Erosion Test Results Research Articles

Experimental and Numerical Investigation of Stress Condition in Unstable Soil

In unstable soils, a special erosion process termed suffusion can occur under the effect of relatively low hydraulic gradient. The critical hydraulic gradient of an unstable soil is smaller than in stable soils, which is described by a reduction factor α. According to a theory of Skempton and Brogan (1994) [1], this reduction factor is related to the stress conditions in the soil. In an unstable soil, the average stresses acting in the fine portion are believed to be smaller than the average stresses in the coarse portion. It is assumed that the stress ratio and the reduction factor for the hydraulic gradient are almost equal. In order to prove this theory, laboratory tests and discrete element modelings are carried out. Models of stable and unstable soils are established, and the stresses inside the sample are analysed. It is found that indeed in unstable soils the coarse grains are subject to larger stresses. The stress ratios in stable soils are almost unity, whereas in unstable soils smaller stress ratios, which are dependent on the soil composition and on the relative density of the soil, are obtained. A comparison between the results of erosion tests and numerical modeling shows that the stress ratios and the reduction factors are strongly related, as assumed by Skempton and Brogan (1994) [1].

New features of solid particle erosion damage of control stage blades in supercritical steam turbine

Reducing solid particle erosion of blades is one of the most urgent problems for high-parameter steam turbine power generation technology. Based on the erosion rate model and particle rebound model of blade materials obtained through accelerated erosion test under high temperature, erosion characteristics of flaky particles in control stage of a typical supercritical steam turbine were systemically studied using three-dimensional numerical simulation method. The erosion mechanism of hard coatings on nozzle suction surface is first revealed, and erosion resistance of boride coating with large oxide particles is validated through high-temperature erosion test. Results show that serious erosion damage of boride coating on the latter half of nozzle suction surface is caused by the combined rebounded impingement of large particles between 1000 µm and 2000 µm after their initial impingement on the nozzle pressure surface and the leading edge of rotating blade. The average particle impingement velocity can reach up to 150–180 m/s, and the impingement angle is in the range of 18°–28°. High-temperature erosion test results show that boride coating will soon broken and fall off under the continuing impact of millimeter-sized particles, which confirms that hard coatings are difficult to resist the high-intensity impingement from these large particles. Therefore, separating particles before entering the nozzle chamber with the employment of an inertial separator should be the optimal choice for improving the erosion resistance of turbine. The results of this study enrich the types of blade erosion damage and provide a new idea for reducing erosion damage of control stage blades.

Improved similarity criterion for seepage erosion using mesoscopic coupled PFC–CFD model

Conventional model tests and centrifuge tests are frequently used to investigate seepage erosion. However, the centrifugal test method may not be efficient according to the results of hydraulic conductivity tests and piping erosion tests. The reason why seepage deformation in model tests may deviate from similarity was first discussed in this work. Then, the similarity criterion for seepage deformation in porous media was improved based on the extended Darcy-Brinkman-Forchheimer equation. Finally, the coupled particle flow code–computational fluid dynamics (PFC-CFD) model at the mesoscopic level was proposed to verify the derived similarity criterion. The proposed model maximizes its potential to simulate seepage erosion via the discrete element method and satisfy the similarity criterion by adjusting particle size. The numerical simulations achieved identical results with the prototype, thus indicating that the PFC-CFD model that satisfies the improved similarity criterion can accurately reproduce the processes of seepage erosion at the mesoscopic level.

The Study on Erosive and Abrasive Wear Resistance of Different Multilayer Coatings Obtained on Titanium Alloy Ti6Al4V

