Frictional Interaction Research Articles

Modeling of Surface Fracture in Friction Interaction of Fiber Composites

The model of the frictional interaction of a fiber composite material with a rigid non- wearing body is proposed, which makes it possible to study the effect of the mechanical and strength characteristics of the fiber and matrix materials and the composite structure on its stress state, in particular, at the fiber-matrix interface. Analysis of the stress distribution in the subsurface layers of the composite was carried out for different values of the ratio of matrix to fiber materials hardness, the sliding friction coefficient and the distance between the fibers. For the known failure criteria of fiber composites, the conclusions about the effect of the structure and relative strength properties of a fiber (fiber bundle) and matrix on the pattern of subsurface fracture of the composite under sliding friction conditions are made

Effects of solvent osmolarity and viscosity on cartilage energy dissipation under high-frequency loading

Articular cartilage is a spatially heterogeneous, dissipative biological hydrogel with a high fluid volume fraction. Although energy dissipation is important in the context of delaying cartilage damage, the dynamic behavior of articular cartilage equilibrated in media of varied osmolarity and viscosity is not widely understood. This study investigated the mechanical behaviors of cartilage when equilibrated to media of varying osmolarity and viscosity. Dynamic moduli and phase shift were measured at both low (1 Hz) and high (75–300 Hz) frequency, with cartilage samples compressed to varied offset strain levels. Increasing solution osmolarity and viscosity both independently resulted in larger energy dissipation and decreased dynamic modulus of cartilage at both low and high frequency. Mechanical property alterations induced by varying osmolarity are likely due to the change in permeability and fluid volume fraction within the tissue. The effects of solution viscosity are likely due to frictional interactions at the solid-fluid interface, affecting energy dissipation. These findings highlight the significance of interstitial fluid on the energy dissipation capabilities of the tissue, which can influence the onset of cartilage damage.

Sensitivity of a vibroacoustic signal to a change in the state of the surface layer of ceramics during frictio

The high information content of the vibroacoustic signal in the frequency range of 10‒16 kHz to the change in the state of the surface layer of the ceramic sample during frictional interaction with the steel disk was established. The results obtained indicate the possibility of using vibration diagnostics systems for monitoring the state of ceramic parts during operation and fi tests.

Polymeric Composite Materials of Tribotechnical Purpose with a High Level of Physical, Mechanical and Thermal Properties

Polymeric composites (PC) of tribological applications with a high level of physical, mechanical and thermal properties based on aromatic polyamide and silica gel have been developed. Regularities have been obtained that describe the effect of the filler content in PC on the friction coefficient, temperature on the friction surface and the intensity of linear wear rate of the studied PC-steel friction pair. It was found that the optimal silica gel content in the polymer matrix is 10 wt %. The morphology of the steel surface of friction after friction interaction with PC based on aromatic polyamide and silica gel was studied. The formation of an antifriction film on the steel surface of friction was discovered, which contributes to a decrease in the friction coefficient, temperature on the friction surface, and the linear wear intensity of the studied PC. The influence of the load and sliding speed on the main tribotechnical characteristics of the PC-steel friction pair has been studied. Mathematical laws were derived that describe the influence of the main external factors (load and sliding speed) on the friction coefficient and intensity of linear wear rate of the studied friction pair. Physical, mechanical and thermal investigations of the developed PC were carried out and it was found that the introduction of 10 wt % silica gel contributes to their 5–10 % increase.

The correlation of the vibroacoustic signal with the wear of a ceramic part during frictional interaction with a steel disc

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Robust Superlubric Interface across Nano- and Micro-Scales Enabled by Fluoroalkylsilane Self-Assembled Monolayers and Atomically Thin Graphene.

