Average Crater Research Articles

Optimal Leg Height of Landing Legs to Reduce Risk of ‎Damage from Regolith Ejecta by Retrorocket Exhausts

Over the past decade, there has been a rapid increase in rocket launches. 2022 was a record-breaking year for the ‎aerospace ‎industry, with 180 successful rocket launches into orbit, 44 more than the previous year. Reducing as ‎many risks as possible is ‎essential as interplanetary rocket launches and reusable booster landings become more ‎frequent. One such risk occurs when a ‎rocket/booster lands. During the landing process, the retrorockets spray debris ‎from the loose ground, which may damage the ‎rocket/landing module. Retrorockets are rocket engines that provide ‎a thrust opposing the spacecraft’s motion, causing it to ‎decelerate. This paper studies the effect of landing leg height ‎on ejecta velocity, the volume of debris ejected, and ground ‎surface temperature change. Four landing leg heights ‎were tested with an Estes® E-16 consumer model rocket motor: 0 mm, ‎‎50 mm, 75 mm, and 100 mm. The ‎experiment suggests that the optimal height above the ground’s surface for a simulated ‎landing module based on ‎the volume and velocity of the ejecta is 50 mm. Landing legs that elevate a model rocket this height ‎create an ‎average crater volume of 610.5 mL and a max crater diameter of 10.34 cm. After determining the optimal height, a ‎‎landing leg system was developed. This system was attached to an Aerodactyl TS® model rocket and utilized ‎landing legs that ‎elevated the rocket to a height of 50 mm above the ground at landing.‎‎

Ballistic Performance of Ti6321 Titanium Alloy under Vertical and Oblique Penetration

For the new marine Ti6321 titanium alloy, the penetration tests were carried out under vertical and oblique penetration conditions. The ballistic properties of Ti6321 titanium alloy with different structures and the macro and micro damage characteristics of the target were obtained. The influence of the structure on the ballistic performance and failure mechanism of the titanium alloy target plate was analyzed. The results show that Ti6321 titanium alloy exhibits different properties under vertical and oblique penetration conditions. In the vertical penetration test, the absolute penetration depth and the average crater diameter of the equiaxed target plate are smaller than those of the bimodal and Widmanstatten structure, which show a better resistance to vertical penetration. In the oblique penetration, the safety angle of the bimodal structure was smaller and showed better resistance to the oblique penetration.

Penetration performance and fragmentation mechanism behind target of tungsten fibre/zirconium-based bulk metallic glass matrix composite rod

Penetration performance and fragmentation mechanism behind target of tungsten fibre/zirconium-based bulk metallic glass matrix composite rod

Damage of a large-scale reinforced concrete wall caused by an explosively formed projectile (EFP)

To quickly break through a reinforced concrete wall and meet the damage range requirements of rescuers entering the building, the combined damage characteristics of the reinforced concrete wall caused by EFP penetration and explosion shock wave were studied. Based on LS-DYNA finite element software and RHT model with modified parameters, a 3D large-scale numerical model was established for simulation analysis, and the rationality of the material model parameters and numerical simulation algorithm were verified. On this basis, the combined damage effect of EFP penetration and explosion shock wave on reinforced concrete wall was studied, the effect of steel bars on the penetration of EFP was highlighted, and the effect of impact positions on the damage of the reinforced concrete wall was also examined. The results reveal that the designed shaped charge can form a crater with a large diameter and high depth on the reinforced concrete wall. The average crater diameter is greater than 67 cm (5.58 times of charge diameter), and crater depth is greater than 22 cm (1.83 times of charge diameter). The failure of the reinforced concrete wall is mainly caused by EFP penetration. When only EFP penetration is considered, the average diameter and depth of the crater are 54.0 cm (4.50 times of charge diameter) and 23.7 cm (1.98 times of charge diameter), respectively. The effect of explosion shock wave on crater depth is not significant, resulting in a slight increase in crater depth. The average crater depth is 24.5 cm (2.04 times of charge diameter) when the explosion shock wave is considered. The effect of explosion shock wave on the crater diameter is obvious, which can aggravate the damage range of the crater, and the effect gradually decreases with the increase of standoff distance. Compared with the results for a plain concrete wall, the crater diameter and crater depth of the reinforced concrete wall are reduced by 5.94% and 9.96%, respectively. Compared to the case in which the steel bar is not hit, when the EFP hit one steel bar and the intersection of two steel bars, the crater diameter decreases by 1.36% and 5.45% respectively, the crater depth decreases by 4.92% and 14.02% respectively. The EFP will be split by steel bar during the penetration process, resulting in an irregular trajectory. • Experiments of a large-scale reinforced concrete wall damaged by an explosively formed projectile (EFP) are conducted. • A three-dimensional (3D) numerical model is established considering the combined load of EFP penetration and explosion impact. • Crater diameter and crater depth of the reinforced concrete wall are better reproduced by the Riedel-Hiermaier-Thoma (RHT) model with modified parameters. • Effects of EFP penetration and explosion impact on the damage of the reinforced concrete wall are discussed respectively. • Effects of steel bars and impact positions on the impact performance of EFP are further numerically discussed.

