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This study investigated the influence of press-fitting on the stress concentration and fatigue life of axles. Models of finite element analysis (FEA) with and without the press-fitting effect were developed using Abaqus software. These models were used to analyze the axle strength and profile the stress histories under various loads and running conditions, such as bending load, wheel-rail contact force, lateral force, and press-fitting force. Their combined loads were responsible for the axle fracture. Also, the prediction of fatigue life was extended to a three-dimensional stress state under fully reversed cyclic loading and variable overload spectra using commercial Fe-safe software with a strain-based Brown-Miller Morrow fatigue algorithm. With the press-fitting effect, the maximum von Mises stress at the groove notch transition zone of the axle was 6% higher than without the press-fitting effect. Press-fitting reduced the fatigue life of an axle by 37% compared to the ones without press-fitting, and the most damage happened at the same node as the maximum von Mises stress. [ABSTRACT FROM AUTHOR]

This paper investigates the coefficient of friction and wear rate of crude palm oil (CPO) and palm-mineral oil blend as lubricant in roller element bearing application at the room temperature. Contact between a rolling element and raceway in bearing is simply modeled as a pin-on-disc contact. Crude palm-based vegetable oil and its blend with a commercial mineral oil at a ratio of 1:1 by volume were used as lubricant in pin-on-disc contact tribometer. The commercial mineral oil was also evaluated for comparison purpose. Influence of palm-mineral oil composition is highlighted by comparing coefficient of friction and wear rates. The results exhibited that the blend of mineral oil and CPO has lower coefficient of friction and wear rate compared to the pure mineral oil or CPO 100%. [ABSTRACT FROM AUTHOR]

In this paper, the equations of contact curves of rolls of rolls of roll machines are developed, where the rolls have coatings with different stiffness. The influence of the deformation and geometrical parameters of the roll pair and the material on the shape of the roll contact line is analyzed. It was revealed that the roll contact line are described by equations of the same type in cases where the deformation of the material being processed occurs along the vertical and along the radii of the rolls. [ABSTRACT FROM AUTHOR]

Rolling element bearings are widely used in machinery and heavy industries. Friction between rolling elements may cause surface damage and subsequently cause component and machine failure. Lubricant is used in the rolling contact to reduce friction and wear between the components by the formation of a lubricant film between the components. However, the use of mineral grease can be detrimental to the environment. In this work, palm grease is developed and used as a rolling contact lubricant. The experiment was carried out using a roller test rig to represent the contact in a roller bearing. The surface degradation of the roller bearing lubricated with palm oil grease with and without additives are investigated. Surface roughness measurement is performed using an Infinite Focus Microscope to characterize the surface degradation and wear. Surface roughness parameters include surface roughness (Ra), surface skewness (Rsk) and surface kurtosis (Rku) of the roller are investigated. The findings show that the roller surface lubricated with palm grease containing nanoparticles has less surface damage compared to pure palm grease. [ABSTRACT FROM AUTHOR]

This paper discusses the railway curve squeal and the relationship with the creep curve. The wear of the rail and wheel are closely related with the level of creep and friction level. The wear profiles are discussed based on the literature and the ensuing wear map from which the effect of lubricant can be seen to drastically reduce the wear by a factor of 3. Previous data of palm oil grease were derived from the four ball tester which can be difficult to apply to railway squeal and wear. The development of palm oil methyl esthers as grease for curve lubricant and also for friction modifier require the evaluation of testing procedure and rig. The challenges associated with the tools and the interpretation of the results from the twin-disc machine are discussed. High correlation of the twin-disc experimental with rail track measurement indicated that the twin-disc machine is indispensable in the study of the effectiveness of palm oil grease as friction modifier and curve lubricants. Further work of development of palm oil for railway application would require the use of the twin-disc machine. [ABSTRACT FROM AUTHOR]

