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Showing papers in "Tribology Transactions in 2015"


Journal ArticleDOI
TL;DR: In this paper, it is suggested and supported by the evidence presented within this article that WEC is neither related to the presence of nonmetallic inclusions nor related to other impurities in the steel.
Abstract: White etching crack (WEC) failure is distinct to classical fatigue and driven by the composition of lubricants under special loading conditions; for example, slippage and electricity. The white etching area (WEA) within WEC contains carbon supersaturated ferrite (bcc-iron) and carbides, with a size of a few nanometers. This article presents investigations supporting the hypothesis that WEC processes start within a failure-free period by successive accumulation of a structural distortion. This can be measured by acoustic emission. Failure statistics show a steep ascent in the Weibull diagram (s values beyond 1) leading to the assumption that WEC processes start unsuspicious, as one would see as a failure-free period, but imply a hidden subsurface accumulation of material defects. It is suggested and supported by the evidence presented within this article that WEC is neither related to the presence of nonmetallic inclusions nor related to other impurities in the steel. Instead, the failure is a sequence and...

75 citations


Journal ArticleDOI
TL;DR: In this article, the influence of graphite particulates on the dry sliding wear behavior of aluminum alloy 7075 (AA7075)graphite composites has been evaluated using a pin-on-disc apparatus.
Abstract: The influence of graphite particulates on the dry sliding wear behavior of aluminum alloy 7075 (AA7075)–graphite composites has been evaluated using a pin-on-disc apparatus. The materials were fabricated by a liquid casting technique. Composites with 5–20 wt% graphite particles were processed. The casted composites were subjected to T6 heat treatment. The effect of sliding speed and sliding distance has been studied under dry sliding conditions. The hardness of the composites is measured using a Brinell hardness tester and their tensile strength is measured using a universal testing machine. The wear rate of the composites reduced with the addition of graphite content and reached a minimum with 5 wt% graphite content. The coefficient of friction is decreased with the addition of graphite content and reached a minimum at 5 wt% graphite. The effect of graphite on hardness and tensile strength is also studied. The worn surfaces of the pin specimen are analyzed with scanning electron microscopy. The 7075 alum...

70 citations


Journal ArticleDOI
TL;DR: In this paper, the authors used both a controlled stress and a controlled strain rheometer to characterize lubricating grease in shear, creep, stress relaxation, and oscillatory flow, with a main focus on determining the yield stress.
Abstract: An experimental study using both a controlled stress and a controlled strain rheometer has been undertaken to characterize lubricating grease in shear, creep, stress relaxation, and oscillatory flow, with a main focus on determining the yield stress. The yield stress was examined using a cone–plate and parallel-plate system with smooth and rough surfaces. Clear discrepancies were observed in the yield stress values obtained using different techniques where oscillatory strain sweep measurements seem to be the best choice. This technique is less sensitive to wall slip, shows good reproducibility, and is relatively easy to perform. The method also shows that the yield stress is a function of the imposed frequency and therefore of the time domain. At lower values of shear—that is, in the linear viscoelastic regime—there is no structural breakdown and the rheology of the grease can be described by the Maxwell model where the stress and the strain are almost proportional to each other. Based on this observation, a novel method to determine the yield stress is proposed: “The yield stress can be determined from the point where this linearity no longer applies.” This method is compared to those that are commonly used. The yield stress was found to depend exponentially on temperature and linearly on frequency.

67 citations


Journal ArticleDOI
TL;DR: In this paper, the additive package of an SAE 5W30 engine oil was modified in order to stably disperse the nanoparticles and avoid counterproductive interactions with the other components of the package (antifoam, antioxidant, detergents, antiwear and antifriction additives).
Abstract: The development of new advanced lubricants is a key factor for the production of cleaner and more durable internal combustion engines. New improved antifriction and antiwear additives are required. The inclusion of nanoparticles known as solid lubricants (MoS2 and WS2 inorganic fullerenes) in fully formulated engine oils could help to improve the performance of the lubricant and of the engine.The AddNano Consortium, partially funded by the European Commission, investigated the possibility of including inorganic fullerenes in the formulation of engine oils. MoS2 nanoparticles integrated in the additive package of an SAE 5W30 engine oil showed a 50% reduction in the coefficient of friction in tribological lab-scale experiments. The nano-oil was formulated by modifying the additive package in order to stably disperse the nanoparticles and avoid counterproductive interactions with the other components of the package (antifoam, antioxidant, detergents, antiwear and antifriction additives).In the present work, ...

