Frictional Slip Research Articles

Analytical approach to estimating the influence of friction slip contact between surrounding rock and concrete lining on mechanical response of deep rheological soft rock tunnels

For a deep-buried tunnel in soft ground, the contact condition between the surrounding rock and lining significantly affects the mechanical response. This is because the slip bond relationship on the contact surface has a direct influence on the tangential slip, resulting in the redistribution of displacement and stress on the contact surface between the surrounding rock and lining. However, previous studies have not paid sufficient attention to this problem, and a well-established method for quantitatively evaluating this influence remains unavailable. Therefore, the influence of the contact behavior between the surrounding rock and lining was examined in this study using an analytical method. First, the concept of friction slip contact and corresponding theoretical equations are proposed based on the real contact behavior between the surrounding rock and lining. Second, considering the friction slip contact between the surrounding rock and lining, a mechanical model of the tunnel excavation-support process was established, and analytical solutions for the stress and displacement of the tunnel within a viscoelastic rock material were realized. Third, the effectiveness and reliability of the proposed solutions were validated. The results could be degenerated to those that do not consider the influence of the mechanical behavior of the contact surface. In addition, there was good agreement between the analytical results and further numerical calculation results. Finally, a comprehensive parametric investigation was conducted, including the influences of the initial release coefficient, friction coefficient, and installation time of the lining. Some useful recommendations for tunnel lining design are provided herein.

Visualization of stick-slip shear failure process of granite by 3D reconstruction technique and DEM

Understanding the mechanism of stick-slip instability of faults is of great significance for earthquake forecast and seismic fortification. In this paper, combined with the 3D reconstruction technology and discrete element method (DEM), the stick-slip shear failure process is visualized and the evolution mechanism of each stage of stick-slip process is studied. First, the 3D morphology scanning tests are carried out to define the 3D topography of the sample interface, which is imported into PFC3D to generate particle assembly, and micro-parameters of the particle assembly are calibrated by the experimental results. Second, the loading conditions are applied to the particle assembly, the stick-slip instability of the simulated fault occurs spontaneously, and the evolution of fault displacement and velocity distribution during the whole stick-slip period are studied. Third, the effects of normal stress, shear loading rate and interface roughness on stick-slip instability are investigated. Finally, nine parameters related to the steady-state friction coefficient, namely normal stress, natural density, Young's modulus, Poisson's ratio, maximum static friction coefficient, reference slip velocity, reference friction coefficient, a-b and slip velocity, are selected to establish the steady-state friction coefficient forecast model based on back propagation neural network (BPNN), and the relative importance analysis of relevant parameters is also implemented. Our research is helpful to reveal the seismogenic mechanism.

Effect of Wear-Induced Surface Deformation on Stick-Slip Friction of Galvanized Automotive Steels.

This study examined the influence of worn surfaces on the stick-slip friction of galvanized automotive steel and revealed the intrinsic role of surface topography parameters in the stick-slip friction with wear. The results show that the surface deformation induced by wear significantly affects the stick-slip friction. The stick-slip friction can be suppressed by increasing the vertical area of the surface deformation because of reductions in the difference between the static and kinetic friction coefficients. The friction behavior changes from stick-slip friction to smooth sliding when the skewness exceeds a critical value, thus suggesting that this parameter can be used as an effective surface topography parameter to describe the stick-slip friction of galvanized automotive steel with worn surfaces. The findings can help improve the understanding of the mechanism of the stick-slip friction of materials with worn surfaces and provide an approach to suppress the noise and vibration caused by the stick-slip friction of galvanized automotive steel.

Experimental studies on slip friction device using symmetric friction connections

The use of friction-based energy dissipater is rapidly growing in seismic active zones to avoid interruptions and costs resulted from local or global damage to buildings due to severe earthquakes. Well designed and detailed friction devices using symmetric friction connections (SFCs) are often considered as an efficient way to dissipate energy for not only their stable hysteretic behaviour and low strength degradation but also the comparable assembling cost to that of conventional construction. The sliding commences when the designed sliding shear force is achieved, which relates to the contact surface’s Coefficient of Friction (CoF) and the total amount of clamping force. This paper reports 15 quasi-static testing of a slip friction device utilizing SFC clamped by two grade 10.9 M20 black finished high strength structural steel bolts in a single row. Shims using brass, aluminium, high strength steel, semi-metallic brake pads and copper-iron alloy were tested. Results show that all five shim materials tested can provide a stable hysteretic behaviour under a cumulated sliding distance of more than 4000 mm. The effect of installed bolt tension, loading rates and bolt-bearing mode are also discussed. Given the stable hysteretic response and the low strength degradation observed, the proposed slip friction device can be considered as a low damage energy dissipater.

