Friction Theory Research Articles

Does climate policy uncertainty influence the corporate cost of debt?

This paper employs a sample of Chinese A-share listed companies spanning from 2011 to 2022 to empirically investigate the influence of climate policy uncertainty on the corporate cost of debt, based on the theory of financial friction. We find that climate policy uncertainty significantly increases the corporate cost of debt, and the result is supported by robustness tests. To avoid biases arisen from endogeneity, this paper introduces an instrumental variable approach and propensity score matching method for verification. The endogeneity test results support the baseline regression results as well. Finally, this paper also discovers that financing constraints are the potential mechanism behind the impact of climate policy uncertainty on the corporate cost of debt.

Improving comprehensive properties of Cu−11.9Al−2.5Mn shape memory alloy by adding multi-layer graphene carried by Cu51Zr14 inoculant particles

In order to improve the comprehensive properties of the Cu−11.9Al−2.5Mn shape memory alloy (SMA), multilayer graphene (MLG) carried by Cu51Zr14 inoculant particles was incorporated and dispersed into this alloy through preparing the preform of the cold-pressed MLG−Cu51Zr14 composite powders. In the resultant novel MLG/Cu−Al−Mn composites, MLG in fragmented or flocculent form has a good bonding with the Cu−Al−Mn matrix. MLG can prevent the coarsening of grains of the Cu−Al−Mn SMA and cause thermal mismatch dislocations near the MLG/Cu−Al−Mn interfaces. The damping and mechanical properties of the MLG/Cu−Al−Mn composites are significantly improved. When the content of MLG reaches 0.2 wt.%, the highest room temperature damping of 0.0558, tensile strength of 801.5 MPa, elongation of 10.8%, and hardness of HV 308 can be obtained. On the basis of in-depth observation of microstructures, combined with the theory of internal friction and strengthening and toughening theories of metals, the relevant mechanisms are discussed.

Investigating on the Tribological Behavior of Binderless WC Matrix Composite

The purpose of this study was to investigate the dry friction and wear behavior of WC-4.3wt.%MgO-2wt.%ZrO2 (WM2Z) composite. WM2Z composite prepared by high-energy ball milling and spark plasma sintering (SPS) technology exhibited excellent comprehensive mechanical properties and dense microstructure. Dry friction test results indicated that the increase of sliding speed will lead to the decrease of friction coefficient, while at the same sliding speed, the extension of sliding time has no significant effect on the friction coefficient. The wear volume increased proportionally with the sliding time, while the wear rate stabilized after reaching a certain duration. The wear mechanism was mainly slight abrasive wear. Additionally, some oxidation occurred on both the WM2Z composite and the Si3N4 ball during friction, forming an oxide film that contributed to the reduction of the friction coefficient. The novelty of this study lies in the first systematic investigation of the effects of sliding speed and time on the wear performance of WM2Z composite, and the revelation that in high-speed sliding environments, even with shorter sliding times, the material experiences faster wear. This discovery emphasizes the important role of sliding speed in the wear process and provides new insights into understanding the wear mechanism of materials in practical applications. This study not only enriches the friction and wear theory of binderless WC matrix composites, but also provides important experimental data and theoretical support for the design and application of related materials, laying a solid foundation for wear resistance optimization and industrial applications.

Load-bearing characteristics of surface conductor in deepwater gas hydrate formations

The surface conductor is the first structural casing in deepwater natural gas hydrate (NGH) development, bearing the top load while suspending the casings of various layers. NGH decomposition leads to formation settlement, changing the mechanical properties of the formation and reducing the bearing capacity of the surface conductor, threatening the safety and stability of the wellhead. Understanding the bearing characteristics of the surface conductor in the hydrate formation can guide the safe drilling operation in the field. By introducing the negative skin friction theory of pile foundations and based on conventional bearing capacity models, a method for calculating the bearing capacity of surface conductors in NGH formations was developed. Using an NGH drilling simulation apparatus, the accuracy of the bearing capacity theoretical model was verified, empirical coefficients under different conditions were obtained, and the influence of soil parameters, hydrate saturation, and decomposition temperature on the bearing capacity of surface conductors was quantified. The results indicated that compared to clay, sandy soils have higher porosity and significantly weakened strength after the decomposition of NGH; when the hydrate saturation in the formation is 20%, the reduction in bearing capacity of the surface conductor in sand exceeds 30%, and in clay soils, it decreases by 25% after complete decomposition of NGH; as the hydrate saturation increases, the reduction in the bearing capacity of surface conductors after decomposition becomes more significant. Verified through Experimentation, the error of the hydrate-bearing strata-bearing capacity model is around 10%. For short-term test production operations of NGH in water, the design depth for surface conductors is around 100 m. These research results can provide a scientific theoretical basis for the design of conductor depth below the mud， and reduce operational risks.

