Solid Friction Research Articles

Capillary hysteresis in sloshing dynamics: a weakly nonlinear analysis

The sloshing of water waves in a vertical cylindrical tank is an archetypal damped oscillator in fluid mechanics. The wave frequency is traditionally derived in the potential flow limit (Lamb, Hydrodynamics, Cambridge University Press, 1932), and the damping rate results from the combined effects of the viscous dissipation at the wall, in the bulk and at the free surface (Case & Parkinson, J. Fluid Mech., vol. 2, 1957, pp. 172–184). Still, the classic theoretical prediction accounting for these effects significantly underestimates the damping rate when compared to careful laboratory experiments (Cocciaro et al., J. Fluid Mech., vol. 246, 1993, pp. 43–66). Specifically, theory provides a unique value for the damping rate, while experiments reveal that the damping increases as the sloshing amplitude decreases. Here, we investigate theoretically the effects of capillarity at the contact line on the decay time of capillary–gravity waves. To this end, we marry a model for the inviscid waves to a nonlinear empiric law for the contact line that incorporates contact angle hysteresis. The resulting system of equations is solved by means of a weakly nonlinear analysis using the method of multiple scales. Capillary effects have a dramatic influence on the calculated damping rate, especially when the sloshing amplitude gets small: this nonlinear interfacial term increases in the limit of zero wave amplitude. In contrast to viscous damping, where the wave motion decays exponentially, the contact angle hysteresis can act as Coulomb solid friction, thus yielding the arrest of the contact line in a finite time.

Наносекундная динамика разрушения гетерогенных природных тел при трении

Abstract —Luminescence caused by friction of heterogeneous solids (basalt and granite) was investigated, the spectra are recorded, and the dynamics of the luminescence intensity were studied. Under friction, the crystal lattices of these bodies are destroyed, and the luminescenting ≡Si–O^– free radicals and Fe^3+ ions and electron traps located on the surface of microcracks are formed. The dynamics of accumulation of microcracks is investigated at a time resolution of 2 ns, and their sizes determined to be about 6–10 μm.

Evaluation of mechanical performance of friction welded AISI304L grade stainless steel joints

Austenitic stainless steel (ASS) rods of AISI304L Grade when welded have the significant issue of hot breaking and loss of erosion resistance. To reduce these problems the solid state friction welding is the best way to weld the AISI304L alloy and required testing is needed for the further process. In this research work, friction welded AISI304L rods of 10 mm diameter have been used for conducting the experimental testing of tensile strength (TS), fatigue strength (FS), hardness strength and temperature transformation during the friction welding. The results obtained show that the maximum tensile strength of the friction welded joint is 532 MPa, which is equivalent to 94.16% of the base metals tensile strength. The fatigue strength of the notched specimens is lower than un-notched specimens due to the high crack propagation in notched specimens.

Evaluation of mechanical performance of friction welded AISI304L grade stainless steel joints

Austenitic stainless steel (ASS) rods of AISI304L Grade when welded have the significant issue of hot breaking and loss of erosion resistance. To reduce these problems the solid state friction welding is the best way to weld the AISI304L alloy and required testing is needed for the further process. In this research work, friction welded AISI304L rods of 10 mm diameter have been used for conducting the experimental testing of tensile strength (TS), fatigue strength (FS), hardness strength and temperature transformation during the friction welding. The results obtained show that the maximum tensile strength of the friction welded joint is 532 MPa, which is equivalent to 94.16% of the base metals tensile strength. The fatigue strength of the notched specimens is lower than un-notched specimens due to the high crack propagation in notched specimens.

How does temperature govern mechanisms of starch changes during extrusion?

Potato and pea starches were processed on a twin-screw extruder under various moisture and thermomechanical conditions, chosen to keep material temperature Te close to starch melting temperature, Tm, whilst avoiding die expansion. Extruded rods were analysed by asymmetrical flow field flow fractionation coupled with light scattering, X-ray diffraction, DSC, and light microscopy with image analysis. Molar mass of extruded materials decreased more for potato than for pea starch, when specific mechanical energy SME increased, likely because of larger amylopectin sensitivity to shear. No crystallinity was detected when ΔT = (Tm-Te) ≤ 0. Residual gelatinization enthalpy ΔHg decreased with ΔT. As illustrated by larger ΔT values for ΔHg = 0, decreasing moisture favored melting, likely by increasing solid friction. The fraction of granular remnants of potato starch was inversely correlated to SME. These results could be explained by considering starch melting during extrusion as a suspension of solid particles embedded in a continuous amorphous matrix.