On the Choice and Implications of Rheologies That Maintain Kinematic and Dynamic Consistency Over the Entire Earthquake Cycle

AbstractViscoelastic processes in the upper mantle redistribute seismically generated stresses and modulate crustal deformation throughout the earthquake cycle. Geodetic observations of these motions at the surface of the crust‐mantle system offer the possibility of constraining the rheology of the upper mantle. Parsimonious representations of viscoelastically modulated deformation through the aseismic phase of the earthquake cycle should simultaneously explain geodetic observations of (a) rapid postseismic deformation, (b) late in the earthquake cycle near‐fault strain localization. To understand how rheological formulations affect kinematics, we compare predictions from time‐dependent forward models of deformation over the entire earthquake cycle for an idealized vertical strike‐slip fault in a homogeneous elastic crust underlain by a homogeneous viscoelastic upper‐mantle. We explore three different rheologies as inferred from laboratory experiments: (a) linear Maxwell, (b) linear Burgers, (c) power‐law. The linear Burgers and power‐law rheologies are consistent with fast and slow deformation phenomenology over the entire earthquake cycle, while the single‐layer linear Maxwell model is not. The kinematic similarity of linear Burgers and power‐law models suggests that geodetic observations alone may be insufficient to distinguish between them, but indicate that one may serve as an effective proxy for the other. However, the power‐law rheology model displays a postseismic response that is non‐linearly dependent on earthquake magnitude, which may offer a partial explanation for observations of limited postseismic deformation near some magnitude 6.5–7.0 earthquakes. We discuss the role of mechanical coupling between frictional slip and viscous creep in controlling the time‐dependence of regional stress transfer following large earthquakes and how this may affect the seismic hazard and risk to communities living close to fault networks.

Stick–slip in hand guidance of palletizing robot as collaborative robot

Stick–slip is a challenging problem in palletizing robots and constitutes one of the main problems in precision positioning control. This study analyzed the stick–slip of a four-degree-of-freedom ceiling-mounted hand-guiding collaborative robot in a working space. A brief perspective on the focus of the experimental design is presented on the stick–slip friction of a palletizing robot’s hand guidance as a collaborative robot. The palletizing robot typically has a simple mechanical structure but possesses over 16 bearings to constrain the motion of the dual-parallelogram linkage mechanism. First, the hand-guiding force was successfully measured. Second, an image model was built based on the obtained measurement results. Third, the stick–slip results for the working space were analyzed using an image model. Finally, related conclusions and recommendations are provided for precision positioning control. A significant aspect of this study is identifying the hand-guiding force in the working space of a ceiling-mounted collaborative robot. Stick–slip in hand guiding is a critical issue and is therefore important for collaborative robot users. The main contribution of this study is developing a feasible method for helping researchers understand where stick–slip occurs.

Research on Interface Slip Characteristics of Heritage Composite Timber Columns under Inclined Deformation

In order to study the mechanical performance and friction slip mechanism of the interface of a composite timber column under inclined deformation, the unilateral contact mechanical model of an ancient composite timber column under inclined deformation is proposed in this paper. According to the limit of the inclination angle of slip point and the limit of the inclination angle of slip surface, the failure modes of the combination’s interface can be divided into three stages: the fully sticky stage, the partially sticky stage and the sliding stage. The theoretical results of the sliding displacement and shear stiffness of the combination’s interface under the effect of iron hoops were obtained by using the elastic mechanics method. Based on the shear sliding test of a composite timber column’s interface under the effect of iron hoops, the influences of different parameters on the shear sliding performance of the combination’s interface were investigated. The test results show that the number and the spacing of the iron hoops and the inclination angle of the interface are important factors affecting the shear strength of the combination’s interface. The shear strength of the interface increased with the increase in the number of iron hoops and the inclination angle of the interface. Since hoop spacing that is too large or too small cannot effectively improve the shear capacity of the interface, there is an optimal value for the hoop spacing.

