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T G Mathia - One of the best experts on this subject based on the ideXlab platform.
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roughness and wettability of surfaces in boundary lubricated Scuffing wear
Tribology International, 2016Co-Authors: L Wojciechowski, Krzysztof Kubiak, T G MathiaAbstract:The diversity of multidisciplinary approaches suggests that fundamentals of Scuffing require systemic, complex multi-scale and multi-physics analysis of an irreversible process as it is postulated in present study. That is probably one of the reasons of lack of an unequivocal model of this irreversible transitional process from stable more or less lubricated wear to Scuffing described only by one or few authors in equation(s) form. Therefore, it is useful to characterize the tribological surface properties in frame of systemic approach looking simultaneously for the optimal compromise between rheological, morphological and physicochemical features of contacting surface׳s layer. Hypothetical role connected to any group of features in the topological approach is elucidated and experimentally confirmed via the wettability, strongly combined with surface roughness and surface free energy. Due to the fact that the free energy is directly related to the surface wettability it can as well affect the Scuffing activation process. For scientific and rhetoric reasons some selected results of limited boundary lubrication investigations under double blind trial conditions in case of gear oil with anti-wear (AW) and extreme pressure (EP) additives are elucidated here. The results issued from Scuffing tests on AISI 4140 ground steel burnished under different forces in order to generate different surface roughness, residual stresses and surface energy are analyzed. It was stated and numerically correlated that the wettability by lubricating medium influences the Scuffing resistance. Additionally, the dependence of wettability on selected parameters of roughness and a time to Scuffing activation have been stated. On that basis, it is proposed to reinforce concept of “oleophilic” and “oleophobic” properties of metallic surfaces as autonomous invariants determining the activation of catastrophic wear process under boundary lubricated conditions.
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proposal of invariant precursors for boundary lubricated Scuffing
Wear, 2015Co-Authors: łukasz Wojciechowski, T G MathiaAbstract:Abstract One of the fundamental problems in tribology is the difficulty in predicting final performance and, in particular, the longevity of lubricated or not frictional components. In most cases of the hydrodynamic or elastohydrodynamic lubricated parts, if the load is too high or the motion of the rubbing elements is too slow, boundary lubrication occurs and predicting the performance of the bodies may become complicated due to the Scuffing that can appear. The authors of this paper aimed to shear their knowledge and contribute to better understanding of this transitional phase dealing frequently with catastrophic wear. An analysis of various factors (residual stresses, surface free energy and surface morphology) that contribute to and allow for the identification of conditions that lead to the starting phase of the Scuffing process will be presented in this paper. The double-blind strategy of experiments was implemented to achieve a higher standard of scientific rigour thus leading to a new concept of the Scuffing invariant precursors.
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fundamentals of ductile cast iron Scuffing at the boundary lubrication regime
Tribology International, 2015Co-Authors: łukasz Wojciechowski, S Eymard, Zenon Ignaszak, T G MathiaAbstract:Abstract The friction regime of partially lubricated and highly loaded contact when the oil does not entirely separate the rubbing surfaces and its thickness is comparable to the roughness of the surfaces poses, in some cases, risk of Scuffing and catastrophic wear. The present study, on life prediction of tribological systems from ductile cast iron, steel and brass, is shown by an analysis of the fundamental mechanisms of Scuffing. Ductile cast iron according to DIN EN 1563 with nodular graphite standard EN ISO 945 is submitted to systematic tribological tests of Scuffing and analysed in the context of quasi-conventional tribometry lubricated with reference and reclaimed naphthenic oils. The 3D morphologies of the rubbing surfaces are characterised and the fundamental conditions of the Scuffing process are investigated. The results are elucidated in order to propose a phenomenological description of the analysed wear process and its invariants. Therefore, the role of solid materials as well as the nature of lubricants is both taken into consideration.
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the polarity of metallic surfaces in the context of the corrosive and Scuffing wear control
Tribology International, 2015Co-Authors: łukasz Wojciechowski, T G MathiaAbstract:Abstract The concept of the metallic surfaces polarity in the context of Scuffing performance is postulated and elucidated in the presented paper. The machining by grinding and surface treatment by burnishing is applied to control introducing changes in surface polarity and acid/base component of surface free energy is used for their quantitative determination. A clear relationship between the acid/base component of surface free energy and an activation of Scuffing for the steel–cast iron friction pairs lubricated by oils with the surface-active sulphur-based additives is found. Obtained results are commented and clarified; thanks to the negative-ion concept of extreme pressure action of organo-sulphur compounds. Additionally, surface reactivity investigations are performed in order to determine the influence of acid/base component of surface free energy on the corrosion wear. It recognised a clear relationship between the acid/base component of surface free energy and the mass decrement of steel surfaces in the hydrochloric acid environment. On the basis of both parts of the investigations (Scuffing and reactivity tests), an optimal surface polarity is determined for steel–cast iron friction pairs lubricated by lubricants with surface-active sulphur-based additives.
