Two-disk Test Research Articles

An Investigation into the Wear Behavior of Martensitically Transformed Nitrided Layers

To improve the service behavior of gears, surface heat treatments such as nitriding or induction hardening can be performed. Since these processes are limited in their achievable maximum hardness or depth of hardness, a combination treatment could allow benefits from the advantages of both processes. The aim of this work was to show the correlation between the microstructure resulting from combination treatment and the performance of the surface layer using the example of wear behavior. The investigations focused on the impact of different nitrided states, in the combination treatment of the material EN31CrMoV9, on wear resistance. The wear was evaluated after running the two-disc test gravimetrically and optically. Nitrided-only specimens showed better wear resistance compared to those subjected to induction hardening after nitriding. Substantial differences in weight loss indicate that induction hardening worsens the wear behavior. The variants with the compound layer removed in the nitride-only state as well as in the induction hardened state showed a better wear behavior compared to the respective conditions with a compound layer. This was attributed to the lower surface roughness and the higher hardness due to less retained austenite after combination treatment.

Investigation of combined surface treatments and coatings to increase the wear behavior of heat treatable steels

A combination treatment of nitriding and induction hardening can achieve high hardness depths in short treatment times and can therefore be seen as an alternative to deep nitriding. However, the compound layer, which makes a significant contribution to the wear resistance of nitrided components, decomposes during the induction heat treatment of the nitrided part. Therefore, the tribological behavior of parts processed this way is affected. In the present work, the wear behavior of surface layers resulting from combined heat treatment of EN42CrMo4 and PVD a-C:H(:Si) coating is investigated and evaluated. For the wear testing, a two-disk test rig was used. The wear was determined gravimetrically and by optical evaluation of the wear tracks. It was found, that the wear resistance of the investigated heat-treatable steel can be improved by duplex surface treatments such as nitriding and induction hardening as well as nitriding and PVD a-C:H(:Si) coating compared to the heat treated-only condition. By triplex treatment, no further improvement of the wear resistance could be observed.

Tribological behavior of different doped ta-C coatings for slip-rolling contacts with high hertzian contact pressure

PurposeThe curved and tribologically highly stressed surfaces of bearing components pose a major challenge for steel alloys or tribological resistant coatings like tetrahedral amorphous carbon (ta-C) coatings which in particular have an increased risk of delamination due to the significantly increased residual stresses. A possibility to prevent coating failure is the use of dopants while maintaining or even increasing tribological properties. This study aims to compare the tribological behavior of several doped diamond-like-carbon coatings with an undoped ta-C coating under varying slip conditions and Hertzian pressure up to 1800 MPa.Design/methodology/approachFor this purpose, the tribological behavior was studied using of a ball-on-disc tribometer and a two-disc test rig under mixed/boundary conditions. The tests were conducted with coated specimens against uncoated 100Cr6 steel. Additionally, the influence of lubrication additives was studied due to the use of two fully formulated PAO-based oils, one without and one with molybdenum containing additives. The friction was measured in situ, and the wear was analyzed trough laser scanning microscopy and tactile measurement.FindingsIt was shown that the use of doped ta-C coatings exhibited a tendency for a more favorable tribological behavior compared to undoped ta-C coatings, with no general dependence on the lubricants used. The use of the most suitable coatings reduced the wear of the steel counter-body considerably.Originality/valueTo the best of the authors’ knowledge, this is the first approach of testing the tribological behavior of these doped ta-C coatings, developed for friction efficiency, in dependency on lubrication additives under the given load collective. The approach is relevant to determine whether the friction reduction and the wear inhibition of these coatings are suitable for higher contact pressures and load cycles.Peer reviewThe peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-11-2022-0336/

Effect of material non-uniformity and residual stress on wear and transient rolling contact behaviour in laminar plasma quenched (LPQ) rails

Laminar plasma discrete quenching of rail surfaces significantly improves the wear resistance of quenched rails by forming a discrete hardened layer on the rail surface, while also introducing residual compressive stress. However, in practice, laminar plasma quenched (LPQ) rails demonstrate numerous fine cracks and spalling at the edges of the hardened layer, potentially threatening the safety of railway traffic. However, most previous studies have focused on the microstructure of LPQ materials and two-disc tests, with few of them including a finite element analysis of the mechanical properties of the quenched rails. In this paper, an ANSYS/LSDYNA explicit finite element (FE) model of the transient rolling contact between the quenched rail and the wheel is developed for the rolling contact behaviour and wear characteristics of the LPQ rail. The innovation of the model is the fact that it takes the inhomogeneous material properties between the substrate and the hardened layer of the rail surface into account, as well as the real residual stress. It was found that the inhomogeneous material properties of the substrate and the hardened layer may be the main cause of micro-cracking at the edges of the hardened layer. Residual compressive stress within the hardened layer has a non-negligible effect on the rolling contact characteristics of the rail. The research methodology in this paper further develops the FE model for LPQ rails, while the results obtained will be important for controlling rail damage.

