A mechanistic model for the prediction of ductile erosion

Mechanisms operative in dust erosion of ductile materials were determined with the aid of scanning electron microscope studies. Dimensional analysis was employed in the development of a mathematical model for predicting the erosion of ductile materials. The basis of the model was an identified erosion mechanism (target melting) and the model was verified in an erosion testing program. The target materials in the testing program were three stainless steels, two aluminum alloys, a beryllium copper alloy and a titanium alloy. The erosive agents were three dusts with hard angular particles and one dust with spherical particles. Maximum particle velocities were 130 or 250 ms^?1.     

Experimental verification of a model of erosion due to the impact of rigid single angular particles on fully plastic targets

A previously described rigid-plastic model of the erosion of ductile targets by the impact of single angular particles was experimentally verified over a wide range of particle angularities, incident angles of attack, and incident orientation angles. The model assumes that the particle is perfectly rigid and thus is non-deforming, while the target material response is fully plastic, so that elastic rebound effects are neglected.Measurements of particle rebound kinematics, crater volume, and crater shape revealed generally good agreement with those predicted by the rigid-plastic model, and erosion mechanisms resulting from particles tumbling either forwards or backwards, were identified. For highly angular particles, target material removal sometimes occurred due to tunnelling of the particles below the target surface, leading to early break-off of a machined chip, behaviour that could not be predicted by the rigid-plastic model. Besides providing insights into fundamental erosion mechanisms, the results of the present study can be used to predict particle rebound kinematics, crucial for simulations of erosive streams which take into account interference between incident and rebounding particles.     

Correlation between solid particle erosion of metals and their melting energies

A new correlation is presented for the ductile erosive wear of metals by an impinging stream of abrasive particles. The specific erosion energy (the kinetic energy per unit volume of metal removed) is shown to be directly proportional to the melting energy per unit volume of the target metal. By analogy with grinding, this direct correlation is attributed to the extreme strains and strain rates which characterize the erosion process, thereby leading to near adiabatic plastic deformation of the metal to its energy limit.     

Study of particle erosion damage in Haynes Stellite 6B I: Scanning electron microscopy of eroded surfaces

The erosion behavior of metals and alloys by solid particles entrained in relatively slow moving gases is of current interest as a result of ongoing efforts in coal conversion and the consequent production of dust-laden gases. Haynes Stellite 6B represents a typical alloy used for erosive wear resistance in such situations and also provides an appropriate alloy for the study of the mechanisms of erosion because it comprises essentially large brittle carbide phases in a ductile matrix. A scanning electron microscope study of the surface of Stellite 6B after erosion by alumina particles is described, and the types of erosion damage incurred by the ductile metal matrix and the brittle carbides are characterized. The only mechanism of material loss of the ductile metal for which positive evidence was found was cutting, with the possibility that fracture on a very fine scale may also be involved. The mechanism of material removal from the carbides appeared to be by surface crack interlinkage. Under the conditions studied, corners of the eroding alumina particles were found to break off and to adhere to the alloy or carbide surface; at the highest impact velocity studied an extensive layer of embedded alumina fragments was built up on the alloy surface and probably modified its erosion behavior.     

Identifying Erosion Mechanism: A Novel Approach

Understanding the erosion mechanism is a key to improve the performance of material subjected to erosive condition. Capability to predict the erosion mechanism could prove to be useful tool. In this work, a parameter named “erosion mechanism identifier,” ξ, is proposed to predict the erosion mechanism in materials. Suitability of ξ in predicting erosion mechanism of ductile and brittle materials was evaluated using the data reported in the literature. It was observed that ξ is able to predict the erosion mechanism for both categories of material. The predictability of ξ was not restrained by different operating conditions.     

Numerical simulation of solid particle impacts on Al6061-T6 Part II: Materials removal mechanisms for impact of multiple angular particles

In the accompanying paper (M. Takaffoli, M. Papini, Numerical simulation of solid particle impacts on Al6061-T6 Part I: Three dimensional representation of angular particles), it was demonstrated that realistic 3D models of angular particles could be generated and used with a smoothed particle hydrodynamics model to simulate the damage done to an Al6061-T6 target due to many non-overlapping particle impacts. In this paper, the same methodology was used to simulate overlapping impacts, and thus the material removal mechanisms associated with the solid particle erosion of this material. The evolution of the topography of the blasted surface was simulated, and the surface ripple patterns that typically form during the erosion of aluminum alloys were observed. The predicted volumetric erosion rates at different impact angles were, on average, within 7% of those measured in erosion experiments. An investigation of the simulated trajectory of the impacting particles revealed the cooperative contribution of overlapping impacts to material loss, and solid particle erosion mechanisms such as the micromachining of chips, the ploughing of craters, and the formation, forging and knocking off of crater lips. The results indicate that numerical simulation of the solid particle erosion of ductile metals by realistic angular particles is possible.     