Cavitation Plays a Vital Role in Stone Dusting During Short Pulse Holmium:YAG Laser Lithotripsy.

Objective: To investigate the mechanism of stone dusting in Holmium (Ho): YAG laser lithotripsy (LL). Materials and Methods: Cylindrical BegoStone samples (6 × 6 mm, H × D) were treated in water using a clinical Ho:YAG laser lithotripter in dusting mode (0.2-0.4 J with 70-78 μs in pulse duration, 20 Hz) at various fiber tip to stone standoff distances (SD = 0, 0.5, and 1 mm). Stone damage craters were quantified by optical coherence tomography and bubble dynamics were captured by high-speed video imaging. To differentiate the contribution of cavitation vs thermal ablation to stone damage, three additional experiments were performed. First, presoaked wet stones were treated in air to assess stone damage without cavitation. Second, the laser fiber was advanced at various offset distances (OSD = 0.25, 1, 2, 3, and 10 mm) from the tip of a flexible ureteroscope to alter the dynamics of bubble collapse. Third, stones were treated with parallel fiber to minimize photothermal damage while isolating the contribution of cavitation to stone damage. Results: Treatment in water resulted in 2.5- to 90-fold increase in stone damage compared with those produced in air where thermal ablation dominates. With the fiber tip placed at OSD = 0.25 mm, the collapse of the bubble was distracted away from the stone surface by the ureteroscope tip, leading to significantly reduced stone damage compared with treatment without the scope or with scope at large OSD of 3-10 mm. The average crater volume produced by parallel fiber orientation at 0.2 J after 100 pulses, where cavitation is the dominant mechanism of stone damage, was comparable with those produced by using perpendicular fiber orientation within SD = 0.25-1 mm. Conclusion: Cavitation plays a dominant role over photothermal ablation in stone dusting during short pulse Ho:YAG LL when 10 or more pulses are delivered to the same location.

Investigation on High Velocity Impact of Projectile on Double Layered Geomaterial

Investigation on High Velocity Impact of Projectile on Double Layered Geomaterial

Cavitation is the primary mechanism for stone dusting in holmium:YAG laser lithotripsy

Ureteroscopy with holmium(Ho):YAG laser lithotripsy (LL) is the primary treatment modality for kidney stone patients. Despite this, the mechanism of stone dusting in LL is unclear. In this work, we treated 6 × 6 mm cylindrical BegoStone phantoms using 0.2–0.4 J and 20 Hz at various fiber-to-stone standoff distances (SD) either in water or air with perpendicular fiber orientation; the latter eliminates the contribution of cavitation. The laser fiber was advanced at different offset distances (OSD) from a flexible ureteroscope tip to alter LL-induced bubble dynamics. Furthermore, stones were treated in parallel fiber orientation to minimize thermal ablation while isolating cavitation damage. Our results demonstrate that stone damage in water is 2.5- to 90-fold of those produced in air. At OSD = 0.25 mm when the bubble collapsed away from the stone surface due to the presence of the scope tip, stone damage was greatly reduced to the level in air. Moreover, the average crater volume produced by parallel fiber orientation after 100 pulses was comparable with those produced by perpendicular fiber within SD = 0.25–1 mm. Altogether, we conclude that cavitation is the primary mechanism over photothermal ablation for stone dusting in Ho:YAG LL.

