Erosive wear of ductile metals by a particle-laden high velocity liquid jet

A liquid-solid particle jet impingement flow apparatus is described and experimental measurements are reported for the accelerated erosion of copper, aluminum and mild steel sheet metal by coal suspensions in kerosene and Al₂O₃ and SiC suspensions in water. Slurry velocities of up to 130 ft s^?1 (40 m s^?1) and impingement angles of 15°–90° were investigated. The maximum particle concentration used was 40 wt.%. For high velocity the results of this work show two erosion maxima; these are found at impingement angles of 90° and 40°. However, in corresponding gas-solid particle investigations maximum erosion occurs at approximately 20°. In this work both particle concentration and composition were varied. A polynomial regression technique was used to calculate empirical and semitheoretical correlation constants.     

Monte carlo calculations for the mechanical relaxation of a self-assembled monolayer and for the structures of alkane/metal interfaces

Configurational-bias Monte Carlo calculations have been used to study the mechanical relaxation of a monolayer of CH₃(CH₂)₁₅S admolecules on a gold substrate when subjected to indentation by a force-microscope tip. Compression leads to substantial but reversible changes in molecular tilt angle and chain conformations. The same Monte Carlo technique has been used to probe the structural properties of liquid hexadecane films in contact with a flat metal substrate.     

Influence of tilt angle of plate on friction and transfer layer—A study of aluminium pin sliding against steel plate

In the present investigation, unidirectional grinding marks were attained on the steel plates. Then aluminium (Al) pins were slid at 0.2°, 0.6°, 1.0°, 1.4°, 1.8°, 2.2° and 2.6° tilt angles of the plate with the grinding marks perpendicular and parallel to the sliding direction under both dry and lubricated conditions using a pin-on-plate inclined sliding tester to understand the influence of tilt angle and grinding marks direction of the plate on coefficient of friction and transfer layer formation. It was observed that the transfer layer formation and the coefficient of friction depend primarily on the grinding marks direction of the harder mating surface. Stick-slip phenomenon was observed only under lubricated conditions. For the case of pins slid perpendicular to the unidirectional grinding marks stick-slip phenomenon was observed for tilt angles exceeding 0.6°, the amplitude of which increases with increasing tilt angles. However, for the case of the pins slid parallel to the unidirectional grinding marks the stick-slip phenomena was observed for angles exceeding 2.2°, the amplitude of which also increases with increasing tilt angle. The presence of stick-slip phenomena under lubricated conditions could be attributed to the molecular deformation of the lubricant component confined between asperities.     

Molecular dynamics study of optimal packing structure of OTS self-assembled monolayers on SiO2 surfaces

Optimal packing structure of Octadecyltrichlorosilane (OTS) self-assembled monolayer (SAM) adsorbed on a SiO₂ (1 0 0) surface with a Si substrate was studied performing molecular dynamics (MD) computational simulations. Molecular substitution, substitution pattern and molecular orientation of the OTS molecules on the SiO₂ (1 0 0) are the main factors studied in order to determine the optimal packing structure taking into account energetic balance. We have used the optimal packing structure to study other properties usually used to characterize SAMs as molecular and system tilt angles, film thickness and gauche defects. These properties and monolayer stability were studied performing MD simulations in a temperature range from 100 to 600 K and we found that results obtained agree with those from experimental measurements. We found that OTS films are stable up to 500 K. The optimal structure obtained could be used in further MD simulations studies in order to determine tribological properties of OTS–SiO₂ systems.     

Characterization of nitride thin films by electron backscatter diffraction

Thin films incorporating GaN, InGaN and AlGaN are presently arousing considerable excitement because of their suitability for UV and visible light‐emitting diodes and laser diodes. However, because of the lattice mismatch between presently used substrates and epitaxial nitride thin films, the films are of variable quality. In this paper we describe our preliminary studies of nitride thin films using electron backscattered diffraction (EBSD). We show that the EBSD technique may be used to reveal the relative orientation of an epitaxial thin film with respect to its substrate (a 90° rotation between a GaN epitaxial thin film and its sapphire substrate is observed) and to determine its tilt (a GaN thin film was found to be tilted by 13 ± 1° towards [101 0]_GaN), where the tilt is due to the inclination of the sapphire substrate (cut off‐axis by 10° from (0001)_sapphire towards (101 0)_sapphire). We compare EBSD patterns obtained from As‐doped GaN films grown by plasma‐assisted molecular beam epitaxy (PA‐MBE) with low and high As₄ flux, respectively. Higher As₄ flux results in sharper, better defined patterns, this observation is consistent with the improved surface morphology observed in AFM studies. Finally, we show that more detail can be discerned in EBSD patterns from GaN thin films when samples are cooled.     

