Showing papers in "Journal of Tribology-transactions of The Asme in 2015"

Performance of Lubricated Rolling/Sliding Concentrated Contacts With Surface Textures: A Review

Abstract: Benefits of surface textures for improving the performance behaviors of tribo-contacts are being explored and established by the investigators across the globe. But the consolidated information of findings of such explorations are spread. Therefore, the objective of this paper is to summarize the information available related to the preparation of surface textures and performance outcomes in the presence of surface textures at the concentrated contacts. Mainly, recent research findings and practices followed for the study of friction, wear, lubrication, contact fatigue, vibration, and noise at the generic concentrated contacts in presence of surface textures are reviewed for current status of research in the area and outlining the future prospects.

Simulation of the Cold Spray Particle Deposition Process

Abstract: Cold spray is a rapidly developing coating technology for depositing materials in the solid state. The cold spray particle deposition process was simulated by modeling the high velocity impacts of spherical particles onto a flat substrate under various conditions. We, for the first time, proposed the Couple Eulerian Lagrangian (CEL) numerical approach to solve the high strain rate deformation problem. The capability of the CEL numerical approach in modeling the Cold Spray deposition process was verified through a systematic parameter study, including impact velocity, initial particle temperature, friction coefficient and materials combination. The simulation results by using the CEL numerical approach agree with the experimental results published in the literature. Comparing with other numerical approaches, which are Lagrangian, ALE and SPH, the CEL analyses are generally more accurate and more robust in higher deformation regimes. Besides simulating the single particle impact problem, we also extended our study into the simulation of multiple impacts. A FCC-like particles arrangement model that inspired by the crystal structure was built to investigate the porosity rate and residual stress of deposited particles under various conditions. We observed not only the 3D profiles of voids, but also their distributions and developments during different procedures. Higher impact velocity and higher initial temperature of particles are both of benefit to produce a denser cold spray coating. The compressive residual stresses existed in the interface between the particle and substrate is mainly caused by the large and fast plastic deformation. Another simplified model for multiple impacts was created for the simulation of surface erosion. A severe surface erosion is the result of a high impact velocity, a high friction coefficient and a low contact angle. Two element failure models suitable for high-strain-rate dynamic problems were introduced in this study. For a ductile material as Copper, it followed two fracture modes in our study, which are tensile failure mode and shear failure mode. The former one mainly occurred beneath the substrate surface and the periphery of substrate craters, nevertheless the latter one was found predominately at the surface of craters. Four steps were found during the propagation of crack: void formation; crack formation; crack growth; coalescence and failure. A simple criterion equation was derived based on the simulation results for predicting the initiation of damage, which the erosion velocity v_{ero} is a function of contact angle and erosion velocity for normal impact v_{pi/2}. The equivalent plastic strain could also be a parameter for identifying the onset of damage, identified as being 1.042 for Copper in our study.

Optimization of Eight Pole Radial Active Magnetic Bearing

Abstract: 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. [DOI: 10.1115/1.4029073]

A Transient Thermoelastohydrodynamic Lubrication Model for the Slipper/Swashplate in Axial Piston Machines

Abstract: A transient lubrication model has been developed for the sliding interface between the slipper and swashplate in axial piston hydraulic pumps and motors. The model considers a nonisothermal fluid model, microdynamic motion of the slipper, as well as pressure and thermal deformations of the bounding solid bodies through a partitioned solution scheme. The separate contributions of elastohydrostatic and elastohydrodynamic lubrication are studied. Although hydrostatic deformation dominates, hydrodynamic effects are crucial for actual operation. Finally, the impact of transient deformation on lubricant pressure is explored, with its consideration necessary for accurate analysis.

Development of Analytical Equations for Design and Optimization of Axially Polarized Radial Passive Magnetic Bearing

Abstract: In the present research work, analytical equations have been developed for design and optimization of radial axial polarized passive magnetic bearing (PMB) with single layer for facilitating easy and quick solution, obviating the need of costly software. Seven design variables: eccentricity, rotor width, stator width, rotor length, stator length, clearance, and mean radius were identified as the main factors affecting the design and were thus considered in the development of analytical equations. The results obtained from the developed analytical equations have been validated with the published results. The optimization of the bearing design, with minimization of magnet volume as the objective function, was carried out to demonstrate the accuracy and usefulness of the developed equations. [DOI: 10.1115/1.4028488]

Research on the Static and Dynamic Characteristics of Misaligned Journal Bearing Considering the Turbulent and Thermohydrodynamic Effects

Abstract: 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.

