Stefan J. Eder

• DI Dr.
• Principal Scientist at AC2T Research GmbH / TU Wien

We consider a nanomachining process of hard, abrasive particles grinding on the rough surface of a polycrystalline ferritic work piece. Using extensive large-scale molecular dynamics (MD) simulations, we show that the mode of thermostatting, i.e., the way that the heat generated through deformation and friction is removed from the system, has cruci...

Using molecular dynamics, we simulate the abrasion process of an atomically rough Fe surface with multiple hard abrasive particles. By quantifying the nanoscopic wear depth in a time-resolved fashion, we show that Barwell’s macroscopic wear law can be applied at the atomic scale. We find that in this multiasperity contact system, the Bowden-Tabor t...

In this work we perform molecular dynamics simulations to quantify and parametrize the evolution of a bcc Fe work piece topography during nanometric grinding with multiple hard abrasive particles. The final surface quality depends on both the normal pressure and the abrasive geometry. We fit the time development of the substrate's root mean squared...

A post-processing method for molecular dynamics (MD) simulations of friction based on the smooth particle approach is proposed, allowing--among other features--the introduction and evaluation of a solid-solid contact area arising due to direct asperity interaction. In order to illustrate the feasibility of this scheme, a large number of MD calculat...

We present a molecular dynamics (MD) model system to quantitatively study nanoscopic wear of rough surfaces under two-body and three-body contact conditions with multiple abrasive particles. We describe how to generate a surface with a pseudo-random Gaussian topography which is periodically replicable, and we discuss the constraints on the abrasive...

Friction and wear of metals are critically influenced by the microstructures of the bodies constituting the tribological contact. Understanding the microstructural evolution taking place over the lifetime of a tribological system therefore is crucial for strategically designing tribological systems with tailored friction and wear properties. Here,...

Friction and wear of metals are critically influenced by the microstructures of the bodies constituting the tribological contact. Understanding the microstructural evolution taking place over the lifetime of a tribological system therefore is crucial for strategically designing tribological systems with tailored friction and wear properties. Here,...

Scratch testing has been a widely used technique to obtain valuable information about the mechanical properties of materials, including their hardness, adhesion, and wear resistance. Scratch tests have the advantage over tension, compression, or torsion tests to be a non-destructive technique that does not require complex geometries in its test spe...

The understanding and experimentation of abrasive wear mechanisms at high speeds is still poorly investigated in literature. This is mainly due to a lack of suitable, well-instrumented test rigs for fundamental, single abrasive wear events. Standard scratch tests, which are often utilized for studies of abrasion phenomena, operate in the low-speed...

An efficient optimization of surface finishing processes can save high amounts of energy and resources. Because of the large occurring deformations, grinding processes are notoriously difficult to model using standard (mesh-based) micro-scale modeling techniques. In this work, we use the meshless material point method to study the influence of abra...

Reactive molecular dynamics simulations of Ti 3 C 2 T x with three different surface terminations were used to understand friction and failure of MXenes during sliding at normal pressures from 2–20 GPa and temperatures from 300–1100 K. The O-terminated MXene had the smallest shear stress at low pressures and temperatures, but failed at more severe...

This review explores the intersection of tribology and dermatology, explicitly focusing on studying the human skin and drawing inspiration from natural systems. It investigates animal adaptations and their implications for biotribological applications, with examples such as the friction anisotropy and wear tolerance of snakeskin, the healing proper...

The understanding and experimentation of abrasive wear mechanisms at high speeds is still poorly investigated in literature. This is mainly due to a lack of suitable, well-instrumented test rigs for fundamental, single abrasive wear events. Standard scratch tests, which are often utilized for studies of abrasion phenomena, operate in the low-speed...

Many modern applications rely on the safe operation of components sliding at high speeds, e.g., in the fields of e-mobility, high-speed manufacturing, or impact-resistant materials. While the impact of mechanical energy and heat on the friction and wear behavior of dry metallic interfaces has been the focus of extensive research in the past, the ef...

Reactive molecular dynamics simulations of Ti 3 C 2 T x layers with three different surface terminations were used to understand friction and failure of MXenes during sliding. O-terminated MXenes had the smallest shear stress at low pressures and temperatures, but failed at more severe conditions due to interlayer bonding and the formation of Ti-O-...

Coarse-grained, metallic materials undergo microstructure refinement during tribological loading. This in turn results in changing tribological properties, so the microstructural evolution is a parameter which should not be underestimated while designing tribological systems. Single-trace experiments were conducted to understand the initiation of d...

