Stick-slip Effect Research Articles

Non-linear vibration analysis of hard rock TBMs with multiple state-dependent delays and stick–slip effects

Hard rock tunnel boring machines (TBMs) vibrate significantly during tunnelling, accelerating structural damage and cutter wear. The vibration mechanism and dynamic behaviours of TBMs are focused on in this study. A four degrees-of-freedom model that accounts for axial, torsional, pitch, and yaw vibrations that are coupled through the disc cutters–rock interaction is established. Then the state-dependent delay differential equations of motion of a TBM are derived. To determine the penetration in both normal cutting and cutter bounce states, the evolution of the cut surface profile for each cutter is governed by a partial differential equation that is then cast into a series of ordinary differential equations by using Galerkin projections. Numerical simulation shows that new unstable regimes appear due to cutterhead shimmy. Two instability mechanisms that are the cutterhead shimmy and the complete axial bounce, are revealed. It is found that multiple state-dependent delays, especially some of them associated with multiple regenerative effects, result in chaotic behaviours. The chaotic characteristics are in reasonable agreement with those observed from practical projects. The axial stick–slip effect works slightly in the cutterhead shimmy dominated regimes. However, it prevents complete axial bounce from occurring, and changes the predominant mechanism from the complete axial bounce to the cutterhead shimmy.

Design and performance evaluation of a stick–slip actuator with Z-shaped beam and two-stage amplification system

Abstract In the domain of piezoelectric driving, actuators that utilize the stick–slip effect at high speeds and low frequency have garnered significant interest. This study presents an innovative linear piezoelectric actuator that integrates a two-stage amplification system with a Z-shaped beam mechanism. The designed actuator has good driving speed at low frequency while overcoming the disadvantage of such actuators requiring two flexible mechanisms to achieve reverse motion and poor reverse performance. The structure and scale of the actuator are explained and designed through theory and simulation. The experimental results demonstrate the prototype’s capability for bidirectional motion. Subjected to a 400 Hz and 140 V excitation, the maximum speed of the actuator is 12.88 mm s−1. The maximum load capacity is tested to be of 0.35 N. This research introduces a new approach for the design of high-speed bidirectional motion stick–slip piezoelectric actuators.

Giant Cushioning Effect in Facile Polymer/Nanoclay-Coated Flexible Polyurethane Foams.

In this work, a flexible polyurethane (PU) foam/polymer/clay (PUF/PAASep) composite is prepared via a simple dip-coating method. The composite exhibits excellent damping properties under quasi-static compression, vibration transmissibility, and impact resistance. For the composite preparation, sepiolite (Sep) dispersion in a polyacrylic acid (PAA) solution is first homogenized and evaluated using microscopy, and the obtained PAASep suspension is used to coat the PU foam uniformly for optimization of the quasi-static mechanical performance of the foam composites. The PU foam struts coated with 1 wt % PAA and 3 wt % sepiolite are strengthened, resulting in an 8-fold improvement of the stiffness and three-times increase of the impact force resistance compared to the uncoated PU foams. More importantly, the PU foam composites show a remarkable vibration damping capability, with the loss modulus 57 times that of the uncoated PU foams, enabled by micro friction and stick-slip effects mediated by the PAASep coatings. The facile prepared PAASep-coated PU foams have significant potential for cushioning, packaging, and broad engineering applications involving energy absorption.

Design and development of closed-loop controllers for trajectory tracking of a planar vibration-driven robot

