Friction Theory Research Articles

First‐principles Investigation of Frictional Characteristics of Brucite: An Application to Its Macroscopic Frictional Characteristics

AbstractBecause sheet‐structure minerals are often observed in natural faults and have lower friction coefficients than the other common rocks and rock‐forming minerals, it has been suggested that their frictional characteristics are related to fault strength. Despite their importance for understanding fault dynamics, what controls their frictional characteristics has not been clarified yet. Because the friction coefficients of these minerals depend on the mineral species, the atomic‐scale crystal structure can be a clue for understanding the mechanism. In this study, the variation of potential energy on the brucite (0001) shear plane (potential energy surface, PES) was calculated by using first‐principles calculations based on density functional theory. The shear stress along the sliding path is calculated by computing the displacement derivative of the PES. According to the adhesion theory of friction, we found that the atomic‐scale frictional parameters obtained by using the PES could explain the macroscopic friction coefficients when taking the experimental indentation strength into account. Then, we propose how to estimate the constitutive parameter a of the rate‐ and state‐dependent friction law from the PES of sheet‐structure minerals. The estimated value is consistent with the typical range for minerals investigated by previous experiments. The difference in the PES among sheet‐structure minerals can therefore be a key property to explain their frictional characteristics such as the tendency for frictional instability of natural faults.

Challenges to Coordination: Understanding Intergovernmental Friction During Disasters

While idealized crisis response involves smooth coordination between relevant actors, friction between levels of government and between the state and civil society in responding to catastrophe may be more common. This article builds a theory of cross-level friction during and after crisis by analyzing the conditions when discord is most likely. With a medium-N dataset (N = 18) of disaster responses from, among other countries, Chile, Haiti, Japan, North America, the Philippines, and Somalia, I carry out quantitative and qualitative analysis of cases with a variety of levels of friction to investigate the conditions that lead to misalignment. Tobit regression, qualitative comparative analysis, and case studies that take into account levels of economic development, government structure, nongovernmental organization density, and levels of damage demonstrate that low levels of development, lower levels of economic costs from the crisis, and poor planning and logistical infrastructure correlate with a higher likelihood of friction between disaster response stakeholders. Although not definitive, these findings come with theoretical and practical implications as climate change makes extreme weather events and future disasters more likely and more powerful.

Phenomenology of Topochemical Kinetics and Potentialities for the Development of Kinetic Approach to the Theory of Friction

The article considers the phenomenology of the topochemical kinetics of the formation and growth of adhesion cores, as one of the main processes of the kinetic approach in the theory of fracture of materials during friction. The basic provisions of the models and laws of the formation and growth of setting nuclei are investigated. Peculiarities of ideas about the processes of nucleation and the laws of their growth by various authors are considered, questions are raised that require further research in the development of mathematical models of topochemical kinetics.

Zwanzig Theory Application for Bromide and Iodide Ions in Pure Solvents at 25°C

The Zwanzig theory of dielectric friction has been applied to trimethylsulfonium ion, bromide and iodide ions in different solvents at 25°C. The radius values which obtained from the slope (hydrated radius) and that one which obtained from the intercept (hydrodynamic radius) were calculated and the reason for such difference discussed on the basis of the assumptions of Zwanzig theory.

Zwanzig Theory Application for Bromide and Iodide Ions in Pure Solvents at 25°C

The Zwanzig theory of dielectric friction has been applied to trimethylsulfonium ion, bromide and iodide ions in different solvents at 25°C. The radius values which obtained from the slope (hydrated radius) and that one which obtained from the intercept (hydrodynamic radius) were calculated and the reason for such difference discussed on the basis of the assumptions of Zwanzig theory.

Dynamic modeling of a gear transmission system containing damping particles using coupled multi-body dynamics and discrete element method

The reduction in vibration in gear transmission systems is an engineering task. Particle damping technology attenuates vibration by means of friction and inelastic collisions between damping particles. This study proposes a dynamic model for a spur gear transmission system that contains damping particles inside the holes on gear bodies, using two-way coupling with multi-body dynamics and discrete element method. The equations of motion for the multi-body system are derived using Euler–Lagrange formalism. The discrete element method with a soft contact approach is used to model the dynamic behavior of damping particles. Hertzian contact theory and Coulomb friction theory are applied to modeling contacts. The effects of particle radius, coefficient of friction and restitution coefficient on the dynamic characteristics are explored. Numerical results show that vibration in the transmission is appreciably attenuated by the particle damping mechanism and that the contact friction, and not contact damping, dominates the energy dissipation of the multi-body system in such a centrifugal scenario.

