AbstractIn the present research, a comparison of worn surface morphologies and wear mechanisms observed for worn deep drawing dies and sheets from the automotive car body manufacturing and worn surfaces obtained by a slider‐on‐flat‐surface (SOFS) tribometer has been carried out. Abrasion and adhesion were identified as the main surface damage mechanisms on the investigated dies and sheets. Comparison of the results obtained in laboratory testing using the SOFS tribometer showed that the test method properly simulates the tribological conditions occurring in actual sheet metal forming operations. Copyright © 2007 John Wiley & Sons, Ltd.
AbstractIron‐based hardfacing alloys are widely used to protect machinery equipment. A strong correlation is given between microstructure and chemical composition of welding deposit with the resulting wear behaviour. Concerning precipitation of metallurgical hard phases and synthetic added hard particles, the bonding strength of the hard phases in the metallic matrix seems to play a dominating role to obtain high wear resistance.The main objective of this study was to evaluate the wear behaviour for pure abrasion, combined impact/abrasion and high impact wear, respectively, for four different Fe‐based hardfacing alloys. Tests were performed with a standard ASTM G65 dry‐sand/rubber‐wheel tester. An impeller–tumbler apparatus enabled investigation of impact abrasion wear tests. Additional wear tests with high impact loading were performed on a drop hammer apparatus. Fracture surface analysis was carried out after drop hammer testing and results were correlated with microstructure and interfacial bonding behaviour of precipitations in metallic matrix. Copyright © 2008 John Wiley & Sons, Ltd.
Utilisation of hydrogen is expected to be one of the solutions against the problems of exhaustion of fossil fuels and reduction of carbon dioxide emissions. Evaluation of the materials for hydrogen utilisation machines is required. The objectives of this study are the characterisation of fretting fatigue strength of low-alloy steel SCM435H and heat-resistant steel SUH660, and the validation of effectiveness of nitriding in hydrogen gas environment. Fretting fatigue tests were conducted up to 3 × 107 cycles. The decrease of fretting fatigue strength in hydrogen gas environment was found at the long-life region exceeding 107 cycles. The amount of the decrease of the fretting fatigue limit at 3 × 107 cycles was 11% for SCM435H and 15% for SUH660. However, at the stress level above the fretting fatigue limit in air, the finite life in hydrogen gas increased more than that in air. The cause of extension of fatigue life was the delay of start of stable crack propagation. Fretting fatigue crack, which was smaller than 200 µm in length, consumed approximately 60% of the fatigue life in hydrogen gas environment. Fretting fatigue crack was steadily propagated after the test was started in air. Observations of the fretted surface showed that the fretting wear process in hydrogen gas environment was dominated by adhesion. Tangential force coefficient was higher in hydrogen gas environment than that in air. It is considered that the adhesion has a close relation to crack initiation in hydrogen gas environment, and as a result, the failure of specimen occurred at a lower stress level comparing the fretting fatigue limit in air. Copyright © 2008 John Wiley & Sons, Ltd.
AbstractThis paper presents an experimental study of tribological characteristics of electroless Ni‐P (EN) coatings and optimisation of coating process parameters based on Taguchi method coupled with grey relational analysis. A grey relational grade obtained from the grey relational analysis is used as performance index to study the deposition of EN coating with multiple tribological performance characteristics. Experiments are carried out by utilising the combination of process parameters based on L27 Taguchi orthogonal design with four process parameters, namely, bath temperature, concentration of nickel source solution, concentration of reducing agent and annealing temperature. It has been observed that concentrations of nickel source solution and bath temperature are the most significant parameters for controlling the friction and wear behaviour of EN coating. The surface morphology, composition and wear mechanism of coatings are also studied with the help of scanning electron microscopy, energy dispersed X‐ray analysis and X‐ray diffraction analysis. Copyright © 2008 John Wiley & Sons, Ltd.
