Steady-state Wear Research Articles

Short-term clinical and radiographic outcomes of total hip arthroplasty with PMPC-grafted highly cross-linked polyethylene liners against 32-mm femoral heads

We evaluated the clinical and radiographic outcomes of femoral head penetration and total hip arthroplasties with untreated and poly (2-methacryloyloxyethyl phosphorylcholine) (PMPC)-grafted highly cross-linked polyethylene (HXLPE) acetabular liners against 26-, 28-, and 32-mm cobalt–chromium alloy femoral heads 3 years after the index surgery. Three combinations of the articulating surfaces were evaluated in the present study: untreated or PMPC-grafted HXLPE liner against 26- or 28-mm femoral heads (n = 16, 24) [control (26 or 28 mm) and PMPC (26 or 28 mm)] and PMPC-grafted HXLPE liner against 32-mm femoral heads (n = 64) [PMPC (32 mm)]. The clinical outcomes improved at 3 years postoperatively for the groups. No periprosthetic osteolysis or acetabular component migration was detected, and no revision surgery was performed among the groups. The steady-state wear rate of the PMPC (26 or 28 mm) group (0.021 mm/year) was lower than that of the control (26 or 28 mm) group (− 0.015 mm/year); the steady-state wear was under the clinical threshold. In contrast, the steady-state wear rate of the PMPC (32 mm) group (-0.006 mm/year) showed no significant difference when compared to that of the PMPC (26 or 28 mm) group (p < 0.01). The results obtained in the present study clearly demonstrate that PMPC-grafting onto an HXLPE surface improved the wear resistance of acetabular liners, even when coupled with larger femoral heads. Although further follow-up evaluations are required, PMPC-grafted HXLPE acetabular liners may be a promising approach to extend the longevity of artificial joints.

Исследование эксплуатационных свойств стальных пар трения с антифрикционными покрытиями из медных сплавов, полученных методом электроискрового легирования

Improving the reliability, durability and safety of operation of heavily loaded friction units is an urgent problem in physics, chemistry and surface mechanics. The tribotechnical characteristics of coatings made of bronzes BrAZhMts10-3-1.5 and BrMtsF3-6, applied by electrospark alloying on bushings made of structural steel 30KhGSN2A for operation under conditions of high contact pressure under friction without lubrication, have been investigated. Modes of coating deposition from the standpoint of tribology (the value of the electric discharge current in a pulse, the value of the longitudinal electrode feed per one rotation of the part, the rotation speed of the workpiece, the number of passes during processing, finishing of the coating) have been developed. It was found that when applying bronze BrMtsF3-6 to obtain a high-quality coating, the process must be performed in a protective atmosphere of argon to prevent phosphorus burnout. The tribotechnical efficiency of coatings when working under dry friction conditions is shown. For the steady-state wear mode, the friction coefficient is 0.10 – 0.13 at a pressure of 200 – 250 MPa, the wear resistance of coated steel is doubled. Steel with a bronze coating BrAZhMts10-3-1.5 has a higher bearing capacity, with BrMtsF3-6 coating — a higher antifriction. The ways of increasing the service life of steel-coated steel friction pair are analyzed.

Topographic evolution of balls used in microabrasion tests

This work aims to contribute to the understanding of the topographic modification of the surface of the counter-body during micro-abrasion and its complex relationship with specimen wear. The topographic evolution of the surface of five different balls (Ø25.4 mm) was monitored: one ceramic (Si3N4), one metal (AISI 52100 steel), and three thermoplastic polymers (polypropylene, polyacetal and polyamide 6.6). AISI 304 austenitic stainless steel specimens were tested in a fixed-ball micro-abrasion test rig using a silica slurry (10%wt. in water), rotation speed of 150 rpm, and total test time of 90 min (in 15 min intervals). The topographic evolution of the ball topography was monitored by laser interferometry of the abrasive tracks at each measurement interval, always in the same region. The parameters Sq, Sz, Ssk, Sku, λq, Sdq and Str were computed. Significant wear and changes of the surface topography of the balls were observed along the tests. Harder balls underwent evident grooving, while the softer polymeric balls showed fibrillation characteristics, alignment of polymeric chains and transfer film. For the initial 15 min of test, before reaching a steady-state wear regime, the softer balls (polypropylene, polyamide 6.6 and polyacetal) showed, in general, an increase in Sq, λq and Sdq, possibly by the generation of a transfer film on the surface, which was not observed for the harder balls. After the steady-state regime was achieved, all balls reduced their values of Sq, λq and Sdq. Plots of Sku x Ssk identified non-Gaussian height distribution curves (mostly with high kurtosis and negative asymmetry) for all balls. Sq and Sdq presented a linear relationship with the wear coefficients of the specimens (k) dependent on the material of the ball, whereas an overall linear relationship between λq and k was observed independently of the ball material. Str was a good indicator of aligned grooving abrasion, but showed a linear relationship with k only for the steel ball.

