Effect Of Impact Angle Research Articles

Effect of impingement angle on slurry erosion behaviour and mechanisms of 1017 steel and high-chromium white cast iron

In the present work a series of systematic erosion tests were carried out to investigate the influence of impingement angle on erosion mechanisms of 1017 steel and high-Cr white cast iron using a slurry whirling-arm test rig. Scanning electron microscopy (SEM), image analysis system, optical microscopy as well as gravimetric and microhardness measurements were utilized to identify the slurry erosion process. Test results showed that, the effect of impingement angle on erosion mechanisms of 1017 steel has three regions. In the first region ( θ ≤ 15°) shallow ploughing and particle rolling were the dominant erosion mechanisms, microcutting and deep ploughing in the second region (15° < θ < 75°), while indentations and material extrusion prevailed in the third region ( θ ≥ 75°). For high-Cr white cast iron the test results showed that, the erosion mechanisms involved both plastic deformation of the ductile matrix and brittle fracture of the carbides. At low impingement angles (up to 45°) observations of microphotographs of the impacted surfaces revealed that, plastic deformation of the ductile matrix was the dominant erosion mechanism and the carbides fracture was negligible which lead to small erosion rate. Whereas, at high impingement angles (greater than 45°) gross fracture and cracking of the carbides were the main erosion mechanisms in addition to indentation with extruded lips of the ductile matrix.

Numerical simulations of hypervelocity impact of asteroid/comet on the Earth

In this study, numerical simulations of asteroid/comet impact on the earth were carried out by using the hydrocode AUTODYN-2D (Century Dynamics Inc.). The ejected mass into the atmosphere originated from different sources was recorded at different altitudes as a function of time. It is claimed that the mass extinction at the Permian–Triassic (P/T) boundary was caused by an extraterrestrial impact and the following abrupt climate/environment change. The objective of this work is to substantiate the claim with numerical analysis. It is demonstrated that the materials from different origins are splashed into the atmosphere and that the crater size is a function of the diameter as well as the kinetic energy of the impactor. The effect of impact angle to the appearance of ejected materials is also investigated using two-dimensional plane strain model.

Three-dimensional numerical analysis of the deformation behavior of droplets impinging onto a solid substrate

The collision dynamics of water droplets impacting onto a solid is studied by means of three-dimensional computer simulations. The Navier–Stokes equations for unsteady, incompressible, viscous fluids in the three-dimensional Cartesian coordinate system are approximated and solved by a finite difference method. The volume-of-fluid (VOF) technique is used to track the free liquid surface. Normal and oblique collisions of droplets with the substrate are simulated at low droplet impact inertia. The effect of impact angle on the deformation behavior of droplets is investigated. The experimental observations and the numerical results are in reasonable agreement. Theoretical aspects of the physics of the collision phenomena are addressed.

Investigation of the effect of impingement angle on tribocorrosion using single impacts

Using highly sensitive measurement and analog digital conversion devices it was possible to detect the repassivation transients after particle impingement on aluminium. Simultaneous use of a newly constructed slurry-jet and μ-electrodes as targets allowed the highly reproducible detection of single-particle impacts. This, in turn, allowed correlating the charge consumed during repassivation in a potentiostatic experiment with the damage caused. Variation of the experimental geometry allowed tuning the impingement angle to predetermined values. Current transients and the craters resulting from the particle impact were analyzed for impingement angles between 30° and 90°. It was found that both peak current and charge increase with decreasing angle. As a result of the nano-roughness of the impacting zirconia particles used it was possible to ascribe the crater morphologies to the different mechanisms of indentation and scratching. A model that links the normal and lateral components of the kinetic energy to these two wear mechanisms is proposed.

