Mass Erosion Research Articles

Light-Triggered Structural Modulation of Nanofibrous Meshes to Promote Deep Penetration of Cultured Cells.

Although nanofibrous meshes are considered promising cultivation beds for maintaining cell differentiation, 3D cultivation is not possible because their nanoporous structures impede cell infiltration. To facilitate transverse cell migration across nanofibrous meshes, electrospun nanofibers are prepared with structures that vary in response to red laser light. Polyoxalate (POX), composed of oxalate linkers and oligomeric caprolactone, is synthesized and electrospun into fibrous meshes with a photosensitizer (chlorin e6, Ce6). These meshes exhibit morphological and chemical changes upon laser irradiation, and mass erosion rates of the meshes are faster after laser irradiation. Cell cultivation on POX meshes reveals that red laser effectively facilitates traverse migration of the cells without affecting cell viability. The use of light-triggered change of meshes is envisioned to promote the migration of cells during 3D matrix cultivation.

Study of Impact Characteristics of ZrO2 Ceramic Composite Projectiles on Ceramic Composite Armor.

Exploring new armor-piercing materials is crucial for improving the penetrative ability of projectiles. Based on the process of in situ solidification injection molding through ceramic dispersant hydrolytic degradation, a ZrO2 ceramic material suitable for use as the tip of a 12.7 mm kinetic energy (KE) projectile was prepared. The ZrO2 ceramic tip can be matched with the metal core of a conventional projectile to form a ceramic composite projectile, increasing the damage to the Al2O3 ceramic composite armor. Specifically, the ZrO2 ceramic tip can increase the impact load on the Al2O3 ceramic panel, prolonging the pre-damage phase and reducing the stable penetration phase, shortening the mass erosion time of the metal core compared with a 12.7 mm metal KE projectile tip. The ceramic composite projectile with the ZrO2 ceramic tip has a lower critical penetration velocity than a 12.7 mm metal KE projectile for Al2O3 ceramic composite armor. Furthermore, the residual velocity, residual length, and residual mass of the metal core of the ceramic composite projectile that penetrated the Al2O3 ceramic composite armor are greater than those of a 12.7 mm metal KE projectile.

An Appraisal of Soil Erosion in Dehradun Valley

In the recent past, there has been a very rapid increase in the developmental activities in the Himalayas in general and Dehradun Valley in particular. These comprise large-scale construction, roads, mining activity, overgrazing, and deforestation etc. leading to the land degradation. A near exponential population growth has placed a further heavy demand on already limited natural resources. High rainfall coupled with fragile rocks and good relief provides a dense network of stream system. The debris from landslides and mine waste cause inequilibrium in flow regime causing meandering in both mountain and valley streams. These problems pose serious threat to environmental and ecological balance in an already fragile eco-system. Landslide, river sedimentation, disruption to communication lines and depletion of water sources are some of the direct consequences of mass erosion problem. The effect of majority of casualties and other natural hazards due to mass erosion often disrupts economic and social fabric over a much wider area than the hazard site and prompt action is required in order to minimize these losses. There are several mass erosion problems but landslides, mine spoil stabilization and stream bank erosion problems are dominant and therefore selected for the present study.

Study on the penetration of elliptical cross-section projectiles into concrete targets: theory and experiment

To better understand the penetration mechanism of the elliptical cross-section projectile (ECSP) into semi-infinite concrete target, penetration experiments using three types of ECSPs with different shape ratios (1, 1.25 and 1.61) and with striking velocities ranged from 550 m/s to 1050 m/s were conducted. Penetration depths, penetration trajectory and mass erosion rates of the projectile were obtained after the experiments. The experiment results show that the penetration performance and ballistic stability of the ECSP are equivalent to those of the circular cross-section projectile (CCSP). Based on the theory of complex variable function and conformal transformation, a semi-analytical model which can calculate the cavity boundary stress distribution of elliptical section cavity controlled by the displacement boundary condition was established and the model was validated by comparing the model degenerate solution with Kirsch problem results. Theoretical calculation results show that the radial stress of elliptical section cavity increases progressively from the minor axis to the major axis. In addition, a formula combining with the semi-analytical theoretical model and the local interaction theory was developed. The predicted penetration depths were compared with 30 groups of experiment data with different projectile parameters and striking velocities and coincide quite well with the corresponding experimental data. Finally, the influence of shape ratio and caliber-radius-head (CRH) on the penetration performance of projectile and the application prospect of ECSPs on hypersonic weapon platform were studied.

