A preliminary investigation of frictional heating during abrasive wear

The frictional heating occurring under conditions of slow abrasive wear was estimated by measuring the thermoelectric output between abrasive particles and a wear pin. It is suggested that wearing surfaces locally reach temperatures high enough to affect properties determining the wear rate, and this is discussed with reference to specific materials.     

Shock machine for the mechanical behaviour of hip prostheses: a description of performance capabilities

The aim of this study was to describe the behaviour of a shock machine designed for testing hip prostheses. A microseparation between head and cup occurs inducing a shock of several times the body weight, leading to fracture of ceramic femoral components. Femoral heads and cups of diameter 32 mm manufactured from alumina were tested in dry and wet conditions. Implants were subjected to shocks with a load profile of 9 kN load at 2 Hz and various microseparations. Position is monitored and force is measured with two acquisition systems. The working range and the device capabilities were investigated. Only cups tested in dry conditions failed. Observations by scanning electron microscopy revealed intergranular and transgranular fractures. Two wear stripes were observed on the heads. Three‐dimensional roughness of wear stripes was measured. Since experimental results are in good agreement with retrieved femoral heads, the shocks machine reproduces the in vivo degradations. Copyright © 2011 John Wiley & Sons, Ltd.     

Investigation of wear of knee prostheses in a new displacement/force-controlled simulator

The performance of two knee simulators designed by ProSim (Manchester, UK) was evaluated by comparison of the wear seen in the press-fit condylar (PFC) Sigma (DePuy) knee prosthesis. Twelve specimens of the same design and manufacturing specification, were subjected to a wear test of 2 x 10(6) cycles duration using bovine serum as a lubricant. The anterior/posterior displacement and internal/external rotation inputs were based on the kinematics of the natural knee. International Standards Organization (ISO) standards were used for the flexion and axial load. The wear rates and wear scar areas were compared across all stations. The mean wear rates found were 17.6+/-5 mm3/10(6) cycles for stations 1 to 6 and 19.6+/-4 mm3/10(6) cycles for stations 7 to 12, resulting in an overall mean wear rate of 18.1+/-3 mm3/10(6) cycles. The differences between the two simulators were not significant. The average wear scar area seen on inserts from stations I to 6 was calculated at 32.4+/-1 per cent of the intended articulating surface. Similarly on stations 7 to 12 the average wear scar area was 30.7+/-3 per cent. The wear scars seen were a good physiological representation of those found from clinical explant data. This study has shown good repeatability from the simulator, both within and between the simulators.     

An investigation of sliding wear behaviour of WC-Co coating

Dry sliding wear tests on specimens of mild steel (MS) and WC coated mild steel (MSC) specimens were performed against a hardened EN32 steel (EN32) and a WC coated EN32 steel (EN32C) discs. Four different combinations of specimen and counter surface were tested under dry sliding conditions. Results suggest that wear mechanisms differ depending on the combination of materials under sliding contact. Expectedly the MS specimen suffered high wear loss, but the MSC specimen showed interesting results. When slid against EN32, MSC specimens showed negative wear results whereas positive wear results occurred against EN32C. Steady wear rate was attained after a critical sliding distance.     

Friction and wear behaviour of pyramidal nanoscaled surface features

This study reports on the friction and wear behaviour of nanoscaled pyramidal surface features of chromium nitride thin films in relation to the dimensions of those features. The pyramidal features were created, and their size controlled, by PVD based in-process structuring. Microtribological tests analysed both the evolution of wear-induced surface alterations and the correlated evolution in the coefficient of friction as functions of normal load and duration of the loading. Results indicate that the severity of wear diminishes tremendously with increasing feature size when tested at the same normal load. So, wear-induced damage similar to that seen on surfaces with small-sized features was observed for the largest surface features tested only after a 100 times longer test duration. The less severe wear of the largest pyramids leads also to friction up to 75% lower compared to surfaces with the smallest features.     

A preliminary investigation of the design parameters of an air induction nozzle

In the present study, an experimental study on design parameters of an air induction nozzle was performed. These nozzles are capable of producing large size droplets, including microbubbles, which in turn results in high drift reduction. A magnified 2D version of an air induction nozzle was designed and manufactured. The manufactured geometries have the ability to be disassembled easily, thus several geometrical parameters are replaced sequentially. The effects of a venturi throat, air orifices and discharge orifice diameters along with the length of the mixing chamber are analyzed. Analysis of the parameters revealed their strength of prediction on the air liquid ratio and the nozzle performance.     

