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In view of the uneven lubricating film of M50 aviation bearings under high load, it is of great significance to explore how to improve its friction performance through the synergistic lubrication of solid lubricant and lubricating oil. Inspired by the material transport of leaf veins, a bionic microchannel was designed for the contact interface. M50, M50-SnAgCu (MS) and M50-SnAgCu-Nb2C (MSN) biomimetic composites are prepared, respectively. The tribological properties of the material under dry friction and three grades of Mobil oil (DTE 24, DTE 25 and DTE 26) were investigated through ball-on-disk friction. The high-hardness Si3N4 ball is used as the counterpair. The results show that the average friction coefficient and wear rate of MSN are reduced by 29.63% and 28.36%, respectively. In addition, the furrows on the worn surface were significantly reduced. The synergistic lubrication of SnAgCu-Nb2C and the DTE 26 oil makes M50 have a excellent antifriction and wear resistance. The results can provide guidance for the research of synergetic lubrication behavior of materials.

The article considers the main factors influencing the magnitude and nature of the change in friction torque in rotating pairs and shows the influence of deviations of the shape of holes on its magnitude. The scheme of laboratory installation used in experiment for measurement of the friction torque is resulted. Statistical estimates of the values of deviations of the shape of ring samples and their influence on the change of friction torque under dry friction conditions are given. The nature and types of wear of the rotating element of the pair are determined.

The article presents the characteristics of antifriction treatments for pairs of rotation mechanisms of technological equipment operating under dry friction conditions. Based on the criterion of the least wear of the rotating element during running-in and operation, choices are made in regards to their rational combination.

A calculation method for the friction coefficient and meshing efficiency of plastic line gear (LG) pair under dry friction conditions was studied theoretically and experimentally, taking a polyoxymethylene parallel line gear pair (POM PLGP) as an example. Firstly, the geometric and mechanical models of PLGP were built by considering the effects of misalignment and loaded deformation under the actual operating condition. Then, the friction coefficient of POM specimens was obtained via the ball-on-disk experiment, of which the value varies between 0.35 and 0.45 under the experimental conditions. The calculation formula for the friction coefficient of POM LG pair was obtained by fitting the friction coefficient of the POM specimens, and the meshing efficiency of POM LG pair was calculated based on the calculation formula for friction coefficient and the meshing efficiency calculation approach. Finally, the meshing efficiency of POM PLGP specimens was measured using a homemade gear meshing efficiency test rig. The experimental results validated the feasibility of the proposed calculation method for the friction coefficient and meshing efficiency of the plastic LG pair. This study provides a method for the calculation of the friction coefficient and meshing efficiency of plastic gear pairs under dry friction conditions. It also provides the basis for the wear calculation of plastic LG pair under dry friction conditions.

International audience; Parametrically excited oscillators are used in several domains, in particular to improve the dynamical behaviour of systems like in the case of the parametric amplification or parametric energy harvesting. Although dry friction is often omitted during system modelling due to the complexity of its nonsmooth nature, it is sometimes necessary to account for this kind of damping to adequately represent the system motion. In this paper, it is proposed to investigate the effect of dry friction on the dynamical behaviour of a nonlinear parametric oscillator. Using the pendulum case as example, the problem is formulated according to a Mathieu-Duffing equation. Semi-analytical developments using the harmonic balance method and the method of varying amplitudes are used to find the solutions of this equation and their stability. These results are validated thanks to a comparison with time integration simulations. Effects of initial conditions on the basins of attractions of the solutions are also studied using these simulations. It is found that trivial and nontrivial solutions of the oscillator including dry friction are not connected, giving birth to isolated periodic solutions branches. Thus, both initial displacement and phase between the excitation and the oscillator displacement must be carefully chosen to reach periodic solutions. Finally, a method based on the energy principle is used to find the critical forcing amplitude and frequency needed to obtain the birth of nontrivial solutions for the nonlinear parametric oscillator including dry friction.

