Frictional Coupling Research Articles

TRIBOINFORMATICS: MACHINE LEARNING METHODS FOR FRICTIONAL INSTABILITIES

The study of friction is traditionally a data-driven area with many experimental data and phenomenological models governing structure-property relationships. Triboinformatics is a new area combining Tribology with Machine Learning (ML) and Artificial Intelligence (AI) methods, which can help to establish correlations in data on friction and wear. This is particularly relevant to unstable motion, where deterministic models are difficult to build. There are several types of friction-induced instabilities including those caused by the velocity dependency of dry friction, coupling of friction with another process (wear, heat generation, etc.), the elastic Adams instabilities, and others. The onset of sliding is also an unstable process. ML/AI methods, such as Topological Data Analysis and various ML algorithms, which have been already used for various aspects of data analysis on friction, can be applied also to the frictional instabilities.

Passive earth pressure on vertical rigid walls with negative wall friction coupling statically admissible stress field and soft computing

It is well known that the roughness of a wall plays a crucial role in determining the passive earth pressure that is exerted on a rigid wall. While the effects of positive wall roughness have been extensively studied in the past few decades, the study of passive earth pressure with negative wall friction is rarely found in the literature. This study aims to provide a precise solution for negative friction walls under passive wall conditions. The research is initiated by adopting a radial stress field for the cohesionless backfill and employs the concept of stress self-similarity. The problem is then formulated in a way that a statically admissible stress field be developed throughout an analyzed domain using a two-step numerical framework. The framework involves the successful execution of numerical integration, which leads to the exploration of the statically admissible stress field in cohesionless backfills under negative wall friction. This, in turn, helps to shed light on the mechanism of load transfer in such situations so that reliable design charts and tables be provided for practical uses. The study continues with a soft computing model that leads to more robust and effective designs for earth-retaining structures under various negative wall frictions and sloping backfills.

A Time-Dependent Damage Constitutive Model for Brittle Rock Materials Based on Subcritical Damage Theory.

In the domain of geotechnical engineering, a profound understanding of the long-term mechanical deformation characteristics of rocks is indispensable for the design and construction of structures, dams, tunnels, and various engineering projects. The deformation behavior of rocks under long-term loads directly impacts the stability and safety of engineering structures. This study employs micromechanical methods to investigate the subcritical extension of microcracks under stress corrosion. By examining the accumulated damage resulting from this phenomenon, the research explores the patterns of aging damage development and establishes a constitutive model for aging that incorporates cumulative damage over the stress history. The accuracy of the proposed model is evaluated through a comprehensive comparison of numerical results with experimental data. The experimental data set encompasses traditional triaxial compression tests, single-stage creep, multistage creep, and single-stage relaxation tests conducted under varying confining pressures. The predicted results exhibit strong consistency with the entire data set. Furthermore, this paper employs crack damage stress as an indicator characterizing the long-term strength of rock. Through frictional damage coupling analysis and derivation, an analytical expression for the long-term strength of rock materials containing microcracks is provided, serving as a theoretical basis for investigating the long-term mechanical performance of brittle rock materials and ensuring the long-term stability of large-scale rock engineering projects.

A purely centered and non-redundant piezoelectric stick-slip rotary stage with force amplification

This paper proposes a purely center-rotation and non-redundant piezoelectric stick–slip rotary stage with force magnification. A bridge driving mechanism with centrosymmetric actuation feet is proposed, and its tilt angle can be adjusted to regulate the clamping force amplification characteristics, thus improving load capacities. Meanwhile, only a single piezoelectric actuator is used, and the driving mechanism is built in the circular slider, hence achieving non-redundant, purely centered rotation and improving the structural compactness. Theoretical calculations and simulation analyses of single-step rotation angles and force amplification of the rotary stage are carried out. In addition, a system dynamics model with electromechanical, rigid-flexible, and friction coupling properties is established. Finally, a prototype is fabricated, and various experiments are conducted. The designed bridge driving mechanism amplifies the piezoelectric actuation force by 2.8 times, and the stick–slip rotary stage has a maximum load of up to 9 kg. Also, the stage can rotate more than 360°, and the angular resolution is 0.1265 μrad, demonstrating superior performances of the non-redundant center-rotation stage.

