Erosion Mode Research Articles

Using differential structure-from-motion photogrammetry to quantify erosion at the Engare Sero footprint site, Tanzania

Hominin footprint sites are excellent sources of data that provide insights into early human physiology, anatomy, and social structures. They are also potential tourist attractions that are often situated in relatively under-developed parts of the world. Unfortunately, many footprint sites are also located in high energy environments and/or are pressed into poorly indurated sediments, which make them highly susceptible to erosion. This paper proposes a non-invasive and low-cost method employing Structure-from-Motion photogrammetry to quantify erosion rates in the absence of permanent ground control points. Using point cloud comparison algorithms between data collected at different times, it is possible to quantitatively analyze the locations, volumes, and rates of material loss. We applied this technique to several footprints within the Engare Sero footprint site in northern Tanzania to assess erosional change between 2010 and 2017. Our comparisons show that prints are vertically eroding at average rates ranging from 0.10 to 0.17 mm/yr with some localized areas experiencing much higher rates over shorter durations. We identify three primary modes of erosion: 1) flaking, 2) abrasion, and 3) boring of holes. Erosion appears to have occurred episodically with major events, such as flooding, separated by periods of relative stability. The methods presented here are valuable for paleoanthropologists to better understand how footprint erosion might adversely affect inferences regarding print-makers, and they are valuable for decision-makers, who can create conservation plans to better protect and maximize the utility of known hominin footprint sites.

Slurry Erosion Behavior of AlxCoCrFeNiTi0.5 High-Entropy Alloy Coatings Fabricated by Laser Cladding

High-entropy alloys (HEAs) have gained extensive attention due to their excellent properties and the related scientific value in the last decade. In this work, AlxCoCrFeNiTi0.5 HEA coatings (x: molar ratio, x = 1.0, 1.5, 2.0, and 2.5) were fabricated on Q345 steel substrate by laser-cladding process to develop a practical protection technology for fluid machines. The effect of Al content on their phase evolution, microstructure, and slurry erosion performance of the HEA coatings was studied. The AlxCoCrFeNiTi0.5 HEA coatings are composed of simple face-centered cubic (FCC), body-centered cubic (BCC) and their mixture phase. Slurry erosion tests were conducted on the HEA coatings with a constant velocity of 10.08 m/s and 16–40 meshs and particles at impingement angles of 15, 30, 45, 60 and 90 degrees. The effect of three parameters, namely impingement angle, sand concentration and erosion time, on the slurry erosion behavior of AlxCoCrFeNiTi0.5 HEA coatings was investigated. Experimental results show AlCoCrFeNiTi0.5 HEA coating follows a ductile erosion mode and a mixed mode (neither ductile nor brittle) for Al1.5CoCrFeNiTi0.5 HEA coating, while Al2.0CoCrFeNiTi0.5 and Al2.5CoCrFeNiTi0.5 HEA coatings mainly exhibit brittle erosion mode. AlCoCrFeNiTi0.5 HEA coating has good erosion resistance at all investigated impingement angles due to its high hardness, good plasticity, and low stacking fault energy (SFE).

Erosion characteristics of ethylene propylene diene monomer composite insulation by high-temperature dense particles

In this study, a dense particles erosion test motor which can simulate the erosion state of a solid rocket motor under high acceleration was developed. Subsequently, erosion experiments were carried out for the ethylene propylene diene monomer composite insulation and the microstructure of the char layer analysed. A turning point effect was found from the influence of the particle impact velocity on the ablation rate, and three erosion modes were determined according to the micro-morphology of the char layer. A reasonable explanation for the different structures of the char layer in the three modes was presented based on the formation mechanism of the compact/loose structure of the char layer.

Effect of Initial Surface Roughness on Cavitation Erosion Resistance of Arc-Sprayed Fe-Based Amorphous/Nanocrystalline Coatings

The arc spraying process was used to prepare Fe-based amorphous/nanocrystalline coating. The cavitation erosion behaviors of FeNiCrBSiNbW coatings with different surface roughness levels were investigated in distilled water. The results showed that FeNiCrBSiNbW coating adhered well to the substrate, and was compact with porosity of less than 2%. With increasing initial surface roughness, the coatings showed an increase in mass loss of cavitation erosion damage. The amount of pre-existing defects on the initial surface of the coatings was found to be a significant factor for the difference in the cavitation erosion behavior. The cavitation erosion damage for the coatings was a brittle erosion mode. The evolution of the cavitation erosion mechanism of the coatings with the increase of the initial surface roughness was micro-cracks, pits, detachment of fragments, craters, cracks, pullout of the un-melted particle, and massive exfoliations.

