Intermittent Contact Research Articles

A compliant mechanism actuated bistable hybrid mode triboelectric nanogenerator

Abstract Triboelectric nanogenerators (TENGs) working in sliding mode offer higher power generation capability compared with those working in contact-separation mode (CS-TENGs). However, unlike CS-TENGs, sliding action can limit TENG lifespan due to wear and tear. A TENG combining both modes with intermittent sliding actions can overcome this limitation. In this study, we propose a bistable hybrid mode TENG (BHM-TENG) that can leverage the functionalities of the traditional sliding TENG and CS-TENG and achieve both durability and satisfactory performance, enabled by a compliant mechanism design. A self-rotating base introduces sufficient sliding during intermittent contact, leading to significant improvement in charge transfer (44%) and voltage output (58%) compared with the conventional TENGs while minimising wear and tear. The prototyped device, excited using compliant beams, can be effectively actuated even at extremely low input frequencies (<0.1 Hz), as explained by a mathematical model. The real-world energy harvesting applications enabled by BHM-TENG is proposed based on the output of BHM-TENG.

Corrosion mapping of intermetallic in a dissimilar weldment using in-situ alternating current scanning electrochemical microscopy

In the present work, in-situ corrosion activity mapping across explosively welded 304 L SS-Zr-4 dissimilar joint interfaces was performed using intermittent contact alternating current-scanning electrochemical microscopy (IC-AC-SECM). Two weld joint samples, one with a regular interface and another with an irregular interface, were examined for their local surface activities at an open circuit potential in tap water without using a redox mediator. The SEM micrographs showed the formation of intermetallics at localized regions of the irregular interface weld sample but not in the regular interface sample. The 304 L SS regions of the welds were relatively anodic, with current and impedance magnitude values of 270 ± 20 nA and 380 ± 20 kΩ respectively, when compared to the Zr-4 regions with the corresponding values of 160 ± 20 nA and 630 ± 20 kΩ, due to galvanic coupling effect. The IC-AC-SECM technique enabled the in-situ determination of corrosion activity of localized intermetallic region within the weldment. The current and impedance magnitude values of the intermetallic region were ∼ 240 nA and ∼ 450 kΩ, respectively, showing only a slightly lesser anodic activity as compared to the 304 L SS base metal. The results obtained from the IC-AC-SECM mapping showed a good correlation with the EDS elemental mapping of the dissimilar weldment with intermetallic. The findings indicate the effectiveness of the IC-AC-SECM technique for the in-situ localized corrosion mapping of dissimilar weld joints, showcasing its potential for various applications in assessing weld integrity.

Effects of air damping on quality factors of different probes in tapping mode atomic force microscopy

Abstract The AFM probe in tapping mode is a continuous process of energy dissipation, from moving away from to intermittent contact with the sample surfaces. At present, studies regarding the energy dissipation mechanism of this continuous process have only been reported sporadically, and there are no systematic explanations or experimental verifications of the energy dissipation mechanism in each stage of the continuous process. The quality factors can be used to characterize the energy dissipation in TM-AFM systems. In this study, the vibration model of the microcantilever beam was established, coupling the vibration and damping effects of the microcantilever beam. The quality factor of the vibrating microcantilever beam under damping was derived, and the air viscous damping when the probe is away from the sample and the air squeeze film damping when the probe is close to the sample were calculated. In addition, the mechanism of the damping effects of different shapes of probes at different tip–sample distances was analyzed. The accuracy of the theoretical simplified model was verified using both experimental and simulation methods. A clearer understanding of the kinetic characteristics and damping mechanism of the TM-AFM was achieved by examining the air damping dissipation mechanism of AFM probes in the tapping mode, which was very important for improving both the quality factor and the imaging quality of the TM-AFM system. This study’s research findings also provided theoretical references and experimental methods for the future study of the energy dissipation mechanism of micro-nano-electromechanical systems.

