Search Results (123)

Although cemented carbides have been manufactured by the powder metallurgy (P/M) technology for over a century now, systematic developmental efforts are still underway. In the present study, tool life improvements in metal grooving applications are the key objective. Four PVD-coated cemented carbides compositions, dedicated to groove steel, stainless steel, cast iron, and aluminium alloys, have been newly designed, along with their manufacturing conditions. Physical, mechanical and chemical characteristics—such as sintered density, modulus of elasticity, hardness, fracture toughness, WC grain size, and the chemical composition of the substrate material, as well as the chemical composition, microhardness, structure, and thickness of the coatings—have been studied. A series of grooving tests have also been conducted to assess whether modifications to the thus far marketed tool materials, tool geometries, and coatings can improve cutting performance. In order to compare the laboratory and application properties of the investigated materials with currently produced by reputable companies, commercial inserts have also been tested. The experimental results obtained indicate that the newly developed grooving inserts exhibit excellent microstructural characteristics, high hardness, fracture toughness, and wear resistance and that they show slightly longer tool life compared to the commercial ones. Full article

To enhance the electromagnetic performance of flat-wire permanent magnet synchronous motors, three different groove structures were designed for the rotor, and a multi-objective optimization algorithm combining a genetic algorithm (GA) with the TOPSIS method was proposed. Firstly, an 8-pole 48-slot flat-wire motor model was established, and the cogging torque was analytically calculated to compare the motor’s performance under different groove schemes. Secondly, global multi-objective optimization of the rotor groove dimensions was performed using a combined simulation approach involving Maxwell, Workbench, and Optislang, and the optimal rotor groove size structure was selected using the TOPSIS method. Finally, a comparative analysis of the motor’s performance under both rated-load and no-load conditions was conducted for the pre- and post-optimization designs, followed by verification of the mechanical strength of the optimized rotor structure. The research results demonstrate that the combined optimization approach utilizing the genetic algorithm and the TOPSIS method significantly enhances the torque characteristics of the motor. The computational results indicate that the average torque is increased to 165.32 N·m, with the torque ripple reduced from 28.37% to 13.32% and the cogging torque decreased from 896.88 mN·m to 187.9 mN·m. Moreover, the total distortion rates of the air-gap magnetic flux density and the no-load back EMF are significantly suppressed, confirming the rationality of the proposed motor design. Full article

The aim was to investigate the impact of laser parameters on the surface morphology of ablated graphene and elucidate the interaction mechanism between carbon materials and femtosecond lasers. A pulsed laser with a wavelength of 1030 nm is employed to infer the ablation threshold of the surface and interface of graphene coatings formed through ultrasonic spraying. The ablation threshold of the coating–substrate interface is verified by numerical simulation. Incorporating the data of groove width and depth obtained from a three-dimensional profilometer and finite element simulation, an in-depth analysis of the threshold conditions of laser ablation in coating materials is accomplished. The results indicate that when the femtosecond laser frequency is 10 kHz, the pulse width is 290 fs, and the energy density reaches 0.057 J/cm², the graphene material can be effectively removed. When the energy density is elevated to 2.167 J/cm², a complete ablation of a graphite coating with a thickness of 1.5 μm can be achieved. The findings of this study validate the evolution law and linear relationship of ablation crater morphology, offering new references for microstructure design and the selection of controllable laser processing parameters. Full article

Aimed at hydrogen turbines, this research employs advanced noncontact cylindrical sealing and optimizes its sealing structure to enhance efficiency. Therefore, this paper considers the variable density and viscosity cylindrical sealing model with actual gas effects and explores the impact of groove parameters on load capacity, leakage, and friction force under two different temperature and pressure conditions. A multivariate linear regression analysis model is established. Subsequently, the NSGAII algorithm is used to perform multi-objective optimization design under operational conditions. The TOPSIS methods are applied to select the optimal parameters. This study shows that the groove depth of the spiral groove has the most significant impact on sealing performance when the groove depth is 2 μm. Full article

