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سال ۱۳۹۷ سال حمایت از کالای ایرانی گرامی باد

Wear

  1. Publication date: 15 July 2018
    Source:Wear, Volumes 406–407

    Author(s): Leiming Gao, Zikai Hua, Robert Hewson

    Total Hip Replacement (THR) is generally a highly successful treatment for late stage hip joint diseases and wear, however, wear continues to be one of the major causes of metal-on-metal THR's failure. Hip replacements typically experience a two-stage wear; a higher initial wear rate in the beginning followed by a lower steady-state one with the surface profile changed. This alludes to the potential use of a cup with a non-spherical interior cavity with an initial geometry similar to a worn surface which may benefit from lower wear rate. In this paper wear is numerically simulated with a cup having a non-spherical geometry inspired by the initial stage of wear. A wear model was recently developed by the authors for the THR, which considered the lubricated contact in both elastohydrodynamic lubrication (EHL) and mixed lubrication regime, rather than a dry contact used in most of other studies of wear modelling in the academic literature. In this study the wear model has been updated by introducing the ‘λ ratio’ (the ratio of film thickness to surface roughness) and addressing the non-Newtonian shear-thinning properties of the synovial fluid. This wear model was able to describe the non-linear wear evolution process due to the change of worn profiles. Firstly the wear of a spherical hip joint was simulated until a steady-state wear rate is achieved. Then a non-spherical joint was proposed in which the cup bearing geometry was generated by the previously predicted worn profile from the spherical joint. At last the wear of this “pre-worn” hip bearing was simulated and compared to the spherical one. Approximately 40% reduction in the steady-state wear rate and 50% in the total accumulated wear has been observed in the non-spherical hip joint. This study presented a full numerical analysis of the relationship between lubrication, wear reduction and the geometry change, and quantitatively suggested the optimal geometry to reduce running-in wear.





  2. Publication date: 15 June 2018
    Source:Wear, Volumes 404–405

    Author(s): Michael Watson, Matthew Marshall

    Abradable seals are used at the interface between blade tips and compressor casings in modern gas turbine engines. These materials wear in preference to the blade tips leaving a track which perfectly fits the blades, thus improving sealing at the blade tip an increasing both efficiency and stall margin of the compressor. The wear mechanisms occurring at this interface have been characterised for two common abradable materials. Changes to these mechanisms with blade speed, incursion rate and abradable hardness have been investigated and described statistically. The wear mechanisms proposed in this work and previously suggested have been used as the foundation for linear models which have been fitted to the results. These models have been used to test the quality of the mechanisms and indicate which processes are poorly understood. The models were well correlated to results for forces with normally distributed residuals indicating rubbing force systems are well represented by the proposed mechanisms. Temperature and blade length change results were less well correlated indicating these processes are more poorly understood. This work shows that simple linear models based on a mechanistic understanding of underlying processes can be used for describing forces.





  3. Publication date: 15 March 2018
    Source:Wear, Volumes 398–399

    Author(s): G.E. Morales-Espejel, P. Rycerz, A. Kadiric

    The present paper studies the occurrence of micropitting damage in gear teeth contacts. An existing general micropitting model, which accounts for mixed lubrication conditions, stress history, and fatigue damage accumulation, is adapted here to deal with transient contact conditions that exist during meshing of gear teeth. The model considers the concurrent effects of surface fatigue and mild wear on the evolution of tooth surface roughness and therefore captures the complexities of damage accumulation on tooth flanks in a more realistic manner than hitherto possible. Applicability of the model to gear contact conditions is first confirmed by comparing its predictions to relevant experiments carried out on a triple-disc contact fatigue rig. Application of the model to a pair of meshing spur gears shows that under low specific oil film thickness conditions, the continuous competition between surface fatigue and mild wear determines the overall level as well as the distribution of micropitting damage along the tooth flanks. The outcome of this competition in terms of the final damage level is dependent on contact sliding speed, pressure and specific film thickness. In general, with no surface wear, micropitting damage increases with decreasing film thickness as may be expected, but when some wear is present micropitting damage may reduce as film thickness is lowered to the point where wear takes over and removes the asperity peaks and hence reduces asperity interactions. Similarly, when wear is negligible, increased sliding can increase the level of micropitting by increasing the number of asperity stress cycles, but when wear is present, an increase in sliding may lead to a reduction in micropitting due to faster removal of asperity peaks. The results suggest that an ideal situation in terms of surface damage prevention is that in which some mild wear at the start of gear pair operation adequately wears-in the tooth surfaces, thus reducing subsequent micropitting, followed by zero or negligible wear for the rest of the gear pair life. The complexities of the interaction between the contact conditions, wear and surface fatigue, as evident in the present results, mean that a full treatment of gear micropitting requires a numerical model along the lines of that applied here, and that use of overly simplified criteria may lead to misleading predictions.