Graphite Nozzle Erosion Trends in Paraffin/Oxygen Hybrid Rockets

Nozzle erosion predictions are fundamental to increase the technology readiness level of hybrid rocket engines. In this work, Reynolds-averaged Navier–Stokes simulations of the internal ballistics of paraffin/oxygen engines coupled with graphite nozzle ablation are performed under various operating conditions. Additional simulations considering uniform inlet conditions at the postchamber entrance underline the complex interaction between nozzle erosion and the radially nonuniform flowfield originating from incomplete mixing and combustion. Moreover, the favored combustion efficiency resulting from an increase of the postchamber length is evaluated in terms of nozzle erosion in a wide range of oxidizer-to-fuel ratios. Because of the interaction between wall and gas-phase reactions, erosion mass fluxes are observed to monotonically grow with decreasing equivalence ratios.

Numerical Analysis of Nozzle Erosion in Hybrid Rockets and Comparison with Experiments

Nozzle throat erosion in hybrid rocket engines is generally more emphasized than in solid rockets due to a greater concentration of oxidizing species in the combustion products. Therefore, its accurate understanding and modeling is of fundamental importance in order to correctly predict motor performance and possibly to help reducing the associated losses. Moreover, throttling and/or mixture ratio shift can significantly alter the conditions under which the thermal protection material is operating, further complicating the problem. The aim of this work is to numerically investigate the graphite nozzle erosion in hybrid rockets burning high-density polyethylene and oxygen. Nozzle throat erosion rate and wall temperature are evaluated as a function of the operating conditions by performing numerical simulations with a proven in-house computational fluid dynamics solver. The results obtained from a detailed parametric analysis are discussed and then used to derive a general closed-form regression law for rapid estimation of nozzle throat erosion rate for the analyzed propellant combination that is dependent on the operating conditions, chamber pressure and mixture ratio, and on the nozzle geometry. The possible role of combustion efficiency is also discussed. The regression law is then validated through comparison with the experimental results obtained from several lab-scale 2-kN-thrust-class firing tests, underlining a good ability to correctly capture the average nozzle erosion mass flux behavior with the operating conditions and highlighting the different role of the driving parameters.

Provenance controls on volcaniclastic beach sand: example from the Aeolian archipelago, Mediterranean Sea

Abstract Sand and sandstone composition of volcanic origin may be clues to the provenance of the sediments and sedimentary rocks. Volcaniclastic provenance studies contribute significantly to unravelling the generation and provenance of sediment under investigation, which in the Aeolian archipelago comprises preserved units of outcrops dominated by lava flows intercalated with airfall tephras as source rocks. The focus of this paper is the study of the petrographical composition and textures of beach sands, which can then be used as a guide in the interpretation of provenance and origin of beach sand(stone)s rich in volcanic debris transported into deeper water. The composition of Aeolian beach deposits defines a single immature petrofacies with a large amount of unweathered glass and mafic minerals. Panarea island is dominated by dacites and new grain categories have been proposed to differentiate this provenance. Surface processes such as mechanical erosion (mass wasting and surface runoff) produce an overestimation of mafic components compared to the felsic components in the beach sand fraction.

Experimental Study on the Impingement Characteristics of Self-Excited Oscillation Supercritical CO2 Jets Produced by Organ-Pipe Nozzles

