Crater Formation Research Articles

Identifying the influence of bubble size and position on crater formation during underwater nanosecond laser ablation of stainless steel

Underwater laser ablation can be employed both as a means to produce nanoparticles and to texturize surfaces of various materials. In this approach, a stationary or flowing water layer above the target surface confines laser induced plasma which cools to form short lived cavitation bubbles, positively influencing the amount of removed material per laser pulse. Plasma and cavitation bubble evolution additionally give rise to bubbles which may persist in the water throughout the ablation process. These bubbles are known to have a detrimental effect on material removal rates particularly in stationary water, but the quantitative influence of bubble dimensions and position on removed material volume is currently unknown. Here we show the laser intensity profile changes induced by bubbles located at 0–0.4 Rayleigh lengths above a stainless steel surface and couple these changes to removed crater volume. Our results show that water flowing at Reynolds numbers in the range of 1–100 positively contribute to crater volumes for pulse frequencies up to 1 kHz. At 1 kHz, it was found bubbles have insufficient time to flow from the vicinity of the laser spot, regardless of the Reynolds number within the range investigated. These conclusions assist in selecting an appropriate combination of laser and flow conditions to optimize laser ablation material removal rate.

Breaking mechanism and damage evolution rule of abrasive water jet impacting reinforced concrete

AbstractAs time passes, a significant number of reinforced concrete (RC) constructions will require maintenance and transformation. RC repair and renovation often require localized crushing and removal of the distressed area. Abrasive water jet (AWJ) crushing RC has significant advantages in terms of safety, environmental protection, and quality. However, AWJ works with high specific energy consumption and the effective crushing range of the jets is small, and the key to solving these problems lies in an in‐depth study of the general destructive law and cracking mechanism of RC materials under the action of high‐speed liquid impact. Therefore, this thesis focuses on the above key scientific issues, combining mechanical impact tests, smooth particle hydrodynamics numerical simulation methods and computer tomography scans techniques to carry out systematic research. Through the study, it is found that: The fracture characteristics of RC are mainly reflected in crushing pits and cracks, which will produce macrocracks extending along the reinforcement on the side of RC. AWJ impacting RC is mainly divided into three stages: crater formation, upper concrete fragmentation, and concrete damage development in the reinforcement impact area. During the whole impact process, the shear stress, compressive stress and tensile stress of the reinforcement will change continuously with the increase of the impact time of the AWJ.

Understanding the interaction between erosion and corrosion of pipeline steel in acid solution of different pH

The pure corrosion, erosion-corrosion and pure erosion behaviors of X65 pipeline steel in acid NaCl solution of different pH levels (ranging from 1.5 to 5.0) were studied using a rotation disc system, aiming to understand the interaction between erosion and corrosion of pipeline steel operating in acid slurry. The corrosion and erosion-corrosion performances of the steel were electrochemically measured in conjunction with surface characterizations. The pure erosion performance was studied by applying cathodic protection to eliminate the corrosion component. The propagation of the localized erosion-corrosion at different pH levels were probed using wire beam electrode. Results show that pH = 3.5 is a critical value for the transition of cathodic reaction under erosion-corrosion. In the acid fluids of pH < 3.5, the reduction of H+ is the main cathodic reaction, leading to a general erosion-corrosion feature with scattered small pits, which are initiated from the inclusions. Negative erosion-enhanced corrosion (E-C) is found at pH < 3.5 due to the wear of Fe3C networks. The oxygen reduction becomes the main cathodic reaction in the acid slurry of pH ≥ 3.5, resulting in the formation of erosion-corrosion pits and craters. The removal of the rust layer would result in positive E-C performance at pH > 3.5. Significant localized erosion-corrosion would occur at pH ≥ 3.5, where fixed major anodic sites are visualized. Obvious erosion-corrosion pits and craters would form with the occurrence of oxygen reduction. More serious corrosion-enhanced erosion (C-E) prefers to occur at the pitting areas where high macro-cell currents are registered.