Friction and Wear Study on Friction Pairs with a Biomimetic Non-smooth Surface of 316L Relative to CF/PEEK under a Seawater Lubricated Condition

Current studies of a seawater axial piston pump mainly solve the problems of corrosion and wear in a slipper pair by selecting materials with corrosion resistance, self-lubrication, and wear resistance. In addition, an appropriate biomimetic non-smooth surface design for the slipper pair can further improve the tribological behavior. In this paper, 316L stainless steel and CF/PEEK were selected to process the upper and bottom specimens, and the biomimetic non-smooth surface was introduced into the interface between the friction pair. The friction and wear tests were performed on a MMD-5A tester at a rotation speed of 1000 r/min and load of 200 N under seawater lubricated condition. The results indicate that the main friction form of the smooth surface friction pair corresponds to abrasive wear and adhesive wear and that it exhibits a friction coefficient of 0.05–0.07, a specimen temperature of 56 °C, a high wear rate, and surface roughness. Pits on the non-smooth surface friction pairs produced hydrodynamic lubrication and reduced abrasive wear, and thus the plowing effect is their main friction form. The non-smooth surface friction pairs exhibit a friction coefficient of 0.03–0.04, a specimen temperature of 48 °C, a low wear rate, and surface roughness. The study has important theoretical significance for enriching the lubrication, friction, and wear theory of a seawater axial piston pump, and economic significance and military significance for promoting the marine development and the national defense military.

Mechanical Behavior of Hybrid Soil Nail-Anchor System

Prestressed soil-nail system has two reinforcing components: steel bar and PC strands. The steel bar with relatively less elongation yields earlier than PC strands. Thus, yield displacements of these two components should be matched to maximize the design load (capacity) of prestressed soil-nail. To achieve this, PC strands need to be prestressed before applying pullout load. In this study, load transfer mechanisms of soil-nail and prestressed soil-nail were determined based on skin friction theory and load transfer theory. The load transfer was derived analytically based on the assumption that skin friction at the interface was fully mobilized. It was then compared with results from field pullout tests performed to identify in-situ load transfer mechanism. Additionally, optimum prestress level required to maximize the pullout loading capacity was evaluated and compared with those obtained from field tests.

Fabrication of the laser textured nickel surface and its tribological property under the water lubrication

Friction is one of the main causes of mechanical component failure and material waste. It is known from the friction theory that changing the roughness of the surface of the material can change the friction property of the material. Laser surface texturing is a good method for constructing a rough surface. In the experiment, the texture of the circular pits with different areal densities was constructed on the nickel surface. The coefficient of friction of the circular pit under the water-lubricated friction condition was kept at about 0.17, while the untreated metal nickel under the same conditions exceeds 0.65. The circular pit texture improves the frictional properties of the nickel surface.

Caracterización experimental y teórica de conexiones metálicas asimétricas susceptibles a falla de pernos.

This article describes and proposes a model of the force versus elongation behaviour of asymmetrical connections prone to bolt failure when subjected to quasi-static axial load. 14 connections were assembled with one bolt varying the distance from the bolt to the edge of the clamped zone, and 14 connections were assembled with two bolts varying the distance between bolts. Results show that the axial force versus elongation behaviour of the connection is approximately trilinear, that while the connection stiffness is not sensitive to the bolt location in the clamped zone, the plastic elongation of the connection is. The model shows that the stiffness of the asymmetrical connection can be predicted from the stiffness of the connection components assessed by means of spring elements or beam elements, and that the load capacity of the connection can be predicted using the dry friction theory of Coulomb and the shear bolt capacity.

HIGH-FREQUENCY VIBRATIONS IN THE CONTACT OF BRAKE SYSTEMS

The processes and interactions that occur due to friction in the brake are still not fully understood today. In particular, the processes in the boundary layer have been shown to be responsible for a variation in the coefficient of friction and the associated wear. Dynamic contact structures in the boundary layer are made responsible for this behaviour. Vibration analyses on brake systems usually concentrate on operating vibrations analyses of the brake system components. In order to gain an understanding of the cause of such phenomena and oscillations, it is necessary to understand the mechanism of origin in the contact area. Therefore, highly specialized tribotesters have been developed at the Institute for Dynamics and Vibration to investigate the dynamic processes through experiments and simulative investigations. It can be shown that ultrasonic frequencies are generated in the friction boundary layer. These ultrasonic frequencies could not only be found in pin-on-disc testers, but also in complete vehicle brake systems. It was possible to identify that the vibration signatures between 20 and 80 kHz depend on a whole series of different influencing variables and have no dependence on the testing machine. In connection with the friction theories, it is an open question whether these oscillations can be made responsible as a kind of trigger pulse for the squealing of 1 to 20 kHz. In addition, it is a problem that the parking sensors installed in the vehicle work on an ultrasonic basis in the same frequency range and can therefore lead to failure due to these frequencies.

