Georg Vorlaufer

Georg Vorlaufer
AC2T Research GmbH | AC2T · Modelling & Simulation

Dipl. Ing. Dr.

About

71
Publications
15,705
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545
Citations
Additional affiliations
November 2002 - present
AC2T Research GmbH
Position
  • Group Leader

Publications

Publications (71)
Article
The aim of this work is to quantify the relationship between different methods of artificial oil alteration as well as engine oils collected from a passenger car using FTIR (Fourier-transform infrared) spectroscopic data and chemometric methods. We propose a comprehensive procedure for the analysis of FTIR spectra: First, a reconstruction-error bas...
Article
Hardness is routinely utilized to link the bulk material properties to surface contact mechanics. Besides possible differences in the material properties between bulk and surface, there is no established relation between hardness and the thermo-viscoplastic flow stress of materials used in the context of metal forming processes. The purpose of this...
Article
Full-text available
The existing knowledge of interfacial forces, lubrication and wear of bearings in real-world operation has significantly improved their designs over time for prolonged service life. As a result, self lubricating bear-ings have become a viable alternative to traditional bearing designs in industrial machines. However, wear mechanisms are still inevi...
Article
Full-text available
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...
Conference Paper
Full-text available
The visual examination of the interfaces in relative motion is impossible, which hampers wear state recognition. Furthermore, the time-based maintenance strategies involving visual inspection also result in machine downtime. As an alternative to these non-efficient examination strategies, real-time monitoring using sensors and machine learning (ML)...
Article
Full-text available
Tribologists often rely on triboexperiments to investigate factors that affect a tribosystem. The inherent dynamic behavior of the respective tribometer setups and its effect on data interpretation remain often unknown. In this study, a comprehensive analysis of sensor data obtained from lubricated and dry triboexperiments is performed. Data are ge...
Article
Full-text available
Functional surfaces in relative contact and motion are prone to wear and tear, resulting in loss of efficiency and performance of the workpieces/machines. Wear occurs in the form of adhesion, abrasion, scuffing, galling, and scoring between contacts. However, the rate of the wear phenomenon depends primarily on the physical properties and the surro...
Article
Full-text available
For a tribological experiment involving a steel shaft sliding in a self-lubricating bronze bearing, a semi-supervised machine learning method for the classification of the state of operation is proposed. During the translatory oscillating motion, the system may undergo different states of operation from normal to critical, showing self-recovering b...
Article
Full-text available
The contact between solids in metal-forming operations often involves temperature-dependent viscoplasticity of the workpiece. In order to estimate the real contact area in such contexts, both the topography and the deformation behaviour should be taken into account. In this work, a deterministic approach is used to represent asperities in appropria...
Article
During the production of cardboard food cans, the packaging bottom and the cylindrical wall are joined in the seaming process. In order to achieve a high-quality, crack-free surface of the cardboard seam, low friction between the seaming chuck and the cardboard must be ensured. The goal of this study was to minimise the friction between the seaming...
Article
In the cardboard package production process, the cardboard roll and the cardboard bottom are joined in the seaming process. During the process, the cardboard is plastically deformed and damage to the cardboard surface can occur. The purpose of this study was to optimise the macrogeometrical parameters of the seaming chuck in order to minimise the c...
Article
For the production process of cardboard cans, the bottom of the packaging and the paper roll are joined together (flanged and glued) in a flanging process. During this process, the paperboard is plastically deformed and high elongations can occur in the product, which, under unfavourable process conditions, lead to damage of the paperboard surface....
Article
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...
Article
Pure elastomers usually show poor sliding properties due to their high adhesion tendency. In order to improve these sliding properties, intermediate materials (oils, greases, lacquers, etc.) are used to separate or functionalise the contact surfaces. Another possibility for an improvement of sliding properties is to reduce the adhesion tendency, fo...
Preprint
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...
Article
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...
Article
Die Senkung von Entwicklungszeiten und Kosten sind wesentliche Treiber für die produzierende Industrie. Gerade die Entwicklung neuer Werkstoffe zeigt dahingehend ein großes Potential, dass die derzeit eingesetzten Standardentwicklungsprozesse extrem zeit- und kostenaufwendig sind. In diesem Beitrag wird eine Lab-2-Field Methode vorgestellt, welche...
Article
In this paper we present a routine to predict wear behaviour of multiphase materials commonly used in brake applications. The material selection for friction materials have to take into account numerous influencing factors, partially with strong mutual dependencies. Thus, increasing the life-time based solely on traditional engineering experience i...
Article
Full-text available
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...
Article
Experiments carried out during the last 50 years have elucidated the basic mechanism of the Biefeld-Brown effect. Recent research has focused on establishing design rules in order to maximize the lifting force resulting from this effect. For this purpose, a numerical estimation that takes the effect of altitude into account is needed. In the presen...
Article
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...
Article
Full-text available
The containers used for steel slag transportation to the recycling depot undergo high-temperature gradients and often deform plastically. Also, parts of the thereby solidified slag adhere to the pot walls, causing demolding problems and wear. A thorough finite-element analysis of the heat transfer, initiated by filling the pots and essentially driv...