Volumetric efficiency degradation prediction of axial piston pump based on friction and wear test

The axial piston pump (APP) is being developed towards higher pressure and higher rotational speeds to enhance operational power density. The piston-cylinder friction pair is a critical component of the APP. Due to its lack of self-compensation capability, the leakage of the piston-cylinder friction pair escalates rapidly under increasingly severe wear conditions. An innovative method for predicting the performance degradation and lifespan of APPs based on friction and wear tests has been proposed. This method can effectively predict the performance degradation trends of APPs under different operating conditions. The actual contact force on the piston pair (PP) during operation is determined through dynamic analysis. Friction and wear tests were conducted on 38CrMoAl piston and ZCuPb15Sn8 cylinder materials under various conditions using a testing apparatus. Utilizing friction and wear theory, the volumetric efficiency of APP under various operating conditions was derived as a function of operational time. The reliability of the theoretical analysis was validated through leakage tests on the APP. The results indicate that volumetric efficiency decreases exponentially with increasing working pressure at rated speed. This research provides theoretical guidance and an experimental foundation for the failure prediction of volumetric efficiency degradation in APP.

Friction theory and conflict prevention in legal analysis

Friction theory and conflict prevention in legal analysis

Role of strain softening and viscoelastic memory for the rolling friction of two tire tread compounds.

Rolling friction is of great importance for many applications, such as tires and conveyor belts. We study the rolling friction for hard cylinders rolling on flat rubber sheets. The rolling friction depends on the number of rolling cycles, the rolling speed, and the temperature. We show that when the rubber is cooled down below the glass transition temperature, the deformations of the rubber surface are frozen-in, resulting in a non-flat rolling track where uphill and downhill rolling movements strongly affect the rolling force. The experimental data are analyzed using the Persson rolling friction theory; good agreement with the experiments is obtained when the non-linear (strain-softening) properties of the viscoelastic modulus are taken into account.

Nonadiabatic dynamics of molecules interacting with metal surfaces: Extending the hierarchical equations of motion and Langevin dynamics approach to position-dependent metal-molecule couplings.

Electronic friction and Langevin dynamics is a popular mixed quantum-classical method for simulating the nonadiabatic dynamics of molecules interacting with metal surfaces, as it can be computationally more efficient than fully quantum approaches. In this work, we extend the theory of electronic friction within the hierarchical equations of motion formalism to models with a position-dependent metal-molecule coupling. We show that the addition of a position-dependent metal-molecule coupling adds new contributions to the electronic friction and other forces, which are highly relevant for many physical processes. Our expressions for the electronic forces within the Langevin equation are valid both in and out of equilibrium and for molecular models containing strong interactions. We demonstrate the approach by applying it to different models of interest.

A theory of phonon-induced friction on molecular adsorbates

In this manuscript, we provide a general theory for how surface phonons couple to molecular adsorbates. Our theory maps the extended dynamics of a surface's atomic vibrational motions to a generalized Langevin equation, and by doing so captures these dynamics in a single quantity: the non-Markovian friction. The different frequency components of this friction are the phonon modes of the surface slab weighted by their coupling to the adsorbate degrees of freedom. Using this formalism, we demonstrate that physisorbed species couple primarily to acoustic phonons while chemisorbed species couple to dispersionless local vibrations. We subsequently derive equations for phonon-adjusted reaction rates using transition state theory and demonstrate that these corrections improve agreement with experimental results for CO desorption rates from Pt(111).