59 citations


Journal ArticleDOI
TL;DR: In this paper, the tribological behavior of Ti-containing MoS2 film is studied under sliding and rolling contacts. And the rolling contact performance of the Ti-MoS2 films was evaluated using a thrust bearing tribometer and ball-on-rod tribometers at ∼1 GPa Hertzian contact stress.
Abstract: In this work, the tribological behavior of Ti-containing MoS2 film is studied under sliding and rolling contacts. Ti-MoS2 films deposited on AISI 52100 and M50 specimens contain ∼16 at% Ti are slightly substoichiometric in sulfur and have an amorphous structure. Experiments show that the friction and wear performance of Ti-MoS2 films is influenced by humidity and temperature.For the first time, the rolling contact performance of Ti-MoS2 films was evaluated using a thrust bearing tribometer and ball-on-rod tribometers at ∼1 GPa Hertzian contact stress. Rolling contact measurements performed in humid air indicate that the useful life of Ti-MoS2 as a solid lubricant depends upon the amount of coating material retained in the contacts. Results of the rolling contact experiments performed in a vacuum indicate that Ti-MoS2 film on balls may function extremely well as a solid lubricant for ball bearings operating in vacuum.

56 citations


Journal ArticleDOI
TL;DR: In this article, the friction and tribology properties of modified epoxy resins were compared with properties of neat resins with three different nanoparticle configurations: 0.3% MWCNT, 0.5% BN, and 0.4% BORON NITRIDE.
Abstract: Epoxy resins are widely used in engineering applications. However, their low thermal stability limits their usage at high sliding velocities and loads. The mechanical properties and thermal stability of a machine element subjected to friction and wear are very important. In this study, friction and tribology behaviors of multiwalled carbon nanotubes (MWCNTs) and boron nitride (BN)-modified epoxy resin have been investigated. Epoxy resin modified by three different nanoparticle configurations, 0.3% MWCNT, 0.5% BN, and 0.5% MWCNT/0.3% BN, was investigated. The tribological characteristics of nanoparticle-modified epoxy resin were compared with properties of neat resin. The friction and tribological behavior of modified epoxy resin were tested using a ball-on-disc test stand at 1.2 and 1.5 ms−1 sliding velocities under 10 N applied load. The tests were done under dry condition and 1,800 m distance. The friction coefficient, wear loss, and temperature increase during testing were recorded and compared with th...

56 citations


Journal ArticleDOI
TL;DR: In this paper, the authors investigated the dry sliding friction and wear behavior of 316L austenitic stainless steel and found that for small abrasive particles, the friction coefficients increase with increasing normal load.
Abstract: The present work investigates the dry sliding friction and wear behavior of 316L austenitic stainless steel. Wear tests are performed on a pin-on-plane configuration against abrasive silicon carbide grains ranging from very large (200 μm) to small (15 μm) particles. The experiments are conducted at room temperature under different normal loads of 25–75 N. The wear damage mechanisms and wear debris are analysed using scanning electron microscope (SEM) observations. It is shown that for small abrasive particles, the friction coefficients increase with increasing normal load. However, for large abrasive particles, a reverse trend is observed. This difference is partly explained by a change in wear mechanisms.Finally, surface roughness measurment of the worn surfaces are performed after wear tests. The relationship between the 3D fractal dimension and wear rate is investigated based on fractal theory. The 3D fractal analysis of the worn surfaces showed that higher values of fractal dimensions indicate a large...