Modelling Fine Sediment Dynamics: Towards a Common Erosion Law for Fine Sand, Mud and Mixtures

This study describes the building of a common erosion law for fine sand and mud, mixed or not, in the case of a typical continental shelf environment, the Bay of Biscay shelf, characterized by slightly energetic conditions and a seabed mainly composed of fine sand and muddy sediments. A 3D realistic hydro-sedimentary model was used to assess the influence of the erosion law setting on sediment dynamics (turbidity, seabed evolution). A pure sand erosion law was applied when the mud fraction in the surficial sediment was lower than a first critical value, and a pure mud erosion law above a second critical value. Both sand and mud erosion laws are formulated similarly, with different parameters (erodibility parameter, critical shear stress and power of the excess shear stress). Several transition trends (linear or exponential) describing variations in these erosion-related parameters between the two critical mud fractions were tested. Suspended sediment concentrations obtained from simulations were compared to measurements taken on the Bay of Biscay shelf with an acoustic profiler over the entire water column. On the one hand, results show that defining an abrupt exponential transition improves model results regarding measurements. On the other hand, they underline the need to define a first critical mud fraction of 10 to 20%, corresponding to a critical clay content of 3–6%, below which pure sand erosion should be prescribed. Both conclusions agree with results of experimental studies reported in the literature mentioning a drastic change in erosion mode above a critical clay content of 2–10% in the mixture. Results also provide evidence for the importance of considering advection in this kind of validation with in situ observations, which is likely to considerably influence both water column and seabed sediment dynamics.

Slurry erosion behavior of high entropy alloys

High entropy alloys (HEAs) represent a new paradigm of structural alloys comprising of multiple principal elements in equimolar or near-equimolar concentration. The superior corrosion and oxidation resistance of HEAs at high temperature make them attractive for several structural applications. In this context, erosion behavior of HEAs has been largely unexplored. In this study, the slurry erosion performance of single phase Al0.1CoCrFeNi high entropy alloy was investigated. For comparison, mild steel and stainless steel (SS316L) were also investigated under similar conditions. The slurry erosion was conducted at different impingement angles and at a constant velocity of 20m/s. The microstructural and mechanical characterization were conducted using scanning electron microscope (SEM), energy dispersive spectroscopy (EDS), x-ray diffraction (XRD), nanoindentation and micro-hardness testing. Similar to the mild steel and stainless steel, HEA also showed ductile mode of erosion. The erosion rate for HEA was found to be higher compared to stainless steel, however in spite of lower tensile strength and hardness, HEA exhibited higher erosion resistance compared to mild steel. The high erosion resistance of HEA compared to mild steel is explained on the basis of its work hardening behavior, low stacking fault energy, and superior corrosion resistance. Erosion response of the investigated materials showed significant correlation with ultimate strength and ultimate resilience. In depth analysis of the eroded HEA samples showed ploughing as the prominent material removal mechanism at oblique angles compared to micro-cutting for SS316L and mild steel. In contrast, highly deformed and work-hardened platelets were observed at normal impingement angle for all materials.

Effects of erodent flow energy and local exposure time on the erosion of cement-based composites at high-speed hydro-abrasive flow

The objective of the paper is the quantification of effects of erodent flow kinetic energy and exposure time on the erosion of cement-based composites with high-speed hydro-abrasive jets. The erodent flow kinetic energy is varied due to changes in erodent velocity, traverse rate and erodent particle mass-flow rate. For a given traverse rate, the relationship between volumetric erosion rate and erodent flow kinetic energy follows a power function with power exponents between 0.49 and 0.66. The kinetic energy of the erodent flow is not a sufficient measure for the material removal capacity of high-speed hydro-abrasive flow. A critical exposure time must be realized in order to eliminate traverse rate effects. Exposure time effects are characterized with a Weibull-type function, whereby the shape parameter k of the function depends on erosion mode and material response. If incremental erosion modes dominate the material removal process: k>1. If continuous erosion modes control the material removal process: k≤1. It is supposed that k exceeds unity if a threshold fracture toughness of the composites is exceeded.

