Running-in Wear Research Articles

The investigation of different particle size magnesium-doped zinc oxide (Zn0.92Mg0.08O) nanoparticles on the lubrication behavior of paraffin oil

Magnesium-doped zinc oxide (Zn0.92Mg0.08O) (ZMO) nanoparticles of 23 nm particle size have been synthesized by auto-combustion method. The variation in particle size of these nanoparticles has been performed by their further calcination at 800 and 1000 °C for 2 h and the corresponding calcined particles are designated as ZMO-1 and ZMO-2, respectively. The nanoparticles have been characterized by powder-XRD, scanning electron microscopy (SEM), energy dispersive X-ray and transmission electron microscope. The effect of particle size on the antiwear lubrication behavior of paraffin base oil has been investigated on four-ball lubricant tester. The tribological tests of these nanoparticles as antiwear additives have been studied at an optimized concentration (0.5 %w/v) by varying load for 30 min test duration and by varying the test durations at 392 N load. Various tribological parameters such as mean wear scar diameter, friction coefficient (µ), mean wear volume, running-in and steady-state wear rates show that these nanoparticles act as efficient antiwear additives and possess high load-carrying ability. From these tribological tests it has been observed that the lubrication behavior of studied nanoparticles is strongly size-dependent. The best tribological behavior is shown by nanoparticles of the smallest size, ZMO. Being sulfur, halogen and phosphorous free, ZMO nanoparticles have potential to be used as low SAPS lubricant additives. The SEM and atomic force microscopy analysis of the worn surfaces lubricated with ZMO nanoparticles at 392 N applied load for 60 min test duration show drastic decrease in surface roughness. The values of surface roughness of different additives are in good agreement with their observed tribological behavior.

A novel approach to model effects of surface roughness parameters on wear

Engineering surfaces with similar average or RMS roughness exhibit different values of skewness and kurtosis due to different machining processes. As the surfaces evolve during operation and the wear process, the roughness parameters undergo significant changes. To investigate the change in the roughness parameters and their effect on wear rate, it is of significant importance to investigate and simulate deep wear scars. In this study, a novel method to simulate wear on rough surfaces is proposed. The surface is treated as a collection of asperities of different radii at different heights. The method is applied to a linear elastic material model and the contact parameters are calculated using the Hertzian contact theory. Material removal is simulated by a simple truncation model and Archard's wear law is used at asperity level to evaluate wear depth. Surfaces with various values of RMS roughness, skewness and kurtosis are investigated and two distinct wear rates are obtained for each surface, running-in (severe) wear and steady state (mild) wear. It is also predicted that surfaces with high roughness, kurtosis and positive skewness exhibit higher wear rates. This investigation highlights the importance of studying the effects of surface parameters on wear rate and demonstrates that although a linear wear law is assumed at each asperity, a non-linear wear rate of rough surfaces can be obtained computationally, which are similar to trends observed in experiments.

Experimental study on the chaotic attractor evolvement of the friction vibration in a running-in process

Running-in wear experiments were conducted on a pin-on-disk tester. The attractors of friction vibration were investigated by applying the chaos theory, and the evolvement mechanism of the friction vibration chaotic attractors in the running-in process was analyzed. The experimental results indicate that the friction vibration has a chaotic nature, and the chaotic attractor in the phase space is an always open trajectory with a specific hierarchy and structure. The chaotic attractor of the friction vibration gradually converges and tends toward a balanced state in the running-in process. The evolvement of the friction vibration chaotic attractors indicated that the wear state changes from the running-in stage to the stable wear stage.

Investigation on Frictional Vibration Behavior of Tribological Pairs Under Different Wear States

In this paper, the frictional vibration behavior under different wear states was investigated by the friction and wear experiments of the piston ring against the cylinder liner of marine diesel engine on CFT-I tester. The time-frequency features of frictional vibration were analyzed by harmonic wavelet packet transform (HWPT) and the variation of frictional vibration from running-in wear to steady wear and violent wear states was studied by defining characteristics parameter K using singular value decomposition (SVD). The result shows that the time-frequency features of frictional vibration vary with the wear time and can reflect the wear states of tribological pairs. The variation of characteristic parameter K of the frictional vibration is accordingly consistent with that of the friction coefficient and indicates that the wear progress of the tribological pair goes through various stages, namely, running-in wear, steady wear, and violent wear. Therefore, the frictional vibration can be used to predict the wear process and identify the wear states of tribological pairs.