AbstractCoefficients of friction and wear rates for polyacetal and polytetrafluoroethylene are measured on small‐scale cylinder‐on‐plate tests and large‐scale flat‐on‐flat tests. Three models for extrapolation between small‐ and large‐scale test results, which are based on experimental parameters, are presented: (i) one single mechanical parameter (normal load), (ii) the contact‐pressure–sliding‐velocity model (temperature limit), and (iii) a macroscopic geometry model. The last model is most extensively evaluated and considers thermal effects, sample geometry and contact conditions. After correction for the thermal sliding regime and viscoelastic deformation, the coefficients of friction can be extrapolated while the wear rates are more sensitive to the contact situation. High‐temperature tests on small scale are not representative for high‐load tests on large scale. Besides mechanical effects such as stress concentrations and debris mobility, variations in polymer structure under sliding (formation of rigid amorphous phase) and chemical interactions (wear debris polymerisation) also change with testing scale. The latter effects are explicitly illustrated from spectroscopic measurements on the worn surfaces. Copyright © 2008 John Wiley & Sons, Ltd.
AbstractThis work deals with the development of a new tribometer designed for the characterisation of the frictional properties at the tool/chip/workpiece interfaces in cutting processes. Based on a plane–sphere contact configuration, the experimental set‐up enables a continuous regeneration of the pin–workmaterial contact. The average contact pressure can be selected up to 3 GPa under sliding velocities reaching 16 m/s. Under such severe conditions, which are not reachable with conventional tribometers, the apparent friction coefficient is quantified in parallel to the heat flux transmitted to the pin. This new system has been applied to the characterisation of the frictional properties during the dry machining of a 27MnCr5 annealed steel with a carbide cutting tool. The influence of the sliding velocity and of an additional TiN layer deposited by PVD on the carbide pins has been investigated in dry conditions. It has been shown that the sliding velocity is the more influential parameter, followed by the coating. Copyright © 2007 John Wiley & Sons, Ltd.
AbstractAfter having checked in a previous study the influence of stroke and normal load in laboratory fretting tests accomplished with thin steel roping wires, in this paper the effect of the contact pressure (test configuration), environmental conditions (relative humidity) and reduction of the friction coefficient (lubricants) on the wear behaviour were analysed. The wires were 0.45 mm in diameter and the material was a cold‐drawn eutectoid carbon steel (0.8% C) with a Tensile Strength over 2800 MPa. The tests were performed on an oscillating test rig and the volumetric wear of both specimens of the tribocouple was determined separately from three‐dimensional topographies of the wear scars acquired by means of a confocal profiler, and a calculation algorithm developed in using MATLAB®. The strong effect of humidity and lubrication on wear behaviour was proved, whereas a slight effect of contact pressure was derived. Copyright © 2007 John Wiley & Sons, Ltd.
Comparison of two test methods for evaluation of forming tool materials, Tribotest, v 14, n 3, July 2008, p 147-58
In this study, we present the development of model scale tribological test methods using the model ring-on-disc. The methods enable the demonstration of processes that occur in sliding materials during operation and subsequent breakdown. Currently, existing test methods are not able to visualise these complex processes to the same extent. We designed adapted test programmes for the visualisation of different material properties. This paper discusses the suitability and the significance of these test programmes. We benchmarked the test methods on selected metal-based and plastic tribomaterials (CuPb22Sn2 and Polytetraflaoroethylene (PTFE) and bronze (Bz)) under lubricated and non-lubricated conditions. We conducted an extensive damage analysis of the surfaces and surface layers. Furthermore, the classification of the damage patterns and the tribometric results are the basis for the development of models that are capable of representing the most important states during operation. The models are of sufficient quality to assist in the further optimisation of the materials. Copyright © 2008 John Wiley & Sons, Ltd.
In the course of a Kplus research project which focused on the internal thread moulding process, a test methodology for evaluating the efficiency of forming oils was developed. The various tests should provide tribological characteristic values, such as coefficient of friction, with respect to the real production environment. To guarantee the transferability of results, the complex of loads acting on the components in the model tests must correspond to the real forming process. Especially parameters such as contact pressure, relative speed in the forming zone and the increase of surface of the workpiece during the forming process must be considered in tribological testing. The tribological data provided information to select components of thread moulding oils and to optimise the formulation. Best practice moulding oils must satisfy different demands in respect of physical, physical–chemical, chemical and additional properties. In addition to the cooling function and the reduction of friction, there is also a significant influence on the quality of the workpiece and the moulding process itself. Copyright © 2008 John Wiley & Sons, Ltd.