Damage Equivalent Test Methodologies as Design Elements for Journal Bearing Systems

The current paper addresses the field of experimental research of journal bearing systems. In this regard, the challenges are dealt with concerning simultaneous testing with a close correlation to the industrial application and with a high resolution of tribological processes. Concerning this aspect, two damage equivalent laboratory test methodologies for journal slide bearing systems are presented, and their ability to visualize certain performance parameters of bearing systems are emphasized (for instance friction performance, (start stop) wear processes, and seizure events). The results clearly emphasize that the applied methodologies provide accurate findings regarding specific effects of selective parameters/changes on the performance of bearing systems, such as polymer overlays may result in improved mixed friction sliding conditions if designed properly, and they provide superior start stop wear resistance; the use of specific corrosion inhibitors can successfully prevent tribo-corrosion on bronze bearings; a decrease of oil viscosity increases solid friction share but decreases fluid friction; lubricant anti-wear additives are able to improve seizure resistance and sliding properties of bearing systems depending on formulation harmonization; and novel bearing material coatings, e.g., sputtered SnCu, can significantly improve emergency running capabilities.

THEORETICAL DEPENDENCE OF WEAR VALUE OF FRICTION PAIR «CENETR PLATE – CENTER PAD» ON A FREIGHT CAR MILEAGE

Purpose. The paper considers the interaction of the cylindrical surfaces of the friction pair «center plate – center pad» of the freight car and theoretically investigates the wear process. It is also necessary to obtain the wear value dependence of center pad on the mileage, taking into account the power load, the physical-mechanical and tribo-technical properties of the interacting materials for the subsequent modeling and control of the value of overhaul mileage by the wear criterion of the corresponding resource-determining elements of freight cars. Methodology. For theoretical studies of the wear value of friction pair «center plate – center pad» on the freight car mileage, the theory of friction and wear of solids was used. Findings. In this paper interaction of cylindrical surfaces of the friction pair «center plate – center pad» of a freight car in the form of a «shaft-sleeve» model is considered. Dependences of the permanent and variable wear of a given friction pair are proposed for cases in which forces act in the transverse and longitudinal directions. Obtained dependence of the wear value of center pad on the freight car mileage takes into account the power load, physical and mechanical and tribo-technical properties of the conjugated materials. On its basis, using new materials for repair with various properties, one may simulate the wear state of cylindrical surfaces of the friction pair «center plate – center pad», which will make it possible to control the value of overhaul mileage of freight car. Also (on the example of gondola 12-7023) on the basis of obtained expression there were constructed dependences of the average wear value of center pad for the cases of different values of the mileage use coefficient and the train movement speed. It was shown that with an increase in the train speed to 100 km/h, the average wear value of the gondola 12-7023 center pad is lower by 25% than at the speed of 80 km/h. Originality. In the work on the wear criterion, the interaction of cylindrical surfaces of the friction pair «center plate – center pad» of a freight car is considered. For the first time it was obtained the dependence of wear value of center pad on the mileage taking into account the power load, physical and mechanical and tribo-technical properties of the conjugated materials. Applying new materials for repair with different properties, based on the obtained dependence one can carry out a simulation of the wear state of cylindrical surfaces of friction pair «center plate – center pad», that is to control the value of between-repair mileage of freight car. Practical value. The results of the work make it possible to establish the wear value of canter pad for the corresponding operating mileage of the freight car.