Degradation of poly(L‐lactic acid) coating on permanent coronary metal stent investigated ex vivo by micro Raman spectroscopy

Poly(lactic acid) (PLA) is a biodegradable polymer with a variety of applications, such as functional coatings on implants, due to its biodegradability, good biocompatibility and very low toxicity. In this study, the degradation behavior of high molecular weight poly(L‐lactic acid) (L‐PLA), which was used as polymer coating on permanent coronary metal stent, was investigated ex vivo. Poly(methyl methacrylate) (PMMA)‐embedded histological specimens of stented porcine coronary arteries (left anterior descending artery, left circumflex artery and right coronary artery) were used to follow the degradation at various implantation times (6, 12, 24 and 36 months). Micro Raman spectroscopy was applied as an alternative technique for the determination of the residual content of the L‐PLA coating. For this purpose, the PMMA‐embedded cross sections of stented porcine coronary arteries were characterized through a previously developed Raman method for in situ quantitative analysis of PLA in a PMMA matrix. The residual content of L‐PLA coating on the surface of the coronary metal stent was determined through the relative Raman band area ratio of the C–COO stretching band of PLA at 873 cm−1 and the C–O–C symmetric stretching band of PMMA at 813 cm−1. This study demonstrated that Raman spectroscopy provides an alternative, non‐destructive technique for quantification of L‐PLA coating on permanent coronary metal stent in an animal model. The results suggest that the complete absorption of the L‐PLA coating required more than 24 months for the layer thickness applied in this study and that the degradation of high molecular weight L‐PLA in a porcine model is carried out by a hydrolytic degradation through the bulk erosion mode. Copyright © 2017 John Wiley & Sons, Ltd.

The applicability of microbially induced calcite precipitation (MICP) for internal erosion control in gravel–sand mixtures

Seepage-induced internal erosion in earth-filled embankment dams has been attracting the attention of civil engineering researchers and practitioners for decades. Microbially induced carbonate precipitation (MICP), owing to its proved performance in soil enhancement and permeability control, can potentially be used for internal erosion control. This paper examines the applicability of MICP for internal erosion control in gravel–sand mixtures using a large one-dimensional column test apparatus which incorporates the implementation of MICP. Visual observations, erosion characteristics and hydro-mechanical behaviours of non-MICP and MICP treated gravel–sand mixtures were investigated through a series of constant-pressure erosion tests. Test results confirm that MICP treatment can reduce the cumulative erosion weight, erosion rate and axial strain relative to non-MICP soil. The magnitudes of hydraulic conductivity for all tested samples before the erosion process fall into a range from 5·5 × 10−5to 8·0 × 10−3 m/s. After the erosion process, non-MICP soils and MICP treated soils with low cementation concentrations experience a significant increase in hydraulic conductivity. Furthermore, a hydro-mechanical coupling analysis was conducted and different erosion modes were identified for low and high concentrations of cementation solution. Fundamentally, the efficiency of internal erosion reduction is controlled by the calcium carbonate precipitation content within the tested soils. Higher precipitation content can facilitate the formation of larger clusters of cemented sand particles, thus reducing the likelihood of erosion.

Taguchi analysis on erosive wear behavior of cobalt based microwave cladding on stainless steel AISI-420

Abstract The strength, hardness, wear and corrosion resistance are the most important mechanical properties of the tribological components. Martensitic stainless steel plays very important role to represent these characteristics. The AISI-420 stainless steel widely used to manufacture the hydraulic and gas turbine components. The present work deals with microstructure and slurry erosive wear studies of cobalt based clad developed through microwave energy at a frequency of 2.45 GHz. The scanning electron microscope (SEM) and energy dispersive X-ray spectroscopy (EDS) analysis result reveals the presence of cobalt and chromium rich solid solution in the intercellular substances. The Taguchi orthogonal array was used to gauge the factors affecting the wear significantly. The influence of various factors such as speed, particle size and impingement angle on wear behavior was evaluated by Means and ANOVA (analysis of variance). It was observed that the slurry speed significantly influenced the more mass loss on unclad substrate. The wear mechanism of the worn surface was studied through a scanning electronic microscope. It shows the mixed mode of erosion in the form of microcutting, ploughing, and fractures appeared are major wear mechanisms.