48 citations


Journal ArticleDOI
TL;DR: In this paper, an experimental study of trymethylolpropane (TMP) ester as an energy-saving and biodegradable lubricant was conducted and compared with commercial lubricant and paraffin mineral oil using a four-ball tribometer.
Abstract: The purpose of this research is an experimental study of Calophyllum inophyllum (CI)-based trymethylolpropane (TMP) ester as an energy-saving and biodegradable lubricant and compare it with commercial lubricant and paraffin mineral oil using a four-ball tribometer. CI-based TMP ester is a renewable lubricant that is nonedible, biodegradable, and nontoxic and has net zero greenhouse gases. The TMP ester was produced from CI oil, which has high lubricity properties such as higher density, higher viscosity at both 40°C and 100°C and higher viscosity index (VI). Experiments were conducted during 3,600 s with constant load of 40 kg and constant sliding speed of 1,200 rpm at temperatures of 50, 60, 70, 80, 90, and 100°C for all three types of lubricant. The results show that CI TMP ester had the lowest coefficient of friction (COF) as well as lower consumption of energy at all test temperatures, but the worn surface roughness average (Ra) and wear scar diameter were higher compared to paraffin mineral oil and c...

46 citations


Journal ArticleDOI
TL;DR: In this paper, a general approach for estimating rolling bearing lifetimes is proposed, in which the surface-originated damage is explicitly formulated into the basic fatigue equations of the rolling contact.
Abstract: Until now the estimation of rolling bearing life has been based on engineering models that consider an equivalent stress, originated beneath the contact surface, that is applied to the stressed volume of the rolling contact. Through the years, fatigue surface–originated failures, resulting from reduced lubrication or contamination, have been incorporated into the estimation of the bearing life by applying a penalty to the overall equivalent stress of the rolling contact. Due to this simplification, the accounting of some specific failure modes originated directly at the surface of the rolling contact can be challenging. In the present article, this issue is addressed by developing a general approach for rolling contact life in which the surface-originated damage is explicitly formulated into the basic fatigue equations of the rolling contact. This is achieved by introducing a function to describe surface-originated failures and coupling it with the traditional subsurface-originated fatigue risk of the rol...

46 citations


Journal ArticleDOI
TL;DR: In this article, the influence of hybrid reinforcements including silicon carbide and graphite particles with a size 37-50 μm on the wear characteristics of AZ91 magnesium alloy was studied and the results show that the wear resistance of composites was much better than that of the base matrix material under the test conditions.
Abstract: The influence of hybrid reinforcements including silicon carbide and graphite particles with a size 37–50 μm on the wear characteristics of AZ91 magnesium alloy was studied. The dry sliding wear test was conducted using a pin-on-disc wear testing machine in the load range of 20 to 80 N at different sliding velocities in the range of 1.047 to 2.618 m/s. The results show that the wear resistance of composites was much better than that of the base matrix material under the test conditions. At a speed of 1.047 m/s and load of 40 N, the wear rate (mm3/km) of the unreinforced alloy was 6.3, which reduced to 3.8 in the case of 3% reinforced composite. The antiwear ability of magnesium alloy composite was found to improve substantially with the increase in silicon carbide and graphite content from 1 to 3% by weight and the wear rate was found to decrease considerably. At a speed of 1.047 m/s and load of 80 N, the wear rate (mm3/km) reduced from 11.8 to 9.1 when the reinforcement content increased from 1 to 3%. Ho...

45 citations


Journal ArticleDOI
In-Ju Kim1
TL;DR: In this paper, a wear concept and theory model were suggested to explore the underlying tribological characteristics of the shoe surfaces and identify its impact on pedestrian walkway slip-resistance performance.
Abstract: Shoe surfaces are continuously changed during pedestrian ambulation. Such changes include significant damage mechanism of shoe soles/heels, but their importance, fundamental perception, and effects on slip-resistance properties have hardly been discussed in the literature. This study aimed to understand wear development on shoe surfaces and identify its impact on pedestrian walkway slip-resistance performance. A wear concept and theory model were suggested to explore the underlying tribological characteristics of the shoe surfaces. Dynamic friction tests were conducted between two double-density polyurethane shoes and ceramic tiles. Wear formation and development on the shoe surfaces were quantitatively and qualitatively examined by surface roughness parameters and microscopic observations before and after the tests. Overall results clearly showed that the topographic structures of the shoe surfaces were largely changed by a series of wear mechanisms such as abrasion, ploughing, adhesion, and fatigue. Thi...