Contact probabilities of an angular ball bearing under a combined axial and radial load

A contact probability model of an angular ball bearing is developed in this study by means of multi-body dynamics and a spherical grid division method. The model is used to analyze the contact probability of a ball surface of a typical angular ball bearing under different loading conditions. It is found that the contact probability of the ball with the inner and outer races of the bearing under a pure radial loading will have the largest probability distribution along the ball's circular profile intersecting the two contact points between the ball and the inner and outer races. Whilst the axial load on the ball bearing plays a decisive role in the stable distribution of the contact probability of the ball under various combinations of axial and radial loads. The study also shows that a steady-state wear will accumulate on the ball surface and the raceways when a large constant axial load is applied to the angular ball bearing.

Thirteen-year results of cementless total hip arthroplasty with zirconia heads on highly cross-linked polyethylene

Objectives Zirconia ceramic was introduced for femoral heads because of its mechanical strength and fracture toughness. Highly cross-linked polyethylene has been shown to achieve wear reduction compared to conventional polyethylene. The purpose of this study was to investigate the long-term results of cementless total hip arthroplasty with zirconia femoral heads on highly cross-linked polyethylene. Methods Radiographic measurements of two-dimensional femoral head penetration into the polyethylene were performed with a computerized method (PolyWare) in 93 hips at a mean follow-up of 13 years. The steady-state wear rates were measured based on the radiographs from the first year after surgery to the final follow-up. Results The mean Merle d’Aubigné and Postel score had improved significantly from 10.9 points preoperatively to 15.3 postoperatively (p < 0.001). Osteolysis was not found around the implant, and no zirconia heads had fractures. The total head penetration rate was 0.04 mm/year, and the steady-state wear rate was 0.02 mm/year. Kaplan–Meier survivorship with the endpoint of revision was 97% (95% confidence interval [CI], 92% to 99%) at 10 years. Conclusion Zirconia on highly cross-linked polyethylene demonstrated extremely low wear properties at long-term follow-up.

Applying experimental micro-tool wear measurement techniques to industrial environments

Productivity in micro-milling is hindered by premature fracture of tools and difficulty predicting wear. This work builds upon previous investigations into tool wear mechanisms and coatings for micro-mills.The technology readiness level of this work exceeds previous studies by investigating the micro-mills for practical applications and comparing this data. 0.5 mm micro end mills are tested with different coatings on CuZn38, and wear curves produced both in the case of simple straight slot testing and milling of complex parts representing industrial applications. The results show that curves produced using straight slots can be used to predict the behaviour of tools used to machine industrial parts. Due to interrupted cutting, tools used in straight slot tests reach the end of steady state wear after approximately 12 s of cutting as compared with 170 s in continuous milling. Typical cutting forces seen for the tools are in the order of 2–4 N. Catastrophic failure is seen towards the end of tool life for a TiAlN tool with a cutting force of over 30 N seen. For the first time a comparison has been made between fundamental tool wear studies and tool wear observed when producing test pieces representative to micro-industrial parts. This presents a novel perspective on tool wear and facilitates the integrating of existing micro-milling research into industry

Hydrogen ion induced mechanochemical wear of soda lime silica glass in acid solutions

In this study, the friction and wear behaviors of soda lime silica (SLS) glass are studied by rubbing against Pyrex glass ball in various acid solutions. The experimental results show that as the solution pH increases from 0.5 to 6, the steady-state friction coefficient and wear volume of SLS glass increase firstly and then decrease. Further analyses indicate that the hydrogen ion concentration induced surface charge effect play critical roles in the wear behavior of SLS glass in acid solutions. When the solutions pH is 2.5, substantial direct contact at sliding interface will cause the highest friction and wear. In contrast, when the solution pH is lower or higher than 2.5, the interfacial direct contact can be weakened by the surface charge effect, therefore the friction and wear of SLS glass would be lower. These results may provide deeper understanding the material removal of oxide glasses during manufacturing and serving processes.