The inherent result of cooperation of elements in a wheel-rail set is the existence of friction between a wheel flange and a lateral surface of a rail head, happening mainly on track curves. Due to the occurrence of large lateral forces when vehicle runs over track curves, it is possible to measure the magnitude of the forces at the wheel-rail contact for various vehicle's bogie structures. The new system described in this paper is based on non-direct measuring lateral forces in bogie elements. As a part of project development there where numerical calculations and experiments on a vehicle carried out. As a main issue, there were investigated stress signals from extensometers mounted on guiding elements of wheelsets. The article also presents a method of further processing of the obtained analog signal in order to eliminate the disturbances present from the useful signal. The measurement method presented in the article was used in the tests of rail vehicles. [ABSTRACT FROM AUTHOR]

An important indicator of a multi-unit in-pipe robot capability to move through pipelines is the value of the minimum passable radius of the curved sections of a pipeline. At the design stage, this indicator cannot be found without mathematical simulation of the robot spatial movement and interaction of its running gear with the pipeline. The article describes the solution of this problem for a two-unit in-pipe wheeled robot by mathematical simulation of the robot motion in the pipeline in the Universal Mechanism multibody simulation program with the use of the standard elements of the mechanical system modeling and a special-purpose wheel – pipeline contact model developed by the authors. [ABSTRACT FROM AUTHOR]

Bearing plays a vital role in every rolling part of the mechanical machine. A sudden failure of it results in machine breakdown and cost huge production loss as well as a delayed production schedule. So, for every mechanical machine, Predicting the bearing's remaining useful life with precision is essential. There are several methods being investigated right now for calculating the bearing's Remaining serviceable Life, However, none of them is reliable since data noise impairs the forecast of the Remaining Serviceable Life. Bearings failure occurs because of several failure modes, each of which gives a different failure behavior pattern. This research paper focuses on the experimental platform for testing bearing at different speeds and load conditions. The experimental setup gives accurate vibration signal data processed through Arduino and A rolling contact bearing's remaining serviceable life is forecasted mathematically using Matlab. The objective of work is to build theoretical model for the bearing fault vibration signature to identify localized defects on the bearing and validate with experimental results [1]. [ABSTRACT FROM AUTHOR]

Recently, the usage of textured surfaces, as well as the slip boundary induced by hydrophobic coating for increasing the performance of tribopairs, has received a lot of attention. The purpose of this research is to investigate the differences in bearing characteristic performance between a step texture and a slip boundary. The two-dimensional slider bearing is employed in this study by adjusting the step or slip length. In this study, the simulations are conducted by solving the Navier-Stokes equation based on the finite volume method. The numerical result indicates that step bearing outperforms hydrophobic bearing in terms of load-bearing capacity irrespective of the step length ratio. However, for friction characteristics, the hydrophobic bearing is superior for all values of slip length ratio. Another interesting finding is that for each pattern, in terms of the load support, the optimal step or slip length ratio is highlighted. [ABSTRACT FROM AUTHOR]

Main objective of this research work is to perform fracture analysis of railway rail track. For this analysis finite element analysis has been opted as an analysis tool. A three-dimensional model of railway track and wheel contact was generated using solidworks. For stress and deformation analysis load of (20-100) KN was applied. Von mises stress distribution was evaluated using minimum to maximum load application. Three different types of loading was applied i.e. rolling contact, braking and cornering. FEA analysis results shows that braking load is less responsible for fracture in comparison to rolling and cornering loads. [ABSTRACT FROM AUTHOR]

Theoretical description of the roller pressing of fibrous materials is one of the most difficult problems in modern mechanics. The difficulty lies in the need to jointly solve two problems: the first problem is a contact interaction in two-roll modules (a contact problem); the second problem is moisture filtration in a deformable inhomogeneous porous medium (a hydraulic problem). The article deals with the main hydraulic problems of the theory of roller pressing of leather. Mathematical models were developed for the patterns of changes in the hydraulic pressure in the zone of pressing leather and in the residual moisture of the roller pressing of leather. It was found that the rate of moisture filtration along the abscissa at the boundaries of the compression (recovery) zone is zero, and takes negative (positive) values inside the zone. It was revealed that the hydraulic pressure changes from zero at the beginning and end of the roll contact zone to a maximum at a point lying on the line of centers. [ABSTRACT FROM AUTHOR]

