Search Results (6,004)

This paper presents a detailed numerical investigation of the effect of hub-mounted riblets on the thermal and aerodynamic performance of a radial turbine rotor. While prior studies have shown that riblets reduce wall shear stress and improve aerodynamic efficiency, their influence on heat transfer and thermal losses remains underexplored. Using numerical simulations, this study examines the heat transfer characteristics within the rotor passage, comparing ribbed and smooth hub configurations under the same operating conditions. Results reveal that although riblets reduce frictional drag, they also enhance convective heat transfer—leading to a 6% increase in the heat transfer coefficient at the hub and 2.8% at the blade surfaces. This intensification of heat transfer results in a 4.3% rise in overall thermal losses, counteracting some of the aerodynamic gains. The findings provide new insights into the thermofluidic implications of surface modifications in turbomachinery and emphasise the importance of considering surface finish not only for aerodynamic optimisation but also for thermal efficiency. These results can inform future turbine design and manufacturing practices aimed at controlling surface roughness to minimise heat loss. Full article

Addressing the issue of stress concentration at the toe of steel plate shear walls, which is susceptible to local buckling and brittle failure under seismic loading, this paper innovatively proposes a disc spring-laminated rubber energy dissipation device (DSLRDD) newly designed for application at the wall toe of the shear wall structures. Firstly, the structure characteristics and energy dissipation principle of the DSLRDD are described. Secondly, the finite element model of the DSLRDD is established in ABAQUS. Furthermore, the optimal design parameters’ values of DSLRDD are analyzed and given by taking the stacking arrangement of disc springs, the thickness ratio of steel plate to rubber layer, and the yield strength of steel plate as three main parameters. It is recommended that in DSLRDD, the disc spring stacking arrangement adopts either two pieces in series or a composite of series–parallel. At the same time, the range of the thickness ratio between the steel plate and the rubber layer is defined as being between 1.25 and 2.5, and the yield strength value of the steel plate is determined as 400 MPa. Finally, to verify the energy dissipation capacity of the DSLRDD, a double corrugated steel plate shear wall (DCSPSW) is taken as the experimental structure. The model has been verified against the test data, with a maximum damping force error of 14.4%, ensuring reliable modeling. DSLRDD models with the disc spring stacking arrangements of two pieces in series and composite of series–parallel were established, respectively, and they were installed at the toe of the DCSPSW. The seismic performance of the DCSPSW before and after the installation of two different DSLRDDs is studied. The results show that the DSLRDDs have obvious energy absorption capabilities. The energy dissipation factors of DCSPSW before and after installing DSLRDD were increased by 10.0% and 8.9%, respectively. DCSPSW with DSLRDD exhibits better plasticity and bearing capacity under seismic action, and the stress and deformation are mainly concentrated on the DSLRDD instead of the wall toe. Moreover, it is recommended to use the stacking arrangement of two series disc springs with a simple structure. In conclusion, the DSLRDD has excellent energy dissipation capacity and can be fully applied to practical projects. Full article

Structures that possess negative Poisson’s ratio are termed “Auxetic” structures. They elongate laterally on longitudinal–tensile loading and compress laterally on longitudinal–compressive loading. Auxetic structures are a composition of unit cells that are available in various geometries, which include triangular, hexa-triangular, re-entrant, chiral, star, arrowhead, etc. Due to their unique shape, these structures possess remarkably good mechanical properties such as shear resistance, indentation resistance, fracture resistance, synclastic behavior, energy absorption capacity, etc. However, they have poor load-bearing capacity. To improve the load bearing strength of these structures, this paper presents a numerical analysis of oriented re-entrant structured (ORS) beams with auxetic clusters aligned at various angles (0°, 45° and 90°), using Finite Element Methods. Oriented re-entrant unit cell clusters enclosed by a bounded frame were modeled and a three-point bending test was conducted to perform a comparison study on deformation mechanisms of the different oriented re-entrant honeycomb structures with honeycomb beams. The computational analysis of ORS beams revealed that the directional deformation and normal strain along the x-axis were the lowest in ORS45, followed by ORS90, ORS0, and honeycomb. Among all the beams, ORS45 displayed the best load-bearing capacity with comparably low mass density. Full article