Classical tribology and charge-energy evolution theory cooperate to determine nitrided ceramic coating/metal substrate interfacial friction

Who governs interfacial friction, classical tribology theory or charge-energy evolution theory? Since it was widely recognized that the origin of friction is interatomic forces, attention has gradually shifted towards the characteristics of local nanoscale interfaces. The new theory believes the charge density evolution during the friction process has more significant attributes in determining the interfacial friction. Here, we discuss the frictional failure mechanism at the ceramic/metal interface formed after the nitriding. The increase in N-doped interface friction is supported by classical tribology theory and corresponds to high interface adhesion work. On the other hand, the H-doped interface with the lowest adhesion work exhibits the highest friction. Unlike other interface systems (metallic bonding), the failure interface after H doping is an ionic bonding interface. Stronger ionic bonds are formed and broken in relative sliding, significantly increasing charge density. This emphasizes the crucial role of charge density in this process, aligning with the principles of the new theory. Nevertheless, the classical tribology theory can still be used when measuring interfacial friction of the interface with the same chemical bonds, and it may be more convincing than the new theory. Overall, these research results reveal the intrinsic origin of H/N's influence on TiN/Ti interfacial friction and provide new insights into understanding natural failures at the nanometer level.

Modelling of Static and Dynamic Elastomer Friction in Dry Conditions

Understanding the tribological behavior of elastomers in dry conditions is essential for sealing applications, as dry contact may occur even in lubricated conditions due to local dewetting. In recent decades, Persson and co-authors have developed a comprehensive theory for rubber contact mechanics and dry friction. In this work, their model is implemented and extended, particularly by including static friction based on the bond population model by Juvekar and coworkers. Validation experiments are performed using a tribometer over a wide range of materials, temperatures and speeds. It is shown that the friction model presented in this work can predict the static and dynamic dry friction of various commercial rubber materials with different base polymers (FKM, EPDM and NBR) with an average accuracy of 10%. The model is then used to study the relevance of different elastomer friction contributions under various operating conditions and for different roughness of the counter surface. The present model will help in the development of novel optimized sealing solutions and provide a foundation for future modeling of lubricated elastomer friction.

Exploring Density, Viscosity, and Friction Theory in the Interaction of Linalool (3,7-Dimethylocta-1,6-dien-3-ol) with 2-Alkanol

Exploring Density, Viscosity, and Friction Theory in the Interaction of Linalool (3,7-Dimethylocta-1,6-dien-3-ol) with 2-Alkanol

Controlling the Friction Coefficient and Adhesive Properties of a Contact by Varying the Indenter Geometry

In the present paper, we describe a series of laboratory experiments on the friction between rigid indenters with different geometrical forms and an elastic sheet of elastomer as a function of the normal load. We show that the law of friction can be controlled by the shape of the surface profile. Since the formulation of the adhesive theory of friction by Bowden and Tabor, it is widely accepted and confirmed by experimental evidence that the friction force is roughly proportional to the real contact area. This means that producing surfaces with a desired dependence of the real contact area on the normal force will allow to “design the law of friction”. However, the real contact area in question is that during sliding and differs from that at the pure normal contact. Our experimental studies show that for indenters having a power law profile f(r) = cnrn with an index n < 1, the system exhibits a constant friction coefficient, which, however, is different for different values of n. This opens possibilities for creating surfaces with a predefined coefficient of friction.