The main purpose of this paper is to investigate deeply the effect the contact pressure function on the thermo-mechanical behavior of the friction clutch system during the slipping time (heating stage). The other purpose is to explore theoretically the complex interaction among the contact pressure, sliding speed and frictional characteristics of frictional facings to specify the magnitude and distribution of the frictional heating generation on the contact surfaces of the dry friction clutch under different applied pressure. It was developed a numerical code based on finite element method (ANSYS/APDL 2019) to determine accurately the contact pressure, temperature and frictional heat generated on contact surfaces of the friction clutch disc that has two effective frictional faces at any instant during the slipping period. It was found a significant effect of the magnitude and variation of applied pressure during the heating phase on the surface temperatures, contact pressure and frictional heat generated. Where, the hot spot can be appeared when the applied pressure is constant. Under such circumstances, high amount of temperature and contact pressure focused on a small zone of the nominal contact area. This phenomenon is considered one of the main reasons for the early failure of the contacting surfaces of friction clutch.

An optimal control problem is solved for a two-body limbless locomotor crawling along a straight line on a horizontal rough plane. Coulomb’s dry friction acts between the locomotor’s bodies and the underlying plane. The control is performed by the force of interaction between the bodies. The system should be moved from the state of rest by a given distance in a minimal time, provided that the relative positions of the bodies in the initial and terminal states coincide and the velocities of the bodies at the terminal instant are equal to zero. A particular attention is given to the case where the bodies are prohibited to change the direction of their motion.

The simple textbook problem of a particle on a vertical, rotating hoop is analysed both in theory and through experiments. We begin by detailing out a somewhat generalised theory, where the effect of dry friction as well as the possibility of a shift in the vertical axis of rotation are incorporated. The bifurcation curves (plots of the angular position of stability versus the angular frequency of rotation) are obtained for all cases (i.e. with and without friction and a shift of the axis). Thereafter we present the experimental set-up fabricated by us and elaborate on the various measurements performed. Finally, we demonstrate through our experiments how well the theoretical results on the bifurcation curves tally with the experimental findings. The match between theory and experiment is found to be reasonably satisfactory. We conclude by mentioning how various aspects of this simple problem as well as its generalisations and extensions, are linked with different advanced areas of physics.

Rational free upsetting regimes are determined for sintered powder materials for subsequent application of the results obtained during preparation of complex shaped components. Free upsetting of heated porous specimens is performed under dry friction conditions at contact surfaces. The production equipment used during specimen upsetting is a hammer with a striker weighing 40 kg and a maximum ascent height of 2.5 m. Machining is carried out in a 16K20 lathe. Analysis of the dependences obtained shows a reduction in specimen mechanical properties with an increase in their transverse dimensions (parameter kR is transverse (radial) deformation, i.e., the ratio of specimen average diameter after upsetting to the original). A particularly sharp reduction in mechanical properties is observed for specimens made with an original porosity Π0 = 30 and 20% of Astaloy 85 Mo and Distaloy HP-1 respectively with an increase in coefficient kR. This makes it possible to conclude that there is lower ductility during free upsetting of these materials, in each of which sections (kR ) are separated with amounts of plastic deformation specifying a slow reduction in mechanical properties, and then a sharp reduction is observed leading to failure.

The article is devoted to the preparation of ecologically clean composites by powder metallurgy and the study of tribological properties. Tribological tests are conducted in an MMW-1 friction machine with vertical block using a “pin-on-disk” mechanism, and a steel disk as the counterbody. It is established that test specimen tribological properties remain unchanged with different loads.

In this paper, we study and compare performance and robustness of linear and nonlinear Lanchester dampers. The linear Lanchester damper consists of a small mass attached to a primary system through a linear dashpot, whereas the nonlinear Lanchester damper is linked to the primary mass through dry friction forces. In each case, we propose a semi-analytical method for computing the frequency response, for different values of the design parameters, in order to evaluate the performance and robustness of the two kinds of damper. Overall, it is shown that linear Lanchester dampers perform better than nonlinear damper both in terms of attenuation and robustness. Moreover, the nonlinear frequency response curves, that include the intrinsic non-smooth nature of the friction force, may serve as reference curve for further numerical studies.

