Fretting corrosion damage of total hip prosthesis: Friction coefficient and damage rate constant approach

This paper analyzes friction coefficient evolution between materials related to total hip prosthesis. Fretting corrosion tests were conducted with stainless steel and poly(methyl methacrylate) interacting surfaces. In the course of fretting corrosion tests, the Coulomb friction coefficient is determined as a function of the number of cycles. It was found that the friction coefficient growth rate can be expressed as a power-law function. The influences of ionic strength, applied potential, pH, and albumin content on fretting corrosion were then investigated on the basis of the evolution of the friction coefficient. Finally, we identify the damage rate constant as being relevant for linking the mechanical and chemical parameters in the evolution of damage.     

Wear analysis of materials used as orthopaedic implants

In the biomedical field, about 6% of the hip total prostheses must be replaced after 9 years. One of the main causes of the aseptic loosening may be attributed to fretting corrosion between the prosthesis and the bone cement. To understand this degradation, a fretting test between a stainless steel, 316L and PMMA has been used in Ringer solution. Fretting maps for the contact 316L/PMMA were determined in air and in Ringer solution. It has been shown that the lubricant effect of the aqueous environment shifts the gross slip/partial slip transition towards larger normal forces or lower displacements.To understand the fretting degradation behaviour of 316L against PMMA, fretting corrosion experiments have been investigated under constant applied potential. The first conclusion is that the dissipated energy is maximum at about −600 mV/SCE. The wear on PMMA does not depend on the applied potential. Moreover, the wear coefficient is lower than that in air due to the lubricant effect of the Ringer solution. Wear on 316L depends on the applied potential. The wear volume is minimum at −600 mV/SCE although the dissipated energy is maximum. The wear on 316L in Ringer solution is attributed to a dissolution process due to the local destruction of the passive film by fretting. The effect of potential on the wear of 316L may be accounted for by changes in the aqueous environment confined in the contact zone due to a restricted mass transport from the bulk solution and to the large local current densities consecutive to the destruction of the passive film. Accordingly, the wear volume on 316L is correlated to the time. Finally, the proton reduction, inside the contact, is believed to contribute significantly to the dissolution process.     

人工髋关节组合界面微动腐蚀研究进展

关节组合界面的微动腐蚀行为将直接影响人工关节假体的使用寿命。综述髋关节组合界面微动腐蚀的基本原理,介绍假体组合方式、组合界面材料、设计参数、手术操作及患者和生理因素5个方面对组合面微动腐蚀影响的研究进展,提出未来研究的重点是通过建立人工髋关节多尺度模型,利用试验测试和仿真计算方法,考察关节力、关节运动及滑动面摩擦学、材料配副、不同设计的组合件及环境介质等条件对微动腐蚀行为的影响规律。     

Characterization of fretting wear behavior of Cu–Al coating on Ti–6Al–4V substrate

Fretting wear and fretting fatigue are two commonly observed material damages when two contacting bodies with a clamping load are under the oscillatory motion. In this study, fretting wear damage of Cu–Al coating on titanium alloy, Ti–6Al–4V substrate was investigated using the dissipated energy approach. Fretting tests were conducted with either no fatigue load or the maximum fatigue load of 300 MPa and stress ratio of 0.1 on the substrate (specimen). In order to investigate the effect of contact load and contact size, different pad sizes and contact loads were used in the tests. Accumulated dissipated energy versus wear volume data showed a linear relationship regardless of fatigue loading condition on specimen with the smaller pad size. However, two separate linear relationships were observed based on the fatigue loading condition with the larger pad size, such that a relatively more dissipated energy was required for a certain amount of wear with fatigue load on the specimen. The linear relationship between the accumulated dissipated energy and wear volume for both pad sizes extended from partial to gross slip regimes and was not affected by the applied contact load. Further, fretting tests with and without fatigue load resulted in different shapes of fretting loops when the larger pad size was used.     