  4. Publication date: 15 February 2018
    Source:Wear, Volumes 396–397

    Author(s): A. Cabboi, J. Woodhouse

    Recent work (Cabboi et al. [1]) has shown promising agreement between measurements and theoretical modelling of high-frequency dynamic sliding friction. This paper confirms and extends this agreement by presenting results for a wide selection of contacting materials. Additional measurement techniques are also introduced, to give independent confirmation of parameter identification and improve the robustness of the identification process. The results show that virtually every individual measurement can be fitted accurately by the proposed theoretical model, and that in all cases where rapid wear of the contacting materials was not an issue it was possible to achieve a good global fit to sets of tests at different normal loads and sliding speeds. The evidence suggests that this measurement procedure is able to characterise the dynamic behaviour at a frictional interface up to kiloHertz frequencies, and consequently provide the means to discriminate among, and calibrate, proposed dynamic friction models. Identifying a reliable model could significantly improve the prediction accuracy for friction-induced vibration such as vehicle brake squeal.

    Graphical abstract






  5. Publication date: 15 November 2017
    Source:Wear, Volumes 390–391

    Author(s): Vipin C. Shukla, Pulak M. Pandey, Uday S. Dixit, Anish Roy, Vadim Silberschmidt

    Ultrasonic assisted magnetic abrasive finishing process (UAMAF) is a precision manufacturing process that results nano-scale level finish in a part. Normal force on a particle helps indenting the particle in the work surface whereas horizontal force provides finishing torque that in-turn helps the particle to perform micro-machining. Better understanding of the effect of these forces on material removal and wear pattern of the work-piece necessitates mathematical modeling of normal force and finishing torque and subsequently its validation with experimental results. In the present study, single particle interaction concept is considered to develop a model which is subsequently applied for all active particles of magnetic abrasive powder (MAP). Separation point theory is applied to consider the effect of ploughing below a critical depth and shearing above that depth. Normal components of shearing and ploughing forces are considered for calculating normal force and horizontal components of shearing and ploughing forces are taken to calculate finishing torque. Johnson-Cook model is applied to calculate shearing strength of the work material during UAMAF. The impact of ultrasonic vibrations is considered while calculating strain rate. Images are taken with the help of scanned electron microscope and atomic force microscope to study the material removal and wear mechanism during UAMAF process. Predicted values of force and torque model are validated with the experimental values.





  6. Publication date: 15 November 2017
    Source:Wear, Volumes 390–391

    Author(s): E.E.T. ELSawy, M.R. EL-Hebeary, I.S.E. El Mahallawi

    Mill roller shells are amongst the most important manufacturing-line elements in the sugar production process. They are carefully designed according to many surface criteria amongst which wear resistance is the most important. To increase the life of the mill roller shells, the resistance of the surface to failure by abrasion should be increased. In this investigation, a series of sixty-six cast iron samples with varied contents of chromium, manganese and silicon were prepared. The microstructure and the mechanical properties were studied. Hence, the wear of all the specimens was evaluated using the pin-on-disc test, with a high-speed steel disc. The accumulated weight loss was measured and the wear rates were determined at constant normal test load of 20N and constant pin velocity of 1.28m/s during the pin-on-disc test. The accumulated weight loss was measured as a function of the number of revolutions. From test results, it was found that the wear rate, for all conditions under investigation, decreases with the increase of manganese and chromium additions at constant silicon additions. The wear rate obtained for the samples containing 3% manganese and 2.02% silicon was equal to 1.2267mg/s, and the minimum wear rate was obtained for the samples containing 3% manganese, 2.11% silicon, and 2.11% chromium (equal to 0.3400mg/s). The enhancement in the wear resistance of the chromium alloyed samples was attributed to the increase in the chromium carbides volume fraction.