Re-Melting Technique with High Intense Pulsed Plasma Beams Applied for Surface Modification of Steel - Own Investigations

The plasma beams were generated in a Rod Plasma Injector (RPI) operated in the Deposition by Pulsed Erosion (DPE) and Pulse Implantation Doping (DPE) modes. Samples of unalloyed and austenitic stainless steels were irradiated with short (μs scale) intense (energy density 2.0-5.0 J/cm2) pulses. The near surface layer - thickness in μm range - was melted and simultaneously doped with active element like nitrogen, cerium and lanthanum. Heating and cooling processes were of non-equilibrium type. The most important obtained results were: (i) austenitic structure was present in unalloyed steels after HIPPB modification processes and (ii) modified surface layers of austenitic stainless steel showed significant improvement of tribological properties and increase of high temperature oxidation resistance as compared with initial material.

Comparison of simplified physically based dam breach models

Three simplified physically based earthen embankment breach models, NWS BREACH (Revision 1), HR BREACH (Version 4.1) and DLBreach, are used to calculate the breaching of twelve dams, and the results are compared against the measured data and the predictions by three parametric breach models. It is found that NWS BREACH may have large errors for cohesive embankments, since it uses a noncohesive sediment transport model and does not consider headcut erosion as a typical mode of cohesive dam breach. HR BREACH considers headcut and surface erosion modes and adopts various surface erosion equations for noncohesive and cohesive soils. DLBreach adopts a nonequilibrium total-load sediment transport model and headcut erosion model for noncohesive and cohesive embankment breaching, respectively. All the three physically based models can handle overtopping failure of homogeneous and composite dams, as well as piping failure. HR BREACH and DLBreach consider both one- and two-sided widening, whereas only DLBreach allows subbase erosion. The comparison shows that DLBreach has best overall performance. Sensitivity studies show that sensitivity of these three models to soil erodibility is case dependent, but overall, DLBreach and HR BREACH are more sensitive than NWS BREACH. In addition, it is demonstrated that an adequate physically based breach model can perform better and provide more detailed results than a parametric model.

Electrospark coatings produced by ceramic nanostructured SHS electrode materials

The paper considers the possibility to expand the number of materials used for electrospark alloying. Ceramic nanostructured TiB2–TiC–Al2O3–ZrO2-based materials produced by means of SHS extrusion are used as electrodes. The regularities of the alloyed layer formation with electrospark alloying (ESA) are studied. Three different modes of anode erosion and cathode gain are observed for single pulse energies ranging from 0.05 to 2.5 J. The microstructure of the coatings is studied. It is shown that, in the case of ESA by ceramic SHS electrodes, nanosized crystallites are formed. The microhardness of the alloyed layer is 1250 HV. The tribological tests of the protective coatings demonstrate a high wear resistance (10–5 mm3/N/m) and low friction coefficient (0.2).

Simulating Biofilm Deformation and Detachment with the Immersed Boundary Method

AbstractWe apply the immersed boundary (or IB) method to simulate deformation and detachment of a periodic array of wall-bounded biofilm colonies in response to a linear shear flow. The biofilm material is represented as a network of Hookean springs that are placed along the edges of a triangulation of the biofilm region. The interfacial shear stress, lift and drag forces acting on the biofilm colony are computed by using fluid stress jump method developed by Williams, Fauci and Gaver [Disc. Con-tin. Dyn. Sys. B11(2):519–540, 2009], with a modified version of their exclusion filter. Our detachment criterion is based on the novel concept of an averaged equivalent continuum stress tensor defined at each IB point in the biofilm which is then used to determine a corresponding von Mises yield stress; wherever this yield stress exceeds a given critical threshold the connections to that node are severed, thereby signalling the onset of a detachment event. In order to capture the deformation and detachment behaviour of a biofilm colony at different stages of growth, we consider a family of four biofilm shapes with varying aspect ratio. For each aspect ratio, we varied the spacing between colonies to investigate role of spatial clustering in offering protection against detachment. Our numerical simulations focus on the behaviour of weak biofilms (with relatively low yield stress threshold) and investigate features of the fluid-structure interaction such as locations of maximum shear and increased drag. The most important conclusions of this work are: (a) reducing the spacing between colonies reduces drag by from 50 to 100% and alters the interfacial shear stress profile, suggesting that even weak biofilms may be able to grow into tall structures because of the protection they gain from spatial proximity with other colonies; (b) the commonly employed detachment strategy in biofilm models based only on interfacial shear stress can lead to incorrect or inaccurate results when applied to the study of shear induced detachment of weak biofilms. Our detachment strategy based on equivalent continuum stresses provides a unified and consistent IB framework that handles both sloughing and erosion modes of biofilm detachment, and is consistent with strategies employed in many other continuum based biofilm models.