Einfluss des Substratmaterials bei der Transferschmierung von Stahl- Bronze-Kontakten mit PA66-PTFE-cb Trockenschmierstoffen

In this work, the dependence of the friction and wear behaviour in dry-lubricated steel-bronze contact on the dry lubricant used and on the substrate material (steel or bronze) under constant load was investigated. For this purpose, a block two-disc test rig was used, with the dry lubricants PA66-PTFE-cb as blocks, which were produced via chemical bonding (cb) of polyamide 66 (PA 66) and radiation-modified polytetrafluoroethylene (PTFE). The results provide a good basis for the selection of a suitable dry lubricant and the counter body for the transfer of the dry lubricant in dry lubricated worm gears consisting of a steel worm and a bronze wheel.

Development of a Thin-Film Sensor for In Situ Measurement of the Temperature Rise in Rolling Contacts with Fluid Film and Mixed Lubrication.

The following study presents an in situ sensor system which can measure the temperature change of rolling contacts for heavy duty during fluid as well as mixed friction. This thin-film sensor was optimized with regard to its size, spatial resolution, and wear resistance. Extensive tests were carried out with a two-disk test rig and the data of the temperature change were presented. The results show the complex processes within a rolling contact and the strongly interaction of pressure, friction, and temperature development within the contact zone. Due to the detailed sensor and disk characterization, the data are suitable for comparing calculation methods.

Study on squeal noise generated on railway curved section using the two-disc test rig

Study on squeal noise generated on railway curved section using the two-disc test rig

Study on squeal noise generated on railway curved section using the two-disc test rig

Study on squeal noise generated on railway curved section using the two-disc test rig

An energetic approach for the prognosis of thermally induced white etching layers in bearing steel 100CrMn6

Abstract Thermally induced white etching layers (WEL) are known to increase the risk of rolling contact fatigue (RCF) cracks. This study focuses on the potential of an energetic approach for the prognosis of thermally induced WEL in oil-lubricated rolling/sliding contacts. For the determination of power and energy density thresholds a laser surface treatment was selected. The thresholds were determined using non-lubricated flat specimens made of 100CrMn6 bearing steel. The applicability of the energetic approach for the prognosis of WEL appearance in oil-lubricated rolling/sliding contacts was shown using a two-disc test rig. The formation of WEL was achieved by an acceleration process under varying contact parameters such as speed and load. The appearance of WEL was confirmed through metallographic investigations.

Rolling contact fatigue: Damage function development from two-disc test data

The concept of the rail damage function provides vital understanding of the operational performance of rail grades in terms of surface degradation. Previously, material specific damage functions have been derived from measurements in track combined with vehicle-track simulations. However, from the occurring wide range in track loading conditions it is difficult to achieve clear characterisation results from track data only.To reach more controlled loading conditions, a rolling-sliding two-disc laboratory set up could be applied. The validation of a two-disc test approach in order to define rail/wheel interface wear and RCF response is the topic of the here presented study.

Thermal-induced surface damage of M50 steel at rolling-sliding contacts

The thermal-induced surface damage of M50 steel at rolling-sliding contacts under heavy load and high speed is investigated. A two-disk test rig is used for testing the surface damage of M50 steel at scuffing. The thermal response and near-surface deformation of M50 steel at rolling-sliding contacts are analyzed based on its high-temperature properties. The results show that the surface damage of M50 steel at rolling-sliding contacts is basically caused by thermal softening of near-surface material, which is generated by the heat of both the friction and plastic deformation. A high temperature due to the frictional heat at rolling-sliding contacts first reduces the yield strength of M50 steel. A large plastic deformation of near-surface material is therefore generated, which, in turn, causes a large temperature rise. Scuffing occurs at a quick increase in thermal softening of M50 steel.

