Friction Distribution Research Articles

Influence of Cavitation and Shaft Deformation in the Analysis of Lubrication of the Stern Bearing

The cavitation phenomenon and shaft deformation have a significant impact on the tribological performance of the journal bearing. A mixed lubrication model is developed that takes into account surface roughness and asperity contact, as well as the effects of cavitation and deflection. The fluid–solid coupling effect in bearing deformation, asperity contact, and film pressure are investigated. The effect of boundary conditions on the lubrication regimes is discussed. The results of simulations with and without cavitation are compared under steady-state conditions. The results show that when cavitation is considered by the mixed lubrication model under a given load, the eccentricity is reduced, and the maximum oil film pressure is also reduced. The speed range of the bearing simulated with the mixed lubrication model increases after considering deflection deformation. The mixed lubrication model proposed in this paper is able to provide accurate results of pressure distribution and coefficient of friction and can be applied in the design and analysis of journal bearings.

Investigating elastic recovery of monocrystalline silicon during plunging experiments with chamfered diamond tools

This study investigates the relationship between elastic recovery and friction during ductile mode machining of monocrystalline silicon. Plunging experiments were performed on an ultra-precision CNC machining center as the silicon work material was rotated. This approach allowed for investigating the combined effect of varying crystal directions and increasing depth on elastic recovery, pressures, and friction. A diamond cutting tool with a chamfered edge that maintains a constant negative rake along the cutting edge was used in plunging tests. Considering the importance of flank face contact area on friction and pressure distributions at the cutting zone, a non-linear expression is proposed to model the elastic recovery ratio as a function of groove depth. It is then employed in an analytical machining model to calculate the variation of pressure and coefficient of friction. The influences of pressure variation and changes in pressure direction as the machining mode transitions from ductile to brittle are investigated based on resolved stresses on the identified active slip plane. The methodology proposed in this study can be extended to study other monocrystalline materials, and the findings can be utilized in the process planning of advanced optics manufacturing.

Effects of intergranular friction and grain size distributions on the initial void ratio of granular sample

This paper investigates the influence of intergranular friction and grain size distributions on the initial void ratio of a granular sample subjected to isotropic compression loading. In the field of geomechanics, besides the loading path and evolution of microscopic properties, the initial void ratio is a crucial and key factor that governs the mechanical behavior of geomaterials. By using Discrete Element Model (DEM) performed on an idealized 2D assembly of disks, this study demonstrates that the initial void ratio can be affected by several parameters during isotropic compression stage. By varying a wide range of intergranular coefficients of friction and grain size distributions, our numerical results suggest that increasing the intergranular coefficient of friction during the isotropic compression phase leads to looser samples. Furthermore, when the diversity of grain sizes is rich, smaller grains can move and occupy voids, thereby increasing the density of the granular sample. A power-lawrelationship is then proposed that connects the minimum void ratio and the diversity degree of the sample.

Thin film flow of blood-based hybrid nanoparticles subject to slip effects: A stability assessment

The objective of this research is to predict the thermal observations for hybrid nanofluid conveying the thin film flow influenced by the suction phenomenon and slip consequences. The copper and aluminum nanoparticles are utilized to explore the hybrid nanofluid features. In addition, a uniform magnetic field perpendicular to the motion of the nanoliquid has been generated. By utilizing appropriate dimensionless quantities, partial differential equations (PDEs) are transformed into nonlinear ordinary differential equations (ODEs). The controlling method for boundary value problems (BVP4C) has been applied against the thermal profile. The coating film’s thickness has been kept fixed. The skin friction and Nusselt number distribution are calculated for blood over the shrinking sheet in the attendance of the radiation and velocity slip parameters. The effects of various variables and spray rate through coating are clearly represented. The numerical calculation is computed for assessing the wall shear force. It is observed that a dual branch has been discovered. In addition, a stability analysis has been conducted and the upper branch has been determined to be the stable branch.