60NiTi: A Review of Recent Research Findings, Potential for Structural and Mechanical Applications, and Areas of Continued Investigations

Recent advances in the manufacture and processing of high purity NiTinol 60 (60 wt% Ni–40 wt% Ti) has spurred a renewed interest in the use of this alloy for structural and mechanical component applications. NiTinol 60 (60NiTi) exhibits excellent corrosion resistance, can be hardened to high levels, has a low elastic modulus and extensive elastic range that imparts high mechanical contact load resilience. It is dimensionally stable, has good bio-compatibility, can be machined into precision components and is non-magnetic. This unique set of characteristics make the intermetallic 60NiTi suitable for a wide variety of applications in the marine, medical, aerospace and food processing industries. This article surveys and reviews a broad range of historic and recent publications on 60NiTi to highlight what is known and areas that require further study. In particular, recent results indicate a dichotomy in friction and wear behavior. Under good lubrication (liquid or solid) both friction and wear are low but in dry un-lubricated sliding, wear exceeds that of other materials such as steel that have comparable hardness. This unexpected behavior is proposed as an important topic for future investigations before any of widespread adoption in engineering applications.

How drops start sliding over solid surfaces

It has been known for more than 200 years that the maximum static friction force between two solid surfaces is usually greater than the kinetic friction force—the force that is required to maintain the relative motion of the surfaces once the static force has been overcome. But the forces that impede the lateral motion of a drop of liquid on a solid surface are not as well characterized, and there is a lack of understanding about liquid–solid friction in general. Here, we report that the lateral adhesion force between a liquid drop and a solid can also be divided into a static and a kinetic regime. This striking analogy with solid–solid friction is a generic phenomenon that holds for liquids of different polarities and surface tensions on smooth, rough and structured surfaces. A liquid droplet is shown to slide across a solid surface subject to friction forces analogous with those between two solids. The phenomenon is generic, and closes a gap in our understanding of liquid–solid friction.

Studies on Fractures of Friction Stir Welded Al Matrix SiC-B4C Reinforced Metal Composites

Studies pertaining to joining of Al alloy metal matrix composites reinforced with B4C and SiC by solid state friction stir welding (FSW) are presented in this paper. FSW tool dimensions are designed and fabricated to suit the weld sample dimensions and subsequently, the implications of the tool pin profile on the weldability is investigated. Through experimental recordings, the heat generated during the friction stir joining process of composites is estimated by developing relative equations. Maintaining the tool traverse speed constant, the rate of rotation and its effects on the tensile strength at the joints are investigated which reveals reduced ductility. The study emphasizes that when the speed is maintained between 100–400 mm/min, the tensile strength is at its optimal maximum while speeds higher or lower than the optimal range indicate detrimental effects on the tensile strength. This is followed by fracture studies on samples welding with varying traverse speed and rate of welding. Traverse speed appears to govern the fracture modes while brittle fracture is predominantly noticed indicating the importance of feeding optimal heat input during joining.

Frictional Cooling of Granular Gases: A Molecular Dynamics Study

We study the free evolution of frictional granular gases using large scale molecular dynamics simulation in three dimensions. The system cools due to solid friction among the interacting particles. At early stages of evolution, the density field remains homogeneous and the velocity field follows the Maxwell-Boltzmann (MB) distribution. However, at later times, the density field shows clustering and the velocity field shows local ordering. The ordering in the velocity field is studied by invoking analogy from phase ordering systems. The equal-time correlation function of velocity field follows dynamical scaling. The correlation length of velocity field, Lv(t), exhibits power law growth: Lv(t) ∼ t1/3.

Nanomaterials of SHS technology for tribological applications: A review

A review of results of applying the powder technology of self-propagating high-temperature synthesis (SHS) for obtaining various nanomaterials that can be used according to the tribotechnical indentation is given. First, these are low-cost nanopowders of sulfides, oxides, nitrides, carbides, borides, and metals which are suitable as solid lubricants and friction modifiers for liquid and plastic lubricating materials. Second, these are solid compact nanostructured ceramic and composite materials for the fabrication of tribotechnical construction. This type of nanomaterial can be fabricated both ex situ from SHS nanopowders by sintering or introduction into the melt both in situ in one stage from initial powders reagents by gasostatic SHS technology, forced SHS compaction, SHS casting, and SHS in the melt, which considerably simplifies and cheapens the production of such materials. Third, these are SHS materials for the deposition of nanostructured coatings of various thicknesses with a high wear resistance and low friction coefficients, such as nanostructured materials for surfacing and spraying, electrospark alloying electrodes, multicomponent targets for magnetron sputtering, cathodes for vacuum-arc evaporation, and nanodispersed fillers of electrochemical and chemical coatings.

