Статті в журналах: "Interfaces à contact intermittent"

1

Labardi, M., P. Tripathi, S. Capaccioli, and R. Casalini. "Intermittent-contact local dielectric spectroscopy of nanostructured interfaces." Nanotechnology 33, no. 21 (February 28, 2022): 210002. http://dx.doi.org/10.1088/1361-6528/ac52be.

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Abstract Local dielectric spectroscopy (LDS) is a scanning probe method, based on dynamic-mode atomic force microscopy (AFM), to discriminate dielectric properties at surfaces with nanometer-scale lateral resolution. Until now a sub-10 nm resolution for LDS has not been documented, that would give access to the length scale of fundamental physical phenomena such as the cooperativity length related to structural arrest in glass formers (2–3 nm). In this work, LDS performed by a peculiar variant of intermittent-contact mode of AFM, named constant-excitation frequency modulation, was introduced and extensively explored in order to assess its best resolution capability. Dependence of resolution and contrast of dielectric imaging and spectroscopy on operation parameters like probe oscillation amplitude and free amplitude, the resulting frequency shift, and probe/surface distance-regulation feedback gain, were explored. By using thin films of a diblock copolymer of polystyrene (PS) and polymethylmethacrylate (PMMA), exhibiting phase separation on the nanometer scale, lateral resolution of at least 3 nm was demonstrated in both dielectric imaging and localized spectroscopy, by operating with optimized parameters. The interface within lamellar PS/PMMA was mapped, with a best width in the range between 1 and 3 nm. Changes of characteristic time of the secondary (β) relaxation process of PMMA could be tracked across the interface with PS.

2

Ayala, Jose R. Ruiz, Kwangjin Lee, Mujibur Rahman, and J. R. Barber. "Effect of Intermittent Contact on the Stability of Thermoelastic Sliding Contact." Journal of Tribology 118, no. 1 (January 1, 1996): 102–8. http://dx.doi.org/10.1115/1.2837063.

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In many sliding systems, the sliding surfaces are not coextensive, so that points on one surface experience alternating periods of contact and separation. This intermittent process can be expected to influence the sliding speed at which the system is susceptible to frictionally-induced thermoelastic instability (TEI). This question is explored in the context of a simple system consisting of a rotating thin-walled cylinder whose end face slides against a rigid surface. The results show that at low Fourier number—i.e., when the frequency of the process is high compared with the thermal transient of the system—only the time-averaged frictional heat input is important and the critical speed is an inverse linear function of the proportion of time in sliding contact. At higher Fourier number, lower critical speeds are obtained, but the dependence on Fourier number is relatively weak.

3

Li, Yufeng, and Aric R. Kumaran. "The Determination of Flash Temperature in Intermittent Magnetic Head/Disk Contacts Using Magnetoresistive Heads: Part II—Experimental Investigation." Journal of Tribology 115, no. 1 (January 1, 1993): 179–84. http://dx.doi.org/10.1115/1.2920973.

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The flash temperature during intermittent head/disk contacts was measured using specially fabricated magnetoresistive heads. Microasperities were intentionally created on disk substrates, and ZrO2 was sputtered on disc surfaces as overcoat. It was found that with a disk spinning speed of 20 m/s, flash temperature could reach 50 to 100°C for transient contact (head was moving in disk radial direction), but less than 40°C for dwell on track contact (head was stationary). The contact times were in the range from submicroseconds to several microseconds, contact widths on the order of several micrometers, and temperature sensitivity coefficients in the range from 0.15 to 0.7 for a 2.5–μ high magnetoresistive sensor.

4

Li, Yufeng, and Aric R. Kumaran. "The Determination of Flash Temperature in Intermittent Magnetic Head/Disk Contacts Using Magnetoresistive Heads: Part I—Model and Laser Simulation." Journal of Tribology 115, no. 1 (January 1, 1993): 170–78. http://dx.doi.org/10.1115/1.2920972.

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The feasibility of using a magnetoresistive magnetic head to determine the flash temperature of intermittent magnetic head/disk contacts is investigated. A finite difference model is developed to study the effects of the magnetoresistive sensor height, the contact power intensity and the contact duration on the temperature response characteristics of the magnetoresistive sensor. A pulsed neody-minum:yttrium-aluminum-garnet laser is used as the heat source to simulate the contact and verify the model. The simulation results agree well with the theoretical model. Based on the theoretical model and laser simulation, a temperature sensitivity coefficient ζ is proposed to determine the surface temperature rise.

5

Peng, Wei, James Kiely, and Yiao-Tee Hsia. "Wear Analysis of Head-Disk Interface During Contact." Journal of Tribology 127, no. 1 (January 1, 2005): 171–79. http://dx.doi.org/10.1115/1.1843832.

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To achieve a higher storage density in a hard disk drive, the fly height of the air bearing slider, as part of the magnetic spacing, has to be minimized. At an ultralow fly height, the intermittent–continuous contact at the head–disk interface (HDI) is unavoidable and directly affects the mechanical and magnetic performance of the hard disk drive, and is of great interest. The HDI wear has a nonlinear and time-varying nature due to the change of contact force and roughness. To predict the HDI wear evolution, an iterative model of Coupled Head And Disk (CHAD) wear, is developed based on the contact mechanics. In this model, a composite transient wear coefficient is adopted and multiple phases of the wear evolution are established. A comprehensive contact stiffness is derived to characterize the contact at the HDI. The abrasive and adhesive wear is calculated based on the extended Archard’s wear law. The plastic and elastic contact areas are calculated with a three-dimensional (3D) sliding contact model. Based on the CHAD wear model, for the first time, the coupling between head and disk wear evolutions is thoroughly investigated. Accelerated wear tests have also been performed to verify the disk wear effect on the slider wear. A wear coefficient drop with time is observed during the tests and it is attributed to a wear mechanism shift from abrasive to adhesive wear. A shift in the type of contact from plastic to elastic accounts for the wear mechanism change.

