Solid Friction Research Articles

Optimization of Sliding Wear Parameters for Copper Surface Composites Reinforced with AlCoCrCuFe HEA

The present research pacts with fabrication of Cu – HEA surface MMC through solid state Friction Stir process (FSP) and analysis of wear characteristics. AlCoCrCuFe HEA with higher hardness values vacillated up in the level of 770HV is selected as reinforcement. The wear test is performed for 16 parameter combinations based on Taguchi method with the aid of Pin-on-Disc apparatus. The input parameters considered are HEA percentage, applied load, sliding velocity and distance whereas wear rate and coeffi cient of friction are chosen as response. WR signifi cantly decreases with HEA additions and increases with increase in load, sliding velocity and sliding distance. The consequence of HEA addition on CoF during dry sliding wear test is contradictory to its effect over WR. ANOVA results confi rmed the signifi cant effect of reinforced HEA over wear characteristics of copper composite. TOPSIS methodology is followed to fi nd the best possible parameter combination that yields better wear rate and coeffi cient of friction.

45 YEARS OF DELIBERATIONS ON THE THERMO-MECHANICAL INTERPRETATION OF FRICTION AND WEAR PART I – THE MACROSCOPIC INTERPRETATION OF THE TRIBOLOGICAL PROCESS

This first part will consider the friction couple or its part, identified with the open thermodynamic system. Dependences among extensive parameters and energetic interactions in the system and its boundaries with the environment are described in analytical terms. The dimensions of the energy dissipation zone, where the friction of solids takes place, are established. The thermo-mechanical nature of the tribological process is demonstrated. The wear conditions and distribution of energy generated by its particular elements are determined. A new quantity is introduced – the specific work of wear, which characterises the wear resistance of the tribological system and its parts. The effect of the reciprocal cover of solids’ friction surfaces on the energy balance structure in calorimetric testing is analysed. The concept of generalised wear is introduced and standardised. The discussion is restricted to processes at the macroscopic level of matter organisation.

Swamp Wetlands in Degraded Permafrost Areas Release Large Amounts of Methane and May Promote Wildfires through Friction Electrification

Affected by global warming, permafrost degradation releases a large amount of methane gas, and this part of flammable methane may increase the frequency of wildfires. To study the influence mechanism of methane emission on wildfires in degraded permafrost regions, we selected the northwest section of Xiaoxing’an Mountains in China as the study area, and combined with remote sensing data, we conducted long-term monitoring of atmospheric electric field, temperature, methane concentration, and other observation parameters, and further carried out indoor gas–solid friction tests. The study shows that methane gas (the concentration of methane at the centralized leakage point is higher than 10,000 ppm) in the permafrost degradation area will release rapidly in spring, and friction with soil, surface plant residues, and water vapor will accelerate atmospheric convection and generate electrostatic and atmospheric electrodischarge phenomena on the surface. The electrostatic and atmospheric electrodischarge accumulated on the surface will further ignite the combustibles near the surface, such as methane gas and plant residues. Therefore, the gradual release of methane gas into the air promotes the feedback mechanism of lightning–wildfire–vegetation, and increases the risk of wildfire in degraded permafrost areas through frictional electrification (i.e., electrostatic and atmospheric electrodischarge).

A Generalized Mathematical Model of External Sliding Friction in Solids

A Generalized Mathematical Model of External Sliding Friction in Solids

Tuning the shear thickening of suspensions through surface roughness and physico-chemical interactions

Shear thickening denotes the reversible increase in viscosity of a suspension of rigid particles under external shear. This ubiquitous phenomenon has been documented in a broad variety of multiphase particulate systems, while its microscopic origin has been successively attributed to hydrodynamic interactions and frictional contact between particles. The relative contribution of these two phenomena to the magnitude of shear thickening is still highly debated, and we report here a discriminating experimental study using a model shear-thickening suspension that allows us to independently tune both the surface chemistry and the surface roughness of the particles. We show here that both properties matter when it comes to continuous shear thickening (CST) and that the presence of hydrogen bonds between the particles is essential to achieve discontinuous shear thickening (DST) by enhancing solid friction between closely contacting particles. Moreover, a simple argument allows us to predict the onset of CST, which for these very rough particles occurs at a critical volume fraction much lower than that previously reported in the literature. Finally, we demonstrate how mixtures of particles with opposing surface chemistry make it possible to finely tune the shear-thickening response of the suspension at a fixed volume fraction, paving the way for a fine control of the shear-thickening transition in engineering applications.