Real-time modeling of the riveting process forces for aircraft panel structures

The riveting of large panels in aircraft manufacturing requires an automatic drilling and riveting machine capable of precise and stable operation. However, the significant nonlinearity and time-varying nature of riveting process forces severely impact the control capacity and operational accuracy of these machines. So, the objective is to provide technical assurance for the precise operation of the machine and ensure high-quality riveting of the panels. Therefore, a real-time modeling method for the automatic riveting process forces on aircraft panels is proposed, which focuses on the rivet die's downward compression displacement as the core variable and accounts for the non-uniform deformation of rivets. This method assumes a constant volume for the rivet rod. It combines power-law hardening and Coulomb's friction theories to establish three sub-models for different riveting stages: the elastic stage, the plastic deformation stage, and the driven head formation stage. Further, considering the continuity of rivet's deformation, rivet rod's cross-section stress, and the driven head dimensions changes with the driven head's downward compression displacement, a novel real-time continuous dynamic load model for the full compression riveting process of a single-rivet is developed. The results indicate that the model is effective, with a maximum deviation of 7.50 % between experimental and predicted values, demonstrating its accuracy and reliability. In conclusion, this research provides a real-time, continuous description of the riveting process force, enabling automatic machines to promptly detect defects and deformations in the riveting.

Mechanisms of solid-liquid evolution and current-carrying characteristics at contact interface under the magneto-thermal effect

The contact state of the armature/rail (A/R) interface directly affects the launch performance and service life of the electromagnetic launcher (EML). Accordingly, this study employs the modified heat capacity method to construct a finite element model, considering the magneto-thermal effect based on electromagnetic field theory, energy conservation principles, Joule’s law, and frictional heat generation theory. The model simulates the solid-liquid evolution of the A/R interface during the electromagnetic launch process. The investigation elucidates the influence of the magneto-thermal effect on the electrical contact behavior of the interface by quantitatively analyzing how interface current-carrying characteristics change under different contact conditions. These findings offer fundamental insights for controlling the magneto-thermal behavior of the A/R interface in conditions of high-speed and high-current operation.

Diffusion in multicomponent mixed solvent electrolyte systems

Thermodynamic ideality is often assumed in diffusion calculation, implying concentrations are assumed equal to the activities with activity coefficients of one. A general set of diffusion flux and molar flux equations are developed, incorporating equilibrium thermodynamic models for non-ideal conditions in well-known non-equilibrium diffusion theory. Derivations are based on the Maxwell-Stefan friction theory with the chemical potential as the driving force. Isothermal and isobaric conditions are assumed, and the theory does not include the Soret coefficient or the Onsager formalism.In this work, Fick's law is derived from the general diffusion theory, also as a function of activity gradients. The results illustrate that concentration cannot just be substituted by activity. Using a similar approach demonstrates that the Nernst-Planck (NP) equation may be derived from the general theory incorporating terms for migration and convection. An extended NP equation is derived including the thermodynamic correction factors (TCF) to account for the non-ideality of the liquid. The derived equation shows the improvement of the self-diffusion terms and friction coefficients in the NP equation and that the TCF enhances the observed effective diffusivities.Examples of TCF are presented using the extended UNIQUAC thermodynamic model. This is done for the CO2-NaOH-monoethyleneglycol-water system, which is typically found in wet natural gas pipeline CO2 corrosion systems. pH-stabilization is classically used in the prevention of corrosion, but the results show that glycol has a noticeable effect of the diffusion on key components in the corrosion mechanism. A TCF of 0.4 to 1.3 may be expected. This indicates that the flux calculation deviates up to 60 % from the real-life scenario if ideality is assumed. The thermodynamic model may therefore improve the diffusion calculations considerably.

Degradation induced superlubricity on the rough surface of black phosphorus composite

A rough surface composed of asperities was considered as the obstacle for achieving superlubricity in traditional friction theory. Here, microscale superlubricity with the friction coefficient of 0.0086 was observed on a relatively rougher soft surface of black phosphorus (BP) composite due to the degradation of BP with oxygen and moisture via the atomic force microscopy (AFM) experiment equipped with diamond-like carbon (DLC) microsphere probe. Comparative analyses corroborated that the produced phosphorus oxides (oBP) with abundant P=O and P−OH bonds and the local graphitized amorphous carbon film at the sliding interface decreased the possibility of direct contact between original rough peaks and provided an ultra-low shear strength for achieving superlubricity. Furthermore, a certain nanoscale roughness structure on the composite surface facilitated a more reliable superlubricity state, which supplied the larger contact area and locking capillary force to hold and retain the lubricating liquid film formed by the water absorption of oBP. These findings provided fundamental insights into the nature of tribological mechanisms and suggested a new method to achieve ultra-low friction of polymer composite materials in engineering.

