Robert Jackson

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• PhD, Georgia Institute of Technology
• Professor at Auburn University

Rolling element bearings are an integral component of electric vehicles, supporting radial and axial loads in powertrain components such as electric motor shafts and wheel bearings. Fast-switching inverters enable precise, variable-control of motor performance at the cost of possible stray current leakage into mechanical components. These currents...

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 co...

This work presents a finite element (FE) study of a perfectly elastic axisymmetric sinusoidal-shaped asperity in contact with a rigid flat for different amplitude to wavelength ratios and a wide range of material properties. This includes characterizing the pressure required to cause complete contact between the surfaces. Complete contact is define...

In many devices and applications, electrical contacts are exposed to vibrations, sliding, or rolling conditions and are prone to the fretting-based degradation. Thus, lubricants are often employed in such contacts to reduce sliding wear and fretting corrosion. However, due to the non-conductive behavior of the lubricants with fluorocarbons and hydr...

Electrical contact is fundamental to almost every aspect of modern industry including the fast-growing electric vehicle industry. In metallic contacts in atmospheric conditions, most of the electrical current passes via the micro-junctions formed between two electrodes. The classic electrical contact theory predicts an infinite current density at t...

Surface characterization of additively manufactured specimens is confounded by their intricate geometries and the presence of various features, including asperities, undercuts, and deep, sharp valleys. Despite the need to understand the impact of surface features on many practical applications, there is a lack of consensus regarding the variability...

Surface roughness of additively manufactured metal parts has significant impacts on the part’s performance (e.g., fatigue resistance) and poses a significant roadblock to the wider adoption of metal additive manufacturing. This work aims to show that, in some cases, it is possible to estimate the depth of the deepest valley of an additively manufac...

As the performance and efficiency requirements of electric vehicles (EVs) continue to expand, the demand for advanced driveline lubricants has grown exponentially. Unlike traditional internal combustion engine (ICE) vehicles, EVs experience unique challenges, including increased acceleration and deceleration rates, higher operating speeds, and elev...

Electrical contact is fundamental to almost every aspect of modern industry, including the fast-growing electric vehicle industry. In metallic contacts in atmospheric conditions, most of the electrical current passes via the micro-junctions formed between two electrodes. The classic electrical contact theory predicts an infinite current density at...

As public attention is increasingly drawn toward more sustainable transportation methods, the popularity of electric vehicles (EVs) as part of the solution is rapidly expanding. Operating conditions within EVs can be severe compared to standard combustion powertrains, and the risk of electrical arcing across mechanical surfaces from electric leakag...

The random process model, also known as the multi-asperity contact model or statistical model, is one of the dominant methodologies for analyzing the contact between nominally flat rough surfaces. In 1975, Bush, Gibson, and Thomas developed a complete random process model (known as the BGT model) assuming that solid-solid contacts occur on the summ...

The authors realized that a few items should be discussed. Although the work is for elastic sliding contact, it could be adapted for elastic–plastic contact by employing an existing sliding elasto-plastic model [2,3]. These models are slightly different but originated at the same time. The paper by Jackson et al. provides equations to predict the t...

Leakage currents accelerate surface degradation of metal contacts via small scale arcing across lubricating films, but recent observations suggest that metallic nanoparticle additives in lubricants may be useful to improve contact performance. These findings prompted a study that examined electrically induced surface pitting of steel contacts in th...

The flash temperature in the sliding frictional contact between micro asperities has an important influence on the frictional characteristics of advanced functional ceramics. In this paper, the elastic sliding frictional contact of single three-dimensional micron/submicron scale asperity pair is considered. A three-dimensional finite element model...

Electrified mechanical contacts and electrical connectors are an integral part of electric vehicles, and their reliable performance is essential. This has become increasingly important for electric vehicles where leakage current could potentially load the motor bearings and many other contacts in the drive system. Such leakage current has been show...

Leakage currents accelerate surface degradation of metal contacts via small scale arcing across lubricating films, but recent observations suggest that metallic nanoparticle additives in lubricants may be useful to improve contact performance. These findings prompted a study dealing that examined electrically induced surface pitting of steel contac...

This work develops a numerical methodology for predicting the performance of an automotive piston ring system by considering contact and lubrication mechanics. The rough surface contact mechanics and lubrication occurs on a scale much smaller than the size of the piston rings and therefore the key aspect of the model is an algorithm that simultaneo...

There is a need to support the biofuel sector by utilizing waste materials for its production and utilizing co-products through an integrated approach. Due to bio-oil's diverse composition, its applications for foams and resins syntheses are emerging, but most importantly, as biolubricants, product with increasing global demand. In this study, four...