Article
Full-text available
To describe and predict wear in a tribosystem, theoretical wear formulas and empirical models exist. Most of the existing formulations have a short range of validity and can only be applied for a specific contact situation. In this paper, the aim is to investigate a specific technical application of a tribocontact in an internal combustion engine....
Article
A computational scheme is presented that takes into account the topography, i.e. the shadowing and hence the local emission angle of the electrons when evaluating AR-XPS data of macroscopic rough surfaces. The topography of the sample surface is supposed to be recorded by atomic force microscopy and/or optical microscopy. The emitted photoelectrons...
Conference Paper
Full-text available
To decrease mechanical losses in internal combustion engines (ICE) a deeper understanding of the friction and wear processes in the main tribosystems is necessary. In particular, the interrelation between frictional energy and wear has to be analyzed. For this reason the hard to measure quantity of coefficient of accumulation of frictional energy,...
Conference Paper
Full-text available
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...
Article
In order to numerically simulate the contact pressure distribution and area during sliding when wear occurs, the combined finite element method and boundary element method (FEM–BEM) developed by the authors is extended based on a linear wear law merged with the space- and time-resolved cumulative dissipated frictional energy. In each computed time...
Article
Full-text available
Because of the machine size of high pressure piston compressors mainly journal bearings are used in the crank drive. Tribological system properties at hydrodynamic lubrication are minimizing friction and wear. Numeric modelling and simulation on the basis of the Finite-Element-Method (FEM) is used to describe the dynamic lubrication conditions in c...
Article
In the present contribution, the strategy of atomic force microscope mapping of periodical rough surfaces is combined with an extension of the polyhedral model. Atomic force microscope images are numerically interpolated, applying non-uniform rational B-splines, which also have the advantage that simultaneously to the interpolation, they provide th...
Article
The experimentally determined topographies of engineering surfaces are decomposed using multiresolution analysis to better understand the impact of surface roughness on angle-resolved XPS. Multiresolution analysis is a powerful mathematical tool based on wavelets, which allows one to unambiguously distinguish between the roughness, waviness, and sh...
Article
Full-text available
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...
Article
An extremely small roughness of constant height magnitude is considered on the femoral head of an artificial hip joint in order to determine the consequences of various regular shapes and clearances on the mechanical performance of this hip prosthesis via a properly coupled finite and boundary element method. In addition, different material combina...
Conference Paper
Full-text available
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...
Conference Paper
Full-text available
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...
Conference Paper
Full-text available
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...
Article
Full-text available
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...
Article
Grinding processes causes the formation of a characteristic surface structure, known as chatter marks. In this work, an angle-resolved light scattering technique is used to characterise them. In order to identify the chatter marks in a measured profile, the fast Fourier transform (FFT) is usually applied to the measured data. The FFT, however only...
Article
Material transfer in a low-power direct-current switchgear is commonly known to cause contact failures to open due to mechanical interlocking, which is determined by (i) the shape of the material transfer pip-and-crater formation and (ii) the relative movement of the contact pieces during contact separation. The aim of this work is to analyze the i...
Article
Industrially ground surfaces often have a characteristic surface topography known as chatter marks. The surface finishing is mainly monitored by optical measurement techniques. In this work, the monitoring of an industrial belt grinding process with a light scattering sensor is presented. Although this technique is primarily applied for parametric...
Article
A two-scale approach to the diffuse light scattering from rough surfaces is proposed and applied for the first time. On the microscopic scale, the inter- and intra-layer contributions to the complex optical conductivity tensor are quantum mechanically calculated ab initio, based on the Luttinger formalism and by means of a contour integration withi...
Article
Full-text available
The functionality of the lifting is exploited scheme to analyze several white light confocal images of tribological/ engineering surfaces in terms of their roughness, waviness and form. The roughness parameters obtained are then compared with those resulting from other standard filtering techniques, like Gaussian filtering. Based on the wavelet tra...
Conference Paper
Full-text available
Shear of three rough boundary-lubricated tribosystems (fatty acid on Fe) with different asperity geometries was simulated at the critical lubricant density (i.e. at load-dependent occurrence of solid-solid contact) for various loads.
Conference Paper
Full-text available
In this article, an overview of the concept of multiscale modelling is given. Two of the mentioned methods are used as examples how different approaches have to be taken to solve contact mechanical problems at different length and time scales. The first, a coupled finite element – boundary element scheme, describes surface topography changes at the...
Conference Paper
Full-text available
In the present work, the tribological properties of different prototypical automotive lubricant additives are studied and compared. The simulated model tribosystems are made up of two amorphous iron substrates. The boundary lubricant between these sliders consists of one self-assembled monolayer (SAM) of fatty acid or fatty acid methyl ester (FAME)...
Conference Paper
Full-text available