Numerical simulations and local entropy generation in a two-phase transcritical carbon dioxide Ranque-Hilsch vortex tube

The Ranque-Hilsch vortex tube arouses a renewed interest as a robust expansion device able to produce thermal energy separation. However, its two-phase transcritical CO2 operation remains unclear. In this work, 3D computational fluid dynamics simulations are performed using the open-source SU2 solver which key features are the implicit time integration and the real gas density-based formulation. The homogeneous equilibrium two-phase model is coupled with both the k−ω shear stress transport and the standard k−ϵ turbulence closures while a fast tabulated version of the Span and Wagner equation of state enables to compute the CO2 properties. First, the validation is performed on pressure measurements, condensation onset positions and visualizations in a transcritical CO2 nozzle available in the literature. Then, the vortex tube transcritical CO2 temperature, energy and phase separations are thoroughly investigated as well as the integral and local entropy generations due to viscous and heat dissipations. The results reveal that the temperature separation is produced below the inlet temperature at both outlets due to real gas effects. It is also shown that the energy separation is reversed as well as the available vortex tube outlet powers for heating and cooling purposes. Furthermore, higher irreversibility due to fluctuating components is unveiled near the vortex tube sharp angles at high cold mass fraction and high inlet operating pressure. Throughout this analysis, compelling arguments in favor of the friction theory for the energy separation phenomenon are also disclosed. Overall, the present work gives useful operation guidelines and sheds light on the complex phenomena at play in a Ranque-Hilsch vortex tube for transcritical CO2 heat pumps.

Viscosities of fatty acid esters: A study on various semi-empirical models

The viscosity information of fatty acid esters (FAEs) is crucial for the utilization of biodiesels. In order to accurately describe the viscosity of fluids, researchers have developed several semi-empirical models, but their different performance for FAEs has not been thoroughly discussed. This work focuses on a comprehensive comparison of several popular semi-empirical viscosity methods, including the absolute rate theory (AR), free-volume (FV), hard-sphere (HS), friction theory (FT), and entropy scaling (ES) models. Three equations of state (EoS), namely SRK, CPA, and PC-SAFT, are also selected, which represent the thermodynamic methods with varying levels of complexity and accuracy. Then, the density and viscosity of 14 saturated FAEs and 4 mixtures are calculated using the five viscosity models coupled with three EoS, and the influence of EoS performance on the viscosity results is analyzed. Special attention is paid to the viscosity models and the SRK EoS, to test the calculated viscosities with such a simple EoS. At last, considering both simplicity and accuracy, the AR and FV models can give the best overall performance for calculating the viscosity of FAE systems, and the FT model is also a potential approach.

Frictional evolution process and stability properties of Longmaxi shale under fluid injection

The frictional stability of rocks is fundamental in controlling the instability and activation of faults. Given the strong correlation between seismic events in the Sichuan Basin of China and hydraulic fracturing for shale gas extraction, we conducted a series of velocity-stepping friction experiments with Longmaxi shale from the Changning shale gas extraction block under fluid injection. The experimental results indicate that the frictional process of Longmaxi shale can be divided into four distinct stages and the effective normal stress can demonstrate the influence of injection pressure. Additionally, the phenomenon of a decreasing friction coefficient μ with increasing effective normal stress can be explained by the frictional adhesion theory and a competitive mechanism between the deformation of asperities and microscopic dilatant slip. As the injection pressure increases, the friction state of Longmaxi shale transitions from velocity-strengthening to velocity-weakening, which is beneficial for potential seismic slip. After friction, the fracture surface experiences wear, and the surface morphology of the left and right parts exhibits a symmetrical distribution. With increasing effective normal stress, the morphological evolution of fractures becomes more prominent, which is related to the variation in the effective contact area. Based on the experimental results, we propose that the uneven distribution of fluid pressure on the Longmaxi shale fracture may also contribute to the transformation of frictional stability. When studying the frictional properties of rocks under fluid injection, it is also necessary to focus on the evolution of fluid pressure distribution on the fracture surface during the frictional process.