Aseismic slip and recent ruptures of persistent asperities along the Alaska-Aleutian subduction zone

The frictional properties and slip behaviors of subduction thrusts play a key role in seismic and tsunami hazard assessment, especially in weakly coupled “seismic gaps”. Here, we rely on GPS observations in the Shumagin Gap of the Aleutian subduction zone to derive the slip distribution of the 2020 Mw 7.8 Simeonof Island, Alaska earthquake and of the subsequent afterslip during the first 87-day period. Our modeling results show that the mainshock ruptured at depths of ∼30–40 km beneath Simeonof Island. Kinematic and stress-driven models indicate that the afterslip occurred both updip and downdip of the mainshock rupture. Physically plausible locking models derived from interseismic GPS velocities suggest that the 2020 Simeonof and 2021 Mw 8.2 Chignik earthquakes ruptured persistent asperities on the subduction thrust. We infer that there are several additional persistent asperities at depths of 20–50 km west ∼157°W. However, it is still uncertain whether there are additional locked asperities at shallow depths because of the current lack of geodetic observations close to the trench.

Discrete-element modelling of concrete behaviour under uniaxial compressive test

This paper presents a three-dimensional (3D) simulation of the concrete behaviour in a uniaxial compressive test using discrete-element modelling (DEM). The aim of this paper is to validate the numerical model developed and to study the cracking initiation and failure process in order to better understand the fracture behaviour of concrete. The particles were distributed using an algorithm that is based on sieve test analysis. The parameters were set up in order to validate the numerical model with the experimental result. It was observed that the 3D model is in line with the laboratory test in term of stress-strain response and macroscopic cracks development. Once the bond between the spheres was broken, it led to the formation of microscopic cracks, which were not visible in laboratory tests. From the observation recorded during the testing, it is clear that DEM is capable of capturing concrete behaviour both quantitatively and qualitatively. At the yielding point in the concrete the strain energy is released in the form of kinetic energy, frictional slip energy, energy of dashpot and local damping. Hence, it can be concluded that DEM can be used to study the random nature of the cracking and fracturing of concrete structures.

Dry friction damping mechanism of flexible microporous metal rubber based on cell group energy dissipation mechanism

Flexible microporous metal rubber (FMP-MR) is a high-damping material that dissipates energy by dry friction through internal spiral metal wires in contact with each other. However, the FMP-MR energy dissipation mechanism is not fully understood owing to its disordered grid interpenetrating structure. In this work, computer-aided preparation technology is used to accurately reconstruct the complex spiral network structure of FMP-MR multipoint random contact, and a cell group model with an energy dissipation mechanism is proposed to obtain the dynamic energy distribution of the contact friction in both space and time dimensions. By judging the effective contact point, a global displacement ablation phenomenon of hooked staggered porous materials is induced. The macro- and micro-equivalent frictions are introduced to effectively explain the characteristics of the strong energy dissipation in FMP-MR under fretting excitation. A real and effective damping hysteresis constitutive model is then constructed to dynamically capture the mapping relationship between the complex nonlinear topological structure effect of the materials and spatial random contact dry friction in real time. The results indicate that the contact behavior between turns of the FMP-MR wire follows a clear quasi-Gaussian distribution under an external load, forcing the topological results to change. The energy dissipation of the materials revealed peak energy consumption lagging behind the loading limit for a certain distance, which can be determined by the effective contact point and contact dry friction slip. The consistency between the quasi-static compression tests and constitutive curves of the model was quantitatively verified through residual analysis. The data demonstrated the differential behavior of the FMP-MR meso-structure to follow a phased growth law during loading with different action mechanisms in the guiding, main growth, and relaxation stages of the energy consumption displacement curve. In summary, these findings provide an acceptable theoretical basis for the damping energy consumption mechanism and lifetime prediction of FMP-MR.

Synchronous properties of the friction phenomenon

The phenomenon of frictional slipping and sticking is one of crucial problems in mechanical engineering. This paper is focused on the numerical analysis of vibrations induced by friction in oscillator model which assumes an influence of the normal degree of freedom on the friction force. Analysis of Poincare maps, time courses and corresponding spectrum of Lyapunov exponents of the proposed three degrees of freedom dynamical system is demonstrated. It is revealed that the friction force, acting on the main slider, reflects dynamic behavior of the system response, i.e., some synchronous correlation between them is observed, even in the range of hyperchaotic behavior of the system, characterized by two positive Lyapunov exponents. On the other hand, an interesting effect of the coexistence of irregular friction force at the contact point of the frictional brush and ground surface with the regular response of the system in the quasi-periodic regime is reported.

Non-monotonic Dynamics in the Onset of Frictional Slip

The transition from static to dynamic friction is often described as a fracture instability. However, studies on slow sliding processes aimed at understanding frictional instabilities and earthquakes report slow friction transients that are usually explained by empirical rate-and-state formulations. We perform very slow (sim nm/s) macroscopic-scale sliding experiments and show that the onset of frictional slip is governed by continuous non-monotonic dynamics originating from a competition between contact aging and shear-induced rejuvenation. This allows to describe both our non-monotonic dynamics and the simpler rate-and-state transients with a single evolution equation.