The damage characteristics and formation mechanism of ultrahigh strength 7055 aluminum alloy under hypervelocity impact

This paper studies the damage morphology evolution of ultrahigh strength 7055 aluminum alloy plate under the hypervelocity impact of aluminum projectile, and analyzes the formation mechanism of crater morphology at different impact velocities. It is found that the impact crater evolves from spherical crown shape to spherical-conical composite shape, and eventually transforms into hemispherical shape with the increase of impact velocity. The evolution of crater shape is highly associated with the ratio of steady-state shock pressure and the strength of the alloy. The variation of crater diameter as a function of impact velocity follows the hypothesis of hemispherical theory, while the crater depth shows a great deviation due to the formation of conical region at the crater bottom and spall fracture at the back of the target. It is demonstrated that the formation of conical crater is related to the poor resistance to shear localization of 7055 aluminum alloy due to its low strain hardening capacity under dynamic loading. Hence, adiabatic shear bands are generated and evolve into shear cracks, thereby causing the formation of conical region at the crater bottom. It is suggested that the resistance to shear localization should be highly considered for the design, evaluation and selection of protection materials for spacecraft.

Morphological characteristics of impact craters with diameters of 5–20 km on the Moon

The morphology of impact craters on the Moon plays an important role in understanding impact cratering process, surface and subsurface properties, and their evolutions. In this study, we systematically analyzed the depth, rim height, slope, and rock abundance of 15,135 impact craters between 5 and 20 km in diameter on the Moon, covering the simple and simple-to-complex transitional crater regimes. We found that the decline rates of inner average slopes of mare craters are generally larger than those of non-maria craters and that the degradation rate of inner upper wall slopes around rim crest is not uniform, which decreases rapidly when the depth/diameter ratio (d/D) lies in 0.25–0.15 but slowly when d/D is in 0.15–0.05. However, we found that there is no difference in crater rim height between different terrains (e.g., maria and highlands). In addition, we also found the decrease in rock abundance is more rapid than the ejecta infilling of the crater floor, especially for large simple craters. Moreover, we investigated the diameter-dependent morphological features of fresh craters in different terrains and revised the onset of transitional crater diameters based on the 180 freshest craters. We found that crater initial depth depends on target properties (e.g., strength and porosity) whereas that the degradation rate of the crater depth is independent of terrains. Furthermore, we found that the power-law relations for depth and diameter of fresh simple craters are d = 0.293D0.865 (mare), d = 0.297D0.884 (highland), d = 0.221D0.959 (north pole) and d = 0.209D0.981 (south pole). The onsets of transitional crater diameters are ∼14.2 km (mare), ∼15.7 km (highland), ∼16.6 km (north pole), and ∼ 16.8 km (south pole). These morphological characteristics and their differences in different terrains suggest that target properties (e.g., strength, layering, and porosity) affect the formation and degradation of larger simple and transitional craters.

Analysis of arc plasma characteristics and energy distribution in EDM based on two-temperature model

Arc plasma is the heat source in electrical discharge machining (EDM), it affects the material removal and discharge crater formation directly, so it is necessary to clarify its characteristics. However, it is challenging to understand the physical mechanisms behind each pulse discharge through experimental methods, as it is a transient, multi-physical process that occurs in a very short time and small gap. In this paper, a two-temperature model was proposed to investigate the characteristics of the arc plasma and the energy distribution considering the multi-physics fields in the steady state. In this model, the electrons and the heavy species of the arc plasma were considered separately in the energy conservation equations, so that the temperature of the electrons and heavy species can be calculated separately. Besides, the velocity distribution, pressure distribution, electrical potential distribution, and diameter of the arc plasma, as well as the heat flux distribution and the energy distribution into the anode and cathode were analyzed. Then the variations in arc plasma properties and energy distribution with different discharge conditions were studied. The results showed that, at a lower discharge current, the electron temperature was higher than the heavy species temperature, which means that the arc plasma did not reach a local thermodynamic equilibrium (LTE) state under these discharge conditions. To validate the simulation results, the arc plasma was observed with a high-speed camera, and the diameter of craters on the surface of both the cathode and anode was measured with single-pulse discharge experiments. The experiment results were consistent with the simulation results.