6

Maeno, Takashi, and David B. Bogy. "Effect of the Rotor/Stator Interface Condition Including Contact Type, Geometry, and Material on the Performance of Ultrasonic Motor." Journal of Tribology 116, no. 4 (October 1, 1994): 726–32. http://dx.doi.org/10.1115/1.2927326.

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The purpose of this paper is to show the dynamic contact characteristics and the motor performance of several types of ultrasonic motors. First, we compare the performance of “intermittent” and “traveling” contact type ultrasonic motors by using the locally deforming rotor model. We show that the motor performances are the same when the shape of the stator’s amplitude, and the rotor’s interpenetration are the same. Then, we show that the performance of these two types of motors are different according to the effects of inertia and actual three dimensional displacement by using the FE (finite element) analysis. Finally, the effects of the teeth and a surface layer at the contact interface on the performance of the ultrasonic motor, including T-N (torque-speed) characteristics and friction loss, are analyzed.

7

Polycarpou, A. A., and A. Soom. "A Two-Component Mixed Friction Model for a Lubricated Line Contact." Journal of Tribology 118, no. 1 (January 1, 1996): 183–89. http://dx.doi.org/10.1115/1.2837076.

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A two-component, two-dimensional friction model for a lubricated line contact, operating in boundary and mixed lubrication regimes, is developed. The friction is explicitly decomposed into the solid and the fluid shear components. The solid component is due to the asperity interactions and the fluid shear arises from the lubricant present at the interface. The friction model includes the sliding velocity, the instantaneous separation of the sliding bodies, normal to the sliding direction, the normal load and fluid properties. The model is based on unsteady friction experiments carried out under constant normal loads and time-varying sliding velocities. The model is applied to quasi-steady sliding, unsteady continuous and intermittent sliding, including sticking and momentary reversals of motion. In each case it becomes possible to track the instantaneous fluid shear and solid friction components.

8

Lotfi, Mohammad, Saeid Amini, and Hossein Ashrafi. "Theoretical and numerical modeling of tool–chip friction in ultrasonic-assisted turning." Proceedings of the Institution of Mechanical Engineers, Part E: Journal of Process Mechanical Engineering 233, no. 4 (November 15, 2018): 824–38. http://dx.doi.org/10.1177/0954408918812271.

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Decrease of friction in tool–chip contact zone is a key subject in metal cutting operation. Therefore, effect of ultrasonic vibration in this area is analyzed by using experimental and simulation methods. In this study, a theoretical model is firstly developed based on the shear friction model, and then sticking–sliding contact zones plus their contact lengths are defined in order to simulate conventional and ultrasonic-assisted turning. Accordingly, shear angle, sticky length, and cutting forces were measured in experiments as input parameters for the calculation of friction coefficients. As a result, intermittent contact of vibrated tool decreases the time of thermal conduction in tool–chip interface, resulting in a significant reduction in friction coefficient and contact length, particularly, in sticky region.

9

Barber, J. R., T. W. Beamond, J. R. Waring, and C. Pritchard. "Implications of Thermoelastic Instability for the Design of Brakes." Journal of Tribology 107, no. 2 (April 1, 1985): 206–10. http://dx.doi.org/10.1115/1.3261021.

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Thermal distortion in brakes due to frictional heating causes localized contact and high temperatures (hot spots) with consequent thermal damage to the sliding components. This paper examines the effect of brake design and operating parameters on the maximum temperature reached. Previous solutions for steady-state sliding are reviewed and the effects of hot spots being in intermittent contact due to the geometric design of the brake are discussed. Approximate solutions for transient thermoelastic contact are extended to the case of uniform deceleration to determine the duration of the stop for which thermoelastic effects will be significant. If the stop is sufficiently slow for hot spots to develop, the temperatures will generally be high. However, high temperatures are also reached in sufficiently rapid stops due to the high rate of energy dissipation. An optimum is found between these extremes.

10

Li, Shiqi, and Tianyang Ma. "Dynamic performance fluctuation of solid-lubricated rotating mechanism for intermittent operation caused by launch vibration load." Proceedings of the Institution of Mechanical Engineers, Part J: Journal of Engineering Tribology 232, no. 4 (July 3, 2017): 401–14. http://dx.doi.org/10.1177/1350650117716371.

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Space mechanism is the key to success of long-term space missions. The service life of solid-lubricated space mechanisms is affected by various mechanical loads before in-orbit operation, among which the load caused by the launch vibration is the most severe one. Dynamic performance is an indication of the operating state of solid-lubricated mechanisms. The fluctuation of dynamic performances caused by the load of launch vibration is an unanswered but important question. In this paper, the fluctuation of dynamic performances of solid-lubricated rotating mechanisms for intermittent operation was studied by means of experiments and theoretical analyses. One group of rotating mechanisms for intermittent operation with solid-lubricated ball bearings were subjected to sine sweep tests and random vibration tests, followed by continuous operation test. The dynamic performance of mechanisms was obtained throughout all tests. The other group of mechanisms were studied with continuous operation test only for comparing the effects of vibration on the dynamic performance of mechanisms. At the same time, the sample moments of the dynamic performance of mechanisms were calculated and analyzed. The contact stress in the vibration tests was calculated by the Hertz theory. The fluctuation of the dynamic performances of solid-lubricated rotating mechanisms for intermittent operation caused by the load of launch vibration was then concluded with further discussion.

