Steady-state Erosion Rate Research Articles

Experimental Investigation of Slurry Erosion Wear Analysis of Epoxy Resin Reinforced with Aramid Woven Fabric with Taguchi Experimental Design

Abstract: Fibre reinforced polymer composites as hybrid composites are commonly used for certain applications in which erosion wear and fracture are serious issues. These composites have engineering/structural applications in which they are subjected to sand slurries and dusty environment. Composites with different fibre loading are used to evaluate steady state erosion behavior for different operating conditions on slurry jet erosion testing machine. In this chapter Slurry jet erosion test rig is used for experimental investigation of steady state erosion rate of aramid composite samples as per ASTM standards. Steady state erosion test is conducted by defining certain control factors and fixed parameters. Test is conducted in two cases. In first case by varying impact angle and keeping impact velocity and discharge rate constant and in second case by varying impact velocity and keeping impact angle and discharge rate constant. Steady state erosion rate is calculated for both the cases. The Taguchi experimental design (orthogonal array) is used to optimize the design parameters and used to analyse the effect of control factors on output parameters, which reduces overall testing time and cost. To understand the effect of control factors and their iterations ANOVA (analysis of variance) is used. Results of steady state erosion rate and Taguchi experimental design are analysed to selection best suitable material for turbine blade application based on minimum erosion rate

Effect of microstructure, impact velocity and angle on erosive wear of medium carbon, dual phase and fully martensitic steels

The present study has been conducted to analyze the effect of microstructure on erosive wear of medium carbon (N), dual phase (DP) and fully martensitic (FMS) steels at different velocities (30 m/s, 60 m/s, 90 m/s and 120 m/s) and impingement angles (15°, 45°, 75°, and 90°) with Al2O3 as an erodent. The findings suggest that the steady state erosion rate increases with an increase in impact velocity for all materials, whereas it decreases with an increase in impact angle for all steels except for FMS. At low and high impact angles, N steel exhibits the highest erosive wear characterized by micro cutting and ridge formation. Except at 90° and 120 m/s, FMS has shown the highest erosion rate compared to all steels due to its inherent brittle nature, which makes it prone to easy crack propagation. In DP steel, the cracks get arrested by the hard martensite island and their easy propagation is inhibited, which leads to only low angle cutting and micro ploughing. This reflects the advantage of using a dual phase structure. DP steels showed higher erosion resistance because they offer a balanced combination of strength and ductility at an adequate level of toughness. The material removal in N steel is found to occur by micro cutting, ridge, and crater formation, whereas shallow micro ploughing and craters are observed in FMS. However, the material removal for DP steels has been found to occur due to a combination of micro ploughing, micro cutting and crater formation.

The effects of storms and a transient sandy veneer on the interannual planform evolution of a low-relief coastal cliff and shore platform at Sargent Beach, Texas, USA

Abstract. Coastal cliff erosion is alongshore-variable and episodic, with retreat rates that depend upon sediment as either tools of abrasion or protective cover. However, the feedbacks between coastal cliff planform morphology, retreat rate, and sediment cover are poorly quantified. This study investigates Sargent Beach, Texas, USA, at the annual to interannual scale to explore (1) the relationship between temporal and spatial variability in cliff retreat rate, roughness, and sinuosity and (2) the response of retreat rate and roughness to changes in sand and shell hash cover of the underlying mud substrate as well as the impact of major storms using field measurements of sediment cover, erosion, and aerial images to measure shore platform morphology and retreat. A storm event in 2009 increased the planform roughness and sinuosity of the coastal cliff at Sargent Beach. Following the storm, aerial-image-derived shorelines with annual resolution show a decrease in average alongshore erosion rates from 12 to 4 m yr−1, coincident with a decrease in shoreline roughness and sinuosity (smoothing). Like the previous storm, a storm event in 2017 increased the planform roughness and sinuosity of the cliff. Over shorter timescales, monthly retreat of the sea cliff occurred only when the platform was sparsely covered with sediment cover on the shore platform, indicating that the tools and cover effects can significantly affect short-term erosion rates. The timescale to return to a smooth shoreline following a storm or roughening event, given a steady-state erosion rate, is approximately 24 years, with the long-term rate suggesting a maximum of ∼107 years until Sargent Beach breaches, compromising the Gulf Intracoastal Waterway (GIWW) under current conditions and assuming no future storms or intervention. The observed retreat rate varies, both spatially and temporally, with cliff face morphology, demonstrating the importance of multi-scale measurements and analysis for interpretation of coastal processes and patterns of cliff retreat.