Wear Behavior of Carbonitrided and Nitrided Hot Working Steels*

Abstract During forging the tools have to resist high thermal and mechanical loads. Therefore, forging dies are usually nitrided in order to increase the wear resistance of the surface areas. Compared to nitriding carbonitriding increases the hardness depths in shorter treatment times. Due to the (carbo-)nitriding, the surface near region gets a better hot hardness and a better wear resistance than the untreated material. In a second process step by nitriding after carbonitriding, a wear and corrosion resistant compound layer can be created at the surface. In the present work the wear behavior of carbonitrided and nitrided hot working steel ENX38CrMoV5-3 (1.2367) was investigated. The evaluation concerning abrasion and thermal fatigue in the contact of forging die and workpiece was carried out by model wear tests like the two-disc test (Amsler test), the ball-on-disc test and a cyclic induction heating and quenching. The conditions of the heating cycles were chosen close to the forging process. The surface areas were investigated after several cycles in order to gain information about the mechanisms of the surface modification. Finally, the treatment combination carbonitring/nitriding was transferred to forging dies and the wear behavior was investigated in fatigue-life experiments under application conditions.

Effect of Wear on Surface Crack Propagation in Rail–Wheel Wet Contact

The interaction between wear and rolling contact fatigue in wet contact was investigated by means of experiments on a two-disk test bench. Specimens of various railway wheel steels were coupled with specimens of the same rail steel, subjected to rolling and sliding wet contact with varying sliding/rolling ratio. Some tests with a dry rolling–sliding contact phase preceding wet contact were carried out as well (dry–wet tests). The pressurization of the fluid entrapped in the surface cracks was the cause of a rapid and severe damage in the dry–wet tests, due to the nucleation of surface cracks by ratcheting in the dry phase, which subsequently propagate in the wet phase. In the wet tests, the fluid pressurization effect was much mitigated due to the absence of initial surface cracks; the specimens subjected to higher sliding/rolling ratio showed the best performance against rolling contact fatigue, due to the effect of wear in reducing the length of surface cracks. A model for assessing the interaction between wear and rolling contact fatigue was proposed, based on the correction of the classical Paris law for crack propagation by taking into account the effect of wear on crack length reduction. The application of the model to the experimental tests allowed finding a correlation between the model predictions and the occurrence of fatigue failure.

Influence of Slip and Lubrication Regime on the Formation of White Etching Cracks on a Two-Disc Test Rig

A common cause for maintenance and downtime in multiple fields of the mechanical transmission industries are premature rolling bearing failures due to white etching cracks (WEC). Within this work, WEC have been successfully recreated on a two-disc test rig under rolling contact loading without additional loading such as hydrogen pre-charging. This paper summarizes the state of the investigations regarding the influence of the slip type and the lubrication regime on the WEC formation on the two-disc test rig.

Reproduction of white etching cracks under rolling contact loading on thrust bearing and two-disc test rigs

A common challenge in multiple fields of the mechanical driveline technology is the premature failure of rolling bearings due to white etching cracks (WEC). This failure mode is characterized by three-dimensional cracks, bordered by regions of altered material microstructure, which eventually lead to cracking or spalling of the raceway. Ultrasonic analysis of cylindrical roller thrust bearings have already shown that WEC are mainly located in the region under negative slip, which agrees with a cumulative frictional energy criteria. In this study, WEC were reproduced on a two-disc test rig using inner rings from radial cylinder roller bearings without pre-charging the samples with hydrogen. The investigations revealed an influence of the sliding direction and the lubrication regime on the WEC formation. The tests showed that a WEC failure induced by sliding occurs under boundary lubrication regime. Furthermore, it was determined that while single axial cracks and small WEC networks formed in the sample under positive slip; large WEC networks formed in the sample under negative slip.

Experimental determination of heat partition in elastohydrodynamic contacts

Experimental and theoretical analyses are reported to study the heat generation and partition in an elastohydrodynamic rolling/sliding point contact. Heat is generated within the lubricant in the Hertzian region by shearing and compression of the oil film. This heat is essentially conducted to the contacting surfaces as the amount convected from the Hertzian zone by the lubricant can be neglected due to the very low lubricant mass flowrate. A two-disk test rig was used for the experimental tests using crowned, superfinished 76.2 mm diameter disks fixed on parallel shafts. Each disk was fitted with six thermocouples in two rows of three located 3 mm and 6 mm below the surface to measure the temperature distribution of the disks during the tests. In addition, the disks were insulated on both plane sides by ceramic washers to minimise heat transfer to the surroundings over those surfaces. A numerical model was developed to calculate the circumferential mean disk temperature distribution in the outer 6 mm annular ring using the inner row of thermocouples to provide a boundary condition. The model was used to predict the temperature distribution for given values of the fraction of the total heat entering the fast disk, β, and the heat transfer coefficient, h, for the disk running surfaces. Minimisation of error between predicted and experimentally measured temperatures at the thermocouple positions, together with consideration of the physical relationship between fast and slow shaft heat transfer coefficients led to the conclusion that β lies in the range 0.71–0.77 for the experiments reported in the paper and that approximately 75% of the frictional heat dissipated within the lubricant film flows into the faster disk. This result indicates that the likely mechanism of heat dissipation within the lubricant film is by slip at or near the faster surface and that consideration of heat partition is a more discerning judge of lubricant rheological behaviour than the usual consideration of traction measurements alone.

