The purpose of this investigation is to develop an appropriate model for the friction-induced vibration of a tribological system, where there is at least an order of magnitude difference in the stiffness between the mating subsystems. The significance of this system is that neither system can analytically be considered rigid or aspects of the dynamics that are exhibited experimentally are lost. This leads to the necessity of creating a multi-degree of freedom model, where the multiple degrees of freedom are distributed between the two systems. Experiments have shown that both subsystems contribute to the dynamical response. The modeling starts with the simplest system model, in terms of degrees of freedom, and then progresses to the level required to demonstrate the experimentally observed behavior. An example of such a system is an elastomer sliding against a steel counterface. It has been observed on a variety of dissimilar test devices (linear and rotational) that the subsequent response contains similar dynamical behavior relative to friction-induced vibration. The striking similarities of the dynamic behavior is demonstrated in the friction(time) response, which is subsequently evidenced in the autospectra of friction with an identifiable characteristic form. Specifically, with the exception of scaling in amplitude and frequency, due to system differences, the autospectrum are contained within a characteristic envelope that is determined by both subsystems. While not specifically attempting to model any particular test device or system, representative values of stiffness and estimated friction (velocity) relationships have been incorporated to lend realism to the models.

Absence of any tribological considerations in design can lead to quality and durability problems in automobile engines, which arc unearthed only during the testing phase of an engine. The usage of an overall engine friction model in conjunction with robust design techniques facilitates the concurrent design of engine components with tribological considerations. The case study under investigation involves developing robust top-level design specifications with tribological considerations for principal lubricated components in an automobile engine. The Robust Concept Exploration Method is adopted as a framework to address tribological considerations in preliminary engine design, involving three major action items: design space exploration (design of experiments), system modeling (engine friction computer modeling and system approximation using response surface methods) and system synthesis (Compromise DSP). The usage of these action items helps in achieving an efficient and effective design process and makes possible exploration of different design scenarios. The details of the case study, the implication of the results and the conclusions that can be drawn, are elaborated in this paper. Our focus in this paper is to demonstrate a method of abstracting tribological issues to the preliminary stages of design, rather than the results per se .

Noise and vibration have become key issues in the design of automotive braking systems. Efforts to improve present day braking systems must take noise and vibration behaviour into account. Good knowledge of the mechanisms involved in the generation of brake noise has thus become an important competitive factor in the design of automotive brake systems. The present paper summarizes some facts and hypotheses concerning the generation of brake noise. First the different brake noise phenomena are classified. Then several approaches, including models of various levels of detail which have been suggested to explain the root causes of brake noise generation are discussed in detail. It will be pointed out that friction and wear processes at the interface of brake pad and rotor play an important role in the understanding of brake noise generation. Unfortunately, our present day knowledge on these processes is quite limited. Further research of basic processes is still needed to improve the quality of analytical and numerical models of friction and wear processes, before reliable predictions of brake noise generation become possible. Based on a discussion of simple models frequently used in engineering practice, guidelines for further research in tribological modelling of the interface processes in pad/rotor interaction will be formulated.

The study used a fatigue test model to investigate the surface fatigue strength of a specific carburized gear material, i.e. AISI 4118. A set of test specimens is designated to simulate the mechanics of gear tooth meshing. A friction, wear, and tribological tester is used to conduct the surface contact stress generated between the test specimens. The surface fatigue lives of the test specimens under different levels of contact stresses have been detected. Based on the maximum likelihood method proposed by Ling and Pan, the R-S-N curves of the surface durability of the specific material have been established using the experimental data of the fatigue test. Especially the fatigue strength for long fatigue lives at required reliability can be estimated.

The surface fatigue failures of the traction drive rollers are different to that of gears and bearings because of the high traction force, skew and small slip ratio. In this research, fatigue tests of traction rollers were performed in different slip ratios and skew angles. The effects of running conditions on the fatigue lives of traction drive rollers are clarified and explained based on the surface crack growth and wear situations. Although a higher slip ratio will make a lower fatigue life, the fatigue strength will increase inversley under the skew conditions, because of the differences in mechanical and tribological condition for surface crack growth and the severe surface wear, which diminishes the surface crack length. For evaluation of the effects of such as slip ratio and skew on the fatigue strength of traction rollers, a new method is put forward in which the relationship between the surface temperature index and fatigue life is used instead of S-N curve.