AbstractThis special issue is dedicated to the tribology of coated surfaces. It comprises five papers which treat the issue from different viewpoints. They cover, e.g. the selection and design of tribological experiment and analyses of coatings tribology in lubricated contacts. Copyright © 2008 John Wiley & Sons, Ltd.
The paper describes an experimental investigation on the influence of the surface roughness of diamond-like hard carbon (DLC) coatings on the friction and wear in sliding contact against steel under conditions of starving lubrication. Experimental studies employed a reciprocating ball-on-flat tribometer in two different modes of operation. The study showed a micro-lubrication effect in terms of lubrication assistance achieved by microscopic cavities in the topography of a DLC coating and good sliding behaviour even in the case of starving oil lubrication. Post-process polishing of the coated surfaces was adopted for eliminating unnecessary friction losses due to asperity interactions and micro-abrasive wear. Copyright © 2008 John Wiley & Sons, Ltd.
Solid and hollow cylindrical rollers in pure rolling contact have been modelled. The two rollers are subjected to a combined normal and tangential loading. The tangential loading is one‐third of the normal loading value. The finite element package, ABAQUS, is used to study the stress distribution and the resulting deformations in the bodies of the rollers. Then the Ioannides–Harris fatigue life model for rolling bearings is applied on the ABAQUS numerical results to investigate the fatigue life of the solid and hollow rollers. Using the fatigue life of the solid rollers as the reference fatigue life, the relative fatigue lives of hollow rollers are determined. Four main different hollowness percentages are been studied: 20, 40, 60 and 80%. The hollowness percentage is the ratio of the diameter of the hole to the outer diameter of the cylinder. For each of those hollowness percentages, two cases are studied – when the two rollers in contact are hollow and when one hollow roller is in contact with a solid roller. This study includes two main models: Model 1, where the two cylindrical rollers in contact are of the same size, and Model 2, where the two rollers in contact are not of the same size. The estimated relative fatigue lives of hollow rollers showed a great improvement of the fatigue life compared with solid rollers under the same loading conditions. This was a result of the redistribution of stresses in the contact zone in the case of hollow rollers. Redistribution of stresses over a larger volume of the roller body decreased the peak stress and reduced the volume under risk. Increasing the hollowness percentage from 20 to 60% increased the flexibility of the roller, and better stress distribution was achieved, which resulted in improving the fatigue life. Although 80% of hollowness rollers have more flexibility than 60% of hollowness rollers, the bending stresses ( σ b ) on the inner surface of the rollers tend to decrease the fatigue life. Copyright © 2007 John Wiley & Sons, Ltd.
AbstractWire ropes, due to their construction and application, are prone to fretting damages. In order to know the wear behaviour of individual wires under fretting conditions, laboratory tests are required. The present work describes the preliminary fretting tests accomplished with thin steel wires to optimise the testing procedure. The tests were carried out with ‘crossed‐cylinders’ configuration varying the stroke and normal load. Afterwards, the fretted surfaces were characterised by means of an optical and scanning electron microscope, and a diamond stylus. No significant influence of selected parameters was detected and a good correlation was proved for on‐line measured parameters and off‐line obtained values. Copyright © 2007 John Wiley & Sons, Ltd.
AbstractIn this work, thermal and transient effects on non‐conformal lubricated contacts are investigated through experimental analyses. Experiments between a ball and a plane surface of a disc are described. Friction coefficients and film thicknesses are measured (the film thickness only for the glass‐on‐steel contact). A paraffin base mineral oil is used as a lubricant.First experiments are carried out under steady‐state conditions. To include effects due to different thermal properties of contacting materials, a steel‐on‐steel and a glass‐on‐steel contact with different slide‐to‐roll ratios are tested. If the contacting materials have different thermal properties, as in the case of a glass‐on‐steel contact, thermal effects like the temperature–viscosity wedge action could clearly be shown. It is found that the friction coefficients are influenced by the slide‐to‐roll ratio and the thermal properties of the contacting materials.Under transient conditions, the entraining velocity is varied with a sinusoidal law. Squeeze effects explain ‘loops’ of friction and film thickness found also in previous works. The formation of friction loops is related to the measured film thickness differences. However, also under non‐steady‐state conditions, thermal effects, like the temperature–viscosity wedge action, influence the friction coefficients. Copyright © 2007 John Wiley & Sons, Ltd.
