Frictional Sliding Research Articles

Stability of Frictional Sliding With the Coefficient of Friction Depended on the Temperature

Friction-induced instabilities can be caused by different separate mechanisms such as elastodynamic or thermoelastic. This paper suggests another type of instability due to the temperature dependency of the coefficient of friction. The perturbations imposed on the surface temperature field during the frictional sliding can grow or decay. A stability criterion is formulated and a case study of a brake disk is performed with a simple model without including effects of transforming layer and chemical/physical properties change with temperature. The disk is rigid and the coefficient of friction depends on temperature. We show that the mechanism of instability can contribute to poor reproducibility of aircraft disk brake tests reported in the literature. We propose a method to increase the reproducibility by dividing the disk into several sectors with decreased thermal conductivity between the sectors.

Effect of Surface Hard Layer and Forging Conditions on the Resistance of Plastic Deformation of Hot Forging Tools

Tool damages including plastic deformation and wear are affected by forging load, thermal load and frictional slide applied to tool surface. Plastic deformation of forging tools proceeds in the tool corer owing to elevated temperature, high contact pressure and severe frictional slide. Hard layers on the tool surface increase plastic deformation resistance and thermal resistance. The optimal design of hard layer structure reduces the tool damage and improves tool life. Temperature and equivalent strain of forging tools are influenced by friction shear factor, contact thermal conductance and contact time between the tool and the workpiece. At the friction shear factor of less than 0.4, equivalent strain of the tool is reduced. At the friction shear factor of approximately 0.4 or greater, equivalent strain increases sharply and concentrates in the vicinity of the surface hard layer. This tendency becomes more significant when the contact time between the tool and the workpiece increases. Equivalent strain is reduced by low workpiece temperature.

Slow Cracklike Dynamics at the Onset of Frictional Sliding

We propose a friction model which incorporates interfacial elasticity and whose steady state sliding relation is characterized by a generic nonmonotonic behavior, including both velocity weakening and strengthening branches. In 1D and upon the application of sideway loading, we demonstrate the existence of transient cracklike fronts whose velocity is independent of sound speed, which we propose to be analogous to the recently discovered slow interfacial rupture fronts. Most importantly, the properties of these transient inhomogeneously loaded fronts are determined by steady state front solutions at the minimum of the sliding friction law, implying the existence of a new velocity scale and a "forbidden gap" of rupture velocities. We highlight the role played by interfacial elasticity and supplement our analysis with 2D scaling arguments.

Thermo-mechanical Research on Frictional Sliding between Elasto-plastic Rough Solid and Rigid Flat

A thermo-mechanical coupling model for a rigid flat plane and an elastic-plastic rough surface based on three-dimensional fractal theory is established.The model considers the interaction between asperities,and integrates the heat flux coupling on the contact interface.To obtain the transient stress/temperature distribution of the rough solid,the thermo-mechanical problem under this 3D model is solved by using the nonlinear multiphysics field of the ANSYS software.The numerical results from the analysis and simulation show that the maximum contact temperature of the rough surface increases quickly in the initial sliding due to the velocity mutation,but the temperature rises slowly during the constant sliding process.The results also show that the VonMises equivalent stress distribution of the rough surface is very uneven.And a tension stress zone exists at a certain depth from the contact surface in the rear of the contact asperity.The results demonstrate that the VonMises equivalent stress of the contact surface,the maximum tensile stress and the layer thickness of the tensile stress increase obviously in transient sliding contact and forming of instantaneous flash temperature.These results provide a theoretical basis for crack initiation and propagation.

Modeling and Analysis of a Frictional Sliding Soft Fingertip, and Experimental Validations

We have proposed a dynamic model of a soft fingertip to investigate its sliding motion on a plane with friction. The fingertip is comprised virtually of a finite number of elastic, compressible and bendable cantilevers whose free ends act as contact points. Moreover, we utilize virtual linkage spring–damper elements between the contact points to represent interactions between neighboring cantilevers on the contact surface. By introducing Coulomb's law into each contact point, we are able to capture the frictional characteristic during sliding motions of the fingertip, especially stick–slip motions. We also present experimental results to validate this model.