High-pressure axial piston pumps operate in high-speed and high-pressure environments. The contact state of the slipper against the swashplate can easily change from an oil film lubrication to a mixed oil film/asperity contact, or even dry friction. To improve the dry friction performance of slipper pairs and to avoid their potentially rapid failure, this study examined the effects of material matching on the dry friction performance of the slipper pair for high-pressure axial piston pumps. A FAIAX6 friction and wear tester was developed, and the dry friction coefficients of the slipper pairs matched with different materials were studied using this tester. Based on the thermo-mechanical coupling of the slipper pair with the working process, the contact surface temperatures of the slipper pairs matched with different materials were calculated and analyzed for the same working conditions. Following this, the effects of the material properties on the temperature increase at the slipper sliding contact surfaces were revealed. The reliabilities of the temperature calculations and analysis results were verified through orthogonal tests of slipper pairs matched with different materials. The results indicate that the influence of the material density on the friction coefficient is greater than that of the Poisson’s ratio or the elastic modulus, and that the slipper material chosen should have a high thermal conductivity, low density, and low specific heat, whereas the swashplate material should be high in specific heat, density, and thermal conductivity; in addition, the slipper pair should be a type of hard material to match the type of soft material applied; that is, the hardness of the swashplate material should be greater than that of the slipper material.

The structure and properties of detonation coatings and composite powder materials of various composition were studied. The detonation spraying of coatings does not lead to the separation of components, which promotes a uniform fine coating structure, similar to the structure of composite materials. Comparative studies of detonation composite coatings in dry friction against steel were carried out.

The mechanical characteristics of high-entropy alloys and their constituent metals were examined by dry friction against diamond at low sliding velocities in air. The friction tests were performed at a velocity of 16 mm/sec and a diamond load of 2.2 N. With increasing friction coefficient, the wear rate of the metals and alloys tends to become higher. The linear wear ranges from 1.06 · 10–7 for chromium to 12.76 · 10–7 for aluminum. In addition, the linear wear of multicomponent alloys is lower than that of their constituent metals and ranges from 0.35 · 10–7 to 4.38 · 10–7. The linear wear of high-entropy alloys is a half to a quarter of the linear wear of individual metals because they differ in hardness, the friction coefficients being equal.

In this paper, the nonsmooth dynamics of two contacting rigid bodies is analysed in the presence of dry friction. In three dimensions, slipping can occur in continuously many directions. Then, the Coulomb friction model leads to a system of differential equations, which has a codimension-2 discontinuity set in the phase space. The new theory of extended Filippov systems is applied to analyse the dynamics of a rigid body moving on a fixed rigid plane to explore the possible transitions between the slipping and rolling behaviour. The paper focuses on finding the so-called limit directions of the slipping equations at the discontinuity. This leads to a complete qualitative description of the possible scenarios of the dynamics in the vicinity of the discontinuity. It is shown that the new approach consistently extends the information provided from the static friction force of the rolling behaviour. The methods are demonstrated on an application example.

Specimens of steels 30KhGSA, 38KhS and 40Kh, strengthened by plasma hardening, are tested under dry friction conditions in a disk-on-block system. Good wear resistance of hardened steels is established for alloy systems Cr–Mn–Si (30KhGSA) and Cr–Si (38KhS). The wear resistance of single-component system 40Kh is less by a half. This can be explained by the higher carbon equivalent of 30KhGSA steel. Blocks in contact wear to the least with hardened steel 38KHS discs.

In this paper, a new pounding model is presented, which allows for the modification of the pounding condition during the excitation time period. The formulation consists of a Hertz spring, a nonlinear damping, and a dry friction element. In this respect, the gap function, i.e., the condition for penetration, is extended. This allows for an efficient pounding description, including possible damage and material dissipation to be described within the potential collision regions of the structures. Numerical results on a simple example are presented and discussed. It is shown that the new pounding model is indeed able to efficiently describe possible surface damage effects, in particular, if multiple collisions are observed during the excitation time period.

The structure and properties of composite materials have been studied versus their composition. Comparative analysis of intermetallic titanium materials in dry friction with steel has been carried out. The intermetallic titanium material whose structure is represented by an intermetallic matrix with solid-phase inclusions has the highest tribotechnical properties.

We studied the properties of cubic nonlinear systems with dry friction damping on the prospect of ‘non-resonance’. An approximate method was used to get the frequency-response function. And the critical dry friction which ensures no displacement transmissibility amplified in whole frequency range was determined through the frequency-response function. We also researched those characters which may influence the effect of the non-resonance in this system, and proved those results by empirical experiments. The above conclusions have a theoretical significance for the design of nonlinear vibration isolators.

International audience; We consider a system of two masses connected by linear springs and in contact with a belt moving at a constant velocity. One of the masses can collide with a fixed rigid obstacle. The contact forces between the masses and the belt are given by Coulomb’s laws. Moreover, when the colliding mass is in contact with the obstacle, we assume that a perfect elastic impact occurs. Several periodic orbits including contact against the fixed obstacle followed by slip and stick phases are obtained in analytical form.