Supercritical carbon dioxide (SCO2) jets are a promising method to assist drilling, enhance oil–gas production, and reduce greenhouse gas emissions. To further improve the drilling efficiency of SCO2 jet-assisted drilling, organ-pipe nozzles were applied to generate a self-excited oscillation SCO2 jet (SEOSJ). The impact pressure oscillation and rock erosion capability of SEOSJs under both supercritical and gaseous CO2 (GCO2) ambient conditions were experimentally investigated. It was found that the impact pressure oscillation characteristics of SEOSJs produced by organ-pipe nozzles are dramatically affected by the oscillation chamber length. The optimum range of the dimensionless chamber length to generate the highest impact pressure peak and the strongest pressure oscillation is within 7–9. The dimensionless pressure peak and the pressure ratio decreases gradually with increasing pressure difference, whereas the pressure oscillation intensity increases with increasing pressure difference and the increasing rate decreases gradually. The dominant frequency was observed to decrease monotonically with increasing chamber length but increases with the increase of pressure difference. Moreover, the comparison of impingement characteristics of SEOSJs under different ambient conditions showed that the values of dimensionless peak impact pressure are similar under the two ambient conditions, and the SEOSJ achieves higher pressure oscillation intensity and dominant frequency in SCO2 at the same pressure difference. The rock breaking ability of the SEOSJ is closely related to its axial impact pressure. The erosion depth and mass loss of sandstone caused by the organ-pipe nozzle with the best impact pressure performance is higher than those produced by other nozzles. The SEOSJ results in a deeper and narrower crater in SCO2 than in GCO2 under the same pressure difference. The reported results provide guidance for SEOSJ applications and the design of an organ-pipe nozzle used for jet-assisted drilling.

A Review on Existing Methods to Assess Hydraulic Erodibility Downstream of Dam Spillways

In recent years, rock scouring or erosion downstream of dams has become an increasing dam safety concern. Several theoretical, semi-theoretical, semi-analytical and numerical methods can be used to assess the rock erosion in hydraulic structures. Semi-theoretical approaches determine the correlation between the erosive intensity of fluid flow and the resistive capacity of rock. Such approaches establish the scour thresholds as a function of erosive intensity of water and several rock mass indices by using in situ data and a curve-fitting approach. In some studies, the excavatability index, initially developed for rock mass stability analysis, was used to analyse the rock mass resistance in hydraulic erodibility analysis. The effectivity and weight of the geomechanical parameters used are yet to be determined on the basis of the erodibility phenomenon. The semi-analytical methods are developed on the basis of the mechanical and hydraulic interaction of rock mass and water. Four methods developed by Bollaert et al. are important in determining the erodibility in the plunge pool, but they are not applicable in the case of spillways. They used the comprehensive fracture mechanics for closed-end joints, quasi-steady impulsion, and dynamic impulsion (DI) for blocky rock erosion. The application of these methods to each site is necessary to identify constants that are difficult to determine. Few numerical methods are available to assess the rock mass erosion in hydraulic structures. In the case of numerical methods, the erosive agent is indistinct, and the hydraulic hazard parameter on the spillway surface is almost challenging to apply. This study comprehensively reviews the mechanism of erosion and the methods for assessing the risk of potential rock mass erosion downstream of dams and hydraulic structures. The advantages and disadvantages of all methods are discussed and the potential future research directions in this domain are proposed.

Identification of Hydraulic Parameters Influencing the Hydraulic Erodibility of Spillway Flow Channels

The rock mass erosion of dam spillways, a phenomenon involving the interaction between the hydraulic load of water and the capability of the rock mass to resist its destruction, remains a critical safety issue. The erosion resistance of a rock mass can be estimated through several erodibility indices, including those of Kirsten, Pells or Bollaert. Several indices have been developed to link rock resistance to the hydraulic parameters of water, i.e., the hydraulic load applied on a rock mass. The developed indices use the average flow velocity, the average shear stress on the bottom of the flow channel, the stress applied to the internal joints of fractured rock mass, the dynamic impulse force, and the power dissipation of water to represent the erosive force of water. From these indices, several methods of assessing hydraulic erosion have been developed, and all use the threshold line concept. Nonetheless, several uncertainties are associated with these methods. This paper presents and discusses the various means of calculating the erosive force of water as a hazard parameter for predicting potential rock erosion. The representativeness of these approaches is also discussed, and we clarify nuances associated with each method. We then provide guidelines for future research aimed at improving estimates of the erosive force of the water within spillway flow channels.