Sliding resistance on gear teeth can have a dominant effect on housing vibration and noise, due to fluctuating excitation and high force transmissibility in the off-line of action direction. Hence reliable modeling of friction from tribological considerations, supported by experimental data, is of utmost importance. This paper examines some lubrication theories and validates them with 2-disk tests and quasi-static loaded gear tests. From the knowledge of friction characteristics, a lumped parameter system is synthesized for a pair of spur gears. This model includes sliding friction, mounting compliances and lateral-torsional vibration coupling. A different formulation has been applied, which unlike most current models, accounts for energy dissipation in the system due to friction. The influence of various excitations like transmission error, friction and parametric variations, on dynamic response of gears is investigated. Finally, the model is evaluated with dynamic tests carried out on a spur gear set, under varying conditions of torque, speed and lubricant.

In this work, elliptical contact is modeled in spiral bevel gear with a suitable ellipticity ratio. The elliptical point contact is modeled using constant velocity and varying velocity with side leakage. A loaded tooth contact analysis was carried out to determine the kinematic and gear mesh force developed during one mesh cycle. The kinematic parameters of the meshing gear pair, namely the contact cells, rolling velocity, sliding velocity and the load distribution in one mesh cycle are used in the elliptical point contact calculation to calculate the pressure and film thickness distribution. The effect of elliptical point contact and varying velocity on the pressure and film thickness distribution are studied. The time-varying contact parameters which are obtained from the tooth contact analysis are used in the tribological calculations. The effect of shaft misalignments on the elastohydrodynamic pressure distribution is also studied in this work.

In this paper, the establishment of a prognostic approach based on a nonlinear degradation model for reliability assessment focusing on health state and remaining useful life estimation is considered. A model able to describe the non-linearity of degradation to predict future damage progression for real-time application has to be defined. Real-time data are generated during operation, so incomplete data about failure and usage up to the end of life are expected. For the accurate prediction of system lifetime, estimation of future degradation from the point of assessment is required. At this point, the unavailable data are numerically calculated by integrating linearized gradients adaptively by considering nonlinearity in current degradation. The coefficients used to define future degradation gradients are identified according to different states assuming future linear degradation increments. These coefficients are determined using an optimization-based algorithm simultaneously with the calculation of consumed lifetime by extending the previously established state machine lifetime model. For performance evaluation of the approach, the effectiveness of predicting remaining useful life using tribological experiments data is investigated. The results show the potential of this approach to deal with nonlinearity in the degradation progression.

Assessment of system health and prediction of remaining useful life can be performed effectively through the evaluation of degradation levels configured by multiple states. Commonly, degradation progression is modeled according to the specific configuration using existing algorithms with assuming numbers and state conditions. However, due to the complexity, especially in the case of a system with multiple hidden states, the proper configuration is hard to assign and to identify. The need for unsupervised state estimation process to assist degradation modeling preventing under or over assumption becomes obvious. Among the existing approaches is the application of clustering methods to classify data and to estimate the number of degradation states might exist. However, integration into the lifetime prediction framework is still infancy and often not considered. Therefore, in this work, a previously developed state machine lifetime model is extended to allow flexibility in configuring state topology based on K-means clustering algorithm and cluster validity index for the optimal number of states identification. Combining unsupervised state estimation process with a new state machine lifetime model has transformed it into a semi-supervised prognostic approach. For validation, hydraulic pressure data from tribology experiment are deployed for training and test the algorithm. Based on the evaluation, this approach demonstrates the ability to improve health state assessment and lifetime prediction in a more flexible way to address the variability in the system.

To investigate the effect of the inlet starvation severity on the flash temperature, which dictates the scuffing failure, a thermal mixed elastohydrodynamic lubrication model is developed for line contacts operating under the starved lubrication condition. The scuffing failure of high speed gearing applications is commonly associated with the very high sliding condition occurring in the vicinity of either the root or the tip, where the shear thinning effect that decreases the lubrication film thickness and increases the contact pressure is significant. Utilizing a generalized Newtonian Reynolds equation, the lubricant viscosity dependence on the shear rate, as well as on the pressure and temperature, is incorporated for the proper and accurate modeling of the tribological behavior under the high sliding condition. A film fraction parameter is employed in the Reynolds equation to include the starvation and cavitation description, eliminating the need for the measured or assumed meniscus location in the inlet zone. Considering different operating and surface roughness conditions, a parametric study is performed to show an asymptotic relationship between the flash temperature and the inlet starvation severity.

This paper outlines a preliminary case study which examines the effect of friction on select thermoplastics during high load, low velocity, and dry sliding wear applications. The primary factors investigated were temperature increase, mass loss, and surface condition of the material. The goal of this research is to identify the best material choice for this application. Eight different thermoplastics were observed in this study. The thermoplastics include variations of polyethylene (PE), polyamide (Nylon), and polytetrafluoroethylene (PTFE). An overarching goal of this study is to develop a standard wear property table for the select thermoplastics, as they are not readily available like material property tables for other materials. The results obtained show that the temperature of the materials generally increased over time, with some materials experiencing greater temperature increase than others. The PTFE materials exhibited the most substantial material loss while the PE materials had the highest increase in temperature during the testing period. Most Nylon composites generated noise during testing, with the exception of one variant: Bearing Grade Nylon. After all factors were considered, Bearing Grade Nylon was chosen for the aforementioned application due to its negligible mass loss, minor surface damage, and temperature increase relative to other thermoplastics tested throughout all trials.