Formation mechanism of craters on the surface of AA6111 aluminum alloy irradiated by quasi-relativistic high-current electron beam

The factors contributing to the formation of craters on the surface of the AA6111 aluminum alloy after processing with a high-current pulsed electron beam were investigated. Microstructural studies of the crater formation area were conducted both on the surface of the irradiated layer and on the cross-sectional side. Inhomogeneity in the distribution of alloying elements was observed both across the irradiated surface and along the cross-sectional surface of the irradiated alloy layer. The regularities of crystallization of phases in the presence of various alloying elements and their effects on the formation of crater geometry were identified. The size and shape of craters were analyzed, and it was determined that the depth of all craters was less than the thickness of the layer remelted by the high-current pulsed electron beam. A mechanism was proposed whereby the formation of craters in the AA6111 alloy is the result of uneven crystallization of the surface layer melted by the high-current pulsed electron beam.

Molecular dynamics simulation of cathode crater formation in the cathode spot of vacuum arcs

A three-dimensional model based on molecular dynamics has been developed to describe the formation of a single cathode spot in vacuum arcs. The formation of the cathode spot is assumed to be controlled by the plasma ions, the effect of which is simulated in LAMMPS through the process of ion bombardment. The cathode is represented by structured copper atoms, while the ions are continuously injected into the domain with a certain velocity towards the cathode surface. Ion bombardment leads to the appearance of a crater, which is caused by the accumulation of pressure effect against the relaxation of substrate temperature. The size of the crater is found to be determined by the spatial distribution of the injected ions. The formation of the cathode spot is also scrutinised by electron emission from the cathode surface with variable surface temperature during the cathode spot development process. In addition, the evaporated atoms forming the metal vapour are observed. This study provides a description of the formation of the cathode spot at microscale, which shall be helpful to further studies of the arc rooting and arc contact (electrode) erosion in vacuum environment.

Simulation of cathode spots crater formation on electrodes with micro-scale and nano-scale alloy materials in a vacuum arc

In the field of vacuum interrupting, an important research is to improve the erosion resistance properties of contacts. In this paper, a two-dimensional axisymmetric swirl model based on basic parameters has been proposed to describe the formation and development of cathode spots of micro-scale alloy and nano-scale alloy electrode in a vacuum arc. In this model, the peak ion density of the plasma cloud, the mean charge state in near-cathode region, the electron temperature, and the near-cathode voltage drop are adopted as external parameters. Ions and electrons originating from the plasma cloud, thermo-field (T-F) emission, vaporization of metal atoms, backing ions and back-diffused electrons are all taken into consideration. The morphology and temperature of cathode spots crater and the liquid metal velocity of pure copper electrode (Cu), copper-chromium (Cu-Cr) electrode and tungsten-copper (W-Cu) electrode under the conditions of micro-scale grains and nano-scale grains are compared, respectively. Simulation results show that the cathode spot crater of the Cu-Cr electrode is smaller than that of the pure copper electrode. Moreover, it can hold more current and inhibit the formation of new cathode spots nearby. Cathode spots appearing on tungsten grains are smaller in size and have a lower probability of forming liquid metal droplets than Cu-Cr electrodes. Contacts made of nano-scale grain alloys have stronger erosion resistance properties than that of micro-scale alloy contacts and can reduce the maximum temperature of the cathode. The simulation results are in good agreement with other researchers’ results.

Characterization of surface cratering and particle deformation during high speed microparticle impact events

Simple-to-use damage models are important in predicting the outcome of high speed particle impacts for high speed vehicles traveling in particle laden flows. Such models largely hinge upon experimental data from well-characterized single-impact events. In this study we developed and applied an experimental system to systematically examine surface cratering and particle deposition driven by high speed micrometer particle impacts onto Aluminum 6061-T6 substrates and Inconel 718 substrates. Monodisperse ferrous sulfate particles 1.8 and 6.2 micrometer in diameter were accelerated using a converging-diverging nozzle to achieve varying impact velocities in the range of 0.29–0.84 km s-1 as measured by laser Doppler velocimetry. Post-mortem surface characterization was carried out using a combination of atomic force microscopy and scanning electron microscopy. For the aluminum samples, we then utilize traditional non-dimensional groups to develop scaling relationships between crater size, particle size, velocity and incident angle. Measurement results are found to agree with data from previous studies at higher impact velocities, but notably with a sharper slope between dimensionless crater size and dimensionless impact energy, indicative of a non-negligible amount of particle elastic rebound influencing the outcome of the impact process. In addition, in contrast to crater formation observed on aluminum, equivalent impacts onto Inconel 718 led to no discernible crater formation and instead adhesion and deformation of the impacting particles.