Molecular dynamics (MD) simulations constitute a powerful tool to gain insight into physico-chemical lubricant behaviour, plastic substrate deformation and other structural changes in nanotribological junctions. MD operates at resolutions high enough to visualise and analyse these tribologically relevant phenomena sufficiently, yet it is capable of...
Article
In this work, a comparison of three different methods for analysing topographies and roughness on machined metal surfaces is presented. To obtain comparable results, the measurements were done on one and the same set of samples. For this purpose, an atomic force microscope (AFM), a confocal white light microscope, and a scattering light system were...
Article
Full-text available
A novel formulation of elastic multi-asperity contacts based on the boundary element method (BEM) is presented for the first time, in which the influence coefficients are numerically calculated using a finite element method (FEM). The main advantage of computing the influence coefficients in this manner is that it makes it also possible to consider...
Conference Paper
Full-text available
The present work makes use of atomistic simulations to shed some light on the key processes involved when a boundary lubricant fails, resulting in direct interaction between solid nano-asperities, which causes a rise in the coefficient of friction and increased wear. The simulated model tribosystems are made up of two amorphous iron substrates with...
Conference Paper
Material transfer in low-power direct-current switchgear is commonly known to cause contact failures to open due to mechanical interlocking, which is determined by (i) the shape of the material transfer pip-and-crater formation and (ii) the relative movement of the contact pieces during contact separation. A novel method is presented, which allows...
Article
Stick-Slip phenomena in wet friction disc systems used in drive trains of modern vehicles can canse comfort decreasing vibration or noise. For the investigation and characterization of these phenomena, a disc-on-disc tribometer is used at the Austrian Center of Competence for Tribology (AC 2T research GmbH). This study presents a method which allow...
Conference Paper
Full-text available
The nanotribological characteristics of lubricated friction contacts generally differ greatly from their macroscopic properties. Especially as the gap between the counteracting bodies decreases in size, (entering the boundary lubrication regime) and atomistic effects come into play, continuum mechanics cease to deliver viable results. Molecular dyn...
Article
Stick-Slip phenomena in wet friction disc systems used in drive trains of modern vehicles can cause vibration or noise which considerably decrease comfort of drives and passengers. For the investigation and characterization of these phenomena, a disc-on-disc tribometer is used at the Austrian Center of Competence for Tribology. A method is presente...
Conference Paper
Contacts, switching DC loads, can create material transfer pip and crater formations which may cause non opening faults due to interlocking. Both, the material transfer formation and the capability to open the contacts at pronounced material transfer, are affected by the design parameters of the contact system. Since the decoupling of these two phe...
Conference Paper
Full-text available
The steep increase in available computational power in the past decade has enabled the development of an atomistic theory of friction. Nanoscopic computer simulations have since uncovered shortcomings and even flaws in previous models, and allowed a deeper insight into friction mechanics.
Article
Modelling and simulation are more and more upcoming tools in various fields in engineering. Most tasks request specialization in terms of the technical background as well as of the mathematical methods used. In this paper an overview is given about some commonly available software tools for simulation with respect to the specific conditions in the...
Article
Amorphous carbon film, also known as DLC film, is a promising material for tribological application. It is noted that properties relevant to tribological application change significantly depending on the method of preparation of these films. These properties are also altered by the compositions of these films. DLC films are well known for their sel...
Article
Diamondlike carbon (DLC) coatings are well known for their self-lubricating properties. Metal-containing DLC films exhibit reduced internal stress, improved adhesion and reduced sensitivity to humidity. Furthermore, Ti-containing DLC coatings are compatible with biological environments. In view of this, the primary aim of the present work was to ev...
Conference Paper
The behavior of tribological systems with hybrid lubrication using solid lubricants on graphite basis and/or liquid lubricant can be optimized. This can be achieved by a detailed knowledge of the transfer mechanisms induced by the tribological stress and consequential material and surface design adaptations. Our first approach is a finite element m...
Article
The article deals with the influence of cleaning processes on the topography of tribologically tested steel specimen. The attention was focused on the wear scar and the area next to the wear scar. The tested specimen underwent a successive cleaning process using various solvents. Afterwards the area was topographically evaluated by means of a 3D co...
Article
Full-text available
The operation of most radio-frequency components in accelerators rely on the conditioning obtained usually by gradually increasing the power fed into these devices. This effect is related to the reduction of the desorption yields and of the secondary electron yields of surfaces exposed to electron bombardment. In LHC, similar decreases will also li...
Technical Report
Full-text available
The secondary electron emission of surfaces exposed to the impact of energetic electrons contributes significantly to the electron cloud build-up. For the prediction of the consequences of this effect the measurements of the secondary electron yield carried out at CERN are an important source of information. New experimental results concerning the...
Article
An investigation of gas kinetic temperatures in a supersonic hydrogen plasma jet has been performed. Under the conditions used the broadening of the Balmer alpha line is predominantly caused by Doppler broadening due to thermal motion. The spectral resolution needed was achieved by the insertion of a planar Fabry-Pérot interferometer into the paral...