Robust maglev hybrid nanogenerator with an airflow-based motion conversion mechanism for exploiting low-frequency mechanical energy

Triboelectric nanogenerator (TENG) has been widely recognized as an efficient technology for exploiting low-frequency (LF) mechanical energy, but the sparse outputs at low frequencies and insufficient durability at high frequencies hinder its extensive applications. Herein, a robust and high-output triboelectric-electromagnetic hybrid nanogenerator (TEHG) is proposed with an ingenious airflow-based motion conversion mechanism (AMCM) and a well-designed maglev mechanism. Distinct from conventional MCMs generally constructed with complicated rigid components, the AMCM transforms LF-motions to fast rotation through a flexible bladder and air tubes. Enabled by the AMCM, the TENG part can provide power density up to 274 mW/kg at an output frequency 70 times higher than the excitation frequency. The normalized voltage of the TENG part stabilizes at 84.1 % after 8-day durability test with the specially designed maglev mechanism, which allows the TENG part to operate in intermittent (sliding) contact state under slow rotation to replenish tribo-charges with minor material wear whereas switch to non-contact state without material wear under fast rotation. By combining the complementary output characteristics of triboelectric and electromagnetic technologies, a storage capacitor can be charged to a higher voltage level within remarkably reduced time. The practical feasibility of the AMCM-TEHG was verified by arranging it on a footpath to charge a wireless digital camera and a wireless sensing system. This study provides a promising strategy for multiplying the output frequencies as well as increasing the durability of TEHGs for efficiently exploiting LF-mechanical energy.

High-frequency nonlinear vibration analysis through low-frequency stereo-camera systems

This paper describes a new methodology that expands the capabilities of low-frame, high-resolution stereo-camera systems in studying the dynamic behavior of components in the presence of nonlinear phenomena. A new downsampling technique called the Smoothed Harmonics Analysis (SHA) is proposed. This technique addresses the limitations due to the low-frame rate cameras for the study of high-frequency periodic steady-state nonlinear oscillations. SHA enables accurate reconstruction of downsampled signals, thus opening up numerous potential applications. The feasibility of this technique is demonstrated by analyzing the motion of a beam with nonlinear behavior. The nonlinearity is caused by intermittent contact while the beam is subjected to harmonic excitation.

Adaptive optimal concurrent control for detumbling space non-cooperative target via multipoint repeated contact

Space debris generally exhibits complex tumbling motions, and its direct capture may cause damage to space manipulator and base spacecraft. Current detumbling strategies typically require continuous contact collisions with the target and do not take into account actuator limitations. Thus, this paper presents an adaptive optimal concurrent control of space free-floating multi-fingered robot (SFMR) for multipoint repeated contact detumbling of non-cooperative targets. Firstly, the multipoint repeated intermittent contact model between the SFMR and the target is established. Further, an optimal admittance control that considers manipulator actuator limits and target motion bounds is formulated to generate a compliant detumbling trajectory. Through transforming the state and input inequality constraints into extended dynamical subsystems and saturation functions, respectively, the optimal control problem (OCP) is transformed into a readily solvable equality constraint problem. Moreover, an enhanced nonsingular terminal sliding mode (ENTSM) control with radial basis function neural network (RBFNN) compensation is presented in the presence of lumped uncertainties and external disturbances, which achieves rapid finite-time convergence and low-chattering. The simulation results show that the proposed method can reduce the velocity of the space target effectively without causing base spacecraft interference while achieving accurate trajectory tracking.

Analysis of Wear Characteristics of Hydrodynamic Seals During Startup Using 3D Fractal Characterization and Study of Opening Performance Degradation Mechanism

An experimental study was conducted to investigate the degradation mechanism of the opening performance of hydrodynamic seals during multiple startups, and a model was proposed to analyze the wear characteristics during the startup process. The study that the state evolution of the hydrodynamic seal during the single startup process occurs in five stages: low-speed and heavy-load stage, mid-speed and mid-load stage, high-speed and light-load stage, intermittent contact stage, and noncontact stage. The main factor that influences the deterioration of the initial performance of hydrodynamic seals during multiple startups is the decrease in the depth of the root groove. To prevent the heavy deterioration of the opening performance of the hydrodynamic seal, it is important that the remaining depth of the tip of spiral groove (TSG) is greater than 47.67% of the initial value and the dimensionless startup time should not exceed 0.42 for a complete passage through the mid-speed and mid-load stage.

