The erosion of aluminum by solid particle impingement at normal incidence

A rotating arm apparatus was used to study the erosion of polycrystalline aluminum by 1.58 mm diameter WC-6% Co spheres impinging at normal incidence. Dynamic hardness values were obtained from measurements of the impact craters and compared with corresponding quasi-static values. In addition, material removal was monitored gravimetrically, and quantitative information was obtained on threshold and incubation phenomena and steady state erosion behavior. The variation of the velocity dependence of erosion with the number of particle impacts was derived from these data. Supporting scanning electron microscope studies suggest that the mechanism of material removal responsible for ductile erosion at near normal incidence is somewhat different from that which operates at shallower angles. The similarities and differences between these mechanisms are discussed, and it is suggested that together they account for the characteristic variation of ductile erosion with angle of impingement.     

Erosion of a strong aluminum alloy

The erosion of a strong aluminum alloy (7075-T6) and annealed commercially pure aluminum was modelled with impacts by ball bearings of diameter 5 mm at velocities of 140–185 m s^?1. Single impacts caused significant erosive loss only at low impact angles (20°–35°). Single impacts normal to the surface removed negligible amounts of metal. Erosion by impacts normal to the surface occurred only when the deformation field from one impact overlapped that of an earlier impact.Erosion resistance, as measured by velocity threshold for weight loss, was much lower for the high strength 7075-T6 alloy than for pure aluminum. Thus alloying for strength diminishes erosion resistance. Treatments that improve the fracture toughness of the 7075 alloy did not improve erosion resistances.Metal left the target as one or two chips per impact. These separated along narrow bands of intense shear. While particle impacts always deform the surface, it is postulated that this deformation results in metal loss (erosion) only when a shear instability (adiabatic shear) develops under the ball prior to the tensile stresses set up in the surface upon particle rebound.     

钻井液固液分离旋流器壁面磨损特性

针对石油钻井过程中,由于钻井液中泥沙等固体颗粒产生的冲蚀磨损导致的旋流器失效问题,采用CFD-DPM模型开展以非牛顿流体为钻井液时旋流器冲蚀磨损研究,探讨不同流速、稠度系数、流动性指数、含砂体积比和入口倾角对旋流器内壁冲蚀磨损的影响。结果表明：旋流器内壁磨损呈螺旋状,锥段处磨损率随着半径的减小而增大,底流口处是受损最为严重的部位;在流速5～15 m/s、含砂体积比1%～9%时旋流器的最大冲蚀率随着流速增大呈指数型增长,冲蚀面积明显扩张;低流速下含砂体积比对最大冲蚀率影响较弱,而高流速下最大冲蚀率与含砂体积比呈正相关;入口倾角的增大同时增大了向下的轴向速度,使得颗粒能更快地到达底流口减小了与壁面的接触,其冲蚀率呈线性减小;最大冲蚀率随稠度系数的增大整体呈现平缓下降的趋势,随着流动性指数的增大而急速下降,流动性指数对冲蚀破坏的影响相比稠度系数更剧烈一些。     

30CrMo合金钢的冲蚀磨损性能研究

采用自制的喷射型冲蚀磨损试验机,研究在水力压裂工况下,高速携砂液对高压管汇材料30CrMo的冲蚀磨损作用,分析冲蚀磨损机制以及冲蚀角度和冲蚀速度对30CrMo合金钢冲蚀性能的影响。结果表明,30CrMo合金钢在高速粒子冲击下,其耐冲蚀磨损性能表现一般,属于典型的金属塑性材料;冲蚀角度为30°时,30CrMo的冲蚀磨损量最大;30CrMo的磨损机制与冲蚀角度有直接的关系,冲蚀角度小于30°时,冲蚀磨损机制以切削模型为主,大于30°时以局部塑性变形模型为主;冲蚀磨损量随冲击速度增加而显著增加,在高速冲击时,30CrMo钢的冲蚀磨损较为严重。     