  7. Publication date: 15 November 2017
    Source:Wear, Volumes 390–391

    Author(s): A. Kontou, M. Southby, H.A. Spikes

    Due to incomplete combustion, high levels of soot can accumulate in engine lubricants between drain intervals. This soot can promote wear of engine parts such as timing chains and cam followers. One standard approach to reducing wear is to increase the hardness of the rubbing components used. According to the Archard wear equation, wear rate should be broadly inversely proportional to hardness. To explore this approach for controlling soot wear, wear tests have been conducted in a High Frequency Reciprocating Rig (HFRR) with HFRR steel discs of various hardness against a hard steel ball. Carbon black (soot surrogate) dispersions in model lubricants based on solutions of ZDDP and dispersant in GTL base oils have been studied. Wear volumes have been measured and wear scars and tribofilms analysed using scanning white light interferometry and SEM-EDS. It is found that, while most oils show wear that reduces with increasing hardness, for blends that contain both ZDDP and carbon black, wear rate markedly increases with disc hardness as the latter approaches the hardness of the ball. The results support the prevalence of a corrosive-abrasive wear mechanism when carbon black and ZDDP are both present in a lubricant and suggests that selection of very hard surfaces may not be a useful way to control soot.





  8. Publication date: 15 April 2017
    Source:Wear, Volumes 376–377, Part A

    Author(s): Darshil Kapadia, Radu Racasan, Luca Pagani, Mazen Al-Hajjar, Paul Bills

    This paper details a novel method to characterize and quantify edge wear patterns in ceramic-on-ceramic acetabular liners using a roundness measurement machine to measure the post-wear surface. A 3D surface map is produced which encompasses the measured surface covering the wear patch, the uncontrolled edge geometry and form of the bearing surface. The data is analysed to quantify linear penetration and volume. The developed method was applied in a blind study to a set of six 36mm ceramic-on-ceramic acetabular cup liners that were measured and analysed to characterise the edge wear. The in-vitro linear wear penetration ranged from 10μm to 30μm. The computed volumetric wear results obtained from the blind roundness measurement study were compared against the measured gravimetric results indicating a strong correlation between the results (0.9846). This study has also highlighted that measured liners exhibited an area of localised edge wear locates above the bearing surface as well as a smearing effect on the bearing surface caused by debris from edge wear. A study was carried out to test the repeatability of the measurement method and the inter-operator variability of the analysis. The results of the study show a standard deviation for the entire measurement and analysis process of 0.009mm3 for first user and 0.003mm3 for second user over twenty datasets. Hence the method displays high repeatability of the measurement and analysis process between users. This method allows for the delineation of form and wear through the determination of local geometry changes on what is essentially a freeform surface. The edge geometry is only partially controlled from a GD&T perspective and its geometry relative to the bearing surface varies from part-to-part. This method whilst being subjective allows for the determination of wear in this area with a high level of repeatability. However the limitation of this method is that it can only measure 5mm wide band of the liner due to the limited gauge travel range of 2mm





  9. Publication date: 15 April 2017
    Source:Wear, Volumes 376–377, Part A

    Author(s): Isaac P.H. Leung, Leigh Fleming, Karl Walton, Simon Barrans, Karen Ousey

    Pressure ulcers are a common injury of the skin which leads to pain and potential infection for patients and financial burden to the healthcare providers across the global due to treatment costs, litigation and extended hospital stays. The current study focuses on one of the causes of pressure ulcer formation, ischemia. Blood vessels are deemed to be deformed and blood flow restricted when skin is subjected to external mechanical loads including friction, pressure and the combination of both. Hence, normal oxygen delivery to cells or metabolic waste removal are locally stopped which causes cells deaths and ultimately pressure ulcers. The current study proposes a 3D finite element analysis model which is capable of demonstrating the effect of friction, pressure and the combination of both to the deformation of blood vessels. The results of simulation suggested that applied pressure collapsed the blood vessels while friction opened up the blood vessels. However, as a combination effect of pressure and friction, the cross-sectional areas of blood vessels were reduced significantly. This model is clinically and physiologically relevant in terms of loading regime and blood vessels structures. The model with further development can be adopted to be an effective tool to evaluate the effects of medical devices to the possibility of pressure ulcer formation.