Study on the generation mechanism of curve squeal and its relationship with wheel/rail wear

This paper aims to create a friction coupling finite element model of the wheelset–track system, taking into account various curve radii and corresponding wheel/rail contact states. This model will serve as a tool to analyze the underlying causes of curve squeal phenomena. Furthermore, we conducted an investigation into the impact of rail and wheel wear on system stability. This paper utilized a complex eigenvalue analysis (CEA) method to accurately calculate and predict vibration instabilities in the system. The results show that the smaller the radius of the curve, the more prone to it is lateral creep between the rail and the leading wheelset, so that the system is more prone to self-excited frictional vibrations, ultimately resulting in the generation of curve squeal. In addition, the wear of the wheel tread/rail head increases the instability of the system. When the train passes through a section with rail corrugation, rail corrugation suppresses the occurrence of curve squeal.

Sliding frictional and adhesive coupling contact analysis of FGPM layered half-space under an insulating indenter

This paper proposes an analysis model for the sliding frictional and adhesive coupling contact problem in the plane strain state between the FGPM layered half-space and an insulating indenter. The electro-mechanical properties of FGPM layer vary exponentially along the thickness direction. By applying the Fourier integral transformation and superposition principle to the governing boundary value problem, the general solution for the sliding frictional and adhesive coupling contact problem can be derived by using the Maugis type of adhesion theory and extended Amonton’s law of friction. A Cauchy singular integral equation is further derived for present problem which is then numerically solved. The primary aim of this paper is to provide insight into the likely behavior for the effect of the gradient index, friction coefficient and adhesion parameters on the surface electro-mechanical response of FGPM layered half-space. For given values of parameters R, w, βh and μ, when value of σ0 decreases from infinity to zero there is a continuous transition from the JKR approximation to the DMT approximation. The research not only helps to further understand the frictional and adhesive damage mechanisms of MEMS devices composed of FGPM, but also provides reference basis for FGPM layer experimental analysis and intelligent structure design.

Providing ceramics high-temperature self-lubrication by inducing vacancies concentration variation via thermal and frictional synergies

Based on the new conception of lattice low-shear stress induced by zero-dimensional point defects, the Al2O3 composite ceramics doped by TiO2 with good high-temperature tribological properties are prepared. According to the results, temperature could control the continuity of the resintering friction layer and the activation of the plastic deformation ability of ceramics. The lattice oxygen in TiO2 leaves the original lattice occupation due to thermal and frictional coupling action, and breaks away from the worn surface, which significantly increases the vacancy concentration level. Aforesaid structural defects are considered to be a crucial reason for the reduction of shear force. Compared with friction coefficient (0.53) for Al2O3 at 1100 °C, COF of TiO2-doped Al2O3-based ceramics is 0.26 about half of that. This vacancy quantitative change strategy of temperature-sensibility is expected to become a controllable method for providing lubrication during high-temperature.

Experimental study on flow-induced vibration under laminar flow and turbulent flow transition state in helical coiled tube

This study investigates the vibration characteristics induced by single-phase flow at low velocities within helical coiled tube, encompassing laminar and turbulent flow transition regimes. Modal experiments were conducted to ascertain the natural frequencies in the radial and vertical directions within the helical coiled tube. The influence of fluid mass in tube on vibration was considered, revealing the fluid mass has a greater influence on the vibration frequency in the vertical direction. When the coil was filled with water, the radial natural frequency decreased by 0.1 Hz, while the vertical natural frequency decreased by 0.8 Hz.By simplifying the spiral coil into a spring system, the intrinsic causes of the influence of mass on the natural frequency are studied and verified with the experimental data. The results show that the radial natural frequency is only related to the local mass change of the pipe, while the vertical natural frequency is related to the static deformation of the system under the influence of gravity.By conducting single-phase flow induced vibration experiments inside the pipeline, the radial and vertical vibration response characteristics were obtained, and the modal experimental results were analyzed. Findings indicated larger vibration displacements when laminar flow prevailed within the tube, with radial RMS (Root Mean Square) at 10.1 μm and vertical RMS at 14.5 μm. After the transition to turbulent flow, significant reductions in vibration displacements were observed, reducing the radial RMS to 2.3 μm and vertical RMS to 5.5 μm.Based on statistical and frequency-domain analysis methods, the influence mechanism of secondary flow on the vibration of helical coils at low flow rates was revealed, and the importance of friction coupling was clarified. Moreover, this study considered the impact of fluid viscosity on vibration response and experimentally validated the critical role of friction coupling in exciting secondary flows.