Response of transient rock uplift and base level knickpoints to erosional efficiency contrasts in bedrock streams

AbstractKnickpoints in bedrock streams are often interpreted as transient features generated by a change in boundary conditions. It is typically assumed that knickpoints propagate upstream with constant vertical velocities, though this relies on a stream being in erosional steady state (erosion rate equals rock uplift rate) prior to the knickpoint's formation. Recent modeling and field studies suggest that along‐stream contrasts in rock erodibility perturb streams from erosional steady state. To evaluate how contrasts in rock erodibility might impact knickpoint interpretations, we test parameter space (rock erodibility, rock contact dip angle, change in rock uplift rate) in a one‐dimensional (1D) bedrock stream model that has variable rock erodibility and produces a knickpoint with a sudden change in rock uplift rate. Upstream of a rock contact, the vertical velocity of a knickpoint generated by a change in rock uplift rate is strongly correlated with how the rock contact has previously perturbed erosion rates. These knickpoints increase vertical velocity upon propagating upstream of a hard over soft contact and decrease vertical velocity upon propagating upstream of a soft over hard contact. However, interactions with other transient perturbations produced by rock contacts make for nuances in knickpoint behavior. Rock contacts also influence the geometry of knickpoints, which can become particularly difficult to identify upstream of soft over hard rock contacts. Using our simulations, we demonstrate how a contact's along‐stream horizontal migration rate and cross‐contact change in rock strength control how much an upstream reach is perturbed from erosional steady state. When simulations include multiple contacts, the knickpoint is particularly prone to colliding with other transient perturbations and can even disappear altogether if rock contact dips are sufficiently shallow. Caution should be taken when analyzing stream profiles in areas with significant changes in rock strength, especially when rock contact dip angles are near the stream's slope.

Impact of rock fracture geometry on geotechnical barrier integrity – A numerical study

The effect of fracture geometry on bentonite erosion for a generic repository site in crystalline host rock environment was investigated by means of 2-d numerical simulations. Fracture geometry was varied systematically using random aperture normal distributions with a mean aperture of 1 mm and standard deviations between 0 and 0.7 mm, respectively. Moreover, two aperture correlation lengths (0.2 m and 2 m) were applied. Based on the synthetic fracture aperture fields generated the cubic law in conjunction with the Darcy equation is used to simulate fracture flow fields for mean flow velocities in the fracture between 1 × 10−5 m/s and 1 × 10−7 m/s. These flow fields are used in a two-way coupling approach to bentonite erosion simulations.The results of the study clearly show the influence of variable fracture aperture on bentonite erosion behaviour and erosion rates (kg/a). Increasing fracture aperture standard deviation leads to increasing heterogeneous flow velocity distributions governing the erosion behaviour and erosion rates. Calculated steady state erosion rates are in the range of ~0.25 kg/a down to ~0.014 kg/a. The highest erosion rate is calculated for the highest mean flow velocity in conjunction with the highest standard deviation. The effect of aperture heterogeneity diminishes for the lowest flow velocities.In summary, the results show the effect of fracture heterogeneity on bentonite erosion, especially for high to medium mean flow velocities combined with high to medium fracture heterogeneity under the model boundary conditions and model capabilities and limitations considered. An increase of up to ~83% in erosion rate compared to the constant aperture case highlights the need to consider fracture aperture heterogeneity and its effect on the bentonite erosion in the assessment of the safety and evolution of a high-level nuclear waste repository.

Erosion behaviour of HVOF sprayed WC.Co-NiCrAlYSi (35%-65%) coatings

In the present study, WC.CO-NiCrAlYSi(35%-65%) cermet coatings were deposited on a Fe-based super alloy designated as SS316 (Midhani Grade) to reduce the damage caused by erosion boiler applications. Erosion studies were conducted on uncoated as well as HVOF coated steels. The erosion experiments were carried out using an air-jet erosion test rig according to ASTM G-76 standard at a velocity of 30 m/s and at different impingement angles of 30°, 60° and 90°. Alumina particles of size ranging between 50 and 80 μm were used as erodent. Analysis of weight-loss data and Volumetric steady state erosion rates for different coatings and substrate alloys are evaluated. The bare SS316 steel followed ductile erosion mode where as WC.CO-NiCrAlYSi(35%-65%) coating exhibited brittle behaviour respectively. Selection and/or Peer-review under responsibility of The First Materials Research Society of Thailand International Conference.