One of the areas in which increased durability is of particular significance is the use of machine elements in conditions of intensive exposure to erosive wear, for example, turbine blades of aircraft engines and power turbines in ventilation systems, and machine elements working in a dusty environment. As it is apparent from the analysis of the state of the art, high possibilities to increase the erosive and abrasive wear resistance of machine elements are created by appropriately designed coatings and layers, especially multilayer coatings composed on the base of materials with different plasticity properties. This is associated with particular characteristics of this type of multilayer coatings that allow the absorption of external energy reaching the surface without causing permanent damage to the coating, while significantly reducing the erosive wear rate.The article presents the results of material research and the results of erosion test of three different materials solutions of surface engineering, i.e. multilayer coatings (Cr / CrN) x8, (TiN / ZrN)multinano and a (Ti-Al) intermetallic / AlCrTiN hybrid layer, obtained on titanium alloy Ti6Al4V. The (Cr / CrN) x8 and (TiN / ZrN)multinano multilayer coatings were obtained by arc evaporation, and the (Ti-Al) intermetallic / AlCrTiN hybrid layer was prepared using a hybrid technology combining diffusion saturation in aluminium powders and arc evaporation in a single technological process. The selected material solutions of the surface layer were subjected to the analysis of the structure by scanning electron microscopy (Hitachi 3000). Measurements of hardness and Young's modulus were conducted using the nanohardness Tester CSM. The results of this study allowed the authors to compare the erosive wear resistance and wear resistance of selected material solutions, and this led to the conclusion that the (Ti-Al) intermetallic / AlCrTiN hybrid layer is the most effective solution.

Microstructure and erosion characteristics of Ni-AlN thin films prepared by electrodeposition

AbstractNi-AlN thin films were successfully fabricated via direct-current (DC), pulse-current (PC), and ultrasonic-assisted pulse-current (UAPC) deposition. The microstructure, microhardness, and erosion characteristics of the Ni-AlN thin films were determined with the use of scanning probe microscopy (SPM), X-ray diffraction (XRD), Vickers hardness test, electrochemical station, and scanning electron microscopy (SEM). SPM results revealed that the Ni-AlN thin films synthesized by UAPC deposition have a compact and fine morphology with average grain diameters of the Ni and AlN particles of approximately 97.7 and 40.2 nm, respectively. Based on the XRD results, the Ni-AlN thin films consist of Ni and AlN phases. The Ni-AlN thin films prepared by DC, PC, and UAPC deposition at 4.5 A/dm2 current density exhibited an optimum microhardness value of 904, 943, and 987 HV, respectively. Based on the erosion test results, the films prepared by UAPC deposition possesses the best corrosion resistance among the prepared thin films. The corrosion potentials of the DC-, PC-, and UAPC-deposited films were -0.552, -0.473, and -0.446 V vs. SCE, respectively.

Study Regarding the Cavitation Erosion Behaviour and Residual Stresses of Impact Resistant Hardfacing Materials

In the last twenty years the cavitation erosion resistance of various welded materials was subject of extensive studies. Despite these, the research field is still opened. The multitude of materials used for the fabrication of hydraulic equipment and the variety of the operating conditions in hydropower units require adapted solutions. This paper presents the investigations made on welded overlays realized using an impact resistant hardfacing alloy, recommended by manufacturers for protection against cavitation erosion. The material was characterized by metallographic investigations (light microscopy, scanning electron microscopy and EDX–analyse), Vickers micro hardness tests, residual stresses measurements carried out by the hole-drilling strain-gage method and cavitation erosion tests using the vibratory method. The results of the cavitation erosion tests were correlated to the behaviour of the martensitic stainless steel 1.4313 (grade X3CrNiMo13-4 corresponding to EN 10088-3) frequently used for the manufacturing of the hydraulic turbine components.

Heat treatment effect on erosion behavior of poly(methylmethacrylate) for optical transmittance efficiency

Influence of heat treatment on optical transmittance of poly(methyl methacrylate) (PMMA) samples was investigated under solid particle erosion. Heat treatment was employed at 85°C for 1, 2 and 3h. Effect of heat treatment on physical, chemical, mechanical and thermal properties of PMMA samples was investigated by differential scanning calorimeter (DSC), thermogravimetric analysis (TGA), Fourier transform infrared (FTIR) spectroscopy, Vickers microhardness measurement methods. After these analysis, both pristine and heat treated PMMA samples were eroded at 15°, 30°, 45°, 60°, 75° and 90° impingement angles. Then, optical transmittance of all eroded PMMA samples was inspected by a UV–Vis spectrometer. Scanning electron microscopy (SEM) was used to explain the erosion mechanisms and to compare the roughness and optical transmittance of eroded PMMA surfaces.Heat treatment under glass transition temperature of PMMA increased the Tg and hardness values. According to erosion test results, both pristine and heat treated PMMA samples were showed ductile erosion behavior. However; maximum and minimum optical transmittance values of eroded pristine PMMA samples were obtained for the angles of 15° and 90°, respectively. A positive effect of heat treatment on optical transmittance of PMMA was obtained for all impingement angles, but most pronounced effect was seen for 15°.