Monte Carlo Simulation of Sudden Death Bearing Testing

Monte Carlo simulations combined with sudden death testing were used to compare resultant bearing lives to the calculated bearing life and the cumulative test time and calendar time relative to sequential and censored sequential testing. A total of 30,960 virtual 50-mm bore deep-groove ball bearings were evaluated in 33 different sudden death test configurations comprising 36, 72, and 144 bearings each. Variations in both life and Weibull slope were a function of the number of bearings failed independent of the test method used and not the total number of bearings tested. Variations in L ₁₀ life as a function of number of bearings failed were similar to variations in life obtained from sequentially failed real bearings and from Monte Carlo (virtual) testing of entire populations. Reductions up to 40% in bearing test time and calendar time can be achieved by testing to failure or the L ₅₀ life and terminating all testing when the last of the predetermined bearing failures has occurred. Sudden death testing is not a more efficient method to reduce bearing test time or calendar time when compared to censored sequential testing.     

Numerical investigation of prop-rotor and tail-wing aerodynamic interference for a tilt-rotor UAV configuration

We investigated the aerodynamic interference between the prop-rotor and the tail-wing, and its effect on the lateral stability of a tiltrotor UAV configuration during transient flight modes. Unsteady flow calculations were conducted using an unstructured mesh flow solver, coupled with an overset mesh technique. It was shown that as the sideslip angle increases, the interference between the prop-rotor and the tail-wing is enlarged. This interference magnifies the fluctuating amplitudes of the yaw and roll moments. The increased sideslip angle also induces an imbalance of the thrust force generated by the right and left prop-rotors, affecting the lateral stability. The effect of the nacelle tilt angle on the lateral stability was also investigated for the nacelle tilt angles of 80° and 90°. When the nacelle tilt angle was 90°, the interference between the prop-rotor and the tail-wing was reduced.     

An elastic-plastic stress analysis in silicon carbide fiber reinforced magnesium metal matrix composite beam having rectangular cross section under transverse loading

In this work, an elastic-plastic stress analysis has been conducted for silicon carbide fiber reinforced magnesium metal matrix composite beam. The composite beam has a rectangular cross section. The beam is cantilevered and is loaded by a single force at its free end. In solution, the composite beam is assumed perfectly plastic to simplify the investigation. An analytical solution is presented for the elastic-plastic regions. In order to verify the analytic solution results were compared with the finite element method. An rectangular element with nine nodes has been choosen. Composite plate is meshed into 48 elements and 228 nodes with simply supported and in-plane loading condations. Predictions of the stress distributions of the beam using finite elements were overall in good agreement with analytic values. Stress distributions of the composite beam are calculated with respect to its fiber orientation. Orientation angles of the fiber are chosen as 0°, 30°, 45°, 60° and 90°, The plastic zone expands more at the upper side of the composite beam than at the lower side for 30°, 45° and 60° orientation angles. Residual stress components ofσ _x andτ _xy are also found in the section of the composite beam.     

A combined cold extrusion for a drive shaft: experimental assessment on dimensional compatibility

A combined cold extrusion process is experimentally visualized to manufacture a drive shaft. Due to the requirements of a face width of about 92.00 mm for the spur gear section and a groove depth of roughly 22.70 mm for the internal spline region, a preform is adopted to prevent excessive accumulation of plastic deformation. AISI 1035 medium carbon steel material is spheroidized and annealed to use as the initial billet workpiece. In order to verify the deformed configuration and the dimensional accuracy, both shoulder angles of (θ₁, θ₂) are selected to be (30°, 30°) and (45°, 45°) on each extrusion die for the preform forging and the combined extrusion. Using the prepared tool components, experimental investigations on the dimensional relevancy of the cold forged drive shaft are performed. When the shoulder angle set of (30°, 30°) is applied, the required dimensions with respect to the face width and the groove depth are sufficiently satisfied, but unpredictable forging defects are observed. With the shoulder angles of (45°, 45°), the drive shaft is well deformed and fabricated without any cold forging defects. As a result, it is confirmed that the drive shaft can successfully be actualized with the dimensional precision satisfied by the combined cold extrusion.