Improvement of solid particle erosion resistance of helicopter rotor blade with hybrid composite shield

In the present study, the solid particle erosion behavior of polyurethane (PU) tape (3M-8663) material, bidirectional carbon fiber reinforced epoxy (CF/EP) and glass fiber reinforced epoxy (GF/EP) composites has been characterized experimentally and numerically. In the experimental part, steady-state erosion rates of aforementioned materials have been evaluated at different impact angles (20°, 30°, 45°, 60°, and 90°) and different impact velocities (70, 110, 150, and 190 m/s), and compared with those of stainless steel (SS304) and pure nickel materials (Ni) which are commonly used for erosion shield of helicopter rotor blades. Tests were conducted at room temperature using silica (SiC) particles (average diameter of 175 µm) as an erodent. Erosion behaviors on the shield surface of the same materials were investigated numerically under different impact velocities (110, 150, 190, and 230 m/s) for a pitch angle of 0°. Numerical erosion simulations were realized with commercial ANSYS-Fluent software using the finite volume method, an erosion model, and a discrete phase method with the Eulerian-Lagrangian approach. The experimental results showed that the GF/EP and the CF/EP composites indicated the maximum erosion rate at the impact angles ranged from 60° to 90°, whereas the PU tape material exhibited the maximum erosion rate at the impact angle of 30°. The results also showed that the PU tape surface clearly provided much better erosion resistance than the GF/EP and CF/EP composite surfaces, and the hybrid erosion shield having the PU/SS304 surface significantly improved the erosion resistance of the helicopter rotor blade up to the impact velocity of 150 m/s. A good agreement was also observed between the experimental and the numerical results.

Numerical Simulation of Solid Particle Erosion of Epoxy by Overlapping Angular Particle Impacts

The solid particle erosion of polymers occurs in a wide variety of industries and has been extensively studied experimentally. However, numerical models capable of accurately simulating the associated material removal mechanisms and predicting erosion rate do not yet exist. In this paper, a coupled smoothed particle hydrodynamics (SPH)/finite element (FE) model was developed to simulate the erosion of an epoxy by successive overlapping impacts of angular 22 µm, 97 µm and 152 µm silicon carbide particles at various angles of attack. The epoxy was modeled using a strain-rate-dependent elastic–plastic material model that fails at a critical plastic strain. It was found that, once the critical plastic strain was calibrated using a single experiment, the numerical model could predict both the length of the incubation period and the steady-state erosion rate to within 6% and 11%, respectively, of the measured values. It was found that fundamental material removal mechanisms such as cutting, ploughing and the accumulation of plastic deformation due to multiple overlapping impacts were all successfully simulated. Overall, it has been demonstrated that numerical models can be used to investigate the effect of influential parameters on the solid particle erosion of a polymer. This may have important implications for the development of effective methods to improve the erosion resistance of polymers.

Erosion behaviour of boiler component materials at room temperature and 400 °C temperature

Degradation of boiler tube components in Indian thermal power plants is mainly done through solid particle erosion due to exposure in erosive ash environment. Some important parameter such as hardness, erodent velocity, temperature, impact angle, shape and size are majorly affected the erosion wear. In this study, the erosion wear behaviour of SAE 208 grade steel, SAE213-T12 boiler steel, SAE213-T91 boiler steel and IS 2062 structural steel were investigated using an air jet erosion test rig. The erosion tests were carried out at the impact angles of 30° and 90°, impact velocity of 42.3 m/s at room temperature and 400 °C. The position of sample holder was adjusted in such a way that erosion wear scar occur at the central region of the samples. For each experiment, the erosion test was continued until the steady state erosion rate was achieved as per ASTM standard. The variation in erosion rate data has been plotted against cumulative mass of erodent for boiler and structural steel samples. The steady state erosion rates for different steel samples are calculated and compared. The surfaces of tested samples are analyzed using scanning electron microscopy to understand the erosion mechanism. The results showed that the ductile behaviour of erosion mechanism is dominated at both room temperature and 400 °C temperature. Mechanism involved at 90° impact angle is plastic deformation with formation of craters and at 30° impact angle is cutting and ploughing.