Effect of mechanical properties and impact angles on erosion behavior of B4C/TiB2 matrix ceramic nozzle materials

B4C/TiB2/Mo and B4C/TiB2/Al2O3 ceramic nozzle materials were obtained by uniaxial hot-pressing. Mechanical properties and erosion behavior of the two series ceramic nozzle materials were investigated. Volume erosion rate was used to rank the erosion behavior of the nozzle materials. The relationship between mechanical properties and volume erosion rate, as well as impact angles and volume erosion rate of nozzle materials were discussed. SEM technique was employed to observe the eroded surfaces of ceramic nozzle materials. The logarithmic volume erosion rate of B4C/TiB2 matrix ceramic nozzle materials decreased linearly with increasing the logarithmic hardness and fracture toughness of the nozzle materials. The erosion rate increased with increasing the impact angle and reached the maximum at an impact angle of 90°. There were obvious differences between erosion resistance of the nozzle materials using SiC and Al2O3 as abrasive particles. The wear of B4C/TiB2 matrix ceramic nozzle materials was divided into two sections by ln(Hp/H)=1.1. The nozzle materials were eroded by hard particles (SiC) and the erosion was serious as ln(Hp/H)>1.1. Soft particle wear became the main erosion mode while Al2O3 was used as the erodent abrasive, and the erosion was more mild as ln(Hp/H)<1.1. SEM analysis of B4C/TiB2 matrix ceramic nozzle materials eroded at entry showed that the main erosion mechanism was brittle fracture.

Erosion behaviour of WC–10Co–4Cr coating on 23-8-N nitronic steel by HVOF thermal spraying

WC–10Co–4Cr coating was deposited by high-velocity oxy-fuel (HVOF) process on cast and solution treated (1220°C/150min) 23-8-N nitronic steel substrates. Solution treated substrate has shown higher toughness, ductility and impact energy with a marginal reduction in hardness as compared to cast substrate. This influence the coating deposition efficiency and erosion behaviour. Erosion resistance of coatings was evaluated by air jet erosion tester on two different impact angles (30° and 90°). Phases, microstructure and eroded surface of the coating were characterised by X-ray diffraction (XRD) analysis and field-emission scanning electron microscopy (FESEM) respectively. It is observed that coating on solution treated substrate was superior to cast substrate. The reason being that coating has dense and well-bonded structure with low porosity, less decarburization and inter-splat oxidation. Higher erosion resistance of coated solution treated 23-8-N nitronic steel was attributed to combination of high fracture toughness and hardness of coating including optimum mechanical properties of the substrate. FESEM analysis reveals that erosion response of WC–10Co–4Cr coating also dependent on the relative size of the impact crater with respect to the WC grain size. Coating is removed by combined mode of ductile and brittle erosion.