Bearing behavior of rock socketed pile in limestone stratum embedded with a karst cavity beneath pile tip

This paper investigates the bearing behavior of axially loaded rock socketed piles in limestone stratum embedded with a karst cavity beneath the pile. The pile foundation supporting a cross-river bridge located in a karst area in China is considered. Based on this project, three-dimensional finite element analyses are performed to capture the effects of pile length, pile diameter, limestone cohesion, and cavity roof thickness. Their impact on the bearing characteristics of the pile is comprehensively outlined through analysis of load-settlement curves, variations in pile bearing capacity, distributions of axial pile force and pile side friction, as well as contours of vertical ground and cavity roof displacement. It is found that the load-settlement curves exhibit the saltation type, based on which the pile-bearing capacity can be conveniently obtained. The pile bearing capacity increases nonlinearly with increasing the pile length, whereas almost linearly with an increase in the pile diameter, limestone cohesion, and cavity roof thickness. For the considered conditions, larger magnitudes of vertical ground displacements occur primarily surrounding the pile side in the pebble layer and at the pile bottom. This is attributed to the weakening effect of the karst cavity on the bearing capacity of the cavity roof. The achievements from this study are beneficial for the design optimization of rock socketed piles in karst areas.

Boxes-Based Representation and Data Sharing of Road Surface Friction for CAVs

Vehicles can easily lose control unexpectedly when encountering unforeseen hazardous road friction conditions. With automation and connectivity increasingly available to assist drivers, vehicle performance can significantly benefit from a road friction preview map, particularly to identify where and how friction ahead of a vehicle may be suddenly decreasing. Although many techniques enable the vehicle to measure the local friction as driving upon a surface, these encounters limit the ability of a vehicle to slow down before a low-friction surface is already encountered. Using the connectivity of connected and autonomous vehicles (CAVs), a global road friction map can be created by aggregating information from vehicles. A challenge in the creation of these global friction maps is the very large quantity of data involved, and that the measurements populating the map are generated by vehicle trajectories that do not uniformly cover the grid. This paper presents a road friction map generation strategy that aggregates the measured road-tire friction coefficients along the individual trajectories of CAVs into a road surface grid. In addition, through clustering the friction grids further, an insight of this work is that the friction map can be represented compactly by rectangular boxes defined by a pair of corner coordinates in space, a friction value, and a confidence interval within the box. To demonstrate the method, a simulation is presented that integrates traffic simulations, vehicle dynamics and on-vehicle friction estimators, and a highway road surface, where friction is changing in space, particularly over a bridge segment. The experimental results indicate that the road friction distribution can be measured effectively by collecting and aggregating the friction data from CAVs.

Heat-Transfer Gauge Arrays for Identifying Spot Initiation in Hypersonic Transitional Boundary Layers

The initiation and growth of turbulent spots in transitional hypersonic boundary layers can influence the transition length and the distribution of heat transfer and skin friction through the transitional region. There is debate in the literature about whether spots initiate in a small band at the start of transition or throughout the transitional region. This paper presents a new design of arrays of thin-film heat transfer specifically designed to detect whether spots initiate in a small band. The gauges were arranged in two spanwise rows at different streamwise locations and were tested on a 7° blunt cone in the T4 Stalker Tube. It is shown that such instrumentation is capable of identifying that some spots initiate between the rows when other spots have already formed upstream of the first row. This demonstrates that the breakdown of laminar boundary layers is not concentrated in a region of small streamwise extent in the current hypersonic flows.

A numerical study of fatigue life in high-speed angular contact ball bearings with thermal and centrifugal expansion

PurposeFix-position preloading, centrifugal force and higher temperatures cause the bearing units in angular contact ball bearings to expand, changing the contact load and affecting bearing life. This study aims to examine the effect of thermal and centrifugal expansion on the fatigue life of fix-position preloaded angular contact ball bearings in high-speed operating conditions.Design/methodology/approachThe contact loads on the inner and outer bearing rings were resolved according to the thermal and centrifugal expansion factors in the quasi-static position preloading model. The pressure and frictional stress distribution were used to calculate the subsurface stress in the contact area, while the Zaretsky model was used to determine the relative fatigue life of the inner and outer bearing rings.FindingsUnder fix-position bearing preloading, thermal and centrifugal expansion significantly affected the contact load and relative fatigue life. At the same axial preload, the inner ring contact load was higher than the outer ring contact load, with a maximum difference of 132.3%. The decrease in the inner ring relative life exceeded the outer ring contact load, with a maximum difference of 7.5%, compared to the absence of thermal and centrifugal expansion.Originality/valueThis study revealed the influence of thermal and centrifugal expansion on the fatigue life of angular contact ball bearings in high-speed service conditions.Peer reviewThe peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-03-2023-0065/

Research on the wear characteristics of magnetorheological fluid in sealing interface considering the interaction between surface roughness and magnetic particles

In this paper, the influence of magnetorheological fluid (MRF) on the wear mechanism of sealing pairs under different surface roughness is studied from the perspective of theoretical analysis and experimental verification. Simulation analysis shows that the coupling of roughness and microparticles changes contact pressure and frictional stress distribution on O-ring acted by asperities. Combined with wear morphologies, it is further proved that roughness affects the movement pattern of particles in the sealing gap, thereby determining the tribodynamic behavior of MRF. Specifically, the roughest sample shows low friction coefficient and best wear resistance, while the smoothest sample exhibits worse tribological performance. The above analysis is the reason for the sealing wear under MRF is completely opposite to that of base oil.

