Friction Area Research Articles

Polymer composite with enhanced thermal conductivity and mechanical strength through orientation manipulating of BN

Herein, we report a fabrication of epoxy resin/oriented BN composites via a facile hot-pressing strategy. Benefitting from the force exerted vertically on the BN platelets, a well-ordered BN microstructure in the composites has been achieved, which renders the prepared composites an elevated thermal conductivity up to 6.09 W m−1K−1 at 50 wt% loading, while it is only 2.44 W m−1K−1 for epoxy resin/random BN composites. In addition, the composites show an enhanced tensile strength (31.79 MPa) and Young's modulus (4.63 GPa) when comparing with epoxy resin/random BN composites at the same 50 wt% loading (21.21 MPa and 1.48 GPa). We attribute the improved thermal conductivity to the well-aligned BN platelets in higher heat conduction direction based on the anisotropic thermal conduction ability of BN. The enhanced mechanical properties are ascribed to the increased friction area along the tensile in-plane direction and the decreased defects which are easily incorporated during the fabrication process. This study sheds a light for exploring future thermal management materials to meet the increasing heat dissipation demands.

A molecular dynamics study on Young's modulus and tribology of carbon nanotube reinforced styrene-butadiene rubber.

Styrene-butadiene rubber is a copolymer widely used in making car tires and has excellent abrasion resistance. The Young's modulus and tribology of pure styrene butadiene rubber (SBR) polymer and carbon nanotube reinforced polymer composites have been investigated using molecular dynamics simulations. The mechanism of enhanced tribology properties using carbon nanotube has been studied and discussed. The obtained Young's modulus shows the enhancement in mechanical properties of SBR polymer when carbon nanotubes are used as reinforcement. The concentration, temperature and velocity profiles, radial distribution function, frictional stresses, and cohesive energy density are calculated and analyzed in detail. The Young's modulus of SBR matrix increases about 29.16% in the presence of the 5% CNT. The atom movement velocity and average cohesive energy density in the friction area of pure SBR matrix was found to be more than that of the CNT/SBR composite. Graphical abstract Initial and final conditions of (a) pure SBR matrix and (b) CNT/SBR matrix subjected toshear loading and frictional stresses of top Fe layers of both pure SBR and CNT/SBR composite.

Boundary conditions analysis of the possible use of bushings made from copper composite materials for a towing vehicle’s chassis

The paper analyzes the possible boundary conditions for the application of new type of bushings in the vehicle’s chassis. The bushings have been manufactured from the copper-based antifriction composite material alloyed by nickel and molybdenum, with the addition of CaF2 as a solid lubricant (DN5M3KF9). The structure and tribotechnical properties at heavy loaded reversing friction (the temperature of 400-6000С and pressure up to 6.0 MPa in air) have been examined. The study focuses on the distribution of CaF2 in the composite with a Cu–Ni–Mo matrix, its role in self-lubrication of the material, and the behavior of CaF2 in the friction area under extreme operating conditions. It was shown that the solid lubricant is evenly distributed over the contact surfaces as it piles up over the entire friction area during heavy loaded reversing friction. It is established that the tribofilms formed in the presence of the CaF2 solid lubricant provide high wear resistance. Tribological properties allow for extending the application boundaries of the new bushings based on copper in the vehicle chassis for towing artillery guns.

Investigation of flow between deformed disks in hydro-viscous drive

Abstract In order to investigate the dynamic behavior of oil film between deformed disks in hydro-viscous drive, revised mathematical models based on steady-state and axisymmetric flow conditions are developed. The models consist of two forms of thermal deformation that are caused by the combined effect of frictional heat and radial constraint. An approximate solution to the theoretical model is obtained assuming that the fluid viscosity remains constant. And the model considering the effect of variable viscosity is solved by means of computation fluid dynamics code FLUENT. Then the analytical and numerical solution profiles are compared. The results show that peak velocity at the outlet, pressure gap and temperature rise between the inlet and outlet of the film increase with increasing axial deformation size. The effect of radial deformation on the increase of friction area of the disks leads to the increase of the flow rate. The friction pairs should be kept in reasonable deformation size in case of turbulent flow. It is also found that both axial deformation and radial deformation significantly contribute to the increase of viscous torque on condition that the deformation size is controllable. Based on the comparison with the experimental results, the performance of the theoretical model is found satisfactory.