Wear analysis of Cu–Al coating on Ti–6Al–4V substrate under fretting condition

Fretting behavior of Cu–Al coating on Ti–6Al–4V substrate was investigated with and without fatigue load. Soft and rough Cu–Al coating resulted in abrasive wear and a large amount of debris remained at the contact surface, which caused an increase in tangential force during the fretting test under gross slip condition. Fretting in the partial slip condition also showed the wear of coating. To characterize wear, dissipated energies during fretting were calculated from fretting loops and wear volumes were obtained from worn surface profiles. Energy approach of wear analysis showed a linear relationship between wear volume and accumulated dissipated energy. This relationship was independent of fatigue loading condition and extended from partial slip to gross slip regimes. As an alternate but simple approach for wear analysis, accumulated relative displacement range was correlated with the wear volume. This also resulted in a linear relationship as in the case of accumulated dissipated energy suggesting that the accumulated relative displacement range can be used as an alternative parameter for dissipated energy to characterize the wear. When the maximum wear depth was equal to the thickness of Cu–Al coating, harder Ti–6Al–4V substrate inhibited further increase in wear depth. Only when a considerable energy was supplied through a large value of the applied displacement, wear in the substrate material could occur beyond the thickness of coating.     

Fretting corrosion of materials for orthopaedic implants: a study of a metal/polymer contact in an artificial physiological medium

The fretting corrosion behaviour of a 316L SS flat against a PMMA counterface has been investigated in an artificial physiological medium. A specific device has been used to visualize the in situ degradation at the contact interface. Simultaneous analysis of the coefficient of friction and free corrosion potential has shown four distinct stages during fretting experiments. An energy-oriented approach to the fretting process was conducted in tandem with measurement of wear. This method has shown a linear progression in the wear volume of the samples as a function of the interfacial energy dissipated during fretting. The presence of chlorides contributes to a considerable acceleration of the degradation of the stainless steel surface. This process was explained by a mechanism related to crevice corrosion activated by friction.     

Application of an energy wear approach to quantify fretting contact durability: Introduction of a wear energy capacity concept

A friction energy formalism is considered and adapted to formalize the fretting wear responses of adhesive wear and non-adhesive wear interfaces. It is shown that for non-adhesive wear tribocouples like hard coatings (TiN, TiC, etc.) the wear kinetics can be formalized using the accumulated friction dissipated energy. By contrast, adhesive wear contacts involving aluminium and titanium alloys display a critical dependance regarding the applied sliding amplitude. The wear kinetics of such systems is captured by considering a sliding reduced energy wear formulation. A combined composite energy wear formulation is then introduced to formalize the fretting wear response whatever the tribocouple behaviour. It is shown that a local approach, focusing on wear depth analysis, is required to predict interface durability. A FEM investigation demonstrates that the wear depth kinetics can be predicted by considering the accumulated energy density. It concludes that interface durability can be related to a single energy density capacity variable (χ) defined as the maximum accumulated energy density which can be dissipated in the interface before contact failure.     

The relationship between AE and dissipation energy for fretting wear

This paper describes the behavior of acoustic emission (AE), especially the correlation between the AE output and the dissipation energy under the fretting conditions. Fretting tests are conducted with a ball contacting with a flat disc in air. The specimens used are a bearing steel for a ball, and a bearing steel or an aluminum alloy for a flat disc. The results show that the behavior of the AE output and the dissipation energy during each fretting cycle is not so similar to each other throughout the test, but the total AE root-mean-square and the total dissipated energy during the test have a good correlation between them.     

Fretting Wear Behavior of Cu–Al Coating on Ti-6Al-4V Substrate under Dry and Wet (Lubricated) Contact Condition

The fretting wear behavior of Cu–Al coating was investigated with and without fatigue load under the dry and wet (lubricated) contact conditions. The Cu–Al coating was plasma deposited on titanium alloy, Ti-6Al-4V. Fretting regime was determined from the shape of fretting hysteresis loop. Fretting regime changed from partial slip to total (gross) slip at ∼15 μm of the applied relative displacement, and this transition point was independent of fatigue loading and contact surface (lubricated versus dry) conditions. Wet contact condition reduced frictional force during cycling, as evidenced by the lower-tangential force. Wear analysis using the accumulated dissipated energy approach did not show any effect of contact surface condition. In other words, the relationship between the accumulated dissipated energy and wear volume showed a linear relationship, and it was independent of loading and contact surface conditions, as well as of the fretting regime. Further, the relationship between the wear depth and accumulated dissipated energy did not show any effect of loading and contact surface conditions, as well as of the fretting regime up to instant when the maximum wear depth was equal to the coating thickness. The views expressed in this article are those of the authors and do not reflect the official policy or position of the United State Air Force, Department of Defense, or the U.S. Government.     