Development of gully erosion processes: A 3D investigation based on field scouring experiments and laser scanning

Gully erosion is a severe form of soil erosion. However, current understanding of the relative dominance of processes that drive the development of gully erosion is limited. This study investigated the development of gully erosion, and the contribution of mass movement and water erosion to gully erosion based on fourteen scouring experiments on two field plots and terrestrial laser scanning (TLS). A three-dimensional (3D) method was proposed to derive the volume of gully erosion based on point clouds with topographic change information. The results showed that TLS-derived gully sediment yields were in a high agreement with the measured sediment yield (R2 > 0.85, p < 0.01, and mean relative/absolute error < 11.38%/5.47 kg), which demonstrated the reliability of TLS and the newly proposed 3D volumetric calculation method in the gully erosion monitoring. We found that the development of gully erosion consisted of horizontal and vertical cycles. The horizontal development of gullies was dominated by a cycle of gully head retreat that was mainly driven by water erosion as well as gully head expansion that was considerably driven by collapses. The vertical development was driven by the co-evolution of collapses and caves that enhance the development of one another. Our experiments showed that mass movements were generally not a major source of gully erosion mass (1.09%–50.80%) or sediment yield (0.90%–24.71%), although they considerably contributed to the morphological development of gully heads (e.g. 26.74% to 96.09% of the increase in the maximum length of gully head and 39.03% to 94.80% of the change in gully head area). We also found that mass movements significantly impacted gully erosion mass (p < 0.05), while their relationships with sediment yield tended to be complex and depended on the impact of mass movements on the broader runoff and erosion processes. Besides, the extremely high collapses were also found to heavily impact the relationship between the collapse mass and the development of gully erosion, implying that further experiments are needed in the future to enrich the observations and thus improve the above-mentioned understanding. We conclude that by using TLS data in an experimental set-up, gully erosion processes can be captured with fine detail. This provides new insights into the process-understanding of gully erosion.

Study on mass erosion model of projectile penetrating concrete at high speed considering variation of friction coefficient

When the projectile penetrates into the concrete medium at high speed, the mass loss and nose blunting occur due to the strong local interaction between the projectile and the target. In order to further explore the mass erosion effect of high-speed projectile penetrating concrete target and its influencing factors, based on the thermal melting mechanism and variable friction coefficient model, the mass erosion model of high-speed projectile penetrating concrete target was modified considering the change of projectile nose shape during penetration. In order to verify the reliability of the model, based on the 30 mm ballistic gun platform, the oval projectile penetrating typical concrete targets at high velocities ranging from 700 to 1000 m/s was carried out, and the mass erosion results of high-speed penetration were obtained. Combined with the theoretical model, the reliability of the modified model is verified by analyzing the test data in this paper and the literature. The results show that the sliding friction term accounts for 10%−40% of the total friction in the process of projectile penetration, and its influence on the penetration process can’t be ignored. The prediction results of mass erosion model considering the variation of friction coefficient are in good agreement with the existing test data, and the maximum error with the test data in this paper is less than 7%, which can accurately predict the mass loss of projectile under different working conditions.

Experimental study on erosion resistance evaluation of single-layer metal mesh screen

In order to predict the erosion life and erosion failure time of the metal mesh, based on the rotating erosion experiments under different working conditions, the erosion mass loss of the metal mesh under different factors was measured by the weight loss method and the erosion mathematical prediction model was put forward. The erosion wear mechanism of the single-layer metal mesh was explored by using electron microscope scanner and optical microscope. The results show that the erosion rate increases exponentially with the increase of liquid velocity (0.5, 1.0, 1.5, 2.0 m/s). When the solid mass fraction (0.3%, 0.5%, 0.8%) and erosion Angle is 15°–45°, the erosion rate is proportional to the solid mass fraction and erosion Angle. After erosion, the mesh samples suffered different degree of pitting corrosion, ploughing and cutting wear, and the mesh wear was local wear. Compared with the experimental value, the error of the erosion mathematical model is less than 20%, which has a certain reliability, and has an important reference significance for guiding the production control of sand oil Wells.

