mode valid also for the pulsed regime? Is there any difference between dc and rf pulsing in terms of sputtering? It is found that the pulse length is a crucial parameter for the crater shape and thermal effects. Sputtering with pulsed dc and rf modes is found to be similar. The observed sputtering effects at various pulsing parameters helped to interpret and optimize the depth resolution of GD OES depth profiles.

Crater formation caused by nanoparticle impact: A molecular dynamics study of crater volume and shape

Fil: Anders, Christian. University Kaiserslautern. Physics Department and Research Center OPTIMAS; Alemania

Resuspension onset and crater erosion by a vortex ring interacting with a particle layer

This paper presents results from an experimental investigation of the interaction of a vortex ring with a particle layer. The flow dynamics during the onset of particle resuspension are analysed using particle image velocimetry, while a light attenuation method provides accurate measurements of the final eroded crater shape. This work is a continuation of the research described in R. J. Munro, N. Bethke, and S. B. Dalziel, “Sediment resuspension and erosion by vortex rings,” Phys. Fluids 21, 046601 (2009)10.1063/1.3083318, which focussed on the general resuspension onset dynamics and initial crater formation. Here, we analyse the velocity induced by the vortex ring on the particle layer surface during the resuspension of particles for different particle sizes, and the shape and size of the final craters that are formed by the impact of the vortex ring. We find that the boundary condition is characterised by a quasi-slip velocity at the particle layer surface, independent of the particle size. The particle diameter, and thus bed permeability, is found to have a significant effect on the final crater characteristics.

FE SIMULATION AND EXPERIMENTAL VALIDATION OF POWDER MIXED EDM PROCESS FOR ESTIMATING THE TEMPERATURE DISTRIBUTION AND VOLUME REMOVED IN SINGLE CRATER

This study reports the results of a finite element simulation of powder mixed electric discharge machining process for H11 Hot Die steel material using relevant boundary conditions and reasonable assumptions. The crater shape was developed using simulated temperature profiles to estimate the volume removed in a single crater. The temperature distribution on the workpiece was used to predict the cooling rate and calculate the stresses generated due to thermal loading. Subsequently, the simulation results were experimentally validated by physically measuring the crater shape and volume. From the results it was concluded that about 25% of heat is transmitted to the workpiece during machining at the process conditions used in the experiment. The microscopic pictures showed bigger craters with increase in current. The machined surface showed overlapping craters with surface cracks suggesting a high cooling rate.

Surface sputtering with nanoclusters: the relevant parameters

In this contribution, we compare the results of our recent molecular dynamics simulations with data already published by us and by other authors to identify the relevant physical parameters governing observables such as the range, the damaged volume, the crater shape, the sputtering yield, the emission of molecules and fragments, and the chemical reactions induced in organic solids by cluster projectiles. Among the considered physical quantities, we show for instance that the total cluster energy, the energy per atom/per nucleon in the cluster and, importantly, the mass matching between the cluster and target constituents have a major effect on the physics of the interaction. The evolution of the observables as a function of these basic physical parameters is illustrated and discussed as well as certain implications for organic surface characterization using cluster ion beams. Copyright © 2012 John Wiley & Sons, Ltd.