A Laboratory Study on Erosional Properties of the Deposit Bed of Kaolinite Sediments

본 연구에서는 환형수조를 이용한 침식실험을 통하여 국내 최초로 퇴적저면의 침식매개변수들이 정량적으로 산정되었다. 퇴적저면은 고농도의 고령토 슬러리를 기 설정된 시간 동안 압밀시켜 조성되었으며, 각기 다른 압밀구조를 갖는 퇴적저면 조건 하에서 총 4회의 침식실험이 수행되었다. 침식실험 결과에 따르면, 흐름전단응력 <TEX>${\tau}_b$</TEX>에 대한 저항력을 나타내는 저면전단강도 <TEX>${\tau}_s$</TEX>는 압밀시간 및 저면(퇴적층) 깊이가 깊어짐에 따라 증가하는 것으로 나타났다. 한편, 침식률<TEX>${\epsilon}$</TEX>은 흐름전단응력과 저면전단강도의 차로 주어지는 잉여전단응력 <TEX>${\tau}_b-{\tau}_s$</TEX>과 상관성이 매우 큰 것으로 나타났는데, <TEX>${\tau}_b-{\tau}_s{\leq}0.1N/m^2$</TEX>인 경우에 침식률의 로그 값은 잉여전단응력과 선형적 관계에 있으나, <TEX>${\tau}_b-{\tau}_s{\leq}0.1N/m^2$</TEX>인 조건에서는 잉여전단응력이 작아질수록 침식률이 급격하게 작아지는 경향이 있는 것으로 나타났다. 또한 본 연구에서는 과거 연구결과와의 비교검토를 통하여 본 침식실험 결과에 대한 타당성이 입증되었으며, <TEX>$0.1N/m^2$</TEX> 이하의 잉여전단응력 구간에서 침식률을 보다 잘 표현할 수 있는 새로운 침식률 산정식이 제시되었다. In this study, the erosional parameters for deposit beds were quantitatively estimated domestically for the first time through the erosion tests using an annular flume. Four erosion tests were carried out for the deposit beds with different consolidation structures, which were obtained by consolidating the kaolinite slurries for a given time durations. Results of erosion tests showed that the bed shear strength <TEX>${\tau}_s$</TEX> increased with the consolidation time and bed depth. The erosion rate <TEX>${\epsilon}$</TEX> was also shown to be related well with the excess shear stress <TEX>${\tau}_b-{\tau}_s$</TEX> which was given by the difference between flow shear stress <TEX>${\tau}_b$</TEX> and bed shear strength <TEX>${\tau}_s$</TEX>. While the logarithm of the erosion rate was linearly related with the excess shear stress as <TEX>${\tau}_b-{\tau}_s{\geq}0.1N/m^2$</TEX>, however, the erosion rate decreased rapidly with it when <TEX>${\tau}_b-{\tau}_s{\leq}0.1N/m^2$</TEX>. These erosion test results were also shown to be good enough to verify by comparing with the test results from previous studies and a new equation was suggested to describe the erosion rate more well in the region of <TEX>${\tau}_b-{\tau}_s{\leq}0.1N/m^2$</TEX>.