Characterization and Erosion Behavior of Plasma Sprayed NiCrAlY and Ni-20Cr Coatings on an Fe-based Superalloy

Degradation of materials due to solid particle erosion is encountered in a variety of engineering industries, either at room temperature or elevated temperatures. Nickel-based coatings are commonly used in applications where wear resistance, combined with oxidation or hot corrosion resistance, is required. In the present work, NiCrAlY and Ni-20Cr metallic coatings were deposited on an iron-based superalloy by a shrouded plasma spray process. The coatings were characterized by scanning electron microscopy, optical microscopy, microhardness testing, and x-ray diffractometry. Erosion studies were conducted using an air-jet erosion test rig at a velocity of 40ms−1 and impingement angles of 30 and 90deg. Scanning electron microscopy was used to analyze the eroded surfaces. 3D surface roughness profiles of the eroded samples were taken using a Veeco Optical Profilometer. NiCrAlY coatings had slightly lower average porosity and lower microhardness as compared to Ni-20Cr coatings. The observed erosion rate of the NiCrAlY coatings, however was lower than that of the Ni-20Cr coatings at both 30 and 90deg impingement angles. Ni-20Cr coating had shown higher erosion rate at 90deg impingement angle than that at 30deg, whereas the effect of impingement angle on the erosion rate is negligible for plasma sprayed NiCrAlY coating. The higher bond strength of NiCrAlY coating might be one of the major contributing factors for lower erosion rate of NiCrAlY coating as compared to Ni-20Cr coating under the tested conditions. Erosion mechanisms of plasma sprayed coatings are discussed.

Modelling impact angle effects on erosion–corrosion of pure metals: Construction of materials performance maps

In studies of the effect of erosion–corrosion in aqueous conditions, impact angle effects are frequently ignored. This is despite the fact that erosion has a function of impact angle and can vary frequently depending on the nature of particle/target interactions. In such cases, the impact angle effects may change depending on whether the eroding particle encounters a metallic surface or an oxide film. This work describes extension of a model already developed for erosion–corrosion of Fe to a range of pure metals, Ni, Cu, and Al at a range of pHs. The impact angle effects were estimated based on models from the solid particle erosion literature. The corrosion stability regimes were identified using Pourbaix diagrams for various pure metals. The results were used to generate erosion–corrosion mechanism maps showing the differences in the impact angle effects at various pHs for the pure metals. The changes in wastage regime for the various pure metals as a function of impact angle and pH were demonstrated. Materials performance maps were generated using such models showing how wastage rates may be optimised for exposure to impact angle, pH and electrochemical potential.

Impact angle effects on the erosion–corrosion of superlattice CrN/NbN PVD coatings

Wastage due to the combined effects of erosion and corrosion is a serious issue in a wide range of industrial environments. The extent of wastage is dependent on a range of parameters relating to properties of the particle, target and the environment. In such cases, surface engineering (through providing a protective coating) may be used to avoid the deleterious effects of both processes. In recent years, there has been an increasing interest in the potential of CrN/NbN superlattice PVD coatings to provide resistance to erosion–corrosion in such conditions. Initial studies on the effects of velocity have shown that they significantly outperform conventional coatings, although the behaviour depends on the conditions. There is however, poor understanding on the effects of many important tribological variables, such as particle size and impact angle, on the performance of such coatings. In this work, the effect of impact angle on the erosion–corrosion of a range of CrN/NbN superlattice coatings was assessed at a range of applied potentials in a carbonate/bicarbonate solution. The mechanisms of erosion–corrosion of the coatings, as a function of impact angle and applied potential, showed significant differences when these parameters were varied. Erosion–corrosion maps were constructed based on these results showing the change in mechanisms and wastage rates as a function of impact angle and applied potential. Possible reasons for the differences in erosion–corrosion regimes for coated and uncoated specimens are described in this paper.

Analysis of impact damage of agglomerates: effect of impact angle

The effect of impact angle on the breakage of two types of agglomerates of a synthetic detergent formulation is analysed. The agglomerates are in the same size range (0.60–0.71 and 1.00–1.18 mm) with the same formulation but have different structures arising from the processing method. In contrast to previous work reported in the literature for other materials, it is observed that for the types of agglomerates used in this work the extent of breakage increases as the impact angle is decreased from normal in the velocity range tested (15–35 m s −1). Furthermore, when the agglomerates break in the chipping regime, i.e. by surface damage at low impact velocities (less than 15 m s −1), the normal component of the impact velocity determines the extent of breakage independent of the impact angle. However, at higher impact velocities where fragmentation occurs, the role of the tangential component of the impact velocity becomes increasingly important. The difference in the failure mode of agglomerates tested here and those reported in the literature is thought to be the main reason for the dissimilarity. The granules examined here are sensitive to shearing because of the synthetic detergent formulation and their failure is predominantly due to ductile failure, whilst the previous materials fail mainly through brittle and semi-brittle mode of breakage.