Cavitation Erosion Resistance Assessment and Comparison of Three Francis Turbine Runner Materials

Cavitation erosion is the most important erosion mechanism in Francis turbine runner blades. For this reason, knowledge of a material’s ability to resist cavitation is important in defining how suitable it is for use in a Francis turbine. In this study, three Francis turbine materials were subjected to cavitation erosion in a high-speed cavitation tunnel. One of the materials was a low-alloy steel, and the other two were stainless steels. The cavitation tunnel produced an annular cavitation field on one face of a cylindrical specimen. The test specimens underwent cavitation erosion until the erosion had reached a maximum penetration depth of about 0.5 mm. The material surface profiles were measured at regular intervals to calculate volume and mass loss. These losses were compared to those of several other materials that had undergone the same tests with the same setup and operational parameters. The materials were compared according to their steady-state erosion rates. The steady-state erosion rate represents a material’s ability to resist cavitation erosion once cavitation damage has already started to develop. The low-alloy steel eroded four times faster than the two stainless steels. One of the stainless steels tested here (Stainless steel 1) had the lowest erosion rate, along with another previously tested stainless steel. The other stainless steel (Stainless steel 2) had a slightly greater erosion rate than the first, falling into the same class as other lower-grade stainless steels and a nickel aluminum bronze alloy. The results show that in choosing a turbine blade material, stainless steels outperform nonstainless ones. The choice of which type of stainless steel to use is significant in turbines with cavitation problems. The eroded surfaces were analyzed with scanning electron microscopy in order to study the erosion mechanisms, and these studies showed that most of the damage is probably due to low-cycle fatigue.

A multiscale model for sediment impact erosion simulation using the finite volume particle method

The erosion of a surface by a sediment-laden flow is an inherently multiscale phenomenon which includes physical interactions covering many orders of magnitude in both length and time scales. Conforming to the nature of the problem, we propose a novel multiscale model for simulating this complex process. On the one hand, a macroscale model encompassing the whole domain of interest solves the turbulent sediment transport problem. On the other hand, a microscale model simulates the sediment impacts against the surface. A sequential multiscale strategy is used to link the submodels, such that the microscale model provides closure to the macroscale model in terms of the calculated steady state erosion rate and restitution coefficients, therefore reproducing the original coupled problem. The proposed methodology is validated against experimental data for the slurry jet erosion of a copper plate at three impingement angles. Both the global erosion rate and the erosion depth profile are predicted with mean relative errors of 18% compared to the corresponding experimental values, achieving a significant improvement over correlation-based approaches.

Production of 21Ne in depth-profiled olivine from a 54 Ma basalt sequence, Eastern Highlands (37° S), Australia

In this study we investigate the cosmogenic neon component in olivine samples from a vertical profile in order to quantify muogenic 21Ne production in this mineral. Samples were collected from an 11 m thick Eocene basalt profile in the Eastern Highlands of southeastern Australia. An eruption age of 54.15±0.36 Ma (2σ) was determined from 40Ar/39Ar step-heating experiments (n=6) on three whole-rock samples. A 36Cl profile on the section indicated an apparent steady state erosion rate of 4.7±0.5 m Ma−1. The eruption age was used to calculate in situ produced radiogenic 4He and nucleogenic 3He and 21Ne concentrations in olivine. Olivine mineral separates (n=4), extracted from the upper two metres of the studied profile, reveal cosmogenic 21Ne concentrations that attenuate exponentially with depth. However, olivine (Fo68) extracted from below 2 m does not contain discernible 21Ne aside from magmatic and nucleogenic components, with the exception of one sample that apparently contained equal proportions of nucleogenic and muogenic neon. Modelling results suggest a muogenic neon sea-level high-latitude production rate of 0.02±0.04 to 0.9±1.3 atoms g−1 a−1 (1σ), or <2.5% of spallogenic cosmogenic 21Ne production at Earth’s surface. These data support a key implicit assumption in the literature that accumulation of muogenic 21Ne in olivine in surface samples is likely to be negligible/minimal compared to spallogenic 21Ne.