Reactive molecular dynamics simulations were used to investigate reactions between di-tert-butyl disulfide and ferrous surfaces. Tribochemical reactions were characterized with and without a model base oil, n-dodecane, and on either Fe(100) or H-passivated Fe2O3 surfaces. Reaction yield increased with both temperature and pressure for all model sys...

With the rapid development of nano-polishing technology, ultra-precise micro-nano components require tighter tolerances for the surface engineering of the Invar alloy. Due to its low hardness and high chemical activity, it is a challenge to obtain high-quality surfaces with a nanometric finish for Invar, and the mechanical mechanism guiding the nan...

The microstructural evolution in the near-surface regions of a dry sliding interface has considerable influence on its tribological behavior and is driven mainly by mechanical energy and heat. The emerging field of computational materials tribology (CMT) aims to shed light on the interactions between tribology and materials science by modeling engi...

Chemical reactions in sliding contacts driven by the combined effects of heat, pressure, and shear underlie the function of lubricant additives that protect surfaces from friction and wear. However, the interplay between thermal and mechanical effects in driving these important reactions, as well as the roles of base oil molecules and the surface c...

With the rapid development of nano-polishing technology, ultra-precise micro-nano components require tighter tolerances for the surface engineering of the Invar alloy. Due to its low hardness and high chemical activity, it is a challenge to reveal the nano-polishing mechanism experimentally. In this work, we studied the effect of polishing paramete...

Scratch tests are a powerful and inexpensive tool for studying the mechanical properties of materials. The tests are typically applied for determining the deformation behavior of materials and serves as quality assessment method for measuring the adhesion and delamination properties of coatings. However, the extraction of quantitative material para...

Many modern applications rely on the safe operation of components sliding at high speeds, e.g., in the fields of e-mobility, high-speed manufacturing, or impact-resistant materials. While the impact of mechanical energy and heat on the friction and wear behavior of dry metallic interfaces has been the focus of extensive research in the past, the ef...

In this work, we employed a custom-built tribometer that allows simultaneous testing of five porous journal bearing systems to perform lifetime tests on combinations of bearing materials and lubricants at various temperatures. Test parameters and contact conditions were tailored to promote mixed/boundary lubrication and accelerated wear tests. Fail...

Coarse-grained, metallic materials undergo microstructure refinement during tribological loading. This in turn results in changing tribological properties, so understanding deformation under tribological load is mandatory when designing tribological systems. Single-trace experiments were conducted to understand the initiation of deformation mechani...

Depending on the mechanical and thermal energy introduced to a dry sliding interface, the near-surface regions of the mated bodies may undergo plastic deformation. In this work, we use large-scale molecular dynamics simulations to generate “differential computational orientation tomographs” (dCOT) and thus highlight changes to the microstructure ne...

In this work, we present a fully atomistic approach to modeling a finishing process with the goal to shed light on aspects of work piece development on the microscopic scale, which are difficult or even impossible to observe in experiments, but highly relevant for the resulting material behavior. In a large-scale simulative parametric study, we var...

A fundamental optimization of a grinding process usually involves expensive equipment and experimental matrices covering a large parameter space. To aid this often cumbersome procedure, here we present three simulation approaches that are intrinsically related and even use the same software, but consider the grinding process at different levels of...

Artificial lift systems are widely used in oil production, of which sucker rod pumps are conceptually among the simpler ones. The reciprocating movement of the plunger triggers the opening and closing of two ball valves, allowing fluid to be pumped to the surface. Their built-in ball valves are subject to long-time erosion and fail as a consequence...

State-of-the-art forming applications, machining, and wear processes generally involve large deformations under high speeds which are often limited to surface near zones. Hence, knowledge about a material’s behaviour under such conditions is essential to understand wear or deformation. In this work, two techniques are combined to study the behaviou...

Depending on the mechanical and thermal energy introduced to a dry sliding interface, the near-surface regions of the mated bodies may undergo plastic deformation. In this work, we use "differential EBSD tomography" to highlight changes to the microstructure near tribological fcc alloy surfaces, allowing us to detect subtle differences in lattice o...

The microstructural evolution in the near-surface regions of a dry sliding interface has considerable influence on its tribological behavior and is driven mainly by mechanical energy and heat. In this work, we use large-scale molecular dynamics simulations to study the effect of temperature on the deformation response of FCC CuNi alloys of several...

In this study, we perform accelerated wear tests with porous journal bearings (PJBs) on a lab test rig, providing statistically reliable results under realistic operational conditions. To this end, a custom-made tribometer consisting of 5 mechanically independent but centrally controlled units was used to test five identical bearings in parallel. T...