Peter J. Blau - One of the best experts on this subject based on the ideXlab platform.
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Scuffing tendencies of different metals against copper under non lubricated conditions
Wear, 2011Co-Authors: Andriy Kovalchenko, Peter J. Blau, Steven DanylukAbstract:Abstract Metallic components in sliding contact are sometimes subjected to high-loads with little or no lubrication. Such starved conditions can lead to a phenomenon called Scuffing. Various definitions exist for this term, but in the present case, three criteria were used to signal its onset: changes in friction, vibrations, and noise, coupled with surface examination. On this basis, Scuffing initiation was determined for seven technically pure metals (Al, Mo, Nb, Ta, Ti, W, Cu) and stainless steel, all rubbing against Cu. A flat-ended pin-on-disk test configuration was used with normal loads of 1–3 N, and with step-wise increases in sliding speed from 0.16 to 2.56 m/s. Al was only weakly resistant to Scuffing, presumably due to its solubility in Cu, its high ductility and its relatively low elastic modulus. Niobium provided satisfactory sliding behavior at low speeds and loads, presumably due to protective oxides; however, it scuffed at higher loads when the oxide broke through. Stainless steel, Mo, and Ta had higher friction coefficients than Al and Nb, presumably because the relatively high strengths of the former prevented severe wear even when their oxide films failed. Like Al, Ti scuffs on Cu, probably because of its high relative solubility; however, Ti's higher elastic modulus resists the more severe forms of surface damage than does Al. Of all the materials slid against Cu, W displayed the least Scuffing, even under maximum speed and load. Tungsten's negligible solubility in Cu may have reduced its adhesion, and W's high elastic modulus resisted shear-deformation, even at high frictional heating. Self-mated Cu couple scuffed when the speed was increased. The oxides on the Cu surface serve as solid lubricant avoiding Scuffing at lower speeds.
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Scuffing transition diagrams for heavy duty diesel fuel injector materials in ultra low-sulfur fuel-lubricated environment
Wear, 2005Co-Authors: John J. Truhan, Peter J. Blau, Harry M. MeyerAbstract:In order to meet stricter emissions requirements, advanced heavy duty diesel fuel injection systems will be required to resist Scuffing at higher pressures, temperatures and in ultra low-sulfur fuels. Using a 3D friction-Scuffing mapping technique, Scuffing transition diagrams were generated for diesel fuel injector materials to exemplify the effects of surface finish and sliding velocity on Scuffing characteristics in a fuel-lubricated environment. On-highway #2 diesel fuel and Jet A aviation fuel were selected as a baseline and a surrogate of ultra low-sulfur fuel, respectively. Two material combinations, self-mated AISI 52100 steel and MgO partially stabilized zirconia (TTZ) against 52100 steel, were tested at three composite roughness levels. Scuffing generally initiated at the low-sliding-velocity stroke ends, which had the worst lubrication condition. Materials survived longer in the diesel fuel than in the aviation fuel. TTZ/steel showed higher Scuffing resistance than steel/steel. Among the three roughness levels, self-mated steel exhibited best Scuffing resistance at the intermediate level, while TTZ against steel seemed to favor the roughest level. Surface morphology examination (optical and scanning electron microscopy) and chemical analysis (energy dispersive spectroscopy and scanning auger microprobe) were conducted to investigate the wear modes and tribochemical film compositions. A mixture of abrasive wear, adhesive wear, and plastic deformation has been observed. The worn surfaces in #2 diesel fuel presented higher non-carbide carbon concentration and a thinner iron oxide-rich layer than those in Jet A fuel.
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Investigation of the Scuffing characteristics of candidate materials for heavy duty diesel fuel injectors
Tribology International, 2005Co-Authors: John J. Truhan, Peter J. BlauAbstract:The objective of this study is to characterize and understand the evolutionary processes that produce changes in the friction and surface damage in materials for possible use as heavy duty diesel fuel injector plungers. This work has involved the development of test methods to impart reciprocating motion to various metals, ceramics, and coated specimens in the presence of diesel fuel-like fluids. Commercial and candidate plunger materials, including 52100 steel, zirconia, cermets (TiC in Ni3Al matrix), and TiN coatings, were evaluated on a crossed-cylinders-like Scuffing test we call the ‘pin-on-twin’ geometry. Contacts were lubricated by on-highway #2 diesel and Jet A aviation fuels. Using friction-based criteria, the material ranking was in good agreement with field experience with actual injectors from the diesel engine industry. Zirconia and cermets exhibited promising Scuffing resistance in both fuels. Scuffing generally became more severe in the Jet A fuel. Experimental results indicated that smoother surfaces that are required to sustain higher injection pressures could be more vulnerable to Scuffing due to their thinner lubricant films. Material transfer was the major Scuffing mechanism of zirconia, cermets, and TiN coatings against steel. Micro-scratches were also observed on the matrix material of cermets.