The destabilizing damage of rock structures in coal beds engineering is greatly influenced by the bearing rupture features and energy evolution laws of rock–coal assemblages with varying height ratios. In this study, we used PFC3D to create rock–coal assemblages with rock–coal height ratios of 2:8, 4:6, 6:4, and 8:2. Uniaxial compression simulation was then performed, revealing the expansion properties and damage crack dispersion pattern at various bearing phases. The dispersion and migration law of cemented strain energy zoning; the size and location of the destructive energy level and its spatiotemporal evolution characteristics; and the impact of height ratio on the load-bearing characteristics, crack extension, and evolution of multiple energies (strain, destructive, and kinetic energies) were all clarified with the aid of a self-developed destructive energy and strain energy capture and tracking Fish program. The findings indicate that the assemblage’s elasticity modulus and compressive strength slightly increase as the height ratio increases, that the assemblage’s cracks begin in the coal body, and that the number of crack bands inside the coal body increases as the height ratio increases. Also, the phenomenon of crack bands penetrating the rock through the interface between the coal and rock becomes increasingly apparent. The total number of cracks, including both tensile and shear cracks, decreases as the height ratio increases. Among these, tensile cracks are consistently more abundant than shear cracks, and the proportion between the two types remains relatively stable regardless of changes in the height ratio. The acoustic emission ringing counts of the assemblage were not synchronized with the development of bearing stress, and the ringing counts started to increase from the yield stage and reached a peak at the damage stage (0.8${\sigma }_{\mathrm{c}}$) after the peak of bearing stress. The larger the rock–coal height ratio, the smaller the peak and the earlier the timing of its appearance. The main body of strain energy accumulation was transferred from the coal body to the rock body when the height ratio exceeded 1.5. The peak values of the assemblage’s strain energy, destructive energy, and kinetic energy curves decreased as the height ratio increased, particularly the energy amplitude of the largest destructive energy event. In order to prevent and mitigate engineering disasters during deep mining of coal resources, the research findings could serve as a helpful reference for the destabilizing properties of rock–coal assemblages. Full article

Expandable polystyrene (EPS) nozzle covers can be used to replace traditional metal nozzle covers due to their excellent mechanical properties, as well as being lightweight and ablatable. As an important part of the solid rocket motor, the nozzle cover needs to be designed according to the requirements of the overall system. This study lays a theoretical foundation for the engineering design and performance optimization of the EPS nozzle cover. In this paper, the method of combining test research and numerical simulation is used to explore the pressure bearing capacity of EPS nozzle covers with different thicknesses under linear load. Firstly, the quasi-static tensile, compression and shear tests of EPS materials were carried out by universal testing machine, and the key parameters such as stress-strain curve, elastic modulus and yield strength were obtained; Based on the experimental data, the constitutive model of EPS material with respect to density is fitted and modified; The VUMAT subroutine of the material was written in Fortran language, and the mechanical properties of the nozzle cover with different material model distribution schemes and different thicknesses were explored by ABAQUS finite element numerical simulation technology. The results indicate that the EPS nozzle cover design based on the two material model allocation schemes better aligns with practical conditions; when the end thickness of the EPS nozzle cover exceeds 3 mm, the opening pressure formula for the cover based on the pure shear theory of thin-walled circular plates becomes inapplicable; the EPS nozzle cover exhibits excellent pressure-bearing capacity and performance, with its pressure-bearing capacity showing a positive correlation with its end thickness, and an EPS nozzle cover with a 9 mm end thickness can withstand a pressure of 7.58 MPa (under internal pressure conditions); the pressure-bearing capacity of the EPS nozzle cover under internal pressure conditions is higher than under external pressure conditions, and when the end pressure-bearing surface thickness increases to 9 mm, the internal pressure-bearing capacity is 3.13 MPa higher than under external pressure conditions. Full article