Vibration-driven robots constitute an innovative paradigm for achieving locomotion, leveraging periodic vibrations to meticulously control the movement of an internal mass, thus affording them a high degree of precision while navigating surfaces with varying friction characteristics. This paper is dedicated to the refinement of trajectory tracking in planar vibration-driven robots, achieved through the meticulous design and implementation of a Proportional-Integral-Derivative (PID) controller and Sliding Mode Controller (SMC). The considered vibration-driven robot is propelled using two parallel reciprocating unbalanced masses which allows the robot to have various maneuvers in two dimensions. The movement of the robot is improved by employing bristles to make non-isotropic Coloumb’s friction on the surfaces. At first, the governing dynamic equations of the robot are derived by considering the stick-slip effect and using the Euler–Lagrange method. Moreover, a PID controller for accurate trajectory tracking within the robot’s natural coordinate system is designed and employed. The fine-tuning of the PID controller’s coefficients is accomplished through the application of the NSGA-II optimization method. Subsequently, a SMC strategy is introduced to enable the robot’s control in an absolute coordinate system. The paper culminates with the presentation, in-depth analysis, and evaluation of the simulation results, shedding light on the significant enhancements in performance and capabilities achieved by vibration-driven robots. In conclusion, the pivotal role of the NSGA II algorithm in optimizing controller parameters is emphasized, and although the PID controller excels in trajectory tracking, challenges with sudden acceleration changes are identified.

Development of a pressure-, velocity-, and acceleration-dependent phenomenological friction model using experimental data of sliding tests between 11 polymers and stainless steel

This paper experimentally investigates the frictional behavior between stainless steel and 11 polymers. Particularly, the dependence of the friction coefficient on the sliding velocity, pressure, and acceleration is quantified. The novelty of this work lies in quantifying the acceleration-dependent nature of friction, correlating it to the well-documented Stick-Slip effect. The experimental setup consisted of two parallel stiff steel beams, one above the other, with a separation of 95 mm, and steel surfaces welded at the inner sides for sliding the polymers. Cylindrical polymer pads were placed between the stainless-steel surfaces and connected to a dynamic actuator to apply the displacement protocol. The protocol consisted of consecutive nominally constant-velocity ramp cycles covering velocities from 1 mm/s to 300 mm/s (with 20 mm/s increments). An additional vertical force was applied with a hydraulic actuator to reach nominal pressures in the polymers between 5 and 80 MPa. The results showed that the friction coefficient depends on the velocity, pressure, and acceleration of the motion, and a phenomenological model on these three variables is proposed. The velocity dependence can be represented through a logarithmic relationship, while the pressure dependence is through an exponential decay relationship. The acceleration dependence was represented through a linear relationship, which could capture the stick-slip effect. Overall, this work contributes to a better understanding of friction for seismic isolation systems. Since friction is the main source of energy dissipation in such structures, the proposed model will allow a higher accuracy in predicting variables of interest during the dynamic analyses of seismically isolated structures with frictional systems.

Influence of pipe rocking on the effectiveness of the load transfer along the drillstring during slide drilling: A comprehensive experimental study

The application of surface rocking-pipe-assisted drilling (SRPAD) technology is largely dependent on the ability driller to transfer an appropriate amount of weight to the bit. However, the impact of surface torque oscillations on the longitudinal drag and frictional torque is not thoroughly understood. For this purpose, in this study, a novel experimental apparatus was developed to study the load transfer characteristics along a drillstring during SRPAD. In the experiment, the forces and torques at both ends of the simulated drillstring were recorded, and the mechanical responses at various positions on the drillstring are monitored using a strain-measuring method. The experimental results suggest that properly rocking the drillstring back and forth can help operators regain most of the friction-reducing performance of conventional rotating drillstrings. Furtherore, we found that, if the pipe-rocking parameters, including the rocking velocity, rocking angle, surface hookload, and holding time, are properly controlled, the load transfer efficiency can be effectively improved. In particular, the rocking angle and surface hookload should be increased to reduce the stick-slip effect and buckling distortion. The experimental results provide important guidance for improving the performance of SRPAD system, though the flowing of drilling fluid and the influence of bent-housing motors are not taken into consideration.