Electron transfer dominated triboelectrification at the hydrophobic/slippery substrate—water interfaces

Triboelectric nanogenerator (TENG) based on triboelectrification has attracted wide attention due to its effective utilization of green energy sources such as marine energy. However, researches about liquid-liquid triboelectrification are still scanty as solid—liquid triboelectrification has been widely studied. Herein, this work focuses on the hydrophobic/slippery substrate—water interfacial triboelectrification based on the solid friction materials of polytetrafluoroethylene (PTFE) nanoparticles. The hydrophobic/slippery substrate—water interfacial triboelectrification are studied by assembling PTFE coated Al sheets and perfluoropolyether (PFPE) infused PTFE coated Al sheets (formed the slippery lubricant-infused surfaces (SLIPSs)) as the friction electrode, and water as liquid friction materials, respectively. The results show that the hydrophobic TENG output performances improved as the PTFE nanoparticles cumulating, and the SLIPSs TENG output performances increased with the thinner PFPE thickness. Both the triboelectrification behavior of hydrophobic/SLIPSs TENG assembled in this work are dominated by the electron transfer. Thanks to the introduction of SLIPSs, the SLIPSs TENG exhibits superior stability and durability than the hydrophobic TENG. The investigation of hydrophobic/slippery substrate—water interfacial triboelectrification contributes to optimize the TENG performances, and expands the application in harsh environments including low temperature and high humidity on the ocean.

On the vacancy nature of the high-temperature background of internal friction in solids

High-temperature internal friction in an amorphous CuTi alloy is investigated. Exponential regions with different activation energies are observed on the dependence of internal friction on temperature on both sides of the glass transition temperature. An exponential increase in the background of internal friction with temperature in both sites is associated with the migration of vacancy-like defects in the amorphous structure under the influence of mechanical stresses, while frozen defects of constant concentration migrate to the glass transition temperature. After the transition to a state of thermodynamic equilibrium, the concentration the number of migrating defects increases exponentially. Based on the experimental results of measuring the high-temperature background, estimates of the activation energy of migration and the formation of vacancies of similar defects in the amorphous structure of the alloy under study are made. Keywords: Internal friction, relaxation time, high temperature background, amorphous alloy.

Prediction of mechanical characteristics of friction welded dissimilar EN 10028P 355 GH steel and AISI 430 steel joint by fuzzy logic analysis

A solid state friction welding is one of the metal fastening processes is to produce defect free joints when compared to fusion welding techniques. The material EN 10028P 355 GH Steel and AISI 430 Steel find extensive applications in heat exchanger tubes, pressure vessels, and pump shafts. In the present study, the artificial intelligence tool fuzzy logic analysis was utilized for earlier prediction of mechanical characteristics like tensile strength, impact toughness and axial shrinkage of friction welded dissimilar joint. The necessary parameters considered in this process are rotational speed, forging pressure, friction pressure, friction time, and forging time. The L27 based experimental plan is used to execute the experiment. The Mamdani model and triangular membership function methods are adopted in the fuzzy logic analysis. The developed 3D surface model helps to analyze the variation of the parameter to attain the desired properties. The forecasted values from the fuzzy model are compared with experimental values and found that the fuzzy model is good as it yields a minimum percentage of error.