Using 10Be cosmogenic isotopes to estimate erosion rates and landscape changes during the Plio-Pleistocene in the Cradle of Humankind, South Africa

Concentrations of cosmogenic 10Be, measured in quartz from chert and river sediment around the Cradle of Humankind (CoH), are used to determine basin-averaged erosion rates and estimate incision rates for local river valleys. This study focusses on the catchment area that hosts Malapa cave with Australopithecus sediba, in order to compare regional versus localized erosion rates, and better constrain the timing of cave formation and fossil entrapment. Basin-averaged erosion rates for six sub-catchments draining the CoH show a narrow range (3.00 ± 0.28 to 4.15 ± 0.37 m/Mega-annum [Ma]; ±1σ) regardless of catchment size or underlying geology; e.g. the sub-catchment with Malapa Cave (3 km2) underlain by dolomite erodes at the same rate (3.30 ± 0.30 m/Ma) as the upper Skeerpoort River catchment (87 km2) underlain by shale, chert and conglomerate (3.23 ± 0.30 m/Ma). Likewise, the Skeerpoort River catchment (147 km2) draining the northern CoH erodes at a rate (3.00 ± 0.28 m/Ma) similar to the Bloubank-Crocodile River catchment (627 km2) that drains the southern CoH (at 3.62 ± 0.33 to 4.15 ± 0.37 m/Ma). Dolomite- and siliciclastic-dominated catchments erode at similar rates, consistent with physical weathering as the rate controlling process, and a relatively dry climate in more recent times. Erosion resistant chert dykes along the Grootvleispruit River below Malapa yield an incision rate of ∼8 m/Ma at steady-state erosion rates for chert of 0.86 ± 0.54 m/Ma. Results provide better palaeo-depth estimates for Malapa Cave of 7–16 m at the time of deposition of A. sediba. Low basin-averaged erosion rates and concave river profiles indicate that the landscape across the CoH is old, and eroding slowly; i.e. the physical character of the landscape changed little in the last 3–4 Ma, and dolomite was exposed on surface probably well into the Miocene. The apparent absence of early Pliocene- or Miocene-aged cave deposits and fossils in the CoH suggests that caves only started forming from 4 Ma onwards. Therefore, whilst the landscape in the CoH is old, cavities are a relatively young phenomenon, thus controlling the maximum age of fossils that can potentially be preserved in caves in the CoH.

Mechanical properties and solid particle erosion of MCD films synthesized using different carbon sources by BE-HFCVD

Mechanical properties and solid particle erosion of chemical vapor deposition (CVD) diamond films are strongly influenced by the adopted carbon source in the deposition process. In the present study, methane, acetone, methanol and ethanol are respectively used as the carbon source to deposit micro-crystalline diamond (MCD) films on SiC substrates by the bias-enhanced hot filament CVD (BE-HFCVD) method. A standard air–sand erosion rig is employed to conduct erosion tests, using angular SiC sands of 320meshes as impact abrasives. The impact velocity ve and impact angle αe are fixed as 100m/s and 90°, respectively. The steady-state erosion rate εs, film life tr and a unit film life tru are defined to assess the erosion behaviors of as-deposited films, which have close relationships with the mechanical properties, as measured by the Rockwell hardness tester and the nanoindentation test. It's found that under the condition of the same film thickness, the methane-MCD film shows the lowest εs and the longest tr, owing to the highest surface hardness and the most favorable film-substrate adhesion which is equivalent to the highest fracture strength, but the opposite is true for the methanol-MCD film. Moreover, due to the relatively higher growth rate, the acetone- and ethanol-MCD films both perform even longer tru than the methane-one, indicating better “average” erosion behavior. Consequently, the optimal efficiency and economy can be achieved when adopting either the acetone or the ethanol to deposit MCD films of sufficient thickness on working surfaces of erosion resistant components suffering severe erosive wear, especially in the case of mass production.

