Journal of The Brazilian Society of Mechanical Sciences and Engineering最新文献

One of the most crucial considerations when developing any slurry transportation system is evaluating slurry erosion because it significantly contributes to the system’s many component’s ineffective operation and eventual failure. In the present work, the impact of the thermo-mechanical process (TMP) on the resistance of the slurry erosion wear of the target material has been investigated at a high solid concentration (50–70% fly ash by weight) and different rotational speeds (300–600 rpm) of the specimen. SS431 was used as the target material, and the Gleebles® 3800 simulator was used to perform the TMP on the target material. In the Gleebles® 3800 simulator, four strain rates (0.01, 0.1, 1, and 10 s⁻¹) were used for the deformation at two temperatures (950 °C and 1050 °C). A slurry pot tester evaluated the slurry erosion wear for 15 h at room temperature. TMP specimens exhibit superior resistance to slurry erosion wear compared to as-received SS431 material at all flow parameters. The best resistance to slurry erosion was observed in specimens that had been TMP at 1050 °C with a strain rate of 1 s⁻¹. Correlations had been found between various target material properties (hardness and grain size) as well as flow properties (solid concentration and rotational speed of the specimens) and the slurry erosion wear, all of which contribute to the erosion mechanism.

The rational design of artificial materials with dynamic performance abilities is necessary due to their applications in different fields. Meta-structures are being explored intensively because of their unusual qualities from natural materials, and these traits include Negative Poisson's ratio, high stiffness, high energy absorption, and negative thermal expansion. Meta-structures can be fabricated using additive manufacturing (AM) and obtained from macro- to meso scale; hence are scale-independent. AM fabricates designed geometry using materials like metals, metal alloys, composites, shape memory alloys, and elastomers. AM is a versatile process that can manufacture meta-structures with different geometries, including chiral, re-entrant, cellular, etc. This work comprehensively reviews the materials necessary to manufacture meta-structures, their alternative geometries, and the impact of configuration changes on their mechanical properties. Subsequently, the applications in many disciplines, such as vibration mitigation, noise cancellation, and electromagnetic shielding, as well as their limits and future potential, are also examined.

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Vibration-assisted cutting (VAC) is an effective way of improving machining quality. Through vibration-assisted cutting experiments, the cutting mechanism of carbon fiber-reinforced polyetheretherketone (CF/PEEK) composites during vibration-assisted cutting and the influencing factors on the quality of machined surfaces were investigated. The effect of cutting-directional vibration-assisted (CDVA) and normal-directional vibration-assisted (NDVA) on cutting force, cutting temperature evolution, chip and surface morphology were analyzed. The experimental results demonstrate that compared with the traditional cutting (TC), the cutting ability of the tool in VAC was enhanced. When the fiber orientation is 0°, 45°, 90° and 135°, the maximum reduction of cutting force in CDVA is 36.48%, 23.43%, 27.19% and 13.04%, and the maximum increase of cutting temperature in NDVA is 23.91%, 28.88%, 14.07% and 19.82%, respectively. VAC can effectively cut fibers and reduce machining damage, and the quality of machined surface is the best in NDVA. Intermittent cutting with vibration in the direction of the main cutting force results in shorter chip contact times and thus lower chip temperatures in CDVA. This study provides insight into the ultrasonic vibration-assisted cutting performance of CF/PEEK and offers ideas for the next generation of high-performance manufacturing of composite materials.

A multi-purpose test rig has been manufactured to perform an in-depth study of the flow field around a tandem-rotor generic helicopter in hovering flight. The survey includes the flow field study around the blades and also the overall trust and power measurements near the ground for both overlapped and non-overlapped blades. A single-rotor configuration has also been tested as a baseline. The results have approved the existence of a fountain flow region between the twin rotors, about which, very limited experimental data are available in the literature. It has been shown that in tandem rotors, the ground effect increases the pressure within the fountain flow which gives rise to the lift. For the overlapping blades, this favorable effect has been shown to be more prominent than the non-overlapping configuration. It has also been found out that the ground proximity remarkably enhances the tandem-rotors’ trust in comparison with the single rotor. As increasing the overlap between the rotors, both the power required by the blades and the thrust produced in the ground effect increase.

Cold extruded internal thread is a kind of green processing method with many advantages. However, the torque is greater than cutting, if the lubrication effect is not ideal, it can easily cause excessive wear and even breakage of taps. With the intention of mitigating the frictional wear of the tap in the forming process, this paper studied the effect of friction between extrusion taps and workpieces on the forming quality through simulation and experiment. The effects of friction factor on extrusion torque, extrusion temperature, effective strain, forming work and metal flow velocity were analyzed separately. The results indicate that the extrusion torque, extrusion temperature and forming work increased with the increase of friction factor. In addition, the effective strain increased and then decreased with the increase of friction factor. The metal flow velocity at the crest and root decreased with the increase of the friction factor. Finally, the lubricating properties of the four lubricants were analyzed in the experiments. The results showed that all the lubricants used in the experiment were able to reduce the extrusion torque, among which the industrial white oil had the best torque reduction performance, with a torque reduction of 32.9% compared with dry extrusion.