In the process of roller pressing of a leather semi-finished product, two phenomena occur simultaneously - contact interaction and moisture filtration. This, in turn, requires the joint solution of two types of problems - contact problems and hydraulic problems. The main contact problem of the theory of roller pressing of wet materials is the mathematical modeling of the shape of the contact curves of the rollers and the regularities of the distribution of contact stresses along the contact curves of the rollers. The article deals with the basic contact problems of the theory of roller squeezing of leather. A formula was derived that describes the model of friction stresses. It was revealed that the shapes of the roll contact curves of the two-roll module do not depend on the change in the moisture content of hides in the contact zone of the rollers. It was established that the model of friction stresses in a two-roll module for pressing leather does not depend on the inclination of the material layer fed to the center line. [ABSTRACT FROM AUTHOR]

An algorithm for calculating the vertical vibrations of a two-support object moving along the rails of the rocket track is presented. Calculations of the stability of oscillations of a rocket train stage are presented. [ABSTRACT FROM AUTHOR]

A numerical analysis method was developed for a stress-strain state stock material at the elastic strain deformation zone during cold rolling. Considering the deformation of rolls, the stock material was divided into finite volumes, where the system of equations for relationships of stresses and deformations of the theory of elasticity and the equations of equilibrium were analytically solved. A size of the elastic and plastic sections and the contact stresses at their boundaries were determined. Was established that ultimate strain at the elastic zone of a strip recovery and contact stresses at the border between elastic and plastic zones at the exit from deformation zone increases at decreasing strip compression and increasing friction ratio. A boundary condition was found, in cases of exceeding that condition it comes to significantly increasing arc of contact length and rolling force. In a case when the elastic strip deformation does not reach this boundary condition, the elastic strip deformation does not impact significantly at the rolling force. According to the presented method considering an elastic strip deformation while s=0.05 lead to increasing arc of contact length and rolling force at 10–17%, at implementation in a practice rolling cases. An inaccuracy of using known methods was estimated. [ABSTRACT FROM AUTHOR]

A line for the production of hot-deformed pipes on a pipe-rolling plant 220 equipped with an automatic elongation mill is considered. In the maintenance the appearance of longitudinal end defects typical for thin-walled pipes was revealed. On the basis of a software package implemented with the use of FEM, a model of the deformation zone of a two-stage process of the lengthwise rolling of pipes on a short mandrel has been simulated. Analysis of the flow of the hollow bloom metal in this process makes it possible to establish the nature of the defect formation, as well as to calculate its influence on the power parameters of the process. The formation of a defect at the rear ends of the pipe is associated with the loss of stability of the hollow bloom section when the hollow bloom metal flows into the roll caliber outlets, which leads to an increase in the contact surface of the rolls with the workpiece and the mandrel with the workpiece, as well as to contact with the surfaces of the rolls that are not intended for direct interaction with heated metal. As a result, a technical solution has been proposed that allows restricting the loss of stability of the rear end of the pipe and eliminating a decrease in the loads on the working tool of the rolling stand, due to the degeneration of the rear end defects of the pipes. This solution is justified using FE modeling. [ABSTRACT FROM AUTHOR]

It is proposed applications of the theory of combined dry friction [1-10] in the problem of the ball rolling on boundaries of two identical frames. Father development of this model can be used in investigation of the dynamic of the a so-called "Butterfly" robot, consisting of two identical shaped plates rigidly placed parallel to each other on a small distance aimed at manipulating a ball that can freely roll on the plates' boundaries as on rails [11]. The friction force and torque are computed by the integration over the contact area so that the exact dynamically coupled integral model accounting the relationship of all the components of friction is obtained. This exact model is replaced by approximated analytical model [10] which is completely satisfy to all analytical properties of integral model as function kinematics parameters without increasing the number of coefficients. [ABSTRACT FROM AUTHOR]