In turbine blade environments, the combination of blade curvature and accelerating flow gives rise to streamwise pressure gradients (SPGs), which substantially impact coolant–mainstream interactions. This study investigates the effect of SPGs on film cooling performance using Large Eddy Simulation (LES) for a shaped cooling hole at a density ratio of $\mathrm{DR}=1.5$ under two blowing ratios: $M=0.5$ and $M=1.6$. Both favorable pressure gradient (FPG) and zero pressure gradient (ZPG) conditions are examined. LES predictions are validated against experimental data in the high blowing ratio case, confirming the accuracy of the numerical method. Comparative analysis of the time-averaged flow fields indicates that, at $M=1.6$, FPG enhances wall attachment of the coolant jet, reduces boundary layer thickness, and suppresses vertical dispersion. Counter-rotating vortex pairs (CVRPs) are also compressed in this process, leading to improved downstream cooling. At $M=0.5$, however, the ZPG promotes greater lateral coolant spread near the hole exit, resulting in superior near-field cooling performance. Instantaneous flow structures are also analyzed to further explore the unsteady dynamics governing film cooling. The Q criterion exposes the formation and evolution of coherent vortices, including hairpin vortices, shear-layer vortices, and horseshoe vortices. Compared to ZPG, the FPG case exhibits a greater number of downstream hairpin vortices identified by density gradient, and this effect is particularly pronounced at the lower blowing ratio. The shear layer instability is evaluated using the local gradient $Ri$ number, revealing widespread Kelvin–Helmholtz instability near the jet interface. In addition, Fast Fourier Transform (FFT) analysis shows that FPG shifts disturbance energy to lower frequencies with higher amplitudes, indicating enhanced turbulent dissipation and intensified coolant mixing at a low blowing ratio. Full article

Magnetorheological fluid exhibits shear-thinning behavior when subjected to high temperature environments exceeding 100 °C, which will significantly compromise the operational stability and reliability of the associated mechanical systems. To enhance the performance of magnetorheological fluid, this study selects soft magnetic particles, base carrier fluid, and surfactants based on their resistance to high temperatures and shear-thinning effects. A novel magnetorheological fluid with enhanced thermal stability and shear stability is subsequently developed by carefully selecting flake-shaped carbonyl iron powder, dimethyl silicone oil, and surfactant exhibiting both sedimentation stability and high temperature resistance. The apparent rheological properties and mechanical performance of the fluid are systematically evaluated. Experimental results indicate that the sedimentation rate of the prepared magnetorheological fluid is 3.86% after standing for 10 days, the thermal expansion rate at 200 °C is 12.8%, and the evaporation rate following repeated high temperature applications is only 0.66%. The shear yield stress of the prepared magnetorheological fluid is 31.2 kPa under the magnetic field of 817 mT. The prepared magnetorheological fluid demonstrates excellent thermal stability and shear-thinning resistance, which holds significant potential for enhancing the performance of magnetorheological devices in future applications. Full article

Steel–ultra-high-performance concrete (UHPC) composite beams with small-rib-height perfobond strip connectors (SRHPBLs) exhibited advantages of light weight and high bearing capacity, demonstrating the potential for applications of UHPC in bridge engineering. During service stages, the composite beams were usually under combined tension–shear loads, rather than pure shear loads. Nevertheless, there were research gaps in the static behavior of SRHPBLs embedded in UHPC under combined tension–shear loads, which limited their applications in practice. To address this issue, systematic experimental and theoretical analyses were conducted in the present study, considering the test variables of tension–shear ratio, row number, and strip number. It was demonstrated that the tension–shear ratio had less effect on ultimate shear strength, initial shear stiffness, and ultimate slip of SRHPBLs. When the tension–shear ratio was increased from 0 to 0.42, the shear capacity, initial shear stiffness, and slip at peak load of SRHPBLs decreased by 24.31%,19.02%, and 22.00%, respectively. However, increasing the row number and strip number significantly improved the shear performance of SRHPBLs. Compared to the single-row specimens, the shear capacity and initial shear stiffness of the three-row specimens increased by an average of 92.82% and 48.77%, respectively. The shear capacity and initial shear stiffness of the twin-strip specimens increased by an average of 103.84% and 87.80%, respectively, compared to the single-strip specimens. Finally, more accurate models were proposed to predict the shear–tension relationship and ultimate shear capacity of SRHPBLs embedded in UHPC under combined tension–shear loads. Full article

To explore the influence of waste plastics on the self-healing ability of bitumen, the healing effect of multiple damages, and enlarge the utility of waste plastic in pavement through dynamic shear rheology (DSR) tests, multiple repeated loading tests with fatigue–healing–fatigue as the basic cycle were conducted on modified bitumen samples containing five types of waste plastics (PET, HDPE, PP, PS, and PVC) with different dosages. The damage healing ability of bitumen of the same waste plastic with different dosage ratios and the same dosage of different waste plastics under the same healing time, loading strain, and damage degree through single and multiple loading were explored and analyzed. The results show that based on the three sets of data of the complex shear modulus, phase angle, and fatigue factor, the PS and PVC-modified bitumen have a better recovery performance than that of the other three types of modified bitumen, and the latter also has the best fatigue resistance property. To maximize the improvement effect on the healing index of bitumen, the recommended optimal dosages of PET, HDPE, PP, PS, and PVC are 2%, 2%, 2%, 6%, and 4%, respectively. PS has the best promoting effect on the damage healing ability of bitumen after undergoing multiple damages, while PET has the worst improvement effect. The findings can provide theoretical support and guidance for the wide application of waste plastic-modified bitumen pavement. Full article

