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Research Papers: Applications

J. Tribol. 2015;137(2):021101-021101-7. doi:10.1115/1.4028606.

The objective of design optimization is to determine the design that minimizes the objective function by changing design variables and satisfying design constraints. During multi-objective optimization, which has been widely applied to improve bearing designs, designers must consider several design criteria or objective functions simultaneously. The particle swarm optimization (PSO) method is known for its simple implementation and high efficiency in solving multifactor but single-objective optimization problems. This paper introduces a new multi-objective algorithm (MOA) based on the PSO and Pareto methods that can greatly reduce the number of objective function calls when a suitable swarm size is set.

Commentary by Dr. Valentin Fuster
J. Tribol. 2015;137(2):021102-021102-17. doi:10.1115/1.4029042.

Analytical relationships for calculating three rolling element bearing loads (Fx, Fy, and Fz) and two tilting moments (My and Mz) as a function of three relative race translations (dx, dy, and dz) and two relative race tilting angles (dθy and dθz) have been given in a previous paper. The previous approach was suggested for any rolling element bearing type, although it has been recognized that the assumption of a constant rolling element-race contact angle is not well supported by deep groove ball bearings (DGBB) or angular contact ball bearings (ACBB). The new approach described in this paper addresses the latter weaknesses by accounting for the variation of the contact angle on the most loaded ball and also shows that misalignment effects on spherical roller bearing (SRB) loads are negligible. Comparisons between the simplified approach (option 1) and the “enhanced” numerical approach (option 2, which requires a summation of the load components on each ball with the appropriate contact angle included) is made, showing a good correlation as long as the relative misalignment remains reasonable or occurs in the plane corresponding to maximum radial displacement. Option 2 can, however, be recommended since it is easy to program and quite accurate at any misalignment level. Other pros and cons of both options are described. As in the previous paper, a full coupling between all displacements and forces, as well as roller and raceway crown radii, are considered, meaning that Hertzian point contact stiffness is used in roller bearings at low load with a smooth transition toward Hertzian line contact as the load increases. This approach is particularly recommended for programming the rolling element bearing behavior in any finite element analysis or multibody system dynamic tool, since only two nodes are considered: one for the inner race (IR) center, usually connected to a shaft, and another node for the outer race (OR) center, connected to the housing.

Commentary by Dr. Valentin Fuster

Research Papers: Coatings & Solid Lubricants

J. Tribol. 2015;137(2):021301-021301-6. doi:10.1115/1.4028921.

Self-lubricating composite NiAl–Cr–Mo–CaF2–Ag was fabricated by powder metallurgy technique. The NiAl matrix composite with 10 wt.% Ag provides self-lubricating properties at a broad temperature range between room temperature and 1000 °C. Especially at 800 °C, the composite offers excellent friction reduction about 0.2 and wear resistance about 0.7 × 10−4 mm3 N−1 m−1. The lubricous behavior at a wide temperature range could be attributed to the synergistic effect of Ag, CaF2, CaCrO4, and CaMoO4.

Commentary by Dr. Valentin Fuster

Research Papers: Contact Mechanics

J. Tribol. 2015;137(2):021401-021401-10. doi:10.1115/1.4029165.

This study focuses on the influence of roughness lay directionality on micropit crack formation, using a computational approach. A mixed lubrication model is implemented to find the surface tractions, which are used in a stress model to compute the near surface stress concentrations. With the stress amplitudes and means determined, the crack formation lives are assessed according to a fatigue criterion. It is found when the roughness lays of the two surface are parallel to the rolling direction and are out-of-phase, the resulted micropitting area percentage is minimum. The most severe micropitting activity is observed on the surface whose roughness lay is parallel to the rolling direction, while the roughness lay of its counterpart is normal to the rolling direction.

Commentary by Dr. Valentin Fuster
J. Tribol. 2015;137(2):021402-021402-8. doi:10.1115/1.4029537.

In the current study, a semi-analytical model for contact between a homogeneous, isotropic, linear elastic half-space with a geometrically anisotropic (wavelengths are different in the two principal directions) bisinusoidal surface on the boundary and a rigid base is developed. Two asymptotic loads to area relations for early and almost complete contact are derived. The Hertz elliptic contact theory is applied to approximate the load to area relation in the early contact. The noncontact regions occur in the almost complete contact are treated as mode-I cracks. Since those cracks are in compression, an approximate relation between the load and noncontact area can be obtained by setting the corresponding stress intensity factor (SIF) to zero. These two asymptotic solutions are validated by two different numerical models, namely, the fast Fourier transform (FFT) model and the finite element (FE) model. A piecewise equation is fit to the numerical solutions to bridge these two asymptotic solutions.