Graphene, being a two-dimensional monolayer of carbon, exhibits an exceptionally increased surface-to-volume ratio due to its atomic thinness and high aspect ratio, making it a material of considerable interest in advanced technology applications. Recent developments have leveraged their unique surface characteristics, such as nanoscale ripples and grooves, to enhance energy storage, sensing, catalysis, and environmental remediation performance. Its extensive surface area enables rapid ion adsorption and desorption, significantly improving energy and power densities in supercapacitors and lithium-ion batteries while enhancing stability over prolonged cycles. In sensing, the high surface-to-volume ratio supports the immobilization of biomolecules and nanoparticles, improving sensitivity in detecting gases, biomarkers, and pollutants, thereby advancing diagnostic and environmental monitoring applications. Its expansive surface area and unique electronic properties contribute to high catalytic efficiencies, enabling sustainable chemical processes, such as hydrogen production, water treatment, and pollutant degradation. Unlike many review articles that primarily explore the functionalization of graphene, this study mainly emphasizes the evaluation of methodologies aimed at augmenting graphene’s surface area. This review systematically evaluates recent advancements in the optimization of graphene surface characteristics, with a primary focus on their role in enhancing energy storage systems while also addressing emerging applications in healthcare and environmental sustainability. Full article

The groove parameters on the friction base of wet clutches significantly affect the temperature distribution of the steel plates. However, existing methods have not thoroughly investigated the mechanisms by which these parameters influence the thermoelastic instability of wet clutches. To address this gap, a comprehensive co-simulation model of the friction sub-multi-physical field was developed to systematically examine the effects of groove inclination, groove density, and groove depth on the surface temperature and mechanical response of the steel plates. The results indicate that both the tilt angle of the grooves and the number of grooves substantially influence the surface temperature distribution of the steel plates. Specifically, increasing the number of grooves leads to a more concentrated distribution of high-temperature hot spots in the circumferential direction, gradually transitioning the surface temperature–hot spot pattern from isolated hot spots to a more uniform high-temperature tropical distribution, which subsequently reduces the maximum surface temperature. On the other hand, increasing the groove inclination angle causes the high-temperature distribution to shift from localized hot spots to a more tropical pattern, with a relatively minor impact on the peak surface temperature. Furthermore, increasing the groove depth results in the dispersion of the high-temperature tropical zone in the circumferential direction, causing the maximum temperature to initially decrease and then increase. Full article

The influence of regular relief formation modes on the microhardness of the formed groove surface near the apex at the bottom of the groove has been studied. It has been established that the rate of plastic deformation, expressed as the feed rate of the deforming element, has a significant impact on the plastic deformation mechanism, and the microstructure of the formed subsurface layer, as well as on the microhardness of the groove surface. The influence of the type of partially regular reliefs on the degree of plastic deformation was also investigated. It was found that the third type of partially regular relief, which has the highest groove density, provides higher microhardness values than the first and second types. This is explained by the significantly greater density of these type of partially regular relief grooves, which exert a mutual strengthening effect on the surface during formation. The experimental study conducted enabled the derivation of regression equations describing the influence of the feed rate of the deforming element and the type of partially regular relief created on the surface microhardness beneath the lateral ridges and the bottoms of the plastically deformed traces. Full article

The ejection of disturbed surfaces under multiple shocks is a critical phenomenon in pyrotechnic and inertial confinement fusion. In this study, the elastic–plastic ejection from grooved aluminum surfaces under double supported shocks was investigated using the SPH method. A spallation region developed at the bottom of the bubble during the first ejection, and the subsequent second ejection comprised three distinct components: low-density; high- and medium-velocity ejecta; and high-density, low-velocity ejecta. Recompression of the spallation material generated high- and medium-velocity ejecta, resulting in a limited second ejecta mass. The significant increase in the defect area of the bubble and the convergence of the first ejecta generated low-velocity ejecta, resulting in a substantial increase in the second ejecta mass. The shock pressure threshold required for the second ejection was significantly reduced compared with the first ejection. The second ejecta mass increased with shock pressure, but the increase rate gradually decreased, primarily affecting the low-velocity ejecta. The time interval between shocks primarily influenced the second ejection, driven by the evolution of the spallation region at the bottom of the bubble and the convergence of the first ejecta. The second ejecta mass increased and asymptotically approached a constant value with increasing time intervals. Full article