  10. Publication date: 15 April 2017
    Source:Wear, Volumes 376–377, Part B

    Author(s): J.C. Walker, T.J. Kamps, J.W. Lam, J. Mitchell-Smith, A.T. Clare

    This paper investigates the use of Electrochemical Jet Machining to surface texture a hyper-eutectic Al-Si cylinder liner material. Samples were lapped to a 6μm finish followed by immersion in 1mol NaOH to expose the primary silicon colonies above the aluminium surface. Texturing was carried out using a NC system comprising of a fine gauge nozzle (cathode) jetting a solution of 2.3mol NaCl on the surface (anode) whilst applying a current density of 220A/cm2. An array of hemispherical dimples at 1.5mm spacing was created, with an average diameter of 420μm and depth of 40μm, corresponding to an ε ratio of 0.095. Lubricated reciprocating sliding was carried out at stroke length of 25mm in a bath of PAO (4cSt) against a 52100 cylinder of 6mm diameter and 16mm length. Sliding frequencies were incremented at 1Hz intervals between 1–15Hz at 50N load increments from 50-200N. Stribeck curves indicated a reduction of the friction coefficient due to texturing of up to 0.05 in the mixed lubrication regime, representing a decrease of 38.5%. Optical profilometry and SEM indicated that abrasion and formation of a surface tribo-layer was mitigated in regions of the Al-Si surface where textured features were present parallel to the sliding direction.

    Graphical abstract






  11. Publication date: 15 March 2017
    Source:Wear, Volumes 374–375

    Author(s): Claire L. Brockett, Silvia Carbone, John Fisher, Louise M. Jennings

    New bearing materials for total joint replacement have been explored as the need to improve longevity and enhance performance is driven by the changing demands of the patient demographic. Carbon-reinforced PEEK has demonstrated good wear characteristics in experimental wear simulation in both simple geometry pin-on-plate studies and in total hip joint replacement. Carbon reinforced PEEK CFR-PEEK has the potential to reduce tibial insert thickness and preserve bone in the knee. This study investigated the wear performance of PEEK and CFR-PEEK in a low conformity total knee replacement configuration. Custom-made flat inserts were tested against cobalt-chromium femoral bearings in a knee wear simulation for a period of three million cycles. Wear was assessed gravimetrically at intervals throughout the study. The wear rates of both PEEK and CFR-PEEK were very high and almost two orders of magnitude higher than the wear rate of UHMWPE under comparable conditions. Evidence of mechanical failure of the materials, including surface cracking and delamination was observed in both materials. This study highlights that these materials may not be suitable alternatives for UHMWPE in low-conformity designs.





  12. Publication date: 15 March 2017
    Source:Wear, Volumes 374–375

    Author(s): Alessandra Ciniero, Julian Le Rouzic, Iain Baikie, Tom Reddyhoff

    Triboemission – i.e. the emission of photons, electrons and other charged particles that arise from a sliding contact – may play a key role in tribochemical processes, such as lubricant degradation. However, the mechanisms that give rise to this type of emission are not well understood. For the first time, we present spatially resolved measurements of electron emission, obtained as a range materials are worn. These are obtained from scratch tests, carried out under vacuum conditions (10−5 Torr), in which microchannel plates coupled to a phosphor screen are used to image electron emission. The results show that electron emission occurs at specific locations on the worn surface and, depending on the conductivity of the material, these sites remain active and decay with a time constant of up to several seconds. SEM images of the worn surface at these sites reveal that either surface fractures or grain defects are present. This suggests that fractoemission mechanisms are at least partially responsible for triboemission (however, the possible contribution of tribocharging mechanisms are also discussed). Specifically, this provides evidence to support the theory that triboemission results from the imbalance of charge on opposing faces of wear cracks and that this generates an electric field sufficient to accelerate molecular fracture products, which then bombard the surface leading to secondary emission. The strong geometric correlation between damage topography and electron emission distributions shows the potential of using this technique to monitoring wear and crack formation in real time and under high (30x) magnification.