Flood-flipped boulders: In-situ cosmogenic nuclide modeling of flood deposits in the monsoon tropics of Australia

During the Quaternary, extreme floods along the Durack River, in the Kimberley, northern Australia, dislodged, transported, and stacked massive meter-sized boulders from the underlying bedrock channel floor. Field evidence identified a population of the boulders to have been overturned after detachment. We measured in situ cosmogenic 10 Be and 26 Al concentrations in six imbricated boulders to constrain the timing of flood events. We present a simple numerical model that simultaneously solves the expressions for the predicted nuclide concentrations from the exposed and hidden surfaces of a flipped boulder to calculate the time since it was overturned. The ability of the model to unequivocally discern whether a boulder was overturned depends on boulder thickness and the site-specific steady-state erosion rate. Of the six boulders sampled, our model successfully determined four finite flip ages, whereas the other two boulders indicated steady state and were either not flipped or flipped sufficiently long ago for the nuclide profile to have returned to steady state. While the two older model ages (ca. 150 ka and ca. 260 ka) are strongly sensitive to assumptions made for the local erosion rate correction, the two younger flip ages, 5.6 ± 1.0 ka and 10.3 ± 1.9 ka, are robust against such corrections. Early to mid-Holocene major floods have been recorded in other parts of northern Australia. We suggest that similar Holocene floods occurred in the Kimberley and that such extreme events may have been widespread in northern Australia in the late Quaternary. Our boulder-flip model can be applicable to similar deposits associated with other extreme events such as paleo-tsunamis.

Prediction of Erosion of Polyetherimide and Its Composites Using Response Surface Methodology

This paper presents an approach to establish the model for predicting the steady-state erosion rate of polyetherimide and its glass fiber composites. Three-factor and two-level, face-centered composite design is used for experimentation. The parameters which affect the erosion rate are selected as glass fiber percentage (0–40%), impingement angle (30 deg–90 deg), and impact velocity (30–90 m/s). Response surface methodology is used to derive second-order quadratic model with interactions. Investigation showed all the parameters have significant effect on controlling steady-state erosion rate of these composites. The interactions of impact velocity-fiber percentage and impact velocity-impingement angle are significant. The increase in erosion rate with the increase in impact velocity is found to be satisfying a power law. Maximum erosion rate for these composites found at around 45 deg–60 deg impingement angle indicates their semiductile erosion behavior. Scanning electron microscopy photographs indicate ploughing, microcutting, development of cracks, and exposure of fibers as the dominating erosion mechanisms for these composites.

Fracture and solid particle erosion of micro-crystalline, nano-crystalline and boron-doped diamond films

Chemical vapor deposition (CVD) diamond film has been considered as a good candidate protective coating under hostile and abrasive conditions due to its outstanding erosion behavior. In the present study, the conventional micro-crystalline diamond (MCD) film, nano-crystalline diamond (NCD) film and the boron-doped diamond (BDD) film are respectively fabricated by the hot filament CVD (HFCVD) method. Solid particle erosion tests are conducted on diamond films in an air–sand erosion rig under different impact velocities (v) and angles (α) with angular SiC sands as the erodents, and WC–Co and SiC materials are adopted as comparisons. The field emission scanning electron microscopy (FESEM), X-ray diffraction (XRD), Raman spectroscopy, Rockwell hardness tester and surface profilometer are respectively used to characterize diamond films before and after tests, exhibiting that compared with MCD and NCD films, the BDD film performs relatively higher fracture strength and better adhesion. Typical solid impact erosion stages of the different diamond films are observed. The solid particle erosion behavior of diamond films has close relationships to their fracture strength and adhesion. As a result, when the impact angle α ≤30°, the steady-state erosion rate of the BDD film is lower than those of MCD and NCD ones. More importantly, under all the impact angles and velocities, much quicker film delamination and removal can be noticed on the MCD and NCD films, especially the NCD one. By contrast with WC–Co and SiC materials, diamond films present much better erosion resistance and higher velocity exponents, which should be attributed to different impact mechanisms caused by the different hardness of eroded samples.