RPM-Synchronous Grinding (RSG) opens up a wide range of applications, as this manufacturing process enables the efficient production of components with a functional macro geometry as well as a functional micro geometry of the surface. Unlike conventional non-circular grinding approaches, the RSG process strategy requires no oscillation of the infee...

Artificial lift pumps are widely used in oil production, and among them, sucker rod pumps are conceptually the simplest ones. The reciprocating movement of the plunger triggers the opening and closing of two ball valves, allowing fluid to be pumped to the surface. These valves are subject to long-time erosion and fail as a consequence of this damag...

Microstructural changes in the near-surface regions of a material determine its mechanical properties and consequently also its tribological behavior. This work is a study of the microstructural development of nanocrystalline ferrite subjected to a grinding process using molecular dynamics simulations. We visualize the work piece by producing vario...

The origin of friction and wear in polycrystalline materials is intimately connected with their microstructural response to interfacial stresses. Although many mechanisms that govern microstructure evolution in sliding contacts are generally understood, it is still a challenge to ascertain which mechanisms matter under what conditions, which limits...

Purpose This paper aims on a methodology to overcome the fact that conventional service life testing of porous journal bearings (PJBs) requires long test times and is not economical. Design/methodology/approach This paper sketches out a pathway to strongly accelerated life tests for PJBs enabled by high load and elevated temperature, which saves m...

Tribochemistry, the study of chemical reactions in tribological interfaces, plays a critical role in determining friction and wear behavior. One method researchers have used to explore tribochemistry is “reactive” molecular dynamics simulation based on empirical models that capture the formation and breaking of chemical bonds. This review summarize...

In this work we present a combined finite element model of a standing valve and a travelling valve in a down-hole pump used in oil extraction. The model allows the self-consistent simulation of several pump cycles without the need to assume artificial coupling conditions between two separate valves, at the cost of large variations in length of the...

The surfaces of lubricated mechanical components operating under extreme conditions are protected by films that form in the presence of additives in lubricant formulations. Film formation is believed to be accelerated by heat, load, and shear force in the sliding interface, but the individual contributions of these factors are poorly understood. In...

Abrasive wear limits the lifetime of key components and wear parts used in various applications. Damage is caused by indentation of harder particles into the wearing materials and subsequent relative motion resulting in ploughing, cutting, and fracture phenomena. The wear mechanisms depend mainly on the applied materials, loading conditions, and ab...

In some forming industrial applications, hot steel components leave the rolling train with speeds ranging from 1 to 10 m/s, sliding against fixed components. Scratching of the surface is often inevitable, especially in presence of hard oxides. The experimental assessment of this tribosystem is highly challenging since scratch experiments are typica...

We employ a variant of the joint time-frequency analysis (JTFA) for identifying transient, temperature-dependent noise emitted from porous journal bearings operated at temperatures between −40 °C and 0 °C. This phenomenon, called “cold squealing” is difficult to reproduce in laboratory environments, as it requires a suitable (and typically system-s...

We present a lab-2-field type approach to comparing the wear resistance of several material pairings of ball valves used in oil production. With the ongoing transition from stellite to hard metals in down-hole pump valve components, the durability and service life of these new material pairings must be known. We have established a workflow based on...

The innovative RPM-Synchronous Grinding process enables highly efficient manufacturing of various geometries in an ordinary plunge grinding process. An oscillation of the infeed axis, which is coupled to the rotary workpiece spindle axis, like in conventional non-circular grinding approaches is not required. This is achieved by using a fixed ratio...

Iron sulfide films are present in many applications, including lubricated interfaces, where protective films form through the reactions of lubricant additive molecules with steel surfaces during operation. Such films are critical to the efficiency and useful lifetime of moving components. However, the mechanisms by which films form are still poorly...

This paper describes the measures undertaken to increase the run life of sucker rod pump (SRP) installations in the past five years in OMV Austria. Around 500 wells are currently operated with SRPs with an average water cut of 95%. Recurrent pump failures, caused by corrosion, mechanical wear, gas and sand production, significantly contribute to th...

A meshless generalized interpolation material point method for simulating the micro-milling process was developed. This method has several advantages over well-established approaches (such as finite elements) when it comes to large plastic strains and deformations, since it inherently does not suffer from tensile instability problems. The feasibili...

We performed large-scale molecular dynamics (MD) simulations to study the transient softening stage that has been observed experimentally in sliding interfaces subject to strain path changes. The occurrence of this effect can be of crucial importance for the energy efficiency and wear resistance of systems that experience changes in sliding directi...