Characterization of the Candidate Landing Region for Tianwen‐1—China's First Mission to Mars

AbstractThis paper presents our efforts to characterize the candidate landing region (109°–133°E, 23°–30°N) for Tianwen‐1, China's first mission to Mars, in terms of engineering safety and scientific significance. Topographic analysis reveals that the region has a low elevation around −4,230 m, and 98% of the region have slopes smaller than 8°. The geomorphological mapping and analysis show that the region has an average crater density of about 28 craters (≥200 m in diameter) per 100 square kilometers, with several clusters of high crater densities distributed around the center of the region. There are also pitted cones distributed mainly in the southern part of the region, with a density of approximately 6.6 cones per 100 square kilometers in specific local areas. The region has rock abundances ranging from 1% to 23%, with local clusters of low and high rock abundances. The region comprises four main geological units, including a lowland unit formed in the Late Hesperian and a volcanic unit formed in the Amazonian and Hesperian period. Their specific surface ages are estimated through the analysis of crater size‐frequency distribution. Combining the engineering constraints on surface slopes, crater density, cone density, and rock abundance, a hazard map of the candidate landing region is generated for landing site evaluation and safety assessment. Based on the results, we further discuss the potential scientific outcomes from the exploration in this region. The findings will be helpful for the mission planning and maximization of the scientific return from Tianwen‐1, and complement existing Martian scientific research.

An insight into microstructure and machining performance of deep cryogenically treated cemented carbide inserts

Abstract Cryogenic treatment is one of the potential techniques to enhance cutting tool performance. The present work investigates the microstructure and machining performance of cemented carbide (WC-Co) inserts through deep cryogenic treatment. For this, ISO P30 WC-Co inserts were exposed to deep cryogenic treatment (−196 °C), accompanied by tempering at 200 °C. The cryogenic treatment cycle helps to develop η (eta) phase carbides by redistributing cobalt (Co) phase on the surface of cryogenically treated WC-Co inserts. Microhardness of specimens indicated a slight increase in the hardness of cryogenically treated inserts than its untreated counterpart. A comparative performance evaluation between cryogenically treated tungsten carbide insert and the untreated insert was studied by turning of AISI 316 austenitic stainless steel through tool flank wear, crater wear, and chip morphology. Machining operation was carried out by considering three different cutting speeds (i.e. at 100, 150, and 200 m/min.) with constant feed rate and depth of cut of 0.2 mm/rev and 1 mm, respectively. After cryogenic treatment, significant improvement in the average flank wear and crater wear of WC-Co insert was observed. The enhancement of tool wear in the cryogenically treated insert is explained in detail by analyzing their microstructures.

Absolute model age of lunar Finsen crater and geologic implications

As the primary source of materials measured inside of Von Kármán crater by the Chang'e-4 rover, the absolute model age (AMA) of Finsen crater is derived by the crater size-frequency distribution (CSFD) measurements. Both cumulative and differential fits reveal an AMA of ~3.5 Ga, indicating Finsen crater is Imbrium-aged. Based on thickness estimation of the Finsen crater ejecta-sourced fine-grained regolith at Chang'e-4 landing site (~12 m) (Lai et al., 2019; Li et al., 2020), the average regolith growth rate at the landing site is estimated to be about 3.4 m/Gyr. The current depths of 25 largest craters on the floor of Finsen crater are calculated by the profile-average-depth method, and their original depths are estimated under the assumption that the initial depth-to-diameter (d/D) ratio is 0.2. Depth differences between current and estimated original depths, together with the AMA of Finsen crater, derive the average crater degradation/infilling rate within Finsen crater is about 21 ± 3 m/Gyr.