The rolling bearing is one of the key components for the functioning of sophisticated machinery in the demanding industrial world today. For efficient and smooth operation, bearings need to sustain wear, fatigue, high loads, and sometimes, heat and harsh environments. Preceding failure analysis of the current work concluded that the recurring failure of the bearings under consideration is predominantly caused by the excessive wearing of the bearing track, and false brinelling due to harsh corrosive environment. This work, as a remedial measure, aims at enhancing the bearing life by suitably applying nitrocarburizing, a thermochemical heat treatment, to bearing parts. By heat treatment, nitrogen and carbon are diffused in hardened bearing races and rolling elements at a relatively lower temperature of 560-580 °C followed by controlled oxidation. Structural transformation during the process formed a compound layer at the sub-surface consisting of s−Fe2-3(N, C) and y'-Fe4(N, C) phases and a thin continuous layer of Fe3O4 on the compound layer as confirmed by X-Ray diffraction and microstructural analysis. Microhardness profile confirmed progressively declining hardness from the surface towards the core. Salt spray tests performed on the nitrocarburized parts indicated excellent corrosion-resistance properties. [ABSTRACT FROM AUTHOR]

The test stand for proper operation shall have a equipped of auxiliary systems. One of them is the track gauge adjustment system. The original gauge adjustment mechanism revealed shortcomings caused by the wear in operation. The new solution of track gauge setup on the test stand consists of hydraulic circuit design, construction, control and subsequent verification of reliability and proper operation. For proper operation and accurate results, the test bench was fitted with an apparatus for centering the rotating rail. The measuring apparatus shows what gauge is set on the rotating rails and in which position the individual rail are located. Measurements have been made to verify the functionality of the system and to help set the correct function of the hydraulic cylinders. By examining the transverse forces at unloaded rotating rails, the proper function of the hydraulic system has been verified. After load of the rotating rails with wheelset was monitored by the process of the guiding (transverse), longitudinal and wheeled (vertical) forces. [ABSTRACT FROM AUTHOR]

Advanced planetary roller screw mechanisms (PRSM) are divided into mechanisms with gaps and gapless devices, where gaps are compensated using various methods. Gapless mechanisms are superior in accuracy and rigidity compared to mechanisms with gaps, but inferior to them in load capacity and useful life, i.e. there appears a contradiction between accuracy and rigidity, on the one hand, and load capacity and useful life, on the other. The given article is aimed at overcoming this contradiction and proposes a new method for compensating gaps in a PRSM and a new design of gapless mechanism. This design consists of a power mechanism and a mechanism for converting rotational motion into translational motion. The most important component of the power mechanism is a split collet, which when interacting with the housing reduces the pilot hole diameter. The most significant component of the mechanism designed to convert rotational motion into translational motion is a solid nut manufactured in the form of a thin-walled cylindrical shell. When the split collet is compressed, the solid nut-shell is deformed in radial direction and compensates for gaps between all the threaded components. Two half nuts are used in the known designs of a gapless PRSM. It should be noted that in this case only a single half nut is exposed to the working axial force, and in the new design of a gapless PRSM that is the solid nut. Therefore, the new mechanism is provided with significantly greater load capacity and ensures longer useful life. [ABSTRACT FROM AUTHOR]

Creating of gradient structures with the grain size changing from microns to nano-scale through the thickness of processed metallic materials represents a new advanced strategy for producing a superior combination of high strength and good ductility. Predetermined strain gradient can be considered as a mechanism of creating of gradient structures. Strain gradient through sheet thickness can be achieved by special rolling techniques. Searching the process parameters, which provide predetermined strain gradient, is very important. This paper presents the distributions of the plastic strain through sheet thickness of low-, medium- and high- strength aluminum alloys processed by different rolling techniques: skin pass rolling with high contact friction and high-ratio differential speed rolling (HRDSR). Effects of sheet thickness, contact friction, thickness reduction per pass, rolls speed ratio, back and front tensions were investigated by the rigid-plastic finite element analysis. The results of the numerical simulation have demonstrated that plastic strain is more severe in the material surface, where the circumferential speed of the work roll is lower. In all cases, strain is continuously and unidirectionally increased from the minimum value on the contact with faster roll to the maximum value on the contact with slower roll during HRDSR. The non-linear effect of the influence of the rolls speed ratio on strain difference was found. The extremum of the strain difference through the sheet thickness exists. Extremely high strain difference through sheet thickness was found during a single-pass HRDSR. The extremum can be reached, when rolls speed ratio is optimal. Finite element analysis of strain gradients can be used for development of the special rolling techniques for fabrication of metal sheets with gradient structures and improved properties. [ABSTRACT FROM AUTHOR]

