Search Results (946)

This study aims to address the poor extensibility, brittleness, and limited hydration stability of pure sodium alginate (SA) hydrogels, which hinder their use in flexible, skin-adherent applications such as facial masks, by developing bio-based composites incorporating five representative functional additives: xanthan gum, guar gum, hydroxyethyl cellulose (HEC), poly(ethylene glycol)-240/hexamethylene diisocyanate copolymer bis-decyl tetradeceth-20 ether (GT-700), and Laponite^® XLG. Composite hydrogels were prepared by blending 1.5 wt% SA with 0.3 wt% of each additive in aqueous humectant solution, followed by ionic crosslinking using 3% (w/w) CaCl₂ solution. Physicochemical characterization included rotational viscometry, uniaxial tensile testing, ATR-FTIR spectroscopy, swelling ratio analysis, and pH measurement. Among them, the SA/XLG composite exhibited the most favorable performance, showing the highest viscosity, shear-thickening behavior, and markedly enhanced extensibility with an elongation at break of 14.8% (compared to 2.5% for neat SA). It also demonstrated a mean swelling ratio of 0.24 g/g and complete dissolution in water within one year. ATR-FTIR confirmed distinct non-covalent interactions between SA and XLG without covalent modification. The hydrogel also demonstrated excellent conformability to complex 3D surfaces, consistent hydration retention under centrifugal stress (+23.6% mass gain), and complete biodegradability in aqueous environments. Although its moderately alkaline pH (8.96) may require buffering for dermatological compatibility, its mechanical resilience and environmental responsiveness support its application as a sustainable, single-use skin-contact material. Notably, the SA/XLG composite hydrogel demonstrated compatibility with personalized fabrication strategies integrating 3D scanning and additive manufacturing, wherein facial topography is digitized and transformed into anatomically matched molds—highlighting its potential for customized cosmetic and biomedical applications. Full article

The pile–soil composite foundation system, highly acclaimed for its remarkable load-bearing capacity and limited deformation characteristics, has emerged as a fundamental element in geotechnical engineering practices. In the applications of adjacent slope engineering, such composite foundations are influenced by intricate loading scenarios. These scenarios involve both active vertical–horizontal combined load and passive soil-displacement forces generated due to the alteration of soil constraints. In this study, a self-designed movable retaining wall model box was employed. By applying different vertical and horizontal loads and controlling the rotation of the retaining wall around its base, a systematic investigation was conducted on the horizontal bearing mechanisms of single-pile and four-pile composite. The experimental data indicate that for every increment of 15 kPa in the vertical load, the horizontal bearing capacity experiences an average growth of approximately 18.9%, and the extreme value of the bending moment shows an average increase of 19.6. The analysis reveals coupled effects in internal force distribution and deformation patterns within load-bearing pile segments under concurrent active–passive loading conditions, while the embedded sections remain unaffected. Among four-pile composite foundations, the horizontal bearing mechanism of the front-row piles is consistent with that of a single-pile system. However, the maximum bending moments of the front-row and rear-row piles, compared to the single-pile system, have reached 0.68 times and 1.74 times, respectively. Notably, the bending moment of the front-row piles under the translational mode of the retaining wall is approximately 2.9 times that under the rotational mode, posing a potential risk of damage to the retaining structure, and necessary intervention is required. The results of this study provide a scientific basis for the force and deformation mechanism of piles at different positions in the composite foundation near foundation pit engineering, as well as their design for bending and shear resistance. Full article