Diffuse Sclerosing Osteomyelitis: A Potential Risk Indicator for Peri-implantitis? A Case Series.

To propose diffuse osteomyelitis as risk indicator for peri-implantitis following the loss of several dental implants in patients that present with highly sclerotic bone areas. A total of six "nightmare cases"-three of which were treated at the Department of Periodontology of the University Hospitals of the Catholic University Leuven and three of which were referred there for a second opinion-were retrospectively analyzed using radiographs obtained via contact with referring clinicians in order to fully reconstruct the treatment pathway and dental history for each of these patients. All patients suffered from early implant failures and/or severe peri-implantitis with bone loss and crater formation up to the apical level, as well as the loss of all or nearly all implants. Re-examination of their preand postoperative CBCTs, in combination with several bone biopsies, confirmed the diagnosis of a diffuse sclerosing osteomyelitis in the treated area. Osteomyelitis could be linked to a longstanding history of chronic and/or therapyresistant periodontal/endodontic pathology. The current retrospective case series seems to suggest that diffuse osteomyelitis should be considered as a risk indicator for severe peri-implantitis. Int J Oral Maxillofac Implants 2023;38:503-515. doi: 10.11607/jomi.9773.

Metallurgical, erosion, and sensitization performance of TiAlN monolayer and TiAlN/TiN multilayer ceramic coatings on AISI 304 boiler steel

In the present work, TiAlN monolayer and TiAlN/TiN multilayer ceramic coatings were deposited on AISI 304 austenitic stainless steel by plasma arc physical vapor deposition (PAPVD) process. The metallurgical, erosion, and sensitization performance of these coatings were compared with uncoated 304 boiler steel. Metallurgical studies depicted formation of Al and Ti nitrides on monolayer and multilayer coated steel surfaces, which resulted into higher nitriding at the surface and dense coating formation on boiler steel substrate. Multilayer film exhibited comparatively lesser porosity, lower surface roughness, and higher hardness than monolayer coated and uncoated steel. The erosion performance was evaluated at 30° and 90° besides 2 g/min and 3 g/min flow rates of Al2O3 erodent material for coated and uncoated steel substrate. Multilayer coated 304 steel possessed lower erosion wear rate as evaluated through lesser weight loss before and after erosive wear, smaller crater formation, and minimal adherence of erodent material along with lesser Fe content on eroded surface relative to monolayer coated and uncoated steel. Multilayer coated steel thermally aged at 750° for 24 h had least degree of sensitization (DOS) compared to monolayer coated and uncoated aged boiler steel. Although monolayer coated steel performed better than uncoated one in erosion and sensitization performance but multilayer coating performance was best among all coated and uncoated steel used for present study. Thus, it was established that TiAlN/TiN multilayer coating on AISI 304 boiler steel has improved its metallurgical, erosion, and sensitization performance.

With Nanoplasmonics towards Fusion

A status report is presented about the Nanoplasmonic Laser Induced Fusion Experiment (NAPLIFE). The goal is to investigate and verify plasmonically enhanced phenomena on the surfaces of nanoantennas embedded in a polymer target at laser intensities up to a few times 1016 W/cm2 and pulse durations of 40–120 fs. The first results on enhanced crater formation for Au-doped polymer targets are shown, and SERS signals typical for CD2 and ND bound vibrations are cited. Trials to detect D/H ratio by means of LIBS measurments are reported. Plasmonics has the potential to work at these intensities, enhancing the energy and deuterium production, due to thus far unknown mechanisms.

Splash erosion and surface deformation following a drop impact on the soil with different hydrophobicity levels and moisture content.

