Insulation wear in implanted cardioverter-defibrillator (ICD) leads may result in serious failure modes, including inappropriate or missing therapy. Tests performed on a custom apparatus developed to simulate in-vivo loading showed order of magnitude differences in specific wear rate between materials commonly used in ICD leads. Wear rates were also dependent on load, suggesting that design and application differences may further differentiate performance between materials.

Diamond-like carbon (DLC) films are excellent candidates to improve tribological properties of silicon nitride (Si 3 N 4 ) ceramic elements. Particular attentions have been paid to the preparation and analysis of DLC films on rings and discs. However, few researches on fabrication of DLC films on ball surfaces were carried out, especially on ceramic ball surfaces, because it is hard to achieve uniform coatings on ball surfaces. In this paper, DLC films on ceramic ball surfaces were studied with both experiment and FEA method. DLC films were deposited on Si 3 N 4 ceramic ball and disc surfaces with plasma immersion ion implantation and deposition techniques (PIII-D). Surface topography of ceramic balls before and after coated with DLC films showed that DLC films on ceramic ball surfaces were uniform. Tribological tests under dry friction were conducted with a ceramic ball sliding against ceramic disc and, alternatively, one of the two surfaces was coated with DLC films. The tests demonstrated that DLC films on disc surfaces were worn, while ball surface films were partly flaked. 3-D FEA models of ceramic ball sliding against ceramic disc were built and the ceramic ball/disc was coated with DLC films alternatively. DLC films were supposed to be bonded with ceramic substrates. The FEA stress fields in DLC films and on film/substrate interface showed that DLC films had great effects on stress distribution due to the low frictional coefficient and material difference from substrates. The friction force caused an increment of the stress near surfaces during sliding process, and the material difference leaded to discontinuous stress distribution on film/substrate interface. The shear stress on film/substrate interface was very slightly different between DLC films coated on ceramic balls and discs. Under almost the same shear stress, the flakes and wear of DLC films were mainly determined on the adherence of DLC films to ceramic substrates.

MoS 2 multi-component nanolubrication system showed significant friction and wear reduction (more than 30% in friction reduction and 50% in wear reduction) in sliding steel surfaces, especially under mixed and boundary lubrication conditions [1–3]. It is believed that the formation of tribofilms in MoS 2 multi-component nanolubrication system under different lubrication regimes is the primary reason for reduced friction and wear. To investigate the in-depth science of the tribo-chemical interface formed by MoS 2 multicomponent nanolubrication system, it is necessary to study the chemical states of tribofilm during its evolution (generation ↔ regeneration) process at tribo-interfaces. Tribofilms from various lubrication regimes were characterized by scanning electron microscope (SEM), energy dispersive X-ray spectroscopy (EDX), Raman microscope, and X-ray photoelectron spectroscopy (XPS) techniques to study the morphology, chemical composition, elemental distribution, and chemical bonding of tribo-chemical surface, respectively. Besides the evolution process, the characterization of tribofilms also reveals the possibility of forming new meta-stable phases (chemical compounds) after tribological testing. Patchy tribofilms and progressive tribofilms have been observed from the SEM analysis and the EDX results showed existence of Mo-S-P as the composition of tribo-chemical films. The Raman spectroscopy analysis of tribofilms showed significant difference (such as formation of poly-molybdates) in chemical information of nanolubricants and tribofilms, which is an indication of the formation of friction polymer [4–5]. Additionally, phosphates and oxides, acting as components of surface protecting layer of tribofilms, have been found on surface by XPS technique. Moreover, MoS 2 nanoparticles are found to navigate into surface asperities to protect the contacting surfaces. The results (information about the chemical states of the tribofilm) obtained from different characterization techniques can be used to explain the mechanism of friction and wear reduction associated with MoS 2 multi-component nanolubrication system that has been reported in the literature.

Tribological properties of pure iron were studied in argon environments containing trace water which is controlled at the value between 1 and 10,000 ppb and virtually no oxygen. The experimental data were compared with those obtained in our previous study with the same conditions of experiment but in hydrogen. The influences of trace water were recognized in both gases and confirmed not peculiar to a hydrogen environment. The coefficients of friction and specific wear rates were different to some extent between argon and hydrogen environments. The differences were supposed to be attributed to the influences of hydrogen atoms which chemisorbed on pure iron atoms appeared on the nascent surface made by sliding. Whether hydrogen and water have synergy effect on influencing tribological properties was not clarified in this study.