Adverse condition testing with hip simulators

Recent clinical failures and abnormal sounds observed in certain prosthetic hip designs have directed attention to adverse condition hip simulator testing. In the present study, hip simulator wear and friction tests were made with a macroscopic separation of the bearing surfaces in the swing phase, steep acetabular cup position, increased load, poor or lacking lubrication, roughened bearing surfaces including titanium third bodies, and with combinations of these. The only conditions that resulted in squeaking were dry sliding with alumina-on-alumina and metal-on-metal, and an extreme peak load of 4kN with serum lubricated metal-on-metal. The wear rate of metal-on-metal increased by an order of magnitude when the cup position was steep, 64°, compared with the optimal position of 48°. The increase of the peak load from 2kN to 3kN with the cup position of 48° increased the running-in wear of metal-on-metal, but the steady state wear rates were equally low, of the order of 1mg per one million cycles. Crosslinked polyethylene was the superior cup material under adverse conditions, including dry sliding and roughened femoral head.

In situ running-in wear assessment in multi-asperity nanotribology

Wear analysis at the micro/nanoscale appears as a great challenge for MEMS/NEMS devices. At this scale classical post mortem analysis – like profilometry or AFM assessment – often failed because (i) the error in wear assessment owing to the elastic recovery is no longer negligible at this scale and (ii) the presence of nanometric tribolayer within the contact cannot be take into account when the contact is opened afterward. So, this paper deals with an in situ wear assessment based on a triboscopic approach where the final position zf of the ball is known without opening the contact because its vertical position is assessed at every instant of the process. This triboscopic assessment considers the initial approach of the surfaces z0 and gives the wear rate by taking into account the presence of any tribolayer within the contact. It requires some corrections as (i) the tilt of the sample and (ii) the initial displacement of the surfaces, which is a function of the mechanical properties of the samples. The latter are determined by using an inverse method combining spherical nanoindentation and boundary element numerical simulations, which are both described too. Validation and application of this in situ approach to the running-in wear assessment of thin soft and hard coatings currently used in MEMS manufacturing are finally presented.

지하철 레일의 미끄럼 마모거동을 고려한 재료설계에 대한 고찰

To assess the wear behavior of rails against subway rail car wheels, we investigate the sliding wear behavior of pins derived from two types of rails (normal rails and heat-treated rails) against a disc derived from a subway rail car wheel, using a pin-on-disc-type tribometer. We base the sliding wear test conditions on the sliding conditions for wheel flange-rail gauge corner contact. We demonstrate the remarkable transition in the wear behavior of the pins derived from the rails, from severe wear to mild wear, as a function of the sliding distance. The wear rate of the heat-treated rail material in the running-in wear region is much lower than that of the normal rail material. Furthermore, the wear rates of the pins in the running-in wear region decrease with increasing hardness and with decreasing sliding speed. However, there is little difference between the heat-treated rail pin and the normal rail pin in the wear rate in the steady-state wear region. Stricter controls on the decarburized layer beneath the surface of rails are required to reduce the wear rate in the running-in wear region.

Tribocorrosion of passive metals in the mixed lubrication regime: theoretical model and application to metal-on-metal artificial hip joints

Wear is a key problem limiting the lifetime and performance of total hip arthroplasty. The synovial fluid, acting as lubricant, can alleviate the wear of implants but also introduces corrosion. The interaction of mechanical wear and electrochemical corrosion, nominally tribocorrosion, has been proposed as one of the crucial degradation mechanisms of implants and recently saw significant progress in mechanistic understanding and modeling. This study presents a predictive wear model based on a mechanistic approach of tribocorrosion and lubrication and taking into account clinical relevant parameters such as normal load, velocity and clearance. Predicted wear rate corresponds well to the running-in wear rate from simulator experimental results and allows to identify the dominating wear mechanism and to evaluate the influence of several parameters.