Seismic displacement response analysis of Friction Pendulum Bearing under friction coupling and collision effects

Friction Pendulum Bearing (FPB) with shearing keys will exhibit friction-coupling effect and collision phenomenon subjected to horizontal orthogonal ground motions. This paper establishes a numerical analysis model of FPB with four shear keys and viscous damping, considering the impact of the friction coupling effect and collision between the FPB and the shear keys on its displacement response. The influence of parameters of FPB on seismic displacement response with considering collision effect under horizontal orthogonal ground motions was studied. The results suggest that adjustments in damping and equivalent stiffness exclusively impact the amplitude of the displacement response, maintaining the response waveform. Conversely, variations in friction significantly alter the response waveform, as friction induces changes in the natural frequency of FPB. A heightened collision impact is noted with reduced spring stiffness. The displacement response is particularly amplified when the collision occurs at the vicinity of peak displacement in the time-history response of FPB. When the restoring stiffness and Peak Ground Acceleration (PGA) are low, the friction coupling effect significantly reduces the amplification of displacement response caused by collision effects. Viscous damping can considerably reduce the impact of collisions on the peak displacement of FPB and prevent the collision effects from noticeably amplifying or diminishing the peak displacement of FPB.

Research and construction of an adaptive drive with increased efficiency based on a balancing friction clutch

Presently, there is significant emphasis on researching the automation of processes, systems, and devices across scientific and technical fields. This emphasis extends notably to sectors like aerospace, robotics, and electric transportation technology. One effective approach to tackling the technical and design challenges of automating various technological tools and processes is through the implementation of adaptive systems. Specifically, achieving efficient and reliable power transmission in electric autonomous and mobile vehicles can be realized by employing an adaptive mechanical drive with two degrees of freedom. The adaptability of this two-mobile system is enabled by introducing an innovative continuous multi-speed drive design featuring an additional friction coupling. The primary attribute ensuring the reliability of this self-adjusting mechanical drive lies in its ability to autonomously adapt to external loads. This is made possible by a balancing friction coupling that establishes a connection between the frictional torque and the relative angular velocity.

Considerations Regarding the Effects of Temperature Increase on the Hardness of Materials in Friction Couplings with Sliding Motion

Abstract The temperature on the surfaces in sliding motion changes as a result of the operating conditions. The temperature distribution generated during the friction process depends on the forces generated in operation, the speed of sliding, the topography of the surface,the properties of the materials that form the friction coupling. The purpose of this paper is to analyze the effects of temperature increase on surfaces in sliding motion with implications on the hardness of friction coupling materials.

Investigation on the vibration localization of mistuned bladed disk with frictional contact

The mistuning phenomenon is commonly seen in the bladed assemblies of turbomachinery, leading to an unreasonably localized energy distribution that may increase the risk of high cycle fatigue and potentially cause blade failure. The friction coupling interaction is often introduced to attenuate the effect of excessive amplification on the structural vibration. To investigate the vibration localization of damped and mistuned bladed-disk system, a typical mistuning characterization is applied to an improved four-degree-of-freedom lumped parameter model to explicit the vibratory properties with coupled frictional contact. The statistical findings of natural frequency and modal localization factor are obtained by employing the Monte Carlo simulation to explore the influence of mistuned variance and coupled stiffness on the modal localization of free and damped bladed-disk system, respectively. The forced response sensitivity featured in the mistuned variance is quantitatively analyzed from the perspective of vibration localization and energy distribution by the nonlinear solution method. The influence of excitation order and normal load are further, respectively, discussed on the response localization level of the mistuned system. The results can provide fundamental knowledge of the impact of the mistuning pattern on vibration localization for the early design of the aeroengine.

Research and design of an efficient adaptive drive with balancing friction coupling

Currently, research related to the automation of processes, systems and devices are of high relevance in the scientific and technical field: in the aerospace industry, robotics and electric transport technology. Successful automation of facilities and processes requires simplified control systems, and an adaptive mechanical system operates without a control system, which increases its reliability and efficiency. In particular, the creation of an efficient and reliable transmission of electric autonomous and mobile vehicles can be achieved by an adaptive mechanical drive with two degrees of freedom. Adaptation of the two-mobile system (2-DoF) is achieved by the proposed completely new type of transmission, namely the design of a stepless multi-speed drive with an additional friction coupling. The property of reliable adaptation of a two-mobile self-adjusting mechanical drive is independent adaptability to an external load with the help of a balancing friction coupling that provides a connection between the frictional moment and the relative angular velocity. The article presents a study of the interaction of the parameters of a two mobile system in order to improve the efficiency of a self-adjusting adaptive drive with a given wide range of regulation based on the use of a friction coupling.