AbstractFourier transform‐infrared reflectance microspectroscopy has been used extensively for the examination of coatings on non‐planar surfaces such as ball bearings. While this technique offers considerable advantages, practical application has many drawbacks, some of which are easily overcome by the use of integrating sphere technology. This paper described the use of an integrating sphere for the quantification of thin layers of lubricant on the surface of ball bearings and the parameters that require optimisation in order to obtain reliable data. Several applications of the technique were discussed including determination of lubricant load on 12.7mm steel ball bearings and the examination of degraded lubricant on post‐mortem specimens. Copyright © 2007 John Wiley & Sons, Ltd.
AbstractTwo solid and hollow cylindrical rollers in pure rolling contact subjected to pure normal loading have been modelled. Using a finite element package called ABAQUS, the stress and strain distributions in the two rollers in contact have been determined. The relative fatigue life of the hollow rollers compared to solid rollers has been investigated using the fatigue life model for rolling bearings developed by Ioannides and Harris. Different hollowness percentages have been studied: 20, 40, 60 and 80%. The hollowness percentage is the ratio of the diameter of the hole to the outer diameter of the cylinder. Both cases were studied – when the two rollers in contact are hollow and when only one of them is hollow while the other one is solid. Making the rollers hollow will result in redistribution of stresses over a larger volume in the contact zone due to the flexibility of the hollow rollers. That decreases the peak stress in the contact zone of the hollow cylinder when compared to the solid cylinder. Hollow cylinders have more flexibility when subjected to normal loading. And so, the stresses are redistributed so that the fatigue life is improved. The best stress redistribution and so fatigue life improvements have been found when both cylinders have around 60% hollowness. Copyright © 2007 John Wiley & Sons, Ltd.
AbstractPolyamides, polyesters and polyacetals are often used in line contacts under reciprocating or continuous sliding. These contacts are simulated on cylinder‐on‐plate (COP) or block‐on‐ring (BOR) tribotests. Comparative tests for pure, oil‐filled and solid lubricated polymers at 100N and 0.3m/s are presented for relative material classification. Differences are discussed according to the sliding geometries. Thermal effects dominate friction and wear behaviour: the polymer glass transition temperature is exceeded in COP tests while the temperature is lower in BOR tests. Thick and brittle films are observed for pure polymers in BOR tests, promoting higher friction. The test configuration is mainly important for evaluation of internal lubricants. The efficiency of oil‐lubricated polymers is not demonstrated in COP tests, while solid lubricants are not efficient in BOR tests. Deformation restricts the diffusion of oil lubricants in COP tests while solid lubricants are deposited on the polymer surface rather than being incorporated in the transfer film in BOR tests. Copyright © 2007 John Wiley & Sons, Ltd.
AbstractThe use of tools manufactured from hard materials is limited by their fracture toughness and there is a need for research aimed at increasing toughness without sacrificing good wear resistance. To aid in this objective, a simple and reliable integrated tribotesting method is needed in which a combined action involving both fracture and abrasion occurs. One such method currently developed is presented in this paper. The method is based on the concept of edge chipping during the initial transition stage of abrasion wear, which is controlled by a brittle fracture process. The empirical relationship between mass loss as a result of edge chipping during the initial transitional stage of abrasive wear and fracture toughness is presented in the form of formulae. Copyright © 2007 John Wiley & Sons, Ltd.
AbstractA novel tribometer has been designed using commercially available components for sliding motion at 40kHz with amplitude between 2.5 and 5µm. The tribometer is equipped with means to measure amplitude, frequency, power required to keep the sample in motion and load applied. The effective motion between the two contacting bodies is monitored. These data are used to evaluate the coefficient of friction. The wear rate was determined after the tests. The set‐up was tested using novel, non‐commercial substrates such as AlFeCrTi‐alloys and tungsten carbide‐based coatings as well as Magnéli‐type coatings (Tin−2Cr2O2n−1 and TinO2n−1). This paper presents the principle of the ultra‐high frequency tribometer and first tribological quantities of materials and coatings tested. Copyright © 2007 John Wiley & Sons, Ltd.