Smoothness and plateauness contributions to the running-in friction and wear of stratified helical slide and plateau honed cylinder liners

Cylinder liner surface has a great influence on frictional and wear performances of combustion engines during the running-in period. Two surface texture anisotropies produced by plateau honing (PH) and helical slide honing (HSH) processes (which consist of 50° and 130° cross-hatched grooves, respectively) are commonly used in automotive industry for thermal combustion engine cylinder liners. They are generated by a three stages process. The first stage, rough honing, removes enough material to obtain the desired cylindricity. The second step, finish honing, generates the honed texture which consists of grooves with a specific cross-hatch angle. The third stage permits to reduce the surface peaks and therefore allows varying plateau superficial roughness amplitude.This paper is devoted to studying the influence of respectively smoothness and plateauness on honed surface wear and friction performances during running-in. For that, HSH and PH textures are generated using different final honing stage durations in order to obtain different levels of surface peak clipping. Then, friction, wear and surface topography evolution were analyzed during running-in tests on a reciprocating ring-liner tribometer under mixed lubrication regime. The results show that the superficial surface roughness generated by helical slide honing has a very low contribution into friction. This is promising for the honing process optimization, in which the third stage can be significantly reduced or avoided.

Research on Friction Wear Characters and Microcosmic Mechanism of Galvanized Sheets

Wear tester UMT-2 was used to study the friction wear characters of galvanized sheets under dry friction and oil lubrication. Three-dimensional morphology instrument WYKONT11 was used to observe the width and maximum depth of wear scars, surface roughness and surface topography. Energy Dispersive Spectroscopy (EDS) analysis of zinc coating compositions and tests of micro hardness were carried out. Then, the friction wear mechanism of galvanized sheets was preliminary discussed. The experimental results indicate that, under dry friction, galvanized sheets experience three stages: run-in wear, abrasive wear and adhesive wear. Meanwhile, zinc coatings exfoliate until they lose efficacy. Good lubrication is propitious to protect zinc coatings and it can reduce friction wear. The research results can provide guidance for formability analysis and mold design of galvanized sheets.

Investigation of the time-dependent wear behavior of veneering ceramic in porcelain fused to metal crowns during chewing simulations

The excessive abrasion of occlusal surfaces in ceramic crowns limits the service life of restorations and their clinical results. However, little is known about the time-dependent wear behavior of ceramic restorations during the chewing process. The aim of this in vitro study was to investigate the dynamic evolution of the wear behavior of veneering porcelain in PFM crowns as wear progressed, as tested in a chewing simulator. Twenty anatomical metal–ceramic crowns were prepared using Ceramco III as the veneering porcelain. Stainless steel balls served as antagonists. The specimens were dynamically loaded in a chewing simulator with 350N up to 2.4×106 loading cycles, with additional thermal cycling between 5 and 55°C. During the testing, several checkpoints were applied to measure the substance loss of the crowns’ occlusal surfaces and to evaluate the microstructure of the worn areas. After 2.4×106 cycles, the entire wear process of the veneering porcelain in the PFM crowns revealed three wear stages (running-in, steady and severe wear stages). The occlusal surfaces showed traces of intensive wear on the worn areas during the running-in wear stage, and they exhibited the propagation of cracks in the subsurface during steady wear stage. When the severe wear stage was reached, the cracks penetrated the ceramic layer, causing the separation of porcelain pieces. It also exhibited a good correlation among the microstructure, the wear loss and the wear rate of worn ceramic restorations. The results suggest that under the conditions of simulated masticatory movement, the wear performance of the veneering porcelain in PFM crowns indicates the apparent similarity of the tribological characteristics of the traditional mechanical system. Additionally, the evaluation of the wear behavior of ceramic restorations should be based on these three wear stages.

