Characterization of Self-Powered Triboelectric Tachometer with Low Friction Force

Self-powered triboelectric tachometers have wide application prospects in mechanical and electrical industries. However, traditional disc-type tachometers typically require large contact force, which burdens rotary load and increases frictional wear. To reduce the friction force of triboelectric tachometers, we present an alternative structure defined by flapping between rigid and flexible triboelectric layers. In this work, we further characterize this type of tachometer, with particular focus on the oscillating relationship between output voltage and rotation speed due to the plucking mechanism. This oscillating relationship has been demonstrated both theoretically and experimentally. For future self-powered triboelectric tachometers, the proved oscillating relationship can be applied as calibration criteria for further enhancing sensitivity and linearity in rotation measurement.

Effect of surface treatment of carbon fibers on the mechanical and frictional properties of polyetheretherketone/polytetrafluoroethylene composites: Experimentation and finite element analysis

Polytetrafluoroethylene has many excellent properties and a wide range of applications, but its poor wear resistance, hardness, and creep resistance have severely limited the use of the polytetrafluoroethylene composites. In this work, the surface of carbon fibers was treated with silane coupling agent acetone solution, and then sintering technology was used to prepare carbon fibers/polyetheretherketone (PEEK)/ polytetrafluoroethylene composites. The mechanical and frictional wear properties of the composites were analyzed using an electronic tensile tester, a Shore hardness tester, and a frictional wear tester, and scanning electron microscopy was applied to analyze the surface morphology of the composites after wear. The experimental results shown that the addition of carbon fibers could significantly improve the mechanical properties of the composites, reduce the radial shrinkage, and increase the Shore hardness of the composites. Under the same experimental conditions, the carbon fibers (20 wt.%) /polyetheretherketone/polytetrafluoroethylene composites has the best wear resistance, with a friction coefficient of 0.196 and the wear rate of 2.41 × 10−6 mm3/N·m. In the theoretical simulation, the thermal conductivity of polytetrafluoroethylene composites was predicted using ANSYS software, with the changes in the temperature and friction force in the friction process. The theoretical simulation results matched with the experimental values, which proved the accuracy of the theoretical simulations.

Tribo-corrosion Behaviour of Bare and Nano-coated Foils Used on High-speed Air Foil Bearings

Irrespective of applying lubricants between high-speed machinery’s shafts and Air-foil bearings (AFBs), wear and friction remain troublesome. Hence, the present study sought novel bare foil and equivalent nanocomposites to form a coating system that could mitigatly lower frictional wear between high-speed machinery’s shafts and Air-foil bearings (AFBs). Bare and coated foils were supplied on rectengular dimensions of 15 × 15 × 5mm3. Mechanical properties were characterized by Instron 3384 testing machine. Universal Tribometer s/n : RTEC2441, USA was utilized for tribological measurements at room temperature. Surface morphologies were examined by Scanning electron microscopy (SEM). Higher hardness and young modulus values were recorded from coated foils. On the other hand, specific wear rates were relatively low from coated foils. Furthermore, abrasive wear index was higher from the F2 coated foil. Friction coeffients were also lower from the coated foils under all engaged tribological conditions. Highly ruptured SEM morphologies were noticed from the bare foil. Nonetheless, mild and negligible aggressions were discovered from the surfaces of nano-coated foils.

A Comparative Study of Mechanical Properties, Thermal Conductivity, Residual Stresses, and Wear Resistance of Aluminum-Alumina Composites Obtained by Squeeze Casting and Powder Metallurgy

Squeeze casting and powder metallurgy techniques were employed to fabricate AlSi12/Al2O3 composites, which are lightweight structural materials with potential applications in the automotive industry. The impact of the processing route on the material properties was studied. Comparative analyses were conducted for the Vickers hardness, flexural strength, fracture toughness, thermal conductivity, thermal residual stresses, and frictional wear. Our results show that the squeeze cast composite exhibits superior properties to those obtained using powder metallurgy.

The Relationship between Tribo-Magnetization and Wear State during Reciprocating Sliding

In order to investigate the relationship between tribo-magnetization and wear phenomena, a series of sliding-friction tests were carried out using a pin-on-block reciprocator type device, which was specially designed to generate sliding friction and to detect magnetic fields. The tribological behavior was observed by a charge-coupled device (CCD) camera in real time, and the magnetic signal was detected by using a two-axis magnetic sensor. It was found that as the friction continues, both the tangential and the normal components of magnetic field on the material surface increase gradually, and that both the average value of the tangential magnetic field ΔH(x)mean and the peak-to-peak value of the normal magnetic field Vpp at the wear scar clearly reflect changes of the wear state. Furthermore, in order to better understand the tribo-magnetization phenomenon, the changes of surface morphology and wear debris in different wear stages were analyzed. Moreover, an improved magnetic dipole model that considered the distribution of magnetic charges on the worn surface was established. This model can successfully describe the tribo-magnetization phenomenon during the stable wear stage, and should be useful for characterizing frictional wear phenomena in the future.