Connecting diaphragm walls as permanent components of underground spaces in relation to basement sidewalls is an effective method for enhancing structural stability, reducing structural footprint, and improving waterproofing performance. To investigate the influence of connection methods between diaphragm walls and sidewalls on the mechanical performance of combined walls and to determine the differences in mechanical behavior between combined and composite walls, four–point bending experiments were conducted based on static loading systems and digital imaging technology. The cracking characteristics, strain response, load–bearing capacity, displacement ductility, and interface mechanical behavior of a combined wall with interface roughening and rebar anchoring, a combined wall with shear grooves, and a composite wall with a high–density polyethylene waterproof layer were comparatively analyzed. The results showed that for the combined walls with interface roughening and rebar anchoring or with shear grooves, through–thickness cracks extended across the interface, with no interfacial slipping failure observed. The combined wall with shear grooves exhibited noticeable through–thickness cracks. For the composite wall, cracks were staggered on both sides of the interface, with significant interface slipping failure. Compared to the composite wall, the combined walls demonstrated superior overall performance with fewer cracks. Additionally, the load–bearing capacity and displacement ductility of the combined wall with interface roughening and rebar anchoring were significantly higher than those of the combined wall with shear grooves and the composite wall. The composite wall exhibited the lowest load–bearing capacity, while the combined wall with shear grooves demonstrated the least displacement ductility. Full article

This research focuses on the prediction and estimation problems for the generalized exponential distribution under Type-II censoring. Firstly, maximum likelihood estimations for the parameters of the generalized exponential distribution are computed using the EM algorithm. Additionally, confidence intervals derived from the Fisher information matrix are developed and analyzed alongside two bootstrap confidence intervals for comparison. Compared to classical maximum likelihood estimation, Bayesian inference proves to be highly effective in handling censored data. This study explores Bayesian inference for estimating the unknown parameters, considering both symmetrical and asymmetrical loss functions. Utilizing Gibbs sampling to produce Markov Chain Monte Carlo samples, we employ an importance sampling approach to obtain Bayesian estimates and compute the corresponding highest posterior density (HPD) intervals. Furthermore, for one-sample prediction and, separately, for the two-sample case, we provide the corresponding posterior distributions, along with methods for computing point predictions and predictive intervals. Through Monte Carlo simulations, we evaluate the performance of Bayesian estimation in contrast to maximum likelihood estimation. Finally, we conduct an analysis of a real dataset derived from deep groove ball bearings, calculating Bayesian point predictions and predictive intervals for future samples. Full article

Hopea chinensis is a representative tree species in evergreen monsoon forests in the northern tropics, but it is currently in a critically endangered state due to destruction by human activities and habitat loss. In this study, we measured and analyzed the number of regenerating seedlings and habitat factors in wild populations of H. chinensis by combining field surveys with laboratory analysis. The aim of this study was to clarify the spatial distribution of H. chinensis seedlings and related factors to provide a scientific basis for conserving its germplasm resources and population restoration. In six populations, most size-class seedlings had aggregated distributions at three scales, and the intensity of aggregation decreased as the sample plot scale increased for most size-class seedlings. In the northern foothills of the Shiwandashan Mountains, size class I seedlings tended to be distributed in habitats with a higher rock bareness rate, whereas size class II and III seedlings tended to be distributed in habitats with a higher canopy density, thicker humus layers, and higher soil moisture content. In the southern foothills of the Shiwandashan Mountains, size class I and II seedlings tended to be distributed in habitats with higher available nitrogen contents, and size class III seedlings tended to be distributed in habitats with higher available nitrogen and soil moisture contents. Therefore, in the southern foothills of the Shiwandashan Mountains, the survival rate of H. chinensis seedlings can be improved by artificially adding soil to increase the thickness of the soil layer in stone crevices and grooves, regularly watering the seedlings during the dry season, and appropriately reducing the coverage of the shrub layer. In the northern foothills, the survival rate of H. chinensis seedlings can be enhanced by regularly applying nitrogen fertilizer and watering to increase the available nitrogen and soil moisture contents. Full article