Influence of the metalworking fluid on the running behavior of gear analogy test parts

Boundary layers protect tooth flanks from solid-state contacts and, therefore, influence friction and wear. The characteristics of boundary layers (e.g. structure, chemical composition) and the running behavior of gears are determined by the manufacturing process (Klocke and Broeckmann in Prod Eng Res Dev 8(461):468, 2014; Brecher et al. in Prod Eng Res Dev 7:265–274, 2013). In this paper, the influence of the grinding fluid on the modification of boundary layers is shown. Analogy test parts are manufactured with varying fluids and additives. The differently ground test parts are measured regarding their boundary layer properties. Furthermore, the effects of the different resulting boundary layers on the running behavior are evaluated in finite life fatigue testing (pitting) on the two-disk test rig. By combining both measurement and test results, possible correlations between manufacturing and operation are investigated to establish a more sustainable and economical design of gears.

Hydroelastic response of floating elastic discs to regular waves. Part 1. Wave basin experiments

AbstractA series of wave basin experiments is reported that investigates the flexural response of one or two floating thin elastic discs to monochromatic waves. The work is motivated by numerical model validation. Innovative techniques are used to ensure the experimental configuration is consistent with the model. This demands linear motions, time-harmonic conditions, homogeneity of the plate and the restriction of horizontal motions of the disc or discs. An optical remote sensing device is employed to record the deflection of the discs accurately. Tests involving a single disc and two discs are conducted for a range of disc thicknesses, incident wave steepnesses, frequencies and, in the case of two discs, geometrical arrangements. A data processing technique is used to decompose the raw data into its spectral harmonics and filter the higher-order components. Pointwise comparisons of the linear first-order component of the experimental deflection with numerical predictions are presented. Satisfying agreement is found, although the model consistently over predicts the deflection. Disc–disc interactions are observed in the two-disc tests. A brief discussion of the shortcomings of the pointwise analysis, with associated possible sources of discrepancy, provides a link to the study reported in Part 2 (Montiel et al. J. Fluid Mech., vol. 723, 2013, pp. 629–652).

Hydroelastic response of floating elastic discs to regular waves. Part 2. Modal analysis

AbstractValidation of a linear numerical model of wave interactions with floating compliant discs is sought using data obtained from the wave basin experiments reported in Part 1 (Montielet al. J. Fluid Mech., vol. 723, 2013, pp. 604–628). Comparisons are made for both single-disc tests and the two-disc tests in which wave interactions between discs are observed. The deflection of the disc or discs is separated into the natural modes of vibrationin vacuo. The decomposition allows the rigid-body motions and flexural motions to be analysed separately. Rigid-body motions are accurately replicated by the numerical model but, although passable agreement is found, the amplitudes of flexural modes are consistently overestimated. Extensions of the numerical model are used to discount the experimental configuration as a source of the discrepancies. An enhanced viscoelastic model for the discs is also proposed, which results in improved model/data agreement for the flexural motions but cannot account for all of the disagreement.

Calculation of Kinematics and Friction of a Spindle Bearing Using a Local EHL Friction Model

A new calculation method was developed to determine the kinematics and friction in high-speed angular contact ball bearings (spindle bearings) under steady-state conditions. The basic idea of this model is to determine the exact ball kinematics by taking the resulting local friction forces on the ball into account. For this purpose, a simple elastohydrodynamic lubrication (EHL) friction model derived from measurement data of a two-disk test rig considering local relative motions, sum velocities, and contact pressures over the area of the Hertzian contact ellipse is proposed. Depending on the assumed bearing kinematics (pitch and yaw angle and ball and cage speed), the resulting forces and torques on the ball vary. By alteration of the ball kinematics, equilibrium in forces and torques can be achieved in order to predict the actual operation conditions. Experiments indicate that this approach allows for a good approximation of the resulting bearing friction torques and the actual pitch angles. The model is applicable for standard angular contact ball bearings as well as for multipoint contact ball bearings.