This work describes an experimental investigation into the influence of geometric micro-groove texture patterns on the tribological performance of stainless steel. Five geometries were studied: one with untextured and four with micro-groove textured making parallel, triangular, square and hexagonal patterns. The micro-groove textures were produced using an MFT-20 laser system as well as a two-step laser surface texturing (LST) process. Tribological performance was measured using a pin-on-disk tribometer. The investigation showed that the two-step LST process could fabricate high-precision micro-grooves. The experimental data indicated that the micro-groove textured surfaces achieved the lower frictional coefficients than the untextured surface and the geometric patterns had significantly affected the tribological properties of samples in both lubricated and unlubricated states. The results were analyzed from the lubricant supplying and fluid dynamic pressure effect under lubricated conditions as well as abrasive capture and remove under dry friction conditions.

In seismic countries of Southern Europe, including Italy, a large stock of existing precast structures for industrial buildings is characterized by beam-to-column dry friction joints. Several failures of this type of structures occurred during recent seismic events, including the Emilia earthquakes in 2012, due to the loss of the friction restraint and shift of the beam out of the support at the top of the column under the combined effects of horizontal and vertical seismic shaking. The seismic behaviour of precast structures with dry-friction joints is investigated based on nonlinear dynamic analysis to support the vulnerability assessment and design of seismic retrofitting interventions of existing industrial buildings. A dry-friction modelling of beam-to-column joints is proposed and case studies are presented to identify the most critical factors affecting the seismic response of precast frame buildings. The results show that flexible systems are more prone to structural failure due to the loss of support of the beam, particularly when the frequency content of the main shock of the seismic excitation includes the natural frequency of the structure in the vertical direction.

We present here an analysis of the friction components in friction pairs of hip joint endoprostheses in conditions of dry friction and biological media. The tribological pairs studied were found to have different behavioral characteristics depending on the external loading and the “hardness” of the kinematic unit itself. The lowest levels of the adhesion component of the coefficient of friction were seen in ceramic−ceramic friction pairs.

The paper is inspired by recent experiment with a two-member discrete column subjected to dry friction force of interaction between the moving column and a moving plane. The experiment was presented in the form of a YouTube film and recommended as an experimental evidence for flutter in the Ziegler column. We show that the tested mechanism cannot be identified with the original Ziegler column.

Polyether-ether-ketone (PEEK) and polyimide (PI) are two kinds of engineering polymer materials widely used as roller bearing cages and rings under extreme environment because of their noise reduction and corrosion resistance properties. The Si3N4 ceramic is the most common ball bearing material. Many current engineering applications of ball bearings require aqueous lubrication. Therefore, this study presents the aqueous lubrication of tribopairs formed by PEEK and PI material sliding against Si3N4 ceramic. Experimental results show that two tribopairs exhibited the similar tribological properties under the dry condition. Water as a lubricant for the PI–Si3N4 tribopair pairs effectively reduces both friction coefficients by 35.5% and wear rates by 32%. The water absorption of PI induces better tribological properties by changing the tribopair surface properties. In addition, the dimples appearing on the PI tribopair surface under water generate additional hydrodynamic lubrication and further improve the friction properties of surface. The PEEK–Si3N4 tribopair shows similar friction coefficients under two kinds of environments. The wear rates under water are approximately more than two times of that under dry sliding. However, water inhibits the appearance of the crush phenomenon and enhances the carrying capacity of the tribopair. Energy dispersive spectroscopy and X-ray diffraction spectra demonstrate no chemical corrosion. The 3D profiler and SEM morphologies illustrate that the transfer film would be formed from the surface of PEEK under water but hindered under dry friction. Overall, the PI–Si3N4 tribopair exhibits better properties than PEEK under water and is promising for future applications in the bearing industry.

We consider a dry friction oscillator on a moving belt with both the Coulomb friction and a small nonlinear addition which can model e.g. the Stribeck effect. By using the perturbation theory, we establish a new condition for the nonlinearity to ensure the occurrence of a stick–slip limit cycle. The test obtained is more accurate compared to what one gets by building upon the divergence test.