Regression model for obtaining peak temperature and heat generation during friction stir welding of stainless steel

Solid state friction stir welding is the process of combining materials, typically with the aid of a tool. This process makes use of welding materials such as aluminium, stainless steel, and steel steel. A regression model is developed in this study to predict peak temperature and heat generation during stainless steel friction stir welding. This model was built using data from the power required, heat generation (unit length), and peak temperature regression models. There was a high correlation between the required power, heat produced per unit length, and peak temperature predicted by the thermal model and regression model. The required power is proportional to the rotating and welding speeds. At a welding speed of 200 mm/min and a rotational speed of 500 rpm, the maximum power was 3733 W. The amount of heat generated and the highest temperature reached increase as rotational speed and welding speed decrease. The maximum heat generated was 1273 J/mm, attained at the welding speed of 101 mm/min and 500 rpm rotational speed.

Study of optimum welding performance in friction stir welding of dissimilar Mg alloys using integrated RSM-TLBO algorithm

Lightweight with excellent strength of magnesium alloys has attracted its use in transportation industries but difficulty in fusion welding of magnesium alloys restricts its application. The present research investigates solid state friction stir welding of dissimilar AZ31-AZ91 magnesium alloys with aim to achieve optimum quality welds. Surface roughness, microstructure and mechanical properties of these joints have been investigated at different tool rotational speed, welding speed and tool shoulder diameter. Maximum joint strength obtained is 89.71% (as compare to AZ31) which is more than the previously reported joint strengths of dissimilar magnesium alloys. Further, mathematical relations for responses have been developed and utilised for multi-objective optimization using teaching-learning-based optimization algorithm. Eventually, teaching-learning-based optimization algorithm results suggest that the optimum value of surface roughness (3.3925 µm), grain size (12.6869 µm), tensile strength (237.9621 MPa), microhardness (69.3652 Hv) and flexural strength (333.2285 MPa) can be achieved at 921 rpm rotational speed, 30 mm/min welding speed and 15 mm shoulder diameter with overall improvement in multiple responses.

SOME COMMENTS ON THE INTERPRETATION OF THE TRIBOLOGICAL WEAR COEFFICIENT

An original model of tribological wear is presented, an alternative to the commonly used J.F. Archard’s model. The impossibility is established of a full conversion of mechanical work into the heat of dissipation and thereby of avoiding wear in the sliding friction of solids. The assumption is consequently questioned that only some contacts of surface asperities are subject to temporary wear. Material wastage is assumed to occur at each contact of asperities. The volume of worn material is dependent on the volumetric wear coefficient of the “energy dissipation zone” in friction. The dimensions of the zone are determined in both the elements in friction. Linear wear intensities and volumetric wear are described in analytical terms. The thermodynamic analysis of the tribological process indicates some limitations to these intensities. Energetic efficiencies of solid wear and heating as a result of friction are defined. Some new interpretations of the wear coefficient are proposed.

Emergence of viscosity and dissipation via stochastic bonds

“Viscosity is the most ubiquitous dissipative mechanical behavior” (Maugin, 1999). Despite its ubiquity, even for those systems where the mechanisms causing viscous and other forms of dissipation are known there are only a few quantitative models that extract the macroscopic rheological response from these microscopic mechanisms. One such mechanism is the stochastic breaking and forming of bonds which is present in polymer networks with transient cross-links, strong inter-layer bonding between graphene sheets, and sliding dry friction. In this paper we utilize a simple yet flexible model to show analytically how stochastic bonds can induce an array of rheological behaviors at the macroscale. We find that varying the bond interactions induces a Maxwell-type macroscopic material behavior with Newtonian viscosity, shear thinning, shear thickening, or solid like friction when subjected to shear at constant rates. When bond rupture is independent of the force applied, Newtonian viscosity is the predominant behavior. When bond breaking is accelerated by the applied force, a shear thinning response becomes most prevalent. Further connections of the macroscopic response to the interaction potential and rates of bonding and unbonding are illustrated through phase diagrams and analysis of limiting cases. Finally, we apply this model to polymer networks and to experimental data on “solid bridges” in polydisperse granular media. We imagine possible applications to material design through engineering bonds with specific interactions to bring about a desired macroscopic behavior.