     

Epifluorescence microscopy study of a quadruple node of triple junctions of grain boundaries in a Eu2+‐doped Kcl:Kbr solid solution by using the doping ion as a fluorochrome

A typical quadruple node (QN) of triple junctions (TJs) of grain boundaries (GBs) in a Eu²⁺‐doped KCl_0.52Br_0.48 solid solution is investigated from the geometrical point of view by epifluorescence microscopy using the doping ion as a fluorochrome. The excitation and fluorescence optical properties of the fluorochrome were previously characterised by spectrophotometry whereas the structural nature of the studied material as well as its Bravais lattice type, unit cell size and long‐range translational order degree was determined by X‐ray diffraction. A three‐dimensional reconstruction was built from the microscopy images of different optical cross‐sections of the studied arrangement of crystal defects. In the close vicinity of the QN, the studied arrangement of crystal defects adopts the geometry of a collapsed tristetrahedron which, centred at the QN, has its legs along the TJs and, hence, has its faces as collapsed in pairs into the GBs. The angles defined by different TJ couples as well as the dihedral angles defined by the different GB couples meeting in every TJ were measured at the QN site. All, the image recording and stacking as well as the measuring procedures are carefully described. The measured TJ angles (97°, 117°, 95°, 117°, 99° and 130° ± 2°) depart from the characteristic angle (109.47°) of a tetrahedron whereas the measured GB angles (101°, 119°, 140°; 125°, 127°, 108°; 133°, 109°, 119°; 129°, 99° and 132° ± 2°) depart from the angular argument (120°) of a 3‐fold symmetry rotation indicating that, in the close neighbourhood of the QN, the studied arrangement of crystal defects is structurally unstable. Such an instability is associated with an observed mismatch in orientation (by angles of 20°, 15°, 33° and 30° ± 2°) between the TJs and some <111> zone axis matrix lattice crystallographic directions ([], [11], [11] and [11]), respectively). Local variations in anionic composition, existing within the solid solution matrix, are discussed to be responsible for this mismatching and, therefore, for the observed structural instability.     

Measurement of spherical aberration,beam tilt and image rotation in tem with a focussed probe

When a crystalline specimen in a transmission microscope is illuminated by a small focussed probe parallel to a zone axis, electrons diffracted at large angles by planes in higher order Laue zones (HOLZ) are imaged as a circle surrounding the direct beam. The diameter of this HOLZ image circle is directly related to the spherical aberration coefficient C_s of the objective lens. For the Philips EM430 at voltages between 50 and 300 kV, the 〈111〉 zone axis in silicon was used to measure an averaged C_s of 2.12 ± 0.04 mm. A displacement of the HOLZ image circle relative to the central probe image is attributed to a small tilt of the beam axis induced by lens interactions when switching between image and diffraction modes. This tilt could affect the quality of lattice images, where we require that both the beam and zone axes should be parallel with the optic axis. Even in an aberration-free lens, multiple diffracted images are observed when the probe is focussed and imaged in a plane below the specimen. This effect is proposed as a convenient method for measuring the direction and sign of g in two-beam defect analysis.     

Influence of triangular wavy baffles on heat and fluid flow characteristics in a channel

Laminar periodic flow and heat transfer in a three-dimensional channel with triangular wavy baffles (TWBs) have been numerically investigated. The baffles with three different angles of attack: 30°, 45° and 60° have been considered for Reynolds numbers ranging from 100 to 1000. For a better understanding in the heat transfer mechanisms, the pressure contour, secondary flow pattern, streamlines of impinging flow, wall streamline and iso-surface are also reported. Apparently, each wavy baffle generates two counter-rotating vortices. The 30° and 45° baffles generate vortices with comparable intensities which are considerably higher than that caused by 60° baffles. At similar conditions, the 30° and 45° baffles give comparable Nu/Nu₀ values which are considerably higher than that provided by the 60° baffles, but the 30° baffles cause lower f/f ₀ than the 45° and 60° baffles. For the range determined, the maximum thermal performances achieved by using baffles with the attack angles of 30°, 45° and 60° are 2.3, 2.2, and 1.88, respectively.     

Electrochemical behaviour of stainless steel 304 alloy in erosion–corrosion conditions and synergism effect

Abstract

A study has been made of the erosion–corrosion behaviour of stainless steel (SS) 304 in tap water in the presence and the absence of solid particles. Water at ambient temperature impinged in various angles (15–90°) on specimen surfaces at different velocities (7·85–14 m s^–1) and sand concentrations (0·43–2%). In this research, potentiodynamic, electrochemical impedance spectroscopy and weight loss measurements were used to study the damage mechanism and to estimate corrosion rate. The SEM micrographs and optical microscopy images were used to study the corrosion morphology. Under test conditions, protective passive film and non-protective film formations formed on SS 304 surface. It was found that maximum corrosion–erosion rate happened at the impact angles between 60 and 75°. The synergism effect was positive in all conditions and it was greater for the lower angles, the higher velocities and the higher solid contents.     