The splash phenomenon and the scale of the surface deformation of post-fire soils in the variants of various hydrophobicity and moisture content were studied. Splash erosion is the result of the impact of a single water drop and was analysed using high-speed cameras, while the surface deformation was parameterized using a structured light scanner. The extremely water-repellent variant (dry_V) showed distinct differences, expressed primarily in the number of ejected particles, which was 2.5 times higher than in the four soils with lower levels of hydrophobicity. It was also observed that as a result of the drop impact onto an extremely hydrophobic soil surface, a form known as liquid marble was created inside the crater. Soil moisture content determined the manner, scale and dynamics of the splash erosion. In the case of wet soils, the phenomenon proceeded up to five times faster, and as a result of the drop impact, a large number of fine particles were ejected, which reached nearly twice the velocities and three times the displacement distances compared to the dry soil group. However, the particles and/or aggregate splashed on the dry samples were larger, which also translated into the formation of craters up to twice as extensive as those in the wet soils.

Simulation of Explosion Crater of Earth Penetrating Nuclear Bomb Based on Equivalency to TNT Mass

&#x0D; &#x0D; &#x0D; The structure size of the crater formed by the earth-penetrating nuclear bomb explosion is one of the important parameters for evaluating the earth-penetrating nuclear bomb damage power. Obtaining the structure size of the crater formed by the earth-penetrating nuclear bomb explosion with different yields is great significance for the evaluation and design of the nuclear bomb damage power. In this study, considering the contradictory relationship between the structure size of the earth-penetrating nuclear bomb and the structure size of the equivalent TNT mass, we propose to use the equivalent energy mapping method to realize the finite element numerical simulation of the earth-penetrating nuclear bomb exploding into craters analyzed and compared the simulation results with the structure size of the crater formed by the ESS nuclear bomb explosion in the United States. The analysis results show that the error between the simulated crater radius and the real crater radius is 3.26%, and the error between the simulated crater depth and the real crater depth is 28.57 %. It meets the calculation accuracy error range of crater formation from nuclear explosion to chemical explosion. Therefore, this method provides an effective numerical simulation method and a means of obtaining the structural size data of the explosion crater for the earth-penetrating nuclear bomb cratering.&#x0D; &#x0D; &#x0D;

Formation mechanism of deep-sea giant pockmarks: A case study of the Reed Basin in the South China Sea

Pockmarks are widely distributed in the seabed around the world, however, mega pockmarks with diameters >1 km are rare, and their formation mechanisms remain enigmatic. Using high-resolution multi-beam bathymetric data, we firstly identified mega pockmarks in the Reed Basin in the South China Sea (SCS). These mega pockmarks of various shapes occur in groups, primarily along the sides of submarine canyons. We propose a new hypothesis about the formation mechanism of the deep-sea pockmarks that pockmarks in the Reed Basin are formed by seafloor gas explosions, widely developed carbonates store buried gas that continuously seeps along NE-SW trending faults, cap layers are undercut by submarine canyons forming lines of mechanical weakness, during periods of rapid sea level fall, depressurization causes buried gas to be rapidly ejected along these lines, forming mega pockmark groups. Submarine pockmarks reported in 21 regions globally have been analyzed, and it is found that the average median of the ratio of depth to radius (d/r) of the pockmarks is close to 0.3. Based on the theory of crater formation, it is found that the d/r ratio of the crater is also close to 0.3, which provides a new idea for the formation mechanism of deep-sea pockmarks. It is also found that the average size of the pockmarks is controlled by the water depth, and giant pockmarks are more likely to form in the deep sea. Because these results correlate easily observed bathymetric features to the presence of buried gas deposits, they have important implications for the exploration and research of deep-sea gas resources.

Numerical Modeling of an Asteroid Impact on Earth: Matching Field Observations at the Chicxulub Crater Using the Distinct Element Method (DEM)

In recent years, an international consortium of research organizations conducted investigations at the Chicxulub Crater in Yucatan, Mexico, to better understand the crater’s formation mechanisms and the effects produced by the impact of the asteroid that is hypothesized to have caused one of the major life extinctions on Earth. This study aims to reproduce the asteroid’s impact mechanics by matching computer simulations obtained with the use of the distinct element method (DEM) against the latest topographic data observed across the crater footprint. A 2D model was formulated using ITASCA’s PFC2D software to reproduce the asteroid’s impact on Earth. The model ground conditions prior to impact were replicated based on available geological and geophysical field information. Also, the proposed DEM model configuration was designed to reproduce a far-field effect to ascertain the energy dissipation of the asteroid’s impact at the model’s boundaries. Impact conditions of the asteroid were defined based on previous asteroid impact investigations. A parametric analysis including the asteroid’s impact angle and the asteroid’s impact velocity was conducted to assess their influence on the crater formation process. Results of the simulations included the final crater topography and stratigraphy, stress profiles, contact force chains, and velocity fields. Numerical simulations showed that both the asteroid velocity and impact inclination play a major role in the crater formation process, and that the use of DEM provides interesting insights into impact crater formation.