Mechanical and chemical wear components in environmental multi-asperity nanotribology

Running-in wear of MEMS can be described as a process which involves mechanical, chemical and physico-chemical phenomena at various scale levels. Extracting each sort of components would enable to better understand wear mechanisms in order to prevent it. Unfortunately, these components are generally hard to extract experimentally because their own time responses are generally not in the same order. A suitable approach is to combine multi-asperity nanotribological tests, using an in situ wear assessment, with numerical simulations using Movable Cellular Automata (MCA), which are able to interact together within the contact. Experimental tests enable to control the actual physico-chemical environment with an environmental enclosure, and MCA simulate the multi-asperity contact, where interactions between automata pairs can be controlled by various fracture and bonds criteria. There is generally an optimal set of interaction criteria which provides numerical results that match correctly with the experimental ones. By studying the influence of experimental environment on this optimal set, assumptions can be made about mechanical, chemical and physico-chemical phenomena that are likely to occur within the actual tribocontact. In this work, these assumptions have been studied for various samples like silicon wafers displaying various crystallographic orientations and nanostructures, and self-assembled monolayers grafted on silicon wafers, and carbon nitride coatings rubbing under different environmental conditions.

Prediction of Surface Topography at the End of Sliding Running-In Wear Based on Areal Surface Parameters

Running in is a complex process, and it significantly influences the performance and service life of wear components as the initial phase of the entire wear process. Surface topography is an important feature of wear components. Therefore, it is reasonable to investigate the running-in process with the help of surface topography for improvement. Because the surface roughness after running in is independent of the nature of initial roughness, it is difficult to predict the surface topography after running in based on unworn surface topography. Aiming to build a connection of surface topographies before and after the running-in process, a black-box model predicting surface topography after the running-in process was established based on least-squares support vector machine (LS-SVM), and the areal surface evaluation parameters were adopted as model variables. To increase the adaptability of the predictive model, the main factors of the work condition were also taken into consideration. The prediction effect and sensitivity of the model were tested and analyzed. The analysis indicates that the hybrid property of surface topographies before and after running in is closely related. Moreover, the surface topography after running in is influenced more by the initial surface topography than by the work condition.

Assessment of Antiwear Properties of Lube Oils Using Online Visual Ferrograph Method

The four-ball wear test is currently a mainstream method for assessing antiwear properties of lube oil. However, the assessment is normally based on a comparison of the final wear scar diameter and wear progressions cannot be well presented. A new experimental method for assessing antiwear properties of lube oil with near real-time (NRT) wear information was developed. Wear debris from a ball-on-disc tribometer under boundary lubrication was deposited by an online visual ferrograph (OLVF) every 6 min, and NRT information on wear debris generation rate was obtained. A mathematical model of the lubrication system serving the ball–disc tribopair was built, and an index of particle coverage area (IPCA) was approximately proportional to wear rate (by weight) of the ball–disc tribopair. IPCA curves characterized the antiwear performance of lube oil by three indictors, running-in duration, index of running-in wear amount, and index of steady-state wear rate. With the three indictors, a rule assessing the antiwear performance between two oils was proposed. Accordingly, wear tests of eight oils were performed, and their antiwear properties were distinguished by the assessment rule. Under the same setting, the assessing experiment of the same oil was conducted five times. According to the statistical analyses, the experimental method exhibited considerable repeatability.

Tribological studies of stearic acid-modified CaCu2.9Zn0.1Ti4O12nanoparticles as effective zero SAPS antiwear lubricant additives in paraffin oil