Robust superlubrication across nano- and microscales is highly desirable at the interface with asperities of different sizes in durable micro/nanoelectromechanical systems under a harsh environment. A novel method to fabricate superlubric interfaces across nano- and microscales is developed by combining a batch of surface modification with atomically thin graphene. The robust superlubric interface across nano- and microscales between hydrophobic 1H,1H,2H,2H-perfluorodecyltrichlorosilane (FDTS) self-assembly monolayers (SAMs) and graphene was achieved under high relative humidity, sliding speed, and contact pressure. The superlubric mechanisms at the interface of FDTS/graphene could be attributed to the following at different scales: the hydrophobicity of FDTS SAMs and graphene preventing the capillary interaction of the interfacial friction under high relative humidity; the high elastic modulus of graphene leading to small interfacial contact area; the compressing and orientating of FDTS SAMs decreasing interfacial shear strength under high contact pressure; the surface modification of FDTS molecules reducing the interfacial potential barriers when sliding on the atomically thin graphene. The robust superlubric interface across nano- and microscales reducing the friction at the complicated interfaces with asperities at different scales and improving the performance and durability have great potentials in the field of micro/nano mechanical systems.

Research of the frictional interaction of a powder coating and a metal counterbody during sliding friction

Methods of metallographic analysis and profilometry are used to study the friction surfaces of wear-resistant coatings with CоAl2O4 and CuAl2O4 modifying additives of ultradispersed spinels during sliding friction with counterbodies made of VK6 hard alloy and St6 steel. To describe the frictional interaction of a powder coating with a metal counterbody during steady-state wear, a statistical model is developed based on the binomial distribution of removed particles. Keywords: coating, counterbody, sliding friction, frictional interaction, wear, statistical modeling, binomial distribution. g.g.vinokurov@iptpn.ysn.ru

Improving the antifriction properties of the housing-rotor coupling in axial turbomachines

The article discusses the frictional interaction of carbon-carbon composite material on steel. Antifriction properties and wear resistance of the material under dry friction at speeds up to 100 m/s are investigated. The effect of velocity and contact pressure on the friction coefficient and wear resistance of a carbon composite is analyzed. The regularities of the change in the coefficient of friction are determined depending on the load-speed factors. The assumption is substantiated that the high thermal stability of the carbon composite, its low hardness, good antifriction properties and high wear resistance allow the material to be used in friction units operating at very high speeds and temperatures. In order to improve the reliability and reduce gas flows in axial turbomachines, on the basis of the study carried out, it is recommended that instead of heat-resistant coatings, a lining of the gas duct casing should be made of carbon composite.

Extraction of microstructural parameters from sculptured thin films nanoindentation

This work deals with the indentation analysis of nanocolumnar thin films and the difficulties encountered to deduce relevant mechanical parameters by this methodology. SiO 2 thin films prepared by physical vapour oblique angle deposition with different nanocolumnar microstructures have been subjected to indentation analysis. Despite the fact that the films had been made of the same material, deposited on the same substrate and had similar thickness, their indentation responses were different and depended on their particular microstructure. It has been also reali s ed that the measured hardness and elastic modulus variation with the indentation depth were length scale dependent and that there is not a unique analytical thin-film nanoindentation model to extract the mechanical properties from the experimental nanoindentation curves. To overcome these limitations a numerical finite element model (FEM) of the nanocolumnar coatings has been built to figure out the contributions of the different physical phenomena intervening in the indentation process. This FEM simulation relies on a description of the elasto-plastic microstructural units of the coatings and the contact friction interactions between them. Based on this simulation a parametrical representation, incorporating two length scales and the contributions of densification and/or the buckling of nanocolumnar units, has been developed to account for the evolution of the apparent elastic modulus deduced from numerical indentation tests . A Hall-Petch modification of this description considering two length scales instead of the common approximation considering a single length scale has rendered the best agreement with the elastic values determined experimentally. Although, at the present stage, the particular microstructure of the films can not be deduced from the evolution of their elastic moduli with the indentation depth, the obtained results and their interpretation constitute a first though essential step for the elaboration of an inverse analysis methodology capable of correlating microstructure and elastic response of nanocolumnar coatings. • The indentation response of multi-layered PVOAD columnar coatings greatly depends on their microstructure. • Buckling but also densification drive the evolution of indentation elastic modulus and hardness with indentation depth. • FEM of a columnar structure under indentation allow s to reproduce the experimental response of multi-layered PVOAD coatings. • Size dependent model allows to extract length scale parameters from elastic response of PVOAD coatings.