In this article an analysis of the cone-type rotary piercing process of seamless tubes by means of a finite element model is presented. The originality of the proposed study is the utilisation of the shear strain of the material for the experimental validation of the model. The cone-type rotary piercing process is a complex procedure in which the material is subjected to severe plastic deformation and to surface twisting that leads to shear deformations. In addition, extreme friction conditions and high temperatures occur during the process which increase the difficulty of the process itself and its simulation. Consequently, the experimental validation of numerical models of the process cannot be accomplished exclusively based on power and velocity terms, as it is usually done. Instead, in this paper it is demonstrated how still another experimental parameter is required for the correct simulation of the process, which is the shear strain of the material, measured through the values of longitudinal surface twisting. This way, a new methodology for the analysis of the cone-type piercing process is proposed in the paper, which establishes a relationship between the material contact with the elements of the piercing mill and the resulting power consumption, process performance, forces exerted and longitudinal surface twisting of the material. Thanks to this methodology, it is shown that the relation between the material contact with the mandrel and the rolls in their initial surface region is responsible for the process performance, while the contact with the rolls in the region where the tube exits the piercing mill defines the surface twisting of the material and thus its shear deformation. [ABSTRACT FROM AUTHOR]

Replacements of dangerous product to eco-friendly product has been tried hundred years ago. Brake pads must have strong enough and much harder to stop rolling tire of vehicles. In this research, Palm slag reinforced tire dust was used as new filler in fabrication of brake pads. Weight percentage between palm slag and tire dust was varied to get the best result of wear and hardness properties. Palm slag reinforced waste tire dust composites shows higher hardness than waste tire dust composites but lower than palm slag composites. Palm slag reinforced waste tire dust composites were tested by using polisher grinder machine. The brake pad composite show increasing hardness properties with addition of palm slag materials. Wear rate was found higher in waste tire dust composites without palm slag content whereas better wear rate was found in sample C4 with 30% weight of palm slag and 10% weight of waste tire dust. Morphology of palm slag reinforced waste tire dust composites shows formation of pits and secondary plateaus was existed on surface of composites after wear test was applied. [ABSTRACT FROM AUTHOR]

A finite element analysis of the dynamic wheel-rail response generated by the polygonization of the wheel tread was conducted based on a three-dimensional wheel-rail rolling contact model using LS-DYNA explicit code, where the sub rail foundation and the stiffness and damping of sleeper support were also considered in the finite element model. Typical dynamic vertical wheel-rail contact force and the related stress and strain states were obtained. Influences of nonperiodic and periodic wheel polygonizations on the dynamic wheel-rail response are compared, and the influence of train speed was also examined. The results indicate that the dynamic wheel-rail contact force induced by wheel polygonization is sensitive to the wheel radial deviation and train speed; and the large wheel-rail contact force induced by the polygonal wheel will lead to the large von-Mises equivalent stress and plastic strain in the wheel-rail contact zone. These findings are very helpful to guide the maintenance and repair of wheel-rail components in rail transportation. [ABSTRACT FROM AUTHOR]