This study investigated the aerodynamic structures generated by transverse jet injection in supersonic flows around high-speed vehicles. The unsteady evolution of these structures was analyzed using an improved delayed detached Eddy simulation (IDDES) approach based on the Reynolds stress model (RSM). The simulations successfully reproduced experimentally observed shock systems and vortical structures. The time-averaged flow characteristics were compared with the experimental results, and good agreement was observed. The flow characteristics were analyzed, with particular emphasis on the formation of counter-rotating vortex pairs in the downstream region, as well as complex near-field phenomena, such as flow separation and shock wave/boundary layer interactions. Time-resolved spectral analysis at multiple monitoring locations revealed the presence of a global oscillation within the flow dynamics. Within these regions, pressure fluctuations in the recirculation zone lead to periodic oscillations of the upstream bow shock. This dynamic interaction modulates the instability of the windward shear layer and generates large-scale vortex structures. As these shed vortices convect downstream, they interact with the barrel shock, triggering significant oscillatory motion. To further characterize this behavior, dynamic mode decomposition (DMD) was applied to the pressure fluctuations. The analysis confirmed the presence of a coherent global oscillation mode, which was found to simultaneously govern the periodic motions of both the upstream bow shock and the barrel shock. Full article

The co-continuous microstructure represents an ideal configuration for polymer-modified asphalts. Consequently, determining the optimum polymer content hinges on establishing this critical network between polymer and bitumen. In this study, epoxy asphalt bond coats (EABCs) exhibiting three distinct morphologies (epoxy-dispersed, co-continuous, and bitumen-dispersed) were prepared. Phase structure evolution and the final cured morphology were analyzed using a laser scanning confocal microscope (LSCM). Rotational viscosity–time characteristics, tensile properties, single-lap shear strength, and pull-off adhesion strength were characterized using various techniques. Results indicated that the viscosity of EABCs at the late stage of the curing reaction increased with increasing epoxy resin (ER) concentration, whereas the time required for EABCs to reach a viscosity of 5 Pa·s decreased. LSCM analysis revealed that EABCs exhibited three distinct morphologies dependent on ER concentration: (1) a bitumen-continuous morphology with dispersed epoxy domains (41–42 vol.% ER) formed via a nucleation and growth mechanism; (2) a co-continuous structure (43–45 vol.% ER); and (3) an epoxy-continuous structure with dispersed bitumen domains (46 vol.% ER). Furthermore, the EABC with 42 vol.% exhibited a transitional morphology between bitumen-continuous and co-continuous structures. A significant improvement in mechanical properties occurred during the transition from the bitumen-continuous (41 vol.% ER) to the co-continuous morphology (43 vol.% ER): tensile strength, elongation at break, and toughness increased by 524%, 1298%, and 2732%, respectively. Simultaneously, pull-off adhesion strength and single-lap shear strength rose by 61% and 99%, respectively. In contrast, mechanical properties increased only gradually during the co-continuous phase and the subsequent transition to an epoxy-continuous morphology (45–46 vol.% ER). Considering cost, rotational viscosity–time dependence, and mechanical performance, an ER concentration of 43 vol.% (within the co-continuous region) is optimal for EABC production. Full article

As one of the mooring foundation types for floating wind turbine platforms, research on the anchor pullout bearing characteristics of mooring pile foundations remains insufficient, and the underlying mechanism of anchor pullout bearing capacity needs further investigation and clarification. This paper conducts a numerical study on the bearing characteristics of mooring pile foundations under tensile anchoring forces with loading angles ranging from 0° to 90° and loading point depths of 0.2L, 0.4L, 0.6L, and 0.8L (where L is the pile length). The research findings indicate that the anchor pullout bearing capacity decreases as the loading angle increases from 0° to 90°, and exhibits a trend of first increasing and then decreasing with the increase in loading point depth. For rigid pile-anchors, the maximum anchor pullout bearing capacity occurs at a loading point depth of 0.6–0.8L, while for flexible piles, it appears at 0.4–0.6L. Both the bending moment and shear force of the pile shaft show abrupt changes at the loading point, where their maximum values also occur. This implies that the structural design at the loading point of the mooring pile foundation requires reinforcement. Meanwhile, the bending moment and shear force of the pile shaft gradually decrease with the increase in the loading angle, which is attributed to the gradual reduction of the horizontal load component. The axial force of the pile shaft also undergoes an abrupt change at the loading point, presenting characteristics where the upper section of the pile is under compression, the lower section is in tension, and both the pile top and pile tip are subjected to zero axial force. The depth of the loading point significantly influences the movement mode of the pile shaft. Shallow loading (0.2–0.4L) induces clockwise rotation, and the soil pressure around the pile is concentrated in the counterclockwise direction (90–270°). In the case of deep loading, counterclockwise rotation or pure translation of the pile shaft results in a more uniform stress distribution in the surrounding foundation soil, with the maximum soil pressure concentrated near the loading point. Full article