Dissipated energy and fretting damage in CoCrAlY-MoS2 coatings

This paper describes fretting wear behaviour of low friction CoCrAlY-MoS₂ coatings on titanium alloy substrates in terms of dissipated energy and friction coefficient. Experimental characterisation was achieved by measuring the friction coefficient vs fretting cycles, or slid distance. Test results were analysed using exponential evolution functions for fretting damage. Dissipated energy was derived, and predicted and measured values compared. Quantitative evaluation of the fretting damage was performed by measuring substrate area emerged. Results show that the friction coefficient evolution rate of CoCrAlY-MoS₂ coating correlates well with the damaged area fraction and the accumulated dissipated energy.     

Effect of shot peening on the fretting wear of Ti–6Al–4V

In this paper, we report on the fretting wear behaviour of polished and shot peened Ti–6Al–4V specimens. For fretting experiments, due to micro-displacements at the interface between two contacting surfaces, two types of damage can be observed: crack initiation and debris formation. Shot peening, which is already well known for improving fatigue resistance of titanium alloys, is shown to have a beneficial effect on the crack initiation and propagation under fretting wear loading, as cracks observed on specimens after cylinder-on-flat fretting tests are shorter in shot peened specimens than in polished ones. It is also demonstrated that shot peening decreases the friction coefficient only at the beginning of the test, as long as the asperities induced by shot peening are not worn-off. The effects of displacement amplitude, normal force and test duration on the wear volume have been investigated: in all cases, shot peening has no significant impact on the wear process. The same amount of debris are formed and ejected for both polished and shot peened specimens. Moreover, it is found that, for both types of specimens, the linear relation, developed for steels and hard coatings, between wear volume and cumulated dissipated energy is not valid in the present case as different wear volumes are measured for the same cumulated dissipated energy, depending on the experimental conditions (normal force, displacement amplitude). Using the test duration as the variable parameter, energy wear coefficients are calculated for different experimental conditions.     

微动图和能量的方法在微动研究中的应用

介绍了微动的两种研究方法：微动图和能量的方法。归纳了微动图的组成、分类、作法及其在减轻微动损伤方面的作用。讨论了能量的方法在微动摩擦学研究中的应用，包括微动磨损体积与摩擦过程中释放的总能量的关系及能量分布在解释微动实验现象中的成功运用。最后指出微动摩擦学的研究仍然面临巨大挑战。     

Surface damage of poly(methylmethacrylate) under fretting loading

The initial fretting damage in a glass/PMMA contact was investigated by means of experiments and numerical (F.E.M.) simulations. Both micro-crack nucleation at the contact edges and particle detachment were identified on the PMMA's surface. Micro-crack initiation was related to the combination of high tensile stresses and positive hydrostatic pressures which are known to enhance crazing. During the early stages of the fretting tests, the distribution of the detached particles within the contact was correlated to the spatial distribution of the cumulative interfacial energy dissipated by friction. As the number of cycles was increased, it was observed that detached particles moved toward the middle of the contact. On the basis of FEM simulations, this particle displacement within the contact was attributed to the existence of differential micro-displacements during the fretting cycle.     

Development of a friction energy capacity approach to predict the surface coating endurance under complex oscillating sliding conditions

In the case of surface coatings application it is crucial to establish when the substrate is reached to prevent catastrophic consequences. In this study, a model based on local dissipated energy is developed and related to the friction process. Indeed, the friction dissipated energy is a unique parameter that takes into account the major loading variables which are the pressure, sliding distance and the friction coefficient. To illustrate the approach a sphere/plane (Alumina/TiC) contact is studied under gross slip fretting regime. Considering the contact area extension, the wear depth evolution can be predicted from the cumulated dissipated energy density. Nevertheless, some difference is observed between the predicted and detected surface coating endurance. This has been explained by a coating spalling phenomenon observed below a critical residual coating thickness. Introducing an effective wear coating parameter, the coating endurance is better quantified and finally an effective energy density threshold, associated to a friction energy capacity approach, is introduced to rationalize the coating endurance prediction. The surface treatment lifetime is then simply deduced from an energy ratio between this specific energy capacity and a mean energy density dissipated per fretting cycle. The stability of this approach has been validated under constant and variable sliding conditions and illustrated through an Energy Density–Coating Endurance chart.     