Objectives: This study aimed to compare the clinical durability, mechanical performance, and stress behavior of three NiTi rotary systems—BlueShaper (Blue), BlueShaper Pro (Dual Wire), and BlueShaper Gold (fully gold-treated NiTi)—through a multimodal evaluation that included simulated instrumentation in 3D-printed replicas, mechanical testing, and finite element analysis (FEA). Methods: Sixty instruments (n = 20 per group) were tested. Simulated canal preparation was conducted in standardized 3D-printed mandibular molars with a 40° mesial root curvature until fracture occurred. Mechanical tests included torsional and flexural loading using a universal testing machine and stainless steel blocks with a standardized 40° curvature. FEA simulations evaluated von Mises stress, shear stress, total deformation, cyclic fatigue behavior, and contact pressure between the instrument and canal wall. Results: BlueShaper Gold prepared an average of 7.5 canals before fracture, followed by BlueShaper Pro (5.67 canals) and Blue (5.00 canals) (p < 0.001). Gold exhibited the highest torsional resistance (6.08 ± 3.08 N) and the longest fatigue life (325 ± 55.7 cycles), with the lowest von Mises stress and damage factor in FEA. BlueShaper Pro showed the longest time to fracture in mechanical testing (73.85 ± 7.10 s) and balanced mechanical behavior. Blue demonstrated the lowest performance across most parameters, including the shortest fatigue life and highest stress concentration. Conclusions: BlueShaper Gold exhibited the highest mechanical strength and fatigue resistance. BlueShaper Pro demonstrated the longest fatigue life and balanced mechanical behavior. Blue showed the lowest performance across most parameters. The strong correlation among clinical, mechanical, and FEA data reinforces the critical role of alloy composition in determining instrument durability, even when design remains constant. Full article

In weak carbonate rock masses, small-sized karst features ranging from greater than 2 cm to over 1 m in diameter can significantly compromise slope stability, yet they are often overlooked in traditional geotechnical models. This study employs the equivalent porous medium (EPM) approach to incorporate these small-sized voids into two-dimensional finite element slope stability analysis using RS2 software (Version 11.022). By treating the matrix of karst hollows as a porous continuum, we simulate the mechanical and hydraulic influence of their presence on pit slope performance. Results show that even small voids substantially reduce the factor of safety, with destabilization intensifying as void density and pore fluid infiltration increase. Distinct failure mechanisms—including circular sliding, localized subsidence due to cavity collapse, and rockfalls from intersecting shear planes—emerge from the simulations. The stress trajectories and yield elements highlight how minor voids influence the distribution and initiation of shear and tensile failures. These findings reveal that karst features previously considered negligible can be critical structural discontinuities that trigger failure. The EPM framework thus provides a computationally efficient and mechanistically sound means of modelling the cumulative impact of small-sized karst features, bridging a significant gap in geotechnical design for karst-prone weak rock slopes. Full article

The plastic deformation during equal-channel angular pressing (ECAP) can be affected by various material- and processing-related factors. For instance, the initial crystal orientation and grain size play an important role in determining the material flow, which may cause localized deformation in terms of macroscopic deformation banding. In this study, we use a continuous cast AA1080 aluminum alloy with coarse columnar grains to analyze the influence of casting texture on the local material flow during ECAP. Billets are extracted with their columnar grains inclined either in the same direction as the ECAP shear plane or opposite to it. Visio-plastic analysis is performed on split billets. The pass is interrupted halfway through the ECAP tool to accurately capture steady-state deformation conditions. Flow lines at several positions within the billet are identified based on the positions of deformed and undeformed marker points and fitted to a phenomenological model based on a super-ellipse function. For further characterization, hardness measurements, optical and electron microscopy are carried out on the ECAP-deformed samples. Significant differences in terms of local material flow and microstructure evolution regarding the resulting crystal orientation and deformation banding are observed. Our results confirm and emphasize the importance of initial grain size and texture effects for ECAP processing. Full article