Initial tool wear behavior in high-speed turning of Inconel 718

Three distinctive regions of tool wear, known as initial wear, steady-state wear, and accelerated wear, are well understood. However, the effects of cutting parameters on the initial tool wear mechanism, morphology, and size have received less attention as compared to the other two regions. Knowing that adequate control of initial tool wear may lead to extended tool life, in particular in hard-to-cut metals such as superalloys, this topic has become a source of attention. Amongst superalloys, Inconel 718 is considered as one of the most difficult to cut materials, which has a wide range of industrial applications. This study intends to evaluate the effects of cutting parameters on initial tool wear, as well as tool wear progression, when turning Inconel 718. Therefore, microstructural evaluation of the initial tool wear mode under various cutting conditions, as well as tool wear measurements, were conducted. It was observed that certain elements of the workpieces were migrated to the insert flank face. This is evidence of adhesion at the initial moments of the cutting process. In contrast to many other easy-to-cut materials, the steady-state wear period when turning Inconel 718 is significantly short under a higher level of cutting speed and feed rate.

Minimum 10-Year Follow-Up of Cementless Total Hip Arthroplasty With a 32-mm Cobalt-Chromium Head on Highly Cross-Linked Polyethylene and a Tapered, Fiber Metal Proximally Coated Femoral Stem

BackgroundThe clinical and radiographic results of cementless total hip arthroplasty using a 32-mm cobalt-chromium head on remelted highly cross-linked polyethylene (HXLPE) and a tapered, fiber metal proximally coated femoral stem were evaluated at a mean follow-up of 12 years. MethodsA total of 57 cementless total hip arthroplasties using remelted HXLPE combined with a 32-mm cobalt-chromium head, and a tapered, fiber metal proximally coated femoral stem were performed from October 2004 to December 2006. Clinical evaluation was performed using the Merle d’Aubigné and Postel scoring system. Standardized anteroposterior and lateral radiographs of the pelvis and femur without weight-bearing were analyzed. Radiographic measurements of two-dimensional femoral head penetration into the polyethylene were performed with a computerized method. The steady-state wear rates were measured based on the radiographs from the first year after surgery to the final follow-up. ResultsThe mean Merle d’Aubigné and Postel score improved significantly from 10.7 points preoperatively to 15.6 postoperatively (P < .001). No osteolysis was found around the implant. Stem fixation in all cases showed stable bone ingrowth. Third-degree stress shielding was found in 46% of all stems. The total head penetration rate was 0.05 mm/y, and the steady-state wear rate was 0.01 mm/y. The Kaplan–Meier survivorship with the end point of revision was 95% (95% confidence interval, 85%-98%) at 12 years. ConclusionA 32-mm cobalt-chromium head on remelted HXLPE demonstrated low wear properties, and a tapered, fiber metal proximally coated femoral stem showed good results at long-term follow-up.

Using Methods of Analysis of Optical Images of Friction Surfaces of Ti–Al–N Based Coatings for Assessing Accumulation of Damage and Diagnostics of Failure in Tribological Tests

The processes of damage accumulation and failure in thin ceramic coatings based on the Ti–Al–N system deposited on ductile steel and brittle sitall substrates have been investigated during tribological tests under dry friction conditions. Fractal analysis was carried out to quantitatively assess damage to friction surfaces, as well as Fourier and wavelet analysis of their images obtained using optical microscopy. It is shown that the spectral analysis (Fourier and wavelet analysis) make it possible to reveal an unambiguous correlation between the quantitative parameters obtained and the rate of wear of coatings at the stage of steady wear. At the same time, the fractal dimension provided an estimate of the dynamics of accumulation of damage at the run-in stage but did not allow one to be produced at the stage of steady-state wear.