Pressure-sensitive adhesion arises at a specific rheological behavior of polymer systems, which should correlate with their relaxation properties, making them potentially useful for predicting and altering adhesive performance. This work systematically studied the rheology of eco-friendly pressure-sensitive adhesives based on non-crosslinked polyisobutylene ternary blends free of solvents and byproducts, which serve for reversible adhesive bonding. The ratio between individual polymer components differing in molecular weight affected the rheological, relaxation, and adhesion properties of the constituted adhesive blends, allowing for their tuning. The viscosity and viscoelasticity of the adhesives were studied using rotational rheometry, while their adhesive bonds with steel were examined by probe tack and shear lap tests at different temperatures. The adhesive bond durability at shear and pull-off detachments depended on the adhesive composition, temperature, and contact time under pressure. The double differentiation of the continuous relaxation spectra of the adhesives enabled the accurate determination of their characteristic relaxation times, which controlled the durability of the adhesive bonds. A universal linear correlation between the reduced failure time of adhesive bonds and their reduced formation time enabled the prediction of their durability with high precision (Pearson correlation coefficient = 0.958, p-value < 0.001) over at least a four-order-of-magnitude time range. The reduction in the formation/failure times of adhesive bonds was most accurately achieved using the longest relaxation time of the adhesives, associated with their highest-molecular-weight polyisobutylene component. Thus, the highest-molecular-weight polymer played a dominant role in adhesive performance, determining both the stress relaxation during the formation of adhesive bonds and their durability under applied load. In turn, this finding enables the prediction and improvement of adhesive bond durability by increasing the bond formation time (a durability rise by up to 10–100 times) and extending the adhesive’s longest relaxation time through elevating the molecular weight or proportion of its highest-molecular-weight component (a durability rise by 100–350%). Full article

The shear-compression failure of key strata leads to stair-step collapse and severe mine pressure, posing significant safety risks in coal mines. Existing theories fail to account for the boundary conditions and breaking sizes of key strata, making accurate description of shear-compression failure difficult. A periodic breakage mechanics model for key strata was developed using Timoshenko Beam and Winkler Foundation Theory, incorporating transverse shear deformation. The deflection, rotation angle, bending moment, and shear force were calculated, and a shear-compression failure criterion function f(x) was derived. The main conclusions include the following: (1) shear-compression failure is influenced by the thickness–span ratio, cohesion, internal friction angle, and elastic modulus of the key strata, but not by the elastic foundation coefficient and shear modulus; (2) shear-compression failure occurs when the thickness–span ratio reaches 0.4; (3) when the internal friction angle is 25°, 30°, 35°, or 40°, shear-compression failure does not occur if cohesion exceeds 8.0, 7.5, 7.0, or 6.5 MPa, respectively, with a larger internal friction angle corresponding to a smaller critical cohesion; (4) when cohesion is 6 MPa, 8 MPa, 10 MPa, or 12 MPa, shear-compression failure does not occur if the internal friction angle exceeds 44°, 32°, 19°, or 8°, respectively, with larger cohesion correlating to a smaller critical internal friction angle; and (5) once cohesion or internal friction angle surpasses a critical value, the failure criterion approaches a constant value, preventing failure; the elastic modulus has a greater effect on shear-compression failure than the shear modulus, with higher elastic modulus increasing the likelihood of failure. Full article