Influence of woven structure on coir rolled erosion-control products

ABSTRACT: Rolled erosion-control products (RECPs) are used in erosion-prone zones to hold the soil until permanent vegetation is established. A variety of materials are available for controlling soil erosion, but RECPs made of coir or jute offer several advantages such as better moisture retention in comparison with synthetic materials for the growth of vegetation, and they are durable and biodegradable. In this study, the application of plain, 2/1 twill and 4-end satin-woven RECPs were investigated for soil erosion control. Runoff soil erosion tests were carried out in a bench-scale setup according to ASTM D7101 with modifications at 15°, 30° and 45° slope angles. Simulated rainfall was applied to the test tray filled with soil brought from the lower Himalayan Shiwalik ranges. Germination tests were performed according to ASTM D7322. It was observed that twill woven RECPs showed better performance in germination tests with the highest total rooting and vegetation in the range 86.4–96.6% in comparison with 81.9–84.1% for plain woven structures. The soil erosion test results were found to depend on the soil slopes. At lower and medium slopes, twill woven structures were found to perform better whereas plain woven structures were found to perform better for steeper slopes.

Microstructure and properties of Ag/SnO2 coatings prepared by cold spraying

Cold spraying was used to fabricate Ag/SnO2 coatings on copper substrate with high energy ball milled Ag/SnO2 composite powders. The cold sprayed coatings were annealed under vacuum at a temperature of 600°C and 850°C for 2h. Vickers microhardness and arc erosion tests were conducted to determine the mechanical properties and arc erosion properties of the coatings. The effect of annealing temperature on the microstructure, microhardness and arc erosion of the coatings was investigated. It was found that cold sprayed Ag/SnO2 coatings exhibited denser microstructure and better coating–substrate interface after annealing at 850°C. The hardness of Ag/SnO2 coatings was evidently influenced by annealing temperature. The arc erosion test results indicated that the arc erosion properties of cold sprayed Ag/SnO2 coatings can be improved significantly by annealing; the coatings annealed at 850°C showed the best arc erosion properties.

Surface ripple and erosion rate of stainless steel under elevated temperature erosion by angular solid particles

The actual industrial erosion caused by the impingement of particles swarming from different perspectives is often different from the single-angle impingement of solid particle in the erosion test. In order to predict the erosion problems in practical engineering more reasonably, a series of elevated temperature erosion tests were conducted to study the surface ripple and enduring erosion behavior of heat-resistance stainless steel suffering from the single-angle impingement or multiangle alternative impingement of angular particles. The test results indicated that the surface of target materials with good ductility produced large-scaled transverse ripples and small-scaled longitudinal ripples after experienced a long-time single-angle impingement of angular solid particles under a 773–873-K high-temperature environment. The longitudinal ripples could accelerate the emergence and development of large-scaled transverse ripples. Initial erosion scars caused the differentiation of material deformability and plastic flow in the different locations of concave–convex scars, which further drove the evolution of the surface morphology from disordered scars to coherent ripples under the sustained attack of high-velocity particles. The more dimples the eroded surface of target material produced, it was easier for the target materials to produce coherent ripple. However, the interactions among the erosion behaviors with different attack angles made initial concave–convex scars difficult to evolve to coherent ripples under the multiangle alternative erosion. Further statistical results of erosion tests indicated that it can basically satisfy the practical engineering need by taking the erosion rate of initial surface layer as the erosion rate of the target material within the whole life cycle.

Study on mechanical and erosion wear performance of granite filled glass-epoxy hybrid composites

In this study, a new class of low cost hybrid composites consisting of glass-epoxy and filled with four different weight proportions (0 wt%, 10 wt%, 15 wt% and 20 wt%) of granite particulates (a solid waste generated from stone processing industries) are developed. Mechanical study reveals that hardness, tensile modulus and impact energy of these composites are improving with filler addition while a steady decline in tensile and flexural strength is observed. The erosion rates of these composites are evaluated at different impingement angles (30–90°), impact velocities (33–68 m/s) and erodent sizes (100–250 µm) following the erosion test experiments in an air jet type test rig. An optimal parameter setting is determined for minimum erosion rate and subsequently validated by conducting confirmation experiment as per Taguchi methodology. Erosion test results indicate that the incorporation of granite particulates results in improvement of erosion wear resistance of glass-epoxy composites. Different modes of material removal, wear craters and other qualitative attributes are examined by a scanning electron microscopy during erosion experiment of the samples.