Journal ArticleDOI
TL;DR: In this article, the slurry erosion resistance of laser-clad NiCoFeCrAl3 high-entropy alloy (HEA) coating was investigated by using a jet erosion testing machine.
Abstract: The slurry erosion resistance of laser-clad NiCoFeCrAl3 high-entropy alloy (HEA) coating was investigated by using a jet erosion testing machine. When the impingement angle increased from 15° to 90°, the volume loss of the HEA coating was accelerated firstly and then followed with a slight deceleration. The largest volume loss of this HEA coating was 4.1 mm3, which was acquired at a 45° impingement angle after a 30-min erosion time with a 15 wt% SiO2 particles (350–600 μm) at an impact velocity of 13 m s−1. Under the same erosion situation, the volume loss of 17-7 PH stainless steel was 5.4 mm3, which means that the HEA coating possesses better erosion resistance under this situation. Annealing treatment is beneficial to improve the erosion resistance of HEA coatings. The 950°C annealed HEA coating had the best erosion resistance because the intermetallic compound Cr3Ni2 was precipitated from the matrix and the volume loss was reduced to 3.5 mm3 at a 45° impingement angle. The worn surface morphologies of...

Journal ArticleDOI
TL;DR: In this article, the friction and wear behavior of microwave-clad WC-12Co cermet was examined using a pin-on-disk tribometer as per ASTM G99.
Abstract: In the present work, the friction and wear behavior of microwave-clad WC-12Co cermet was examined using a pin-on-disk tribometer as per ASTM G99. Microwave clads were tested against an EN-31 countersurface in unlubricated conditions. The WC-12Co clads were developed using an industrial microwave applicator at 2.45 GHz and 1.4 kW. The influence of varying normal load on the tribological characteristics of the microwave-induced clads have been investigated. Responses of the WC-12Co microwave clads and AISI 304 stainless steel substrate were monitored and the resulting wear was subsequently analyzed in terms of wear rate, pressure–velocity–time (p-v-t) characteristics, and friction coefficient. The worn surfaces of the WC-12Co microwave clad and AISI 304 substrate were studied using scanning electron microscope. Wear debris was analyzed using scanning electron microscopy and energy-dispersive X-ray spectroscopy. The developed clads exhibit significant resistance to wear attributable to the microwave-induced ...

Journal ArticleDOI
TL;DR: This study revealed that the physical and unique chemical properties in palm oil can optimize the rate of friction and wear on the metal acetabular cup and thus allow for a stable implant of MoM.
Abstract: Metal-on-metal (MoM) hip replacements are commonly used hip implants. However, one of the issues under debate is the interference of friction and wear. The purpose of this feasibility study is to elucidate the performance of palm lubrication between the femoral head and the acetabular cup. In the tribology of hip implants, the use of palm olein, palm kernel oil, and palm fatty acid distillate as synthetic lubricants for human joints has shown tremendous potential. A modified pin-on-disc as hip screening has been used to evaluate the friction and wear on an acetabular cup with an inner diameter of 28 mm. The wear debris was then observed with microscopy image analysis. This study revealed that the physical and unique chemical properties in palm oil can optimize the rate of friction and wear on the metal acetabular cup and thus allow for a stable implant of MoM.

Journal ArticleDOI
TL;DR: In this article, the tribological properties of the Ti composite coatings were systematically investigated using steel ball-on-disc microtribological testing, and it was concluded that the wear resistance of Ti composite coating decreased with a further increase in the Al-Cr-Fe particle content to 30% due to the significantly increased volume of micropores in the composite coating.
Abstract: Titanium (Ti) composite coatings were prepared on commercially available Ti substrates via a cold-spray process. Quasicrystalline Al-Cr-Fe particles were incorporated in the cold-sprayed Ti matrices at different contents to form a new type of wear-resistant Ti composite coating. The tribological properties of the Ti composite coatings were systematically investigated using steel ball-on-disc microtribological testing. The incorporation of 10 wt% Al-Cr-Fe particles gave rise to the higher wear resistance of the Ti composite coating than that of the Ti coating due to the higher wear resistance of the Al-Cr-Fe particles than that of the Ti matrix. As a result, an increase in the Al-Cr-Fe particle content to 20 wt% increased the wear resistance of the Ti composite coating. However, the wear resistance of the Ti composite coating decreased with a further increase in the Al-Cr-Fe particle content to 30 wt% due to the significantly increased volume of micropores in the composite coating. It could be concluded th...