Achieving keyhole-free joints is critical in Friction Stir Spot Welding (FSSW). This study presents a new approach to eliminate this volumetric defect in AA6082-T6 FSSW sheet joints using a continuous multi-layer Friction Stir Deposition (CMFSD) technique, employing a newly designed AA6082-T6 consumable tool. FSSW was performed at various rotational speeds (350, 550, 750 and 950 rpm) with a 5 s dwell time. Comprehensive macro- and micro-scale evaluations, along with mechanical properties (hardness and tensile-shear load) of the produced joints, were conducted. Additionally, microstructures were examined using Optical Microscopy (OM), while fracture surfaces were analyzed via Scanning Electron Microscopy (SEM). Optimal FSSW conditions were identified at 550 rpm, yielding a stir zone (SZ) hardness of 94.6 ± 1.4 HV and a maximum tensile-shear load of 4.73 ± 0.27 kN. The keyhole was successfully refilled using AA6082-T6 rod material via CMFSD, resulting in a defect-free joint of the same base alloy. Electron Backscattered Diffraction (EBSD) technique was also used to examine the microstructural features. A comparative analysis revealed significant enhancements: the refilled FSSW joints exhibited a 46.5% increase in maximum tensile-shear load and a 66.66% improvement in elongation to failure compared to the highest-FSSW joint performance with the keyhole defect. Full article

Polymer flooding is an enhanced oil recovery (EOR) technique that improves oil extraction by injecting polymer solutions into reservoirs. However, the disposal and treatment of polymer flooding waste liquids (PFWL) present significant challenges due to their high viscosity, complex molecular structure, and environmental impact. This study investigates the shear-induced degradation of polymer solutions, focusing on rheological properties, particle size distribution, and morphological changes under controlled shear conditions. Experimental results show that shear forces significantly reduce the viscosity of polymer solutions, with shear rates of 4285.36 s⁻¹ in the rotating domain and 3505.21 s⁻¹ in the fixed domain. The particle size analysis reveals a significant reduction in average particle size, indicating polymer aggregate breakup. SEM images confirm these morphological changes. Additionally, numerical simulations using a power-law model highlight the correlation between shear rate, wall shear stress, and polymer degradation efficiency. This study suggests that optimizing rotor–stator configurations with high shear forces is essential for efficient polymer degradation, offering insights for designing more effective polymer waste liquid treatment systems in oilfields. Full article

To facilitate the development of next-generation gas turbine cooling systems, the present study systematically investigates the influence of inlet temperature differentials on the aerothermal characteristics and mass flow distribution within multi-inlet, multi-outlet corotating-disc cavities, for which inlet temperature differentials of 10 K, 30 K, and 50 K were applied. Steady-state Reynolds-averaged Navier–Stokes (RANS) simulations using the Shear Stress Transport (SST) k-ω model were performed across a range of flow conditions corresponding to Rossby numbers from 0.01 to 0.10, by varying the rotational and axial Reynolds numbers. This study finds that the inlet temperature differentials are a secondary driver of the aerothermal characteristics in the corotating cavity. Meanwhile, Rossby number dictates the main flow structure of radially stratified vortices and governs the thermal mixing between hot and cold streams. A higher Rossby number enhances mixing, causing the radial outlet temperature to rise significantly, while the axial outlet remains cool. A larger inlet temperature differential can induce secondary vortices at high Rossby numbers. Furthermore, the differential is revealed to increase cavity pressure, slightly reducing the radial outlet’s mass flow by up to 2.5% and its discharge coefficient by nearly 5% at high Rossby numbers. These insights allow engine designers to develop more precise and optimized cooling strategies. Full article