Fluid-structure interaction characteristics between natural gas fluid and tubing string in high-pressure high-temperature high-production gas wells

The transient internal flow in high-pressure high-temperature high-production (three-high) gas wells may bring about serious fluid-structure interaction (FSI) between natural gas fluid and tubing string. Then, fatigue failure, wear and leakage of tubing string can easily be caused to threaten the wellbore safety and integrity. However, it is difficult to directly adopt the existing FSI model owing to particularity environment of the three-high gas wells. Based on water hammer, FSI and Timoshenko beam theory, a mathematical model expounding FSI phenomenon of the three-high gas wells is established by Poisson, friction and junction coupling, which considers unsteady friction effect, centrifugal and Coriolis force to make FSI characteristics more consistent with the engineering practice. Then, the improved method of characteristics (MOC) is applied into combination solution of the model. Later, the model and solution method is verified by comparing the results with different reference's ones respectively. On this basis, the effects of shut-in time, well depth position, unsteady friction on FSI characteristics are analyzed and discussed systematically. The calculation results are shown that shut-in time and well depth position have a more significant influence on FSI characteristics in three-high gas wells. In addition, FSI characteristics under action of unsteady friction decay faster, the time of the peak value also is delayed accordingly, and cumulative attenuation and cumulative delayed time of FSI characteristics increases with decrease of shut-in time. The FSI model, solution method proposed in this paper and results can provide theoretical basis and reference for the research on FSI and the formulation of shut-in operation for three-high gas wells, and even for highly deviated or horizontal gas wells.

Dynamic Response of a Polyvinylidene Fluoride (PVDF) Sensor Embedded in a Metal Structure Using Ultrasonic Additive Manufacturing

This study aims to examine the dynamic response of a polyvinylidene fluoride (PVDF) piezoelectric sensor which is embedded into an aluminum coupon using ultrasonic additive manufacturing (UAM). Traditional manufacturing techniques used to attach smart materials to metals on the surface have drawbacks, including the potential of exposing the sensor to adverse environments or physical degradation during manufacture. UAM can avoid these issues by integrating solid-state metal joining with subtractive processes to enable the fabrication of smart structures. A commercial PVDF sensor is embedded in aluminum with a compression technique to provide frictional coupling between the sensor and the metallic matrix. The PVDF sensor’s frequency bandwidth and impact detection performance are evaluated by conducting cantilever and axial impact tests, as well as harmonic excitation tests with an electrodynamic shaker. Under axial loading, the embedded sensor displays high linearity with a sensitivity of 43.7 mV/N, whereas impact tests in the cantilever configuration exhibit a steady decay rate of 0.13%. Finally, bending tests show good agreement between theoretical and experimental natural frequencies with percentage errors under 6% in two different clamping positions, and correspond to the maximum voltage output obtained from the embedded PVDF sensor at resonance.

ASSESSMENTS ON THE FRICTION AND WEAR BEHAVIOR OF SOME POLYMERIC MATERIALS USED IN SLIDING CONTACTS

The effects of friction on polymeric materials are quite difficult to explain due to the micro and macroscopic interactions of the friction coupling surfaces, which slide over each other. The friction and wear behavior of surfaces in sliding motion can be considered important design criteria. By adding different concentrations of reinforcing agent to the base material, the tribological performance of surfaces in sliding motion can be obtained. The experimental study was carried out on a pin-on-disc type tribological stand under dry friction conditions. The friction and wear behavior was analyzed for two base materials (PTFE and PA66) and the same glass fiber reinforced materials (PTFE + 25% fiber-glass and PA66+GF30). The tests were carried out at different sliding speeds and loading forces, v1=0.20 m/s, v2=0.50 m/s, v3=0.75 m/s and loading forces, Fn1=1.0 N, Fn2=2.5 N, Fn3=5.0 N over a friction length of 5000 mm. Research has shown that the coefficient of friction decreases with increasing loading force. Tests have shown that a high value of the friction coefficient does not mean a high wear rate, the wear rate values are between 10-12 and 10-15 m2/N. TheL(1) presences of the reinforcing agent in the base material have a significant importance on the friction and wear behavior under the action of operating factors (load, sliding speed).

Cyclic test evaluation of double skin composite hybrid coupled wall with frictional steel truss coupling beams

The seismic performance of double skin composite shear walls (DSCSWs) has significant superior to conventional reinforce concrete (RC) shear walls. Previous studies have neglected the changes of axial compressive forces and bending moments actting on the top of wall piers. In addition, behaviors hybrid coupled wall (HCW) under real boundary condition have not been fully investigated. Thus, in this study, a novel quasi-static test which incorporates the boundary conditions of substructures in a prototype building was preformed. And a cyclic test was carried out on a 2/3-scaled double skin composite (DSC) HCW with frictional steel truss coupling beams (FSTCBs) using the proposed method. The seismic behavior of specimen under reversed lateral cyclic loads was investigated. The failure modes of the wall piers mainly included local buckling of the steel faceplate, fracture of the side plate, and concrete crushing at the corners of walls. The force-displacement hysteresis curve of FSTCBs was obtainable from the attached instruments as the force transmission path of the steel truss could be clearly observed. DSCSW pier deformation was evaluated based on the deformative relationship between the wall pier and FSTCB. The FSTCB primarily dissipated 80% of the total energy input prior to damage occurring in the DSCSW. Strain distribution curves along the DSCSW showed that the pre-peak-resistance plane section assumption was still valid.