排尘口直径对旋风分离器壁面磨损影响的数值模拟

基于计算流体动力学(Computational fluid dynamic,CFD)的数值模拟方法,在FLUENT软件平台上,应用雷诺应力模型、离散相模型和磨损值计算模型系统地研究排尘口直径对旋风分离器壁面磨损的影响。计算结果表明,旋风分离器壁面磨损的整体变化趋势不随排尘口直径的改变而变化,都呈现局部磨损的形态。排尘口直径减小,环形空间壁面磨损值保持不变,分离空间壁面磨损值有不同程度的增加,在锥体末端附近增加幅度最大,而这种变化主要是由于排尘口直径变化后分离器内部流动结构的变化引起的。分离空间锥体末端附近壁面的严重磨损主要受气固两相的旋转速度、颗粒浓度、旋进涡核和颗粒受力情况的影响。通过研究揭示合理地进行结构设计在减少磨损中的重要作用,为旋风分离器壁面的防磨提供数值试验方法和依据。     

Cavitation erosion of aluminum considering bubble collapse,pulse height spectra and cavitation erosion efficiency

Water erosion data on 1100-0 aluminum specimens obtained using a cavitating venturi are compared with bubble collapse pulse height spectra measured using a microtransducer. The data are resolved into erosion power and acoustic power. The former is defined in terms of the power applied to the eroded material to cause the observed pitting and volume loss. The ratio between these power quantities is termed the cavitation erosion efficiency η incav and is found to be essentially constant for the range of tests, being approximately 1.4 × 10^?6. The acoustic power which is easily measured can then be used to estimate the eventual material volume erosion rates, i.e. the mean depth of penetration (MDPR), with much greater accuracy than is otherwise possible. The MDPR is measured directly from the weight loss and is calculated from individual pit counts on damaged surfaces. The effects of the degree of cavitation (the extent of the cavitation cloud or the cavitation number) and the throat velocity on the MDPR is examined. An overall velocity damage exponent of n = 4.75 is found.     

Anomalous behaviour of high velocity oblique liquid impact

It is generally believed that erosion caused by impact with liquid drops has a maximum for normal impact. However, although this is true for many situations this paper shows that there are important exceptions, particularly where high velocity impacts are involved. Single impact studies in the velocity range 250–1200 m s^?1 were made. Three examples which show anomalous behaviour are discussed, namely polymethylmethacrylate (PMMA) where mass loss is a maximum at about 15° to the normal, a glass fibre laminate where there is a greater amount of penetration and strength loss at about 20° and a coated laminate where maximum coating loss occurs at 25°. All these phenomena took place only when critical velocities were exceeded. The results demonstrate the problems of extrapolating low velocity data into those higher velocity regimes which are becoming of increasing practical importance.     

Performance of thrust bearings operating with non-Newtonian lubricating films

A general solution for pressure distribution and load capacity is obtained for hydrodynamic bearings with non-Newtonian lubricating fluid films. The flow behaviour index of the power law model assumed for the velocity profile is shown to play a significant role in bearing performance. It is established that the load capacity of a thrust bearing, by way of example, may be increased to several-fold with increased values of the viscometric exponent.     

指数率流体热弹流润滑分析

应用多重网格技术,求得了指数率非牛顿流体线接触热弹流润滑的数值解,分析了油膜压力、厚度和温度等随流变指数、速度参数、滑滚比及载荷参数的变化关系,并与相同工况下的等温解进行了比较。结果表明,随着流变指数的增加,油膜厚度和温度、入口处的当量粘度、最小膜厚、中心膜厚和最大温升均增大,而油膜压力和摩擦因数的变化较小。指数率流体弹流润滑问题的热效应不可忽略;与压缩功项相比,油膜能量方程中的热耗散项对温度的影响最大。同时,无量纲速度参数、滑滚比和载荷参数等均影响热弹流润滑特性。     

The effect of stacking fault energy on the erosion behaviour of copper alloys at oblique impact

The major aim of this investigation was to determine the effect of the stacking fault energy (SFE) on the solid particle erosion rate at oblique impact angles. Such an investigation is essential to establish whether erosion is a deformation- or a fracture-controlled process. Towards this purpose, experiments were carried out at an impact angle of 30° on a series of copper alloys with a wide range of stacking fault energies using spherical steel shot travelling at a velocity of 40 m s^?1 as the erodent. The experimental results clearly show that the erosion rate decreases with decreasing SFE, thereby indicating that erosion is a deformation-controlled process. An inverse relationship between the erosion rate and the strain-hardening exponent is also observed. In addition, the erosion rate at 30° is lower than the erosion rate at 90°. Finally, it is demonstrated that the localization model for erosion is capable of rationalizing all these observations.     