Micro-structure and tribological behaviors of magnetron sputtered WS x /Fe/a-C/Fe multi-layer films with various Fe layer thicknesses

ABSTRACT The WS x /Fe/a-C/Fe multi-layer films with various Fe layer thicknesses were prepared by using magnetron sputtering and alternate deposition of WS x , Fe, and a-C layers on the silicon substrates. The morphology, micro-structure, and composition of the films were characterized by scanning electron microscope, energy dispersive spectroscopy, electron probe micro-analyzer, X-ray diffraction, and X-ray photoelectron spectroscopy. The mechanical and tribological properties of the fabricated films were evaluated by using nano-indenter, film stress tester, scratch tester, and ball-on-disk tribotester. According to the obtained results, all the multi-layer films revealed a featureless micro-structure with a smooth and dense surface. As the thickness of Fe layer increased, the S/W ratio of the films was decreased from 1.38 to 1.16, the hardness, elastic modulus, and adhesion of the films were gradually improved. Both the steady-state friction coefficient and wear rate were declined first and, then, enhanced. The film with the Fe-layer thickness of 4 nm exhibited the highest hardness (10.6 GPa) and adhesion (38.0 N); whereas, film with the Fe-layer thickness of 2 nm showed the best tribological performance with a steady-state friction coefficient of 0.218 and wear rate of 1.63 × 10−15m3 N−1 m−1.

Topology optimization of tribological composites for multifunctional performance at sliding interfaces

This paper presents the first application of topology optimization to designing multifunctional tribological composites. In particular, composites are designed to minimize temperature rise caused by frictional heating associated with wear at sliding interfaces. Wear and frictional heating both have significant influence on the performance of tribological composite systems. A steady-state heat transfer model is used to obtain the thermal field within the sliding body, including a frictional heat flux boundary condition determined by the steady-state wear response of the bi-material composite sliding interface. The material thermal conductivity and frictional heat generated within each material are interpolated using the Solid Isotropic Material with Penalization optimization method. The optimization problem is solved using a gradient-based optimizer, the Method of Moving Asymptotes, with sensitivities obtained by the adjoint method. Two case studies are presented to demonstrate the effectiveness and utility of the established optimization framework. It is found that the average and maximum temperature rises are reduced by 40–60% compared to reference structures with the same material volume fractions.

A lubricated wear model for determining wear surface geometry on journal-bearing surfaces

In this study, the friction fatigue mechanism is employed to describe the quantitative information concerning characterization of the steady-state wear process in journal bearings, which combined with the load sharing notion in mixed lubrication. For this approach, the asperity stress cycle number is estimated by combining the statistical dynamic contact model with the mixed elasto-hydrodynamic lubrication (EHL) simulation model. The maximum shear stress theory is applied together with the subsurface stress distribution of contact asperities to predict the average volume of wear fragment for asperity. Quantitative analysis of steady-state wear profiles for the bearing reveals that the maximum wear depth appears at both ends of the bearing. With the increase of running time, the wear gradually extends to the bearing centre, and the wear rate rapidly decreases to a certain value and then tends to be stable. With this lubricated wear model, the influences of surface roughness, external load, and shaft speed are also discussed. The proposed wear simulation method is based on the interdisciplinary theory, which includes the description of surface micro-morphology (Gaussian rough surfaces), the friction fatigue theory for explaining the generation of wear debris, and the coupling effect of wear and lubrication that is expressed by considering the wear surface geometry in oil film thickness equation. Additionally, the simulation results and available experiment data are compared to demonstrate the fatigue wear modeling scheme.

Running-in period for the abrasive wear of austenitic steels

The initial transient, or running-in, period during abrasive wear has been largely overlooked in the literature, with the focus instead being on steady-state conditions. However, the running-in period of abrasion might determine the evolution to steady-state wear behaviour, as is known to occur in sliding wear conditions. To this end, the running-in period during the abrasive wear of the austenitic stainless steel AISI 316L and Hadfield (15%Mn-1.5%C) steel was analysed through the testing pin (flat-ended)-abrasive paper wear configuration. The effects of the normal load, the size of the abrasive, and the type of material were evaluated, and the wear rate and the strain hardening of the matrix were recorded. The steady-state wear might be influenced by the phenomena occurring during the running-in period. Thus, the hardening, roughness, friction coefficient and wear micromechanisms were correlated with the wear rate to elucidate these possible relationships.