In various gear applications, water contaminated lubricants are a well known problem leading to a significantly decreased lubricant performance under certain circumstances. In FVA-research projects 488/I and 488/II (FVA-Forschungsvereinigung Antriebstechnik: German research association for transmission technology) the influence of a defined water content ranging from 1 000 ppm to 20 000 ppm in typical gear lubricants on the pitting load carrying capacity of case carburized gears was investigated. Regarding the test series with a relatively high water content from 5 000 to 20 000 ppm, a generally negative influence was observed. This influence was differently distinctive for the investigated base oil types. Especially non-polar lubricants were affected negatively. Subsequently, non-polar lubricants, such as polyalphaolefines and mineral oils, were chosen for further investigations as the water content was also lowered on more practice-relevant levels ranging from 1 000 to 2 900 ppm. The water contamination still influenced the pitting load carrying capacity in the upper range with water contents resulting in a relative humidity significantly higher than 100% (absolute water contents from 2250 to 2900 ppm). At the level of 1 000 ppm (rel. humidity approx. ≥ 100%), no significant influence was detected. Thus, it was possible to derive critical threshold limits for the water contamination of non-polar lubricants in practical applications, as from which, the water contamination may affect the pitting load capacity. The water-induced reduction of the pitting load carrying capacity seems to be primarily dependent on the blended additives. The used non-polar base oil type only had a subordinated impact. Based on the results of theoretical investigations, it was possible to derive and expand a general model of damaging mechanisms of water contamination in lubricants, which is split into: interaction lubricant-water, chemical-material-technological influence and tribological influence. In short, it describes the possible impact of water contamination on the lubricant, the material and lubricating-film properties. The results of additional measurements indicate some damaging mechanisms to be dominant under the herein performed test conditions. In detail, decomposition effects of additive components and an increased oil aging effect were identified to be crucial factors, while the influence on the material properties like the measured residual stresses in the gear material seemed to be subordinated. Undissolved water is supposed to affect the pitting load carrying capacity more negatively than dissolved water. Therefore, the relative humidity is recommended as a suitable characteristic of lubricants to evaluate, whether measured water contents in practical gearbox applications may lead to a reduced pitting performance. Based on the results of the experimental and theoretical investigations a threshold limit for the relative humidity of 100 % appears to be reasonable, given that the additive system of the lubricants is not affected negatively.

The research on the dynamic strain of drum brakes is of great significance in performance evaluation, structure optimization and fatigue prediction. Based on current research of strain experiments and measuring technology, a new test procedure is proposed to investigate strain and temperature information of a working drum. Wireless data acquisition system and high-temperature strain gauges are applied. The strain-time and temperature-time curves are studied on the conditions of emergency brake and continuous brake. A tribological and thermo-mechanical analysis are conducted by using software ABAQUS. Results show that the strain is uneven when the drum contacts different zones of friction plates. Seasonal variation is another feature and a set of four wave crests repeats during the rotation. Meanwhile, thermal effect is proved important to strain. The simulation results coincide well with experiments, proving that this method provides a practical way to verify the calculation. The study also lays the foundation for the following fatigue analysis and optimization design.

This study proposes a formulation for the description of the gear mesh mechanical power loss under the thermal tribodynamic condition. A six degree-of-freedom motion equation set that models the vibratory motions of a general spur gear pair is coupled with the governing equations for the description of the gear thermal mixed elastohydrodynamic lubrication to include the interactions between the gear dynamics and gear tribology disciplines in the modeling of the gear mesh mechanical power loss. The important role of the gear thermal tribo-dynamics in power loss is demonstrated by comparing the predictions of the proposed model to those under the thermal quasi-static condition, and the iso-thermal tribo-dynamic condition, respectively.