A machine vision system for tool wear assessment

Automated tool condition monitoring is gaining considerable importance in the manufacturing industry. This can be attributed to the transformation of manufacturing systems from manually operated production machines to highly automated machining centres. Modern image processing techniques and machine vision systems can now enable direct tool wear measurement to be accomplished in-cycle. Such a system, characterized by its measurement flexibility, high spatial resolution and good accuracy, is presented here. The system consists of a fibre-optic light source to illuminate the tool and a CCD camera (used in conjunction with a high resolution video zoom microscope) to capture the reflected pattern. The extent of the flank wear land has been determined using both textural and gradient operators; a texture operator has been implemented in the final system.     

Improvement in the assessment of wear of total knee replacements using coordinate-measuring machine techniques

Total joint replacement is one of the most common elective surgical procedures performed worldwide, with an estimate of 1.5x 10(6) operations performed annually. Currently joint replacements are expected to function for 10-15 years; however, with an increase in life expectancy, and a greater call for knee replacement due to increased activity levels, there is a requirement to improve their function to offer longer-term improved quality of life for patients. Wear analysis of total joint replacements has long been an important means in determining failure mechanisms and improving longevity of these devices. The effectiveness of the coordinate-measuring machine (CMM) technique for assessing volumetric material loss during simulated life testing of a replacement knee joint has been proved previously by the present authors. The purpose of the current work is to present an improvement to this method for situations where no pre-wear data are available. To validate the method, simulator tests were run and gravimetric measurements taken throughout the test, such that the components measured had a known wear value. The implications of the results are then discussed in terms of assessment of joint functionality and development of standardized CMM-based product standards. The method was then expanded to allow assessment of clinically retrieved bearings so as to ascertain a measure of true clinical wear.     

A study of the wear of explanted metal-on-metal resurfacing hip prostheses

Due to their recent introduction there are few studies of retrieved resurfacing hip prostheses. Nine such components associated with groin pain in patients, and five associated with early fracture of the femur, were obtained and analysed using a roundness measuring machine. While the ‘fracture’ components showed no more than 3 μm out of roundness, components associated with groin pain showed between 15 and 92 μm out of roundness values. These latter results indicate wear and correlated with high metal ion levels in these patients, therefore the groin pain was likely associated with an adverse reaction to excessive metal wear debris.     

The design of a finger wear simulator and preliminary results

A dual-cycle finger wear simulator has been designed, manufactured and commissioned. The simulator interspersed dynamic flexion-extension motion under light load with a heavier static 'pinch' load to a test prosthesis immersed in a lubricant heated to 37 degrees C. A validation test was undertaken on a size 2 Swanson prosthesis, leading to prosthesis failure in less than 1 million cycles. A second test was carried out on a Durham metacarpophalangeal prosthesis. After 4.8 million cycles a total wear factor for the joint of 0.60 x 10(-6) mm3/N m was calculated, with no cracks or damage visible. Both test results compare well with earlier tests undertaken on the Stokoe finger wear simulator.     

Triboelectrochemical investigation of the friction and wear behaviour of TiN coatings in a neutral solution

Triboelectrochemical techniques use an electrochemical set-up (mainly of the three-electrode type) for controlling the potential of the surface of a conducting material subjected to rubbing in a tribometer. In this way it is possible to carry out friction and wear tests in electrolytic solutions under well-defined chemical conditions determined by the applied electrode potential. In addition, triboelectrochemical techniques offer the possibility of following in-situ and in real time the kinetics of electrochemical oxidation reactions (corrosion) by the simple measure of an electrical current. In the present study triboelectrochemical experiments were carried out on sputter deposited TiN coatings sliding against alumina in a borate solution (pH 8.4). The surface of selected worn coatings was characterised by X-ray photoelectron spectroscopy (XPS) and the topography by scanning electron microscopy (SEM). Results show that the rate of wear critically depends on the prevailing (electro)chemical conditions which determine the chemical surface state of the TiN coating. The behaviour is attributed to the lubricating properties of surface oxide films having a thickness in the nanometre range.     

A method for the quantitative recovery of polyethylene wear debris from the simulated service of total joint prostheses

The quantitative recovery of polyethylene wear debris is particularly important in the evaluation of the wear of total joint prostheses as it is the only feasible experimental wear parameter and also because of the clinical significance of the rate of release of the debris into the surrounding tissues. A method has been developed to recover the debris from the synovial fluid or serum in the joint; it consists in essence of chemical digestion, filtration and stereological evaluation of the debris volume. This method separates the polyethylene debris from all the other suspended solids present in the joint fluid and can be reliably and reproducibly calibrated. It has revealed that gross differences exist in the wear rates of commercially available total hip prostheses.     