The effect of vibrational smoothing of dry friction has been studied intensively in the past. High-frequency vibrations have been shown to reduce average friction forces and thus smooth the effective characteristics of dry friction. Consequently, undesired friction-induced phenomena, such as friction-induced vibrations or stick-slip motion, can be avoided. While most publications focus on rigid contacts using classical Coulomb friction models, a class of dynamic friction models, namely the Dahl, LuGre and the elasto-plastic model proposed by Dupont et al., is considered here in order to account for contact compliance. Based on a simple 1-DoF friction oscillator, the effect of longitudinal high-frequency vibrations is investigated. An averaging procedure is applied in order to derive the effective friction–velocity characteristics of the system. Using a Galerkin procedure, analytical approximations can be derived for the Dahl and the LuGre friction model, while numerical calculations have to be performed for the elasto-plastic model. In order to validate the results, full timescale numerical simulations are performed. When accounting for contact compliance, the smoothing effect can still be observed. However, the calculated friction forces are higher compared to the classical results using Coulomb friction. Hence, the assumption of a rigid contact leads to overestimation of the smoothing effect.

The tribotechnical properties of the TiB2–30 wt.% B4C composite material in pair with VK6 hard metal are investigated. The material demonstrates high wear resistance under dry friction conditions: the intensity of linear wear of the friction pair does not exceed 1.83 μm/km, the friction coefficient of the friction pair is 0.5. The analysis of 3D profiles of the sample surface shows the effect of smoothing of the surface of the ceramic composite by transfer of hard metal submicron particles on its surface and formation of tribofilm.

In this paper, we derive the solution of the damped oscillator with Coulomb friction, where the damping factor is negative. The aim of this study is to present the stabilization effect of Coulomb friction of an otherwise unstable system. This phenomenon typically occurs in robotic systems, where the dry friction in the drivetrain of the arms compensates for the possible instability caused by the sampling time in the digital controller. The results help to recognize the interplay of these phenomena just by looking at the peculiar qualitative picture of the corresponding vibration signals.

In this study, four kinds of roughness structures were constructed on the Al alloy surface using laser marking technology. The tribological properties of the surfaces under the condition of dry friction were carefully investigated. The results indicate that the fabricated surfaces have similar compositions. The hardness of surfaces can be improved after the laser surface treatment. Besides, the texturing of surfaces can efficiently reduce friction and improve friction resistance. However, the friction-reducing mechanisms are not the same. The surfaces with lined and grating grooves can remove wear debris away from the interfaces between steel balls and surfaces, while those with irregular protrusions and micro-orifices array would be able to trap wear debris in the microstructure. Furthermore, due to the different friction mechanisms of distinct roughness structures, their friction-reducing performances are greatly affected by the actual friction conditions (sliding speed and load), which offers a guide for constructing a specific roughness structure on the Al alloy surface to improve its friction resistance efficiently.

Questions are considered for optimizing and intensifying the traditional technology for preparing carbon fluoroplastic composite for piston compressor friction assemblies. A technology is developed for composite preparation and manufacturing methods in each stage, making it possible to create highly efficient and economically substantiated composites for piston compressor assemblies operating under dry friction conditions.

A spatial model of dilatating soil under triaxial load conditions with different regimes are described on the basis of a hypothesis that the Coulomb dry friction force acts in the plane of tangential particle shear. Spatial soil deformation over time is described in accordance with the theory of inherited creep in the form of the sum of deformations due to changes in volume and shape, with due regard for their interrelation.

The effect of the material and sliding rate (1, 2, 4, 6, and 15 m/sec) of the counterface on the tribological characteristics of a (composite Ti–Mo–BN)–counterface (steels 45, 65G, ShKh15, 40Kh, and Kh18N9T, nitrided titanium, and BrO10 bronze) friction pairs in dry friction in air under a pressure of 0.8 MPa is investigated. It is established that, under these friction conditions, the composite in pair with BrO10 bronze is ineffective. During friction of the composite in pairs with steels 45, 65G, ShKh15, 40Kh, and Kh18N9T, an increase in the sliding rate from 1 to 6 m/sec results in an increase of the friction coefficient, linear wear of the friction pairs, mass loss of the composite and counterface, whereas the temperature of the friction surface increases. The highest temperature of the friction surface of the composite is reached in pair with steel 45. The temperature, sliding rate, and pressure applied lead to the synthesis of a secondary film (on the surface of the composite) of such a phase composition and structure that provide (in pair with steel 45) higher tribological characteristics of the composite than those in pairs with the other steels. At all sliding rates of the counterface, the tribological properties of the friction pairs depend not only on the properties of the composite material (chemical and phase composition, structure, and mechanical characteristics), but also on the same properties of the counterface material.