11

Suzuki, M., and K. C. Ludema. "The Wear Process During the “Running-In” of Steel in Lubricated Sliding." Journal of Tribology 109, no. 4 (October 1, 1987): 587–91. http://dx.doi.org/10.1115/1.3261511.

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Steel cylinders were slid against flat steel disks, using a liquid lubricant, in order to study the progression of events associated with “running-in.” It was found that, when using mineral oil, the electrical contact resistance varied over a small range of high values indicating no metallic contact, whereas with engine oil a high resistance with an intermittent negligible contact resistance was found. A surface film forms from the additives in the engine oil which produces lower wear, slightly higher friction, a retarded running-in, and a rougher surface finish in the direction of sliding than does the mineral oil. A film which is composed only of Fe3O4 is formed when mineral oil is used. In addition, the mineral oil lubricated surfaces develop a conforming waviness across the sliding tracks. The oxide must have enhanced this surface conformity since it was not seen in the surfaces lubricated with engine oil. The role of the oxide may be further seen in experiments in which wear debris that accumulated in the entrance region of specimen contact was removed at frequent intervals. Little conforming waviness was seen in the latter case, suggesting that oxide which gathered in the entrance region abraded grooves in the steel surfaces. After the oxides were dislodged the friction increased and the contact resistance decreased for a time, indicating that the oxide acted like a solid lubricant.

12

Annakodi, Vivek Anand, Ramachandra Arvind Singh, Subramanian Jayalakshmi, Yupeng Zhang, Muhammed Anaz Khan, Koppula Srinivas Rao, and Rajashekhara Shabadi. "Patterning SS304 Surface at Microscale to Reduce Wettability and Corrosion in Saline Water." Metals 12, no. 7 (July 3, 2022): 1137. http://dx.doi.org/10.3390/met12071137.

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Stainless steel 304 (SS304) experiences corrosion when it is exposed to a saline atmosphere, which attains severity due to its high surface wettability. Topographical modification of metallic surfaces is an effective route to reduce wettability and thereby mitigate liquid-mediated corrosion. In this work, topographical modification of stainless steel 304 flat surface in the form of micropillars was done (pillar width: 100 μm, inter-pillar distance: 100 μm and height: 80 μm). Micropillars were fabricated by a chemical etching process. Wetting and corrosion of the micropillars was studied over long-time duration in comparison with flat surface, before and after intermittent and continuous exposures to saline water for 168 h. Wetting was characterized by measuring the static water contact angle on the test surfaces and their corrosion by electrochemical polarization tests (electrolyte: 3.5 wt.% sodium chloride solution). The relationship between the nature of wetting of the test surfaces and their corrosion was examined. Micropillars showed predominantly composite wetting over a long time, which imparted an effective resistance against corrosion over a long time to the SS304 surface. When compared to the flat surface, the corrosion rates of the micropillars were lower by two orders of magnitude, prior to and also upon long-time contact with the NaCl solution. Micropillars lowered corrosion due to composite wetting, i.e., solid-liquid-air interface that reduced the area that was in contact with the NaCl solution. The efficiency of corrosion inhibition (η) of micropillars was 88% before long-time contact, 84% after intermittent contact, and 77% after continuous contact with NaCl solution. Topographical modification in the form of micropillars that can impart composite wetting is an effective route to induce long-term anticorrosion ability to the SS304 surface.

13

Tagawa, N., and M. Hashimoto. "Self-Loading Slider Dynamics for Noncontact Start Stop Operation With Negative Pressure Air-Lubricated Slider Bearing in Magnetic Disk Storage." Journal of Tribology 111, no. 4 (October 1, 1989): 698–702. http://dx.doi.org/10.1115/1.3261997.

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This paper proposes self-loading flying head slider mechanisms to be used for information storage on magnetic disk media under noncontact start/stop mode conditions. The mechanisms consist of a zero-load negative pressure air-lubricated slider bearing, a slider suspension mechanism, and a twin-structure piezoelectric actuator as the head loading mechanism. Experimental research was carried out on fundamental flying characteristics for the slider. The dynamics of a self-loading/unloading negative pressure air-lubricated slider bearing were successfully studied in detail with a laser Doppler vibrometer. No intermittent contact between head and disk was observed in either the self-load or unload cases. A theoretical study on the self-loading phenomenon was carried out, and its conclusions were in good agreement with the experimental results. This suggests the feasibility of achieving a high head/disk interface reliability and, in particular, of overcoming problems regarding stiction and tribology between head and disk.

14

Santhosh, B., S. Narayanan, and C. Padmanabhan. "Nonlinear Dynamics of Shrouded Turbine Blade System with Impact and Friction." Applied Mechanics and Materials 706 (December 2014): 81–92. http://dx.doi.org/10.4028/www.scientific.net/amm.706.81.

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Dry friction dampers are passive devices used to reduce the resonant vibration amplitudes in turbine bladed systems. In shrouded turbine blade systems, in addition to the stick- slip motion induced by dry friction during the contact state in the tangential direction, the interface also undergoes intermittent separation in the normal direction. The problem can thus be treated as a combination of impact and friction. In this work, the dynamics of dry friction damped oscillators which are representative models of dry friction damped bladed system is investigated. A one dimensional contact model which is capable of modeling the interface under constant and variable normal load is used. The steady state periodic solutions are obtained by multi - harmonic balance method (MHBM). Frequency response plots are generated for different values of normal load using the arc length continuation procedure. The MHBM solutions are validated using numerical integration. A single degree of freedom (dof) model under constant normal load with constant and variable friction coefficients, a dry friction damped two dof system under constant normal load and a two dof system under variable normal load are investigated. In the presence of variable normal load, the system shows multivalued frequency response and jump phenomenon. The optimal value of the normal load which gives minimum resonant response is also obtained.