K Wasmer - One of the best experts on this subject based on the ideXlab platform.
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effects of laser surface texturing on the wear and failure mechanism of grey cast iron reciprocating against steel under starved lubrication conditions
Wear, 2017Co-Authors: F Saeidi, M Parlinskawojtan, P Hoffmann, K WasmerAbstract:Abstract The purpose of this work was to investigate the effects of different texture patterns and orientations on the wear and failure mechanisms of grey cast iron sliding against 42CrMo6 steel. Reciprocating tests were performed on 16 different micro-textures under starved lubrication conditions. The textures were designed using a design of experiments (DoE) approach and produced by a nanosecond-laser. Under starved lubrication conditions, the non-textured samples always failed catastrophically by Scuffing, which is a sudden and catastrophic failure. However, textured samples showed two different wear and failure mechanisms. It is revealed that the sudden and catastrophic failure due to Scuffing can be avoided by surface texturing. Choosing the right distance between the micro-textures can change the surface damage mode from Scuffing to a more gradual oxidative wear mechanism. For the studied tribo-system, it was shown that if the distance of micro-textures in the direction of sliding ( DMS ) is less than 3 mm, samples will fail by an oxidation mechanism. For textured samples with DMS greater than 3.5 mm, the failure mechanism is Scuffing, the same as for the non-textured cast iron.
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prediction of failure in lubricated surfaces using acoustic time frequency features and random forest algorithm
IEEE Transactions on Industrial Informatics, 2017Co-Authors: Sergey A Shevchik, F Saeidi, B Meylan, K WasmerAbstract:Scuffing is one of the most problematic failure mechanisms in lubricated mechanical components. It is a sudden and almost not predictable failure that often leads to extensive cost in terms of damages and/or delay in production lines. This study presents a promising solution that can prevent Scuffing for the machinery industry in the future. To achieve this goal, a signal processing approach by means of an acoustic emission is introduced for the prediction of Scuffing. An acoustic dataset was collected from metallic surfaces reciprocating under a constant load (typical conditions for semi journal bearings). The coefficient of friction values were measured during the entire experiments and were referred to as the ground truth of the momentary surface state. Based on the friction behavior, three friction regimes were defined that are running-in, steady-state, and Scuffing. The present approach is based on tracking the changes in acoustic emission by means of three sets of wavelet-derived features. Those features include: 1) energy, 2) entropy, and 3) statistical information about the content of acoustic emission and the response of each feature to the different friction regimes was individually investigated. The applicability of machine learning classification and regression was studied for Scuffing prediction. Both approaches were applied separately but can be unified together to increase the prediction time interval of surface failure. For classification, an extra friction regime was introduced designating as pre-Scuffing and is defined as a time span of 3 min before the real surface failure. Random forest classifier was used to differentiate the features from the different friction regime. The best performance in classification of features from pre-Scuffing regime reached a confidence level as high as 84%. In regression approach, the extracted features sequences were used together with random forest regressor. Our strategy allowed predicting Scuffing up to 5 min preceding its real occurrence.
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origin of Scuffing in grey cast iron steel tribo system
Materials & Design, 2017Co-Authors: F Saeidi, P Hoffmann, Aidan A Taylor, B Meylan, K WasmerAbstract:Abstract The failure mechanism known as Scuffing is a major problem in lubricated sliding mechanical components, specifically for those tribological systems working under starved lubrication conditions. It occurs suddenly and often results in loss of component functionality, and thus high repair costs. Despite the extensive studies on Scuffing over the past 80 years, the basic mechanism of Scuffing is not yet well understood. In the present study, a cast iron-steel tribo-system working under starved lubrication conditions, which resembles a semi journal bearing used in a cutting machine, with the dominant Scuffing failure mechanism is investigated. Based on the experimental observations in this work, a new theory is proposed for initiation of Scuffing in this cast iron-steel tribo-system. According to the proposed theory, Scuffing initiates when the tribo-film iron oxide reduces to α-iron providing metal-metal contact and, consequently, strong adhesion between the sliding surfaces. The reduction of the oxide takes place due to a temperature increase at the contacting asperities together with the presence of carbon, coming from either the lubricant or graphite flakes of cast iron, as the reducing agent.