A Simulation of Soil Dumping Using Moving Particle Semi-Implicit Method

Kim, K.S. and Lee, J.H., 2021. A simulation of soil dumping using moving particle semi-implicit method. In: Lee, J.L.; Suh, K.-S.; Lee, B.; Shin, S., and Lee, J. (eds.), Crisis and Integrated Management for Coastal and Marine Safety. Journal of Coastal Research, Special Issue No. 114, pp. 549–553. Coconut Creek (Florida), ISSN 0749-0208. Soil dumping is one of most important problems on the coastal and ocean construction project. In general, the computational fluid dynamics method used grid system to simulate soil particle under flow with concentration. It can be useful for fast calculation; however, it is restricted to demonstrate its movement. The Moving Particle Semi-implicit (MPS) method follows fully Lagrangian approach, thus it can simulate soil particle behavior due to tracking each particle. In this study, the newly developed MPS method modified for solid particle was used to simulate soil dumping. For the solid particle interaction, drag force and friction force term were implemented instead of viscosity term in the governing equation. The friction force is due to friction between solid particles, and the drag force can be calculated by relative velocity around center particle within effective range. All the solid particle interaction models were validated by corresponding physical phenomena. The numerical results were compared to the corresponding experimental results and they show good agreement in the tendency of behavior.

Experimental testing and validation of the dynamic model of a magneto-solid damper for vibration control

This paper focuses on characterization testing and validation of the dynamic model of a new type of high-damping density electromagnetic-based damping device (EMD) referred to as Magneto-Solid Damper (MSD) in which an eddy current damping mechanism acts in parallel with a solid friction mechanism to dissipate the input kinetic energy. The proposed MSD consists of a ferromagnetic plate, two copper plates placed on two sides of the ferromagnetic plate in parallel, and a planar array of permanent magnets (PMs) placed between the ferromagnetic plate and each of the two copper plates. The PMs arrays are attached to the ferromagnetic plate through non-magnetic friction pads. The friction force is developed between these friction pads and the ferromagnetic plate when the PMs arrays move relative to the ferromagnetic plate. The motion of the PMs arrays relative to the copper plates, on the other hand, generates the eddy current damping. A laboratory prototype of the proposed MSD has been designed and fabricated for the purpose of characterization testing. Finite element and simplified analytical models of this damper have also been developed to analyze the magnetic interaction between the PMs arrays and the ferromagnetic and copper plates. A dynamic model has been developed to characterize the force–displacement behavior of the proposed MSD. The parameters of this dynamic model are identified through a series of characterization tests on the prototype MSD under harmonic excitations of different frequencies. The identified dynamic model is validated by subjecting the prototype MSD to real ground motion records. It is concluded that that the proposed dynamic model is capable of describing the force–displacement behavior of the proposed MSD for a wide range of operating conditions.

Adhesive and normal stress-dependent dynamic friction of a gelatin hydrogel

Adhesion and friction of soft solids on hard surfaces are the important properties for a variety of practical applications. In the present study, Coulomb's law of friction is used for characterizing adhesive friction as well as normal stress-dependent dynamic friction of a gelatin hydrogel on a fixed glass surface. The experimental data, concerning normal stress-dependent dynamic friction of different shear velocity, are obtained from literature. It is observed that both components of friction increase with shear velocity. More importantly, the scaling law shows that adhesive stress varies almost linearly with corresponding coefficient of friction of the hydrogel. A dynamic friction model is also used to analyze the same experimental data to predict a negative normal stress at which dynamic friction reduces to zero, and this result matches closely with the experimental value.

Anchoring and migration of balloon in REBOA

A mechanical theory is described for a phenomenon in the surgical procedure of resuscitative endovascular balloon occlusion of the aorta (REBOA). In this procedure a balloon is pushed into the aorta by a catheter and then inflated in order to stop haemorrhage. One of the hazards of this procedure is the tendency for the balloon to migrate away from its intended position. This work examines the mechanics of balloon anchoring and migration by analysing the effects of pressure waves, the sheet flow and solid friction in the thin gap between the walls of the aorta and balloon. A viscoelastic model is adopted for the aorta wall for pressure waves between the left ventricle and the balloon. The lubrication approximation is used for blood flow in the thin gap between the walls of the balloon and aorta. Samples of quantitative predictions are discussed on how the inflation pressure and balloon characteristics affect the balloon anchoring and migration. The crucial roles of solid friction and balloon placement are pointed out, which should help in guiding the manufacturing of balloons and their usage in the field.