Understanding mechanisms of tribo-electrophysics and tribo-electrochemistry is one of the most important fundamental research due to the application of developing scientific technology. The present paper provides a review regarding tribo-electrical mechanisms under four lubrication regimes, including dry friction, boundary lubrication, thin film lubrication and fluid film lubrication. Moreover, a brief summary and some important aspects in the field of tribo-electrophysics and tribo-electrochemistry were proposed, on which further intensive investigations are still mandatory. It is hoped to provide beneficial guidance to inspire the development of tribological theories and further engineering applications.

High-frequency vibrations have been shown to smooth the effective characteristics of dry friction and overcome undesired effects such as friction-induced vibrations. Although the effect of vibrational smoothing is subject of many theoretical studies and has been applied successfully to metal forming processes, only few publications are known presenting advanced modelling approaches or related experimental results. Using classical Coulomb friction, the agreement between experimental results and related calculations appears not to be sufficient. Therefore, the effect of contact compliance on vibrational smoothing has been discussed recently. Considering a class of dynamic friction models, the effect of high-frequency excitation on a simple 1-DoF friction oscillator has been investigated. The corresponding results show a mostly quantitative impact of compliant contacts on vibrational smoothing, while the qualitative results remain unchanged. Within this contribution, the recent analysis is extended using an elasto-plastic friction model and accounting for stiction and the transition to sliding motion. The corresponding results show similar characteristics, but contain new qualitative aspects and may thus serve as an explanation approach for insufficient agreement between experimental results and classical modelling. In order to validate the advanced approach, an experimental set-up is presented. Measurements are performed showing the hysteretic behaviour of the contact as well as the reduction of average friction forces in presence of vibrational excitation. A comparison of experimental and previously obtained numerical results yields good agreement and thus more insight into relevant aspects of vibrational smoothing.

Microtextures with different groove inclinations are fabricated on the AlCrN-coated surface by a nanosecond laser, and the tribological properties of the textured AlCrN samples sliding against AISI 1045 steel balls are investigated by reciprocating sliding friction tests under dry conditions. Results show that the microtextures can effectively improve the tribological properties of the AlCrN surface compared with the smooth surface. Meanwhile, the angle between the groove inclination and sliding direction has an important influence on the friction and wear properties. The textured sample with the small groove inclination may be beneficial to reducing the friction and adhesions, and the TC-0° sample exhibits the lowest friction coefficient and adhesions of the worn surface. The wear volume of the ball sliding against the TC-0° sample is smaller compared with the UTC sample and the sliding against the TC-45° and TC-90° samples is larger compared with the UTC sample. Furthermore, the mechanisms of the microtextures are discussed.

This work investigates the influence of two coatings on the wear resistance of the SAE 305 aluminum alloy. This material is widely used in power transmission components, and improvement in its surface properties can lead to remarkable impacts in the energy sector. The tested treatments are: (1) anodization and (2) diamond-like carbon coating. Dry friction reciprocate sliding tests using a sphere-on-plane configuration are presented. The untreated reference surface and both treatments are evaluated regarding their roughness, hardness, coefficient of friction, wear rate and morphology. The surface analyzes were carried out using confocal laser and SEM techniques. In comparison with the reference, the diamond-like carbon coating showed a significantly higher wear resistance, whereas the anodization process showed only a minor improvement.

Friction units are made of superhard cubic boron nitride-based materials by vacuum brazing and subjected to end-to-end dry friction testing. It is established that the friction factor decreases as the modulus of elasticity of superhard material is decreased and the loading and friction speed are increased.

We reported on the modification of tribological properties of stainless steel by femtosecond laser surface microstructuring. Regular arranged micro-grooved textures with different spacing were produced on the AISI 304L steel surfaces by an 800-nm femtosecond laser. The tribological properties of smooth surface and textured surface were investigated by carrying out reciprocating ball-on-flat tests against Al2O3 ceramic balls under dry friction. Results show that the spacing of micro-grooves had a significant impact on friction coefficient of textured surfaces. Furthermore, the wear behaviors of smooth and textured surface were also investigated. Femtosecond laser surface texturing had a marked potential for modulating friction and wear properties if the micro-grooves were distributed in an appropriate manner.