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automatic detection of Scuffing using acoustic emission
Tribology International, 2016Co-Authors: F Saeidi, Sergey A Shevchik, K WasmerAbstract:Abstract This study investigates the use of acoustic emission (AE) for in situ monitoring of surfaces sliding under starved conditions until failure due to Scuffing mechanism. Reciprocal lubricated sliding tests having flat-on-flat set-up have been carried out for a cast iron–steel tribo-pair at a constant load of 600 N and a frequency of 6 Hz. According to the friction behavior, three regimes of events have been specified; steady-state, pre-Scuffing, and Scuffing. Acoustic signals for these regimes have been decomposed with wavelet packets, and sub-band energies have been chosen as features. The classification is performed using support vector machine. Experimental results reveal the feasibility of automatic detection of surface pre- and Scuffing states using acoustic emission.
John J. Truhan - One of the best experts on this subject based on the ideXlab platform.
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Scuffing transition diagrams for heavy duty diesel fuel injector materials in ultra low-sulfur fuel-lubricated environment
Wear, 2005Co-Authors: John J. Truhan, Peter J. Blau, Harry M. MeyerAbstract:In order to meet stricter emissions requirements, advanced heavy duty diesel fuel injection systems will be required to resist Scuffing at higher pressures, temperatures and in ultra low-sulfur fuels. Using a 3D friction-Scuffing mapping technique, Scuffing transition diagrams were generated for diesel fuel injector materials to exemplify the effects of surface finish and sliding velocity on Scuffing characteristics in a fuel-lubricated environment. On-highway #2 diesel fuel and Jet A aviation fuel were selected as a baseline and a surrogate of ultra low-sulfur fuel, respectively. Two material combinations, self-mated AISI 52100 steel and MgO partially stabilized zirconia (TTZ) against 52100 steel, were tested at three composite roughness levels. Scuffing generally initiated at the low-sliding-velocity stroke ends, which had the worst lubrication condition. Materials survived longer in the diesel fuel than in the aviation fuel. TTZ/steel showed higher Scuffing resistance than steel/steel. Among the three roughness levels, self-mated steel exhibited best Scuffing resistance at the intermediate level, while TTZ against steel seemed to favor the roughest level. Surface morphology examination (optical and scanning electron microscopy) and chemical analysis (energy dispersive spectroscopy and scanning auger microprobe) were conducted to investigate the wear modes and tribochemical film compositions. A mixture of abrasive wear, adhesive wear, and plastic deformation has been observed. The worn surfaces in #2 diesel fuel presented higher non-carbide carbon concentration and a thinner iron oxide-rich layer than those in Jet A fuel.
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Investigation of the Scuffing characteristics of candidate materials for heavy duty diesel fuel injectors
Tribology International, 2005Co-Authors: John J. Truhan, Peter J. BlauAbstract:The objective of this study is to characterize and understand the evolutionary processes that produce changes in the friction and surface damage in materials for possible use as heavy duty diesel fuel injector plungers. This work has involved the development of test methods to impart reciprocating motion to various metals, ceramics, and coated specimens in the presence of diesel fuel-like fluids. Commercial and candidate plunger materials, including 52100 steel, zirconia, cermets (TiC in Ni3Al matrix), and TiN coatings, were evaluated on a crossed-cylinders-like Scuffing test we call the ‘pin-on-twin’ geometry. Contacts were lubricated by on-highway #2 diesel and Jet A aviation fuels. Using friction-based criteria, the material ranking was in good agreement with field experience with actual injectors from the diesel engine industry. Zirconia and cermets exhibited promising Scuffing resistance in both fuels. Scuffing generally became more severe in the Jet A fuel. Experimental results indicated that smoother surfaces that are required to sustain higher injection pressures could be more vulnerable to Scuffing due to their thinner lubricant films. Material transfer was the major Scuffing mechanism of zirconia, cermets, and TiN coatings against steel. Micro-scratches were also observed on the matrix material of cermets.
Jorge H O Seabra - One of the best experts on this subject based on the ideXlab platform.