15

Lee, Kwangjin. "Frictionally Excited Thermoelastic Instability in Automotive Drum Brakes." Journal of Tribology 122, no. 4 (December 29, 1999): 849–55. http://dx.doi.org/10.1115/1.1286207.

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Thermoelastic instability in automotive drum brake systems is investigated using a finite layer model with one-sided frictional heating. With realistic material properties of automotive brakes, the stability behavior of the one-sided heating mode is similar to that of the antisymmetric mode of two-sided heating but the critical speed of the former is higher than that of the latter. The effects of the friction coefficient and brake material properties on the critical speeds are examined and the most influential properties are found to be the coefficient of friction and the thermal expansion coefficient of drum materials. Vehicle tests were performed to observe the critical speeds of the drum brake systems with aluminum drum materials. Direct comparisons are made between the calculation and measurement for the critical speed and hot spot spacing. Good agreement is achieved when the critical speeds are calculated using the temperature-dependent friction material properties and the reduced coefficient of friction to account for the effect of intermittent contact. [S0742-4787(00)01503-4]

16

Hlava´cˇek, Miroslav. "Squeeze-Film Lubrication of the Human Ankle Joint Subjected to the Cyclic Loading Encountered in Walking." Journal of Tribology 127, no. 1 (January 1, 2005): 141–48. http://dx.doi.org/10.1115/1.1828076.

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Squeeze-film lubrication of the human ankle joint during walking is numerically analyzed, the effect of surface sliding being neglected at this stage. Biphasic mixture models are considered for synovial fluid (an ideal and viscous fluid phases) and for articular cartilage (an ideal interstitial fluid and an elastic porous matrix). In the model, the ideal fluid phase passes through the articular surface and matrix pores. The cartilage matrix is considered both normal and pathological (with primary osteoarthrosis). Calculations show that water and small solutes of synovial fluid imbibe into the articular cartilage during the stance period, while the interstitial fluid of the cartilage exudes and enriches the lubricant during the swing period in a central part of the contact at each step. Soon after the onset of walking, repeatedly near the load culmination of each step, the synovial fluid should be turned into a synovial gel and, shortly after, changed back again into a fluid there. In the pathological case, the protective synovial gel layer is quickly depleted after several steps and the surfaces may come briefly into contact in each cycle. With normal cartilage, however, the protective intermittent gel film (formed briefly at each step) maintains its thickness for a longer time. Normal cartilage also behaves more favorably, when a long walk is broken and then resumed shortly afterwards. With normal articular cartilage, maintenance of a lubricating fluid film is much aided by the cyclic nature of the loading encountered in walking, compared with the steady loading in standing where the fluid film is quickly filtered out into a protective permanent gel film.

17

Pendlebury, R. E. "Unlubricated fretting wear of mild steel surfaces in air at room temperature: II electrical contact resistance measurements and the effect on wear of intermittent loading." Wear 118, no. 3 (August 1987): 341–64. http://dx.doi.org/10.1016/0043-1648(87)90077-9.

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18

Annakodi, Vivek Anand, Ramachandra Arvind Singh, Subramanian Jayalakshmi, Yupeng Zhang, Koppula Srinivas Rao, and Rajashekhara Shabadi. "Anticorrosion Behaviour of SS304 Microgroove Surfaces in Saline Water." Metals 11, no. 10 (September 28, 2021): 1543. http://dx.doi.org/10.3390/met11101543.

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The 304 Stainless Steel (SS304) is severely affected by salt water corrosion due to its high surface wettability. By reducing its surface wettability, its corrosion can be reduced. To achieve this, topographical modification of the steel surface is an effective route. In this work, SS304 flat surfaces were topographically modified into microgrooves (ridge width 250 μm to 500 μm, groove width 200 μm, width ratio = ridge width/groove width >1). Wire cut electrical discharge machining was used to fabricate the microgrooves. Long-term wetting characteristics and long-term corrosion behaviour of flat surface and microgrooves were studied. The influence of the nature of wetting of the tested surfaces on their corrosion behaviour was examined. The sessile drop method and potentiodynamic polarization tests in sodium chloride (3.5 wt. % NaCl) solution (intermittent and continuous exposures for 168 h) were studied to characterize their wetting and corrosion behaviours, respectively. Topographical modification imparted long-term hydrophobicity and, as a consequence, long-term anticorrosion ability of the steel surface. Micropatterning reduced the corrosion rate by two orders of magnitude due to reduction in interfacial contact area with the corrosive fluid via composite wetting, i.e., solid–liquid–air interface. Microgrooves showed corrosion inhibition efficiency ≥88%, upon long-term exposure to NaCl solution. By comparing the wetting and corrosion behaviours of the microgrooves with those of the previously studied microgrooves (ridge width/groove width <1), it was found that the surface roughness of their ridges strongly influences their wetting and corrosion properties.

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Cuberes, M. Teresa. "Intermittent-Contact Heterodyne Force Microscopy." Journal of Nanomaterials 2009 (2009): 1–5. http://dx.doi.org/10.1155/2009/762016.

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Heterodyne Force Microscopy opens up a way to monitor nanoscale events with high temporal sensitivity from the quasistatic cantilever mechanical-diode response taking advantage of the beat effect. Here, a novel heterodyne ultrasonic force method is proposed, in which the cantilever is driven in amplitude-modulation mode, at its fundamental flexural eigenmode. Ultrasonic vibration in the megahertz range is additionally input at the tip-sample contact from the cantilever base and from the back of the sample. The ultrasonic frequencies are chosen in such a way that their difference is coincident with the second cantilever eigenmode. In the presence of ultrasound, cantilever vibration at the difference frequency is detected. Similarly as in heterodyne force microscopy, it is expected that the phase response yields information with increased sensitivity due to the beat effect.