Effect of adhesive interlayers on protective performance of bio-inspired building ceramic covering

The brick-and-mortar microstructure of nacre is usually considered as a source of inspiration for the development of strong and tough artificial materials. In this article, a nacre-inspired layered-and-staggered structural building ceramic protective covering was fabricated, and the effect of four types of adhesive materials on the ballistic performance of the protective covering was investigated through the ballistic test. The experimental results showed that under the impact of the 7.62-mm ordinary rifle bullet at a speed of 790–820 m/s, the average crater diameter in the concrete targets with protective covering was reduced by 40%–72%, and the penetration depth in the concrete was reduced by 70%–100%, compared with those of unprotected concrete targets. For the concrete targets with protective covering, that adopting the silicone sealant interlayers exhibited a smaller crater area but a maximum penetration depth, while that adopting the epoxy adhesive interlayers showed a larger crater area but a minimum penetration depth. Since the targets with the low-cost polyurethane sealant interlayers presented the smallest crater area and the shallower penetration depth, it can be concluded that the concrete with the protective covering using polyurethane sealant interlayers showed the better projectile impact resistance.

Effect of SiC micro and nanopowder in the electrical discharge machining process

Abstract EDM is used to machine difficult to process conductive materials through the conventional machining process. The concentration and particle size of powder shows different results. This research work has confirmed that nanopowder performs better than micro powder and conventional EDM. Enhancement in MRR observed by 12.12% and 57.14% compare to micro powder and conventional EDM, respectively. The surface quality also improved as average crater size enhanced by 34.04% from conventional EDM. Improved morphology of the machined surface analyzes through FE-SEM.

Study on crater depth during material removal in WEDC of Ni-rich nickel–titanium shape memory alloy

The objective of this experimental investigation is to reveal the individual effect of wire electrical discharge cutting (WEDC) process parameters, namely discharge energy density, wire feed rate, spark frequency, wire tension, and spark gap voltage on average crater depth, material removal rate (MRR), and metallographic changes of Ni55.95Ti44.05 shape memory alloy (SMA). The analysis of crater size during material removal in WEDC has been also discussed in this study. The three-dimensional surface topography at higher discharge energy density divulges the formation of deeper and wider craters with high surface roughness on the machined surface compared to lower discharge energy density. MRR and average crater depth increase with the increase in discharge energy density and decrease with the increase in spark frequency and spark gap voltage, whereas wire feed rate and wire tension have the trivial effect. The analysis of X-ray diffraction peaks of the machined surface shows the presence of various compounds such as NiTi, TiO, TiO2, Ni4Ti3, CuZn, Cu2NiZn, NiTiO3, and NiZn and tensile residual stress.

Rock Abundance and Crater Density in the Candidate Chang'E‐5 Landing Region on the Moon

AbstractChang'E‐5 is China's first lunar sample‐return mission, which will be launched in 2019. Understanding the distribution of rocks and craters in the candidate landing region is important for selecting suitable landing sites and studying the surface geology. This paper first separately investigates rock abundance and crater density in the candidate landing region, then provides a joint analysis of them, for the purposes of identifying potential hazards for safe landing and their geological implications. The results indicate that in the region, rocks are mostly concentrated around rocky ejecta craters. About 90% of the region has a rock abundance (the fractional area covered by rocks) of less than 1%. The average crater density is about 250 craters (≥ 100 m in diameter) per 100 km2; on average, 13.5% of the region is covered by craters. The surface ages of geologic units in the region estimated using crater size‐frequency distribution indicate that the eastern part of the region is younger than the western part. The joint analysis of rock abundance and crater density identifies local areas that are relatively unfavorable for safe landing. The joint analysis also indicates an exponential relationship between overall rock abundance and crater density, and a roughly linear relationship between overall rock abundance and surface age. Furthermore, the joint analysis indicates an inverse correlation between rock abundance and the relative maturation of craters. The presented research and results will be helpful for identifying suitable landing sites for the Chang'E‐5 lander. They also provide fresh insights into lunar surface geology.