An engineered infilled frame: Behavior and calibration

The results of an experimental investigation on some engineered infilled frames with high ductility and adjustable strength are presented in this paper. To achieve an engineered infilled frame, an element is added to the infill, called Frictional Sliding Fuses (FSFs). The fuse acts before infill corner crushing and controls the infill so that it is not overloaded. Consequently, it increases the deformation capacity and decreases the strength deterioration. An FSF has a frictional nature, based on which the infill has more appropriate hysteresis cycles, leading to more structural energy damping during earthquakes. The results show that the engineered infilled frames have adjustable strength, as well as high ductility and damping.

Cracklike Processes within Frictional Motion: Is Slow Frictional Sliding Really a Slow Process?

AbstractThe dynamics of frictional motion have been studied for hundreds of years, yet many aspects of these important processes are not understood. First described by Coulomb and Amontons as the transition from static to dynamic friction, the onset of frictional motion is central to fields as diverse as physics, tribology, mechanics of earthquakes, and fracture. We review recent studies in which fast (real-time) visualization of the true contact area along a rough spatially extended interface separating two blocks of like material has revealed the detailed dynamics of how this transition takes place. The onset of motion is preceded by a discrete sequence of rapid cracklike precursors, which are initiated at shear levels that are well below the threshold for static friction. These precursors systematically increase in spatial extent with the applied shear force and leave in their wake a significant redistribution of the true contact area. Their cumulative effect is such that, just prior to overall sliding of the blocks, a highly inhomogeneous contact profile is established along the interface. At the transition to overall motion, these precursor cracks trigger both slow propagation modes and modes that travel faster than the shear wave speed. Overall frictional motion takes place only when either the slow propagation modes or additional shear cracks excited by these slow modes traverse the entire interface. Surprisingly, in the resulting stick–slip motion, the surface contact profile retains the profile built up prior to the first slipping event. These results suggest a fracture-based mechanism for stick–slip motion that is qualitatively different from other descriptions.

Dynamic Transitions in Molecularly Thin Liquid Films under Frictional Sliding

The friction properties of the molecularly thin films of an asymmetric ether, 1,3-dimethylbutyl hexadecyl ether (DBHE), confined between mica surfaces were investigated using the surface forces apparatus. Kinetic friction was measured as a function of normal load and sliding velocity, and the static friction (stiction) was measured as a function of normal load and surface stopping time. Kinetic friction measurements exhibited unstable sliding dynamics: the friction force exhibited cyclic bumps and valleys in the sliding velocity range from about 10(-2) to 1 microm/s, but above and below the velocity range, smooth sliding was observed. Stop-start experiments showed a stiction spike when surface stopping time exceeded a characteristic nucleation time, indicative of the static friction state at very low sliding velocity. These results imply that the friction of the confined DBHE film has at least three responsible friction states--static friction and two different kinetic friction states--depending on the sliding velocity. The unstable sliding (bumps and valleys of the friction force) reflects the dynamic transition between two different kinetic states. The different friction states and their transitions are discussed on the basis of the recent experiments and theories of "inverted" stick-slip friction.

Dynamics of Precursors to Frictional Sliding

We measure the spatial and temporal behavior of the true contact area A along a rough spatially extended interface between two blocks in frictional contact. Upon the application of shear the onset of motion is preceded by a discrete sequence of cracklike precursors, which are initiated at shear levels that are well below the threshold for static friction. These precursors arrest well before traversing the entire interface. They systematically increase in length with the applied shear force and significantly redistribute the true contact area along the interface. Thus, when frictional sliding occurs, the initially uniform contact area along the interface has already evolved to one that is highly nonuniform in space.

Thermoelastic Dynamic Instability (TEDI) in Frictional Sliding of a Half-Space Against a Rigid Non-Conducting Wall

In the sliding of half-spaces with constant friction coefficient, two classes of instabilities are well known: thermoelastic instability (TEI), which occurs for sufficiently long wavelengths and Dynamic Instability (DI), which happens at sufficiently high friction coefficient, and whose growth factor increases linearly with wave number. Although the two phenomena look therefore quite distinct, their coupling is discussed here for an elastic and conducting half-space sliding against a rigid and non-conducting wall. The coupling between thermal and dynamic effects is not always negligible. In fact, surprisingly, new areas of instability are found, called thermoelastic dynamic instabilities (TEDI), similar to TEI at high speeds and DI at low speeds. TEDI lowers the critical speed and friction coefficient in many conditions even to zero. At low speeds, TEDI is ill-posed as DI at small wavelengths, and hence a regularized friction law like the Rice-Ruina one would probably be needed to correct the results.