Research on the mechanism and control methods of mechanical drift in linear ultrasonic motors

Linear ultrasonic motors (LUMs) have advantages such as de-energized self-locking and micro-nano displacement resolution. However, their positioning and control accuracy are negatively affected by mechanical drift, which limits their application in ultra-precision fields. To date, the quantitative mechanism of LUM mechanical drift under power-off conditions remains unreported. To solve the problem, we employ the creep theory to identify the clamp stiffness parameters and consider the internal friction and stick-slip effects of the slider, thereby establishing a non-autonomous dynamic model of the LUM mechanical drift in the power-off state. Subsequently, we utilize this model to investigate how the LUM’s structural parameters influence mechanical drift and explore methods to mitigate this undesirable phenomenon. Finally, we validate the model’s validity through experimental research. Our findings reveal that structural creep is the primary cause of mechanical drift in LUMs. Increasing the tangential stiffness of the clamp component and slider internal friction proves to be an effective approach to reducing mechanical drift. This study holds substantial theoretical and practical significance as it deepens understanding of the mechanisms of mechanical drift in LUMs and offers a pathway to achieve effective mechanical drift control.

A novel experimental setup for axial-torsional coupled vibration impact-assisted PDC drill bit drilling.

The geological conditions of hot dry rock (HDR) reservoirs are complex. The geothermal mining of HDR faces major challenges in the drilling and construction of wells, fracturing to create storage, and flowing to extract heat. Vibration impacts help improve the rock-breaking efficiency, where the axial-torsional coupled vibration impact technology can increase the bit penetration depth and reduce the stick-slip effect. To study the feasibility and efficiency of the axial-torsional-coupled vibration impact-assisted Polycrystalline Diamond Compact (PDC) bit to break high-temperature and high-pressure rocks, a new experimental setup was designed. The system includes a drilling fluid circulation system, an axial-torsional coupled impact drilling system, a formation simulation system, and a data acquisition and control system. This setup can produce a rock-breaking torque of 2000 N·m, a drilling speed of 200rpm, a weight on bit of 100kN, an axial vibration frequency of 100Hz, and a torsional vibration frequency of 50Hz. It can simulate the formation pressure of 70 MPa and the rock temperature of 400 °C. A series of rock-breaking drilling experiments were successfully conducted using this setup. The results show that the axial-torsional coupled vibration-impact assisted PDC bit has a good performance in breaking high-temperature and hard rocks, which can accelerate the application of this new technology in deep formation drilling.

Nanoscale Stick-Slip Behavior and Hydration of Hydrated Illite Clay

The present work is to shed light on the hydration and stick–slip behavior during shear process in interlayer region between clay sheets, because this region is the main location for the diffusion of water and ions, adsorption, hydration, slip, etc. Molecular Dynamics (MD) simulation method has been performed to investigate the interlayer hydration, diffusion, and shear behavior of various hydrated illites. The stick–slip effect found during shear process was explained by the potential energy surface of crystal layers. Simulation results indicated that water film in hydrated illite could be divided into multiple types of water layers. Moreover, the typical stick–slip effect was significantly related to the potential energy surface of illite crystal layers. The higher the hydrostatic pressure or the lower the water content, the more significant stick–slip effect, and the higher the average shear stress. The interlayer bound water played a bonding role during shear process, while free water was mainly for a lubricating role. The friction coefficient and internal friction angle of 10.2 % ∼ 61.2 % hydrated illite system in nanoscale are 0.023 ∼ 0.095 and 1.335° ∼ 5.438°, respectively.

Nanoscale friction at the quartz-quartz/kaolinite interface

The nanoscale friction behavior of quartz-quartz and quartz-kaolinite interfaces is investigated through Steered Molecular Dynamics (SMD) simulations. The effects of normal load, sliding velocity, temperature, and hydration on the friction behavior are discussed, and the friction mechanism of quartz and quartz/kaolinite interface is revealed. The friction coefficients of all systems at different cases are obtained and compared with other experimental results for validation. The simulation results show that the stick-slip effect in all interfaces was found during the friction process, where the higher the sliding velocity and hydration, or the lower the normal load, the weaker the stick-slip effect. The friction load increased with the rising normal load, and the relationship between shear stress and normal load was approximately linear. The friction coefficient and cohesion of the quartz-quartz interface could rise with the increasing sliding velocity or the decreasing temperature. Moreover, the friction coefficient of quartz-kaolinite was significantly smaller than that of quartz-quartz, indicating that the presence of clay could weaken the frictional strength of quartz. The effect of the interlayer water film on friction behavior was rather complex, showing the lubricating or bonding role, which has been discussed and analyzed in the present study.