High-temperature friction units with carbon-containing materials

The frictional interaction of carbon-carbon composites with steel at high temperatures is considered. Antifriction properties of carbon composites are investigated at friction on a steel at speeds of 0,050,25 m/s and pressures of 0,31,0 MPa. The advantages of Hardcarb-T material in comparison with Argalon-2D material are experimentally determined. Keywords: temperature, friction, contact pressure, composites, steel, speed, friction coefficient. roschin50@yandex.ru

A Novel Asymmetric Pneumatic Soft-Surgical Endoscope Design with Laminar Jamming.

Soft pneumatic endoscopes developed for Minimally Invasive Surgeries (MIS) are designed upright which means that the starting positions straight. As the internal chambers are pressurized the endoscopic module starts bending. The relation between the pneumatic pressure and bending is nonlinear as the air needs first to fill the chamber before bending, and additionally frictional interaction to the sheath adds more to this start-up transient behaviour. This highly nonlinear behaviour severely limits the actuator sensitivity, accuracy, and repeatability near the endoscope's center of operating range. This paper introduces a novel pre-bent MR-compatible soft-surgical pneumatic endoscope design aimed to improve the bending performance of soft endoscopes by shifting the start-up transient out of the operating range. The pre-bent design of 12 mm diameter consists of an actuation and stiffening chamber, inextensible shell reinforcement with a backbone and rings, and external sheathing. The design parameters that include cross-sectional area, number of rings and backbone width are determined using Finite Element (FE) analysis. The motion profile of the fabricated endoscope, determined via experimentation, shows a successful shift of the start-up transient while the jamming structure increases the stiffness of the endoscope but limits the bending range. Further design developments of the endoscope are required for clinical application.

Principles of discrete-event modeling of physical processes during technical surfaces contact interaction

The article discusses the advantages and disadvantages of computer modeling used in physical experiments field on rough surfaces contact interaction. Methods for constructing the software model are given. The description of a single irregularity in the form of revolution ellipsoid segment is presented and an algorithm for rough surface three-dimensional modeling based on it is proposed. Some assumptions made for generating surface topography do not significantly affect the simulation validity. Taking into account the individual parameters of each irregularity and the algorithm for their distribution make it possible to create inhomogeneous rough surfaces that are close to real ones relative to the physical experiments being carried out. The general principles of the software architecture and the data storage model of discrete-event modeling system of rough surface contact interaction are described. The developed software can be used for modeling the rough surfaces contact interaction, for researching of tribo-interface units’ parameters, predicting the characteristics of frictional interaction and tribotechnical tests computer simulation.

Regularities in the formation of wear-resistant coatings on steel samples when machining them with electrical discharge

This paper considers the technology of electrical discharge machining of steel friction pairs and reports the results of experimental studies. Analysis of the experimental studies has shown that increasing the "anode-cathode" voltage leads to a sharp decrease in the micro-hardness of the surface layer. The study has also made it possible to determine the characteristic dimensions of the structural elements, the height parameters of surface roughness. The elemental composition of the resulting surface of a steel 15KHGN2TA sample differs from the composition of coatings and the surface layers of samples modified by electrical discharge machining involving various electrodes. Under the "anode-cathode" system operation mode, a thin layer of coating with a stable modified structure forms on the surface of the cathode due to dissipative processes. It is shown that the height of surface irregularities on sections after friction is higher than on the surface sections outside the friction flow, which is associated with the formation of a friction transfer film on the samples' surface. It was established that the interaction of friction of steel samples treated by electrical discharge machining forms a thin film on the surface of friction of steel samples, which leads to a change in the relief of surfaces with an increase in the height of the micro-protrusions, as well as the structuring of the transfer film in the direction of sliding. The effect of machining steel surfaces by electrical discharge on the wear resistance of metal-polymer tribosystem was established. The implementation of the devised technology could provide a significant increase in the wear resistance of metal-polymer tribojunctions