Pressure-Dependent Friction on Granular Slopes Close to Avalanche.

We investigate the sliding of objects on an inclined granular surface close to the avalanche threshold. Our experiments show that the stability is driven by the surface deformations. Heavy objects generate footprintlike deformations which stabilize the objects on the slopes. Light objects do not disturb the sandy surfaces and are also stable. For intermediate weights, the deformations of the surface generate a sliding of the objects. The solid friction coefficient does not follow the Amontons-Coulomb laws, but is found minimal for a characteristic pressure. Applications to the locomotion of devices and animals on sandy slopes as a function of their mass are proposed.

Single particle Brownian motion with solid friction.

We study the Brownian dynamics of a solid particle on a vibrating solid surface. Phenomenologically, the interaction between the two solid surfaces is modeled by solid friction, and the Gaussian white noise models the vibration of the solid surface. The solid friction force is proportional to the sign of relative velocity. We derive the Fokker-Planck (FP) equation for the time-dependent probability distribution to find the particle at a given location. We calculate analytically the steady state velocity distribution function, mean-square velocity and diffusion coefficient in d-dimensions. We present a generic method of calculating the autocorrelations in d-dimensions. This results in one dimension in an exact evaluation of the steady state velocity autocorrelation. In higher dimensions our exact general expression enables the analytic evaluation of the autocorrelation to any required approximation. We present approximate analytic expressions in two and three dimensions. Next, we numerically calculate the mean-square velocity and steady state velocity autocorrelation function up to d = 3 . Our numerical results are in good agreement with the analytically obtained results.

Sensitivity Analysis of Depth-Integrated Numerical Models for Estimating Landslide Movement

Landslides are natural phenomena that occur in slopes with thick layers of weathered soil or weak geological formations. High intensity of precipitation, earthquake, and human interference can cause a huge landslide disaster. To mitigate landslide risk, an appropriate investigation to determine the stability and movement mechanisms is important to predict its potential scale. This paper proposes a sensitivity analysis of depth-integrated numerical model of landslide movement by implementing solid friction and fluid friction as the shear resistance in the constitutive systems. The hyperconcentrated solid-liquid mixture flow model and Voellmy-fluid friction model are employed in the solid friction and fluid friction mechanism, whereas the Mohr-Coulomb model is used in the solid friction mechanism. In order to analyze model characteristics and sensitivity to the inputted parameters, the parametric studies on an imaginary slope were examined. The results show that the internal friction angle among input data strongly affects the runout distance and moving velocity. The Voellmy-fluid friction model produces more lateral tendency and wider deposit in transversal directions of landslide compared to other models. The numerical model along with three constitutive equations of shear resistance was applied to the Bishamon Landslide. The hyperconcentrated solid-liquid mixture flow model and Mohr-Coulomb model yield a good agreement with the actual deposition area, whereas the Voellmy-fluid friction model produces more lateral tendency in transversal directions. The calculated runout distance reaches more than 350 m and 10.3 to 13.9 m/s of maximum velocity.

Numerical simulation of fluidized dense-phase pneumatic conveying of powders to develop improved model for solids friction factor

Accurate prediction of the solids friction factor through horizontal straight pipes is important for the reliable design of a pneumatic conveying system, but it is a challenging assignment to date because of the highly concentrated, turbulent, and complex nature of the gas–solids mixture. Power-station fly ash was transported through different pipeline configurations. Numerical simulation of the dense-phase pneumatic conveying systems for three different solids and two different air flow rates have shown that particle and actual gas velocities and the ratio of the two velocities increases in the flow direction, whereas the reverse trend was found to occur for the solids volumetric concentration. To develop a solids friction-factor model suitable for dense-phase flow, we modified an existing pure dilute-phase model by incorporating sub-models for particle and actual gas velocities and impact and solids friction factor. The solids friction-factor model was validated by using it for scale-up predictions for total pipeline pressure drops in longer and larger pipes and by comparing experimental and predicted pneumatic conveying characteristics for different solids flow rates. The accuracy of the prediction was compared with a recently developed two-layer-based model. We discussed the effect of incorporating the particle and actual gas velocity terms in the solids friction-factor model instead of superficial air velocity.