The design of a hydrostatic bearing pad is limited to simple geometry using analytical equations or one-parameter optimization based on experimental data. This study proposes and investigates a new two-parameter method for estimating optimal hydrostatic bearing pad proportions—recess area and position, using Computational Fluid Dynamics (CFD). In t...

This study investigates a new two-parameter method for estimating optimal hydrostatic bearing pad proportions. The design of a hydrostatic bearing pad is limited to simple geometry using analytical equations or one-parameter optimization based on experimental data. In this study, 3D static CFD model results were verified using analytical results an...

The potential lubrication mechanisms for articular cartilage remain as complex as the material itself. Many studies have examined systematically the effects of sliding velocity on the frictional response of cartilage but a systematic analysis of contact area remains largely uncharted. Here we explore this potential effect three ways: a constant for...

Connectors are widely used in electrical systems and are subject to a variety of degradation mechanisms that can negatively impact electrical performance. One major cause of degradation is vibration induced fretting. While there has been considerable work on the effects of general connector degradation and defects on high frequency characteristics,...

Electrical connectors are found in many electrical systems like computers, light switches, or electric vehicles and are present in a wide range of environments as a result. These contacts can often be subject to degradation from such things as fatigue and wear; if this degradation makes the electrical contact resistance across the connector/contact...

It has been five years since this review of elastic-plastic contact mechanics was published. The area still remains very active and many advancements have been made since then. This discussion summarizes these advances and points out what might be considered the most significant ones. In some cases experimental measurements have confirmed previous...

This work employees the modification of the Reynolds equation for computational efficiency by analyzing rough surfaces in the hydrodynamic flow regime through the use of flow factors. This analysis is aimed towards modeling the surface interactions and pressure variations across power cylinder components of an internal combustion engine, namely the...

In this article, the vital operational characteristics such as reliability, performance and remaining useful life (RUL), pertaining to the electromagnetic solenoid valves (SVs), which govern their successful functioning and safe operation during service, are taken into account via a thorough review of the literature. Significance of the coil insula...

Electrical contacts, although critically important for a wide range of applications, are susceptible to degradation due to fretting corrosion, especially when sliding and vibrations occur. To overcome fretting corrosion and sliding wear, lubricants are often used. However, the use of lubricants can cause other detrimental issues. Lubricants usually...

Carbon nanotube (CNT) reinforced 316L stainless steel (SS) composites were fabricated by laser powder bed fusion (LPBF) additive manufacturing (AM). This study focuses on microstructure evolution, hardness, and wear behavior. The wear behavior for AM 316L SS and 1 wt.% CNT/316L SS was studied by a dry sliding test under normal loads of 10, 15, and...

Recent advances in 2D nanomaterials, such as graphene, transition metal dichalcogenides, boron nitride, MXenes, allow not only to discover several new nanoscale phenomena but also to address the scientific and industrial challenges associated with the design of systems with desired physical properties. One of the great challenges for mechanical sys...

Tribological properties of biomass-derived oils (bio-oils) were experimentally investigated, and the properties were compared with that of standard mineral oils used for lubrication purposes. Bio-oils were obtained from fast pyrolysis (using poultry and pine), gasification (“gasitar” using pine) and hydrothermal liquefaction processes (using Scened...

The solution to an elastic-plastic rough surface contact problem can be applied to phenomena such as friction and contact resistance. Many different types of models have therefore been developed to solve rough surface contact. A deterministic approach may accurately describe the entire surface, but the computing time is too long for practical use....

Thrust bearings are widely used in many rotary industrial applications. In this work, a thrust bearing surface under the mixed lubrication regime is analysed and then optimised with aim for use in an injection moulded polymer bearing. A model which couples the mechanical deformation, boundary lubrication and solid contact is developed to investigat...

This study investigates the predictions of the real contact area for perfectly elastic rough surfaces using a boundary element method (BEM). Sample surface measurements were used in the BEM to predict the real contact area as a function of load. The surfaces were normalized by the root-mean-square (RMS) slope to evaluate if contact area measurement...

This work presents a finite-element model-based study of elastic cylindrical contact. The aim is to evaluate the transition between the plane stress and plane strain-based Hertz solutions when each assumption is most applicable. To accomplish this, a range of curvatures, widths, Poisson’s ratios, and friction coefficients are considered. The finite...

In this study, an experimental method is proposed to measure the real area of contact between an alumina sphere and an Al surface based on the adhesive transfer of the Au film and the scanning electron microscope in the back-scattered mode. A thin film of Au is sputtered on the alumina sphere before the indentation with the Al surface. After indent...

Various types of electrical connectors are available globally. Electrical connectors are one of the critical components in many applications including in the automotive sector. They are primarily used to supply high power (or high currents) to other connected devices such as batteries, electronics, motors, etc. in both conventional and hybrid/elect...