Numerical and theoretical study of bi-planar failure in footwall slopes

Bi-planar failure is the commonest type of failure in steep and high footwall slopes. This paper presents an investigation of the bi-planar failure mechanism and a stability analysis model for footwall slopes based on the study of eleven diabase mines in Hunyuan County, Shanxi Province, China. First, a detailed investigation of the site and tests were carried out to obtain a geological model and calculation parameters for the slope. Then, the failure process in footwall slopes was investigated by a trigon approach performed using the Universal Distinct Element Code (UDEC) software package. A mechanism was then obtained for bi-planar compression–shear failure by combining the results obtained for the stress, displacement, and crack development. Subsequently, based on the limit equilibrium and frictional plasticity theories, a new columnar mechanical model was proposed for bi-planar footwall slope failure. The results demonstrate that the UDEC trigon approach was well suited to simulating bi-planar failure in steep and high footwall slopes. Employing this approach, a sliding failure surface that initiates, develops, and propagates in the discontinuity and intact rock could be correctly captured and the evolution of the damage in the toe of the slope could be quantitatively investigated. The results also indicate that shear failure first occurs at persistent discontinuities and then compression–shear failure occurs in the intact rocks. In addition, the failure surface of the rock emanates from the toe of the slope, is oriented upwards at an angle to the persistent discontinuity thus forming the through sliding surface (this angle can be determined using frictional plasticity theory). The critical heights and safety factors of footwall slopes could be readily obtained by employing this new columnar mechanical model giving results that are consistent with the results of numerical simulations. Furthermore, the results of a parameter-sensitivity analysis show that the dip angle of the toe breakout surface increases as the slope angle increases. However, the angle between the toe breakout and internal shear surfaces remains unchanged as the slope angle increases. Moreover, the critical height of the footwall slope decreases linearly as the slope angle increases. The method proposed provides theoretical guidance for the stability analysis of steep and high footwall slopes. The results produced should also help engineers to gain a better understanding of the mechanisms of bi-planar failure in such rock slopes.

Fault slip envelope: a new parametric investigation tool for fault slip based on geomechanics and 3-D fault geometry

Abstract. By combining a 3-D boundary element model, frictional slip theory, and fast computation method, we propose a new tool to improve fault slip analysis that allows the user to analyze a very large number of scenarios of stress and fault mechanical property variations through space and time. Using both synthetic and real fault system geometries, we analyze a very large number of numerical simulations (125 000) using a fast iterative method to define for the first time macroscopic rupture envelopes for fault systems, referred to as “fault slip envelopes”. Fault slip envelopes are defined using variable friction, cohesion, and stress state, and their shape is directly related to the fault system 3-D geometry and the friction coefficient on fault surfaces. The obtained fault slip envelopes show that very complex fault geometry implies low and isotropic strength of the fault system compared to geometry having limited fault orientations relative to the remote stresses, providing strong strength anisotropy. This technique is applied to the realistic geological conditions of the Olkiluoto high-level nuclear waste repository (Finland). The model results suggest that the Olkiluoto fault system has a better ability to slip under the present-day Andersonian thrust stress regime than for the strike-slip and normal stress regimes expected in the future due to the probable presence of an ice sheet. This new tool allows the user to quantify the anisotropy of strength of 3-D real fault networks as a function of a wide range of possible geological conditions and mechanical properties. This can be useful to define the most conservative fault slip hazard case or to account for potential uncertainties in the input data for slip. This technique therefore applies to earthquake hazard studies, geological storage, geothermal resources along faults, and fault leaks or seals in geological reservoirs.

Study on molecular dynamics of the effect of defects on the friction properties of single crystal metals

In order to study the effect of vacancy defects in different directions and concentrations on the friction force of single crystal iron, Using the process of sliding friction monocrystalline iron matrix with diamond hemispheric probe as the research object, a molecular dynamics model was established and simulated. The results of the study indicate that：The interface barrier potential at the defect of single crystal iron increases the average friction force at the defect, and the friction force of single crystal iron at the defect is greater than that of perfect single crystal iron；The average friction force of single crystal iron increases with the increase of defect concentration; The above research results enrich the theory of friction and wear between the surfaces of the micronanoscale components and provide sufficient theoretical basis and guidance for the design and development of micronanoscale devices.