    Graphical abstract






  13. Publication date: 15 December 2016
    Source:Wear, Volumes 368–369

    Author(s): Niclas Ånmark, Thomas Björk

    This study describes the influence of the steel characteristics of Ca-treated carburising steel grades during hard part turning of synchronising rings in gearbox production. The main focus was on the chemical composition of the non-metallic inclusions in the evaluated workpieces and their effect on the PCBN tool wear. In addition, a Ca-treated carburising steel grade was compared to a standard steel grade. Machining tests were performed at the transmission machining site at Scania in order to evaluate the PCBN cutting tool life as defined by the generated surface roughness during actual production. The progression of flank and crater wear was evaluated by using a scanning electron microscope (SEM) equipped with an energy dispersive X-ray spectrometer (EDS) and a secondary electron (SE) detector. The Ca-treated steel showed a more than doubled tool life than that of the standard steel grade. The superior machinability was linked to the formation of a Ca-enriched slag barrier composed of (Mn,Ca)S and (Ca,Al)(O,S). It is believed that the stability of the protective deposits is essential to minimise diffusion-induced chemical wear of the PCBN tool.





  14. Publication date: 15 October 2016
    Source:Wear, Volumes 364–365

    Author(s): Amir Mir, Xichun Luo, Jining Sun

    Single point diamond turning (SPDT) of large functional surfaces on silicon remains a challenge owing to severe diamond tool wear. Recently, tremendous efforts have been made in understanding the machining mechanics, especially wear mechanism of diamond tools in SPDT of silicon. However, the localised transition of machining mode from ductile to brittle as a result of progressive tool wear has not been well understood yet. In this paper both experimental and numerical simulation studies of SPDT were performed in an effort to reveal the underlying phenomenon of ductile to brittle transition (DBT) as a consequence of diamond tool wear. Series of facing and plunging cuts were performed and the profile of machined surface was evaluated together with the progression of tool wear. The transition stages from ductile to brittle were identified by analysing the surface profiles of plunging cuts using a scanning electron microscope (SEM) and a 2D contact profilometer and a white light interferometer. The progressive degradation of the cutting edge of diamond tool and its wear mechanism was determined using Least Square (LS) arc analysis and SEM. The study reveals that at initial tool wear stage, the ductile to brittle transition initiates with the formation of lateral cracks which are transformed into brittle pitting damage with further tool edge degradation. Numerical simulation investigation using smoothed particle hydrodynamics (SPH) was also conducted in this paper in order to gain further insight of variation of stress on the cutting edge due to tool wear and its influence on brittle to ductile transition. A significant variation in frictional resistance to shear deformation as well as position shift of the maximum stress values was observed for the worn tools. The magnitude and distribution of hydrostatic stress were also found to change significantly along the cutting edge of new and worn diamond tools.





  15. Publication date: 15 June 2016
    Source:Wear, Volumes 356–357

    Author(s): Shojiro Miyake, Junichi Inagaki, Masatoshi Miyake

    Tribological durability properties of extremely thin diamond-like carbon (DLC) films (thickness 0.03–5nm) deposited using filtered cathodic vacuum arc (FCVA) and plasma-chemical vapor deposition (P-CVD) methods were evaluated using load-increase-and-decrease, ball-on-disk, and low-load reciprocating friction tests. Friction durability notably increased at a certain film thickness for FCVA-DLC and P-CVD-DLC films. These thicknesses were nearly equal to surface roughness and corresponded to film thickness at which the nanowear profiles changed from protuberance to grooves and at which nanoscratch resistance increased. Excellent friction durability of FCVA-DLC films (thickness≥0.4nm), evaluated by rapid increase in the friction coefficient, was observed. In contrast, the friction durability of P-CVD-DLC films gradually increased when the film thickness was 0.6nm or greater. When the thickness of the DLC films was 2.0nm or greater, the films did not exhibit a rapid increase in their friction coefficient within the total number of testing cycles. The tribological properties of extremely thin DLC films depend on film thickness; extremely thin FCVA-DLC films exhibit excellent wear resistance. The film thickness at which FCVA-DLC films endured the total number of test cycles was approximately one-fifth the corresponding thickness of CVD-DLC films, evaluated by the three different friction tests.