The application of the zero wear model to joint prostheses

A zero wear model has been used to study various materials combinations employed or under consideration for total joint prostheses. The criteria for applicability of the model are satisfied for a laboratory test employing a ball-on-plane geometry.The use of the model is illustrated by considering the cases of total hip and hinge joint prostheses. There are examples in the literature in which zero wear of prostheses has been observed.It is recommended that, should the prosthesis be subject to finite wear, consideration be given to the generation and accommodation of wear debris.     

A chemical study of wear particles and other features associated with the wear of ceramics

A sapphire convex surface was loaded against a reciprocating flat SiC counterface material. In this particular study the chemical nature of the wear surfaces and associated features such as the wear debris and local areas of material transfer have been studied using analytical techniques such as EDX, XPS and AES. Prior to wear tests the SiC substrate is covered with a thin (1–2 nm) layer of SiO₂. During wear the thickness of this layer is substantially reduced, and wear debris of a cylindrical morphology is produced. Examination of the outer 1–2 μm of the wear debris, as well as the first few atomic layers, by EDX and AES, respectively, showed very similar results in areas rich in oxygen accompanied by varying quantities of Al and Si but litte carbon. It is proposed that the wear debris is initially produced by the fragmentation of asperities on the two wear surfaces followed by the transfer of a wear film of SiO₂. Such equiaxed debris is then agglomerated into a characteristic cylindrical particle that lies normal to the reciprocating motion.     

Improving the wear resistance of machine parts

Various types of operational faults in critical machine parts are analyzed. The possibility of eliminating the factors responsible for such faults at the manufacturing stage is considered. Thermodynamic analysis reveals the relation between the bulk wear rate and the surface quality.     

An investigation of the properties and wear behaviour of plasma-nitrided hot-working steel (H13)

The microstructural properties and wear behaviour of AISI H13 steel which had been plasma nitrided at 530 and 550 °C for times between 4 and 100 h have been investigated. The effect of treatment temperature and time on the microstructure have been examined. The wear behaviour of material treated for 4 and 100 h has also been observed. It was seen that a total case depth of 0.55 mm with a hardness of 1000 HV can be achieved in 100 h. However, the white layer thickness is increased to 17 μm while the core hardness is reduced to 480 HV at 550 °C. The wear rate of the sample treated at 550 °C for 100 h is higher than that of the sample treated at 550 °C for 4 h.     

Influence of simulator kinematics on the wear of metal-on-metal hip prostheses

There is now considerable interest in metal-on-metal bearings for hip prostheses. Extremely low wear rates (0.1 mm3/10(6) cycles) have been reported in some simulator studies, while in vivo studies, although still very low, have shown wear rates of the order of 1 mm3/10(6) cycles. The aim of this study was to compare wear rates of metal-on-metal bearings in two hip simulators with different kinematic inputs. In the simulator with three independent input motions which produced an open elliptical wear path with a low level of eccentricity, the wear rates were very low as recorded previously in other simulators. In the simulator with two input motions which produced an open elliptical wear path with greater eccentricity the wear rate was at least ten times higher and closer to clinical values. The motion and kinematic conditions in the contact are critical determinants of wear in metal-on-metal bearings.     

A finite element method comparison of wear in two metal-on-metal total hip prostheses

The contact mechanics of two metal-on-metal (MOM) total hip prostheses was studied by means of the finite element method (FEM). The purpose of the work was to compare two total hip replacements (Durom and Metasul) with regard to the amount of wear debris released. Wear on the bearing surfaces was evaluated following Reye hypotheses from the pressure distribution, computed by means of three-dimensional FEM models; an approximate analytical model based on Hertz contact theory has also been developed and discussed. The results show that in the dry friction condition the Durom joint releases almost twice as much wear volume as produced by the Metasul joint. Therefore, while Durom implants can improve hip stability by increasing the prosthetic impingement-free range of motion (PIF-ROM), Metasul prostheses can be a valuable solution whenever wear represents a critical choice factor.     

一种自动化冲压生产线上下料系统的开发设计

本文通过一例实际的应用工程,探讨厚板材小工件自动化冲压生产线上下料系统的配置及设计,提出了自动化联线时对压力机及模具的技术要求,并针对遇到的技术问题进行攻关,采取合理有效的解决办法.使整个系统运行稳定、可靠.进而突出自动化冲压生产的优越性.