This research investigates the low-velocity impact behavior of two distinct jute-based composite configurations: flexible composites comprising jute fibers embedded in a rubber matrix and stiff composites consisting of jute fibers embedded in an epoxy matrix. The primary objective is to evaluate their respective energy absorption capabilities under controlled impact loading conditions, with implications for enhancing impact resistance across diverse industrial domains. Mechanisms governing damage in these composite systems are thoroughly examined. Using a specialized testing apparatus, drop weight impact experiments were performed to evaluate the composites’ low-velocity impact response, with an emphasis on how much energy is absorbed and the related damage techniques. Flexible composite with jute/rubber/jute/rubber/jute (JRJRJ) absorbs 15.5% more energy compared to stiff epoxy-based composite with 10 layers of jute (JE10). Jute/rubber/jute (JRJ) exhibits energy absorption of 70.24% more, compared stiff epoxy-based composite with 7 layers of jute (JE7), and jute/rubber/rubber/jute (JRRJ) exhibits 53.44% more energy compared to stiff epoxy-based composite with 9 layers of jute (JE9). The findings indicate that flexible composites, benefiting from the elastomeric properties of the rubber matrix, exhibit superior energy absorption capabilities compared to their stiff counterparts. The inherent flexibility of the rubber matrix facilitates greater deformation upon impact, leading to prolonged impact duration and improved energy dissipation. In contrast, stiff composites demonstrate higher initial stiffness but limited energy absorption capacity due to their inherent rigidity. Detailed damage analysis sheds light on the distinct failure mechanisms within the composite structures. While compliant composites predominantly experience matrix tearing upon failure, stiff composites exhibit matrix cracking, suggesting a more catastrophic failure mode. This suggests that there is a lower risk of a catastrophic breakdown with the suggested compliant materials, rendering them particularly suitable for low-velocity impact applications where controlled energy absorption and damage mitigation are critical considerations.

This paper presents a lightweight design of the winding layer of Type IV hydrogen storage vessel, focusing on two key factors: winding angle and winding bandwidth. For a specific 70 MPa high-pressure hydrogen storage vessel, an accurate finite element analysis model was established using cubic spline functions and netting theory. An optimization method combining surrogate modeling and finite element simulation was proposed. By iteratively constructing surrogate models, a design scheme with the minimum mass of the vessel in the target space was obtained. Furthermore, the influence of different winding bandwidths on the winding layer was studied, and an optimization method based on a mixed winding with multi-bandwidth was proposed. The results show that the surrogate model has high approximation accuracy. After the first optimization step, the mass of the vessel reduced by 1.159 kg. By combining the two optimization methods, the mass of the vessel was further significantly reduced by 2.498 kg.

This study investigates the pseudo-transient behavior of a direct molten salt linear Fresnel solar plant, which thermally assists a steam Rankine cycle. The linear Fresnel system, which is thermally and hydrodynamically modeled using a 1-D, axially discrete formulation, is subjected to annual solar and meteorological TMY data with an hourly resolution. The analysis explores three aspects of the coupled system. First, it performs a parametric analysis quantifying the impact of several parameters on the system’s performance. Next, it performs a multivariable optimization aiming to determine the geometric and operational parameters that minimize the system’s LCOE. Finally, it performs a break-even analysis aiming to determine the cost reduction required for such systems to be economically competitive with CSP systems. The parametric analysis confirms that, as the temperature of the heat transfer fluid increases, the solar field efficiency drops while the power block’s increases. The LCOE has a minimal value of 104.9 US$/MWh considering a solar field with a solar multiple of 4.9 and an outlet temperature for the heat transfer fluid of 568 °C, a power cycle pressure of 171.7 bar producing 300 MW. Finally, the break-even analysis indicated that a solar field cost reduction of approximately 30% would lead to a LCOE around 95 US$/MWh and a plant initial investment of 4508.9 US$/kW, which is competitive with operating CSP plants.

Intersection hole is the key connecting hole in aircraft assembly. The drilling accuracy and quality of intersection hole have great impact on the life and safety of aircraft. Traditional intersection hole takes drill plate as process criterion and uses manual processing methods, with low efficiency, low stability, and higher possibility of positional deviation. Numerical boring mill is a relatively advanced technique of intersection hole processing at present. This article focuses on the effect of processing parameters such as boring speed, feed, and cutting depth on the quality of intersection hole on aircraft vertical and horizontal tails. Surface roughness prediction model and cutting force prediction model are used to construct multi-objective optimized function. Objective constraint conditions are used, and the multi-objective optimized functions are solved by genetic algorithms. The optimization results are experimentally verified. The optimal parameter combination is obtained through the multi-objective optimized design of precision processing parameter of aircraft intersection hole, providing theoretical guidance for the selection of processing parameters in actual production.

The phenomenon of gear backlash is observed to increase as the planetary gears undergo wear, leading to an exacerbation of vibrations within the gear gearbox system. This heightened wear further contributes to the generation of substantial heat, consequently causing an elevation in temperature. As a consequence, the thermal deformation of the gear occurs, thereby affecting its capacity to effectively transmit power. This study presents the development of a nonlinear dynamic model for a gear system, incorporating the influence of wear and temperature. The model is constructed by integrating the Archard wear model with the thermal deformation idea. The present work investigates the influence of wear and temperature on the nonlinear dynamic characteristics of a gear system using a range of analytical techniques, such as bifurcation diagrams, maximum Lyapunov index charts, phase diagrams, and Poincare cross-section diagrams. The results indicate that as the temperature increases, the system transitions from multi-cycle motion to single cycle motion. When there is slight wear (28 microns), increasing the temperature appropriately can suppress the chaotic motion of the system. When there is severe wear (70 microns), the gears must be replaced.