20

Behrend, O. P., F. Oulevey, D. Gourdon, E. Dupas, A. J. Kulik, G. Gremaud, and N. A. Burnham. "Intermittent contact: tapping or hammering?" Applied Physics A: Materials Science & Processing 66, no. 7 (March 1, 1998): S219—S221. http://dx.doi.org/10.1007/s003390051133.

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21

Yang, Xiao Yan, You Gang Xiao, Xian Ming Lei, and Guo Xin Chen. "Contact Pressure of Loose-Fitted Tyre under Intermittent Contact." Advanced Materials Research 816-817 (September 2013): 1015–18. http://dx.doi.org/10.4028/www.scientific.net/amr.816-817.1015.

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The total loads between kiln support are transmitted to the shell cross-section at tyre as shearing forces. According to the character and the condition of shell deformation and force balance, the mathematical models of contact pressure have been set up between tyre and shell under intermittent contact. The contact zones and contact pressures between tyre and shell are solved when the support reactions and gaps are variable. The results show the contact pressures increase with the increase of support reactions and gaps, the contact zones are proportional to support reactions, and inversely proportional to the gaps, which provide the reason for sound axis alignment and gap design.

22

Bekker, Eric Botha, Daniel J. Holland, and Aaron Timothy Marshall. "Electrical Resistive Tomography to Analyse the Flow Behaviour in Redox Flow Batteries." ECS Meeting Abstracts MA2022-01, no. 48 (July 7, 2022): 2016. http://dx.doi.org/10.1149/ma2022-01482016mtgabs.

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Redox flow batteries (RFBs) are re-emerging as a safe, scalable, efficient and versatile means of large-scale energy storage. Growing adoption of renewable energy generation has ushered a new optimism regarding future reduction in fossil fuel dependency; limiting further harm dealt to the climate and wider environment. However, this momentum demands more efficient energy storage solutions to reconcile power demand and the intermittent nature of wind, solar and tidal energy generation [1]. Without proper storage, reliable back-up generation – largely provided by fossil fuels – will continue to be an unavoidable reality [2]. RFBs utilise the electrochemical properties of dissolved metal ions to store and release energy. Independent sizing of electrolyte storage tanks and flexible power delivery contributes to the flexibility of RFBs compared to alternative battery technologies [3]. RFB reactions occur at the electrode-electrolyte interface, and thus the mass transport at this interface is a critical factor in determining the overall RFB performance. Most RFBs use porous electrodes, with a popular choice of material being carbon felt (CF) due to its low cost, chemical stability and high conductivity [4], although the hydrophobic nature of some CF can cause poor electrode ‘wettability’- decreasing the contact area between the electrode and the electrolyte. Further, electrolyte depletion and asymmetric flow can lead to the presence of ‘dead spots’ where the interface is inactive. Many studies have been conducted on CF to improve the electrochemical performance, using surface treatments, compression and channel flow to improve active area, wettability, and species transport [5-7]. These each have direct impact on current density, pressure drop, overpotentials, and energy efficiency. While the flow of electrolyte in the RFB porous electrodes can be modelled using computational fluid dynamics (CFD) [8], and experimentally assessed using x-ray tomography [9,10] and some optical visualisation methods [11], there are limited experimental methods which can be used on entire RFB stacks. In this study, we explore the use of electrical resistive tomography (ERT) to probe the flow of electrolyte through RFB electrodes. ERT has the advantage that it can provide a non-intrusive means of investigating the hydrodynamics of the otherwise opaque cell stack. Measurements were performed using an array of electrodes place around the perimeter of an RFB electrode chamber which contained conventional carbon felt electrodes. Sensitivity maps were generated using the COMSOL Multiphysics platform and compared with experimental measurements. The flow distribution was evaluated by using injections of concentrated KCl solutions into the background electrolyte. Overall, ERT demonstrated promise as a technique for characterising real-time flow dynamics in RFB stacks and for future research into porous electrode and flow field modifications. References [1] Ambec, S., and Crampes, C., Electricity Provision with Intermittent Sources of Energy. Resource and Energy Economics, Elsevier, 2012. 34: p.320-331. [2] Wagner, F., Electricity by intermittent sources: An analysis based on the German situation 2012. The European Physical Journal Plus, Springer, 2014. 129: 20. [3] Wang, W., et al., Recent Progress in Redox Flow Battery Research and Development. Advanced Functional Materials, Wiley, 2013. 23: p. 970-986. [4] Gonzalez-Garcia, J., et al., Characterization of a carbon felt electrode: structural and physical properties. Journal of materials Chemistry, 1999. 9: p. 419-426. [5] Wang, Q., et al., Experimental study on the performance of a vanadium redox flow battery with non-uniformly compressed carbon felt electrode. Applied Energy, Elsevier, 2018. 213: p. 293-305. [6] Wang, S., et al., Nitrogen-Doped Carbon Nanotube/Graphite Felts as Advanced Electrode Materials for Vanadium Redox Flow Batteries. The Journal of Physical Chemistry Letters, ACS Publications, 2012. 3: p. 2164-2167. [7] Kim, K., et al., The effects of surface modification on carbon felt electrodes for use in vanadium redox flow batteries. Materials Chemistry and Physics, 2011. 131: p. 547-553. [8] Oh, k., et al., Three-dimensional, transient, non-isothermal model of all-vanadium redox flow batteries. Energy, Elsevier, 2015. 81: p. 3-14. [9] Eifert, L., et al., Synchrotron X-ray Radiography and Tomography of Vanadium Redox Flow Batteries—Cell Design, Electrolyte Flow Geometry, and Gas Bubble Formation. ChemSusChem, Wiley, 2020. 13: 3154-3165. [10] Trogadas, P., et al., X-ray micro-tomography as a diagnostic tool for the electrode degradation in vanadium redox flow batteries. Electrochemistry Communications, Elsevier, 2014. 48: p. 155-159 [11] Bhattarai, A., et al., Study of flow behaviour in all-vanadium redox flow battery using spatially resolved voltage distribution. Journal of Power Sources, Elsevier, 2017. 360: p. 443- 452.