Effect of Oil-Water Intermittent Wetting on Corrosion Inhibition of Carbon Steel in CO2 Environment

ABSTRACT Produced water can cause internal corrosion in oil pipelines. The flow of hydrocarbons and water can result in intermittent surface wetting, which can impact corrosion inhibition. However, this is still poorly understood. This research studies the impact of intermittent wetting and the wettability of the steel surface on corrosion inhibition, utilizing electrochemical techniques. An inhibitor model compound and model oil were employed at 25°C and 55°C in CO2 saturated solutions. Corrosion inhibition varied with temperature and steel surface hydrophobicity, altering inhibition significantly after intermittent contact with hydrocarbon at 55°C. EIS and wettability results revealed distinct protective mechanisms when oil was present.

Improved stiff string torque and drag prediction using a computationally efficient contact algorithm

ABSTRACT Due to the intermittent contact with the wellbore, determining torque and drag for deviated wells is difficult. Most models have ignored drill string stiffness and assumed continual contact to simplify derivation. However, the accuracy of these ‘soft-string’ models is restricted, especially at high dogleg severities. On the other hand, most ‘stiff-string’ models rely on computationally intensive approaches or continuous contact assumptions. To mitigate these issues, a computationally efficient penalty-based wellbore contact algorithm has been developed based on vector calculation, which at most requires two dot products and three arithmetic operations to determine contact locations. This algorithm is incorporated into a 3D multibody dynamics (MBD) model, which utilizes rigid drill-string segments based on the Newton-Euler formulation, connected via axial, shear, torsional, and bending springs to capture drill string flexibility. This model performs simulations faster than real-time and has been validated using surface measurements from a completed well.

Rotation‐To‐Translation Enabled Robust Triboelectric Nanogenerator for Wind Harvesting and Sensing

AbstractDisc and cylinder‐based triboelectric nanogenerators (TENGs) have great potential for harvesting wind energy. However, a significant challenge faced by these TENGs is the wear issues arising from the required close contact between tribo‐materials, especially at high frequencies. In response to this challenge, a gear‐slider TENG (GS‐TENG) is designed to transition from continuous close‐contact friction mode to intermittent contact. Working in unison with the central gear and two sliders, four units housed within GS‐TENG yield electrical output through periodic contact and separation. During a durability test of 845 000 cycles, the short‐circuit current only experiences a slight decrease, going from 25.38 to 24.03 µA, retaining 94.68% of its initial value. Operating at a matched impedance of 6 MΩ, GS‐TENG at M1 achieves a peak power density of 386 mW m−2, exceeding some previously proposed solutions in wind harvesting. When integrated into a wind speed sensing system, the GS‐TENG has a wide sensing range (13.1 to 28 m s−1) with a maximum error of 3.39%. This work demonstrates a rotation‐to‐translation strategy that lays the foundation for long‐term, high‐frequency wind energy harvesting and the development of a self‐powered wind sensing system.