Ni-ZrO 2 nanocomposite coatings were fabricated by electrodeposition from a modified Watt’s type electrolyte containing ZrO 2 nanoparticles, where an ultrasonic field was imposed during electrodeposition process. The weight percent of ZrO 2 in coatings and the surface morphology of coatings were examined. The microhardness and tribological properties of Ni-ZrO 2 nanocomposite coatings and pure Ni coating were investigated. The results show that ultrasonic agitation can greatly affect the microstructure and the tribological behavior of Ni-ZrO 2 nanocomposite coatings. The Ni-ZrO 2 nanocomposite coatings record variable ZrO 2 contents and surface morphologies by modifying ZrO 2 concentration in electrolyte and ultrasonic parameters. The Ni-ZrO 2 nanocomposite coating fabricated with ultrasonic agitation exhibits finer grains and more compact structure compared to pure Ni coating and the Ni-ZrO 2 nanocomposite coating fabricated without ultrasonic agitation. The dispersed ZrO 2 nanoparticles in coatings and ultrasonic agitation during electrodeposition synthetically contribute to the grain refinement of the coatings. Therefore, the Ni-ZrO 2 nanocomposite coating by ultrasonic electrodeposition exhibits high microhardness and excellent tribological behavior. In general, the improvement in friction and wear properties of Ni-ZrO 2 nanocomposite coatings can be attributed to the homogeneously dispersed ZrO 2 nanoparticles and the finer-grained structure.

Silicon nitride films were attracting extensive research interest in the past few decades as hard disk protective coating, especially the beta-silicon nitride (β-Si3N4) films and amorphous silicon nitride (SiNx) films, which have high hardness, chemical durability and low friction coefficient properties against wear, corrosion and reducing the friction resistance, respectively. Considerable efforts have been made in studying silicon nitride. However, it’s difficult to determine its nano-tribological properties experimentally since the results were affected by a lot of contact and environment conditions. The molecular dynamics (MD) simulation method is employed in this work. A rigid diamond sphere modeled as a spherical tip are sliding over a layered silicon nitride film substrate, respectively, to investigate the tribological properties of silicon nitride films. The effect of the relative sliding velocity and sliding direction, the normal force and the thickness of crystalline silicon nitride films on the friction coefficient of silicon nitride films were investigated.

This paper presents a new experimental test rig and experimental findings on tire elastomer-surface friction characteristics that are necessary for modeling tire thermodynamic characteristics and then tire characteristics, including the μ-curve in the driving and braking modes of operation. Unlike common approaches, the paper offers experimental procedures and test results on both steady and non-steady friction process by introducing (i) velocity factor, (ii) normal pressure distribution, and (iii) a temperature factor in the elastomer-surface contact. The group of (i), (ii), and (iii)-listed factors, taken together, represents the key elements by means of which tribological properties of the tire-road interaction, i.e., an elastomer-surface friction pair, impact the μ-curve.

Differential hypoid gears play an important role on the Noise, Vibration and Harshness (NVH) signature of vehicles. Additionally, friction developed between their teeth flanks under extreme loading conditions adds another source of power loss in the drivetrain which can mitigate vibrational energy. The paper considers the coupling between dynamics and analytical tribology to study dynamic response of hypoid gear pairs with lateral motion of support shafts also included in the analysis framework. Friction of teeth flank pairs is assumed to follow elastohydrodynamic lubrication under elliptical point contact geometry with lubricant film behavior conforming to Non-Newtonian thermal shear, also with surface asperity interactions. Tooth Contact Analysis (TCA) has been used to obtain the input data required for the investigation. The dynamic behavior and efficiency of a differential hypoid gear pair under realistic operating conditions is determined. The proposed tribo-dynamic framework provides a useful platform to conduct an extensive series of parametric studies.

This paper describes a fully analytic solution method for the displacements and sub-surface stresses within a graded elastic layered solid. This method can be utilised to predict the local deformation of nano or micro-scale depositions under contacting conditions. The solid consists of two distinct layers which are considered to be perfectly bonded and comprise of a graded elastic coating whose shear modulus varies exponentially with the depth coordinate and an infinitely deep homogeneously elastic substrate. The solution given in this paper is generic and easily utilised to solve real problems as it requires only known physical characteristics of the solid under study and an applied surface pressure. As a result, this model is very cheap to use and can be easily integrated into tribological codes to predict local deflections.

The reliability and durability of gear components are critical issues especially in advanced power transmissions subject to increased power density and extreme operating conditions. In general the three main tribological failure modes present in gear tooth contact are: wear, contact fatigue/pitting, and scuffing. The present work investigates the influence of surface texturing in the form of micro-scale dimples as a method to enhance scuff resistance. Flat H13 steel samples were micro-dimpled using a laser surface texturing process. For scuffing and wear evaluation the flats were tested in point contact under lubricated linear reciprocating sliding. A threefold increase in scuffing resistance was observed for textured surfaces over comparable non-textured flats, however, for prolonged operation at high loads an increase wear rate of the counterface is observed. For gear application the design and location of surface texture requires careful consideration to balance scuffing resistance with potential influence to increased wear and fatigue pitting.