Hydraulic and Contraction Scour Analysis of a Meandering Channel: James River Bridges near Mitchell, South Dakota

AbstractThe two-dimensional (2D) depth-averaged river model Finite-Element Surface-Water Modeling System (FESWMS) was used to simulate the hydraulic conditions at a contracted bridge site. The site studied was the James River bridges near Mitchell, South Dakota. The parallel bridges are located in a crossing between the two bends of a meander. The floodplain alignment relative to the channel and skewed bridges produces complex 2D flow patterns that cannot be predicted accurately by using a one-dimensional (1D) river model. The 2D model was validated by using flow measurements collected by the USGS during three high-flow events with return periods ranging from 25 to 100 years. The validated model was used to examine the site characteristics that influence the concentrated flow on the right side of the main channel and the exchange of flow between the main channel and floodplains. The rating curves derived from the 2D model and the results of soil erosion tests were used to evaluate live-bed and clear-water...

Cavitation erosion resistance of Ti/TiN multilayer coatings

The results of cavitation erosion tests of the Ti/TiN multilayer coatings protecting the X6CrNiTi18-10 steel are presented in this paper. The Ti/TiN multilayer coatings were deposited on the X6CrNiTi18-10 steel surface by means of the cathodic arc evaporation PVD method. The multilayer coatings were deposited as 4, 12 and 40-layer structures with the Ti layer at the bottom and the TiN layer on the top. All layers showed similar thickness; the total thickness of the Ti/TiN multilayer coatings was approximately 4μm.The coated specimens showed better cavitation erosion resistance than the uncoated stainless steel. With an increase of the number of coating layers the cavitation erosion resistance of the Ti/TiN multilayer coating was lower. It was shown experimentally that the Ti/TiN-4 coating provided the best protection against cavitation erosion.The degree of cavitation erosion was estimated by mass measurements and surface roughness measurement tests. The value of surface roughness of the Ti/TiN-4 coating was closest to that of the uncoated steel. The surface profiles of the Ti/TiN-12 and Ti/TiN-40 coatings showed little undulation, not visible in the profiles of the Ti/TiN-4 coating and the uncoated X6CrNiTi18-10 steel. The microscopic observation showed that deformation of the multilayer coatings developed via cracking, which further propagated by simultaneous fracture of numerous coating layers.

Fe-Si Thermal Spray Coating for Fire Side Corrosion and Erosion Protection in Coal-Fired Boiler

Fe-Si intermetallic thermal spray powders have been developed for sulfidation corrosion and erosion protection for furnace walls in pulverized coal fired boiler. In this paper, evaluation of corrosion and erosion resistance of developed coatings was performed. The corrosion test results showed that the developed coatings almost equal corrosion resistance to conventional corrosion resistant coatings under the low NOX boiler condition. Erosion test results also indicated that Fe-20Si-1B using atmospheric plasma spraying showed higher erosion resistance than the conventional coatings.

New Laboratory-Based Mechanistic–Empirical Model for Faulting in Jointed Concrete Pavement

Faulting is associated with many design- and performance-related factors of concrete pavement, such as traffic load, joint spacing, load transfer, drainage, subbase friction, and subbase erodibility. Subbase erosion is especially key to an understanding of the process of faulting distresses in jointed concrete pavement. However, subbase erosion has not been included explicitly in design-related analysis. As a consequence, design procedures have lacked a prerequisite sensitivity because of a lack of laboratory test procedures and material parameters to relate model prediction to subbase erosion performance. This paper presents a mechanistic–empirical faulting model. It is calibrated from the results of a new erosion test that involves the Hamburg wheel-tracking device and Long-Term Pavement Performance (LTPP) data. The calculated faulting depths from the proposed model match well with the trends of observed LTPP field faulting data.