A finite element analysis of the dynamic wheel-rail response generated by the polygonization of the wheel tread was conducted based on a three-dimensional wheel-rail rolling contact model using LS-DYNA explicit code, where the sub rail foundation and the stiffness and damping of sleeper support were also considered in the finite element model. Typical dynamic vertical wheel-rail contact force and the related stress and strain states were obtained. Influences of nonperiodic and periodic wheel polygonizations on the dynamic wheel-rail response are compared, and the influence of train speed was also examined. The results indicate that the dynamic wheel-rail contact force induced by wheel polygonization is sensitive to the wheel radial deviation and train speed; and the large wheel-rail contact force induced by the polygonal wheel will lead to the large von-Mises equivalent stress and plastic strain in the wheel-rail contact zone. These findings are very helpful to guide the maintenance and repair of wheel-rail components in rail transportation. [ABSTRACT FROM AUTHOR]

The objective of this paper is to discus and to introduce an identification method of stick slip phenomenon when friction of two surfaces occures within multi directional contact friction. This interesting topic is discussed due the complexity of wear mechanism on multi directional contact friction and the attendance of stick slip wear. The identification is based on kinematics of particle on the contact surface. Assumption that stick slip happens more often when contact surfaces moving stop suddenly for awhile and start sliding again is very important principle. Pin on disk tribometer is modeled to be two surfaces contacting. However, pin is set to spin about its axis while the pin revolutes the disk relatively. Therefore, there are two variables of angular velocity, disk rotation and pin rotation. Ratio between pin rotational speed and disk rotational speed is used as the main parameter in this research. The research starts from analyzing particle's paths during contacts, discretizing and creating velocity field of points on the contact surfac of pine, recognizing ratio resulting zero speed points and finally identifying zero speed regions in particular ratios. The suspected stick slip regions, in turn, are verified by experimenting specimens of pin made of Ultra High Molecular Weight Poly Ethylene (UHMWPE). This pin spinning slides on the disk made of steel. The experimen variates four values of speed ratios which is 4.2, 5, 6.5, 10 and 20. Moreover, the surface worn is analized especially on the zero speed regions. Micrograph is taken at 20 times magnification in order to recognize wear mechanisms. The result shows that on all the ratios, the expected stick slip region and the micro graphic contact surface have similar pattern. Abraded and delaminated surfaces caused by adhesive wear occur on the zero speed region. In conclusion, this methodology of stick slip identification for directional contact friction is relatively accurate determination for stick slip path. [ABSTRACT FROM AUTHOR]

High Speed Railways and Dedicated Freight Corridors are the need of the day for fast and efficient transportation of the ever growing population and freight across long distances of travel. With the increase in speeds and axle loads carried by these trains, wearing out of rails and train wheel sections are a common issue, which is due to the increase in friction at the wheel-rail interfaces. For the cases where the wheel-rail interface friction is less than optimum, as in case of high speed trains with very low axle loads, wheel-slips are imminent and loss of traction occurs when the trains accelerate rapidly or brake all of a sudden. These vast variety of traction problems around the wheel-rail interface friction need to be mitigated carefully, so that the contact interface friction neither ascents too high to cause material wear and need for added locomotive power, nor be on the lower side to cause wheel-slips and loss of traction at high speeds. Top-of-rail friction modifiers are engineered surface coatings applied on top of rails, to maintain an optimum frictional contact between the train wheels and the rails. Extensive research works in the area of wheel-rail tribology have revealed that the optimum frictional coefficients at wheel-rail interfaces lie at a value of around 0.35. Application of top-of-rail (TOR) friction modifiers on rail surfaces add an extra layer of material coating on top of the rails, with a surface frictional coefficient of the desired range. This study reviews the common types of rail friction modifiers, the methods for their application, issues related with the application of friction modifiers, and a guideline on selection of the right class of coating material based on site specific requirements of the railway networks. [ABSTRACT FROM AUTHOR]

In this paper, we study the surfactant effect on the motion of an immersed sessile drop. We propose a new approach for the contact-line dynamic, involving forces acting on the drop motion such as the friction force from the wall and the mechanical force balance from the three-phase contact line. The drop shape formula is determined by the principle of minimization surface energy, subjected to mass conservation. Our numerical simulations show that the proposed model is in agreement with the experimental results which performs that surfactant alters the wettability of a surface to become more water-wet. [ABSTRACT FROM AUTHOR]