Skin mapping for the classification of generalized morphea

Generalized morphea lacks cohesive clinical features, limiting its clinical and investigative utility. We sought to use computerized lesion mapping to objectively subtype morphea. We conducted a 2-part cross-sectional study. In part 1, we created a discovery cohort of patients with generalized morphea of whom lesion maps were created to characterize subsets. Clinical and demographic features were compared between proposed subsets to determine if they identified clinically relevant differences. In part 2, we created a validation cohort to determine if proposed criteria were applicable to different individuals. A total of 123 patients with generalized morphea were included. Mapping produced 2 distribution patterns that encompassed the majority in both cohorts: isomorphic (areas of skin friction) and symmetric (symmetrically distributed on trunk/extremities). In the discovery cohort, the isomorphic subset was older (55.6±12.7 vs 42.2±20.1years, P<.001), all female (30/30 vs 38/43, P=.05), and more often had lichen sclerosus changes (12/43 vs 8/43, P=.02); involvement of the reticular dermis, subcutaneous fat, and/or fascia was more common in symmetric (10/43 vs 1/30) (P=.02). These features persisted in the validation cohort. Single cohort was a limitation. Symmetric and isomorphic subsets possess distinctive demographic and clinical features, suggesting they more accurately define the phenotype of generalized morphea. Consideration should be given to revising classification.

A View from Northeastern Europe: The Baltic States and the Russian Regime

Corum's essay explains that to understand what is happening in Russia, one must look at the main confrontation points between the West and Putin, which begin with the three Baltic States. The three Baltic States of Estonia, Latvia and Lithuania are not well known to most Western leaders or academics, but these small countries are a special place to understand modern Russia and its politics. The Baltic republics were not only under Soviet domination, like so many of the new East European NATO allies, but they were part of the USSR from 1940 to 1991. They had to learn Russian (all the people today over 40 are generally fluent in Russian) and the older generation had to serve in the Soviet military. The Baltic States populations believe, for very good reason, that they face an existential threat from Russia, a nation that intensely resents the fall of the Soviet Empire and whose leaders are working to restore a new version of the Soviet Empire in which the Baltic States and all former republics will have a place clearly subordinate to Russian interests. This chapter will examine the view of Russia and the Putin government from the perspective of the Baltic States and focus on the key areas of friction between the Baltic States and Russia.

The clarification of low friction mechanism in oil lubrication for B-DLC coating by in-situ observation of friction area

The clarification of low friction mechanism in oil lubrication for B-DLC coating by in-situ observation of friction area

Analysis of Dynamic Stiffness of Bridge Cap‐Pile System

In order to investigate the applicability of dynamic stiffness for bridge cap‐pile system, a laboratory test was performed. A numerical model was also built for this type of system. The impact load was applied on the cap top and the dynamic stiffness was analysed. Then, the effect of the effective friction area between pile and soil was also considered. Finally, the dynamic stiffness relationship between the single pile and the cap‐pile system was also compared. The results show that the dynamic stiffness is a sensitive index and can well reflect the static characteristics of the pile at the elastic stage. There is a significant positive correlation between the vertical dynamic stiffness index and bearing capacity of the cap‐pile system in the similar formation environment. For the cap‐pile system with four piles, the dynamic stiffness is about four times as large as the single pile between 10 and 20 Hz.