23

Stan, Gheorghe, and Richard S. Gates. "Intermittent contact resonance atomic force microscopy." Nanotechnology 25, no. 24 (May 23, 2014): 245702. http://dx.doi.org/10.1088/0957-4484/25/24/245702.

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24

Hiranaga, Yoshiomi, and Yasuo Cho. "Intermittent contact scanning nonlinear dielectric microscopy." Review of Scientific Instruments 81, no. 2 (February 2010): 023705. http://dx.doi.org/10.1063/1.3274138.

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25

Aloisi, G., F. Bacci, M. Carlà, and D. Dolci. "Intermittent contact hydration scanning probe microscopy." Review of Scientific Instruments 81, no. 7 (July 2010): 073707. http://dx.doi.org/10.1063/1.3458006.

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26

Lazenby, Robert A., Kim McKelvey, Massimo Peruffo, Marc Baghdadi, and Patrick R. Unwin. "Nanoscale intermittent contact-scanning electrochemical microscopy." Journal of Solid State Electrochemistry 17, no. 12 (July 28, 2013): 2979–87. http://dx.doi.org/10.1007/s10008-013-2168-2.

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27

Won, J., and N. Hogan. "Modeling Human Performance of Intermittent Contact Tasks." IFAC Proceedings Volumes 28, no. 15 (June 1995): 587–92. http://dx.doi.org/10.1016/s1474-6670(17)45296-7.

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28

Sahoo, Deepak R., Walter Häberle, Abu Sebastian, Haralampos Pozidis, and Evangelos Eleftheriou. "High-throughput intermittent-contact scanning probe microscopy." Nanotechnology 21, no. 7 (January 18, 2010): 075701. http://dx.doi.org/10.1088/0957-4484/21/7/075701.

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29

Bhalerao, Kishor D., and Kurt S. Anderson. "Modeling intermittent contact for flexible multibody systems." Nonlinear Dynamics 60, no. 1-2 (August 28, 2009): 63–79. http://dx.doi.org/10.1007/s11071-009-9580-2.

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30

Biberger, Roland, Guenther Benstetter, and Holger Goebel. "Displacement current sensor for contact and intermittent contact scanning capacitance microscopy." Microelectronics Reliability 49, no. 9-11 (September 2009): 1192–95. http://dx.doi.org/10.1016/j.microrel.2009.07.007.

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31

Blum, L. "Contact theorems for rough interfaces." Journal of Statistical Physics 75, no. 5-6 (June 1994): 971–80. http://dx.doi.org/10.1007/bf02186753.

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32

Lim, Jong Tae, and Seong-Deok Ahn. "Stretchable interfaces with conformal contact." Materials Express 12, no. 1 (January 1, 2022): 149–54. http://dx.doi.org/10.1166/mex.2022.2125.

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Without conformal contact, stretchable electronic devices are significantly degraded during device operation and post treatment, due to air trapping and the resulting formation of uneven surface. In this work, under the hard condition that a stretchable polyacrylate elastomer (VHB) layer with high porosity which can lead to more pore formation at the VHB interface is introduced in the stretchable device preparation, conformal contact is achieved by vacuum process (VP). Planar images indicate that, although the conventional process results in the formation of pore with a size of 0.1 mm at the vacuum pressure of 10-6 Torr, the VP prevents it until 10-6 Torr. Surface analysis using near-edge X-ray absorption fine structure indicates the VP leads to less corrugation in the surface of graphene electrode located near the VHB; thus, finally resulting in significantly higher performance of an organic light emitting diode having the VHB and the graphene.

33

Uluutku, Berkin, and Santiago D. Solares. "Current measurements in the intermittent-contact mode of atomic force microscopy using the Fourier method: a feasibility analysis." Beilstein Journal of Nanotechnology 11 (March 13, 2020): 453–65. http://dx.doi.org/10.3762/bjnano.11.37.

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Atomic force microscopy (AFM) is an important tool for measuring a variety of nanoscale surface properties, such as topography, viscoelasticity, electrical potential and conductivity. Some of these properties are measured using contact methods (static contact or intermittent contact), while others are measured using noncontact methods. Some properties can be measured using different approaches. Conductivity, in particular, is mapped using the contact-mode method. However, this modality can be destructive to delicate samples, since it involves continuously dragging the cantilever tip on the surface during the raster scan, while a constant tip–sample force is applied. In this paper we discuss a possible approach to develop an intermittent-contact conductive AFM mode based on Fourier analysis, whereby the measured current response consists of higher harmonics of the cantilever oscillation frequency. Such an approach may enable the characterization of soft samples with less damage than contact-mode imaging. To explore its feasibility, we derive the analytical form of the tip–sample current that would be obtained for attractive (noncontact) and repulsive (intermittent-contact) dynamic AFM characterization, and compare it with results obtained from numerical simulations. Although significant instrumentation challenges are anticipated, the modelling results are promising and suggest that Fourier-based higher-harmonics current measurement may enable the development of a reliable intermittent-contact conductive AFM method.