Comparison of Continuous and Pulsating Water Jet during Piercing of Ductile Material.

More efficient ways to process materials are constantly being sought, even in the case of continuous water flow technology, which acts on materials mainly by stagnant pressure. An alternative method is an ultrasound-stimulated pulsating water jet, the basis of which is the repeated use of impact pressure, which reduces the time interval for mechanical relaxation. This article focuses on a comparative study from the point of view of water mass flow rate on material penetration and its integrity. Relatively low pressures (p = 20, 30, and 40 MPa) with varying nozzle diameters (d = 0.4 and 0.6 mm) were used to identify the effectiveness of the pulsating water jet. The time exposure of the jet at a fixed place was varied from t = 0.5 to 5 s for each experimental condition. The results showed that with an increase in the pressure and diameter values, the disintegration depth increased. In addition, the surface topography and morphology images showed signs of ductile erosion in the form of erosion pits, upheaved surfaces, and crater formation. The microhardness study showed an increase of 10% subsurface microhardness after the action of the pulsating water jet as compared to the original material.

Roles of packing fraction, microscopic friction, and projectile spin in cratering by impact.

From small seeds falling from trees to asteroids colliding with planets and moons, the impact of projectiles onto granular targets occurs in nature at different scales. In this paper, we investigate open questions in the mechanics of granular cratering, in particular, the forces acting on the projectile and the roles of granular packing, grain-grain friction, and projectile spin. For that, we carried out discrete element method computations of the impact of solid projectiles on a cohesionless granular medium, where we varied the projectile and grain properties (diameter, density, friction, and packing fraction) for different available energies (within relatively small values). We found that a denser region forms below the projectile, pushing it back and causing its rebound by the end of its motion, and that solid friction affects considerably the crater morphology. Besides, we show that the penetration length increases with the initial spin of the projectile, and that differences in initial packing fractions can engender the diversity of scaling laws found in the literature. Finally, we propose an ad hoc scaling that collapsed our data for the penetration length and can perhaps unify existing correlations. Our results provide new insights into the formation of craters in granular matter.

Back pain: Detrimental Consequences of Monsoon on Health.

Dear Editor, Karachi, the economic hub of Pakistan, is home to a sizable workforce and members of the lower and middle classes. Due to their low cost, two-wheelers are the most preferred mode of transport especially by the workforce. In Karachi, there are reportedly more than 1 million motorcycles. By 2030, this number is anticipated to increase 3 times (1). Karachi’s poorly maintained road infrastructure has been severely damaged by the monsoon spells and the consequent flooding (2). Accumulation of water on roads has led to the formation of craters, potholes and washing away of road carpeting. This battered condition of roads has become a torment for commuters, especially motorcyclists. Multiple reports suggest a relationship between driving on bumpy roads and pathologies related to the back. An article published in The News International reported that more than 50% of the young bikers suffer from backache because of constant strain on backbone and surrounding tissues (3). The disorders caused by the deteriorating condition of roads include but are not limited to slipped discs, cervical spondylitis, and whiplash injuries (4). In addition it may potentially aggravate certain musculoskeletal disorders, for example arthritis (5). The increasing incidence of these pathologies is worrisome, and it is burdening the already overwhelmed healthcare facilities. In addition to this, since there is a lack of awareness, many people do not consult a doctor timely and delayed diagnosis can cause permanent damage. Chronic back pain patients also suffer from psychosocial distress. Hence awareness campaigns should be held, which can be complemented by widespread screening of these pathologies. Motorcyclists should be advised regular exercise, physiotherapy, and medicated lumbosacral support during riding which can decrease back sprain. People who have already been diagnosed with these disorders should also be provided with economical rehabilitation facilities to improve their lifestyle. Lastly, research should be conducted to find out the incidence and prevalence of other disorders related to bumpy roads, and to find out economic prevention and treatment methods.