In many tribological applications, such as journal bearings and gears, a fluid film is used to accommodate velocity between moving surfaces. To model the behavior of this film and to predict its ability to carry load, the Reynolds equation is predominantly employed. As computational processing power continues to increase, computational fluid dynamics (CFD) is increasingly being employed to predict the fluid behavior in lubrication environments. Using CFD is advantageous in that it can provide a more general approximation to the Navier-Stokes equations than the Reynolds equation. Moreover, using CFD allows for the simulation of multiphase flows as could occur during bearing contamination and bearing exit conditions. Because the bearing surfaces move relative to each other as they obtain equilibrium with the fluid pressure, there is a need to incorporate the moving boundary into the CFD calculation, which is a non-trivial task. In this work, a fluid-structure interaction (FSI) technique is explored as an approach to model the dynamic coupling between the moving bearing surfaces and the lubricant. The benefits of using an FSI approach are discussed and the results of its implementation in a lubricated sliding contact model are presented.

The tribological performance of different microtexture shapes is evaluated for the case of gas lubricated textured parallel slider bearings. The geometry of each shape is optimized in terms of load carrying capacity, after which the performance of different shapes is compared relative to each other. The ellipsoidal shape is found to generate the largest load carrying capacity.

A model of elastohydrodynamic lubrication of piston skirt is developed in this paper. The secondary motion of the piston, the lubrication and the elastic deformations of skirt and cylinder are described by a transient strongly nonlinear system coming from the coupling of the dynamics equations of piston secondary motion and the Reynolds equation. The iterative Newton-Raphson method in conjunction with Murty’s algorithm for cavitation was used to solve the problem. An optimum skirt curved profile, which maintain piston in optimum performance characteristics, is adopted. Using the tribological performance of the lubricated skirt-cylinder, the results — minimum oil-film thickness, maximum pressure in the lubricant film and friction — are compared to the elastohydrodynamic solution and the rigid skirt-cylinder solution. The effect of elastic deformation of both skirt and cylinder show that elastohydrodynamic analysis is necessary for an accurate prediction of a piston-cylinder performance. The computational work, applied to a solid skirt piston of a V-8 direct injection diesel engine truck, should be a powerful design analysis tool, which can be used to increase the available engine power through optimum piston performance characteristics.

One of the most commonly used tribological thin-film coatings is Chromium Nitride (CrN), typically deposited by PVD process. Examples of current applications of this coating include cutting and forming tools: ICE piston ring, hydrodynamic pumps, etc. In selecting coating for tribological applications, one of the critical parameter is the coating thickness. In the present work, we experimentally studied the effect of coating thickness on friction and wear performance of CrN coatings under unidirectional sliding. Test were conducted with ∼ 1, 5 and 10 microns thick coatings deposited on a hardened H-13 steel substrate by plasma enhanced magnetron sputtering (PEMS) process. The friction behavior was strongly dependent on coating thickness, especially at relatively low loads. At higher load however, the thinner coating (1 μm) was quickly worn through while the thicker ones (5 and 10 μm) remained intact. Wear in both, the counterface WC material and the coating was also observed to depend on coating thickness. The observed effect on coating thickness on tribological behavior is attributed to differences in the microstructure and mechanical behaviors of coatings as function of thickness.

The paper presents a new idea of foil water-lubricated bearing and the methodology of hydrodynamic characteristics calculations. Two different computer models were built in order to assess the theoretical characteristics of these bearings. Firstly a structural model coupled with a hydrodynamic fluid model which takes into account: fluid flow in the deformed fluid gap — a specific design of bearing support and the friction in bearing support. The second model is based on the fluid structure interaction simulation. Due to the fact that it is necessary to define physical properties of the materials for computer models, special tribology and stiffness tests of actual materials intended to be used in the prototype bearing were performed. The test rig was modernised by installing pressure sensors on bush perimeter in two parallel planes in order to verify the method of the calculation of the bearing.