Journal ArticleDOI
TL;DR: In this article, the surface rolling contact fatigue (SRCF) in rolling bearings is investigated by means of dedicated experiments and numerical simulations of the damage progression in pre-indented inner ring raceways in roller and ball bearings.
Abstract: The mechanism of surface rolling contact fatigue (SRCF) in rolling bearings is investigated by means of dedicated experiments and numerical simulations of the damage progression. Pre-indented inner ring raceways in roller and ball bearings were extensively endurance tested. It is observed that spalls originated from indentations in ball bearings develop initially at the trailing edge of a pre-indented raceway with a typical V-shaped spall. In this location, the raceway material first detaches at the edge of the dent, forming a V-shaped damaged area, before growing at fast rate along the raceway. Roller bearings, however, follow the well-known behavior of slowly growing the spall directly across the raceway, before continuing along the rolling path. An existing physically based rolling contact fatigue model able to predict (1) material particle detachment by surface rolling contact fatigue and (2) the effect of the elastohydrodynamic lubrication (EHL) in such a process is adapted and used to simulate the surface damage growth in the two rolling bearing configurations. It is found that the model is able to describe well the experimental results, shedding some light on the developing mechanism of the two SRCF configurations. The difference between ball and roller bearing damage inception and progression is explained and discussed in detail.

Journal ArticleDOI
TL;DR: In this paper, the tribological properties of 30 vol% carbon fiber and PTFE/graphite-reinforced polyetheretherketone (PEEK-2) sliding against AISI630 steel under seawater lubrication were investigated with a ring-on-ring contact test apparatus.
Abstract: Tribological behaviors of 30 vol% carbon fiber–reinforced polyetheretherketone (PEEK-1) and 30 vol% carbon fiber/PTFE/graphite-reinforced polyetheretherketone (PEEK-2) sliding against AISI630 steel under seawater lubrication were investigated comparatively with a ring-on-ring contact test apparatus. The results revealed that PEEK-2 had a lower friction coefficient and much better wear resistance than PEEK-1, especially under a relatively heavy load. Furthermore, PEEK-2 exhibited much better friction and wear properties under seawater lubrication than under dry friction, and it was slightly inferior to that under pure water lubrication due to the corrosive effect of seawater on the surface of AISI630 steel. Additionally, the worn surface morphology of PEEK composites and AISI630 steel were obtained through scanning electron microscopy (SEM) and optical microscopy, respectively. The main tribological mechanisms of the friction pair under seawater lubrication were abrasive wear and indirect corrosive wear. T...

Journal ArticleDOI
TL;DR: In this paper, a mixed elastohydrodrynamic (EHL) model for journal bearings considering an axial flow due to shaft axial motion and misalignment is developed for lubrication performance evaluation.
Abstract: A mixed elastohydrodrynamic (EHL) model for journal bearings considering an axial flow due to shaft axial motion and misalignment is developed for lubrication performance evaluation A new, faster mixed EHL computing technology utilizing the odd–even successive overrelaxation (OESOR) parallel numerical iterative method is proposed based on the red–black successive overrelaxation (RBSOR) method to minimize the execution time prolonged by the complexity caused by the axial flow and misalignments The multithreaded computing scheme conducted by the OpenMP directive using different meshes and threads suggests that the OESOR method exhibits better efficiency A series of transient analyses was conducted to solve the mixed EHL model with the parallel OESOR method The results show that the axial flow and misalignments significantly affect the average pressure, hydrodynamic and asperity contact pressure, elastic deformation, and other characteristics of the journal bearings