A meshless Generalized Interpolation Material Point Method for simulating the micro-milling process was developed. This method has several advantages over well-established approaches (such as finite elements) when it comes to large plastic strains and deformations, since it inherently does not suffer from tensileinstability problems. The feasibilit...

We employ a variant of the joint time-frequency analysis (JTFA) for identifying transient, temperature-dependent noise emitted from porous journal bearings operated at temperatures between -40°C and 0°C. This phenomenon, called "cold squealing", is difficult to reproduce in laboratory environments, as it requires a suitable (and typically system-sp...

We present an experimental and analysis workflow to characterize the tribological behavior and the wear resistance of porous journal bearing systems operating at high loads and small rotational speeds. Our approach consists of a laser-instrumented tribometer that allows parallel testing of five bearings, an experimental procedure that is optimized...

Abrasive wear of key components is a critical process limiting the lifetime of machinery for mining or farming. However, materials and process parameters are mostly based on empirical data since the underlying wear mechanisms in the field are not well known. In order to assess and predict the effects of abrasive wear on typical tillage machine comp...

We present an experimental and analysis workflow to characterize the tribological behavior and the wear resistance of porous journal bearing systems operating at high loads and small rotational speeds. Our approach consists of a laser-instrumented tribometer that allows parallel testing of five bearings, an experimental procedure that is optimized...

Single-impact tests and molecular dynamics (MD) simulations are performed to evaluate effects at energy- and momentum-variable impact phenomena at two distinct scales and velocity ranges. Therefore, a carbon steel in various heat treatment conditions is examined using the single impact test to evaluate the influence of varying energies and momenta...

We consider a nanomachining process of hard, abrasive particles grinding on the rough surface of a polycrystalline ferritic work piece. Using extensive large-scale molecular dynamics (MD) simulations, we show that the mode of thermostatting, i.e., the way that the heat generated through deformation and friction is removed from the system, has cruci...

Scratch testing is an inexpensive technique used for determining the mechanical/wear properties of materials and coatings. In contrast to instrumented indentation, where quantitative relations have been established, only few studies are devoted to quantitatively understanding the material response during scratch testing. Most modelling approaches r...

In this work we discuss a method to generate laterally periodic polycrystalline samples with fractal surfaces for use in molecular dynamics simulations of abrasion. We also describe a workflow that allows us to produce random lateral distributions of simple but realistically shaped hard abrasive particles with Gaussian size distribution and random...

Mittels einer bei AC²T entwickelten Methodik werden polykristalline Werkstoffe bis zu einer lateralen Größenordnung von 100x100 nm² (zig Millionen Atome) voll atomar modelliert und damit mesoskopische Werkstoffveränderungen aufgrund einer tribologischen Belastung simuliert. Besonderes Augenmerk wird darauf gelegt, dass die Systemvisualisierungen ge...

SPH ist im Gegensatz zur FEM eine netzunabhängige, partikelbasierte Kontinuum Methode und erlaubt es starke Deformationen und Materialablösung, wie sie etwa bei der Rissausbreitung oder bei Ritzversuchen auftreten, zu untersuchen. Unsere SPH-Simulationen zeigen gute Übereinstimmung mit Experimenten und Anlagenkomponenten und können helfen diese zu...

We use a molecular dynamics approach to simulate the wear of a rough ferrite surface due to multiple hard, abrasive particles under variation of normal pressure, grinding direction, and particle geometry. By employing a clustering algorithm that incorporates some knowledge about the grinding process such as the main grinding direction, we can break...

This study deals with a comparison between new experiments on the frictional behavior of porous journal bearings and its prediction by previous numerical simulations. The tests were carried out on bearings lubricated with polyalphaolefin-based oils of distinct viscosities. The theoretical model underlying the simulations includes the effects of cav...

We present an implementation of a (mesh-free) smooth particle hydrodynamics (SPH) algorithm, intended for the application to solid bodies, and use it to simulate scratch-induced surface damage on an elasto-viscoplastic material. If conventional SPH is used to simulate solids, an unphysically high artificial viscosity is required to damp strong osci...

A quantitative molecular dynamics (MD) study of nanoscopic wear under dry grinding and polishing conditions with multiple abrasive particles (grits) is presented. The initial topography of the monocrystalline iron surface has a pseudo-random Gaussian height distribution, and the sixteen rigid abrasive grits have cuboid or spherical geometries. The...