The Clarification of Friction Mechanism in Oil Lubrication for CNx Coating by In-Situ Observation of Friction Area with Reflectance Spectroscopy

The Clarification of Friction Mechanism in Oil Lubrication for CN<i>x </i>Coating by <i>In-Situ </i>Observation of Friction Area with Reflectance Spectroscopy

THE USE OF BIODEGRADABLE CUTTING FLUID FOR THIN AND HARD a-C:H AND TiAlN COATINGS

This paper presents results of tribological tests performed under lubricated friction conditions using a T-01M analyser. The lubricant was biodegradable cutting fluid containing a special-purpose additive – zinc aspartate. The discs for the ball-on-disc configuration were made of HS6-5-2C steel. The study involved testing coated and uncoated steel specimens. The a-C:H and TiAlN coatings were produced using physical vapour deposition (PVD). The structure of the coatings was analysed before and after the tribological tests with a JSM-7100F scanning electron microscope. The coating hardness was measured using a CSM Instruments nano-hardness tester (NHT). The coating surface texture of the coated and uncoated discs was determined by means of a Talysurf CCI Lite profilometer. The thin boundary films that formed in the friction area prevented the surfaces from coming into direct contact. The films improved the motion resistance and provided anticorrosive protection during the tests. The biodegradable cutting fluid used in the study had no negative effect on the environment.

Salt Dependence of the Tribological Properties of a Surface-Grafted Weak Polycation in Aqueous Solution

The nanoscopic adhesive and frictional behaviour of end-grafted poly[2-(dimethyl amino)ethyl methacrylate] (PDMAEMA) films (brushes) in contact with gold- or PDMAEMA-coated atomic force microscope tips in potassium halide solutions with different concentrations up to 300 mM is a strong function of salt concentration. The conformation of the polymers in the brush layer is sensitive to salt concentration, which leads to large changes in adhesive forces and the contact mechanics at the tip–sample contact, with swollen brushes (which occur at low salt concentrations) yielding large areas of contact and friction–load plots that fit JKR behaviour, while collapsed brushes (which occur at high salt concentrations) yield sliding dominated by ploughing, with conformations in between fitting DMT mechanics. The relative effect of the different anions follows the Hofmeister series, with I− collapsing the brushes more than Br− and Cl− for the same salt concentration.

Calculation of Stress-Deformed Condition in Polymer Nanocomposites Filled with Microcapsules with Lubricant

Abstract The article suggests the technology of modifying a polymer matrix by microencapsulation, i. e. the introduction of microparticles (lubricants with nano-additives in polymer shells) into nanocomposites matrix, to form multilevel structures on the tribounit surface. Besides, it suggests the method of predicting the operational elastic properties of multicomponent matrix composites with microcapsules, filled with a liquid substance. The method is based on the generalized singular approximation of the theory of random fields and allows, taking into account the geometric dimensions of the inclusions in the shell. It contains the results of numerical modelling of the effective elastic characteristics (Young’s modulus and Poisson’s ratio) of composites, based on phenylone with dispersed inclusions (microcapsules), which are glycerin-filled spherical shells of the kapton. The paper investigates the effect of the geometric dimensions of microcapsules and the volumetric content of components on the operational elastic properties of tribocomposites. The developed antifriction nanomaterials with microcapsules are able to create an oriented lubricating coating on the friction surfaces, apply lubrication to a certain friction area and carry out the lubrication portion wise precisely in the necessary contact zone of the bodies.

Tribological properties of lubricating oil with micro/nano-scale WS2 particles

ABSTRACTThe tribological properties of lubricating oil containing micro/nano-scale WS2 (90 nm, 2 µm) and ionic liquid [C7H11F3N2O3S] are evaluated using a four-ball friction tester. Results show that the addition of micro/nano-scale WS2 can improve the tribological properties of the base oil; moreover, adding the ionic liquid as a solvent may lead to a better mixing of the micro/nano-scale WS2 and base oil and promote the dispersion of WS2 in the sample oil. The base oil with 90 nm nano-WS2 and ionic liquid presents the best anti-friction and anti-wear properties at 1 wt.% content. The surface analysis of wear scars reveals that ploughing is the main cause of wear in the three bottom balls. Furthermore, the wear furrows of nano-WS2 as lubricating additive are uniform and symmetrical and can homogenously appear on the friction area. This work proves that the micro/nano-scale WS2 plays an important role in improving the performance of tribological properties of lubricating oil.