Study on Neutralization Model for Fly Ash Concrete Subjected to Acid Rain

Based on the theory of diffusion and mass transfer, a theoretical neutralization model for fly ash concrete eroded by acid rain was proposed. The values of the model parameters were studied, and the calculation formula of effective diffusion coefficient DA was established considering both material and environmental aspects. The model was verified by acid rain erosion test results, and the results calculated by the model agree well with test results. The model proposed in this paper can be used to predict neutralization depth of fly ash concrete subjected to acid rain attack.

An Improved Rotating Cylinder Test Design for Laboratory Measurement of Erosion in Clayey Soils

Abstract An improved Rotating Cylinder Test (RCT) device is designed and manufactured for laboratory measurement of erosion in clay soils. The improved device provides for a rapid and practical procedure for sample assembly and allows testing cylindrical samples 100 mm in height and 100 mm in diameter. It also provides the ability for direct and accurate measurement of hydraulic shear stress and erosion rate. The improved RCT apparatus has been calibrated using dummy samples to isolate the torque applied to the soil surface. A control program has been developed to operate the RCT and record test data for analysis. Sample preparation for compacted clay soils has been discussed for both saturated and unsaturated states. Typical erosion test results are presented for a clay soil.

Erosion wear behavior of laser clad surfaces of low carbon austenitic steel

Austenitic steel surfaces are laser cladded using a 4 kW continuous wave CO 2 laser with coaxial powder feeding nozzle to investigate the improvement in slurry erosion characteristics. Colmonoy-6 and Inconel-625 are cladded on AISI 316L steel and AISI 304L steel, respectively by laser cladding. Initially, single-pass clad track is overlaid to optimize the laser processing parameters, namely scanning speed and powder feed rate to obtained a sound clad. Minimum cracks, porosity and distortion were found at scanning speed of 0.1 m/min and powder feed rate of 12 g/min. For these parameters, the dilution was 17.33% for Colmonoy-6 and 40% for Inconel-625. To clad large surface area, the optimized laser processing parameters were used to deposit the clad tracks with 60% overlap. Maximum surface hardness of 746 VHN is obtained in case of Colmonoy-6 clad on AISI 316L steel and is 352 VHN in case of Inconel-625 clad on AISI 304L steel. EDAX analysis shows higher degree of mixing of substrate material in the clad pool of Inconel-625 than Colmonoy-6. The results of slurry erosion test of Colmonoy-6 clad surface have shown improvement in erosion resistance of the order of 1.75–4.5 times of the substrate AISI 316L steel at all impact angles and the maximum wear angle has also increased which can be attributed to the increase in the surface hardness. However, Inconel-625 laser clad surface has shown little improvement in erosion resistance of the substrate AISI 304L steel at shallow impact angles with no significant improvement at normal impact condition. The SEM micrographs of worn out Colmonoy-6 clad surfaces at shallow impact angles show that the material is removed mainly by micro-cutting which increases with increase in the impact angle.

Hydrothermal crystallization effect on the improvement of erosion resistance and reliability of plasma-sprayed hydroxyapatite coatings

The aim of present study is to investigate the crystallization effect of air and hydrothermal heat treatments on the erosion resistance, failure behaviors and reliability of plasma-sprayed HA coatings (HACs). Experimental results show that just 150 °C is required to see a significant increase in crystallinity and phase purity for hydrothermally-treated HACs compared with the high-temperature (600 °C) air heat treatment. The significantly improved bonding strength of hydrothermally-treated HACs can be recognized for the self-healing effect that resulted from the hydrothermal crystallization. Results of erosion test indicated that the erosion resistance decreases with increasing erosion impact angle. The maximum erosion rate occurred at 90° impact angle for all the as-sprayed and heat-treated HACs. The erosion resistance of plasma-sprayed HACs is significantly improved through the crystallization of a coating after heat treatments. Furthermore, it should be worth noting that the erosion resistance for hydrothermally-treated HACs is much better than as-sprayed and air heat-treated HACs at any impact angle. The statistical analysis of Weibull model shows that plasma-sprayed coatings are generally reliable materials with a wear-out failure model (with a Weibull modulus m > 3) of increasing failure rate (IFR). The knowledge of the minimum strength and failure behavior will be very helpful for understanding the HA coating reliability for further biological applications.