The presence of water in biofuels poses the question of how it affects the frictional performance of additives in fuels containing organic substances. To investigate the effect of water on the adsorption of molecules present in fuel and its additives we simulated within the framework of density functional theory the adsorption of ethanol, isooctane...

Van der Waals (vdW) forces play a fundamental role in the structure and behavior of diverse systems. Thanks to development of functionals that include non-local correlation, it is possible to study the effects of vdW interactions in systems of industrial and tribological interest. Here we simulated within the framework of density functional theory...

A quantitative molecular dynamics (MD) study of nanoscopic wear under dry grinding and polishing conditions with multiple abrasive grits is presented. The initial topography of the monocrystalline iron surface has a pseudo-random Gaussian height distribution, and the sixteen rigid abrasive grits have cuboid or spherical geometries. The grinding and...

Very recently, copper nanowires have become promising low-cost candidates for transparent high-performance conductors in dye-sensitized solar cells. As these nanowires are usually mounted to a flexible substrate, a sound knowledge of their mechanical properties on that length scale is critical to their functionality and reliability. Classical tensi...

We present a molecular dynamics (MD) model system simulated with LAMMPS to quantitatively study nanoscopic wear of rough surfaces under two-body (grinding) and three-body (polishing) contact sliding conditions with multiple abrasive particles. We describe how to generate a surface with a pseudo-random Gaussian topography which is periodically repli...

Using a thin film lubrication regime we investigated the PFPE-Z confined lubricant behaviour. The results of our simulations take into consideration the effect both of pressure and relative velocity of the confining walls. The occurring stick-slip phenomena are explored in detail. It was found that the lubricant properties change near the walls. Al...

We show how data obtained from molecular dynamics (MD) simulations of nanoscale friction should be treated for producing constitutive system parameters with a proper error estimation. A visualisation scheme for discrete atomistic geometries based on the smooth particle method (SPM) was parametrised and validated to yield an accurate and computation...

We performed molecular dynamics simulations of boundary-lubricated sliding, varying the boundary lubricant type, its molecular surface coverage, the substrate roughness, and the load. The resulting load versus friction behavior was then analyzed to study how changes in lubricant type, coverage, and roughness affect the extrapolated friction force a...

Nanoscopic changes in the lubricant composition, coverage, or the surface topography affect the tribological performance of a given boundary-lubricated system. The exact knowledge of the underlying mechanisms can enable designers of appliances with thin-film lubricated friction interfaces to tailor and fine-tune the lubrication gap towards certain...

A molecular dynamics simulation study has been conducted in order to point out the effect of steady shear and loading pressure on lubricant thin films. The model used in these simulations is composed of two solid walls and PFPE-Z lubricant. We apply steady shear by moving the walls in opposite directions while at the same time the upper wall exerts...

Tribological phenomena such as friction and wear are of a multiscale nature, they are hierarchical in length and time. Therefore tribological systems can be realistically modeled/simulated only in a multiscale fashion, namely by coupling various computational methods which are suitable within the range of their typical length/time scales. The compu...

The present study describes the most relevant bonding mechanisms and geometries involved in the de-position of organic molecules on a solid metallic surface by means of ab initio calculations. In particular, the deposition of isooctane and ethanol on crystalline Fe are presented in detail in this contribution. First-principles calculations are perf...

Professor Spencer opened the discussion of the paper by Professor Evans: Presumably the profilometry data were measured by some kind of mechanical profilometer, with a well-defined cutoff length corresponding to the size of the stylus. Of course you could have used other methods to include shorter size-scale roughness features. What is the sensitiv...

A post-processing method, which maps the punctiform atoms in molecular dynamics (MD) simulations of boundary lubrication onto smoothed particles, is used to estimate the asperity contact area defined by the minimum cross-section of the formed solid bridges. It is then shown that this asperity contact area excellently agrees with the projected area...

A post-processing method recently developed by the authors is presented which allows one to easily map molecular dynamics (MD) results onto continuum. This is done by replacing the pointwise MD-representation of atoms with smoothed particles (SP), using kernel functions (e.g. cubic splines) which then uniquely define the atomic contributions to any...

In this paper we consider the phenomenon of vaporisation cavitation in a porous journal bearing. To this end, we solve the coupled problem consisting of the Reynolds equation applied in the bearing gap and the well known Darcy's law, which describes the fluid flow through the sintered seat of the journal. The nonlinearities introduced by the emerge...

A large number of molecular dynamics (MD) simulations of lubricated nanotribological systems with plastically-yielding single asperity contacts were carried out and investigated in view of the effect of asperity shape and solid-solid contact on the friction-load dependence using a recently developed post-processing method based on the smooth partic...