Spark plasma sintering is used to produce dense silicon nitride nanoceramics with titanium nitride additions and nanofiber-strengthened composites. The sintered nanocomposites demonstrate quite high mechanical properties (HV ≈ 14–16 GPa, K Ic ≈ 4.8 MPa ∙ m 1/2 ) and low dry friction coefficient (f ≈ 0.65–0.68) and mass wear (~0.2–0.4 mg/km) against ShKh15 steel. The nanocomposite strengthened with 3.8 wt.% silicon nitride nanofibers shows the most balanced mechanical and tribotechnical characteristics.

The wear properties of a La62Cu12Ni12Al14 bulk metallic glass (BMG) using sliding wear system under the various normal loads and the annealing conditions have been investigated. Although the La62Cu12Ni12Al14 BMG is brittle during the tensile testing, it exhibits ductile behaviors during the sliding wear process. The SEM and the EDS analyses of the wear tracks and the debris after the sliding wear processes indicate that the wear mechanism is a combination of abrasion, adhesion, and oxidation. It is found that the wear resistance is significantly affected by the normal loads. With the increases in the wear load, the wear loss and the friction coefficient decrease. In addition, it is found that the wear properties are significantly affected by the annealing conditions. Compared with the annealed BMG alloys, the as-cast BMG alloy with a low hardness exhibits good wear resistance, which is attributed to the better ductility during the wear testing.

TiB2 was chosen to further improve the tribological properties of TiAl matrix self-lubricating composites containing Ag. The possible synergetic action of a combination of TiB2 and Ag was investigated using a pin-on-disk high temperature tribometer from room temperature to 600 °C. The tribological test results indicated that the addition of TiB2 obviously enhanced the wear resistance of the composites over a wide temperature range. Moreover, the composites containing TiB2 had a low friction coefficient at 600 °C. The subsurface analysis of cross sections of worn surfaces showed that TiB2 played the role in wear-resistant skeleton and restricted the plastic flow of Ag during dry friction process. The investigation showed that TiB2 and Ag could exhibit good synergistic effect on improving the tribological properties of composites.

To solve the problem of poor wear resistance in conventional Hadfield steels under medium and low stress, a new kind of steel with high silicon and high manganese Fe–17Mn–6Si–0.3C was designed and its wear resistance was studied. The results showed that it exhibited better wear resistance than conventional Hadfield steel in both dry friction and abrasive friction. The better wear resistance of the new steel with high silicon and high manganese resulted from the stress-induced γ → e martensitic transformation.

International audience; We consider a system composed of two masses connected by linear springs. One of the masses is in contact with a rough surface. Friction force, with Coulomb's characteristics, acts between the mass and the surface. Moreover, the mass is also subjected to a harmonic external force. Several periodic orbits are obtained in closed form. A first kind of orbits involves sticking phases: during these parts of the orbit, the mass in contact with the rough surface remains at rest for a finite time. Another kind of orbits includes one or more stops of the mass with zero duration. Normal and abnormal stops are obtained. Moreover, for some of these periodic solutions, we prove that symmetry in space and time occurs.

Titanium-based composites containing MoS2, MoSe2, CaF2, and BN solid lubricants are synthesized. Their tribological characteristics are investigated without lubrication at different sliding velocities (0.5, 1, 2, 4, 6, and 15 m/sec) and low pressures (0.27, 0.54, 0.8, 1.1, 1.35, 1.47, and 2.7 MPa) in air. In view of the high friction coefficient and large wear, the composite materials cannot be proposed as antifriction ones for operation at small sliding velocities and low pressures. The titanium-based composites are promising as antifriction materials at an increased sliding velocity (15 m/sec) and low pressures when their friction coefficients range from 0.3 to 0.36 and wear ranges from 1.91 to 68.3 mg/km. In dry friction at a high sliding velocity in air, the temperature of their working surface increases resulting from the formation of titanium oxides and then a dense secondary lubricating microheterogeneous film. The composition and structure of the secondary films differ from those of the starting materials and determine their antifriction properties and friction performance.

An oscillator with dry friction under external excitation is considered. The Poincare map can be established according to the series solution near equilibrium in the case of 1:4 resonance. Based on the theory of normal forms, the map is reduced into its normal form. It is shown that the Neimark-Sacker (N-S) bifurcations may occour. The theoretical results are verified with the numerical simulations.