Matching the relationship between rotational speed and load-carrying capacity on high-speed and heavy-load hydrostatic thrust bearing

PurposeRotational speed and load-carrying capacity are two mutual coupling factors which affect high precision and stable operation of a hydrostatic thrust bearing. The purpose of this paper is to study reasonable matching relationship between the rotational speed and the load-carrying capacity.Design/methodology/approachA mathematical model of relationship between the rotational speed and the load-carrying capacity of the hydrostatic bearing with double-rectangle recess is set up on the basis of the tribology theory and the lubrication theory, and the load and rotational speed characteristics of an oil film temperature field and a pressure field in the hydrostatic bearing are analyzed, reasonable matching relationship between the rotational speed and the load-carrying capacity is deduced and a verification experiment is conducted.FindingsBy increasing the rotational speed, the oil film temperature increases, the average pressure decreases and the load-carrying capacity decreases. By increasing the load-carrying capacity, the oil film temperature and the average pressure increases and the rotational speed decreases; corresponding certain reasonable matching values are available.Originality/valueThe load-carrying capacity can be increased and the rotational speed improved by means of reducing the friction area of the oil recess by using low-viscosity lubricating oil and adding more oil film clearance; but, the stiffness of the hydrostatic bearing decreases.

TORSION STRENGTH OF ROUND BAR A6061 FRICTION WELD JOINT INFLUENCED BY FRICTION TIME, UPSET FORCE AND ONE-SIDE CONE GEOMETRY

ABSTRACT Effect of friction time, upset force and one-side cone geometry on torsion strength of A6061 round bar friction weld joint was studied. Round bar commercial A6061 was friction welded with initial compression force of 2.5 kN on stationary part and the rotated part had revolution speed of 1600 rpm with variation of friction time of 45, 50 and 55 minutes. In the upset stage, the variation of upset force of 5 kN, 7.5 kN and 10 kN with the same upset holding time of 110 seconds. The stationary part of the specimen had friction area with variation of cone geometry that represented with ratio of upper diameter, D 1 and lower diameter, D 2 , D 1 / D 2 . It was found friction time and the ratio of D 1 / D 2 affected torsion strength in the upset force below 10 kN. In case of the higher upset force of 10 kN, the upset force more dominant to affect torsion strength of the continuous drive friction weld (CDFW) joint. The specimen with maximum torsion strength has more precipitates in grains of microstructures compared to that of specimen with lower torsion strength. Keywords : Continuous drive friction welding, aluminum, friction time, upset force, one-sdie cone geometry, torsion strength .

Diffusion and mass transfer mechanisms during frictional selective transfer

In the process of friction of certain materials and in the presence of adequate lubricants, the wear phenomenon manifests itself asa transfer of material from one element of a friction couple to the other, this phenomenon is characteristic of the selective transfer process. A selective transfer can be achieved for sure in a friction couple if in the friction area there is a material made of an alloy based on copper, lubricated with glycerin or a special lubricant.The phenomena that take place in the contact area asa result of friction, with a surface of the opposite element of the friction couple, are very complicated. Such phenomena that accompany the material transfer are the diffusion and mass transfer phenomena. In this paper, it is analyzed the diffusion and the mass transfer mechanisms in a friction couple from steel/bronze, which operations in the conditions of the selective transfer, on the basis of the laws who allows quantitative and qualitative estimation of the diffusion and of the mass transfer.

An Integrated Force Probe and Quartz Crystal Microbalance for High-Speed Microtribology

We have developed a technique for measuring frictional forces and contact areas, over a wide range of applied loads, at microscopic contacts reaching high sliding speeds near 1 m/s. Our approach is based on integrating two stand-alone methods: nanoindentation and quartz crystal microbalance (QCM). Energy dissipation and lateral contact stiffness are monitored by a transverse shear quartz resonator, while a spherical indenter probe is loaded onto its surface. Variations in these two quantities as functions of shear amplitude, with the normal load held fixed, reveal a transition from partial to full slip at a critical amplitude. Average values of both the threshold force for full slip and the kinetic friction during sliding are determined from these trends, and the contact area is inferred from the lateral stiffness at low shear amplitudes. Measurements are performed at loads ranging from 5 µN to 8 mN using an electrostatically actuated indenter probe. For the materials chosen in this study, we find that the full slip threshold force is about a factor of two larger than kinetic friction. The forces increase sublinearly with load in close correspondence with the contact area, and the shear strengths are found to be relatively insensitive to pressure. The threshold shear amplitude scales in proportion to the contact radius. These results demonstrate that the probe–QCM technique is a versatile and full-featured platform for microtribology in the speed range relevant to practical applications.