A Numerical Investigation Into Cold Spray Bonding Processes

Abstract: Specific mechanisms underlying the critical velocity in cold gas particle spray applications are still being discussed, mainly due to limited access to in situ experimental observation and the complexity of modeling the particle impact process. In this work, particle bonding in the cold spray (CS) process was investigated by the finite element (FE) method. An effective interfacial cohesive strength parameter was defined in the particle–substrate contact regions. Impact of four different metals was simulated, using a range of impact velocities and varying the effective cohesive strength values. Deformation patterns of the particle and the substrate were characterized. It was shown that the use of interfacial cohesive strength leads to a critical particle impact velocity that demarcates a boundary between rebounding and bonding type responses of the system. Such critical bonding velocities were predicted for different interfacial cohesive strength values, suggesting that the bonding strength in particle–substrate interfaces could span a range that depends on the surface conditions of the particle and the substrate. It was also predicted that the quality of the particle bonding could be increased if the impact velocity exceeds the critical velocity. A method to predict a lower bound for the interfacial bonding energy was also presented. It was shown that the interfacial bonding energy for the different materials considered would have to be at least on the order of 10–60 J/m2 for cohesion to take place. The general methodology presented in this work can be extended to investigate various materials and impact conditions.

Model for Elastohydrodynamic Lubrication of Multilayered Materials

Abstract: A novel model is constructed for solving elastohydrodynamic lubrication (EHL) of multilayered materials. Because the film thickness equation needs the term of the deformation caused by pressure, the key problem for the EHL of elastic multilayered materials is to develop a method for calculating their surface deformations, or displacements, caused by pressure. The elastic displacements and stresses can be calculated by employing the discrete-convolution and fast Fourier transform (DC-FFT) method with influence coefficients. For the contact of layered materials, the frequency response functions (FRFs), relating pressure to surface displacements and stress components, derived from the Papkovich–Neuber potentials are applied. The influence coefficients can be obtained by employing FRFs. The EHL of functionally graded material (FGM) can also be well solved using a multilayer material system. The effects of material layers and property gradient on EHL film thickness and pressure are further investigated.

Three-Dimensional Dynamic Model of TEHD Tilting-Pad Journal Bearing—Part II: Parametric Studies

Abstract: This paper presents a new analysis method for a thermo-elasto-hydro-dynamic (TEHD) tilting pad journal bearing (TPJB) system to reach a static equilibrium condition adopting nonlinear transient dynamic solver, whereas earlier studies have used iteration schemes such as Newton–Raphson method. The theoretical TPJB model discussed in Part I of this research is combined into a newly developed algorithm to perform a bearing dynamic analysis and present dynamic coefficients. In the nonlinear transient dynamic solver, physical and modal coordinates coexist for computational efficiency, and transformation between modal and physical coordinate is performed at each numerical integration time step. Variable time step Runge–Kutta numerical integration scheme is adopted for a reliable and fast calculation. Nonlinear time transient dynamic analysis and steady thermal analysis are combined to find the static equilibrium condition of the TPJB system, where the singular matrix issue of flexible pad finite element (FE) model is resolved. The flexible pad TPJB model was verified by comparison with other numerical results. Simulation results corresponding with the theoretical model explained in Part I are presented and discussed. It explains how the TPJB dynamic behavior is influenced by a number of eigenvector of flexible pad FE model and pad thickness. Preload change under fluid and thermal load is examined.

Cyclic Constitutive Response and Effective S–N Diagram of M50 NiL Case-Hardened Bearing Steel Subjected to Rolling Contact Fatigue