Hybrid modeling of multiphysical processes for particle‐based volcano animation

AbstractMany complex natural phenomena with dramatic spatial and temporal variation are difficult to animate accurately with anticipated performance in many graphics tasks and applications, because oftentimes in prior art, a single type of physical process could not afford high fidelity and effective scene production. Volcano eruption and its subsequent interaction with earth is one such complicated phenomenon that must depend on multiphysical processes and their tight coupling. This paper documents a novel and effective particle‐based solution for volcano animation that embraces multiphysical processes and their tight unification. First, we introduce a governing physical model consisting of multiphysical processes enabling flexible state transition among solid, fluid, and gas. This computational physics model is dictated by temperature and accommodates dynamic viscosity that is changing according to the temperature. Second, we propose an augmented smoothed particle hydrodynamics as the underlying numerical model to simulate the behavior of lava and smoke with several required physical attributes. Third, multiphysical quantities are tightly coupled to support the interaction with surroundings including fluid–solid coupling, ground friction, and lava–smoke coupling. We also develop a temperature‐directed rendering technique with nearly no extra computational cost and demonstrate realistic graphics effects of volcano eruption and its interaction with earth with visual appeal.

Tunable discontinuous shear thickening with magnetorheological suspensions

Discontinuous shear thickening is a phenomenon observed in concentrated suspensions where, at a given applied stress, the flow becomes suddenly partially blocked and the shear rate begins to decrease and to oscillate when the stress is increased above the critical one. In this work, we show that it is possible to control with a magnetic field this abrupt transition from a flowing state to a jammed state, using a suspension of magnetic particles coated with a superplastifier molecule. In the case of experiments made at constant velocity, the transition to the jammed state corresponds to a very high jump of stress which can reach several hundred pascals for fields as low as a few kiloampere per meter. We present also results obtained in microgravity on a magnetic powder, showing that the solid friction between particles plays a key role in the jamming phenomenon.

Emergence of complex behavior in pili-based motility in early stages of P. aeruginosa surface adaptation

Pseudomonas aeruginosa move across surfaces by using multiple Type IV Pili (TFP), motorized appendages capable of force generation via linear extension/retraction cycles, to generate surface motions collectively known as twitching motility. Pseudomonas cells arrive at a surface with low levels of piliation and TFP activity, which both progressively increase as the cells sense the presence of a surface. At present, it is not clear how twitching motility emerges from these initial minimal conditions. Here, we build a simple model for TFP-driven surface motility without complications from viscous and solid friction on surfaces. We discover the unanticipated structural requirement that TFP motors need to have a minimal amount of effective angular rigidity in order for cells to perform the various classes of experimentally-observed motions. Moreover, a surprisingly small number of TFP are needed to recapitulate movement signatures associated with twitching: Two TFP can already produce movements reminiscent of recently observed slingshot type motion. Interestingly, jerky slingshot motions characteristic of twitching motility comprise the transition region between different types of observed crawling behavior in the dynamical phase diagram, such as self-trapped localized motion, 2-D diffusive exploration, and super-diffusive persistent motion.

Nanocrystalline Graphite Formed at Fullerene‐Like Carbon Film Frictional Interface

High performance solid lubricant materials with long wear life remain as one of the challenges in space technology. It is of great significance to lower the solid film's friction and wear and to prolong its service life in vacuum. Hydrogenated fullerene‐like carbon film produced by dc‐pulsed power source behaves ultralong wear life (≫1.8 × 105 cycles) and ultralow wear rate (2.2 × 10−8 mm3 Nm−1) as well as low friction (≈0.14) in high vacuum (2.3 × 10−4 Pa). To understand its long wear life reason, the interfacial structural evolution is investigated after steady state friction is achieved. By observing the interfacial nanostructure evolution, it is found that the friction and wear properties are related to the friction‐induced phase transformation from fullerene like structure to nanocrystalline graphite and the deposition of tribofilm on Al2O3 counterface. And this process is analyzed by X‐ray photoelectron spectroscopy, micro‐Raman spectra and is observed through transmission electron microscopy. The results enrich hydrogenated fullerene‐like carbon film friction mechanisms and expand its potential application in space.