Effect of Radial Directional Vibration-Assisted Ductile-Mode Grinding of Al2O3 Ceramics

Effect of Radial Directional Vibration-Assisted Ductile-Mode Grinding of Al₂O₃ Ceramics

Design method of rack-and-pinion pair with pure rolling variable transmission ratio

Rack-and-pinion pair with variable transmission ratio can achieve the unity of vehicle steering portability and sensitivity, and effectively reduce vehicle steering energy consumption. Therefore, they have gradually become the standard core components of steering system. However, the gear surface of rack-and-pinion pair with variable transmission ratio is seriously worn under long-term service, which leads to the degradation of performance and cannot achieve the theoretically variable transmission ratio. To solve these problems, a new configuration of rack-and-pinion pair for commercial vehicle with herringbone pure rolling variable transmission ratio is proposed in this paper. The tooth surface mathematical model of the fully-conjugate variable transmission ratio is established based on the variable speed envelope principle, and the formula for calculating pure rolling point of tooth surface with variable transmission ratio is derived. The tooth point deviation equation of fully-conjugate variable transmission ratio is proposed, and the method of constructing pure rolling variable transmission ratio tooth surface is formed. The finite element analysis shows that the design of the pure rolling rack-and-pinion pair with variable transmission ratio has good tooth surface quality without the phenomenon of contact spot intermittent and edge contact during the meshing process, and the contact ellipse center of the tooth surface is located at the theoretical pure rolling point of the tooth surface. The measured transmission ratio curve of the samples is in good agreement with the theoretical variable transmission ratio curve, and the transmission ratio error is within a reasonable range. The contact strips of tooth surface impression test are consistent with those of finite element analysis, which indicates that the designed rack-and-pinion pair with variable transmission ratio has the characteristics of pure rolling and point contact. The tooth surface wear test shows that the wear of pure rolling gear surface with variable transmission ratio is obviously less than that of traditional gear surface with variable transmission ratio. The above tests and simulation indicate the correctness of the design method.

Spontaneous Recycling of Electrosprayed Sample by Retrograde Motion of Microdroplets.

Here, we discuss an interesting phenomenon occurring spontaneously near the sample liquid meniscus at the tip of the electrospray emitter. While most ejected droplets move from the emitter tip toward the counter electrode, some of the droplets decelerate and move backward to the liquid meniscus. When they hit the surface of the liquid meniscus, they either merge with the bulk liquid or get recharged during intermittent contact with the liquid meniscus and immediately reaccelerate toward the counter electrode. In some cases, while in contact with the meniscus they spontaneously form a secondary Taylor cone and emit progeny droplets. This observation suggests that the amount of electric charge transferred to such a droplet is sufficient to surpass the Rayleigh limit. Similar effects were previously observed for water as well as for NaCl-water and ethanol-water mixtures. However, here we observed it for electrolyte solutions commonly used in electrospray ionization mass spectrometry: methanol-water solutions with the addition of ammonium acetate, formic acid, or ammonium hydroxide. The reported phenomenon reveals the ongoing recycling of sample liquid in electrosprays. Such recycling can contribute to enhancement of sample utilization efficiency in electrospray ionization.

Numerical continuation and stability of nonlinear systems with distributed delays: Application to fluid-induced impacts of tubes in cross-flow

Fluid–elastic instability is the main source of concern during the design of heat-exchanger tube bundles. The associated research has focused on the understanding of the physical mechanisms behind this phenomenon and the establishing of models capable of predicting its onset; also some concomitant work has been done to establish post-instability behaviour and to prevent from excessive wear in possible sliding contacts. Moreover, the existing studies make use of time-integration methods alone for this purpose, through which it is difficult to get a comprehensive insight of global dynamics. Continuation methods, which give access to unstable branches and precise bifurcation information, are a precious tool to unfold the attainable dynamic regimes. In this paper, the parametric behaviour of two representative systems under cross-flow excitation is explored through pseudo arc-length continuation with mean flow velocity as a main driving parameter, wherein the nonlinear modal equations of motion are solved by harmonic balance at each step. As the quasi-unsteady model used for fluid–elastic coupling introduces convolution integrals, this approach is quite natural and we show that, despite some difficulties regarding the treatment of stiff intermittent contacts, it allows for a thorough exploration of the system’s response. For the first case -a benchmark model-, increasingly complex dynamics arise as more modes are kept in the truncated modal basis, which is due to a series of modal interactions as the impacts distribute mechanical energy from the linearly-unstable first mode to the higher ones. This can be anticipated by studying the nonlinear normal modes of the system, as they expose the allowed internal resonances. In the second case, consisting of a realistic heat-exchanger tube configuration, a similar pattern is observed.