Identification Method for Instantaneous Friction and Wear Energy Density Variation of High-Feed Milling Tool Flank

Instantaneous friction and wear energy density are important indicators of the friction and wear state of the tooth flank of the milling cutter. Existing methods for identifying the friction and wear on the tooth flank of milling cutters mainly focus on the overall level of friction energy consumption and the maximum width of the accumulated wear on the teeth flanks, ignoring the unevenness and variability of the friction energy consumption and wear volume distribution of the tool flank, and the dynamic relationship between the instantaneous friction and wear on each tooth flank of the milling cutter is to be revealed. Transient cutting position of a high feed milling cutter tooth under milling vibration, and the use of the micro-element method to construct a model for solving the transient wear volume on the tool flank. A method of transient friction energy consumption on the cutter flank was proposed. The variation property of the instantaneous friction and wear energy density on the flank was exposed. The identification method of the variation property of the energy density was proposed according to different analysis results of the distribution of friction and wear energy density and verified by experiments. The outcomes indicated the maximum and mean of the energy density at different positions on the flank had a high similarity with the wear depth distribution on the flank. Using this method, the influence property of the friction and wear state and the cutting parameters under the milling vibration of the milling cutter tooth can be identified.

Effects of temperature on the deformation of 6H–SiC during nanoscratching

With the aid of large-scale molecular dynamics simulations, this paper comprehensively investigated the effects of processing temperature on the deformation of single crystal 6H–SiC during nanoscratching. The effect was investigated across a wide range of temperature variations, from 1 K to 900 K. It was found that with increasing the processing temperature, the material removal mechanism of 6H–SiC experience a transition from intermittent cleavage to continuous plastic deformation. The deformation mechanism of 6H–SiC is achieved by the combination of surface amorphization and subsurface dislocations that reside mainly in the cubic diamond structural layer. The processing temperature significantly affects the dislocation distribution, groove morphology, scratching forces and coefficient of friction. The anisotropic effect on chip formation decreases with increasing the processing temperature. By evaluating surface roughness and the maximum subsurface damage depth, the investigation concludes that the scratched surface/subsurface quality of 6H–SiC deteriorates with increasing processing temperature.

Cattaneo-Christov double diffusion based heat transport analysis for nanofluid flows induced by a moving plate

Hybrid nanofluids have gained much attention due to their better stability, enhanced thermal conductivity, and physical strength. This manuscript investigates nanofluid flow, induced due to an infinite plate, which is moving (at a constant velocity) toward/receding from normal stagnation point flow. The surface of the plate is suspended and immersed with water as a base fluid and nanoparticles, namely Copper and Alumina. The flow is governed by Reynolds number (Re), which is proportional to the constant velocity of the moving plate and is an exact reduction of the Navier–Stokes equations. Moreover, Hiemenz’s planar and Homann’s axisymmetric flows normal to the stagnation point are considered. Heat transport analysis is carried out by using Cattaneo–Christov theory with Ohmic heating and heat source/sink effects. The governing equations are solved by bvp4c in MATLAB. The behavior of skin friction, flow, and energy distribution is perceived by variation of pertinent parameters. The numerical and asymptotic solutions are computed for the wall shear stress parameter. It is seen that the numerical solution matches its asymptotic behaviors over an intermediate range of small and large valued Reynolds number. The asymptotic values (small-Re) of wall stress reduces for plate advancing toward the stagnation-point flow and receding from the stagnation-point flow for Hiemenz and Homann flow. The increment in magnetic parameter reduced the fluid flow by generating a resistive force against it; however, the energy of the system is enhanced because of it. The augmentation of nanofluid volume fraction initiates the random motion among the nanoparticles which raises the temperature field. Thermal relaxation time parameter causes the particles to require supplementary time for the conduction of heat toward the adjacent particles, which declines the thermal transport. In general, the thermal transport is enhanced for the hybrid nanofluids rather than mono nanofluids.