34

Tranvouez, E., P. Budau, and G. Bremond. "Topographical and electrical study of contact and intermittent contact mode InP AFM lithography." Nanotechnology 17, no. 2 (December 14, 2005): 455–60. http://dx.doi.org/10.1088/0957-4484/17/2/019.

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35

Kim, Youngbeom, Sungho Choi, Kyung-Young Jhang, and Taehyeon Kim. "Experimental Verification of Contact Acoustic Nonlinearity at Rough Contact Interfaces." Materials 14, no. 11 (May 31, 2021): 2988. http://dx.doi.org/10.3390/ma14112988.

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When a longitudinal wave passes through a contact interface, second harmonic components are generated due to contact acoustic nonlinearity (CAN). The magnitude of the generated second harmonic is related to the contact state of the interface, of which a model has been developed using linear and nonlinear interfacial stiffness. However, this model has not been sufficiently verified experimentally for the case where the interface has a rough surface. The present study verifies this model through experiments using rough interfaces. To do this, four sets of specimens with different interface roughness values (Ra = 0.179 to 4.524 μm) were tested; one set consists of two Al6061-T6 blocks facing each other. The second harmonic component of the transmitted signal was analyzed while pressing on both sides of the specimen set to change the contact state of the interface. The experimental results showed good agreement with the theoretical prediction on the rough interface. The magnitude of the second harmonic was maximized at a specific contact pressure. As the roughness of the contact surface increased, the second harmonic was maximized at a higher contact pressure. The location of this maximal point was consistent between experiments and theory. In this study, an FEM simulation was conducted in parallel and showed good agreement with the theoretical results. Thus, the developed FEM model allows parametric studies on various states of contact interfaces.

36

Dobiński, Grzegorz, Sławomir Pawłowski, and Marek Smolny. "Amplitude Estimation Technique for Intermittent Contact Atomic Force Microscopy." International Journal of Measurement Technologies and Instrumentation Engineering 6, no. 2 (July 2017): 29–42. http://dx.doi.org/10.4018/ijmtie.2017070103.

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This article describes how one of the biggest challenges in designing of high-speed intermittent contact atomic force microscope (AFM) is the construction of a fast amplitude detector. The measurement techniques commonly used in commercial microscopes, such as RMS to DC converters or lock-in amplifiers often do not provide sufficient bandwidth to perform high speed imaging. On the other hand, many techniques developed especially for high-speed AFM are characterized by poor signal-to-noise ratio. In this paper, a novel amplitude estimation method based on the generalized Goertzel algorithm is presented. The detection system, composed of 16-bit 100 mega-samples per second analog-to-digital converter and field-programmable gate array device, allows to measure the signal amplitude within the time comparable to one oscillation cycle of the AFM cantilever. The effectiveness and validity of the designed detector were investigated by computer simulation. High spatial resolution of the presented method implemented in the actual atomic force microscopy system is also demonstrated.

37

Kopanski, J. J., and S. Mayo. "Intermittent-contact scanning capacitance microscope for lithographic overlay measurement." Applied Physics Letters 72, no. 19 (May 11, 1998): 2469–71. http://dx.doi.org/10.1063/1.121397.

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38

Matsuoka, H., S. Fukui, and H. Morishita. "Dynamics of liquid meniscus bridge of intermittent contact slider." IEEE Transactions on Magnetics 38, no. 5 (September 2002): 2135–37. http://dx.doi.org/10.1109/tmag.2002.802692.

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39

Berg, J., and G. A. D. Briggs. "Nonlinear dynamics of intermittent-contact mode atomic force microscopy." Physical Review B 55, no. 22 (June 1, 1997): 14899–908. http://dx.doi.org/10.1103/physrevb.55.14899.

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40

Geijselaers, Hubert J. M., and Annette J. E. Koning. "Finite Element Analysis of Thermoelastic Instability With Intermittent Contact." Journal of Tribology 122, no. 1 (July 21, 1999): 42–46. http://dx.doi.org/10.1115/1.555327.

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The equations that describe the development of corrugations on block braked wheel treads caused by thermoelastic instability are discretized using the finite element method. The perturbations of temperatures and distortions are described by an amplitude function, which is spatially fixed multiplied by a sinusoidal running wave term of fixed wavelength. The governing equations are such that the wave term cancels out. Only the amplitude functions are discretized in the finite element model. The intermittent nature of the contact is directly specified through the boundary conditions. Results are obtained for a simplified two-dimensional model of a train wheel. These results agree with analytical results. [S0742-4787(00)00701-3]

41

Zhang, Yin, and Ya-pu Zhao. "Nonlinear dynamics of atomic force microscopy with intermittent contact." Chaos, Solitons & Fractals 34, no. 4 (November 2007): 1021–24. http://dx.doi.org/10.1016/j.chaos.2006.03.125.

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42

Song, Woo-Bin, Michael S. Sutton, and Joseph J. Talghader. "Thermal contact conductance of actuated interfaces." Applied Physics Letters 81, no. 7 (August 12, 2002): 1216–18. http://dx.doi.org/10.1063/1.1499518.

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43

Jiao, J. P., W.-H. Liu, C.-F. He, B. Wu, and J. Zhang. "Nonlinear Acoustic Interaction of Contact Interfaces." Experimental Mechanics 54, no. 1 (January 9, 2013): 63–68. http://dx.doi.org/10.1007/s11340-012-9710-5.

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44

Biberger, Roland, Guenther Benstetter, Thomas Schweinboeck, Peter Breitschopf, and Holger Goebel. "Intermittent-contact scanning capacitance microscopy versus contact mode SCM applied to 2D dopant profiling." Microelectronics Reliability 48, no. 8-9 (August 2008): 1339–42. http://dx.doi.org/10.1016/j.microrel.2008.06.013.