Reactivity and Penetration Performance Ni-Al and Cu-Ni-Al Mixtures as Shaped Charge Liner Materials.

Energetic structural materials (ESMs) have many potential military applications due to their unique functions. In this work, the reactivity and penetration performance of ESMs have been examined as a shaped charge liner material. The penetration experiments of nickel-aluminum (Ni-Al) and copper-nickel-aluminum (Cu-Ni-Al)-shaped charge liners (SCLs) have been designed and fired into 45# steel. The targets were recovered and analyzed by optical microscopy, electron microscopy, energy dispersive spectroscopy, and Vickers microhardness measurements. The head and tail of the crater walls penetrated by two reactive jets demonstrated unique microstructures. The jet rapidly decayed with the penetration process, but the “white” zone (a mixture of martensite and austenite) was more prominent in the tail, and the microhardness of the tail was much higher than that of the head. The results showed the continued exotherm of Ni-Al reactive jet when it was fired into the target. The addition of Cu reduced the exotherm of Ni-Al, Cu could not only increase the average crater size, but also raise the average penetration depth by 42%. These results offer valuable insight for utilizing ESM as shaped charge liner materials.

Investigating the surface integrity of aluminium based composites machined by EDM

Abstract In the present work, the surface characteristics of Electrical Discharge Machined (EDM) Al (6351) SiC and Al (6351) SiC B4C composites are investigated. The composites are prepared by employing the conventional stir casting technique, as it can produce better particle dispersion in the matrix. The detailed experimental study is performed on the composites by varying current (I), duty factor (τ), pulse on time (Ton), and the gap voltage (V) in order to analyze the Heat Affected Zone (HAZ) formed in the sub surface and the average crater diameter formed on the machined surface of the composites as an output function. The formation of recast layers, presence of bubbles and the surface texture of the composites at various machining conditions are observed. The results show that the increased Metal Removal Rate (MRR) increases the depth of HAZ and the average crater diameter on the machined area. Further, the addition of B4C particles to the composite produces more surface defect than the Al SiC composite.

Evidence of Low-latitude Fluvial and Glacial Activity During the Martian Amazonian Era

The Martian obliquity cycle is predominately influenced by Solar and Jovian tidal forces. The present-day axial tilt of Mars (25 degrees) is predicted to cycle between 0 degrees and 60 degrees (Mischna & Richardson 2005) with excursions up to 80 degrees(Laskar et al. 2004). We focused on Arabia Terra, a region especially well-suited for studying glacial migration due to its location in the northern mid-latitude (20-40 degrees North, 0-30 degrees East) zone, and its heavily cratered terrain. We created glacial and fluvial morphology distribution maps with the ESRI Aeronautical Reconnaissance Coverage Geographic Information System (ArcGIS). We determined the ages of our craters in order to establish a time-domain link between the Martian obliquity cycle and glacial migration; we found the average crater age to be roughly 2 billion years old.

Sensitive in-situ Cr analysis with high resolution and minimal destructive effect using micro-joule picosecond laser generated plasma emission in open ambient air

Abstract A study is performed to demonstrate the feasibility of applying a microjoule picosecond laser for sensitive and high resolution in-situ Cr analysis with minimal destructive effect. It is aimed for application to quality assessment of steel products and proses control in the related industry as well as field inspection and monitoring of products in used. The feasibility and realization of these applications is examined and verified by the successful generation of shock wave plasma responsible for the shock wave induced thermal excitation of the ablated atoms by means of a ps Nd:YAG laser operated in the energy range of 100 μJ–500 μJ and directly focused onto the solid sample in open ambient air without the use of microscope and sample chamber as commonly employed in all existing μLIBS techniques. The time-dependent intensity variation of the generated micro plasma emission is shown to exhibit all the well-known characteristic structural and dynamical features of shock wave plasma emission. This is followed by further experiment for the ascertainment of the most favorable laser energy of 500 μJ and gate delay of 100 ns for its applications to Cr analysis of standard steel, standard Al samples and precious green stone sample. The resulted spectra all feature very sharp emission lines with low background and yielding an estimated detection limit of lower than 1 ppm and an average crater size of around 7 μm. It is therefore, promising for minimally destructive and highly sensitive in-situ Cr analysis.