Plant Micropropagation and Temporary Immersion Systems.

Temporary immersion systems (TIS) have been widely recognized as a promising technology for micropropagation of various plant species. The TIS provides a suitable environment for culture and allows intermittent contact of the explant with the culture medium at different immersion frequencies and aeration of the culture in each cycle. The frequency or immersion is one of the most critical parameters for the efficiency of these systems. The design, media volume, and container capacity substantially improve cultivation efficiency. Different TIS have been developed and successfully applied to micropropagation in various in vitro systems, such as sprout proliferation, microcuttings, and somatic embryos. TIS increases multiplication and conversion rates to plants and a better response during the ex vitro acclimatization phase. This article covers the use of different immersion systems and their applications in plant biotechnology, particularly in plant tissue culture, as well as its use in the massive propagation of plants of agroeconomic interest.

Feasibility of friction stir welding using a hemispherical tool tilted towards the retreating side

The use of a hemispherical tool tilted towards the retreating side for friction stir welding 6061-T6 aluminum alloy is investigated. Joints with smooth surfaces and without internal voids are obtained. Under the same welding and rotational speeds, adapting the tilt angle makes it possible to weld various thicknesses up to 3.5 mm. Plunge depth and tilt angle are demonstrated to be key geometrical parameters driving material flow when using the hemispherical tool. Microstructural features in the weld are equiaxed and refined grains below 5 µm in the stirred zone and narrow thermo-mechanical affected zones. The through-thickness thermomechanical gradient developing beneath the hemispherical tool leads to different extents of dynamic recrystallization and recovery in the stirred zone. The tool orientation towards the retreating side and the division of the tool-workpiece interaction in continuous and intermittent contact leads to an asymmetrical thermal field around the stirred zone. Hence, the new derivative friction stir welding solution allows the welding of multiple aluminum alloy blank thicknesses using the same tool.

Dynamics of a helical spring involving intermittent frictional contact with an oscillating barrier

This study concerns the transverse and longitudinal dynamics of helical springs. When a string is wrapped in helix to form a helical spring, its bulk longitudinal stiffness reduces. This leads to complicated dynamics of the spring in both transverse and longitudinal directions especially when it involves frictional contacts against a barrier. To simulate such dynamics, experiments and numerical simulations were conducted focusing on the intermittent contact between the helical spring and an oscillating barrier. First, to investigate the effects of longitudinal stiffness on the dynamics of the spring, vibration tests were conducted using the helical spring and a piano string with higher longitudinal stiffness. Vibration of the spring showed slower attenuation and involved more frequency components than the piano string. Next, numerical simulations were conducted with intermittent contact and friction between the spring and the barrier along with the deformation of the spring in the longitudinal direction. The computed vibration in the longitudinal direction with friction resulted in also slower attenuation and more frequency components than those of the case without friction. These results indicate that by conducting simulations with longitudinal deformation and friction, the vibration of a helical spring contacting with the barrier can be simulated with high accuracy.

Characteristics of atomic removal and mechanism of damage formation in vibration-assisted nano cutting of copper-nickel alloy