Integration of a gas pressure chamber on a reciprocal tribometer for experiments at ambient pressures up to 10 bar

PurposeThis study aims to focus on the development of an experimental setup for testing tribological pairings under a gas atmosphere at pressures up to 10 bar.Design/methodology/approachA pressure chamber allowing oscillating movement through an outer shaft was constructed and mounted on an oscillating tribometer. Due to a metal spring bellows system, a methodology for the evaluation of the coefficient of friction values separately from the spring forces was developed.FindingsThe selected material concept was qualitatively and quantitatively assessed. An evaluation of the static and the dynamic coefficient of friction was performed, which was crucial for the understanding of the adhesion effects of the tested material pairing. The amount of information that is lost due to averaging the measured friction values is higher than one would expect.Originality/valueThe developed experimental setup is unique and, compared with the existing tribometers for testing under gas ambient pressures, allows testing under contact conditions that are closer to real applications, such as compressors and expanders. An in-depth observation of the adhesion and stick–slip effects of the tested material pairings is possible as well.Peer reviewThe peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-06-2023-0173/

Influence of torsional stick-slip vibration on whirl behavior in drill string system

Torsional and lateral vibrations, which are important causes of drill string failure, are harmful vibration modes that can occur during drilling. As its form of expression, stick-slip and whirl significantly limit the drilling efficiency and the bottom hole assembly (BHA) performance. Prediction of the correlation between these vibration modes has an important significance in adjusting basic parameters to avoid the effects of stick-slip and whirl vibration in the drilling process. In this work, in order to provide a general understanding of the vibration mechanism, a coupled torsional stick-slip and whirl model with 6 degrees of freedom (6-DOF) was proposed, and numerical simulations were conducted. The Lagrange method was used to derive the model, and the stabilizer-borehole wall interaction, drill collar-borehole wall interaction, and bit-rock interaction were additionally considered. Torsional vibrations were modeled with respect to the entire drill string system, while the lateral vibration was restricted to the BHA part. The results showed a correlation between torsional and lateral vibration modes when stick-slip vibration occurs and disappears. These correlations were performed by analyzing the time domain, frequency domain, and correlation coefficients. The relationship between torsional and lateral vibration modes was verified by performing a qualitative comparison with field experiments.

A complex model of a drilling rig rotor with adjustable electric drive

A modified mathematical model of an asynchronous electric drive of the rotor – a drill string – a bit – a rock is considered and implemented, which develops and generalizes the results of previously performed studies. The model includes the following subsystems: a model of an asynchronous drive with vector control; a model of formation of the resistance moment at the bottom of the bit, taking into account the peculiarities of the interaction between the bit and the rock; a model of a multi-mass mechanical part that takes into account the deformation of the drill string; subsystem for the drilling rig energy-technological parameters formation. The integrated model makes it possible to calculate and evaluate the selected drilling modes, taking into account their electro-mechanical, energy and technological efficiency and the dynamics of drilling processes. The performed computer simulation of drilling modes confirmed the possibility of a stick-slip effect accompanied by high-frequency vibrations during bit stops, which may change the direction of rotation of the bit, its accelerated wear and unscrewing of the drilling tool. Long bit stops lead to a significant decrease in the average bit rotation speed, which can explain the decrease in the ROP and increase in energy consumption when drilling in the zone of unstable bit rotation. The model can be used as a base for further improvement of rotary drilling control systems.