Velocity exponent and cavitation number for Venturi cavitation erosion of 1100-O aluminum and 1018 carbon steel

The purpose of the present investigation is to evaluate the effect of Venturi throat velocity on the cavitation erosion of specimens for constant cavitation number, which is here based on Venturi discharge conditions. 1018 carbon steel and 1100-O aluminum were tested in the University of Michigan high speed cavitation tunnel with tap water at 27 °C (80 °F). Results of present tests are consistent with previous work done at the University of Michigan, showing that the velocity-damage exponent varies over the range ±1–5 for the velocity range 10–49 m s^?1.     

Cavitation erosion size scale effects

Size scaling in cavitation erosion is a major problem confronting the design engineers of modern high speed machinery. An overview and erosion data analysis presented in this paper indicate that the size scale exponent n in the relation erosion rate ∞ (size or diameter)ⁿ can vary from 1.7 to 4.9 depending on the type of device used. There is, however, a general agreement as to the values of n if the correlations are made with constant cavitation number.     

Velocity and size dependences of the erosion rate in silicon

The results obtained in this investigation for the velocity and size dependences of the steady state erosion rate in silicon single crystals are consistent with the predicted power law relation only if certain modifications are made. The velocity exponent n must depend on the particle size in such a way that n decreases as D increases, and allowance should be made for the onset of an apparent size threshold effect at small particle sizes. Further theoretical work is needed to extend the existing models, taking into account a number of new physical features. Possible mechanism changes and thresholds seem most important in this context. Further systematic experiments are also needed to establish the important parameters and to extract reliably their phenomenological relations. It is pointed out that a cursory analysis of erosion rate data according to simple power law velocity and size dependence is likely to be inconsistent and a suitable range of D and υ values must be systematically analyzed.     

Morphology of an aluminum alloy eroded by a normally incident jet of angular erodent particles

A morphological study of the erosion of 6061-T6 aluminum alloy by the normal impact of a crushed glass erodent particle jet was conducted. Erosion patterns were studied at several stages by varying the average particle velocity and the exposure time. The surfaces were studied using a scanning electron microscope supplemented with energy-dispersive X-ray spectroscopy. A profilometer was used to measure surface profiles and a depth gauge was used to measure depths. Transformation from deformation to cutting wear induced by the erosion process was observed, and discussion of the dynamics of the erosion process is presented.The morphology of the damage pattern reflects the flow pattern of erodent particles inside the pit. From morphological comparisons of the pits with time over the average particle velocities from 41 to 87 m s^?1 (driving gas pressures from 0.14 to 0.82 MPa), damage mechanisms were postulated and further insight into the erosion process was gained. Four distinct erosion regions were identified. Concentric ripple-type patterns appeared after the width-to-depth ratio of pits reached approximately 2.5. Cutting wear predominated at advanced stages in all erosion zones. Evidence for deformation wear appeared at the initial stage of erosion. The transformation to cutting wear appeared to occur simultaneously as the erosion rate transformed from the incubation period to the acceleration period. The correlation between erosion rate and jet velocity resulted in an exponent of 3.68, which agreed with some earlier normal impingement studies. Embedment of crushed glass was at a maximum at the bottom of the pit, and it decreased gradually from the pit edge to the undamaged region.     

The erosion of carbon fibre reinforced plastic by repeated liquid impact

The erosion of unidirectional carbon fibre reinforced plastic by repeated impact with a liquid jet, has been studied at velocities of up to 90 m/s. The long fibre axis was in the plane of impact. The resistance to erosion is better for type 2 fibre composites than for type 1, but in absolute terms not particularly high; it is virtually independent of fibre volume loading and decreases very rapidly with increasing impact velocity. A certain number of impacts is needed before damage is observed. Then individual fibres are cracked and removed from the surface, and pits develop. It is suggested that failure is started by transverse compression fatigue of the fibres. The performance of composites in which the fibres are end-on to the water jet is better.     

