Search Results (28)

In order to cope with the emergence of energy conservation and consumption reduction initiatives, we used an acrylic emulsion (as the adhesive), combined with silica aerogel (SA) and hollow glass microsphere (HGM) fillers, to synthesize thermal insulation coatings, which were found to have low thermal conductivity and excellent thermal insulation properties. These waterborne coatings are environmentally friendly and were synthesized without organic solvents. Comprehensive testing verified that the coatings met practical requirements. Specifically, the addition of 18% SA resulted in minimal thermal conductivity (0.0433 W/m·K), the lowest density (0.177 g/cm³), as well as a reduced gross calorific value. At a heating surface temperature of 200 °C, the 5 mm coating’s cooling surface temperature was 108.7 °C, yielding a 91.3 °C temperature difference and demonstrating remarkable thermal insulation performance. Furthermore, the coatings showed favorable results in terms of water resistance, corrosion resistance, wear resistance, and adhesion, achieving satisfactory engineering standards. In this work, the influence of different contents of SA on various properties of the coating was studied, with the aim of providing a reference for the modulation of the comprehensive performance of SA thermal insulation coatings. Full article

Silicon is the most commonly used material in the electronic industries due to its unique properties, which also make it very difficult to machine using conventional machining. Electrical discharge machining (EDM) is a non-traditional process that is gaining popularity for machining silicon, although a slower machining rate is one of its limitations. This study investigates two electrode design strategies to enhance the efficiency of EDM by improving the material removal rates, reducing tool wear, and refining the quality of machined features. The first approach involves using graphite electrodes in various array configurations (1 × 4 to 6 × 4) and leg heights (0.2″ and 0.3″). The second approach employs hollow electrodes with differing wall thicknesses (0.04″, 0.08″, and 0.12″). The effects of these variables on performance were evaluated by maintaining constant EDM parameters. The results indicate that increasing the number of electrode legs improves the flushing conditions, resulting in shorter machining times. Meanwhile, the shorter electrode height outperforms the taller electrode, providing a higher machining speed. The thinnest wall thickness for hollow electrodes yielded the best performance due to the increased energy distribution. Both electrode design methodologies can be used for the mass fabrication of features with targeted profiles on silicon using the die-sinking EDM process. Full article

Hollow wear on wheels is a common form of surface damage often observed in high-velocity vehicles. It is widely recognized that hollow wear of the wheel tread degrades the dynamic performance of rail vehicles, especially in the issue commonly referred to as “operational stability”, and leads to abnormal wheel–rail contact interactions. However, the evaluation criteria for vehicle stability are not uniform, which affects the assessment of wheel conditions and the timing of wheel re-profiling during maintenance. Therefore, numerical simulations were conducted by matching the measured worn wheel profiles with standard rails, and three different methods were employed to evaluate vehicle stability in this article. The numerical results revealed that the wheel equivalent conicity exhibits a nonlinear characteristic caused by hollow wear, which means that the nominal equivalent conicity is unable to accurately represent the geometric contact relationship between the wheel and rail. Under identical wheel wear conditions, a certain difference was observed in the critical speed of the vehicle determined by the velocity-reducing method and the bifurcation configuration method. Both methods were capable of reflecting the impact of wheel hollow wear on vehicle stability at the critical speed. Compared to the velocity-reducing method, the bifurcation configuration method can better reflect the transition process of a vehicle from stable running to hunting instability. Furthermore, the lateral vibration acceleration values measured above the bogie frame indicated that slight wheel wear is insensitive to increased speed. However, when the wear was severe, the lateral vibration acceleration of the bogie was found to increase sharply, exceeding the established stability criteria. This phenomenon was consistent with the safety alarms that occurred during actual vehicle operation, indicating that the vehicle had failed to meet stability requirements. Full article

Silica (SiO₂) particles are widely used in various industries due to their chemical inertness, thermal stability, and wear resistance. The present study describes the preparation and potential use of porous hydrophobic and hydrophilic SiO₂ microcapsules (MCs) of a narrow size distribution. First, various layers of SiO₂ micro/nano-particles (M/NPs) were grafted onto monodispersed polystyrene (PS) microspheres of a narrow size distribution. Hydrophobic and hydrophilic sintered SiO₂ MCs were then prepared by removing the core PS from the PS/SiO₂ core–shell microspheres by burning off under normal atmospheric conditions or organic solvent dissolution, respectively. We examined how the size and quantity of the SiO₂ M/NPs influence the MC’s properties. Additionally, we utilized two forms of hollow SiO₂ MC for different applications; one form was incorporated into polymer films, and the other was free-floating. The hydrophobic microcapsules filled with 6% hydrogen peroxide were effective in killing the tomato brown rugose fruit virus (ToBRFV). The hydrophilic microcapsules filled with thymol and thin coated onto polypropylene films were successfully used to prevent mold formation for hay protection. Full article