Commentary by Dr. Valentin Fuster
J. Tribol. 2015;137(2):021403-021403-9. doi:10.1115/1.4029644.

In this paper, a numerical simulation method for generating rough surfaces with desired autocorrelation function (ACF) and statistical parameters, including root mean square (rms), skewness (Ssk), and kurtosis (Ku), is developed by combining the polar method, Johnson translation system, and random switching system. This method can be used to generate Gaussian, non-Gaussian, isotropic, and nonisotropic rough surfaces. The simulation results show the excellent performance of present method for producing surface with various desired statistical parameters and ACF. The advantage of present method is that the deviation of statistical parameters and ACF from the desired ones can be as small as required since it is controlled by iterative algorithms.

Commentary by Dr. Valentin Fuster

Research Papers: Elastohydrodynamic Lubrication

J. Tribol. 2015;137(2):021501-021501-10. doi:10.1115/1.4028881.

The “Stribeck curve” is a well-known concept, describing the frictional behavior of a lubricated interface during the transition from boundary and mixed lubrication up to full-film hydrodynamic/elastohydrodynamic lubrication. It can be found in nearly every tribology textbook/handbook and many articles and technical papers. However, the majority of the published Stribeck curves are only conceptual without real data from either experiments or numerical solutions. The limited number of published ones with real data is often incomplete, covering only a portion of the entire transition. This is because generating a complete Stribeck curve requires experimental or numerical results in an extremely wide range of operating conditions, which has been a great challenge. Also, numerically calculating a Stribeck curve requires a unified model with robust algorithms that is capable of handling the entire spectrum of lubrication status. In the present study, numerical solutions in counterformal contacts of rough surfaces are obtained by using the unified deterministic mixed elastohydrodynamic lubrication (EHL) model recently developed. Stribeck curves are plotted in a wide range of speed and lubricant film thickness based on the simulation results with various types of contact geometry using machined rough surfaces of different orientations. Surface flash temperature is also analyzed during the friction calculation considering the mutual dependence between friction and interfacial temperature. Obtained results show that in lubricated concentrated contacts, friction continuously decreases as speed and film thickness increase even in the full-film regime until extremely high speeds are reached. This is mainly due to the reduction of lubricant limiting shear stress caused by flash temperature rise. The results also reveal that contact ellipticity and roughness orientation have limited influence on frictional behaviors, especially in the full-film and boundary lubrication regimes.

Commentary by Dr. Valentin Fuster
J. Tribol. 2015;137(2):021502-021502-11. doi:10.1115/1.4029358.

A numerical modeling of thermoelastohydrodynamic gas spiral groove face seal behavior is presented. Temperature fields of the fluid film and the seal rings are computed, as they are the elastic and thermal distortions of the rings. Numerical analysis is carried out on a gas spiral groove face seal taking into account of choked flow effect. Analysis results show that both elastic and thermal distortions induce strong influence on the geometry of the fluid film, forming obvious divergent clearance which leads to significant decrease of minimum equilibrium clearance, exceeding 50% in degree. Thermal distortion may induce the same influence degree as elastic distortion on the minimum equilibrium clearance in high pressure cases, but the rotation speed has no obvious influence on the minimum clearance when both elastic and thermal distortions are considered. The thermal distortion as well as elastic distortion should be concerned in high pressure analysis.

Commentary by Dr. Valentin Fuster
J. Tribol. 2015;137(2):021503-021503-9. doi:10.1115/1.4029448.

Heavily loaded point elastohydrodynamically lubricated (EHL) contacts involved in steady purely transitional, skewed transitional, and transitional with spinning motions are considered. It is shown that in the central parts of the inlet and exit zones of such heavily loaded point EHL contacts the asymptotic equations governing the EHL problem along the lubricant flow streamlines for the above types of contact motions can be reduced to two sets of asymptotic equations: one in the inlet and one in the exit zones. The latter sets of equations are identical to the asymptotic equations describing lubrication process in the inlet and exit zones of the corresponding heavily loaded line EHL contact (Kudish, I. I., 2013, Elastohydrodynamic Lubrication for Line and Point Contacts: Asymptotic and Numerical Approaches, Chapman and Hall/CRC). For each specific motion of a point contact, a separate set of formulas for the lubrication film thickness is obtained. For different types of contact motions, these film thickness formulas differ significantly (Kudish, I. I., 2013, Elastohydrodynamic Lubrication for Line and Point Contacts: Asymptotic and Numerical Approaches, Chapman and Hall/CRC). For heavily loaded contacts, the discovered relationship between point and line EHL problems allows to apply to point contacts most of the results obtained for line contacts (Kudish, I. I., 2013, Elastohydrodynamic Lubrication for Line and Point Contacts: Asymptotic and Numerical Approaches, Chapman and Hall/CRC; Kudish, I. I., and Covitch, M. J., 2010, Modeling and Analytical Methods in Tribology, Chapman and Hall/CRC).