Concrete containing waste rubber particles under impact loading

The main objective of this study is investigate of behavior of concrete containing waste tire rubber against impact loads. Impact is one of the dynamic loads that may be occurs at high velocity and exposed concrete structures, such as the military situation. Properties of concrete containing three different sizes of rubber particles 0-1, 1-3 and 3-5 mm that replaced of 0%, 10%, 20%, 30%, 40% and 50% of fine aggregate were determined. Analyses were included compressive and flexural strength, dry unit weight, velocity of ultrasonic wave and scanning of electron microscopy (SEM). For ductility of this kind of concrete, impact test done with gas gun device on it and failure such as penetration depth and average crater diameter determined too. The results indicated that when rubber particles added to concrete mixture, fracture of concrete was softer than normal concrete and concrete containing optimum size and percent of rubber particles has best properties and less failure.

Contribution of CO2 and H2S emitted to the atmosphere by plume and diffuse degassing from volcanoes: the Etna volcano case study

Active subaerial volcanoes often discharge large amounts of CO2 and H2S to the atmosphere, not only during eruptions but also during periods of quiescence. These gases are discharged through focused (plumes, fumaroles, etc.) and diffuse emissions. Several studies have been carried out to estimate the global contribution of CO2 and H2S emitted to the atmosphere by subaerial volcanism, but additional volcanic degassing studies will help to improve the current estimates of both CO2 and H2S discharges. In October 2008, a wide-scale survey was carried out at Mt. Etna volcano, one the world’s most actively degassing volcanoes on Earth, for the assessment of the total budget of volcanic/hydrothermal discharges of CO2 and H2S, both from plume and diffuse emissions. Surface CO2 and H2S effluxes were measured by means of the accumulation chamber method at 4075 sites, covering an area of about 972.5 km2. Concurrently, plume SO2 emission at Mt. Etna was remotely measured by a car-borne Differential Optical Absorption Spectrometry (DOAS) instrument. Crater emissions of H2O, CO2 and H2S were estimated by multiplying the plume SO2 emission times the H2O/SO2, CO2/SO2 and H2S/SO2 gas plume mass ratios measured in situ using a portable multisensor. The total output of diffuse CO2 emission from Mt. Etna was estimated to be 20,000 ± 400 t day−1 with 4520 t day−1 of deep-seated CO2. Diffuse H2S output was estimated to be 400 ± 20 kg day−1, covering an area of 9.1 km2 around the summit craters of the volcano. Diffuse H2S emission on the volcano flanks was either negligible or null, probably due to scrubbing of this gas before reaching the surface. During this study, the average crater SO2 emission rate was ~2100 t day−1. Based on measured SO2 emission rates, the estimated H2O, CO2 and H2S emission rates from Etna’s crater degassing were 220,000 ± 100,000, 35,000 ± 16,000 and 510 ± 240 t day−1, respectively. These high values are explained in terms of intense volcanic activity at the time of this survey. The diffuse/plume CO2 emission mass ratio at Mt. Etna was ~0.57, that is typical of erupting volcanoes (mass ratio <1). The average CO2/SO2 molar ratio measured in the plume was 11.5, which is typical of magmatic degassing at great depth beneath the volcano, and the CO2/H2S mass ratio in total diffuse gas emissions was much higher (~11,000) than in plume gas emissions (~68). These results will provide important implications for estimates of volcanic total carbon and sulfur budget from subaerial volcanoes.