Erosion mechanism of the boron-doped diamond films of different thicknesses

Chemical vapor deposition (CVD) diamond film has extensively applied as the protective coating under hostile and abrasive conditions, the erosion mechanism of which is significantly influenced by the composition and thickness of the film. This paper describes an erosion study, which examines the effects of the film thickness on the erosive wear behavior of the boron-doped diamond (BDD) films deposited on the SiC substrates by the hot filament CVD (HFCVD) method, with the undoped ones as comparisons. A laboratory designed air–sand erosion rig is used to conduct the erosion tests, with the velocities in the range of 100–140m/s and 90° nominal impact angle. The erodents are silica sands with an average diameter of 180μm. The diamond films are examined both pre- and post-test by the field emission scanning electron microscopy (FESEM) in order to determine the erosion mechanisms of the diamond films. Firstly, it is observed that the higher residual compressive stress and critical tensile strength can slow down the formation of the ring cracks. Moreover, the 12μm diamond film has the highest steady-state erosion rate because the depth of the maximum shear stress is much close to the film–substrate interface. Furthermore, the complicated effects of the film thickness on the film lives of both the BDD and undoped diamond films are also further studied, as well as the velocity exponents of the different diamond films. The research results in the present study are conductive to the widespread applications of BDD films on the erosion resistant components.

Surface roughness and erosion rate of abrasive jet micro-machined channels: Experiments and analytical model

Abrasive jet micro-machining (AJM) uses a high velocity particle jet to erode features in target substrates for a variety of applications, including micro-electro-mechanical and micro-fluidic device fabrication. The roughness of micro-channels for micro-fluidic applications made using AJM can affect fluid flow phenomena such as separation efficiency, electro-osmotic mobility and solute dispersion. Moreover, surface roughness plays a major role in micro-scale adhesion contact in MEMS and light scattering in optoelectronics devices.This paper presents experimental data on the effect of particle size, velocity, and angle of attack on the roughness of unmasked channels machined in borosilicate glass using AJM. Single impact experiments were conducted to quantify the damage due to the individual alumina particles. Based on these observations, the assumed location of lateral crack initiation in a relatively simple analytical model from the literature was modified, and used to predict the roughness and erosion rate. The previous model, which calculated an areal roughness, was also modified to yield a 2D linear value of Ra so that it could be compared with linear profilometer scans. This modified model predicted the steady-state roughness and erosion rate of unmasked channels with average errors of 36% and 73%, respectively.

Effect of antecedent conditions and fixed rock fragment coverage on soil erosion dynamics through multiple rainfall events

The effect of antecedent conditions and specific rock fragment coverage on precipitation-driven soil erosion dynamics through multiple rainfall events was investigated using a pair of 6-m × 1-m flumes with 2.2% slope. Four sequential experiments – denoted E1, E2, E3 and E4, involved 2-h precipitation (rates of 28, 74, 74 and 28 mm h-1, respectively) and 22 h without rainfall – were conducted. In each experiment, one flume was bare while the other had 40% rock fragment coverage. The soil was hand-cultivated and smoothed before the first event (E1) only, and left untouched subsequently. Sediment yields at the flume exit reached steady-state conditions over time scales that increased with sediment size. Experiments were designed such that both steady and non-steady effluent sediment yields were reached at the conclusion of E1. Results from subsequent experiments showed that short-time soil erosion was dependent on whether steady-state erosion was achieved during the preceding event, although consistent steady-state effluent sediment yields were reached for each sediment size class. Steady-state erosion rates were, however, dependent on the rainfall intensity and its duration. If steady-state sediment yields were reached for a particular size class, that class’s effluent sediment yield peaked rapidly in the next rainfall event. The early peak was followed by a gradual decline to the steady-state condition. On the other hand, for size classes in which steady state was not reached at the end of the rainfall event (i.e., E1), in the following event (E2), the sediment yields for those classes increased gradually to steady state, i.e., the sharp peak was not observed. The effect of rock fragment cover (40%) on the soil surface was also found to be significant in terms of the time to reach steady state, i.e., their presence reduced the time for steady conditions to be attained. Effluent sediment yields for the bare and rock fragment-covered flumes (E1) showed steady conditions were reached for the latter, in contrast to the former. We used the Hairsine-Rose (H-R) model to simulate the experimental data as it explicitly models soil particle size classes. Experiments E1 and E2 involved soil compaction by raindrops, and in this case the model predictions were found to be unsatisfactory. However, compaction was effectively completed by the end of experiment E2, and the model provided reasonable predictions for experiments E3 and E4.