Commentary by Dr. Valentin Fuster
J. Tribol. 2015;137(2):021504-021504-7. doi:10.1115/1.4029673.

Transient film thickness behavior is investigated using full elastohydrodynamic lubrication (EHL) line contact simulations during film collapse due to sudden halt and impact loading. Due attention is given to realistic shear-thinning behavior and comparisons are made with a largely ignored class of EHL lubricants that exhibit linear pressure–viscosity dependence at low pressures. The EHL film collapse is found to be governed by the piezoviscous response and the linear P–V oils exhibit rapidly collapsing EHL entrapment. Under impact loading, the transient film thickness deviates markedly from the corresponding steady-state behavior and this departure is a function of lubricant rheology.

Commentary by Dr. Valentin Fuster

Research Papers: Friction & Wear

J. Tribol. 2015;137(2):021601-021601-11. doi:10.1115/1.4028998.

Friction is a complex phenomenon that arises from the interaction of deforming surface microasperities and adhesive forces at very small length scales. In this work, we use a computational model to understand the effects of various physical parameters on the friction response between two similar linearly elastic-perfectly plastic surfaces. The main ingredients of the computational model are a statistical model of the surface based on a Gaussian autocorrelation function (ACF), a parametric representation of the normal and shear responses of a single microasperity, and a statistical homogenization procedure to compute the overall friction response. The surfaces are assumed to be isotropic in nature. We employ this computational model to develop constitutive relationships for the friction force and coefficient of friction for Aluminum 6061 and stainless steel surfaces. We study the effects of various quantities such as surface roughness, material properties, normal load, and adhesive forces on the overall friction response. Our results show that the model is able to capture a wide variety of friction responses. Our results also suggest that the root mean squared (RMS) roughness of the surface alone is insufficient to describe the friction characteristics of a surface, and that an additional parameter is needed. We propose one such parameter, the aspect ratio, which is the ratio of the RMS roughness to the correlation length.

Commentary by Dr. Valentin Fuster
J. Tribol. 2015;137(2):021602-021602-8. doi:10.1115/1.4028980.

This paper explores new approaches in design and fabrication of novel composite materials in order to increase corrosion and wear resistance. By mimicking nature, nacreous particles from seashells were used as reinforcement in an aluminum matrix. A powder metallurgy process was developed to fabricate the nacreous-reinforced-aluminum matrix composites. Mechanical properties, corrosion, and wear resistance were characterized. Experimental results showed that the corrosion resistance increases as the nacreous concentration increases. The hardness and wear resistance increased by up to 22% and 10%, respectively. With oxidation of aluminum during heat treatment, the mentioned properties were further improved by about 32–37%.

Commentary by Dr. Valentin Fuster
J. Tribol. 2015;137(2):021603-021603-7. doi:10.1115/1.4028981.

Ti(C,N)-based cermets offer good high temperature strength, perfect chemical stability, excellent wear resistance, and relatively better machinability. In the present work, the tribological behaviors of Ti(C,N)/SiC sliding pairs lubricated in water and seawater were evaluated using a ball-on-disk tribometer. The experimental results show that a relatively low friction coefficient (about 0.025) can be obtained when lubricated with artificial seawater at the sliding speed of 200 mm/s, while the friction coefficient is about 0.2 in purified water. The wear surface profiles and the lubricants collected after running-in process for the high and low friction conditions were compared. In addition, the effects of salt molar concentration of the lubricant on the Ti(C,N)/SiC friction properties were investigated. It was found that the smooth and flat surface is the premise to gain the low friction. At the same time, the proper concentration of silica colloid, which is affected by the salt ions, is also an essential one. Moreover, the high sliding speed (200 mm/s) is beneficial to achieve low friction.

Commentary by Dr. Valentin Fuster
J. Tribol. 2015;137(2):021604-021604-7. doi:10.1115/1.4029248.