Wear simulation of worm gears based on an energetic approach

Wear phenomena in worm gears are dependent on the size of the gears. Whereas larger gears are mainly affected by fatigue wear, abrasive wear is predominant in smaller gears. In this context a simulation model for abrasive wear of worm gears was developed, which is based on an energetic wear equation. This approach associates wear with solid friction energy occurring in the tooth contact. The physically-based wear simulation model includes a tooth contact analysis and tribological calculation to determine the local solid tooth friction and wear. The calculation is iterated with the modified tooth flank geometry of the worn worm wheel, in order to consider the influence of wear on the tooth contact. Experimental results on worm gears are used to determine the wear model parameter and to validate the model. A simulative study for a wide range of worm gear geometries was conducted to investigate the influence of geometry and operating conditions on abrasive wear.

A comparative study between weldability of polycarbonate and nylon-6 using different pin geometries in friction stir welding

The solid state friction stir welding (FSW) has been recently the choice for joining of thermoplastics. The present work aims at analyzing the implementation of FSW in joining of different thermoplastics namely, polycarbonate and nylon-6 sheets using varying tool pin profiles, cylindrical, square, and triangular. The novelty of this article is the comparative assessment that has been made on the weldability of these two thermoplastics by determining the mechanical properties of the joint along with real-time acquired force, torque, and temperature signals. Higher axial force with reduced torque has been observed for nylon-6 as compared to polycarbonate. The joint efficiency was found to be maximum (>50%) at tool rotational speed 1800 rpm and welding speed 20 mm/min using square tool pin profile for each of the base materials. Minor undercut defect along with improved material mixing has been seen during the tool stirring process. The study would be helpful for the industries to choose thermoplastics based on their applications.

Frictional granular flows of rod and disk mixtures with particle shape distributions

Three-dimensional simulations of polydisperse shear flows of rod and disk mixtures are performed using the discrete element method. The effects of particle shape distribution on flow behaviors are investigated assuming that all particles have the same volume and density but different shapes in the simulations. The solid phase stresses and bulk friction coefficients show a strong dependence on the particle alignment and the structural anisotropy of interparticle contacts. The combined effects of interparticle friction and particle shape difference lead to larger stresses for mixtures of different particle shapes than the pure particle species in dense shear flows. For frictionless and frictional flows with particle shape distributions, it is observed that the particle fluctuating velocities follow non-Maxwellian distributions and the fluctuating kinetic energies are unequally partitioned among the different particle species.

Effects of solid friction modifier on friction and rolling contact fatigue damage of wheel-rail surfaces

In railway network, friction is an important factor to consider in terms of the service behaviors of wheel-rail system. The objective of this study was to investigate the effect of a solid friction modifier (FM) in a railway environment. This was achieved by studying the friction, wear, and rolling contact fatigue (RCF) damage on the wheel-rail materials at different slip ratios. The results showed that when a solid FM was applied, the friction coefficient decreased. After the solid FM was separated from the wheel-rail interface, the friction coefficient gradually increased to its original level. With the application of the solid FM, the wear rates of the wheel-rail decreased. In addition, the thickness and hardness of the plastic deformation layers of the wheel-rail materials were reduced. The worn surfaces of the wheel-rail were dominated by pits and RCF cracks. Without the FM, RCF cracks ranged from 84 to 120 µm, and subsurface cracks were generated. However, with the FM, RCF cracks ranged from 17 to 97 µm and no subsurface cracks were generated. These findings indicate possible methods of improving the performance of railway rolling stock by managing friction, and reducing wear and permanent RCF damage affecting both the wheels and rails.