The additional force arising from rolling motions effects the change of two-phase flow resistance. Experimental studies of the characteristics of air-water mixture flow resistance in narrow rectangular channel(40 × 1.4mm2)in rolling motions were carried out with the rolling periods and angles of 8s, 12s, 16s, and 10°, 15°, 30°, respectively. The experimental results showed that the transient frictional factor changed periodically. The variation of rolling frictional factor with time is closely related to the mass quality, the two-phase Reynolds number, rolling period and amplitudes. The larger of mass quality and rolling amplitude and the small rolling period, the larger of fluctuation amplitude of frictional pressure drop were. A new correction for predicting the transient frictional factor of two-phase was proposed with a good accuracy. [ABSTRACT FROM AUTHOR]

In order to get more local interfacial information as well as to further comprehend the intrinsic mechanism of two-phase flow under rolling condition to improve and extend the two-fluid model in rolling condition, an experimental investigation of two-phase flow under rolling as well as vertical steady condition was conducted by using double-sensor optical probe fabricated by the authors. The experimental loop is fixed on a rolling platform, which can simulate the rolling movement of a ship with the rolling period and rolling angle in the ranges of 0-20s and 0-45°, respectively. An optical probe driven by a mechanical traverser is installed on the test section, wherein making it move diametrically. Experimental investigations were conducted on this experimental loop for air-water two-phase flow under rolling and steady conditions. Local void fraction, interfacial area concentration (IAC) and bubble velocity were obtained for further improving the interface transportation equation. Both the measured void fraction and IAC demonstrated wall peak or core peak distributions under vertical condition. The typical distribution of IAC under vertical conditions showed that IAC changes from wall peak to core peak with the gas flow rate increasing; while as the liquid flow rate increases, the distribution changes inversely. In the case of rolling conditions, despite similar to the distribution under vertical condition, the local time-averaged void fraction and IAC have lower value in centerline and high value near wall region. The results also indicated that the rolling amplitude has an influence on the local bubble frequency, void fraction and IAC, except interface velocity, while rolling period almost has no effect on the local characteristics. [ABSTRACT FROM AUTHOR]

The enhancement of surface waves in the near-field of a defect has been reported by several authors. It has been demonstrated that the interaction between the incident Rayleigh wave with the reflected Rayleigh wave, plus the mode-converted surface skimming longitudinal wave, explains the significant increase in signal amplitude that is encountered as a detection point approaches a smooth machined defect inclined normal to the surface. However, this is not a typical defect geometry. For example, rolling contact fatigue in rails grows at an angle to the surface, and stress corrosion cracking grows as branched defects. We present results of experimental measurements on machined slots with varied geometries, including defects which are normal or inclined to the surface, and show the effect of branched defect geometries on the wave propagation and signal enhancement. We use laser generation and detection, and compare results with finite element method (FEM) models. We also investigate frequency enhancements for angled and branched defects, to highlight further potential measurement techniques when using scanning laser detection. [ABSTRACT FROM AUTHOR]

The use of lasers for generating and detecting ultrasound is becoming more established in non-destructive testing. However, there is still scope in developing the techniques to fully realise the benefits of non-contact measurements. One application is the detection of surface defects in metals; for example, rolling contact fatigue in rails, and surface cracking on billets or plates. We present measurements using a pulsed Nd:YAG laser to generate surface ultrasonic waves and an interferometer to detect the surface displacement on the sample, and investigate the interaction of Rayleigh or Lamb waves with surface defects. Signal enhancement in the near-field is observed for Rayleigh waves when either the generator or detector is close to a defect. For a scanned detector measurement, enhancement is observed due to constructive interference of the incident and reflected waves. For a scanned generator measurement, the change in generation conditions when the laser is over the defect also lead to an enhancement. In measurements of plate samples we observe similar enhancement effects whereby higher order modes are observed when the laser is above a defect. We discuss the implications of signal enhancements for detecting and characterising surface cracking. [ABSTRACT FROM AUTHOR]