The Effect of Navier Slip and Skin Friction on Nanofluid Flow in a Porous Pipe

The flow of nanofluids through a porous medium is considered the optimum method for convective heat transfer. In this study, nanofluid flow in a porous pipe with Navier slip is investigated. Two water-based nanofluids, Copper (Cu) and alumina (Al2O3), were considered. The governing equation is presented and non-dimensionalization has been done for momentum and energy equations, initial and boundary conditions, skin friction, and Nusselt number. The governing system was simplified to ordinary differential equations, which were numerically solved and a mathematical model of nanofluid flow was formulated. The results, with regard to variations in various parameters such as temperature, velocity, skin friction, and Nusselt number, are presented graphically and discussed. It was found that the velocity during the flow decreases with the increase of the Navier slip.

A Class of Variational\u2013Hemivariational Inequalities for Bingham Type Fluids

In this paper we investigate a new class of elliptic variational–hemivariational inequalities without the relaxed monotonicity condition of the generalized subgradient. The inequality describes the mathematical model of the steady state flow of incompressible fluid of Bingham type in a bounded domain. The boundary condition represents a generalization of the no leak condition, and a multivalued and nonmonotone version of a nonlinear Navier–Fujita frictional slip condition. The analysis provides results on existence of solution to a variational–hemivariational inequality, continuous dependence of the solution on the data, existence of solutions to optimal control problems, and the dependence of the solution on the yield limit. The proofs profit from results of nonsmooth analysis and the theory of multivalued pseudomontone operators.

Weak, Seismogenic Faults Inherited From Mesozoic Rifts Control Mountain Building in the Andean Foreland

AbstractNew earthquake focal mechanism and centroid depth estimates show that the deformation style in the forelands of the Andes is spatially correlated with rift systems that stretched the South American lithosphere in the Mesozoic. Where the rifts trend sub‐parallel to the Andean range front, normal faults inherited from the rifts are being reactivated as reverse faults, causing the 30–45 km thick seismogenic layer to break up. Where the rift systems are absent from beneath the range front, the seismogenic layer is bending and being thrust beneath the Andes like a rigid plate. Force‐balance calculations show that the faults inerhited from former rift zones have an effective coefficient of static friction μ′ < 0.2. In order for these frictionally weak faults to remain seismogenic in the lower crust, their wall rocks are likely to be formed of dry granulite. Xenolith data support this view, and suggest that parts of the lower crust are now mostly metastable, having experienced temperatures at least 75–250°C hotter than present. The conditions in the lower crust make it unlikely that highly pressurized free water, or networks of intrinsically weak phyllosilicate minerals, are the cause of their low effective friction, as, at such high temperatures, both mechanisms would cause the faults to deform through viscous creep and not frictional slip. Therefore pre‐existing faults in the Andean forelands have remained weak and seismogenic after reactivation, and have influenced the style of mountain building in South America. However, the controls on their mechanical properties in the lower crust remain unclear.

Effect of Loading Rate and Initial Strain on Seismic Performance of an Innovative Self-Centering SMA Brace.

In order to improve the energy dissipation capacity and to reduce the residual deformation of civil structures simultaneously, this paper puts forwards an innovative self-centering shape memory alloy (SMA) brace that is based on the design concepts of SMA’s superelasticity and low friction slip. Seven self-centering SMA brace specimens were tested under cyclic loading, and the hysteresis curves, bond curves, secant stiffness, energy dissipation coefficient, equivalent damping coefficient, and the self-centering capacity ratio of these specimens were investigated, allowing us to provide an evaluation of the effects of the loading rate and initial strain on the seismic performance. The test results show that the self-centering SMA braces have an excellent energy dissipation capacity, bearing capacity, and self-centering capacity, while the steel plates remain elastic, and the SMA in the specimens that are always under tension are able to return to the initial state. The hysteresis curves of all of the specimens are idealized as a flag shape with low residual deformation, and the self-centering capacity ratio reached 89.38%. In addition, both the loading rate and the initial strain were shown to have a great influence on the seismic performance of the self-centering SMA brace. The improved numerical models combined with the Graesser model and Bouc–Wen model in MATLAB were used to simulate the seismic performance of the proposed braces with different loading rates and initial strains, and the numerical results are consistent with the test results under the same conditions, meaning that they can accurately predict the seismic performance of the self-centering SMA brace proposed here.