The present work involves the study of the effect of precipitates on mechanical and tribological properties of AZ91 magnesium alloy. Optical microscopy, scanning electron microscopy (SEM), and nanoindentation were used to characterize the microstructures and mechanical properties of the alloy. In addition, the wear behavior of the alloy was deduced using a pin-on disk tribological configuration under unidirectional sliding against steel (AISI 250). The elastic modulus of AZ91 alloy was found to vary significantly with changing precipitation state. The tribological evaluations showed that the specific wear-rate of solutionized sample is lowest as compared to the aged samples. This was attributed to the absence of γ-Mg17Al12 phase. Examination of worn surfaces suggested that microploughing coupled with the adhesive mode of wear is the main wear mechanism in the aged samples.

Commentary by Dr. Valentin Fuster
J. Tribol. 2015;137(2):021605-021605-10. doi:10.1115/1.4029277.

The influence of the spherical joint with clearance caused by wear on the dynamics performance of spatial multibody system is predicted based on the Archard's wear model and equations of motion of multibody systems. First, the function of contact deformation and load acting on the spherical joint with clearance is derived based on the improved Winkler elastic foundation model and Hertz quadratic pressure distribution assumption. On this basis, considering the influence of clearance size and wear state on the contact stiffness between spherical joint elements, an improved contact force model is proposed by Lankarani–Nikravesh contact force model and improved stiffness coefficient that is the slope of the function of contact deformation and load. Second, due to the complexity for that wear impacts on the surface topography of contact bodies, an approximate calculation method of contact area with respect to the clearance spherical joint is provided for simplifying the computational process of contact pressure in the Archard's wear model. Subsequently, the contact pressure between contact bodies is calculated by the improved contact force model and approximate contact area (ICFM–ACA), which is verified via finite element method (FEM). Moreover, the dynamics model of spatial four bar mechanism considering spherical joint with clearance caused by wear is formulated using equations of motion of multibody systems. Finally, the wear depth of spherical joint with clearance is predicted via two different kinds of contact pressure based on the Archard's wear model (one is from the ICFM–ACA and the other is from FEM), respectively. The numerical simulation results show that the improved contact force model and proposed approximate contact area are correctness and validity for predicting wear in the spherical joint with clearance. Simultaneously, the effect of the spherical joint with clearance caused by wear on the dynamics performance of spatial four bar mechanism is analyzed.

Commentary by Dr. Valentin Fuster
J. Tribol. 2015;137(2):021606-021606-7. doi:10.1115/1.4029485.

In this paper, the frictional vibration behavior under different wear states was investigated by the friction and wear experiments of the piston ring against the cylinder liner of marine diesel engine on CFT-I tester. The time-frequency features of frictional vibration were analyzed by harmonic wavelet packet transform (HWPT) and the variation of frictional vibration from running-in wear to steady wear and violent wear states was studied by defining characteristics parameter K using singular value decomposition (SVD). The result shows that the time-frequency features of frictional vibration vary with the wear time and can reflect the wear states of tribological pairs. The variation of characteristic parameter K of the frictional vibration is accordingly consistent with that of the friction coefficient and indicates that the wear progress of the tribological pair goes through various stages, namely, running-in wear, steady wear, and violent wear. Therefore, the frictional vibration can be used to predict the wear process and identify the wear states of tribological pairs.

Commentary by Dr. Valentin Fuster

Research Papers: Hydrodynamic Lubrication

J. Tribol. 2015;137(2):021701-021701-7. doi:10.1115/1.4028910.

A new hydrostatic spherical hinge is developed in this paper to provide a large load capacity. The static and dynamic Reynolds equations in spherical coordinate system for incompressible Newtonian fluid were established using the perturbation method. Finite difference method was employed to solve the load capacity, power loss, oil flow rate, dynamic stiffness, and damping coefficients. This paper provides a new perspective for analysis on the dynamic characteristics of the spherical hinge.

Commentary by Dr. Valentin Fuster
J. Tribol. 2015;137(2):021702-021702-8. doi:10.1115/1.4028999.

Aerostatic porous bearings have been applied successfully to various precision devices, such as precision machine tools and precision measuring equipment, to achieve higher accuracy of motion. Recently, large aerostatic porous thrust bearings have been used as essential components in a lithography machine for large liquid crystal display (LCD) glasses. Conventional aerostatic porous bearings are made of porous material that covers the whole of the bearing surface area, requiring a large piece of such material for large bearings. However, making large pieces of porous material requires the use of a large electric furnace, which is a very expensive part of the bearing's manufacturing cost. To overcome this problem, this paper proposes an aerostatic thrust bearing with multiple porous inlet ports. The proposed bearing has a number of small porous inlet ports on the bearing surface, thereby avoiding the need for large electric furnaces. The static characteristics of the proposed bearings are investigated numerically and experimentally. The results show that the proposed aerostatic thrust bearing is potentially very useful for the manufacture of large aerostatic thrust bearings, where it would have advantages over conventional aerostatic porous thrust bearings.