Experimental investigation of debris entrapment in annular contacts

In wearing contacts, a part of the wear debris is trapped between the surfaces, creating a wear debris bed. Many researchers report such beds providing a degree of protection against further wear. It was hypothesized, that in an annular contact, the level of debris entrapment increases with the width of the annulus resulting in decrease in wear. To test this hypothesis, two series of experiments using EN1A steel and 6082T6 aluminium alloy annuli, measuring 1, 2 and 4 mm wide were carried out. When steel was used, there was no clear correlation between ring width and total mass loss or steady-state wear rate. When aluminium was used, wear decreased with the ring width according to both metrics. This behaviour appears to correlate with worn surface roughness, suggesting worn surface roughness to be a parameter controlling debris entrapment.

Wear contact problem with friction: Steady-state regime and wearing-in period

A two-dimensional contact problem for an elastic layer of a finite thickness is considered with the effects of friction and wear taken into account. It is assumed that the contact zone is constant, but the shape of a wear-resisting punch changes during the sliding wear process. The punch is loaded by constant external normal and tangential loads, the latter of which is equal to the maximum value predicted by Coulomb’s law. The steady-state profile of the punch, which has been reproduced in the steady-state wear regime, is determined in an integral form. In the case of a very thick layer, explicit formulas are given for the initial vertical displacement of the punch and the moment of contact pressures, both of which vary during the wear process. The duration of the wearing-in process is estimated, and it is shown that the effect of friction extends the wearing-in period.

Wear of large diameter ceramic-on-ceramic hip bearings under standard and microseparation conditions

A novel Ceramic-on-Ceramic hip resurfacing implant offers a bone conserving treatment for young and/or active patients without the metal ion related issues associated with current Metal-on-Metal (MoM) hip resurfacing devices. BIOLOX delta ceramics are currently used as bearing surfaces in total hip replacement and have shown to be low wearing and biocompatible. Wear testing, however, has only been conducted in bearing diameters up to 36 mm and it is unknown how this material will perform tribologically and clinically in larger bearing diameters. The smallest (40 mm diameter) and largest (64 mm diameter) bearings of aceramic resurfacing implant size range were tested to ISO 14242-1 and ISO 14242-2 standards The largest size was also tested under microseparation wear conditions in a physiological hip simulator for 5 million cycles. The wear rate over the full 5mc was shown to not be influenced by the size of implant but at specific time points, there was a statistical significance, and in all cases steady state wear was low (≤0.5mm3/mc). The introduction of microseparation conditions increased the wear rate compared to standard conditions and produced stripe wear on the heads. The low wear and biocompatible nature of the BIOLOX delta material suggests it is a suitable material for use in hip resurfacing which may open this treatment option for patients who are currently not appropriate for MoM hip resurfacing.

Analysis of Steady Wear State of the Drum Brake

In the previous paper [1], the formula of the contact pressure distribution in the steady wear state for drum brake system was derived. The contact pressure distributions on the leading and trailing shoes were found to be different and larger on the leading shoe. Using these contact pressure distributions, it is easy way to calculate the braking torque. Assuming the varying position of the shoe pin, the optimization problem can be formulated by requiring the optimal pin position corresponding to maximal braking torque. The steady wear states and optimal designs were specified for both shoes. The elastic displacement field of the drum brake at the optimal contact pressure distribution is calculated by the finite element system ABAQUS. At given rigid body rotation of the shoe, the wear in the leading and trailing shoes in the steady wear state can be easily found.

Analysis of steady state wear processes for inhomogeneous materials and varying contact loads

Analysis of steady state wear processes for inhomogeneous materials and varying contact loads

Long-term wear prediction of zirconia on alumina ceramic for hip prosthesis

This paper aims to predict wear of hard zirconia-on-hard alumina ceramic hip bearing couple for 20 years of lifetime by considering a realistic wear coefficient. Past studies in hip wear prediction have considered a fixed wear coefficient determined for a shorter sliding distance and used this for long-term wear prediction. In this study, pin-on-disc test between the zirconia and alumina bearing materials for a sliding distance of 60 km has been conducted in a dry and lubrication condition to determine friction and wear coefficient for initial 'running-in' and subsequent steady-states. Finite element method has been employed to compute cumulative linear and volumetric wear of implant for 20 million cycles using the calculated wear coefficient values. Wear prediction showed lesser cumulative linear and volumetric wear for steady state wear coefficient when compared with running-in wear coefficient.