Characteristics of Frictional Sliding Motion in Releasing Manipulation

Focusing on freely frictional sliding motion and based on mathematical analysis and physical concepts, it is clarified that the translational and rotational motions stop simultaneously, and the direction of final motion depends on the final configuration and geometric properties of an object but is independent of initial velocity. One extreme case of initially translation-dominant motion is intensively investigated with simplified approach. A series of important properties and motion monotonicity of sliding motion are obtained. Based on the above results, an inverse problem to determine the necessary initial translational and rotational velocity becomes very easy and straightforward.

Precursors for rock fracturing and failure—Part I: IRR image abnormalities

There are many precursors, including the abnormality of infrared radiation (IRR), for rock fracturing and failure. As the comprehensive effect of rock thermoelasticity and rock friction, the study of the IRR abnormality of loaded rock, as one of the important issues of remote sensing rock mechanics (RSRM), is facilitated by the fast development of IR remote sensing imaging technology. In view of energy input and consumption by the loading system, comprised of loader, rock and air, the mechanism of surface IRR from loaded rock is studied. The concepts that surface IRR is the comprehensive effect of a series of physical–mechanical processes inside loaded rock and that the thermoelastic effect and the frictional–thermal effect are two of the main mechanisms are presented here. Based on retrospective investigation of the fundamental experiments on RSRM during the past decade, it is concluded that there are two kinds of IRR abnormality as precursors of rock fracturing and failure: IRR image abnormality and IRR temperature curve abnormality. The spatial–temporal evolution of abnormal surface IRR images of loaded rock in a condition of uniaxial stress, compressive shear, biaxial stress, frictional slide and impact is systematically analyzed. The fact that large IRR can occur in the fracturing center of compressively loaded and shearing fractured strong and brittle rock is also revealed. Finally, the relation between rock stress and IRR temperature are studied based on thermomechanical coupling theory for solid materials. It is concluded that IRR image abnormalities are important precursors for rock fracturing and meaningful for the forecast of rockbursts and tectonic earthquakes.

Thermal-rheological structure of the lithosphere beneath Jiyang Depression: Its implications for geodynamics

Jiyang Depression, located in the southeast Bohai Bay Basin, has the geomorphologic framework of multiple uplifts intervening with sags. Combined the abundant geo-temperature data and thermo-physical parameters of rock samples derived from oil and gas exploration during the past years, with geothermal approaches, here we investigate the lithospheric thermal regime of this depression. Consequently, based on the obtained thermal structure of the lithosphere, along with rheological modeling, the lithospheric rheological profiles of Jiyang Depression are then determined. Our results show that the temperature at the bottom of sedimentary cover within depression varies from 129℃ to 298℃, accompanied with the basement heat flow ranging between 54.3 and 60.5 mW/m 2 ; and 406℃－436℃ for temperature at the bottom of the upper crust, along with heat flow varying from 47.7 to 52.6 mW/m 2 ; while the temperature at the bottom of the middle crust is between 537℃ and 572℃, as well as heat flow ranging from 41.3 to 56.3 mW/m 2 . The temperature at Moho ranges from 669℃ to 721℃, the heat flow derived from mantle is between 38.1 and 43.1 mW/m 2 , and calculated thickness of the thermal lithosphere beneath depression varies from 71 to 90 km. Lithospheric thermal regime is a close correlation with such factors as crustal thickness and surface heat flow, etc. Usually, the larger the surface heat flow, the larger the deep temperature and heat flow within lithosphere, and the thinner the thermal lithospheric thickness. This high thermal regime of the lithosphere in Jiyang Depression is thought to be related to Cenozoic back-arc spreading during the western Pacific plate subduction into Eurasian continent. Lithospheric rheological modeling shows that the lithosphere in Jiyang Depression is characterized by its distinct rheological stratification as follows: The upper and most part of the middle crust are of brittle, while the lower crust and the lower part of middle crust are all ductile, and lithospheric mantle is dominated by the ductile layer. Additionally, lateral rheological heterogeneities exist in the depression, and the lithospheric strength of sags within depression differs much from each other. The total lithospheric strength of Jiyang Depression is between 1.52 and 2.16×10 12 N/m, effective elastic thickness ( T e ) of the lithosphere in Jiyang Depression is about 24 km, approximating to the thickness of mechanically strong crust (MSC). We suggested that the dehydration of minerals in the subducting zone, along with upwelling of hot materials in the mantle wedge during subduction and back-arc spreading, results in the partial melting at the bottom of curst, which triggers magma intrusion and underplating. This geodynamics process maybe is the reason for the reduction of lower crustal viscosity for ductile flow. Lithospheric rheological stratification controlling the differential deformation styles of brittle fracture or frictional slide in the upper crust and ductile flow in the middle and lower crust, accounts for the basin formation and evolution of Jiyang Depression during Cenozoic.