Effects of Impact Angle on Cone Crack Formation in Impact-Loaded Soda-Lime Glass

In order to investigate the possibility of punching process of brittle material by ball impact, effects of impact angle on cone crack formation in impact-loaded soda-lime glass were evaluated experimentally. Evaluated were also contact area between specimen and sealing, and the optimal condition for cone crack formation in glass plates by impact with small steel balls. It has been found that lateral and radial cracks gradually developed asymmetrically. However, the perfect cone cracks were found to develop almost symmetrically. As the impact angle increased, the growth rate of cone cracks decreased. Regardless of the impact angle, the PMMA sealing was more effective for perfect cone formation than Aluminum and Polyurethane sealing. Thus, the application for industrial technology for hole (or nozzle) punching process of the brittle materials is expected to be feasible, based upon proper selection of sealing materials.

529 窒化ケイ素セラミックスのアブレイシブジェット加工特性(OS11 研削・砥粒加工)

Abrasive jet machining (AJM) attracts attention as ultra-fine processing technology to brittle material, such as glass and ceramics. This study investigates the effect of impact angle on machining efficiency and surface roughness. The AJM test to which the impact angle was changed, were carried out that a part of fracture mode was changed to ductile mode when an impact angle becomes small. Consequently, machining efficiency. was improved in the conditions of a small impact angle. Moreover, it was shown that surface roughness was improved in the condition of a very low impact angle.

Effect of impact angle and velocity on the fragment size distribution of glass spheres

In this paper, the effects of impact angle and impact velocity on the size distribution of glass fragments obtained in single particle impact experiments are investigated. This study suggests that the critical impact velocity required to initiate Hertzian crack in glass spheres under dynamic impact can be reasonably estimated based on slow compression test data. As the fragment size distribution can be characterised using a two-parameter Weibull equation, a simple approach is proposed to predict the fragment size distribution for glass particles failed under different impact arrangement based on the Weibull parameters.

Prediction of fatigue performance in gas turbine blades after foreign object damage

Foreign object damage is a significant cause of failure in gas turbine engines. This paper describes a series of experiments conducted on ‘blade-like’ fatigue specimens. The specimens were impacted with a cubical projectile at 250 m/s using a gas gun. They were subsequently fatigue loaded using the step method of testing to establish the fatigue strength in the damaged state. The effects of impact angle, leading edge radius, and blade wedge angle are investigated. It is shown that damage depth has a significant effect on fatigue strength. Concepts of crack arrest in the small crack regime are then used to predict the variation of fatigue strength with notch size using the Kitagawa–Takahashi diagram. The predictions are compared with the experimental results and it is shown that they constitute a lower bound. The difference between experimental and predicted results is discussed in terms of the residual stresses present close to the notch.

１２％Ｃｒ耐熱鋼のホウ化処理と固体粒子衝突に対する耐エロージョン性

In order to cope with the severe solid particle erosion damage of 12%Cr steel for steam turbine nozzles, erosion tests were conducted at high temperature, by using high velocity iron oxide for solid particles. With respect to the behavior of erosion damage, the effects of impact angles and velocity of iron oxide, hardness and surface treatments of target materials were made clear. And a boronized 12%Cr steel was superior resistant to the erosion. This paper describes the characteristics of boronized layer of 12%Cr steel with excellent erosion resistance, the relationship between damage and some erosion factors and the application of boronized 12%Cr steel nozzles in actual steam turbines.

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 37–60μm in thickness and were erosion tested using angular silica sand with a mean diameter of 194μm at a particle velocity of 268ms−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.

Hypervelocity impact damage to composites

This paper presents the results of hypervelocity impact tests conducted on graphite/PEEK laminates. Both flat plate and circular cylinders were tested using aluminum spheres of varying size, travelling at velocities from 2–7 km/s. The experiments were conducted at several facilities using light gas guns. Normal and oblique angle impacts were investigated to determine the effect of impact angle, particle energy and laminate configuration on the material damage and ejecta plumes. Correlations were established between an energy parameter and the impact crater size, spallation damage and debris cone angle. Secondary damage resulting from the debris plume on adjacent composite structures was studied using high-speed photography and witness plates. It was observed that for hypervelocity impacts, the debris plume particles have sufficient energy to penetrate adjacent structures and cause major structural damage as well.