INFLUENCE OF THE DYNAMICS OF FORCED MOTION ON THE STATIC FRICTION IN METAL-POLYMER SLIDING PAIRS

The resistance during the frictional interaction of polymeric materials with metallic materials is characterized by a significant dependence on the dynamics of the motion inputs. In a metal-polymer friction pair, the static friction resistance during standstill under load depends on the rate of growth of the force causing the relative motion. Tribological tests of selected (polymer-metal) sliding pairs were carried out. The selected polymers were polyurethane (TPU), polysulfone (PSU), and silicone rubber (SI). They interacted with a pin made of normalized C45 steel under unitary pressure p = 0.5 MPa in dry friction conditions at different gradients of the force driving the relative motion (dF/dt = 0.1-20 [N/s]). The static friction coefficient of the selected sliding pairs was determined on the basis of the recorded static friction force values. The test results show a significant influence of the rate of increase in the motion driving force on the values of static friction resistance. This is mainly due to the viscoelastic properties of polymers.

Soft particle clogging in two-dimensional hoppers.

We study the outflow of soft particles through quasi-two-dimensional hoppers with both experiments and simulations. The experiments utilize spheres made with hydrogel, silicone rubber, and glass. The hopper chamber has an adjustable exit width and tilt angle (the latter to control the magnitude of gravitational forcing). Our simulation mimics the experiments using purely two-dimensional soft particles with viscous interactions but no friction. Results from both simulations and experiments demonstrate that clogging is easier for reduced gravitational force or stiffer particles. For particles with low or no friction, the average number of particles in a clogging arch depends only on the ratio between hopper exit width and the mean particle diameter. In contrast, for the silicone rubber particles with larger frictional interactions, arches have more particles than the low friction cases. Additionally, an analysis of the number of particles left in the hopper when clogging occurs provides evidence for a hydrostatic pressure effect that is relevant for the clogging of soft particles, but less so for the harder (glass) or frictional (silicone rubber) particles.

Time scale disparity yielding acoustic nonreciprocity in a two-dimensional granular-elastic solid interface with asymmetry.

We study nonreciprocal wave transmission across the interface of two dissimilar granular media separated by an elastic solid medium. Specifically, a left, larger-scale and a right smaller-scale granular media composed of two-dimensional, initially uncompressed hexagonally packed granules are interfacing with an intermediate linearly elastic solid, modeled either as a thin elastic plate or a linear Euler-Bernoulli beam. The granular media are modeled by discrete elements and the elastic solid by finite elements assuming a plane stress approximation for the thin plate. Accounting for the combined effects of Hertzian, frictional and rotational interactions in the granular media, as well as the highly discontinuous interfacial effects between the (discrete) granular media and the (continuous) intermediate elastic solid, the nonlinear acoustics of the integrated system is computationally studied subject to a half-sine shock excitation applied to a boundary granule of either the left or right granular medium. The highly discontinuous and nonlinear interaction forces coupling the granular media to the elastic solid are accurately computed through an algorithm with interrelated iteration and interpolation at successive adaptive time steps. Numerical convergence is ensured by monitoring the (linearized) eigenvalues of a nonlinear map of interface forces at each (variable) time step. Due to the strong nonlinearity and hierarchical asymmetry of the left and right granular media, time scale disparity occurs in the response of the interface which breaks acoustic reciprocity. Specifically, depending on the location and intensity of the applied shock, propagating wavefronts are excited in the granular media, which, in turn, excite either (slow) low-frequency vibrations or (fast) high-frequency acoustics in the intermediate elastic medium. This scale disparity is due to the size disparity of the left and right granular media, which yields drastically different wave speeds in the resulting propagating wavefronts. As a result, the continuum part of the interface responds with either low-frequency vibrations-when the shock is applied to the larger-scale granular medium, or high-frequency waves-when the shock is applied to the smaller-scale granular medium. This provides the fundamental mechanism for breaking reciprocity in the interface. The nonreciprocal interfacial acoustics studied here apply to a broad class of asymmetric hybrid (discrete-continuum) nonlinear systems and can inform predictive designs of highly effective granular shock protectors or granular acoustic diodes.