Fluorescent oil-film applied to measure skin friction of flat plate with leading edge separation bubble in low Reynolds number

Under low Reynolds number conditions, the airfoil is prone to a laminar separation bubble (LSB), which causes problems such as lift drop and drag increase. In this work, the fluorescent oil film was applied to study the leading edge LSB from the perspective of skin friction. The experimental study is carried out on a flat plate with the leading edge LSB under the Reynolds number of [Formula: see text] (the characteristic length of the plate chord). The camera captures the leading edge LSB that is formed by airflow separation and reattachment, and the flow in the bubble is opposite to the free flow. The position of separation and reattachment is determined by the distribution of skin friction, which is consistent with the visual image of the oil film. Applying the Poincare–Bendixson (P-B) index formula to test the topology of the separation bubble skin friction, the quantitative relations between the critical points and the boundary switching points in the closed region of several permeable boundary all confirm this topology law. The results show that the fluorescent oil film can quantitatively map the flow structure of the LSB, and further verify the advantage of this method in the visual measurement of the complex flow structure.

Fault Diagnosis of Lubrication Decay in Reaction Wheels Using Temperature Estimation and Forecasting via Enhanced Adaptive Particle Filter.

Reaction wheels (RW), the most common attitude control systems in satellites, are highly prone to failure. A satellite needs to be oriented in a particular direction to maneuver and accomplish its mission goals; losing the reaction wheel can lead to a complete or partial mission failure. Therefore, estimating the remaining useful life (RUL) over long and short spans can be extremely valuable. The short-period prediction allows the satellite's operator to manage and prioritize mission tasks based on the RUL and increases the chances of a total mission failure becoming a partial one. Studies show that lack of proper bearing lubrication and uneven frictional torque distribution, which lead to variation in motor torque, are the leading causes of failure in RWs. Hence, this study aims to develop a three-step prognostic method for long-term RUL estimation of RWs based on the remaining lubricant for the bearing unit and a potential fault in the supplementary lubrication system. In the first step of this method, the temperature of the lubricants is estimated as the non-measurable state of the system using a proposed adjusted particle filter (APF) with angular velocity and motor current of RW as the available measurements. In the second step, the estimated lubricant's temperature and amount of injected lubrication in the bearing, along with the lubrication degradation model, are fed to a two-step particle filter (PF) for online model parameter estimation. In the last step, the performance of the proposed prognostics method is evaluated by predicting the RW's RUL under two fault scenarios, including excessive loss of lubrication and insufficient injection of lubrication. The results show promising performance for the proposed scheme, with accuracy in estimation of the degradation model's parameters around 2-3% of root mean squared percentage error (RMSPE) and prediction of RUL around 0.1-4% error.

Sensitivity analysis of nonlinear convective heat transport of a hybrid nanoliquid sandwiched by micropolar liquid using RSM

Petroleum and polymer industries utilize a multilayer flow model for efficient heat transfer. In such applications, the linear Boussinesq approximation is not recommended as the devices used in such experiments would work at moderate or extremely high temperatures. Therefore, the flow and heat transfer in a multilayer vertical channel with a magnetic field and the nonlinear (quadratic) Boussinesq approximation are investigated, with the central region filled with a hybrid nanoliquid and the outer regions filled with an oil-based micropolar liquid. The effects of Joule heating and viscous dissipation are taken into account. The effective viscosity and thermal conductivity are modeled using the experimental data based Esfe model. The modeled equations are coupled and nonlinear, they are solved using the Differential Transform Method (DTM). Results are analyzed for various values of the material parameter, quadratic convection parameter, Brinkman number, mixed convection parameter, Hartmann number, nanoparticle volume fraction (NVF) on Nusselt number, skin friction, velocity, microrotation velocity and temperature distributions. Additionally, multi-objective optimization of Nusselt number and friction factor is performed for three different levels of the quadratic convection parameter , material parameter and the NVF using the Response Surface Methodology (RSM). The material parameter diminishes the velocity whereas enhances the microrotation velocity. Also, the quadratic convection parameter increases the flow field. Sensitivity computations reveal that the Nusselt number is more sensitive to material parameter and NVF whereas the skin friction coefficient is more sensitive to quadratic convection parameter.