Modeling and stability characteristics of bump-type gas foil bearing rotor systems considering stick–slip friction

Frictional energy dissipation inside the foil structure is considered as a key factor in improving the stability of the gas foil bearing (GFB) rotor system. However, the effect and mechanism of friction on the stability of bump-type GFB rotor systems have remained partially addressed. This study aims to develop a novel comprehensive model to investigate the stability and frictional dissipation mechanism of the GFB rotor system. The LuGre dynamic friction model is adopted to capture accurate stick–slip states. The model order reduction technique and simultaneous solution framework are applied to improve the computational efficiency. The effect of friction on linear and nonlinear stability is investigated based on the proposed model, and an analysis of frictional dissipation is performed to explain the mechanism. The results reveal that the dissipation capacity of the foil structure is directly governed by the stick–slip states that are affected by the friction coefficient and disturbance magnitude, so the optimal friction coefficient for nonlinear stability is higher than the one for linear stability of the GFB rotor system. A further comparison between different friction models greatly highlights the necessity of the ability of the friction model to capture accurate stick–slip states.

Influences of friction self-excited vibration characteristics of various types of high-speed trains on rail corrugations in braking sections

To study the typical rail corrugation in braking sections at large slope downhills of Chinese high-speed railways, finite element models of wheelset-rail-brake systems of various high-speed trains are established in the present paper. Then, the complex eigenvalue analysis method is used to study friction self-excited vibration characteristics of wheelset-rail-brake systems in braking sections at large slope downhills. Finally, the influences of friction coefficient of the braking subsystem and vertical fastener stiffness of the wheelset-rail subsystem are analyzed. Results show that the friction self-excited vibration of the entire system induced by the stick–slip friction coupling effect of the wheelset-rail subsystem and the rolling-slip friction coupling effect of the braking subsystem is the dominant cause of rail corrugation. Then, the brake combination of the wheel disc and axle disc is more likely to cause the friction self-excited vibration of the wheelset-rail-brake system than the single braking mode. Parametric analyses show that with the increase of the friction coefficient of the braking subsystem, the self-excited vibration of the entire system increases, which means that the possibility of rail corrugation increases. Furthermore, with the increase of the vertical fastener stiffness of the wheelset-rail subsystem, the self-exicted vibration of the entire system first decreases and then gradually increases. When the vertical fastener stiffness is 30 MN/m, rail corrugations can be suppressed to a certain extent.

InSAR Constrained Downdip and Updip Afterslip Following the 2015 Nepal Earthquake: New Insights into Moment Budget of the Main Himalayan Thrust

We use ALOS-2 and Sentinel-1 data spanning 2015–2020 to obtain the post-seismic deformation of the 2015 Mw 7.8 Nepal earthquake. ALOS-2 observations reveal that the post-seismic deformation was mainly distributed in four areas. A large-scale uplift deformation occurred in the northern subsidence area of the co-seismic deformation field, with a maximum uplift of ~80 mm within 4.5 yr after the mainshock. While in the southern coseismic uplift area, the direction of the post-seismic deformation is generally opposite to the co-seismic deformation. Additionally, two notable deformation areas are located in the region around 29° N, and near the MFT, respectively. Sentinel-1 observations reveal post-seismic uplift deformation on the north side of the co-seismic deformation field with an average rate of ~20 mm/yr in line-of-stght. The kinematic afterslip constrained by InSAR data shows that the frictional slip is distributed in both updip and downdip areas. The maximum cumulative afterslip is 0.35 m in downdip areas, and 0.2 m in the updip areas, constrained by the ALOS measurements. The stress-driven afterslip model shows that the afterslip is distributed in the downdip area with a maximum slip of 0.3 m during the first year after the earthquake. Within the 4.5 yr after the mainshock, the estimated moment released by afterslip is ~1.5174 × 1020 Nm,about 21.2% of that released by the main earthquake.

Model learning of the tire–road friction slip dependency under standard driving conditions

The maximum tire–road friction coefficient is a quantity allowing to increase significantly the performance of the driver-assistance systems. Unfortunately, this value is particularly difficult to estimate under standard driving conditions. Therefore, this paper focuses on a parametric method based on Monte-Carlo Markov Chain techniques to determine it accurately. Our solution combines the advantages of both a maximum likelihood method and an adaptive Metropolis algorithm to determine the tire–road friction coefficient. This approach requires friction measurements and a tire model representing the friction as a function of the slip ratio. After describing the theoretical aspects of the method, this paper focuses on its practical implementation. Several results obtained from both simulated data and real data are given to demonstrate the efficiency of the approach.