Solid particle erosion of mullite

The solid particle erosion of mullite (3Al₂O₃·2SiO₂ plus approximately 12% glass phase) was investigated using angular A1₂O₃ particles whose mean diameters D were varied between 23 and 270 μm. A range of impact angles α between 15° and 90° was used and the impact velocity V was varied from 60 to 100 m s^?1. The results of these experiments are in agreement with the general predictions of the two models developed to describe erosion in brittle materials on the basis of the formation of lateral cracks. The velocity exponent of the steady state erosion rate ΔW is between 2.2 and 2.8, being larger for smaller particles. For normal incidence, $\text{ΔW ∝ D}{}^{\mathrm{<mtext>2</mtext><mtext>3</mtext>}}$ in accord with both theories. For α > 15° only the normal component of velocity need be considered, but for smaller α there is evidence of plasticity both in the α dependence of ΔW and as observed using scanning electron microscopy.     

Investigation of turbulent spray disintegration characteristics depending on the nozzle configuration

The experimental measurements were carried out to examine turbulent disintegration characteristics ejecting from a counter-flowing internal mixing pneumatic nozzle under variable conditions of swirl angles and air pressures. The air injection pressure was varied from 60 kPa to 180 kPa and four counter-flowing internal mixing nozzles with axi-symmetric tangential-drilled holes at swirl angle of 15°, 30°, 45°, and 60° to the central axis have been specially designed. The experimental results were quantitatively analyzed, focusing mainly on the comparison of turbulent atomization characteristics issuing from an internal mixing swirl nozzle. To illustrate the swirl phenomena, the distributions of mean velocities, turbulence intensities, volume flux, and SMD (Sauter Mean Diameter, or D₃₂) were comparatively analyzed.     

Low‐temperature‐SEM study of dihedral angles in the ice‐I/sulfuric acid partially molten system

The transport and mechanical properties of partially molten materials are influenced by the wetting behaviour of the melt with respect to the crystalline solid. The equilibrium microstructure of an ice + melt system was examined using low‐temperature scanning electron microscopy. The samples were prepared by spraying a liquid solution of H₂O‐H₂SO₄ into liquid nitrogen and packing the frozen particulates into aluminium capsules. Samples were then sintered at –35 °C or –55 °C (above the eutectic temperature, T_E=–62 °C) for various durations and were quenched in liquid nitrogen to capture the equilibrium microstructure. This paper reports the first quantitative measurements of dihedral angle in this system. The measured median dihedral angle between the solid and vitrified melt is approximately 26 ± 2° at –35 °C and increases slightly as temperature decreases and approaches the solidus (32 ± 3° at –55 °C).     

Experimental investigation of mixing-enhanced swirl flows

The experimental objective was to compare disintegration characteristics from the internal mixing pneumatic nozzles under the different operating conditions in terms of swirl angles. For this investigation, supplied air pressures and nozzle configuration ratios were fixed. This experimental comparison is of fundamental importance to the understanding and modeling of turbulent atomization because the axisymmetric swirling flows involve relatively complex interactions. For the measurement, four internal swirl mixing nozzles with axisymmetric holes at swirl angles of 15°, 30°, 45°, and 60° to the central axis were employed, which is responsible for the enhancement of mixing in pneumatic jets. To illustrate the swirl phenomena quantitatively, the distributions of mean velocities, turbulence intensities, and SMD (Sauter mean diameter, or D₃₂) variations with different configuration ratio were comparatively analyzed. It indicated that the atomization characteristics are performed well in the case of 30° of swirl angle, and that turbulence intensities are gradually degenerated with the increase of radial distances, showing a slight increment of SMD at downstream region. In particular, measurements showed that nozzle configuration is one of the significant geometrical parameters affecting the spray trajectories. This paper was recommended for publication in revised form by Associate Editor Jun Sang Park     

Structural inspection and troubleshooting analysis of a lab-scale distillation column using gamma scanning technique in comparison with Monte Carlo simulations

In the present study, structural inspection and troubleshooting analysis of a lab-scale distillation column has been performed using gamma scanning technique and Monte Carlo simulations. MCNP4C Monte Carlo code has been used for simulations of the column and calculation of the computational density profile. The tested column is a one-pass tray type with 51 cm diameter. A Cs-137 sealed source and a 1 × 1 inch NaI (Tl) detector has been used for this gamma scanning process. According to the results, both experimental and simulation results showed the specification of trays and another section of the column accurately. Also, in addition to the flooding and damaged tray in the column, defects such as foaming with the density of 0.17 g/cm³ can be distinguished using this technique. Based on the results, using photopeak count approach the differences in the material attenuations can be better distinguished. The effectiveness of this approach in determination of malfunctions increases with the density of the material between the source and the detector. Analyzing the experimental and simulation results are indicative of the fact that the procedures and methods used in this work are quite suitable for improving the accuracy of the troubleshooting analysis based on gamma scanning technique.