Solid particle erosion of CFRP composite with different laminate orientations

The solid particle erosion behavior of epoxy base unidirectional and multidirectional carbon fiber reinforced plastic composites was investigated. The erosion rates of these composites were evaluated at various impingement angles (15–90°) with a particle velocity of 70 m/s. Irregular SiC particles with an average diameter of 80 μm was used. The dependence of impingement angle on the erosive wear resembled the conventional ductile behavior with maximum erosion rate at 15–30° impingement angle. The erosion rate of unidirectional composites at acute impingement angle was higher for [90] than for [45] and [0] while the difference disappeared at normal impingement angle (90°). On the other hand, the erosion rates of multidirectional laminated composites ([0/90], [45/−45], [90/30/−30] and [0/60/−60]) were not much influenced by the fiber orientation except for 15° impingement angle.     

Tribology in coal-fired power plants

Material wear and degradation is of great importance to the economy of South Africa especially within the mining, agriculture, manufacturing and power generation fields. It has been found that unexpected and high rates of fly-ash erosion occur at certain sections of power plants, this is particularly evident at the Majuba power station. The loss of small amounts of material due to erosion can be enough to cause serious damage and significantly reduce the working lifetime of, for, e.g. hopper liners.This study investigated the long-term solid particle erosion of a range of oxide and nitride-fired SiC-based ceramics and alumina with the aim of reducing erosive wear damage in power plants. This entailed carrying out experimental tests on an in-house built erosion testing machine that simulate the problems encountered in the industry. The target materials were eroded with 125–180 μm silica sand at shallow and high impact angles. The surface wear characteristics were studied using both light and scanning electron microscopy (SEM).The results obtained indicate that the erosion rates of the materials remain fairly constant from the onset. It was found that prolonged exposure to erosion results in the progressive removal of the matrix and subsequent loss of unsupported SiC particulates. The fact that the particles were relatively small did not have a significant effect on the erosion rate. This would explain the observed constant rates of erosion for longer periods. These behaviours can be further explained in terms of the composition and mechanical properties of the erodents and target ceramics.     

Fluid dynamic mechanisms of particle flow causing ductile and brittle erosion

Traditional prediction of erosion focuses on the use of velocity and impact angle of particles as independent variables in analytically derived models. This approach is most suitable for numerical predictions of erosion in disperse flow fields where particle trajectories may easily be followed prior to impact. For dense particle flows, the prediction of individual particle or particle cluster movement is nearly never attempted by following trajectories. Instead, two-fluid Eulerian–Eulerian approaches are used in which a continuous particle fluid phase is considered.The present study shows that the impact velocity and angle of attack of particles at the eroding surface are difficult to obtain for dense flows, thus being difficult to consider as parameters for predicting erosion. Instead, it is proposed that the normal and the shearing components of the viscous dissipation of the particulate phase are more suitable as independent flow variables governing the erosion process. These variables describe deformation and cutting wear processes, respectively, and are readily derived from the flow field.Eulerian erosion models are proposed, based on these independent variables. It is possible to implement previous results and theories concerning the material–mechanical interaction between the abrasive and an eroding surface to achieve model improvements. In this work, only a simple model taking into account a threshold elastic strain limit is proposed, to more correctly model the deformation wear.The particle-flow boundary condition — a partial-slip condition — significantly influences the erosion process, particularly the cutting erosion. The boundary condition depends on parameters such as the local particle phase flow, the mean diameter and the sharpness of the abrasive as well as the surface roughness.A simple 2D test application — a jet stream of particles impinging a tilted plate — is presented, and the qualitative angular behaviour of ductile and brittle erosion is reproduced at the target position. A scheme is presented for determination of material constants and suitable boundary conditions to be used in the proposed erosion models.     

Erosion of 304 stainless steel

Erosion rate measurements and scanning electron microscopy observations were made for the steady state erosion of 304 stainless steel eroded by sharp alumina particles. Both the velocity and the particle size dependence of the erosion rates were similar at all angles of impact between 10° and 90°. Micrographic observations of the steady state erosion surfaces disclosed similar overall features at low and high angles of impact. Results reported in the literature for aluminum tend to confirm these observations. It was concluded that a single erosion mechanism can be operative at all impact angles 7in ductile metals such as stainless steel, rather than a superposition of different mechanisms for the low angle and high angle range. The physical basis for a single mechanism of erosion by sharp particles was discussed.     