Three-dimensional deterministic models of rough surfaces can enrich the understanding of the influence of surface texture on contact and friction. However, most of the existing finite element contact models simply use the data measured from real rough surfaces directly and consider the shape between every two neighboring points to be a straight lin...

This study investigates the wear and mechanical properties of additively manufactured (AM) 17–4 precipitation hardening (PH) stainless steel (SS) and compares to those of conventionally manufactured (CM) wrought specimens. Disk shape specimens were fabricated by either a laser beam powder bed fusion (LB-PBF) process or a conventional manufacturing...

Closed-form finite-element empirical models are available for elastic and elastic–plastic spherical and sinusoidal contact. However, some of these models do not consider the effect of interaction with adjacent asperities or require extensive numerical resources because they employ a full 3-D model. Therefore this work has analysed and quantified th...

Fractal descriptions of rough surfaces are widely used in tribology. The fractal dimension, D, is an important parameter which has been regarded as instrument and scale independent, although recent findings bring this into question. A thrust bearing is analyzed in the mixed lubrication regime while considering the fractal nature. Surface data obtai...

Electrical contact failure can cause attenuation and phase shift of signals in communication systems. A major source of contact failure is degradation of the contact interface. Accordingly, it is important to investigate the impact of a degraded contact surface on signal transmission. In the present work, an equivalent model for the contact interfa...

Fresh and frozen cartilage samples of the fetlock, carpus, and stifle were collected from 12 deceased horses. Half were measured immediately following extraction, and half were frozen for seven days and then measured. Seven indentations (various normalized displacements) were implemented with an indention rate of 0.1mm/s. Solid phase aggregate modu...

The traction of a horse’s hooves is crucial in racing, orthopedic applications, and even walking because of the tendency of lower leg injuries such as lameness and hoof axis misalignment. In order to design better horseshoes and orthotics, an attempt was made to characterize the coefficient of friction of horse hooves using a tribometer, samples of...

The goal of this study was to develop a method of friction testing utilizing cartilage counter surfaces with a complete subchondral bone plate and compare the results to the cartilage on glass and metal (steel) counter surfaces. Articular cartilage surfaces with the underlying subchondral bone intact were not isolated through plug removal. Friction...

Measured surfaces are populated with an intermediate resolution by a novel method called spectral interpolation. The spectral interpolation method allows for sharp peaks and intermediate points to be smoothed by adding additional nodes while keeping the original surface and spectrum constant. Then, the effects of different resolutions on the area-l...

Electrical contacts are critically important for a wide variety of applications, including computing, automotive, manufacturing, and renewable energy technologies. Due to a combination of vibrations and environmental conditions, these contacts are often susceptible to fretting corrosion and other wear mechanisms. In many cases it is not possible to...

In the numerical study of rough surfaces in contact problem, the flexible body beneath the roughness is commonly assumed as a half-space or a half-plane. The surface displacement on the boundary, the displacement components and state of stress inside the half-space can be determined through the convolution of the traction and the corresponding infl...

The current work considers the multi-scale nature of roughness in a new model that predicts the static friction coefficient. This work is based upon a previous rough surface contact model, which used stacked elastic–plastic 3-D sinusoids to model the asperities at multiple scales of roughness. A deterministic model of a three-dimensional deformable...

For elastic contact, an exact analytical solution for the stresses and strains within two contacting bodies has been known since the 1880s. Despite this, there is no similar solution for elastic-plastic contact due to the integral nature of plastic deformations, and the few models that do exist develop approximate solutions for the elastic-perfectl...

Recently, the first author has obtained a model for adhesive contact near full contact under the JKR assumptions. The model shows, in the common case of low fractal dimensions, an ‘unbounded’ adhesion enhancement when larger and larger upper “truncation wavenumber” is considered in the spectrum of roughness, i.e. when we increase “magnification”. H...

In typical metallic contacts, stresses are very high and result in yielding of the material. Therefore, the study of contacts which include simultaneous elastic and plastic deformation is of critical importance. This work reviews the current state-of-the-art in the model-ing of single asperity elastic-plastic contact and, in some instances, makes c...

In this study, a new experimental method is proposed to measure the real area of contact between a ceramic sphere and an Al surface based on the adhesive transfer of the Au film and the Scanning Electron Microscope (SEM) in the back-scattered mode. A thin film of Au is sputtered on the ceramic sphere before the indentation with the Al surface. The...

The indentation of flat surfaces deforming in the plastic regime by various geometries has been well studied. However, there is relatively little work investigating cylinders indenting plastically deforming surfaces. This work presents a simple solution to a cylindrical rigid frictionless punch indenting a half-space considering only perfectly plas...

A purely normal contact problem of an elastic half-space with a three-dimensional periodic sinusoidal wavy surface and a rigid flat under the full stick condition is studied. The contacting points from mating surfaces have zero relative tangential displacement under the full stick condition. The scope of this study is restricted to a special case w...