Nanofibers, as nucleating agents, can significantly alter the nucleation and growth dynamics of polymer crystallization, thereby modulating the morphology and structure of crystals to enhance mechanical performance of the materials. In this study, the effects of nanofibrillar nucleating agent 1,3:2,4-di(3,4-dimethylbenzylidene) sorbitol (DMDBS) content, melting temperature, and injection speed on the crystallization behavior and mechanical performance of isotactic polypropylene (iPP) were systematically investigated. The incorporation of DMDBS significantly increased the number of iPP nuclei, reduced crystal size and raised the onset crystallization temperature by approximately 11 °C. Concurrently, the tensile strength and elastic modulus of injection-molded iPP samples improved by 15% and 55%, respectively. However, a rise in the melting temperature led to a decrease in the crystallinity, tensile strength, elastic modulus, and impact strength of both neat iPP and iPP/DMDBS samples. With the increase in injection speed, the tensile strength and elastic modulus of iPP/DMDBS samples increased. During the crystallization process, DMDBS crystallizes prior to the iPP melt, forming the nanofibrillar network that effectively reduced the energy barrier for iPP crystal nucleation. Furthermore, under the influence of shear forces during processing, the presence of these nanofibrillar networks promoted the formation of oriented crystalline structures, which in turn contributed to the enhanced tensile strength and elastic modulus observed in iPP samples. Full article

To address the critical challenge of ensuring bottom water-inrush stability during the excavation of ultra-deep foundation pits for riverside suspension-bridge anchorages under complex geological conditions involving high-pressure confined groundwater, we investigate the application of D-RJP high-pressure rotary jet grouting pile technology for ground improvement. Its effectiveness is systematically validated through a case study of the South Anchorage Foundation Pit for the North Channel Bridge of the Zhangjinggao Yangtze River Bridge. The D-RJP method led to the successful construction of a composite foundation within the soft soil that satisfies the permeability coefficient, interface friction coefficient, bearing capacity, and shear strength requirements, significantly improving the geotechnical performance of the anchorage foundation. A series of field experiments were conducted to optimize the critical construction parameters, including the lifting speed, water–cement ratio, and stroke spacing. Core sampling and laboratory testing revealed the grout columns to have good structural integrity. The unconfined compressive strength of the high-pressure jet grout columns reached 5.45 MPa in silty clay layers and 8.21 MPa in silty sand layers. The average permeability coefficient ranged from 1.67 × 10⁻⁷ to 2.52 × 10⁻⁷ cm/s. The average density of the columns was 1.66 g/cm³ in the silty clay layer and 2.08 g/cm³ in the silty sand layer. The cement content in the return slurry varied between 18% and 27%, with no significant soil squeezing effect observed. The foundation interface friction coefficient ranged from 0.44 to 0.52. After excavation, the composite foundation formed by D-RJP columns was subjected to static load and direct shear testing. The results showed a characteristic bearing capacity value of 1200 kPa, the internal friction angle exceeded 24.23°, and the cohesion exceeded 180 kPa. This study successfully verifies the feasibility of applying D-RJP technology to construct high-performance artificial composite foundations in complex strata characterized by deep soft soils and high-pressure confined groundwater, providing valuable technical references and practical insights for similar ultra-deep foundation pit projects involving suspension bridge anchorages. Full article

This study investigates the effects of modifying a beam model for octet-truss lattice structures to calculate the homogenized material properties using the average stress method. While alignment is observed at low relative densities, the unmodified beam model derives underestimated results at higher relative densities, reaching up to 40% and 30% for elastic and shear modulus values, respectively, for a relative density of 0.5. Beam model modification achieved by increasing strut stiffness at the joints is investigated in detail, and we conclude that both modulus values cannot fit the solid model’s results with this type of modification. This study proposes a novel modification method involving seven spring elements with two constants to capture both the elastic and shear moduli. This study concludes by compensating differences between the solid and beam models’ moduli with the inserted springs, providing an analytical solution for the linear elastic system. The performance of the unit cell models is tested by solving two lattice structures at which the elastic modulus and shear modulus were dominant, respectively, on the mechanical behavior. The results converge to a constant value when the number of unit cells is six, and the beam with a spring model achieved a performance that was close to that of the solid model for the shear-modulus-dominant lattice structure. Full article