Journal ArticleDOI
TL;DR: In this paper, the reduced lubrication performance of hybrid rolling contacts, versus full-steel ones, is studied in detail by means of rolling bearing fatigue experiments and a theoretical micropitting model, and it is found that the large improvement in surface fatigue resistance of hybrid contacts cannot be explained solely on the basis of the unavoidable differences in some of the roughness parameters existing between the full steel and hybrid contacts.
Abstract: Hybrid bearings—that is, bearings with ceramic rolling elements and steel rings—are often used in applications with reduced (i.e., boundary or mixed) lubrication conditions. The mechanisms by which hybrid bearings perform significantly better than full-steel ones in these cases are so far unclear, although a number of published works have shown experimental results in which appreciable performance benefits were obtained by the use of hybrid bearings under boundary or mixed lubrication. In this article, the reduced lubrication performance of hybrid rolling contacts, versus full-steel ones, is studied in detail by means of rolling bearing fatigue experiments and a theoretical micropitting model. It is found that the large improvement in surface fatigue resistance of hybrid contacts cannot be explained solely on the basis of the unavoidable differences in some of the roughness parameters existing between the full-steel and hybrid contacts. It is also necessary to take into account a considerable reduction in...

Journal ArticleDOI
TL;DR: In this paper, a wear mechanism map for aluminum alloys at a very slow sliding speed range ( 0.01m/s) was proposed. But the wear process was placed at the mild wear regime, characterized by oxidation and delamination mechanisms.
Abstract: The investigated slow sliding speeds presented in this work enable the understanding of the wear behavior on aluminum alloys and could possibly facilitate the completion of the previously proposed wear mechanism map for aluminum at this slow sliding speed range. Dry sliding block-on-ring wear tests were carried out on aluminum alloys, AA5754 (Al-Mg), AA6082 (Al-Mg-Si), and AA7075 (Al-Zn-Cu), at a very slow sliding speed range ( 0.01 m/s), the specimens exhibited a wear process placed at the mild wear regime, characterized by oxidation and delamination mechanisms ...

Journal ArticleDOI
Zhiwu Han1, Feng Hailong1, Wei Yin1, Shichao Niu1, Junqiu Zhang1, Chen Daobing1 
TL;DR: In this paper, a bionic coupling method inspired by the morphology and flexibility of desert scorpion (Androctonus australis) carapace was proposed to improve the particle erosion resistance of mechanical surfaces.
Abstract: To improve the particle erosion resistance of mechanical surfaces, a bionic coupling method inspired by the morphology and flexibility of desert scorpion (Androctonus australis) carapace was proposed in this study. The finite element method based on ANSYS/FLUENT was applied to examine the erosion resistance of a bionic V-shaped model. Subsequently, an experimental research was carried out to compare the particle erosion resistance performance of three types of specimens, namely, smooth, bionic V-shaped, and bionic V-shaped and flexibility coupling. Surface erosion microstructure was also examined under a stereoscopic microscope and a scanning electron microscope to characterize erosive damage. The anti-erosion property of the coupling and V-shaped specimens increased by approximately 74.7 and 57.4% compared to that of the smooth specimen in a 10-min test. The mechanism of particle erosion resistance is also discussed in detail. The particle impact marks that were distributed on the surfaces of both of the...

Journal ArticleDOI
TL;DR: In this paper, a transient elastohydrodynamic analysis of the conditions at the contact of two pairs of helical gears operating with different gear ratios is presented, where the effects of the variation in contact geometry, kinematics and tooth loading during the meshing cycle are taken into account together with both tip relief and axial crowning profile modifications.
Abstract: This article presents the results of a transient elastohydrodynamic analysis of the conditions at the contact of two pairs of helical gears operating with different gear ratios. The effects of the variation in contact geometry, kinematics, and tooth loading during the meshing cycle are taken into account together with both tip relief and axial crowning profile modifications. The results are compared with analyses under corresponding steady-state conditions for both point contact and equivalent line contact models. The comparisons show that, away from the ends of the contact lines, steady-state conditions can be used effectively to assess the film-forming capabilities of the gears. Conditions at the end of the contact lines are found to be more adverse with significant transient squeeze film effects. The form of tip relief profile adopted is shown to be highly influential in determining the peak contact pressures and thinnest oil films within the contacts. These conditions are experienced at all axial posi...