In order to improve the wear and corrosion resistance of Ti6Al4V alloy, a Ti-N compound layer was formed on the alloy by plasma nitriding at a relatively low temperature (750 °C) and within an economical processing duration (4 h), in a mixture of NH₃ and N₂ gases with varying ratios. The influence of the gas mixture on the microstructure, phase composition, and properties of the Ti-N layer was investigated. The results indicated that the thickness of the nitrided layer achieved in a mixed atmosphere with optimal proportions of NH₃ and N₂ (with a ratio of 1:2) was substantially greater than that obtained in an atmosphere of pure NH₃. This suggests that appropriately increasing the proportion of N₂ in the nitriding atmosphere is beneficial for the growth of the nitrided layer. The experiments demonstrated that the formation of the surface nitrided layer significantly enhances the corrosion and wear resistance of the titanium alloys. Full article

Under extreme conditions such as high speed and heavy load, 18Cr2Ni4WA steel cannot meet the service requirements even after carburizing and quenching processes. In order to obtain better surface mechanical properties and tribological property, a hollow cathode ion source diffusion strengthening device was used to nitride the traditional carburizing and quenching samples. Unlike traditional ion carbonitriding technology, the low-temperature ion carbonitriding technology used in this article can increase the surface hardness of the material by 50% after 3 h of treatment, from the original 600 HV_0.1 to 900 HV_0.1, while the core hardness only decreases by less than 20%. The effect of post-ion carbonitriding treatment on mechanical properties and tribological properties of the carburized and quenched 18Cr2Ni4WA steel was investigated. Samples in different treatment are characterized using optical microscopy (OM), scanning electron microscopy (SEM), optimal SRV-4 high temperature tribotester, as well as Vickers hardness tester. Under two conditions of 6N light load and 60 N heavy load, compared with untreated samples, the wear rate of ion carbonitriding samples decreased by more than 99%, while the friction coefficient remained basically unchanged. Furthermore, the careful selection of ion nitrocarburizing and carburizing tempering temperatures in this study has been shown to significantly enhance surface hardness and wear resistance, while preserving the overall hardness of the carburized sample. The present study demonstrates the potential of ion carbonitriding technology as a viable post-treatment method for carburized gears. Full article

A large amount of primary energy is lost due to friction, and the study of new additive materials to improve friction performance is in line with the concept of low carbon. Carbon nanotubes (CNTs) have advantages in drag reduction and wear resistance with their hollow structure and self-lubricating properties. This review investigated the mechanism of improving friction properties of blocky composites (including polymer, metal, and ceramic-based composites) with CNTs’ incorporation. The characteristic tubular structure and the carbon film make low wear rate and friction coefficient on the surface. In addition, the effect of CNTs’ aggregation and interfacial bond strength on the wear resistance was analyzed. Within an appropriate concentration range of CNTs, the blocky composites exhibit better wear resistance properties. Based on the differences in drag reduction and wear resistance in different materials and preparation methods, further research directions of CNTs have been suggested. Full article

The flywheel is a widespread mechanical component used for the storage of kinetic energy and angular momentum. It typically consists of cylindrical inertia rotating about its axis on rolling bearings, which involves undesired friction, lubrication, and wear. This paper presents an alternative mechanism that is functionally equivalent to a classical flywheel while relying exclusively on limited-stroke flexure joints. This novel one-degree-of-freedom zero-force mechanism has no wear and requires no lubrication: it is thus compatible with extreme environments, such as vacuum, cryogenics, or ionizing radiation. The mechanism is composed of two coupled pivoting rigid bodies whose individual angular momenta vary during motion but whose sum is constant at all times when the pivoting rate is constant. The quantitative comparison of the flexure-based flywheel to classical ones based on a hollow cylinder as inertia shows that the former typically stores 6 times less angular momentum and kinetic energy for the same mass while typically occupying 10 times more volume. The freedom of design of the shape of the rigid bodies offers the possibility of modifying the ratio of the stored kinetic energy versus angular momentum, which is not possible with classical flywheels. For example, a flexure-based flywheel with rigid pivoting bodies in the shape of thin discs stores 100 times more kinetic energy than a classical flywheel with the same angular momentum. A proof-of-concept prototype was successfully built and characterized in terms of reaction moment generation, which validates the presented analytical model. Full article