Abstract: A combined experimental and numerical method is developed to estimate the continuously evolving cyclic plastic strain amplitudes in plastically deformed subsurface regions of a case-hardened M50 NiL steel rod subjected to rolling contact fatigue (RCF) over several hundred million cycles. The subsurface hardness values measured over the entire plastically deformed regions and the elastoplastic von Mises stresses determined from the three-dimensional (3D) Hertzian contact finite element (FE) model have been used in conjunction with Neuber's rule to estimate the evolved cyclic plastic strain amplitudes at various points within the RCF-affected zone. The cyclic stress–strain plots developed as a function of case depth revealed that cyclic hardening exponent of the material is greater than the monotonic strain-hardening exponent. Effective S–N diagram for the RCF loading of the case-hardened steel has been presented and the effect of compressive mean stress on its fatigue strength has been explained using Haigh diagram. The compressive mean stress correction according to Haigh diagram predicts that the allowable fatigue strength of the steel increases by a factor of two compared to its fatigue limit before mean stress correction, thus potentially allowing the rolling element bearings to operate over several hundred billion cycles. The methodology presented here is generalized and can be adopted to obtain the constitutive response and S–N diagrams of both through- and case-hardened steels subjected to RCF.

Optimization of Test Parameters That Influence Erosive Wear Behaviors of Glass Fiber-Reinforced Epoxy Composites by Using the Taguchi Method

Abstract: This study describes the development of a multicomponent composite system consisting of thermoplastic epoxy resin reinforced with E-glass fiber and silicon dioxide (SiO2) particles and investigates its erosion behavior under different operating conditions. Due to the increasing importance of composites in engineering applications and the need to tackle solid particle erosion in various industrial sectors, the study aims at finding how these composites behave in such type of wear. The composite specimens used for the tests were classified into three types; pure glass fiber (GF)‐epoxy, those with addition of SiO2 particles at an amount of 15% and the last group had SiO2 particles added at 30% of the resin used for the materials. The experiments were carried out by selecting three different impact velocities, three different impingement angles, and angular alumina abrasive particles having approximate sizes of 200 lm. The fiber directions used were 0/90/0 and 45/ � 45/45. SEM views belonging to the specimens were taken before and after the tests in order to investigate the differences and the causes of the surface damages. Moreover, it is found that the Taguchi’s robust orthogonal array method provides a simple, systematic, and efficient methodology for the optimization of the erosion wear parameters. At the end of the tests, the most significant factor in affecting the erosion rate is found to be the impingement angle, followed by the impact velocity, fiber direction, and filler material. [DOI: 10.1115/1.4028226]

A New Three-Dimensional Numerical Model of Rough Contact: Influence of Mode of Surface Deformation on Real Area of Contact and Pressure Distribution

Abstract: Surface roughness causes contact to occur only at discrete spots called microcontacts. In the deterministic models real area of contact and pressure field are widely evaluated using Flamant and Boussinesq equations for two-dimensional (2D) and three-dimensional (3D), respectively. In this paper, a new 3D geometrical contact approach is developed. It models the roughness by cones and uses the concept of representative strain at each asperity. To discuss the validity of this model, a numerical solution is introduced by using the spectral method and another 3D geometrical approach which models the roughness by spheres. The real area of contact and the pressure field given by these approaches show that the conical model is almost insensitive to the degree of isotropy of the rough surfaces, which is not the case for the spherical model that is only valid for quasi-isotropic surfaces. The comparison between elastic and elastoplastic models reveals that for a surface with a low roughness, the elastic approach is sufficient to model the rough contact. However, for surfaces having a great roughness, the elastoplastic approach is more appropriate to determine the real area of contact and pressure distribution. The results of this study show also that the roughness scale modifies the real contact area and pressure distribution. The surfaces characterized by high frequencies are less resistant in contact and present the lowest real area of contact and the most important mean pressure.

Elastic Contact Between a Geometrically Anisotropic Bisinusoidal Surface and a Rigid Base

Abstract: In the current study, a semi-analytical model for contact between a homogeneous, iso-tropic, linear elastic half-space with a geometrically anisotropic (wavelengths are differ-ent in the two principal directions) bisinusoidal surface on the boundary and a rigid baseis developed. Two asymptotic loads to area relations for early and almost complete con-tact are derived. The Hertz elliptic contact theory is applied to approximate the load toarea relation in the early contact. The noncontact regions occur in the almost completecontact are treated as mode-I cracks. Since those cracks are in compression, an approxi-mate relation between the load and noncontact area can be obtained by setting the corre-sponding stress intensity factor (SIF) to zero. These two asymptotic solutions arevalidated 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 sol-utions to bridge these two asymptotic solutions. [DOI: 10.1115/1.4029537]Keywords: periodic elasticity, sinusoidal normal contact, geometrically anisotropic,fracture mechanics, FFT model, finite element model