Journal ArticleDOI
TL;DR: In this article, the effect of Cu nanoparticles on the tribological properties of attapulgite base grease was investigated, and it was found that the friction reduction ability and anti-wear property of the base grease can be improved with the addition of CU nanoparticles.
Abstract: This study investigated the effect of Cu nanoparticles on the tribological properties of attapulgite base grease. It was found that the friction reduction ability and antiwear property of the base grease can be improved with the addition of Cu nanoparticles. Under the lubrication of grease containing Cu nanoparticles, a smoother and more compact tribofilm was formed on the rubbing surface. The tribofilm is mainly composed of Cu, FeO, Fe2O3, FeOOH, CuO, and SiO. In addition, the content of iron oxides and silicate oxide formed in the tribofilm was increased by the introduction of Cu nanoparticles.

Journal ArticleDOI
TL;DR: In this paper, surface texturing in the form of microdimples has been shown in other applications to provide enhanced wear resistance through the trapping of wear debris and through the enhancement of fluid pressures to levels that promote mixed-to full-film lubrication even at low speeds.
Abstract: Considered a self-lubricating, abrasion-resistant biomaterial, ultra-high-molecular-weight polyethylene (UHMWPE) has become the most common acetabular cup material used in artificial hip joints. Artificial hip joints exist primarily in the boundary and mixed regimes, which can lead to premature failure due to surface wear, debris generation, and subsequent osteolysis. The tendency of failure due to the generation of wear debris has turned the hip problem into a complex tribological challenge with a focus on abrasion-resistant surfaces. Surface texturing in the form of microdimples has been shown in other applications to provide enhanced wear resistance through the trapping of wear debris and through the enhancement of fluid pressures to levels that promote mixed- to full-film lubrication even at low speeds. The objective of this investigation is to explore the potential for surface texturing of UHMWPE sliding contacts in enhancing the lubrication regimes present in total hip replacements. Surface textures...

Journal ArticleDOI
TL;DR: In this paper, the tribological performance of two approaches is compared and contrasted: black oxide chemical conversion treatment and tungsten carbide-reinforced diamond-like carbon (WC/a-C:H) thin film hard coating.
Abstract: Surface-initiated damage increasingly limits the service life of rolling element bearings in challenging environments. In particular, operation in the boundary lubrication regime and/or conditions that produce excessive rolling element–raceway slip require the use of surface treatments on roller bodies and raceways to extend surface durability and component life. The tribological performance of two approaches is compared and contrasted: black oxide chemical conversion treatment and tungsten carbide–reinforced diamond-like carbon (WC/a-C:H) thin film hard coating. Black oxide treatment is performed on both rollers and raceways, whereas WC/a-C:H coatings are deposited on rollers only. The cross-sectional layer structure is compared using transmission electron microscopy, and mechanical properties are measured using nanoindentation. Ring-on-ring friction and wear testing is conducted to obtain Stribeck curves and evaluate adhesive wear resistance and cyclic acceleration performance. Tapered roller bearing fa...

Journal ArticleDOI
TL;DR: In this paper, the explicit finite element method (EFEM) and the discrete element method are coupled to investigate dynamics of flexible rotor systems supported by deep-groove ball bearings, where the flexible shaft is modeled with a full 3D elastic formulation using the EFEM rather than the reduced form.
Abstract: This article presents a new approach in which the explicit finite element method (EFEM) and the discrete element method (DEM) are coupled to investigate dynamics of flexible rotor systems supported by deep-groove ball bearings. In this investigation, DEM is used to develop the bearing (dynamic motion) model in which all of the components of the bearing (i.e., inner and outer race, balls, and cage) have 6 degrees of freedom. The flexible shaft is modeled with a full 3D elastic formulation using the EFEM rather than the reduced form, which implements component mode synthesis. The EFEM and DEM were combined to investigate the dynamics of flexible shaft rotor systems supported by ball bearings. Rotor and inner races of the bearings are fully coupled such that both translation and rotation of the flexible rotor are transmitted to the bearings. At each time step, the translational motion and rotation/tilt angle of the rotor cross section at the location of an inner race are applied to the inner race of the bear...