Dynamic analysis of gear pairs with the effects of stick-slip

The instantaneous dynamic contact state analysis is carried out to reveal the process of scuffing failure of the gear tooth pair. A stick-slip dynamic model of a two-gear set is proposed and the coupling effects of time-varying mesh stiffness, tooth separations, friction between the gear teeth surfaces, and potential stick-slip are considered. Dynamic analysis shows that stick contact is an important source of tooth scuffing failure. Additionally, stick contact dramatically increases the vibration amplitudes and causes chaos. Parametric studies show that heavy load and rough tooth surfaces increase the probability of sticking and increase the time of stick state over a single mesh period. This study provides a design guard for avoiding scuffing failure and improving the reliability of gear transmission.

Improved friction model applied to plane sliding connections by a large deformation FEM formulation

Friction is an important source of dissipation in dynamical systems. Properly considering it in the numerical model is fundamental to obtain stable and representative responses in structures and mechanisms. This is especially significant for the well-known Coulomb model due to discontinuity in force when stick-slip transition occurs. In this work an improved friction force model is proposed to smooth the force transition at null velocity, with an additional parameter obtained from the own system state. The improved model is employed in sliding connections of plane frames finite elements. A total Lagrangian Finite Element Method (FEM) formulation based on a positional description of the motion is employed. Using a variational principle, frictional dissipation is added to the total mechanical energy to develop the equations of motion. The resulting nonlinear equations are solved by the Newton-Raphson method accounting for the friction force update in the iterative process. Examples are presented to show the formulation effectiveness and possibilities in simulating dynamical systems that present the stick-slip effect.

Influencing mechanisms of a wax layer on the micro-friction behavior of the β-HMX crystal surface

This study investigated the influence of the wax layer on the micro-friction behavior of the energetic crystal surface by constructing the lubricating interface between wax and β-HMX crystals. The nano-scratch testing of β-HMX crystals with and without wax coating was conducted under the ramp-loading (0–3.5 ​mN) mode and the constant-loading (0.4 ​mN) mode. The testing results are as follows. Compared with the dry friction of β-HMX crystals without wax coating, wax can significantly improve the contact friction between the energetic crystals and the rigid micro-convex body. The influence of wax on the interface friction highly depends on the external load conditions. Under the ramp-loading mode, the wax layer can greatly reduce the average coefficient of friction (COF) from ∼0.7 (dry friction) to ∼0.2 (lubricating interface) and inhibit COF fluctuation. The inherent mechanism of wax reducing the interface friction works in the following way. Wax can effectively suppress the plowing effect of the rigid micro-convex body on the β-HMX crystal surface and further inhibit the occurrence of brittle fracture and crack defects. The wax layer can also suppress the friction anisotropy of the β-HMX crystal surface, significantly reducing the probability of high COF (>0.4). The distribution probabilities of COF in the range of 0–0.1 and 0–0.3 were 33% and 89%, respectively. The stick-slip effect of the friction behavior was observed under the constant-loading mode, with the COF varying periodically with the sliding distance. These study results can help understand the desensitization mechanisms of wax on the energetic crystal surface at a micro-scale quantitative level and provide a necessary basis for building the friction hot-spot model under dry friction and wax lubrication.

Experimental study on dynamic characteristics of axial-torsional coupled percussive drilling

Axial-torsional coupled percussive drilling is a novel technology to enhance the rate of penetration (ROP), which takes advantage of both axial and torsional percussive drilling technologies. Our paper focuses on experimental investigations on coupled percussive drilling. A novel experiment setup, using a rock breaking tester, was developed to carry out dynamic drilling tests on granite specimens under different impact modes, weight on bit (WOB), rotation rates, and lithologies. Based on the optimization analysis of window functions, by combining the fast Fourier transform (FFT) and short-time Fourier transform (STFT) processing methods, the spectrum and 3D time-frequency-amplitude evolution characteristics of coupling impact response signals were demonstrated. According to experimental results, a high-frequency and high-amplitude rotational rate and lower torque are produced in coupling impact. The agglomeration of the cutting force is alleviated and the occurrence of “stick-slip effect” is slowed down. Compared with axial impact, the penetration depth and ROP are increased by 173.38% and 182.74% in coupling impact, respectively. As the WOB increases, a stable-high frequency and high amplitude rock breaking torque is generated, which increases the cutting force and ROP. There is an optimal ratio between the rotation rate controlled by the axial rotator and the torsional impact frequency, which takes advantage of axial and torsional percussion for a bit and obtains the optimal speed-raising effect. The variation of rock mechanical properties has a significant influence on the amplitude of time domain signals in coupling impact. Our results in this paper are of great value for future studies of axial-torsional coupled percussive drilling.