Osmia bicornis L. is a widespread and valued pollinator species. It is considered to be easy to breed, provided that the nesting material in which the bees build their nests is of sufficient quality and quantity. The aim of this study was to test several different types of nesting materials: reeds and commercial structures, including wood, MDF (Medium Density Fibreboard), plastic, paper or polystyrene. The highest levels of nest cavity occupancy were found in reeds (90%) and grooved MDF (over 80%). We have shown that maintaining mason bee colonies in polystyrene leads to reproductive losses (occupancy only 2% of nesting holes). Mason bees built the most cells in MDF (8.02 cells/hole) and wood (7.34 cells/hole), slightly fewer in plastic (6.83 cells/hole) and reeds (6.74 cells/hole), and the fewest in paper (3.67 cells/hole). The most cocoons per nest were obtained from reed (average 5.47), MDF (4.84) and plastic (4.74). We observed the highest mortality in plastic (2 larvae/hole), and the lowest in reeds (0.92 larvae/hole). In nests made of wood, MDF and paper, large nesting losses were caused by the migration of Ch. osmiae mites along and through the nest holes. The most hygienic nesting material turned out to be reed and plastic forms. Full article

Cyclic straining simulations using incompatibility-incorporated crystal plasticity-FEM, which exhibit PSB ladder structure evolutions as detailed in Part I, are coupled with diffusion analyses of produced vacancies. A new vacancy source model is introduced based on the Field Theory of Multiscale Plasticity (FTMP), interpreting the relationship between the incompatibility rate and the flux of dislocation density as edge dipole annihilation processes. Both direct and indirect coupling diffusion analyses, with and without cyclic straining, demonstrate that varying incompatibility rates tend to further promote vacancy diffusion, leading to surface grooving, enhanced extension rates, and eventual transition to cracks. The findings reveal that (i) the evolved PSB ladder structure serves as a site for vacancy formation, (ii) it provides a diffusion path toward the specimen surface, and (iii) it significantly enhances groove extension rates. These factors effectively facilitate the transition from a “groove” to a “crack”, evidenced by the abrupt acceleration of the extension rate, mirroring systematic experimental observations. These achievements validate the FTMP’s capability to simulate complex phenomena and significantly deepen our understanding of slip band–fatigue crack transition mechanisms. Full article

A sudden, unexplained decline and collapse of young apple trees on dwarfing and semi-dwarfing rootstocks has been reported across North America over the past decade. Although viruses have been detected in declining trees, no information is available on their potential causal role in the decline phenomenon. To this end, virus-inoculated apple trees were established in a high-density experimental orchard and monitored over five years. Tree decline was observed in year 4 (2022), resulting in 17% mortality, with declining trees exhibiting marked vascular tissue necrosis. However, none of the eight viruses and one viroid detected in the experimental orchard was significantly more prevalent in declining trees. Extreme temperature fluctuations in January 2022, followed by a severe water deficit in summer 2022, were recorded at the experimental orchard. Similar but distinct observations were made in a nearby commercial orchard with foliar nutrient imbalances documented in trees exhibiting symptoms of rapid decline. Together, our findings suggest that viruses are not primarily responsible for the rapid decline phenomenon and highlight the need for future work to investigate the roles of tree physiology and water stress in tree decline, as well as the potential efficacy of horticultural mitigation practices. Full article

In this study, a new deep-penetration variable-polarity tungsten inert gas (DP-VPTIG) welding process, which is performed by a triple-frequency-modulated pulse, was employed in the welding fabrication of 8 mm AA7075 aluminum plates. The electric signal, arc shape, and weld pool morphology of the welding process were obtained by means of high-speed photography and an electric signal acquisition system under varying parameters of the intermediate frequency (IF) pulse current. The principle of the arc characteristics and the dynamic mechanism of the weld melting during the process are explained. In addition, the macroforming, microstructure, and microhardness of the welded joints were investigated. The results indicate that, with an intermediate frequency pulse of 750 Hz, the arc displayed a higher energy density and a more effective arc contraction, which improved weld appearance and penetration. Moreover, the impact and stirring action of the arc refined the microstructure grains of the weld center. Therefore, this new welding method is feasible for welding medium-thickness aluminum alloy plates without a groove. Full article