Finite Element Simulation of Dynamic Instabilities in Frictional Sliding Contact

This paper describes tools for numerical modeling which enable the understanding of the appearance of vibrations of a structure generated by the frictional contact between two bodies (the excitation source being friction). The dynamic finite element code PLASTD is used to reproduce transitory phenomena generated at the contact interface. This code includes contact and friction algorithms based upon a formulation which uses Lagrange multipliers. A numerical study of the dynamic response of a 2D mechanical model composed of a deformable body in relative translation and unilateral contact with Coulomb friction with a rigid surface is presented. The steady sliding solution is generically unstable and leads to a dynamic response which leads to the generation of instabilities characterized by the appearance of steady-state pulses. It is important to notice that those instabilities appear even with a constant friction coefficient of Coulomb. These simulations provided the local contact conditions (kinematics, tribological state, contact stresses, etc). The kinematics shows the existence of local impacts and sliding at high frequencies. Furthermore, local contact normal stress is found to be much higher than that expected for a smooth surface. Finally, a 3D simulation of brakes is carried out, focusing on the vibrations of the disk and the brake pad which produce noise and are due to the interface instabilities.

The Analysis of Frictional Sliding Behavior on High-Tension Bolted Joints Using the Finite Element Method

The Analysis of Frictional Sliding Behavior on High-Tension Bolted Joints Using the Finite Element Method

Particle Dynamics Simulations of Rate- and State-dependent Frictional Sliding of Granular Fault Gouge

Recent simulations using the particle dynamics method (PDM) have successfully captured many features of natural faults zones as illuminated in laboratory studies. However, 2-D simulations conducted on idealized assemblages of particles using simple elastic-frictional contact laws, yield friction values considerably lower than natural materials, and lack time- and velocity-dependent changes in strength that influence dynamic fault slip. Here, preliminary results of new PDM simulations are described, in which particle motions are restricted as a proxy for particle interlocking and out of plane contacts, and time-dependent contact healing is introduced to capture temporal strengthening of granular assemblages. Frictional strength is increased, and in the absence of interparticle rolling, can attain values observed in the laboratory. The resulting mechanical behavior is qualitatively similar to that described by empirically-based rate-state friction laws, providing new physical insight into the discrete mechanics of natural faults.

Frictional Sliding of Microcracks under Compression

It is of interest to understand damage and failure mechanisms of microcracks and their evolution as a function of loading history, especially in the case of complex loading. Owing to their superior mechanical and physical properties, carbon nanotubes (CNTs) seem to hold a great promise as an ideal reinforcing material for composites of high-strength and low-density. HOWEVER, In most of the experimental results, only modest improvements in the strength and stiffness have been achieved by incorporating carbon nanotubes in polymers. There are many factors that influence the overall mechanical property of CNT-reinforced composites, e.g. the weak bonding between CNTs and matrix, the waviness and agglomeration of CNTs. In the present paper, we use the Mori-Tanaka method to evaluate the effect of these factors on the moduli of CNTs-CNT-reinforced composites. It is established that the waviness and agglomeration may significantly reduce the stiffening effect of CNTs, while the interface between the matrix and CNTs influence the moduli of CNTs-reinforced composites little.In this paper, the frictional sliding of microcracks under complex triaxial loading is analyzed, and the obtained results are incorporated into the constitutive relation of microcrack-weakened brittle materials.