A mathematical model of the erosion process in a channel bend

We develop a mathematical model for the cumulative erosion of a micro-particle in a channel system. At 90∘ bends in the system, a particle may deviate from the flow, impact the wall, and erode material. We highlight the case of the eroded material adhering to the particle, growing in size, and thus demonstrate how the damage accumulates exponentially with time. We describe and quantify the statistical nature of the evolution of particle growth and erosion (mass and location). We perform this analysis according to a number of realistic particle concentration distributions: uniform, Gaussian, and bimodal. A bimodal distribution, corresponding to the tubular pinch effect in suspension flows, results in unequal peak zones of erosion due to the flow characteristics.

The springs from the ”Făget” area of Cluj.

To the south of the city of Cluj, in the perimeter called “Făget”, there are numerous springs often frequented by locals. From a geological point of view, there is a great variety of rocks of different ages and characteristics. The waters cantoned in these geological structures appear on the surface along the valleys, on the slopes or even in the unevenness of the interfluves. Their existence was facilitated by vertical erosion processes and mass movements of the material. Through the inventory of the area, 28 sources were identified and located. They can be divided into several categories: with drain, wells, inactive, dried, captured. Spatial coordinates were determined for each source. Where possible, the flow rate, temperature and concentration of dissolved in water substances were measured. There is a large gap in flow variation, relatively constant temperatures and wide limits of TDS values. The expansion of the urban area involves potential risks of a quantitative and qualitative nature.

A simplified and modified model for long rod penetration based on ovoids of Rankine

This paper proposes an alternative to the Alekseevskii-Tate model, denoted by AT, for erosion of a long rod penetrator. Specifically, the model uses simplified equations of the model for long rod penetration based on ovoids of Rankine developed in (Roisman et al., 2001). The resulting modified ovoid of Rankine model, denoted by MOR, proposes differential equations for the velocity of the projectile’s tail, the penetration velocity into the target, the erosion of the projectile’s mass and the penetration depth, as well as an algebraic equation to determine the point of separation of the target material from the projectile’s surface. The MOR model uses shock conditions to determine the initial value of the penetration velocity and it predicts the initial transient decrease of this velocity to its value for quasi-steady-state projectile erosion. This model also includes an expression for the crater diameter which predicts values close to experimental data. Relative to the AT model, the MOR model introduces a single empirical parameter in a modified evolution for mass erosion which significantly influences the penetration depth without affecting the crater diameter. This parameter models the interface between the deforming projectile’s nose and its rigid tail where the projectile’s tail is rapidly decelerating due to mushrooming and mass erosion. Its value is determined by comparing model predictions of the penetration depth with experimental data. Future research is needed to replace this empirical parameter with an analytical model and to better model the termination process of penetration.

Comparison of cavitation erosion behaviors between the as-cast and friction stir processed Ni–Al bronze in distilled water and artificial seawater

Abstract In this investigation, the friction stir processing (FSP) method was utilized to improve the properties of the surface of the as-cast nickel aluminum bronze (NAB) alloy in two different processing parameters. The microstructure, element distribution and mechanical properties of the alloys before and after FSP were observed and estimated. The cavitation erosion behaviors of the original NAB and FSP NAB in different test solutions were also discussed. The results indicated that the microstructure became finer and more homogeneous and the element distribution became more uniform after FSP. The FSP NAB alloys also possessed better mechanical properties. The lower cumulative cavitation erosion mass loss of FSP NAB in all test solutions indicated the fact that the cavitation erosion resistance of the as-cast NAB could also be improved by the FSP method. Compared to the as-cast NAB, the corrosion effect on the cavitation erosion was more significant for the FSP NAB alloys owing to their better pure cavitation erosion resistance.

Database of Active Faults in Slovenia: Compiling a New Active Fault Database at the Junction Between the Alps, the Dinarides and the Pannonian Basin Tectonic Domains