CVTs are complex tribological systems with high potential concerning increasing efficiency of powertrains. To improve the performance of CVTs it is necessary to deepen the knowledge concerning parameters influencing the system behavior.

When a material is subjected to repeated sliding contact, a surface fatigue and crack nucleation may occur on its surface. This damage weakens the material and can lead to debris formation. In many practical engineering assemblies, a thin PEEK (poly-ether-ether-ketone) coating is applied to reduce the damage, since PEEK exhibits wear resistance, corrosion resistance self-lubricating capacity and is lightweight. However, little is known about the effect of coating thickness on the plastic deformation, residual stresses and energy dissipation of PEEK when placed under sliding load. Moreover, the effect of substrate rigidity on coating stresses and deformation under sliding load are also under-researched. Having such knowledge is of significant importance in order to reduce damage of engineering parts and extend their lifetime. In this study, the effects of PEEK coating thickness and substrate elasticity were analyzed using a 3D ball-on-flat finite element model as well as experimental analysis using a linear reciprocating tribometer. The experimental tests were performed with samples that incorporated PEEK coatings of various thicknesses on alumina and steel substrates. It was found that under a constant normal load, stresses, strain and energy dissipation were sensitive to both substrate material and coating thickness. It is shown from both simulation and experiment, the optimum combination, within the range the experiments were conducted, for minimizing residual stress and possible fatigue damage was an alumina substrate with 35μm PEEK coating thickness.

In this work, the friction and wear of poly-alpha-olefin (PAO10) base oil with 3 wt. % boron nitride (BN), and molybdenum disulfide (MoS 2 ) nanoparticles were studied. The formulations were tested using cast iron cylinder-liner segments reciprocating against aluminum alloy piston-skirt segments at 20, 40, and 100°C. The results showed that at a load of 250 N and reciprocating frequency of 2 Hz BN did not lower friction, whereas MoS 2 nanoparticles were very effective at reducing both friction and wear, compared to the base oil. Raman spectroscopy showed the formation of an aligned MoS 2 layer on the cast iron liner surface, which functioned as a tribofilm. In the case of the cast iron liner tested with BN nanolubricant there were no traces of BN that could be related to tribofilm formation. The effect of surfactant was also studied and it was found that not only it was beneficial in dispersing the nanoparticles in oil, but also produced some reduction in friction and wear even as stand-alone additive in PAO10.

Energy and environment are of major concern in internal combustion engine component design. The piston ring-cylinder liner (PRCL) contact plays an essential part in design and is highlighted in this study. In fact, the rings ensure the sealing property, reducing the environmental impact by avoiding lubricant contamination (blow-by) and lubricant consumption. Unfortunately, when sealing, the rings generate between 11 to 24% of the friction losses in an internal combustion engine [1], thus reducing the energy efficiency of the engine. The cylinder liner surface features a special micro-geometry, a classical one is the cross-hatching pattern, obtained by honing. This texturing acts as a micro-bearing, oil reservoir and debris trap. Understanding the influence of texture parameters as groove depth and width or angle, will allow tribological improvements of the PRCL contact. The 2D transient Reynolds equation has to be solved for this kind of surface. The statistical method using the Patir and Cheng [2] flow factors is widely used. This approach lumps the different components of the surface (grooves and plateaux) and does not consider the roughness directionality. Methods decoupling both components, like the homogenization method [3] are also used. Another alternative is to use a deterministic model on measured surfaces, but this is a “hugely” expensive approach. Multigrid methods [4] are used to drastically reduce the calculational cost. The aim of the current study is to facilitate the understanding of measured surface calculations. Hence, analytical surfaces are used. They allow a flexible handling of the cross-hatching parameters. The plateaux are perfectly smooth and the grooves are sinusoidally shaped. The top ring is modelled using a parabolic profile. Periodic boundary conditions are used in the orthoradial direction and zero pressure conditions (Dirichlet) in the axial direction. To investigate the effect of different parameters, various imposed film thicknesses are applied and the mean load carrying capacity (LCC) over time is calculated. When representing the LCC corresponding to each parameter compared to the smooth LCC, as a function of the logarithm of the minimum film thickness, the curves are quite linear for small values of the film thickness and then for larger values they converge to 1.