Understanding oblique impacts from experiments, observations, and modeling.

Natural impacts in which the projectile strikes the target vertically are virtually nonexistent. Nevertheless, our inherent drive to simplify nature often causes us to suppose most impacts are nearly vertical. Recent theoretical, observational, and experimental work is improving this situation, but even with the current wealth of studies on impact cratering, the effect of impact angle on the final crater is not well understood. Although craters' rims may appear circular down to low impact angles, the distribution of ejecta around the crater is more sensitive to the angle of impact and currently serves as the best guide to obliquity of impacts. Experimental studies established that crater dimensions depend only on the vertical component of the impact velocity. The shock wave generated by the impact weakens with decreasing impact angle. As a result, melting and vaporization depend on impact angle; however, these processes do not seem to depend on the vertical component of the velocity alone. Finally, obliquity influences the fate of the projectile: in particular, the amount and velocity of ricochet are a strong function of impact angle.

Effect of impact angle on the slurry erosion–corrosion of 304L stainless steel

This communication describes an investigation of the effect of impact angle on slurry erosion–corrosion of stainless steel using a new slurry erosion rig. With the new apparatus, it is possible to measure the individual erosion events under impact as both electrochemical current/time transients, and mechanical transients through acoustic emission (AE) simultaneously. Each sharp rise observed in the electrochemical current transient under particle impact is accompanied by an AE event. These sharp current rises are attributed to the rupture or removal of the oxide film on the surface by the abrasive particles. The correlation between the current rise and the maximum of the AE event, although scattered, shows an increase with decreasing impact angle. The current transients due to individual erosion events show that on the average, the current rise is greater and the rise time is longer at oblique angles compared with those at normal incidence. The degree of denudation of the metal surface by individual particle impingements, the process which strips the surface of its passivity, increases at more oblique angles. Weight loss measurements demonstrate that the synergistic effect between erosion and corrosion is enhanced by a more oblique angle of impact. The origin of the synergism is discussed.

Effect of impact angle on glass surfaces eroded by sand blasting

In a previous work, we studied the effects of sand blasting on the roughness, the optical transmission and the mechanical strength of a soda lime glass for sand blasting durations up to 150 min and under a constant impact angle of 90°. In the present work, we examine the effect of impact angles (30 to 90°) for relatively small durations up to 60 min on the surface roughness and the optical transmission. The roughness increases and tends towards a plateau, while the optical transmission decreases and tends towards a threshold estimated at about 50% of the initial transmission. We noticed that the samples erosion damage becomes weaker for impact angles less than 90° (90° angle corresponds to the flux normal to the samples). Microscopic observations reveal that the damage is similar to that of sharp indentation damage type Vickers indentation. There is formation of a plastic imprint with radial cracks and some scaling caused by the development of lateral cracks that extend and curve up to the surface. From the expression of the damage rate as defined in the literature, we introduced a function relating the impact angles and the sand blasting durations to the optical transmission. The experimental data obtained seem to fit quite well to the proposed function.

Effect of post-sintering heat-treatments on the erosive wear behaviour of liquid-phase-sintered aluminas

The influence of microstructure on the indentation-strength and solidparticle erosive wear behaviour of a liquid-phase-sintered (LPS)alumina subjected to coarsening, quenching and crystallisationheat-treatments were investigated. Strength as a function of cracksize using Vickers indentations of varying loads was assessed. Theshort-crack toughness curves (T-curves) of the materials wereevaluated from indentation-strength data which is pertinent to wearproperties, since wear is governed by fracture characteristics atsmall flaw sizes. The effects of impact angle and particle velocityon erosive wear rates were also analysed. The relationship betweenshort-crack toughness behaviour and erosion resistance are discussedwith reference to the material microstructures and phase composition.

126 窒化ケイ素のサンドエロージョンに及ぼす衝突角度と温度の影響(O.S. 機械材料・新素材II)(機械材料・新素材)

126 窒化ケイ素のサンドエロージョンに及ぼす衝突角度と温度の影響(O.S. 機械材料・新素材II)(機械材料・新素材)