Commentary by Dr. Valentin Fuster
J. Tribol. 2015;137(2):021703-021703-9. doi:10.1115/1.4029643.

This paper deals with the experimental analysis of the dynamic characteristics of a foil thrust bearing (FTB) designed according to specifications given by NASA scientists in 2009 (Dykas et al., 2009, “Design, Fabrication, and Performance of Foil Gas Thrust Bearings for Microturbomachinery Applications,” ASME J. Eng. Gas Turbines Power, 131(1), p. 012301). The present work details the new configuration of the same test rig that was used to test start-up characteristics of the aforementioned bearing (Balducchi et al., 2013, “Experimental Analysis of the Start-Up Torque of a Mildly Loaded Foil Thrust Bearing,” ASME J. Tribol., 135(3), p. 031703). The rig has been reconfigured to test dynamic characteristics. The dynamic characteristics of the bump foil structure were measured for static loads comprised between 30 N and 150 N while measurements for the FTB were performed at 35 krpm for 30 N, 60 N, and 90 N. Excitation frequencies were comprised between 150 Hz and 750 Hz. Results showed that the dynamic stiffness of the FTB increase with excitation frequency while the equivalent damping decreases. Both stiffness and damping increase with the static load but are smaller at 35 krpm compared to 0 rpm.

Commentary by Dr. Valentin Fuster

Research Papers: Lubricants

J. Tribol. 2015;137(2):021801-021801-7. doi:10.1115/1.4029332.

Friction tests with point–point contact were carried out using a microtribometer to investigate the tribological characteristics of steel/steel rubbing pair immersed in 57 kinds of esters as lubricant base oils. A set of 57 esters and their wear data were included in the back-propagation neural network (BPNN)-quantitative structure tribo-ability relationship (QSTR) model with two-dimensional (2D) and three-dimensional (3D) QSTR descriptors. The predictive performance of the BPNN-QSTR model is acceptable. The findings of the BPNN-QSTR model show that the extent of polar groups cannot be too large in the molecule to achieve good antiwear performance; and the polar groups with a high degree of relative concentrated charge are favorable for antiwear. A low degree of molecular hydrophobicity of lubricant base oil is beneficial for antiwear behavior. Large molecular dipole moment is disadvantageous for antiwear properties. It is necessary to maintain one large molecular surface in one plane, to have a long and short chain length to be present within the same molecule, and to keep small difference between the long and short chain length to enhance the antiwear performance. Finally, lubricant base oil candidate molecules will have beneficial antiwear properties that they should contain more N groups with three single bonds and more C groups with one double bond and two single bonds; the presence of O atoms with any bonds or CH groups with three single bonds leads to a decrease in the wear resistance performance.

Commentary by Dr. Valentin Fuster
J. Tribol. 2015;137(2):021802-021802-8. doi:10.1115/1.4029388.

The prediction of lubrication characteristics for compounds through tribological models would aid in the discovery of new lubricant additives and improved lubricant design. But until recently, the field of tribological prediction has been sparse and not systematic. Tribological processes are complex and involve molecular energy exchange as well as conformation transitions. We have developed a platform of a “quantitative structure tribo-ability relationship (QSTR),” which enables us to introduce well-developed quantitative structure–activity relationships (QSAR) methods into tribology systematically. The present study applies “evaluation of infrared vibration-based” (EVA) descriptors, which are three-dimensional (3D) QSAR descriptors to simulate infrared (IR) vibration properties of molecules, in order to establish the QSTR prediction model. As structural changes take place under friction loads, the EVA descriptors characterize both molecular energy and conformations. The results show a strong correlation and robust predictability of the EVA model to tribological parameters. The approach paves a way to a systematic QSTR.