Magnesium alloys are the lowest-density structural metals with a wide range of applications, such as aircraft skins, engine casings and automobile hubs. However, its low surface hardness and non-corrosion resistance in natural environments limit its wide range of applications. In this work, Si-DLC coatings (Si: 15 at.%) are fabricated on AZ91 alloy using a hollow cathode discharge combined with a DC bias voltage from 0 to −300 V to increase the deposition rate and modulate the structure and properties of the coatings. The Si interlayer with a thickness of around 0.6 µm is deposited first to enhance the adhesion. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), and Raman spectroscopy are used to investigate the effect of DC bias on the microstructure evolution of Si-DLC coatings. Meanwhile, corrosion and wear resistance of the coatings at various bias voltages have been investigated using electrochemical workstations and pin-on-desk wear testers. It is shown that the bias-free coating has a loose structure and is less resistant to corrosion and wear. The bias coating has a compact structure, small carbon cluster size, high chloride ion corrosion resistance, and high wear resistance against Al₂O₃ spheres. The corrosion potential of the coating bias at −300 V is −0.98 V, the corrosion current density is 1.35 × 10⁻⁶ A·cm⁻², the friction coefficient is 0.08, and the wear rate is 10⁻⁸ orders of magnitude. The formation of SiC nanocrystals and high sp³-C, as well as the formation of transfer films on the surface of their counterparts, are the main reasons for the ultra-high wear resistance of the bias coatings. The wear rate, coefficient of friction, and corrosion rate of the coating are 0.0069 times, 0.2 times, and 0.0088 times that of the AZ91 alloy, respectively. However, the bias coating has only short to medium-term protection against the magnesium alloy and no long-term protection due to cracks caused by its high internal stress. Full article

Low-temperature plasma nitriding is a thermochemical surface treatment that promotes surface hardening and wear resistance enhancement without compromising the corrosion resistance of sintered austenitic stainless steels. Hollow cathode radiofrequency (RF) plasma nitriding was conducted to evaluate the influence of the working pressure and nitriding time on the microstructure and thickness of the nitrided layers. A group of samples of sintered 316L austenitic stainless steel were plasma-nitrided at 400 °C for 4 h, varying the working pressure from 160 to 25 Pa, and the other group was treated at the same temperature, varying the nitriding time (2 h and 4 h) while keeping the pressure at 25 Pa. A higher pressure resulted in a thinner, non-homogeneous nitrided layer with an edge effect. Regardless of the nitriding duration, the lowest pressure (25 Pa) promoted the formation of a homogenously nitrided layer composed of nitrogen-expanded austenite that was free of iron or chromium nitride and harder and more scratching-wear-resistant than the soft steel substrate. Full article

The problem of remaining useful life estimation (RULE) of hollow worn railway vehicle wheels in terms of remaining mileage via wheel tread depth estimation using on-board vibration signals from a single accelerometer on the bogie frame is presently investigated. This is achieved based on the introduction of a statistical time series method that employs: (i) advanced data-driven stochastic Functionally Pooled models for the modeling of the vehicle dynamics under different wheel tread depths in a range of interest until a critical limit, as well as tread depth estimation through a proper optimization procedure, and (ii) a wheel tread depth evolution function with respect to the vehicle running mileage that interconnects the estimated hollow wear with the remaining useful mileage. The method’s RULE performance is investigated via hundreds of Simpack-based Monte Carlo simulations with an Attiko Metro S.A. vehicle and many hollow worn wheels scenarios which are not used for the method’s training. The obtained results indicate the accurate estimation of the wheels tread depth with a mean absolute error of ∼0.07 mm that leads to a corresponding small error of ∼3% with respect to the wheels remaining useful mileage. In addition, the comparison with a recently introduced Multiple Model (MM)-based multi-health state classification method for RULE, demonstrates the better performance of the postulated method that achieves 81.17% True Positive Rate (TPR) which is significantly higher than the 45.44% of the MM method. Full article

Low-temperature plasma nitriding of austenitic stainless steel can ensure that its corrosion resistance does not deteriorate, improving surface hardness and wear performance. Nevertheless, it requires a longer processing time. The hollow cathode discharge effect helps increase the plasma density quickly while radiatively heating the workpiece. This work is based on the hollow cathode discharge effect to perform a rapid nitriding strengthening treatment on AISI 304 stainless steels. The experiments were conducted at three different temperatures (450, 475, and 500 °C) for 1 h in an ammonia atmosphere. The samples were characterized using various techniques, including SEM, AFM, XPS, XRD, and micro-hardness measurement. Potentiodynamic polarization and electrochemical impedance spectroscopy methods were employed to assess the electrochemical behavior of the different samples in a 3.5% NaCl solution. The finding suggests that rapid hollow cathode plasma nitriding can enhance the hardness, wear resistance, and corrosion properties of AISI 304 stainless steel. Full article