Fretting wear behaviour of hypereutectic P/M Al–Si in oil environment

The fretting wear behaviour of forged hypereutectic P/M Al–Si in contact with hardened steel and Cu–Sn–Pb bearing material is investigated. Fretting tests are performed with a view to the movement in the contact between the small end of the connecting rod and the piston pin in a car engine. Therefore, the tests are carried out under engine oil lubrication at temperatures up to 150°C. The behaviour of the Al alloy is compared to that of steel, the current connecting rod material. Some tests under non-lubricated conditions are also performed. The correlation between the friction coefficient, the wear volume and the microscopic wear mechanisms is discussed. After the running-in wear, a stable wear condition is reached for the Al–Si/steel contact.     

Understanding initiation and propagation of fretting wear on the femoral stem in total hip replacement

The femoral stem–bone cement interface in total hip replacement is supposed to experience low amplitude oscillatory micromotion under physiological loading, consequently leading to fretting wear on the stem surface, which nowadays is considered to play an important part in the overall wear of cemented prosthesis. However, initiation and propagation of fretting wear has been poorly documented and a better understanding concerning this issue has not been established as yet. This present study, on the basis of a profound surface investigation of a polished Exeter V40? femoral stem and Simplex P bone cement obtained from an in vitro wear simulation, demonstrated that the edges of the micropores in the cement surface matched pretty well to the boundaries of the worn areas on the stem surface. This would indicate that these micropores contributed significantly to the fretting process at the stem–cement interface.     

Fretting corrosion of orthopaedic implant materials by bone cement

Debonding of bone cement from the stem of the femoral component of a hip prosthesis can result in local tangential oscillatory movement, i.e. fretting, between the two contacting materials as the limb is moved. Patches where such rubbing has occurred are frequently seen on removed implants. Fretting fatigue experiments have been carried out in Hanks solution on austenitic stainless steel and Ti-6Al-4V (IMI 318) with bridges of bone cement clamped to the specimens. Fretting appears to have little effect on the fatigue life of either material but the scanning electron microscope reveals the formation of thick oxide layers which subsequently give rise to loose debris particles by a process of delamination. Further experiments carried out in Hanks solution in an electrolytic cell have shown that there are potential changes when a bone cement rider is fretted against a stainless steel or titanium alloy plate although the change in potential is only one tenth that obtained with a metal-on-metal contact. Fretting by bone cement appears to be producing damage to the metal surfaces which manifests itself as mild wear rather than a diminution in fatigue strength.     

Wear of low temperature nitrided steels under different wear processes

A programme of tests has been carried out to assess the wear resistance of three low temperature nitriding treatments when compared with the untreatedv steel and a standard cyanide case-hardening treatment, under conditions of scuffing, abrasion, fretting and corrosion. The main conclusion is that low temperature nitriding is most suited to applications where scuffing and corrosion are the main wear mechanisms and that the resistance to abrasion and fretting is poorer in general than that of traditional case-hardening. Therefore, care should be taken in assessing the wear process in any application in which these treatments are used. Reference is also made to the wear mechanisms in the different tests.     

基于双重扩展自适应卡尔曼滤波的汽车状态和参数估计

准确实时地获取行驶过程中的状态信息是汽车动态控制系统研究的关键,为此提出了一种新的汽车状态估计器。建立了包含不准确模型参数和未知时变统计特性噪声的非线性汽车动力学模型,针对该非线性系统提出一种双重扩展自适应卡尔曼滤波算法（DEAKF）。该算法采用两个卡尔曼滤波器并行运算,状态估计和参数估计互相更新,同时将带遗忘因子的噪声统计估值器嵌入到状态校正过程和参数校正过程之间,以解决系统的噪声时变问题。基于ADAMS的虚拟试验和实车试验结果表明,该算法的状态估计精度高于EKF方法和DEKF方法的状态估计精度,同时具有良好的模型参数校正能力,对汽车动态控制系统中估计器的设计具有理论指导意义。
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