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45

Huakang, Li, Kehong Lv, Shen Qinmu, Jing Qiu, and Guanjun Liu. "Method of electrical connector intermittent fault reproduction." Aircraft Engineering and Aerospace Technology 90, no. 6 (September 3, 2018): 946–55. http://dx.doi.org/10.1108/aeat-12-2016-0253.

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PurposeThis paper aims to reproduce the electrical connector intermittent fault behaviours with step-up vibration stress while maintaining the integrity of the product. Design/methodology/approachA dynamic model of an electrical connector under vibration is established for contact resistance analysis. Next, the dynamic characteristics of contact resistance are analysed, and cumulative damage theory is used to calculate the damage under different stresses during the intermittent fault reproduction test. To reduce damage and improve efficiency, the step-up stress is used for the reproduction test. FindingsThe proposed method can reproduce the intermittent fault behaviour, and the step-up stress test is more efficient than the constant stress test. Research limitations/implicationsStep-up stress is used for intermittent fault reproduction, and the quantitative relationships between intermittent fault and product damage can be further studied. Practical implicationsIt is expected that the proposed methodology can help engineers to reproduce the intermittent fault behaviours to facilitate the detection and diagnosis of intermittent fault and to improve equipment safety. Originality/valueThe mechanism of electrical connector reproduction is analysed and the step-up stress test is used for intermittent fault reproduction.

46

Benilov, E. S., and M. Vynnycky. "Contact lines with a contact angle." Journal of Fluid Mechanics 718 (February 8, 2013): 481–506. http://dx.doi.org/10.1017/jfm.2012.625.

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AbstractThis work builds on the foundation laid by Benney & Timson (Stud. Appl. Maths, vol. 63, 1980, pp. 93–98), who examined the flow near a contact line and showed that, if the contact angle is $18{0}^{\circ } $, the usual contact-line singularity does not arise. Their local analysis, however, does not allow one to determine the velocity of the contact line and their expression for the shape of the free boundary involves undetermined constants. The present paper considers two-dimensional Couette flows with a free boundary, for which the local analysis of Benney & Timson can be complemented by an analysis of the global flow (provided that the slope of the free boundary is small, so the lubrication approximation can be used). We show that the undetermined constants in the solution of Benney & Timson can all be fixed by matching the local and global solutions. The latter also determines the contact line’s velocity, which we compute among other characteristics of the global flow. The asymptotic model derived is used to examine steady and evolving Couette flows with a free boundary. It is shown that the latter involve brief intermittent periods of rapid acceleration of contact lines.

47

Gehlsen, Gale M., Ronald W. Davis, and Rafael Bahamonde. "Intermittent Velocity and Wheelchair Performance Characteristics." Adapted Physical Activity Quarterly 7, no. 3 (July 1990): 219–30. http://dx.doi.org/10.1123/apaq.7.3.219.

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The purpose of this study was to describe the intermittent velocity variation of wheelchair propulsion and to determine the relationship between selected wheelchair propulsive characteristics and peak velocity. The subjects were 11 (10 males and 1 female) members of the U.S. 1988 Paralympic Track and Field Team. Each subject’s personal racing chair was mounted on a Pro Roller. Intermittent velocity was ascertained by a tach-generator. A stationary 16-mm Locam camera was used to photograph the subject’s sagittal plane propulsive movements. A sonic digitizer was used to digitize three complete propulsive cycles for each subject. Paraplegic and quadriplegic subjects’ stroke frequency mean values were 2.27 and 1.80 Hz, respectively. Significant correlations between the Pro Roller’s computer-generated peak velocity values and hand-handrim positions were indicated. Handrim contact angles and trunk angles were approximately 30 to 40° forward of the same angles reported in the literature. Results indicate that a forward lean of the trunk may allow the athlete to increase the range of hand-handrim contact.

48

Woodward, John T. "Choosing a Cantilever for In Situ Atomic Force Microscopy." Microscopy Today 11, no. 2 (April 2003): 42–43. http://dx.doi.org/10.1017/s1551929500052500.

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What is the best cantilever for intermittent contact mode (often called Tapping Mode™) atomic force microscope (AFM) imaging under water? This is a question I hear often and one that recently generated some interesting discussion on an AFM newsgroup (more on the newsgroup below). The ability of the AFM to image samples En physiologically relevant environments has made it a popular technique in the biological sciences. However, because scanning the AFM tip in contact mode easily perturbs many biological samples, it was the advent of intermittent contact modes that lead to AFM's widespread use in biology.

49

Lumbantobing, A., L. Kogut, and K. Komvopoulos. "Electrical Contact Resistance as a Diagnostic Tool for MEMS Contact Interfaces." Journal of Microelectromechanical Systems 13, no. 6 (December 2004): 977–87. http://dx.doi.org/10.1109/jmems.2004.838388.

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50

Weber, B., T. Suhina, A. M. Brouwer, and D. Bonn. "Frictional weakening of slip interfaces." Science Advances 5, no. 4 (April 2019): eaav7603. http://dx.doi.org/10.1126/sciadv.aav7603.

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When two objects are in contact, the force necessary to overcome friction is larger than the force necessary to keep sliding motion going. This difference between static and dynamic friction is usually attributed to the growth of the area of real contact between rough surfaces in time when the system is at rest. We directly measure the area of real contact and show that it actually increases during macroscopic slip, despite the fact that dynamic friction is smaller than static friction. This signals a decrease in the interfacial shear strength, the friction per unit contact area, which is due to a mechanical weakening of the asperities. This provides a novel explanation for stick-slip phenomena in, e.g., earthquakes.

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