Study of the micro/nano-texture design to improve the friction properties of DLC thin films

In this study, a DLC pattern was fabricated through a photolithography process that constitutes a part of the semiconductor process, to investigate the frictional wear characteristics. The photolithography was used to produce negative patterns with a pattern width of 10 [Formula: see text]m or 20 [Formula: see text]m and a pattern depth of 500 nm on the DLC surface. The change in the coefficient of friction of the surface was investigated through a ball-on-disk tribology test on the fabricated micro/nano-sized DLC pattern. The DLC pattern fabricated by the photolithography process showed a superior coefficient of friction to that of the general DLC sample. These results show that the decrease in the surface friction coefficient of the patterned DLC thin film is due to the reduction in the surface contact area owing to the modification of the micro/nano-texture of the surface as well as the low friction characteristics of the DLC.

Fractal prediction of frictional force against the interior surface of forming channel coupled with temperature in a ring die pellet machine

For the biomass ring die pellet machine, the frictional force against the interior surface of the forming channel is the main cause for its frictional wear and also is key to the research of wear mechanism as well as its prediction. In this study, four ring die samples were used to measure and obtain data on their surface morphology. The fractal dimension D and fractal feature G were calculated using the Yardstick method, and lastly a fractal prediction model of sliding frictional force against the interior surface of forming channel was built, which was coupled with a fractal model of temperature distribution over friction surface. Numerical simulation, as well as friction-wear test were conducted to verify the accuracy of the model. The result showed that: when Ar < Arc, the slope of F was larger, which means the frictional force increased more rapidly, and the larger slope of FD represented a rapidly decreasing unit of frictional force. When true contact area Ar = 3.93%, Aa, FT, and FTD increased with the increase in temperature; FT increased rapidly at first and then gradually slowed down. When Ar was small, FTD increased sharply with the increase in temperature.

NUMERICAL ANALYSIS OF VALVE STRUCTURE OF HIGH POWER MARINE ENGINE

Valve as an important part of the gas distribution mechanism, is an crucial part of the engine. When the engine works, the valve is subjected to high temperature, high impact, frictional wear and corrosion and other harsh working conditions, and the reliable and durable valve has an important impact on the safety and reliability of the engine. In this paper, a model of four-stroke marine diesel engine valve is used as the research object, and the intake valve set and exhaust valve set models are established respectively. Heat transfer simulation and failure analysis of inlet and exhaust valves of different structures and materials under different operating conditions were carried out using finite element analysis. The results show that the different valve structures and manufacturing materials have different effects on the reliability of the valves; Changing the valve structures and choosing different valve manufacturing materials have a greater impact on the heat transfer and deformation, thus affecting the overall reliability of the valves.

Evaluating Degradation Coefficients from Existing System Models

A generalization of the Degradation-Entropy Generation (DEG) theorem to multi-disciplinary multi-physics system-process analysis via a combination with pre-existing system models is presented in this article. Existing models and the DEG methodology are reviewed, and a method for evaluating degradation coefficients Bi is proposed. These coefficients characterize the system’s transformation based on active dissipative mechanisms, including temperature effects. The consistency of entropy generation in characterizing degradation is then inherited by these often-empirical system models, thereby rendering them more robust and applicable to similar systems without the need for numerous tests and measurements for model corrections. The approach applies to all systems and can quickly analyze and predict a system’s performance and degradation, even in the absence of experimental data (using known properties and material constants). Demonstrated applications herein include mechanically loaded systems (frictional wear, grease shearing, fatigue loading), electrochemical energy systems, thermal processes, and others.

Bridging the failure of surface asperities to the macroscopic rupture energy during the onset of frictional sliding

&lt;p&gt;The onset of sliding between two rough surfaces held in frictional contact arises through the nucleation and propagation of rupture fronts, whose dynamics has been shown to obey the elastodynamics of a shear crack. By analogy with the fracture energy controlling the growth of brittle crack in intact material, a frictional rupture is governed by an associated rupture energy. In the context of earthquakes, this rupture energy is expected to control the nucleation and the transition from an accelerating slip patch or localized perturbation to a propagating seismic rupture. The microscopic origin of this rupture energy and its relation to the microcontacts topography remain however unsettled.&lt;/p&gt;&lt;p&gt;In this context, this study aims at bridging the macroscopic description of friction to the failure of contacting asperities and frictional wear prevailing at smaller scales. Recent studies demonstrated how the failure of two contacting asperities arises either by plastic deformation or brittle failure of their apices depending on whether their contact junction is respectively smaller or larger than a characteristic length scale. In this study, we investigate numerically how the different failure mechanisms of microcontact asperities impact the nucleation and propagation of frictional rupture fronts.&lt;/p&gt;&lt;p&gt;At a macroscopic level, we study the ability of an interface to withstand a progressively applied shearing, i.e. its frictional strength, while at the microscopic scale, we observe how the failure process develops across the microcontact junctions. We highlight how the microcontacts topography significantly impacts the nucleation and frictional strength, even when comparing interfaces with identical macroscopic properties and rupture energy. We present how the characteristic length governing microcontacts failure can be used to select which details of the surface roughness are homogenized along the tip of a nucleating slip front. Combining the approach proposed in this work with models solving normal contact between rough surfaces will open up new prospects to study the strength and rupture energy of frictional interfaces at the onset of sliding.&lt;/p&gt;