This paper summarizes the submissions to a recently announced contact-mechanics modeling challenge. The task was to solve a typical, albeit mathematically fully defined problem on the adhesion between nominally flat surfaces. The surface topography of the rough, rigid substrate, the elastic properties of the indenter, as well as the short-range adh...

This work presents a finite element study of elasto-plastic cylindrical contact. The geometry could also be described as a vertically aligned disk whose axis of symmetry is parallel to the contact surface. The cylinder is considered to be in the plane stress state. The material of the cylinder is modeled as elasto-plastic with bilinear hardening (a...

The goal of this experiment was to develop and compare a novel, robust method of friction testing with cartilage counter surfaces, to previously published testing methods using glass and metal counter surfaces.

Recently, generalizing the solution of the adhesive-less random rough contact proposed by Xu, Jackson, and Marghitu (XJM model), the first author has obtained a model for adhesive contact near full contact, under the JKR assumptions, which leads to quite strong effect of the fractal dimension. We extend here the results with closed form equations,...

In this study, the concept of the fracture mechanics is used to solve the (i) frictionless purely normal contact and (ii) the similar material contact under the mutual actions of the normal and tangential load. Consider the contact region is simply connected, the out-of-contact regions can be treated as periodic collinear cracks. Through evaluating...

The behavior of an elastic plastic contact between a deformable three-dimensional sinusoidal asperity and a rigid flat under combined normal and tangential loading is investigated using the finite element method. The sliding inception is determined by the maximum shear stress criterion. The resulting junction growth and static friction coefficient...

During indentation it is often important to determine the relationship between the average pressure and the yield strength. This work uses slip line theory to determine this relationship for the case of a rigid cylinder indenting a frictionless perfectly plastic half-space (i.e. no hardening). The results show that the ratio between the average con...

This letter is in reference to a recent paper by Wiertlewski et al. (1) on the squeeze film levitation mechanism observed in vibrated fingertip contacts. The authors should be commended on an important finding about the squeeze film levitation effect in finger contacts. We would also like to take this opportunity to expand on several previous works...

Many single asperity models have been developed since the original statistical rough surface contact model was created by Greenwood and Williamson. Some models have sought to include plasticity, while others have changed the shape of the asperity such as to a wavy or sinusoidal peak. These models might improve the effectiveness of the statistical m...

This work studies the fractal dimensions of rough surfaces as calculated by several existing methods on measured and generated surface profiles. Two methods for generating rough surfaces are used in this work. The first one is to reconstruct the rough surface through the inverse Fourier transform based on a prescribed Power Spectrum Density (PSD) a...

Closed-form finite-element empirical solutions are available for elastic-plastic spherical and sinusoidal contact. However, some of these models do not consider the effect of interaction with adjacent asperities or require extensive numerical resources because they employ a full 3-D model. The present work has considered these factors during modeli...

This work studies the methods used to extract fractal dimensions from surface profiles and the applicability of fractals to measured surfaces. The work used generated surfaces to first evaluate these methods, and later applies the methods to measured surfaces. Two methods for generating surface profiles are used. The fractal dimension values of all...

Even with the various surface finishing techniques, all surfaces are rough with different structures and geometric characteristics over multiple scales. In this work, a profilometer is utilized to measure the profiles of different rough surfaces, and the profiles are characterized using a variety of statistical, spectral, and fractal methodologies....

High viscosity index (VI) fluids are beneficial in lubricating hydraulic systems because they are able to maintain their viscosity at high operating temperatures. New high viscosity index bio-derived hydraulic fluids were compared to more traditional hydraulic oils based on their lubricity and wear protection. The hydraulic fluids studied were biod...

This work presents a finite element study of a perfectly elastic axisymmetric sinusoidal shaped asperity in contact with a rigid flat for different amplitude to wavelength ratios and a wide range of material properties. This includes characterizing the pressure required to cause complete contact between the surfaces. Complete contact is defined as...

This paper introduces a new type of nanoparticle additive for tribological purposes. A nano-lubricant was synthesized and studied which consists of metallic silver nanoparticles suspended in polyethylene glycol (PEG). Silver nanoparticles were prepared directly in liquid PEG by introducing aqueous silver nitrate and subsequent reduction by PEG. The...

Nanoparticles when suspended in a lubricant can infiltrate small gaps between rough surfaces in contact and alter the contact's tribological performance. Strategically designed experiments were used to investigate the role of nanoparticles in a contact's tribology and the effect of nanoparticles on fully formulated oils. The experiments were run us...

During indentation, it is often important to determine the relationship between the average pressure and the yield strength. This work uses slip-line theory to determine this relationship for the case of a rigid sphere indenting a frictionless perfectly plastic half-space (i.e., no hardening). The results show that the ratio between the average con...