Vibration-assisted machining technology can effectively improve the quality and efficiency of nano cutting, but the characteristics of atomic removal and the mechanism of damage formation have not been systematically studied. In this paper, copper-nickel alloy material is taken as an example. The characteristics of vibration-assisted nano cutting and the plastic deformation behavior of materials were revealed by molecular dynamics simulation. The simulation results show that vibration-assisted nano cutting reduces tangential force, lateral force, and total force, strengthens the anisotropy of atomic motion, and causes greater displacement and removal of Cu/Ni atoms. The intermittent contact is beneficial for the elastic recovery of workpiece atoms, releasing internal stress and atomic strain, reducing the depth of damage and the length of dislocation lines. The difference in surface/subsurface damage to the workpiece is relatively small with an amplitude of 1 Å. With amplitudes of 3 Å and 5 Å, and as the frequency increases, the complete lattice structure is destroyed, resulting in a significant decrease in the number of FCC structural atoms and RDF peak. However, an appropriate increase in frequency can increase the removal of Cu/Ni atoms, improve the topological structure, and reduce RMS. The HCP and BCC structural atoms affect the generation of dislocation lines, with an amplitude of 3 Å and a frequency of 7.5 GHz, achieving the minimum damage depth and dislocation line length. Excessive amplitude of 10 Å results in irreversibly severe damage to the surface/sub-surface of the workpiece. This study will provide a new approach for optimizing vibration-assisted nano-cutting technology and achieving low-damage nano cutting of alloy materials.

Influence of the friction modelling decisions on the acceptance of the running behaviour of a friction-damped locomotive

Multibody simulations are widely used for the dynamic analysis of railway vehicles, including the acceptance of vehicle running behaviour. Among these, the freight vehicles have, generally, friction damped suspensions for which numerical modelling is particularly challenging due to the contacting geometries, the intermittent contact, and the frequent stick-slip transitions. The impact of modelling decisions of friction-damped suspensions on the acceptance quantities for vehicle behaviour is the focus of this work. The selection of friction models and tuning of their parameters is challenging. In particular, the selection of friction coefficients is not straight forward, as friction conditions vary during operation and over time. This work aims to address both problems. A model of a friction-damped freight locomotive is used to simulate the dynamic response of the vehicle under realistic operation conditions and assess the impact of the friction modelling decisions. The results show that the use of different friction models provides similar results if the parameters are appropriately tuned. In contrast, the selection of friction coefficients significantly impacts the acceptance quantities, with emphasis on the wheel-rail forces at small radius curve transitions. The results recommend that the standard should include variations of the friction coefficients used for the friction-damped suspensions.

Analyzing the backbone curve of piecewise-linear non-smooth systems using a generalized bilinear frequency approximation method

Estimating the resonant frequency of non-smooth systems with contacting elements is critical for the design, control, and health monitoring of various mechanical and aerospace structures. The nonlinearity caused by the intermittent contact excludes the use of efficient linear methods; hence, predicting vibration characteristics of these systems becomes computationally challenging. Furthermore, several numerical and analytical approaches that have been developed for analyzing smooth nonlinear systems cannot be applied to analyze non-smooth oscillators. To understand the dynamic properties of non-smooth dynamical systems, the bilinear frequency approximation (BFA) method, a classical analytical tool, was developed to estimate the nonlinear natural frequency of bilinear oscillators by using the linear characteristics of underlying linear subsystems to construct a closed-form analytical solution. However, the traditional BFA method is only applicable to systems in which the gap size between the contacting element is zero, which limits the capability of this efficient analytical technique. In this paper, a generalized BFA method is proposed to extend the capability of the method to capture the nonlinear natural frequency of high-dimensional non-smooth systems where either gaps or prestress exist. The generalized BFA method employs the natural frequencies, mode shapes, and modal amplitudes of the linear subsystems as well as the gap size at the contacting degrees of freedom (DOF) to estimate the nonlinear natural frequencies at different amplitude levels. The backbone curve of non-smooth oscillators can be efficiently constructed using the proposed analytical method. The generalized BFA method is demonstrated on a single-DOF system, a three-DOF system, and a finite element model (FEM) of a cantilever plate with contacting elements. The results show that the proposed method provides an accurate approximation of the backbone curve for the first resonance, which has the most dominant vibration response, with very low computational effort, but a rather poor approximation for higher resonances. The proposed technique can be integrated with high-dimensional FEMs to analyze the nonlinear resonance of complex structures. The performance of the method is validated both numerically and experimentally in this work.