Threshold erosion fracture in the case of oblique incidence

Absract  A model of erosion wear at threshold velocities of incidence of abrasive particles is advanced based on the classic theory of dynamic contact interactions and the structural-time fracture criterion. A formula for calculating the intensity of erosion damage is developed, assuming that erosive particles slip over the surface of the target material during contact. The dependences of erosion wear on the angle of incidence of particles of various sizes are plotted. Original Russian Text ? I.I. Argatov, N.N. Dmitriev, Yu.V. Petrov, V.I. Smirnov, 2009, published in Trenie i Iznos, 2009, Vol. 30, No. 3, pp. 245–253.     

Effect of structural features on erosion resistance of cast irons

Erosion resistance of four types of cast iron of different microstructures and graphite morphologies (viz., grey cast iron, compacted graphite iron, spheroidal graphite iron and austempered ductile iron) was evaluated in three different erosive media. Results indicate that austempered ductile iron has the highest erosion resistance in all three media, followed by spheroidal graphite iron, compacted graphite iron and grey cast iron, in that order. Graphite morphology has a significant effect on the erosion resistance of these irons in quartz-water and iron oxide-oil slurry. However, the matrix microstructure determines the erosion resistance of these irons in quartz-oil slurry. The parameter H/E (which is the ratio of the Brinell hardness number to Young's modulus of the material) has been found to be a good indicator of erosive wear in quartz-oil slurry.     

FEM analysis of erosive wear

Surface damage caused by the impact of dispersed particles in gas or liquid flow is called “erosion”. Much attention has been paid to this phenomenon as one of the most serious problems to be solved, particularly concerning pipe-bends or valves in pneumatic conveying systems. But the phenomena of erosive wear are so complicated and vary depending on the factors of not only the kinds of material, hardness, shapes, sizes and mechanical properties of the particles, but also of blasting angles and velocity.

For the purpose of this study, mild steel was prepared and erosion wear tests were carried out. Steel grits were impacted against target materials at different incident angles. The results showed that the wear losses varied markedly as a function of the impact angles, and that the maximum wear occurred at specific angles. Maximum wear occurred at 20–30° for mild steel, and 60° for ductile iron. This impact angle dependence of wear was simulated by Tabor’s theory and FEM which could analyze the plastic deformation of alloy surface as a result of a single particle impact. In the case of both mild steel and ductile cast iron, it was found that the impact angles play a very important and valid role in the corrosion process.     

Numerical simulation on the erosion wear of a multiphase flow pipeline

The devices in coal chemical industries operate with harsh conditions, involving the high temperature, high pressure, and high concentration of pulverized coal particles. Therefore, leakages or perforations of pipelines occur frequently. In this paper, the numerical prediction on the erosion wear of a coal slurry transmission pipeline was conducted. The dense discrete phase model-kinetic theory of granular flow (DDPM-KTGF) and a modified erosion model were adopted to calculate the particle trajectories and erosion rates. In the numerical calculation, the erosion rate curve of 1Cr9Mo steel obtained in the experiments is incorporated into the erosion model. The results showed that the regions with high erosion risks predicted by the modified erosion model were in agreement with the experimental results. Then, the calculation method is validated. It is also found that the particle movements involve partial agglomeration under the drag of centrifugal force and the secondary flow, when they pass through the elbow. Larger particles are prone to impact on the back of the bend, which has more pronounced effect on the erosion wear. The positions of the maximum erosion rate on all the elbows were discussed, which provides a reference for the inspection on the wall thickness of pipeline.     

Influence of impingement angle on solid particle erosion of carbon fabric reinforced polyetherimide composite

Polyetherimide (PEI) composite reinforced with plain weave carbon fabric (CF) (40% by volume) was developed and characterized for physical and mechanical properties. The erosive wear behaviour of PEI and its composite was evaluated using silica sand particles at a constant impact velocity but varying angles of impingement. It was confirmed that though all the mechanical properties of PEI improved substantially by CF reinforcement, the erosion resistance (W_R) deteriorated by a factor of almost four–six times at all angles of impingement. Both materials showed minimum wear at normal incidence (90° impingement). In spite of the fact that PEI is not a very ductile polymer (elongation to break-60%), it showed maximum wear at 15° which is a characteristic of ductile and semi-ductile mode of failure. The composite (elongation to break-1%) also showed highest wear at 30° (impingement at 15° was not studied). These phenomena were explained using scanning electron micrographs of the eroded surfaces.     