Stearic acid modified ceramic nanoparticles SCCZTO-6 h, SCCZTO-8 h and SCCZTO-12 h of average sizes 60, 80 and 90 nm were prepared from CCZTO-6 h, CCZTO-8 h and CCZTO-12 h respectively (where CCZTO represents CaCu2.9Zn0.1Ti4O12; 6 h, 8 h and 12 h are the sintering times). The SCCZTO nanoparticles have been characterized by Fourier transform infrared spectroscopy (FT-IR) and transmission electron microscopy (TEM). Tribological behavior of these nanoparticles in liquid paraffin oil has been evaluated using a four-ball lubricant tester and compared with conventional high SAPS containing zinc dialkyldithiophosphates (ZDDP). All antiwear tests have been performed using an optimized concentration of the SCCZTO nanoparticles (1% w/v) by varying the load for a 30 min test duration and by varying the test durations at 392 N load. Various tribological parameters such as mean wear scar diameter (MWD), friction coefficient (μ), mean wear volume (MWV), running-in, steady-state and overall wear rates show that all the SCCZTO nanoparticles act as efficient antiwear additives and possess a high load carrying capacity. The best tribological behavior is shown by SCCZTO-6 h, followed by SCCZTO-8 h and then SCCZTO-12 h. The surface morphology and roughness of the wear scar have been studied by Scanning Electron Microscopy (SEM) and Atomic Force Microscopy (AFM) respectively. AFM and SEM micrographs of the wear scar in the presence of SCCZTO-6 h and SCCZTO-8 h at 392 N applied load for a 90 min test duration show a drastic decrease in surface roughness. Energy-Dispersive X-ray (EDX) analysis of the worn surface under similar experimental conditions in the presence of SCCZTO-6 h nanoparticles exhibits the presence of calcium, copper, zinc, titanium and oxygen on the worn steel surface indicating tribosinterization and/or adsorption of the additive on the rubbing surface resulting in the formation of a strong tribofilm. X-ray Photoelectron Spectroscopy (XPS) of the tribofilm shows the presence of CaO, CuO, Cu2O, TiO2, Fe2O3 and adsorbed carbon in the form of –C–C– and –C(O)O– moieties.

An experimental study of the wear behavior of dental feldspathic glass-ceramic and lithium disilicate glass-ceramic

To investigate the tribology characteristics of two ceramic materials in vitro:feldspathic glass-ceramic (veneer porcelain) and lithium disilicate glass-ceramic (heat-pressed ceramic), and to evaluate the wear resistance of different ceramic materials from the dynamic chewing perspective. Wear tests were performed in simulated oral environment with stainless steel ball antagonists (r = 3 mm), veneer porcelain (CERAMCO 3) and heat-pressed ceramic (IPS e.max Press HT type) in the chewing simulator. The tribological tests were carried out under artificial saliva lubrication condition in room temperature with a vertical load of 10 N for 1.2×10(6) cycles (f = 1.5 Hz, uniform circular motion, revolving speed = 90 r/min, radius = 0.5 mm). The wear volumes were measured using three-dimensional profiling, and surface microscopic morphology were observed using scanning electron microscopy at time point of 200 000, 400 000, 600 000, 800 000, 1 000 000, and 1 200 000 cycles. In a simulated oral environment, the wear rates of veneer porcelain were (0.001 20 ± 0.00 018) , (0.000 10 ± 0.000 03) , (0.000 50 ± 0.000 05), (0.000 10 ± 0.000 02) , (0.004 10 ± 0.000 38) , and (0.019 00 ± 0.003 53) (×10(-4) mm(3)/cycles) at 200 000, 400 000, 600 000, 800 000, 1 000 000, 1 200 000 cycles. The wear rates of heat-pressed ceramic were (0.139 50 ± 0.030 94), (0.124 40 ± 0.031 20), (0.054 80 ± 0.005 38), (0.038 80 ± 0.006 10), (0.011 10 ± 0.003 75), (0.198 90 ± 0.045 80) (×10(-4) mm(3)/cycles) at 200 000, 400 000, 600 000, 800 000, 1 000 000, 1 200 000 cycles. Three stages were observed in the wear loss process of the two materials: running-in stage, steady wear stage and severe wear stage. In running-in and steady wear stage, the shallow wear tracks of veneer porcelain were produced by the fatigue effect.While in severe wear stage, the wear tracks turned into ploughing. In running-in stage, the surface of heat-pressed ceramic was characterized by dense and shallow ploughing. In steady wear stage, the wear tracks turned into flake peeling produced by fatigue effect. At last, the whole layer was worn off by the effects of ploughing. In a simulated oral environment, the wear rate and wear loss of heat-pressed ceramic are greater than that of veneer porcelain.

Quantification of combustion valve sealing interface sliding—A novel experimental technique and simulations

The rapid sharpening of the environmental legislation during the last decades has forced engine manufacturers to radical design modifications. It has been shown that the sliding in the sealing interface is one of the major reasons for wear. The sliding wear is expected to have an even more important role in modern engines.This paper presents unique experimental data, acquired using a dedicated technique in a test-rig. The experimental data is complemented by FEM-simulations. The simulations involve validation of the test-rig valve sealing interface sliding behaviour and investigations on how different parameters influence the sliding length. These parameters include combustion pressure, contact angle, contact length, valve head thickness, coefficient of friction, running-in wear, and change of elastic modulus due to temperature variations.