Experimental Investigation of the Tribological Behaviors of Carbon Fiber Reinforced Polymer Composites under Boundary Lubrication.

Friction and wear experiments were performed on carbon fiber-reinforced polymer (CFRP) composites, and the tribological behavior of these materials under boundary lubrication (based on the 5100 4T 10 W-30 engine oil with TiO2 Degussa P25 nanoparticles) was investigated. Experiments were carried out in two directions: one at a different normal load from 6 to 16 N and one at a low sliding speed of 110 mm/min under boundary lubrication conditions. The obtained results reveal the stick-slip effect and the static and dynamic coefficient of friction decreased slightly with increasing normal applied load on the carbon fiber reinforced polymer composite pairs. The second direction highlights through experimental tests on the pin on disc tribometer that the friction coefficient increases with the increase in normal load (20–80 N) and sliding velocity (0.4–2.4 m/s). On the other hand, it is found that the friction coefficient is slightly lower than in the stick-slip phase. During the running-in process, the friction coefficient of the CFRP pair increases steadily as the rubbing time increases, and after a certain rubbing period, it remains constant regardless of the material of the counter face. The obtained results show that for the observed interval, the influence of normal load and sliding velocity have relatively small fraction coefficients and low wear depths. A 3D analysis of the profile demonstrated the texture of wear marks and tracks of these engineering composite materials. Furthermore, the height variations of wear marks and the morphologies of the worn surfaces of specimens under boundary lubrication conditions were analyzed.

Nanoscale Diamane Spiral Spring for High Mechanical Energy Storage.

A compact, stable, sustainable, and high-energy density power supply system is crucial for the engineering deployment of mobile electromechanical devices/systems either at the small- or large-scale. This work proposes a spiral-based mechanical energy storage scheme utilizing the newly synthesized 2D diamane. Atomistic simulations show that diamane spiral can achieve a high theoretical gravimetric energy density of about 564Wh kg-1 , about 14 500 times the steel spring. The interlayer friction between diamane is found to cause a strong stick-slip effect that results in local stress/strain concentration. As such, the energy storage capacity of the diamane spiral can be tuned by suppressing the influence from the interlayer friction. Simulations affirm that higher gravimetric energy density can be achieved by reducing the turn number or adopting a low friction contact pair. The fundamental principles that dominate the energy storage capacity of the spiral spring are theoretically analyzed, respectively. The obtained insights suggest that the 2D vdW solids can be promising candidates to construct spiral structures with a high gravimetric energy density. This work should be beneficial for the design of reliable, stable, and sustainable nanoscale mechanical energy storage schemesthat can be used as an alternative low-carbon footage energy supplier for novel micro-/nanoscale devices or systems.

Lubrication Behavior of n-hexadecane on ZnO Layer at the Nanoscale: A Molecular Dynamic Exploration

In this work, the lubricating models of Cu–Zn alloy with and without the Zinc oxide (ZnO) layer were established. Molecular dynamics (MD) simulation is employed to investigate the lubrication behavior of n-hexadecane on the ZnO layer at the nanoscale. The diffusion of lubricants molecules, and the interaction and stick–slip effect between the friction pairs and the lubricants are systematically explored. The results show that the ZnO layer limits the diffusion of n-hexadecane molecules and the formed lubricating films in the model of the substrate with the ZnO layer are obvious and stable. During the sliding process, ZnO molecules have strong interaction with lubricants molecules and adsorb lubricants molecules on the surface to form adsorption film. The stick–slip effect in the lubricating films generates periodic shear stress and reduces the wear of the friction pair. The ZnO layer causes lubricants molecules to be arranged regularly on the surface into a stable structure.