Vibration and Stability of Frictional Sliding of Two Elastic Bodies With a Wavy Contact Interface

Abstract The stability of steady sliding, with Amontons-Coulomb friction, of two elastic bodies with a rough contact interface is analyzed. The bodies are modeled as elastic half-spaces, one of which has a periodic wavy surface. The steady-state solution yields a periodic set of contact and separation zones, but the stability analysis requires consideration of dynamic effects. By considering a spatial Fourier decomposition of the vibration modes, the dynamic problem is reduced to a singular integral equation for determining the eigenvectors (modes) and eigenvalues (frequencies). A pure imaginary root for an eigenvalue corresponds to a standing wave confined to the interface, while a positive/negative real part of the eigenvalue indicates instability/dissipation. A complex eigenvector indicates a complex mode of vibration. Two types of modes are considered—periodic symmetric modes with period equal to the surface waviness period and periodic antisymmetric modes with the period equal to twice the surface waviness. The singular integral equation is solved by reducing it to a system of linear algebraic equations using a Jacobi polynomial series and a collocation method. For the limit of zero friction it can be demonstrated analytically that the problem is self-adjoint and the eigenvalues, if they exist, are pure imaginary (no energy dissipation). These roots are found for a wide range of material properties and ratios of separation to contact zones lengths. For the limiting case of complete contact, the solution found corresponds to a superposition of two slip waves (generalized Rayleigh waves) traveling in opposite directions and forming a standing wave. With increasing separation zone length, the vibration frequency decreases from the slip wave frequency to the smaller surface wave frequency of the two bodies. With a nonzero separation zone, solutions can exist for material combinations which do not allow slip waves. For nonzero friction and sliding velocities, unstable solutions are found. The degree of instability is proportional to the product of the friction coefficient and the sliding velocity. These instabilities may contribute to the formation of friction-induced vibrations at high sliding speeds.

Stabilization of Frictional Sliding by Normal Load Modulation

This paper presents the stability analysis of a system sliding at low velocities (<100 μm⋅s−1) under a periodically modulated normal load, preserving interfacial contact. Experiments clearly evidence that normal vibrations generally stabilize the system against stick-slip oscillations, at least for a modulation frequency much larger than the stick-slip one. The mechanical model of L. Bureau, T. Baumberger, and C. Caroli validated on the steady-state response of the system, is used to map its stability diagram. The model takes explicitly into account the finite shear stiffness of the load-bearing asperities, in addition to a classical state and rate-dependent friction force. The numerical results are in excellent quantitative agreement with the experimental data obtained from a multicontact frictional system between glassy polymer materials. Simulations at larger amplitude of modulation (typically 20 percent of the mean normal load) suggest that the nonlinear coupling between normal and sliding motion could have a destabilizing effect in restricted regions of the parameter space.

Interaction of Elastic Dilatational and Shear Waves With a Frictional Sliding Interface

The refraction and reflection of plane dilatational and shear waves, which are incident upon a sliding frictional interface between two elastic half-spaces, is considered. The contact interface is governed by Coulomb’s friction law with a constant friction coefficient. The incoming waves interact with the interface to form two reflected waves (shear and dilatational) as well as two such refracted waves. The dependency of the reflected and refracted wave amplitudes on the incoming wave angle is investigated. It is shown that the contact normal stress, shear stress and relative sliding velocity are proportional to each other. The interaction of an isolated interfacial rectangular wave pulse, or of a periodic set of pulses, with the frictional interface is then investigated. It is shown that steady motion of the two bodies can result due to the propagation of interface stick-slip waves. This motion can occur in the same direction or in the opposite direction of the remotely applied shear traction, or without an applied shear traction. The velocity of relative motion as a function of material parameters, friction coefficient, remotely applied shear and normal tractions, and parameters of the pulse is presented and discussed. These results may lead to a new form of ultrasonic propulsion which can be utilized for position or velocity control of a sliding body.