Single crystal piezoelectric motor operating with both inertia and ultrasonic resonance drives

This study presents a novel piezoelectric motor based on a single crystal material with orthorhombic mm2 symmetry class, in which piezoelectric coupling coefficients in sign and magnitude at transverse directions are different, implying that the value of d32 is positive whilst d31 is negative. The single crystal piezoceramic plate in the shape of a truncated rhombus has three conducting electrodes. While two active electrodes dividing one main surface into two equal sections, the common electrode covers the other main surface uniformly. When a signal is applied between one of the active and the common electrodes, the excited section expands and contracts with a larger magnitude. The expansion and shrinkage on one side causes an oblique movement of the side surface, on which a friction tip is attached. The oblique movement is then transferred to a moving element through frictional coupling. The proposed piezoelectric motor design is simpler and less susceptible to manufacturing tolerances as it does not rely on dimensional aspect ratios to couple two eigenmodes to get a useful movement at the friction tip of the stator. The motor can be operated both inertia (stick–slip) and resonance drive principals. In the case of sawtooth voltage excitation, the smallest motion steps are in the range of 100 nm. Using the ultrasonic excitation of both single source and dual source dual frequency resonance (DSDFR) drives, the piezoelectric motor reached a maximum no load velocity higher than 220 mm/s, and a push–pull force capacity of 2.5 N.

Optimization of 3D Printing Parameters for Enhanced Surface Quality and Wear Resistance.

In recent years, there has been a growing interest in the field of 3D printing technology. Among the various technologies available, fused deposition modeling (FDM) has emerged as the most popular and widely used method. However, achieving optimal results with FDM presents a significant challenge due to the selection of appropriate process parameters. Therefore, the objective of this research was to investigate the impact of process parameters on the tribological and frictional behavior of acrylonitrile butadiene styrene (ABS) and polylactic acid (PLA) 3D-printed parts. The design of experiments (DOE) technique was used considering the input design parameters (infill percentage and layer thickness) as variables. The friction coefficient values and the wear were determined by experimental testing of the polymers on a universal tribometer employing plane friction coupling. Multi-response optimization methodology and analysis of variance (ANOVA) were used to highlight the dependency between the coefficient of friction, surface roughness parameters, and wear on the process parameters. The optimization analysis revealed that the optimal 3D printing input parameters for achieving the minimum coefficient of friction and linear wear were found to be an infill percentage of 50% and layer thickness of 0.1 mm (for ABS material), and an infill percentage of 50%, layer thickness of 0.15 mm (for PLA material). The suggested optimization methodology (which involves minimizing the coefficient of friction and cumulative linear wear) through the optimized parameter obtained provides the opportunity to select the most favorable design conditions contributing to a more sustainable approach to manufacturing by reducing overall material consumption.

Analysis of the Influence of Single-Walled Carbon Nanotubes on the Fluid–Structure Interaction Vibration Control in Bionic Hydraulic Pipelines

In previous research, a bionic hydraulic pipeline (BHP) with a three-layer structure for absorbing pulsation was invented. This paper proposes to disperse single-walled carbon nanotubes (SWCNTs) in the elastic layer material, namely silicone rubber (RTV), to enhance its ability to absorb pulsation. Firstly, the RTV-SWCNTs composite specimens with different SWCNT proportions are prepared and tested. It was found that the mechanical property is optimal when the volume content of the SWCNTs is 0.5 vol%. On this basis, BHPs with RTV-SWCNTs composite material as the elastic layer are fabricated to study the influence of the thickness and length of the elastic layer on the absorption flow pulsation. The results show that the addition of SWCNTs significantly improves the mechanical properties of silicone rubber and reduces the friction between the elastic material and oil, so that the BHP can absorb the pressure pulsation better. With the appropriate thickness and length of the elastic layer, the addition of SWCNTs can increase the pulsation suppression effect by 20%. Moreover, to analyze the influence of nanomaterials on pipeline friction, a comprehensive fourteen-equation model for describing the fluid–structure interaction (FSI) of the pipe conveying fluid considering friction coupling is established. And through numerical analysis and modal tests, the evaluation error for the modified dynamic model of the BHP is less than 5%, verifying the correctness of the proposed model and solution method.