Modelling of substance interactions in electrochemical membrane processes by basis of the friction theory

An improved mathematical model for calculating the transfer of substances in electrochemical membrane processes based on the Spiegler friction model is developed and presented. This model differs from those presented in the literature in that it takes into account the combined effect of pressure and electric field on the transfer of particles of the solute and solvent and allows calculating the friction coefficients of the interaction of anions, cations, solvent and membrane pore walls among themselves. Calculated friction coefficients can be used in the theoretical calculations and the prediction of change over time of the kinetic parameters of baromembrane, electromembrane and electrobaromembrane separation processes of industrial solutions in various industries.

On ensuring joint tightness on the basis of technological induction

Introduction. Some theoretical and engineering aspects of sealing joints through magnetostriction, as well as the polarization of the sealed medium under the external induction are considered. Control of surface roughness of joined parts to increase the joint density when induced by an external magnetic field is studied. The creation of electromagnetic barriers for the migration of molecules of the sealed medium through a sealer is considered. The work objective is to validate the technological conditions for sealing movable joints in the cases described above. Materials and Methods. The conditions for ensuring the joint density are shown as a result of the contact problem solution and as a factor determined by the molecular-mechanical friction theory. Geometric, operational and tribological conditions of joint tightness are accepted. Damping properties of the fixed friction contact are determined by the molecular component. The theoretical and calculated analysis of the factors affecting the joint density is presented. Decrease in the smoothing depth, reduction of the ratio of transverse and longitudinal roughness steps, and increase in the contact area are indicated as the target results of the process preparation of the surfaces of the joint parts. Loss of tightness is defined as a specific transfer of molecules. They are transferred to the area of the joined surfaces or migrate freely through the sealer at the stages of sorption, diffusion and desorption. The predominance of any stage occurs when the entropy changes, and it is due to temperature and pressure. The schemes of sealing joints in the controlled magnetic field and of the dependence of magnetostriction and magnetostrictive stresses on the magnetic field strength are visualized. Research Results. The stability of sealers in highly volatile and gaseous media during their polarization and magnetization in an external field is experimentally investigated. In the former case, the magnetic induction vector was first oriented perpendicular to the longitudinal axis of the joint. A drop in the magnitude of the magnetic flux was observed when the compound was under the on-load operation for 268 hours. The total operating time of the joint was 1070 hours. If the magnetic induction vector was oriented longitudinally to the shaft axis, the operating time to the correction of the field strength was 87 hours. In the gas environment, the operating time of the connection to the adjustment of the tension was 187 hours with a total operating time of 935 hours. Discussion and Conclusions . The penetrating ability of pressurized media decreases in the “gas - vapor - liquid” series. It depends on the temperature at the joint contact. Depressurization can be traced through changes in the magnetic flux determined by the intrinsic magnetic permeability of the molecules of the sealed medium as they penetrate the interface surface. To increase tightness, it is required to suppress the activity of molecules. For this purpose, ionization and induction in the constant and alternating magnetic field with the intensity of <60 kA/m are used.

Spring amplification and dynamic friction modelling of a 2DOF/2SDOF system in an electromagnetic vibration energy harvester – Experiment, simulation, and analytical analysis

Abstract A cantilever beam-based vibration energy harvester is generally preferred due to its simplicity and effectiveness as compared to a spring mass system. This paper analyses the use of a spring to amplify the performance of a conventional single degree of freedom (SDOF) cantilever beam-based vibration energy harvester. A spring was introduced to modify the conventional SDOF design into a two single degree of freedom (2SDOF) system and a two degree of freedom (2DOF) system. The motion of the spring was restricted in the vertical motion using a slider and a linear guide rail fixed to the vibrating base, hence introducing a dynamic friction into the system. Both designs were analysed under three different cases to observe the effect of natural frequency reduction on the frequency bandwidth and power harvested by each design. The vibration-friction interaction in the designs was modelled based on the concept of relative motion. Two different friction theories were applied and verified with simulation and experiment. It was shown that the stick condition would not occur in a SDOF system with a dynamic friction interaction. It was also found that it is possible to tune the friction force of a dynamic friction surface to induce a favourable output at the isolation frequencies of a 2DOF system. Analysis shows that the 2DOF design displayed a larger power density than the conventional SDOF design below a certain natural frequency value, being 78.1% higher at 9.5 Hz. The power densities of the 2SDOF design were almost similar to the SDOF design. However, the 2SDOF design displayed a significant drop in power when under the condition of matched natural frequencies. Nevertheless, the frequency bandwidth of the 2SDOF design can be improved by tuning its two resonant peaks closer to each other.