We present the compilation of a new database of active faults in Slovenia, aiming at introducing geological data for the first time as input for a new national seismic hazard model. The area at the junction of the Alps, the Dinarides, and the Pannonian Basin is moderately seismically active. About a dozen Mw &amp;gt; 5.5 earthquakes have occurred across the national territory in the last millennium, four of which in the instrumental era. The relative paucity of major earthquakes and low to moderate fault slip rates necessitate the use of geologic input for a more representative assessment of seismic hazard. Active fault identification is complicated by complex regional structural setting due to overprinting of different tectonic phases. Additionally, overall high rates of erosion, denudation and slope mass movement processes with rates up to several orders of magnitude larger than fault slip rates obscure the surface definition of faults and traces of activity, making fault parametrization difficult. The presented database includes active, probably active and potentially active faults with trace lengths &amp;gt;5 km, systematically compiled and cataloged from a vast and highly heterogeneous dataset. Input data was mined from published papers, reports, studies, maps, unpublished reports and data from the Geological Survey of Slovenia archives and dedicated studies. All faults in the database are fully parametrized with spatial, geometric, kinematic and activity data with parameter descriptors including data origin and data quality for full traceability of input data. The input dataset was compiled through an extended questionnaire and a set of criteria into a homogenous database. The final database includes 96 faults with 240 segments and is optimized for maximum compatibility with other current maps of active faults at national and EU levels. It is by far the most detailed and advanced map of active faults in Slovenia.

A linked-scale coupled model of mass erosion and redistribution in plasma-exposed micro-foam surfaces

Surface evolution due to exposure to harsh environments is of importance in many scientific and technological applications. In plasma-exposed materials, the surface receives charged particles from the plasma, leading to a series of processes that drive the system far from equilibrium and may lead to the severe deterioration of the surface properties. Although surface morphological changes are driven by atomic collisions taking place over picoseconds and nanometers, these processes result in mass loss and redistribution of matter over much larger length and time scales. This necessitates a multi-scale approach capable of capturing the range of processes linking primary atomic collision events with engineering-level surface geometry changes. In this paper, we develop a computational model to simulate the morphological evolution and effective erosion rate of micro-architected tungsten foams during low-energy plasma ion bombardment. The model acts on several length scales, with the energy and angular dependence of the sputtering yield of flat tungsten surfaces determined using the SRIM code based on the binary collision approximation. This information is introduced into a low-fluence, short-term Monte Carlo raytracing model, and further into a high-fluence, long-term particle transport model. In the latter, material particles representing billions of atoms are described in a digitized 3-D representation of the foam structure from X-ray tomography data, and are sputtered off and redeposited using the atomistic information. We show that the redeposition of sputtered atoms leads to partial self-healing in the bottom layers with a sharp reduction in the sputtering coefficient of low density foams, roughly 25% of the solid W value. This is in qualitative agreement with recent experiments on low porosity W structures. At high fluence, the foam structure degrades considerably as there are fewer ligaments available to recapture sputtered atoms and, consequently, the sputtering rate increases again.

Remarkable enhancement of tracking resistance of addition-cure liquid silicone rubber by alkyl-disubstituted ureido siloxane immobilized on the silica filler surface

It is urgent and significant to prepare silicone rubber with excellent tracking resistance in a harsh environment. In this work, alkyl-disubstituted ureido siloxane immobilized on silica (U-SiO2) was prepared by the dehydration condensation of hydrolysates of alkoxy groups in alkyl-disubstituted ureido siloxanes (US) and hydroxyl groups on the silica surface. The effect of U-SiO2 on the tracking resistance of addition-cure liquid silicone rubber (ALSR) was investigated by inclined-plane test (IP test). It was found that U-SiO2 could effectively enhance the tracking resistance of ALSR. Especially, diisopropylureidopropyltriethoxysilane and diisobutylureidopropyltriethoxysilane with isomeric substitution immobilized on silica (DIPUPES-SiO2 and DIBUPES-SiO2) performed the best. With less than 1.00 phr content, ALSR samples could reach 1A4.5 level. The erosion mass was only 0.40 % and 0.62%, respectively. Moreover, ALSR / DIPUPES-SiO2 had excellent water resistance. It could still reach 1A4.5 level and the erosion mass was almost unchanged after ALSR / DIPUPES-SiO2 was immersed in the water for five days. The results of plasma irradiation and thermal treatment showed that U-SiO2 could effectively inhibit the aggregation of platinum in Karstedt's catalyst, which could promote the crosslinking of ALSR chains under the elevated temperature to form a compact ceramic protected layer. It could not only isolate the oxygen and heat and suppress the thermal degradation of ALSR, but also resist the plasma bombardment. Therefore, the tracking resistance of ALSR was remarkably enhanced.