Commentary by Dr. Valentin Fuster

Research Papers: Tribochemistry & Tribofilms

J. Tribol. 2015;137(2):022301-022301-7. doi:10.1115/1.4029199.

Increasing demands concerning the performance of tribological systems for metal forming due to ecological restrictions or increased process loads demand the development of innovative tribological solutions. In preliminary works, it could be shown that surface structures on deep drawing tools manufactured by the incremental forming process machine hammer peening (MHP) have the potential to reduce friction. The friction reduction can be observed in strip drawing when comparing different surface structures against a state-of-the-art reference. A subsequently conducted wear analysis showed an adhesive wear on the structures. This leads to the conclusion that the lubricant film breaks due to increased contact pressures. In order to optimize the wetting of the lubricant and to avoid film break-ups, the molecular interactions in terms of the work of adhesion and spreading pressure between lubricant and MHP tool surfaces are investigated from a physicochemical point of view in this research work. The investigation approach is based on the use of the drop shape analysis.

Commentary by Dr. Valentin Fuster

Technical Brief

J. Tribol. 2015;137(2):024501-024501-4. doi:10.1115/1.4028973.

We show that copper-matrix composites that contain 20 vol. % of an in situ processed, polymer-derived, ceramic phase constituted from Si-C-N have unusual friction-and-wear properties. They show negligible wear despite a coefficient of friction (COF) that approaches 0.7. This behavior is ascribed to the lamellar structure of the composite such that the interlamellar regions are infused with nanoscale dispersion of ceramic particles. There is significant hardening of the composite just adjacent to the wear surface by severe plastic deformation.

Commentary by Dr. Valentin Fuster
J. Tribol. 2015;137(2):024502-024502-7. doi:10.1115/1.4029073.

In the current paper, studies carried out to design an eight pole electromagnetic bearing have been presented. The magnetic levitation force, accounting the copper and iron losses, was maximized for the given geometric constraints. Derivation of winding constraint equation in terms of wire diameter, number of turns, and dimensions of pole has been presented. Experiments were conducted to establish the constraints related to temperature rise. Finally, the dimensions of the electromagnet for maximizing the force obtained using numerical optimization have presented.

Commentary by Dr. Valentin Fuster
J. Tribol. 2015;137(2):024503-024503-7. doi:10.1115/1.4029276.

Wear of abrasive grains is one of the key issues influencing the grinding process and the resulting workpiece quality. Being able to quantify wheel wear in-process allows parameterization of grinding models that can help assuring part surface integrity. However, one of the main problems in measuring wear of abrasive grains is their small size, which makes this task to be not trivial. In this paper, several measuring techniques are compared in order to determine which one offers the best potential to quantify the wear of conventional and superabrasive grinding wheels. The selected techniques include optical macroscopy, optical microscopy, profilometry, and scanning electron microscopy (SEM). Among other results, direct comparisons of the same exact wear flat area measured with different techniques are shown.

Commentary by Dr. Valentin Fuster
J. Tribol. 2015;137(2):024504-024504-8. doi:10.1115/1.4029333.

Journal misalignment usually exists in journal bearings that affect nearly all the bearings static and dynamic characteristics including minimum oil film thickness, maximum oil film pressure, maximum oil film temperature, oil film stiffness, and damping. The main point in this study is to provide a comprehensive analysis on the oil film pressure, oil film temperature, oil film thickness, load-carrying capacity, oil film stiffness, and damping of journal bearing with different misalignment ratios and appropriately considering the turbulent and thermo effects based on solving the generalized Reynolds equation and energy equation. The results indicate that the oil thermo effects have a significant effect on the lubrication of misaligned journal bearings under large eccentricity ratio. The turbulent will obviously affect the lubrication of misaligned journal bearings when the eccentricity or misalignment ratio is large. In the present design of the journal bearing, the load and speed become higher and higher, and the eccentricity and misalignment ratio are usually large in the operating conditions. Therefore, it is necessary to take the effects of journal misalignment, turbulent, and thermal effect into account in the design and analysis of journal bearings.

Commentary by Dr. Valentin Fuster
J. Tribol. 2015;137(2):024505-024505-7. doi:10.1115/1.4029641.

This study deals with carriage drift (which is the differences of the carriage displacements or angular displacements at a certain position on a rail during a forward and return process) in linear-guideway type roller bearings. First, the displacements and angular displacements of the carriage of the “nonrecirculating” linear roller and ball bearings under a reciprocating operation were measured. The experimental results showed that carriage drift (in the horizontal, vertical, yaw, and pitch directions) occurred in the roller bearing and not in the ball bearing. Next, in relationship to roller skew, the generating mechanism of carriage drift in roller bearings was examined by a multibody analysis (MBA), then the generating mechanism of carriage drift was explained. Finally, to reduce carriage drift by restricting the roller skew, an antiskewing brace (ASB) was developed.

Commentary by Dr. Valentin Fuster

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