Running-in wear modeling of honed surface for combustion engine cylinderliners

The texture change during running-in alters the performance and efficiency of a tribo-mechanical system. During mass production of cylinder liners, a final finishing stage known as “plateau honing” is commonly added to reduce the running-in wear process of the liner surface. The majority of researchers think that this operation improves the engine efficiency and decreases oil consumption. It was believed that there are close links between the surface topography of honed cylinders change and their wear resistance during running-in. However, these interactions have not yet been established. Some running-in wear models were developed in the open literature to predict topographical surface changes without considering the running-in conditions.The present paper thus investigates the various aspects of the wear modeling that caused running-in problems in honed surfaces and its implications on ring-pack friction performance. To illustrate this, plateau honing experiments under different conditions were first carried out on an instrumented vertical honing machine. The plateau honing experiments characterize the surface modifications during running-in wear of cast-iron engine bores using advanced characterization method. Based on the experimental evidence, a running-in wear model was developed. Finally, a numerical extension of the developed model was applied to solve the Reynolds equation by taking into account the real surface topographies of the engine bore. This enables us to predict realistic friction performance within the cylinder ring-pack tribosystem.

Transfer film evolution and its role in promoting ultra-low wear of a PTFE nanocomposite

Polytetrafluoroethylene (PTFE) is an important solid lubricant with an unusually high wear rate. For a half-century, fillers have been used to reduce PTFE wear by >100× with >10% loading through hypothesized mechanisms involving mechanical load support, crack arresting, and transfer film adhesion. More recently it was discovered that specific nanoparticles provide a unique nanoscale reinforcement mechanism enabling unprecedented wear reductions of 10,000× with as little as 0.1% nano-fillers. Although the mechanisms responsible for this dramatic improvement remain unclear, there is substantial evidence that the transfer film plays a critical role. This paper uses interrupted microscopy measurements to investigate the evolution of transfer film development for an ultra-low wear PTFE nanocomposite. The run-in wear rates were similar to those of more traditional PTFE composites and transfer films consisted of large plate-like debris. Although the run-in wear rate and debris size decreased monotonically with distance, the run-in transfer films were removed each cycle. Detectible debris vanished and wear rates approached zero at an abrupt transition. During this ultra-low wear transition period, nanoscale and oxidized fragments of PTFE were transferred to the counterface. Most of these fragments persisted for the duration of the test and initiated the transfer film by progressively scavenging trace material from the bulk, growing into small islands, and merging with neighboring islands. The results of this study reflect a complex interplay involving elements of transfer film adhesion, chemistry, debris morphology, and mechanics.

Spectrum loading effects on the running-in of lubricated bronze and surface-treated titanium against alloy steel

Lubricated bearing surfaces like those in engine connecting rods commonly experience transient loading in service. These transients can affect friction, wear rate, and regime of lubrication. It was therefore of interest to investigate the effects of periodically-varying loads on candidate bearing materials under non-steady-state conditions and running-in. Light weight titanium alloys could be used for bearing components in fuel-efficient vehicles if their sliding friction and wear characteristics were improved. Candidate surface treatments and coatings for Ti–6Al–4V alloy were tribo-tested under diesel oil lubrication with time-varying loads. A variable load bearing test (VLBT) apparatus was built for that purpose. Baseline tests of a bearing bronze (CDA 932) against alloy steel (AISI 8620) showed that wear during a variable load test was greater than that for the same duration test under a constant load equal to the average of the spectrum loads. Spectrum loading effects on the running-in and steady-state friction and wear behavior of bronze and several Ti alloy surface treatments and coatings are discussed. Results indicate that the progression of observable wear and surface damage may be difficult to quantify under the nearly full-film lubrication regimes as are found in engine bearings. Implications for screening candidate materials and coatings for lightweight engine bearings are discussed.