Friction and wear behavior of lubricated sliding contact is determined by the operating lubrication regime. A useful approach to determining the operating lubrication regime is the calculation of the λ ratio, which is defined as the ratio of lubricant fluid film thickness (h), and the composite surface roughness (ơ) of contacting surfaces (λ = h/ơ). Thin-film tribological coatings are increasingly being used for application in lubricated machine elements such as gears and bearings. It is usually assumed by design engineers that application of thin-film coatings has no effect on fluid-film lubrication. This paper presents our experimental investigation of the impact of several (5) commercially available coatings on lubrication regime during a unidirectional sliding contact. Using a ball-on-flat contact configuration and lubricated with PAO basestock oil, tests were conducted in which the λ ratio was varied as a function of time, for both uncoated and coated flat specimen. In test with uncoated flat, the various distinctive lubrication regime of hydrodynamic, mixed and boundary were observed as indicated by the measured friction coefficient (Stribeck Curve). In tests with some of the coatings, especially the carbon based DLCs, there was no obvious distinctive transition in lubrication regime. In other coatings (ex. TiCN), various lubrication regime were also observed; although the rate of transition from one regime to the other was different. The effects of coatings are attributed to their inherent mechanical and tribological properties as well as their impact on the run-in process.

Understanding granular flows has always been important for predicting natural phenomena such as rockslides and soil erosion, as well as industrial processes such as coal-based fossil fuel systems and solids processing. As such, it becomes important to understand granular flows from both a classical granular flow and tribological perspective. Inherently important in the study of granular flows is the study of the individual particle level interactions, which define the global behavior of the flow. The current work examines both the coefficient of restitution (COR) and coefficient of friction (COF) for various material combinations. COR and tribological experiments are performed on various sphere and plate (disk) materials, such as low carbon steel, tungsten carbide (WC), and NITINOL 60.

The trend of decreasing of lubricant film thickness in tribological systems is one of the important features of current tribology stirred up by the quest for higher efficiency and energy saving. As a result, the influence of the surface micro geometry on the contact performance and machine component life increases steadily. This has led to a systematic effort to develop a theory that describes unifying mechanism governing the amplitude reduction of harmonic patterns in EHL contact known as amplitude attenuation principle [1–2]. This theory provides formulas that can serve as a simple tool to predict the deformed geometry inside the contact for arbitrary micro geometry when used in combination with a Fourier analysis. Therefore, it is possible to give a reasonable explanation of the basic phenomena involved in real rough surface EHL and mixed lubricated contacts.

Presented in this study is a new class of “greener” lubricants, room temperature ionic liquids, that represent a promising potential solution to many of the problems associated with both conventional lubricants and those based on natural oils. In this study, friction and wear tests were carried out using a pin-on-disk tribometer under ambient conditions to characterize the performance of the ionic liquids as lubricants. Specifically, ionic liquids consisting of salicylate, benzoate (common food additives) and saccharinate (an artificial sweetener) anions with conventional phosponium cations were evaluated as lubricants and compared to petroleum-based lubricants and natural oils in regards to structure and performance. The ionic liquids generally demonstrated better tribological performance than either the petroleum-based lubricants or natural oils. The mechanisms governing the chemical composition and improved tribological performance are discussed while highlighting possible industrial applications of this new class of lubricants.