空间Z形管路液-固两相流冲蚀特性分析

空间Z形管路是油气开采过程典型的结构形式,在工程作业中受到高压高速液-固两相流的作用,容易导致管路系统产生冲蚀磨损失效。基于液-固两相流冲蚀磨损理论,选取合适的冲蚀磨损理论模型,讨论了流速、颗粒直径、质量流量、黏度以及重力等不同流体参数对管路系统弯头处的冲蚀磨损情况。结果表明:管路弯头处的冲蚀区域受内流场的影响存在明显差异,出口端弯头处的最大冲蚀率大于进口端弯管端。流速、颗粒直径、质量流量与整体管路最大冲蚀率呈正相关关系,黏度与整体管路最大冲蚀率呈负相关关系。分析了不同工况下空间Z形管路的冲蚀特性,获得了流体参数对管路冲蚀的影响规律,为工程实际复杂管路系统冲蚀磨损寿命预测提供技术参考。     

Solid particle erosion of diamond coatings under non-normal impact angles

This paper describes an erosion study, which examines the effect of impact angle on the erosion behaviour of diamond coatings deposited on tungsten substrates by chemical vapour deposition (CVD). The coatings were 37–60 μm in thickness and were erosion tested using angular silica sand with a mean diameter of 194 μm at a particle velocity of 268 m s⁻¹. The impact angles used were 30, 45, 60 and 90°. The results show that the damage features, termed “pin-holes” are generated at all angles, though the number of impacts required for pin-hole initiation is significantly increased at lower angles. This work provides useful information in attempting to explain the mechanism by which damage is generated during the high velocity sand erosion of CVD diamond.     

An application of bubble collapse pulse height spectra to venturi cavitation erosion of 1100-o aluminum

Venturi cavitation erosion tests were performed and correlated with bubble collapse pulse height spectra measured by a microtransducer. The effects of the throat velocity and the cavitation number σ (referred to the downstream pressure and throat velocity) on the erosion rate (MDPR) were studied. The velocity damage exponent was 4.11 for 0.62 ? σ ? 0.80, while the MDPR is almost independent of velocity for σ = 0.85. The MDPR decreases with increased σ for 0.62 ? σ ? 0.85. The data were reduced to “acoustic power” (from pulse height spectra) and “erosion power” (the ultimate resilience multiplied by the MDPR). A near-linear relationship was found between these. Their reciprocal ratio η_cav ≈ 7 × 10^?11. For σ = 0.62, the data deviated from the others, possibly because of the work hardening of the eroded surface.     

Determination of particle impacts and impact energy in the erosion of X65 carbon steel using acoustic emission technique

An in-situ acoustic emission (AE) monitoring technique has been implemented in a submerged jet impingement (SIJ) system in an effort to investigate the effect of sand particle impact on the degradation mechanism of X65 carbon steel pipeline material in erosion conditions.A detailed analysis of the acoustic events' count rate enabled the number of impacts per second to be quantified for a range of flow velocities (7, 10, 15 m/s) and solid loadings (0, 50, 200, 500 mg/L) in a nitrogen-saturated solution at 50 °C. The number of impacts obtained from acoustic signals showed a strong agreement with theoretical prediction for flow velocities 7 and 10 m/s. A deviation between practical readings and theory is observed for flow velocity of 15 m/s which may be due to error from detected emissions of multiple rebounded particles.Computational fluid dynamics (CFD) was used in conjunction with particle tracking to model the impingement system and predict the velocity and impact angle distribution on the surface of the sample. Data was used to predict the kinetic energy of the impacts and was correlated with the measured AE energy and material loss from gravimetric analysis. The results demonstrate that AE is a useful technique for quantifying and predicting the erosion damage of X65 pipeline material in an erosion–corrosion environment.     

Design and performance of a high velocity air–sand jet impingement erosion facility

This paper describes the design, construction and capabilities of a high velocity air–sand erosion rig. It has been designed with the aid of computational fluid dynamics to approximately simulate the erosion conditions often experienced by subsea choke valves used in the offshore oil industry. It has also been designed to evaluate the erosion performance of CVD diamond coatings at sonic velocity. The rig is of the gas-blast design in which solid particles, typically sand 60–660 μm in size, are injected into a high velocity air stream and accelerated down a 16-mm-diameter tube, 1 m in length, before striking the sample under test. Tests can be carried out with particle velocities of up to 340 m/s under a wide range of sand fluxes, impact angles and standoff distances. The results of pressure, velocity and sand flux calibration work are described. In addition, preliminary experimental data on tests carried out on mild steel, bulk and sprayed tungsten carbide are also presented. The flexibility of the air–sand rig allows the erosion behaviour of materials to be studied under a wide range of conditions.