Influence of object texture on grasping behaviour

When picking up objects using a pinch-grip there are often numerous places at which one could place the thumb and index finger, yet people seem to be consistent in where they place them. They grasp objects in such a manner that a line connecting the fingers would pass through or above the object's centre-of-mass (COM), presumably in order to minimize torque and therefore the required grip force. However, the required grip force does not only depend on the torque but also on the object's shape, its weight and the surface friction at the points at which it is grasped. Here we investigate whether participants adjust their grasping points if the surface near the COM is slippery while off-centre areas are not. Doing so would increase the torque but decrease the grip force that is required to prevent slipping. Participants were asked to lift polished aluminum bars, while their grasping points were recorded. The bars were oriented horizontally, with their center aligned with the participants' body midline. Two different bar lengths were used: 26cm and 13cm. One end of each bar was covered with anti-slip tape. The bars varied in the horizontal offset between the COM and the edge of this high friction area with offsets of 0, 1 and 2cm. Fully covered bars and bars without any anti-slip tape served as control conditions. We examined whether participants grasp further off-centre in the direction of the high friction area. The slipperiness of the surface affected the height of the grasping points, indicating that participants were aware of the difference in friction. Nevertheless, the influence on the primary measure of interest, the horizontal grasping location, was minimal. This shows that the judged COM largely determines how an object is grasped, with limited importance given to surface friction.

Time-dependent jamming mechanism for Single-Shield TBM tunneling in squeezing rock

The entrapment risk of Tunnel Boring Machine (TBM) tunneling in squeezing rock associated with high overburden is a challenging and time-dependent consideration. However, there is limited advance knowledge of the shield jamming mechanism due to the difficulties in predicting the complex interactions among the ground, the TBM, its system components and the tunnel support. In this paper, time-dependent interactions between rock and shield, i.e., contact, squeezing and friction, for single-shield TBMs in squeezing ground are investigated. An extended Vlachopoulos-Diederichs approach, instead of the Hoek equation, is used to capture the longitudinal deformation profiles. The plastic behavior of squeezing rock is characterized by the Drucker-Prager criterion with the non-associated flow rule. Viscoelastic deformation is determined using the Burgers model. The contact behaviors are captured through the closure of the radial gap. Moreover, a linear relationship exists between the squeezing loads and the shield deformation. Ultimately, the required thrust force is determined by integrating the squeezing loads over a contact interval. Taking the Saint Martin La Porte access adit (Lyon-Turin Base Tunnel) as an example, the effects of standstill time, relaxation time and overcut on the size of the loaded area and the magnitude of squeezing loads after a standstill are investigated in detail. It is found from the obtained results that a longer standstill, smaller overcut or smaller relaxation time leads to a larger frictional contact area, as well as a larger squeezing load acting upon the TBM shield and a larger deformation of the shield. Moreover, the analytical results show that the TBM jamming is mainly caused by the increase of the squeezing loads and the loaded area.

In-situ fast and long observation system for friction surfaces during scuffing of steel

The objective of this study is to better understand the scuffing phenomenon using a specially designed in-situ observation system. The developed in-situ observation system comprises four sets of a digital CCD camera and a xenon flashing lamp. The independent operation of the capture devices could capture four successive images over short time intervals during a long-duration experiment. Scuffing behaviour that occurs in a friction surface between a rotating sapphire disc and a stationary martensitic steel pin in dry conditions was observed by the developed in-situ observation system. The results showed the behaviour of plastic flow that occurred in the frictional contact area. Plastic flow was observed to occur immediately after the transfer layer passed through the contact area. Each instance of plastic flow was a few milliseconds long. The speed of plastic flow was much less than the sliding speed. At the end of the fast plastic flow process, the brightness of the area of the plastic flow increased, which could be attributed to the oxidation of the steel surface.