Insufficient friction at the shoe-floor interface causes a large number of slip and falling accidents each year. Developing solutions for enhancing shoe-floor-contaminant friction requires understanding the mechanisms that contribute to slippery surfaces. Over the past several years, our research group has conducted several experimental and modeling studies to reveal the critical tribological mechanisms contributing to shoe-floor-contaminant friction. This extended abstract will discuss the findings of these studies to: 1) determine the lubrication regime(s) that is/are most relevant to under-shoe conditions during slipping; 2) quantify how under-shoe conditions, shoes and flooring affect the two main contributions to boundary lubrication: adhesion and hysteresis; and 3) describe how this information can be used to design slip-resistant shoes and flooring. To identify the lubrication regime, interfacial pressures at the shoe-floor-contaminant interface were measured and coefficient of friction was monitored. Low viscous fluids and shoes with at least 2mm of tread were found to have negligible interfacial pressures and moderate friction coefficients (0.07–0.40). Untreaded shoes combined with high viscous fluids led to high interfacial pressures that supported up to 40% of the normal load and low friction coefficients (<0.01). These results suggest that mixed/elasto-hydrodynamic lubrication is relevant in some untreaded conditions but that boundary lubrication is relevant for most other conditions. In boundary lubrication, the primary factors contributing to friction are adhesion and hysteresis. Experimental data and finite element models demonstrate that hysteresis friction increases with floor roughness and the ratio of shoe to floor hardness. Adhesion friction is dependent on real area of contact and the shear stress required to break junctions. Experimental data suggests that adhesion is dependent on the fluid lubricant, sliding speed, floor roughness and shoe material. Finite element models confirm that a reduction in the real area of contact occurs with increasing floor roughness and sliding speed, consistent with the experimental adhesion effects. Ensuring that the shoe-floor-fluid interface is operating in the boundary lubrication regime requires establishing minimum tread threshold for fluid lubricants that are likely to be found in a given environment. Designing a high hysteresis shoe-floor combination is preferred because it is relatively unaffected by fluid contaminants or under-shoe conditions (i.e. sliding speed). Therefore, ensuring a minimum tread depth is used along with increasing floor roughness and shoe to floor hardness may be effective in addition to minimum tread thresholds.

Discrete Model is based on the description of the physical state (velocity, position, temperature, magnetic moment, electric potential ..) of a large number of discrete elements that form the media to be studied. It is not basedon a continuous description of the media. Thus, it is particularly well adapted to describe media evolution driven by discontinuous phenomena like the description of multi fracturation followed by debris flow like wear study. Recently, the use of discrete model has been widened to face problem encountered with complex rheological behavior and/or multi-physical behavior. Multi-physical problems face complex mathematical formulation because of the mixing of different families of differential equations when continuous approach is chosen. With the discrete model, each particle has a physical state and state evolution is due to local physical particle interaction: it is often much simple to write. From the beginning of the years 2000, this method has been widely applied for the study of tribological problems. Wear has been investigated[1], thermo-mechanical behavior of a contact[2], subsurface damage due to surface polishing[4]… Recently, it has been shownhow quantitative results can be obtained with this method[4]. To help and promote research in this area, a platform GranOO has been developed under a C++ environment and is distributed under thefree GPL license. The goal of this platform is to offer to researchers, especially in the tribology domain, a numerical and easy to use environment to facilitate the access to Discrete Element simulations. The main aspect of this platform ispresented in the extended abstract and some applicationsgiven as examples. Details can be found on url www.granoo.org.

Several kinds of Polytetrafluoroethylene (PTFE) composites are currently being used in reciprocating hydrogen gas compressors as seal material which should articulate against metal counterfaces in pressurized hydrogen gas. Although their friction and wear behavior has large impact on the efficiency and reliability of gas compressors, available information about tribological characteristics of PTFE composites in high pressure hydrogen gas is quite limited. In this study, friction and wear of graphite filled PTFE and bronze filled PTFE were evaluated in the 40 MPa hydrogen gas environment by using a pin-on-disk type apparatus enclosed in a high pressure vessel to supply experimental data for the design of gas compressors in hydrogen fuelling stations. AISI316L austenitic stainless steel disk was used as a sliding counterface. All experiments were conducted under dry condition with the average contact pressure of 1.8 MPa, the sliding speed of 100 mm/s and the gas temperature of 327 K. The friction force exerted between PTFE composites and stainless steel was evaluated by a load cell during the experiment and the wear rate of composites was evaluated from the weight loss of pin specimens. In addition, chemical analysis of the polymer transfer film formed on the disk surface were conducted by using X-ray photoelectron spectrometer. Friction and wear tests were also conducted in 40 MPa helium gas for comparison. Results indicated that bronze filled PTFE was more sensitive to the gas pressure and gas species; it showed good friction and wear behavior in high pressure hydrogen, although friction in high pressure helium became very high. On the other hand, the effects of high pressure gas environment were relatively small for the friction and wear of graphite filled PTFE.