The problem of the prompt detection of early-stage hollow worn wheels in railway vehicles via on-board random vibration measurements under normal operation and varying speeds is investigated. This is achieved based on two unsupervised statistical time series (STS) methods which are founded on a multiple-model (MM) framework for the representation of healthy vehicle dynamics. The unsupervised MM power spectral density (U-MM-PSD) method employs Welch-based PSD estimates for wheel wear detection and the unsupervised MM autoregressive (U-MM-AR) method for the parameter vectors of multiple AR models. Both methods are assessed via two case studies using thousands of test cases. The first case study includes Monte Carlo simulations using a SIMPACK-based detailed railway vehicle model, while the second is based on field tests with an Athens Metro train. Wheel wear detection is pursued using lateral or vertical vibration signals from the bogie or the carbody of a trailed vehicle traveling with three different speeds (60, 70, 80 km/h) using wheels under healthy conditions or with early stage hollow wear. Both methods exhibit remarkable performance with the U-MM-AR method to achieve the best overall results, reaching correct detection rates of even 100% with false alarm rates below $5\%$ based on a single accelerometer either on the carbody or bogie. Full article

In this work, ethyl cellulose was used as a wall material, propanetriol as a core material, polyvinyl alcohol as a stabilizer and gelatin as an emulsifier. Self-healing microcapsules with a slow-release effect were prepared using the solvent evaporation method. Various analytical techniques, such as 3D confocal microscopy (LCSM), optical microscopy (OM), scanning electron microscopy (SEM), infrared spectroscopy (FT-IR), energy dispersive spectroscopy (EDS), thermal weight loss analysis (TGA), laser particle size tester and electrochemical impedance polarization, are utilized. The morphology, distribution, particle size, corrosion resistance and self-healing ability of the prepared microcapsules and resin-based coatings were characterized and analyzed. The results show that the cross-sectional core–shell structure is clearly seen in the LCSM, showing a smooth, hollow, spherical shape. OM and laser particle size testers have shown that the size of the microcapsules decreases over time. Also, in OM, the microcapsules are uniformly distributed in the emulsion with a smooth and non-adherent surface. In SEM, the microcapsule particle size is about 150 μm, the shell wall thickness is about 18 μm, and the hollow structure of ruptured microcapsules is obvious. FT-IR and TGA confirmed the successful encapsulation of the formulated microcapsules. The results show that when the core-wall mass ratio is 1.2:1 and the amount of microcapsule is 10% of the coating amount, the prepared microcapsule has high thermal stability and certain wear resistance. By electrochemical and immersion experiments, it was found that a 3.5 wt % NaCl solution has the best impedance, the lowest corrosion current density, and good adhesion and tensile toughness. The results showed that glycerol was successfully released from the broken microcapsules and self-healed, forming an anticorrosive coating with excellent corrosion resistance and self-healing ability. Full article

For high-tech manufacturing industries, developing large-scale complex nonlinear dynamic systems must be taken as one of the basic works, formulating problems to be solved, steering system design in a more preferable direction, and making correct strategic decisions. By using effective tools of big data mining, Dynamic Design Methodology was proposed to establish a technical platform for Multidiscipline Design Optimization such as High-Speed Rolling Stock, including three key technologies: analysis graph of full-vehicle stability properties and variation patterns, improved transaction strategy of flexible body to MBS interface, seamless collaboration with weldline fatigue damage assessments through correct Modal Stress Recovery. By applying the above methodology, a self-adaptive improved solution was formulated with optimal parameter configuration, which is one of the more favorable options for higher-speed bogies. While within a velocity (140–200) km/h at λ_e < 0.10, car body instability’s influence on ride comfort can be easily improved by using a semi-active vibration reduction technique between inter-vehicles through outer windshields. Comprehensive evaluations show that only under rational conditions of wheel-rail matching, i.e., 0.10 ≥ λ_eN > λ_emin and λ_emin = (0.03–0.06), can this low-cost solution achieve the three goals of low track conicity, optimal route planning, and investment benefit maximization. So, rail vehicle experts are necessary to collaborate and innovate intensively with passenger transportation and steel rail ones. Specifically, by adopting rail grinding treatment, occurrence probability is controlled at 85% and 5% for track conicity of (0.03–0.10) and (0.25–0.35). By optimizing routing planning, operating across dedicated lines of different speed grades can achieve self-cleaning of central hollow tread wear over time. According to the inherent rigid-flex coupling relationship, geometric nonlinearities of worn wheel-rail contact should be avoided as much as possible for HSR practices. Only under weak coupling interfaces in the floor frame can the structural integrity of an aluminum alloy car body be ensured. Full article