Numerical study of the effect of sidewalls on shock train behaviour

Strongly coupled sequences of shock waves, known as shock trains, are present in high-speed propulsion systems, where the presence of sidewalls substantially modifies the boundary layer thickness, skin friction and streamwise pressure distribution. In the present contribution, scale-resolved numerical simulations are performed on supersonic channel (infinite span) and square duct flows to evaluate the effect of sidewall confinement with and without shock trains. Comparable secondary flow vortices are observed in the duct case with and without the presence of the shock train. The absence of a separation region at the leading shock of the duct case results in lower flow deflection compared with the channel case, leading to a reduced shock strength. The principal effect of the sidewalls is to cause a shock train that is approximately twice as long and composed of a larger number of shocks. A modification of previous models, based on a momentum thickness-based blockage parameter, leads to an improved collapse of the channel and duct cases.

Prediction method of soil horizontal displacement caused by non-uniform distribution of disturbance force in shield construction

Based on the Mindlin solution, this paper considers the influence of factors such as the non-uniform distribution of additional thrust of the cutter head influenced by lateral earth pressure in shield excavation, the non-uniform distribution of friction of shield shell influenced by soil softening and slurry spreading, and the non-uniform distribution of grouting pressure influenced by slurry spreading on the horizontal displacement of soil. The existing prediction formula is revised and verified by engineering examples. It is found that: affected by the shield construction disturbance force, the horizontal displacement behind the excavation surface is larger than that in front of the excavation surface, and the peak value of the horizontal displacement appears around the tunnel axis; through the verification of engineering case, when calculating the horizontal displacement in front of the excavation surface, the calculation results of both the modified formula and the original formula are in good agreement with the measured values, which can reflect the change trend of the measured horizontal displacement; when calculating the horizontal displacement behind the excavation surface, the calculation result of the existing formula has a great error due to the assumption of uniform distribution of disturbance force, which is different from the law of the measured result; the calculation result of the modified prediction formula is obviously in better agreement with the measured deformation value, and the error is smaller, which is more in line with the engineering reality.

On-site and numerical analysis of bidirectional static load testing (BDSLT) on bored pile

High-rise buildings' structural loads are supported by reinforced concrete bored piles. Axial load testing is frequently regarded as the most reliable method for assessing static capacity in actual foundation engineering. The self-reaction test method known as the Bi-Directional Static Load Test (BDSLT or O-cell test) plays an important part in determining the settlement and shaft friction distribution along the pile shaft. The current study sought to ascertain the load carrying capacity of a 1000 mm diameter, 18 m deep bored strain gauge instrumented pile in Dubai, United Arab Emirates, that was tested up to 17875kN using the BDSLT method. To better understand the bored pile's geotechnical behavior, the onsite test results were compared with a numerical PLAXIS 3D analysis. The outcomes from the two studies were quite consistent, indicating that pile-rock behavior had been properly represented.

Machine Learning based reduced models for the aerothermodynamic and aerodynamic wall quantities in hypersonic rarefied conditions

Since their development at the end of the 50s, panel methods were widely used for the fast simulation of aerospace objects reentry. Although improvements were proposed for the continuum regime formulations, the bridging functions usually employed in the transitional regime did not go through major changes since then. With the current interest in designing Very Low Earth Orbit satellites and more efficient reentry vehicles, a greater level of preciseness is now required for the fast computation of the aerodynamic and aerothermodynamic wall quantities in rarefied regime. In this context, this paper presents a new approach to build Machine Learning based surrogates going from the choice of the design variables and the Design of Experiments, to the models training and evaluation. Hence, kriging and Artificial Neural Networks are respectively trained to predict the pressure and heat flux stagnation coefficients, and the pressure, friction and heat flux coefficient distributions in the rarefied portion of any aerodynamic shape’s reentry.

Field tests of grouted ground anchors in the sandy soil of Najaf, Iraq

Abstract This article presents test results documentation for four grouted ground anchors embedded in sandy soil. Three anchors were trial, while one was a working anchor. One trial anchor is instrumented with eight resistance-type strain gauges glued on the corrugated pipe and embedded within the grouted body. An acceptance test was made for all anchors to determine the working load. Acceptance criteria suggested by the Post-Tensioning Institute were applied, and the working anchor did not pass the creep criterion, so it was taken out of service. The strain measurements indicated that the compression stresses were generated along the free length, while the tension stresses were generated along the bonded length. The transition point, which is the point with zero axial stress within the grouted body, was located at a distance of 10–12% of the bonded length, measured from the proximal end of the bonded length. The skin friction distribution along the grouted body was nonuniform, and it had a peak at the transition point. The maximum measured value of the skin friction is almost compatible with the estimated one by Fujita’s formula. The skin friction developed along the free length indicates a significant contribution of the free length to the pullout capacity.