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.

Surface Hierarchy: Macroscopic and Microscopic Design Elements for Improved Sliding on Ice

Frictional interaction with a surface will depend on the features and topography within the contact zone. Describing this interaction is particularly complex when considering ice friction, which needs to look at both the macroscopic and microscopic levels. Since Leonardo da Vinci shared his findings that roughness increases friction, emphasis has been placed on measuring surface coarseness, neglecting the contact area. Here, a profilometer was used to measure the contact area at different slicing depths and identify contact points. Metal blocks were polished to a curved surface to reduce the contact area; further reduced by milling 400 µm grooves or laser-micromachining grooves with widths of 50 µm, 100 µm, and 150 µm. Sliding speed was measured on an inclined ice track. Asperities from pileup reduced sliding speed, but a smaller contact area from grooves and a curved sliding surface increased sliding speed. An analysis of sliding speed versus contact area from incremental slicing depths showed that a larger asperity contact surface pointed to faster sliding, but an increase in the polished surface area reduced sliding. As such, analysis of the surface at different length scales has revealed different design elements—asperities, grooves, curved zones—to alter the sliding speed on ice.

An investigation on the tribological properties of graphene and ZDDP as additives in PAO4 oil

The prime objective of this study was to extend the application of graphene additive in oil solution via investigating the frictional interaction of graphene and ZDDP composite additives in point contact lubrication. Accordingly, 0.05 wt% graphene, 1 wt% ZDDP and their mixtures as additives were added into PAO4 base oil. The ball-on-disk reciprocating experiments were carried out under the load of 30 N, 80 N, 155 N and 310 N. The tribological performance of the single system containing graphene and ZDDP were evaluated separately to compare the tribological property of the composite system containing graphene + ZDDP. The result revealed that the friction coefficient of the graphene/ZDDP composite system was slightly higher compared to PAO4 oil under high load. Whereas the composite system exhibited excellent wear resistance under all loads, reducing the wear rate by 77% in comparison to that of PAO4 oil under a load of 30 N. The reduction in wear is attributed to the formation of the graphene tribofilm and the protective polyphosphate film, which avoided the direct contact with the sliding surface and effectively inhibited the wear of steel materials.

Experimental study of smear formation and removal in heat-assisted magnetic recording

The head-disk interface (HDI) in heat-assisted magnetic recording (HAMR) hard disk drives is a system where a laser beam is launched from a recording head and focused on a recording disk to facilitate data writing. During the laser exposure, material transfers from the disk to the head surface due to the high temperature field and steep thermal gradient. The material accumulation on the head surface, also known as smear, is a challenging reliability issue for HAMR. In this paper, we experimentally investigated the effect of disk temperature and laser exposure time on the smear formation and studied the smear removal by frictional interactions between the head and the disk. In the experiments, the disk temperature and the laser exposure time were controlled separately to generate the smear, which was later characterized by atomic force microscopy (AFM). The AFM images show that the smear forms when the lubricant evaporation occurs for a certain time, and that the smear amount increases with the disk temperature and the laser exposure time. Furthermore, touchdown experiments were performed using the heads with smear. The results indicate that the smear is mostly removed by friction from the head-disk contact. This study reveals the mechanism of the smear formation in HAMR and presents a mechanical approach to mitigate the smear without damaging the head.