The study of the mechanical components on the micro/nano-scale requires the investigation on stress, contact pressure and deformation of the contacting components particularly. On the micro/nano-scale, the discussion on the rolling contact between two mechanical components takes place not only on the general surface but also covers the asperity level on the rough surface scale. During rolling contact of the mechanical components, the model can be simplified to the contact between a roller on a rough surface. This model is occupied in finite element analysis to observe the steady state phase during rolling contact. The steady state phase is the second phase of the new components life-cycle where the plastic deformation, contact stress and contact pressure found their stabilized form and the optimal condition on the contact loading is reached. The steady state phase takes place after running-in phase where the aforementioned parameters still occur in the transient mode and still vary with time. In this paper, two-dimensional model of a cylinder rolls over a surface are employed in the simulation by considering the elastic-plastic material with strain hardening behavior. The contact stress and residual stress of the rough surface due to rolling contact are observed to determine the steady state phase. The results show that the steady state of the contact stress and residual stress has been obtained on the second repeated rolling contact. The stability of the contact and residual stress on the second cycle is not only influenced by the strain hardening behavior but it is also influenced by the flattening of the asperity which produces larger contact area such that the contact load is homogenously distributed on the truncated asperity. [ABSTRACT FROM AUTHOR]

The running-in of rolling contact between a rigid cylinder against a deformable rough surface is simulated by finite element method in this paper. Two-dimensional model of rough surface is employed in the simulation by considering the elastic-plastic material with strain hardening behavior. The topographical changes of the rough surface due to running-in of rolling contact are observed for the applied load or interferences. A relatively high load is applied so that it operates in the elastic-plastic deformation regime. The running-in phase, indicated by the high asperity truncation, is found within the first two cycle of the rolling contact. After the third cycle, the steady state deformation occurs. A comparison between the running-in of rolling contact and the repeated static contact for the same model and is also presented. [ABSTRACT FROM AUTHOR]

The large eddy simulation is performed to study the flow past two side-by-side circular cylinders. The Reynolds number is 5800 based on the free-stream velocity and cylinder diameter. The center-to-center transverse pitch ratio T/D is 3. Both cylinders are slighted heated and the small amount of heat can be treated as a passive scalar. The numerical results are compared with the experimental data. The numerical simulations are in good agreement with experimental observations. [ABSTRACT FROM AUTHOR]

We develop a quantal cumulant dynamics method for the quantum tunneling in dissipative environment. Reduced equations of motion of classical and quantal cumulant variables without bath degrees of freedom are derived. We observed suppression of the tunneling that depends on the sign of a friction constant for an Ohmic approximation and on the magnitude of a bath frequency for a single bath mode approximation. A possible mechanism of the suppression is explored by analyzing an effective quantal potential of the tunneling path. [ABSTRACT FROM AUTHOR]

An oil-film thickness monitoring system capable of providing early warning of lubrication failure in rolling element bearings has been developed. Apparatus is described in which a 6016 deep groove ball bearing can be controllably tested under various operating conditions. A quasistatic spring model is used to calculate oil-film thickness from the measured reflection coefficient data. The ultrasonically measured oil-film thicknesses obtained are shown to agree well with the predictions from classical elastohydrodynamic lubrication theory. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]

The wear behavior of Polyamide 6 (PA6), Polyoxymethylene (POM), Polyetheretherketone (PEEK), and Polyparaphenylene (PPP) materials under rolling contact was investigated. The ball on plate principle, i.e. a steel ball (as counterpart) rolls on a polymer plate specimen in rotational or linear motion, was used. The results are shown for different stress parameters which vary by load (50 N up to 300 N) and testing time (up to 50 hours). Differences in surface fatigue mechanisms were illustrated by microscopic methods. The best performance was found for PEEK. All the neat polymers were superior to any reinforced versions of them. [ABSTRACT FROM AUTHOR]