Abrasive waterjet machining simulation by SPH method

Abrasive waterjet machining (AWJM) is a non-conventional process. The mechanism of material removing in AWJM for ductile materials and existing erosion models are reviewed in this paper. To overcome the difficulties of fluid–solid interaction and extra-large deformation problem using finite element method (FEM), the SPH-coupled FEM modeling for abrasive waterjet machining simulation is presented, in which the abrasive waterjet is modeled by SPH particles and the target material is modeled by FE. The two parts interact through contact algorithm. The creativity of this model is multi-materials SPH particles, which contain abrasive and water and mix together uniformly. To build the model, a randomized algorithm is proposed. The material model for the abrasive is first presented. Utilizing this model, abrasive waterjet penetrating the target materials with high velocity is simulated and the mechanism of erosion is depicted. The relationship between the depth of penetration and jet parameters, including water pressure and traverse speed, etc., are analyzed based on the simulation. The results agree with the experimental data well. It will be a benefit to understand the abrasive waterjet cutting mechanism and optimize the operating parameters.     

Influence of the Erodent Shape on the Erosion Behavior of Ductile and Brittle Materials

Solid particle erosion is identified as a major wear process occurring in numerous industrial applications. A number of test parameters influence the behavior of the materials during this wear process. Particle shape is one of the key factors, which is often discussed for ductile or brittle materials in the literature, but a comparative study of ductile and brittle materials showing an effect of particle shape has not been addressed in detail until now. The present work discusses the influence of erodent shape on the wear behavior of a ductile (Ti-6Al-4 V alloy) and a brittle (TiN coating) material during the erosion process. Investigations are performed in an erosion test rig where the ductile and brittle materials are charged with spherical and angular SiO₂ particles at normal impact. Results show an inverse erosion behavior of ductile and brittle materials with the variation in particle shape. Ductile materials show low material removal with spherical particles, whereas brittle materials show low material removal rates with angular ones. This work also provides an analysis of the material removal phenomenon to understand the effect of particle shape on tested materials. Since materials removal phenomenon in ductile materials is often reported in the literature, this work addresses the material removal behavior especially in ceramic coatings.     

Effects of fibre content and relative fibre-orientation on the solid particle erosion of GF/PP composites

The erosive wear behaviour of glass fibre (GF) reinforced thermoplastic polypropylene (PP) composites was studied in a modified sandblasting apparatus as a function of the impact angle (30, 60 and 90°), relative fibre-orientation (parallel Pa and perpendicular Pe), fibre length (discontinuous, continuous) and fibre content (40–60 wt.%).The results showed a strong dependence of the erosive wear on the relative fibre-orientation at low impact angles (30°), but hardly any difference for 60 and 90° impact angles. In contrast, the fibre length did not affect the erosive wear behaviour especially at high impact angles.The inclusion of brittle GF led to higher erosive wear rates (ER) of the GF/PP composites; the higher the fibre content, the higher was the ER. Nevertheless, the composites still failed in a ductile manner. Different approaches proposed to describe the relationship between ER and fibre content were applied. Best results were generally delivered with the inverse rule of mixture. The modified rule of mixtures proposed for abrasive wear do not seem to apply for erosive wear.     

Wear Performance Forecasting of Chopped Fiber–Reinforced Polymer Composites: A New Approach Using Dimensional Analysis

Solid particle erosion of polymer matrix composites is a complex process in which wear occurs from the target surface by impingement of rigid sand particles in an air medium. The rate of material removal (RMR), also referred to as the erosion rate, mainly depends on target material parameters and the erosion conditions such as impact angle, impact velocity, and erodent size. A new semi-empirical model for prediction of the erosion rate of polymer matrix composites has been developed using a dimensional analysis technique based on Buckingham's π theorem. The predictive model analytically rests upon parameters related to chopped glass fiber composites, erodent (target material properties), and operating variables that mainly affect the erosion process of chopped glass fiber–vinyl ester resin composites. The forecasting ability of the predictive model has been assessed and verified by experimental investigations for chopped glass fiber–reinforced vinyl ester resin (VGF) composites. Validation of the theoretical erosion rates obtained from the predictive model showed that they were in good agreement with the experimentally determined erosion rates, where the average error range was estimated to be ～10 to ～20%.     

A Phenomenological Model for Slurry Erosion Prediction of Thermal Spray Coatings

Erosion is a serious concern for machinery dealing with particle-laden fluids. For protection against erosion, coatings are usually recommended. Laboratory experiments are conducted to evaluate the erosion rates of these coatings. Alternatively, one could consider the use of modeling and simulation to predict the erosion rates. Although several models are available in literature for bulk materials, there is limited work reported in this direction for coatings. In present work, several models from literature were evaluated for their ability to predict the slurry erosion of coatings. A model based upon contact-fracture theory (CFT), proposed in present work, was also evaluated. Another variant of this model considered the effect of splat size. It was observed that none of the existing models evaluated in the present work could predict the erosion rates of the coatings. The proposed CFT model was able to predict the erosion rates with reasonable accuracy, whereas another variant of this model based upon splat size was observed to be inappropriate for predicting erosion rates of coatings. Possible reasons for the observed disparity are discussed.