In this study, under varying PDSP (plunging depths of stirring pin) and process parameters, refill friction stir spot welding tests were performed on 6061-T6 aluminum alloy, relying on a stirring tool with a 12 mm sleeve diameter and an 8 mm stirring pin diameter. The results manifested the internal defects in the weld zone when PDSP was 0, notwithstanding the alterations in process parameters. However, these flaws disappeared when PDSP was 0.5 mm and 1 mm. In the weld zone, PDSP exerted a dramatic effect on the internal metal flow state, particularly the curvature of the “Hook” shape and the width of the bonding ligament. It changed the downward bending of the ‘Hook’ into an upward one, influencing the fracture behavior of the weld zone and elevating the ULSF (ultimate lap shear force) by up to 20% (PDSP = 0.5 mm, welding speed = 30 mm/min, rotation speed is 1200 rpm). Besides, the PDSP intensified the PAZ (pin affected zone) pressure, induced more metal flowing into the SAZ (sleeve affected zone), thus reinforced the SAZ-TMAZ(thermomechanically affected zone) bonding strength, and upgraded the region’s microhardness. In summary, the PDSP is commendable for bolstering the weld zone’s performance, but excessively large PDSP values incur drastic indentations in the PAZ, which diminish the ULSF. Full article

This study presents a novel analytical–numerical framework for investigating the torsional divergence of composite sandwich structures composed of carbon fiber-reinforced skins and an AIREX foam core. A divergence differential equation is derived and modified to accommodate the anisotropic behavior of composite materials through an equivalent shear modulus, extending classical formulations originally developed for isotropic structures. The resulting equation is solved using the Galerkin method, yielding structural section rotations as a continuous function along the wing span. These torsional modes are then applied as boundary inputs in a high-fidelity finite element model of the composite fin to determine stress distributions across the structure. The method enables evaluation of not only in-plane (membrane) stresses, but also out-of-plane responses such as interlaminar stresses and local core-skin interactions critical for assessing failure modes in sandwich composites. This integrated workflow links analytical aeroelastic modeling with detailed structural analysis, offering valuable insights into the interplay between global torsional stability and local stress behavior in laminated composite systems. 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

It is recognized that boats which intervene in dangerous situations are characterized by high maneuverability, have good governance properties, and must be equipped with high-speed propellers. This paper proposes a computerized analysis, using Computational Fluid Dynamics modeling, of a high-speed propeller, in open water, from the perspective of velocity and pressure manifested on the propeller blades. The use of numerical methods allows to determine the thrust forces on the propellers, to highlight the areas in the propeller blade where the maximum and minimum pressures occur, to identify the cavitation zone and to visualize the degree of turbulence of the fluid flow on the propeller blades in rotational motion. The analysis proves to be an efficient procedure in determining the characteristics of a high-speed propeller before deciding its production/manufacture. The Shear Stress Transport method was used for fluid turbulence analysis and the “Thrust–Propeller RPM” diagram and “Torque–propeller RPM” diagram finalized this study, the mentioned diagrams being the most important in choosing an efficient propeller for a given boat. Full article

In this study, aluminum single crystals with a {1 0 0} <0 0 1> (Cube) orientation were rolled under two conditions: with external constraints imposed by an external aluminum frame (3DRC) and without external constraints (3DR). The crystal plasticity finite element method (CPFEM) was used to simulate texture evolution, and the results corresponded well with experimental observations. The minor discrepancies observed were primarily attributed to the idealized conditions in the simulation. The results demonstrate that in the 3DR model, crystal orientations predominantly rotate around the transverse direction (TD), with non-TD rotations playing a secondary role. In contrast, the 3DRC model exhibits similar rotation patterns to 3DR at lower reductions, but at higher reductions, non-TD rotations become comparable to TD rotations. This difference results in more concentrated orientations in 3DR and more dispersed orientations in 3DRC. Additionally, analysis reveals that external constraints cause deformation behavior to deviate from the plane strain condition rather than move closer to it. The presence of external constraints alters stress and strain states, modifying the activation of slip systems and crystal rotations, leading to significant variations in slip activity, shear strain, and crystal rotation along TD. Full article