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influence of mass temperature on gear Scuffing
Tribology International, 2018Co-Authors: J. Castro, Jorge H O SeabraAbstract:Abstract A new Scuffing parameter for gears lubricated with mineral base oils is developed, proposing the existence of gear mass temperatures which are critical for each lubricant (viscosity grade). The introduction of the total cycle of the gear for mass temperatures calculation is supported by a theoretical background that was clearly established without empirical formulation and without any geometrical gear specificity which provides consistent physical support to the proposed Scuffing parameter. The oil dynamic viscosity at the critical mass temperatures is constant, allowing the prediction of critical temperatures for other viscosity grades of the mineral gear oils without the need of additional Scuffing tests.
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influence of lubricant type in gear Scuffing
Industrial Lubrication and Tribology, 2008Co-Authors: Ramiro C Martins, N F R Cardoso, Jorge H O SeabraAbstract:Purpose – This paper aims to investigate the Scuffing load‐carrying capacity of three gear oils: a standard mineral lubricant containing extreme pressure and anti‐wear additives (M0) and two biodegradable saturated esters containing low toxicity additives (E1 and E2).Design/methodology/approach – Four‐ball wear tests were performed, according to standard ASTM D4172. Results from the wear scar diameter and from ferrographic analysis of the test oil samples are presented and related to the lubricant properties. The physical, chemical and biodegradability properties of the lubricants are presented and compared.FZG gear Scuffing tests were performed, according to standard DIN 51535, in order to evaluate the Scuffing load‐carrying capacity of the two oils. Two reference tests were performed, A20/16.6/90 and A10/16.6/90.Findings – Test results include Scuffing load stage, maximum oil bath temperature, pinion weight loss and surface roughness measurement of the teeth flanks.Originality/value – The paper provides...
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global and local analysis of gear Scuffing tests using a mixed film lubrication model
Tribology International, 2008Co-Authors: J. Castro, Jorge H O SeabraAbstract:Abstract Gear tests were performed in a FZG test rig in order to evaluate the influence of the operating conditions (torque, speed and oil bath temperature), gear geometry and base oil viscosity on gear Scuffing. A mixed film lubrication model was used to evaluate the normal pressures and shear stresses in several points along the gear meshing line, for each load stage and for all the gear Scuffing tests performed. The gear Scuffing results were analyzed using two different approaches: one considering global gear parameters defined at the meshing line scale and another based on local parameters at the roughness asperity scale, determined using the mixed film lubrication model. The analysis at the roughness asperity level was used to complete the Scuffing study performed with global gear contact parameters, explaining the occurrence of Scuffing during ‘running-in’, justifying the zones in teeth flanks where the first Scuffing marks appear and supplying indicators for low Scuffing resistance at high oil bath temperatures.
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influence of low friction coatings on the Scuffing load capacity and efficiency of gears
Tribology International, 2008Co-Authors: Ramiro C Martins, R I Amaro, Jorge H O SeabraAbstract:Abstract The influence of multilayer composite surface coatings on gear Scuffing load carrying capacity, gear friction coefficient and gearbox efficiency is discussed in this work. The deposition procedures of molybdenum disulphide/titanium (MoS 2 /Ti) and carbon/chromium (C/Cr) composite coatings are described. Tests reported in the literature, such as Rockwell indentations, ball cratering, pin-on-disc and reciprocating wear, confirm the excellent adhesion to the substrate and the tribological performance of these coatings, suggesting they can be applied with success in heavy loaded rolling–sliding contacts, such as those found in gears. FZG gear Scuffing tests were performed in order to evaluate the coatings anti-Scuffing performance, which both improved very significantly in comparison to uncoated gears. These results in conjunction with the friction power intensity (FPI) Scuffing criterion allowed the determination of a friction coefficient factor X SC to include the coating influence on the friction coefficient expression. The composite coatings were also applied to the gears of a transfer gearbox and its efficiency was measured and compared at different input speeds and torques with the uncoated carburized steel gears. Significant efficiency improvement was found with the MoS 2 /Ti coating.
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Scuffing and lubricant film breakdown in FZG gears. Part I. Analytical and experimental approach
Wear, 1998Co-Authors: J. Castro, Jorge H O SeabraAbstract:This paper presents the influence of the base oil viscosity and of the pitch line velocity on the Scuffing load of a spur gear. Standard FZG A/8.6/90 tests, and constant temperature tests for several pitch line velocities, were performed, for three mineral paraffinic base oils, with different viscosities. These tests were complemented by the analytical evaluation of the most important operating parameters, such as the oil bath temperature and viscosity, the lubricant film thickness and the contact temperature along the gear contact path, for each load stage considered. The analysis of experimental and theoretical results shows a good correlation between the Scuffing loads and Scuffing temperatures and the lubricant film thickness, suggesting that a close relation exists between Scuffing failure and lubricant film breakdown, for a base oil tested in the FZG rig.