Response of vegetated dune–beach systems to storm conditions

Human encroachment on the coasts is extensive and expected to increase over the coming decades. This proximity to the sea is coupled with potentially more frequent strong tropical cyclones and eustatic sea level rise, and thus human life, property and infrastructure are threatened. In this scenario, it is vital to find the means to maintain or increase the resilience and resistance of coastal zones. As an alternative to engineering solutions, ecosystem-based coastal defence strategies have been recommended as better and more sustainable solutions, although it has not been clearly demonstrated that they really work. In 24 wave flume experiments, we studied the effects of four densities of vegetation cover (none, low, medium, high) on the movement of sediment along two beach–dune profiles (with and without a berm), under three storm conditions (mild, moderate and intense). Erosion regimes of collision and overwash were observed in the dune profiles with a berm, whereas swash and overwash regimes were observed when no berm was present. In the profiles with a collision regime, vegetation decreased the amount of erosion. For both profiles, in the tests with the largest wave conditions, vegetation prevented overwash and thereby erosion of the landward side of the dune. Erosion of the dune face was reduced by vegetation, particularly with a strong storm, when Iribarren numbers were greater. In summary, vegetation reduced net erosion on the dune face, regardless of the wave conditions, the morphology of the beach–dune profile, or the mode of erosion.

Study of Solid Particle Erosion Behaviour of SS 304 at Room Temperature

Erosion is one of the major problems in many engineering system including power generation units, steam/jet turbines, chemical processing equipments, and air craft engines. In the present study erosion test were conducted using air-jet erosion test rig on boiler tube steel SS 304. The impact velocity was 40m/s, the impingement angle was 30o and 90o on SS 304 at room temperature. Alumina particles of size 50 microns were used as the erodent. The initial and final weight of the specimens were taken using electronic weighing machine having a resolution of 0.01mg. Erosion rate was determined as the ratio of weight loss of the material to the weight of eroding particles. Scanning electron microscope (SEM), equipped with an energy dispersive X-ray analyser (EDAX) was used to analyse the eroded surfaces. Results indicated that SS 304 showed higher erosion rate at 30o as compared to 90o impact angle, indicating ductile mode of erosion.

Solid Particle Erosion Behaviors of Carbon-Fiber Epoxy Composite and Pure Titanium

Rotor blades of Bell CH-146 Griffon helicopter experience excessive solid particle erosion at low altitudes in desert environment. The rotor blade is made of an advanced light-weight composite which, however, has a low resistance to solid particle erosion. Coatings have been developed and applied to protect the composite blade. However, due to the influence of coating process on composite material, the compatibility between coating and composite base, and the challenges of repairing damaged coatings as well as the inconsistency between the old and new coatings, replaceable thin metal shielding is an alternative approach; and titanium, due to its high-specific strength and better formability, is an ideal candidate. This work investigates solid particle erosion behaviors of carbon-fiber epoxy composite and titanium in order to assess the feasibility of titanium as a viable candidate for erosion shielding. Experiment results showed that carbon-fiber epoxy composite showed a brittle erosion behavior, whereas titanium showed a ductile erosion mode. The erosion rate on composite was 1.5 times of that on titanium at impingement angle 15° and increased to 5 times at impact angle 90°.

Effect of N2 and Ar gas on DC arc plasma generation and film composition from Ti-Al compound cathodes

DC arc plasma from Ti, Al, and Ti1−xAlx (x = 0.16, 0.25, 0.50, and 0.70) compound cathodes has been characterized with respect to plasma chemistry (charged particles) and charge-state-resolved ion energy for Ar and N2 pressures in the range 10−6 to 3 × 10−2 Torr. Scanning electron microscopy was used for exploring the correlation between the cathode and film composition, which in turn was correlated with the plasma properties. In an Ar atmosphere, the plasma ion composition showed a reduction of Al of approximately 5 at. % compared to the cathode composition, while deposited films were in accordance with the cathode stoichiometry. Introducing N2 above ∼5 × 10−3 Torr, lead to a reduced Al content in the plasma as well as in the film, and hence a 1:1 correlation between the cathode and film composition cannot be expected in a reactive environment. This may be explained by an influence of the reactive gas on the arc mode and type of erosion of Ti and Al rich contaminations, as well as on the plasma transport. Throughout the investigated pressure range, a higher deposition rate was obtained from cathodes with higher Al content. The origin of generated gas ions was investigated through the velocity rule, stating that the most likely ion velocities of all cathode elements from a compound cathode are equal. The results suggest that the major part of the gas ions in Ar is generated from electron impact ionization, while gas ions in a N2 atmosphere primarily originate from a nitrogen contaminated layer on the cathode surface. The presented results provide a contribution to the understanding processes of plasma generation from compound cathodes. It also allows for a more reasonable approach to the selection of composite cathode and experimental conditions for thin film depositions.