Anisotropic Combined Dry Friction in Problems of Pneumatics’ Dynamics

Traditionally used shimmy models assume vanishing slip at each point of a roadwheel contact spot, at the same time the observed instable wheel motion observed at unsteady rolling stages with significant sliding could not be described by traditional theories. Thus, a principally new model of the wheel shimmy is required to be consistent with such regimes. A new model of a rolling wheel accounting for the dry friction under the conditions of combined kinematics (i.e. simultaneous sliding, spinning and rolling) as well as for contact pressure distributions in pneumatic tires could become a background for various engineering methods of prediction of the shimmy appearing at unsteady rolling regimes. The proposed model of a pneumatic wheel’s motion is based on the improved dry friction theory accounting for the friction anisotropy; the Coulomb law is assumed for each contact spot’s point where the summary slip velocity is resulted by the simultaneous sliding and spinning, and the contact pressure could be obtained from the finite element simulation of quasistatic tire deforming. The theory of the coupled dry friction is improved by accounting for the anisotropy of the friction factor represented in a form of the second-rank tensor. The general formulation for the resultant vector of dry friction forces, dry friction torque and the rolling friction couple are obtained. The contact pressure for a typical tire is computed numerically, its polynomial interpolation is introduced, and the coefficients of the approximate model of the dry friction are obtained. The constructed model allows an efficient accounting for the dry friction effects on the rolling stability as well as the real contact pressure distribution; thus, it can be interpreted as the second approximation improving the model of the shimmy of quasi-rigid wheel.

Continuum Modeling of Pressure‐Balanced and Fluidized Granular Flows in 2‐D: Comparison With Glass Bead Experiments and Implications for Concentrated Pyroclastic Density Currents

AbstractGranular flows are found across multiple geophysical environments and include pyroclastic density currents, debris flows, and avalanches, among others. The key to describing transport of these hazardous flows is the rheology of these complex multiphase mixtures. Here we use the multiphase model MFIX in 2‐D for concentrated currents to examine the implications of rheological assumptions and validate this approach through comparison to experiments of both frictional and fluidized flows made of glass beads (Sauter mean grain‐size of 75 μm). Because the rheology of highly polydisperse, highly angular, polydensity granular mixtures is poorly known, we focus on simplified monodisperse or bidisperse mixtures described by the frictional flow theory of Schaeffer (1987, https://doi.org/10.1016/0022‐0396(87)90038‐6) and Srivastava‐Sundaresan, often referred to as the Princeton model (Srivastava & Sundaresan, 2003, https://doi.org/10.1016/S0032‐5910(02)00132‐8). We show that simulations including the latter model replicate well the flow shape, kinematics, and pore fluid pressure that match well‐constrained dam‐break experiments of initially fluidized or pressure‐balanced granular flows. Simulations reveal that pore fluid pressure is intrinsically modulated by dilation and compaction of the flow and hence can be generated in concentrated pyroclastic density currents. We use these simulations to interpret basal pore pressure signals from local flow properties (mixture density, solid velocity, and pore fluid pressure). Rheological changes retard these simulated flows considerably near the predicted runout, but most continuum models cannot inherently predict a zero velocity. We suggest an inertial number parameter that can be used to approximate deposition, and this approach could be a valuable tool used to validate simulations against natural pyroclastic current examples.

An optimum indeterminate strut-and-tie model for reinforced concrete corbels

The failure behavior of a reinforced concrete corbel is complicated due to the shear span-to-effective depth ratio, reinforcement patterns, load conditions, and material properties. In this study, an optimum first-order indeterminate strut-and-tie model that reflects all characteristics of the failure behavior is proposed for the rational design of reinforced concrete corbels with a shear span-to-effective depth ratio of less than 1.0. A load distribution ratio that transforms the indeterminate strut-and-tie model into a determinate model is also developed to help structural designers design reinforced concrete corbels using the strut-and-tie model methods of current design codes. For the development of the load distribution ratio, a material nonlinear finite element analysis of the proposed first-order indeterminate strut-and-tie model was conducted repeatedly by changing the combination of primary design variables of the corbels. To examine the validity of our results, the ultimate strengths of 294 reinforced concrete corbels tested to failure by other investigators were predicted using the proposed strut-and-tie model with the load distribution ratio, the existing determinate strut-and-tie models representing arch and truss load transfer mechanisms, and the American Concrete Institute 318 conventional design method based on a shear friction theory. The ultimate strengths predicted by the proposed strut-and-tie model agreed fairly well with the experimental results. The ratio of the experimental strength to the predicted strength (and coefficient of variation) was 1.09 (28.0%), implying that the proposed strut-and-tie model can represent the load transfer mechanisms of corbels most appropriately.