Journal ArticleDOI
TL;DR: In this paper, the friction and wear behaviors of concentrated point contacts formed between lapped bearing steel balls and lapped/laser-textured flat bearing steel surfaces were studied in the boundary/mixed lubrication regimes under reciprocating rolling and sliding motions.
Abstract: The friction and wear behaviors of concentrated point contacts formed between lapped bearing steel balls and lapped/laser-textured flat bearing steel surfaces were studied in the boundary/mixed lubrication regimes under reciprocating rolling and sliding motions. Nanohardness variation in the vicinity of the dimples of the textured surface along with lubricant's wettability of the lapped and textured flat surfaces were measured to understand the tribological behaviors at the concentrated contacts. Moreover, the morphologies of wear debris collected from the contacts were investigated using analytical ferrography and scanning electron microscopy (SEM). It has been observed based on the experimental studies under the adopted operating parameters that the friction coefficient reduces to 33 and 27% at the rolling velocity (0.12 m/s) and sliding velocity (0.16 m/s), respectively, at the heavy load (PH > 0.7 GPa) at the textured point contacts in comparison with lapped point contacts. However, at the light load ...

Journal ArticleDOI
TL;DR: In this paper, a fatigue wear model of plane sliding pairs under dry friction is presented, which describes the quantitative relationship between the wear behaviors of the plane sliding pair and the main factors including the load and sliding speed, material property, friction property, and surface topography.
Abstract: Wear modeling is essential to predict and improve wear resistance of machine parts. This article presents a fatigue wear model of plane sliding pairs under dry friction. The wear model is constructed through developing a dynamic contact model of surfaces and proposing a mean fatigue damage constant of asperities. It is simpler and more practical than existing fatigue wear models because it describes the quantitative relationship between the wear behaviors of the plane sliding pairs and the main factors including the load and sliding speed, material property, friction property, and surface topography of the pairs. Furthermore, the wear model can predict the wear of each component of the sliding pairs. Reasonability and applicability of the wear model are validated via pin-on-disc wear tests. The wear model is applicable to predict the wear of the plane sliding pairs, which is characterized by friction fatigue of contact surfaces. The wear model can also be used to guide the tribological design of sliding p...

Journal ArticleDOI
TL;DR: In this article, the tribological properties of Ti3SiC2/TiAl composite (TTC) sliding against a GCr15 steel counterface were investigated at sliding speeds in the range of 0.2-0.8 ms−1 and loads that ranged from 2 to 8 n.
Abstract: The tribological properties of Ti3SiC2/TiAl composite (TTC) slid against a GCr15 steel counterface were investigated at sliding speeds in the range of 0.2–0.8 ms−1 and loads that ranged from 2 to 8 N. The results showed that the tribological properties of TTC strongly depended on the covering percentage of tribofilm on the TTC worn surface, which varied with changes in sliding speed and load. The tribofilm mainly consisted of Al-Ti-Si oxides, which provided a self-antifriction action that resulted in a reduction in the friction coefficient and an increase in the wear rate.

Journal ArticleDOI
TL;DR: In this paper, the authors simulate the Taylor-Couette shear model by using the discrete element method to study mechanical properties and force chain changes in the granular flow in friction pair clearance.
Abstract: This article simulates the Taylor-Couette shear model by using the discrete element method to study mechanical properties and force chain changes in the granular flow in friction pair clearance. The mechanical properties and force chain structures of a granular system can be studied by changing the granular friction coefficient, granule size, fractional area, inner rotational speed, and other causes. Shear, normal, and unbalanced forces increase with increasing friction coefficient. A higher friction coefficient corresponds to a higher average contact forces. When the surface of the inner ring is rougher, the normal and unbalanced forces are smaller and the shear force is higher. This condition greatly influences the internal force chain structure of the granular media.