Search Results (445)

Pumped-storage power stations (PSPSs) are vital for grid stability, yet pump-turbines (PTs) operating in the S-shaped region often induce severe hydraulic instability. To reveal the mechanism of these self-excited oscillations, this study establishes a nonlinear mathematical model based on rigid water column theory and a cubic polynomial approximation of the PT’s nonlinear characteristics. Both analytical derivations and numerical simulations were conducted. Analytical results indicate that, in the absence of surge tanks, self-excited oscillations occur when the PT’s negative hydraulic impedance modulus exceeds the pipeline impedance. With a single surge tank, the system behaves analogously to the Van der Pol oscillator, exhibiting oscillations that converge to a stable limit cycle governed by system parameters. Numerical simulations for a dual-surge-tank system further reveal that, due to initial negative damping, the PT transitions to alternative stable equilibria. Crucially, the transition direction is governed by the polarity of the initial disturbance: negative perturbations lead to the regular turbine region, while positive ones lead to the reverse pump region. Additionally, pipe friction causes the steady-state discharge to deviate slightly from the theoretical static value, with deviations remaining below 2.96%. This work provides a theoretical basis for stability prediction in PSPSs. Full article

In an effort to reduce global dependence on fossil-based polymers and advance toward a more sustainable materials industry, research over recent decades has increasingly focused on the development of bio-based polymers and broadening their potential applications. Within this context, the present study investigates nanocomposites based on poly(butylene succinate-co-butylene adipate) (PBSA), reinforced with two types of nanofillers: silicon dioxide nanoparticles (SiO₂ NPs) and cellulose nanofibrils (CNFs). The main objective of this work is to examine how the morphology, geometry, and chemical nature of the nanofillers influence the thermal, mechanical, and barrier properties of PBSA, as well as its biodegradability. For each nanofiller, three formulations were prepared, containing 1, 2, and 5 wt% of filler, respectively. Scanning electron microscopy (SEM) analysis confirmed good dispersion and minimal aggregation in the SiO₂-based systems, whereas marked aggregation was observed in the CNF-based samples. Thermal analysis indicated that the intrinsic thermal properties of neat PBSA were largely preserved. Mechanical testing revealed improvements in both the elastic modulus and elongation at break for most nanocomposite samples. In particular, CNFs provided the most consistent reinforcing effect, with enhancements of approximately 40% in the elastic modulus (495.4 vs. 356.4 GPa in neat PBSA) and 52% in elongation at the break (185.1 vs. 122.0% in neat PBSA) with 5 wt% loading. Additionally, the incorporation of nanofillers did not alter the surface hydrophilicity, but it did improve the oxygen barrier performance and enhanced disintegration under composting conditions. Overall, these findings demonstrate the promising potential of PBSA-based nanocomposites for sustainable rigid packaging applications. Full article

Toughening modification of epoxy resin (EP) matrices is important for advancing high-performance fiber-reinforced composites. A promising strategy involves the use of multi-component additive systems. However, synergistic effects in such additive systems are difficult to achieve for multidimensional performance optimization due to insufficient interfacial interactions and competing toughening mechanisms. Herein, a “hard–soft” biphasic synergistic toughening system was engineered for epoxy resin, composed of furan-ring-grafted polyhedral oligomeric silsesquioxane (FPOSS) and liquid polysulfide rubber. The hybrid toughening agent significantly enhanced the integrated performance of the epoxy system: Young’s modulus, tensile strength, and elongation at break increased by 13%, 56%, and 101%, respectively. These improvements are attributed to the formation of enriched molecular chain entanglement sites and optimized dispersion, facilitated by nucleophilic addition reactions between flexible rubber segments and rigid FPOSS units with the epoxy matrix. The marked enhancement in toughness primarily stems from the synergistic toughening mechanism involving “crazing pinning” and “crazing-shear band”. Concurrently, FPOSS incorporation effectively modulated the curing reaction kinetics, rendering the process more gradual while substantially elevating the glass transition temperature (T_g) of the cured system by 16.82 °C and endowing it with superior thermal degradation stability. This work provides a simple and unique strategy to leverage multi-scale mechanisms for the construction of epoxy-based composites with good toughness and strength, and enhanced heat resistance. Full article

Some expressway emergency lanes adopt simplified pavement structures that fail to meet load-bearing requirements after reconstruction. To address the issue of subgrade reinforcement without excavation, a finite element method was employed to analyze the effects of enlarged-borehole grouting (EBG), considering variations in grouting depth and inter-pile subgrade modulus, on pavement load-bearing capacity. Furthermore, field experiments were conducted to evaluate grouting techniques, including enlarged-borehole micro-expansive cement casting (EB-MECC) and enlarged-borehole steel flower pipe split grouting (EB-SFPSG), and three composite grouting schemes. Results indicated that EBG effectively improved the fatigue cracking life of the semi-rigid base layer. Reinforcement effectiveness was positively correlated with grouting depth and subgrade modulus, with the latter exhibiting a more significant influence. Therefore, a 1.5 m grouting depth combined with splitting or compaction is recommended to enhance subgrade stiffness. Field experiments showed that EB-SFPSG effectively enhanced pile–subgrade interaction and mitigated stress concentration around the pile–pavement interface. Comparison of the three composite grouting schemes revealed that both the scheme employing only EB-SFPSG and the hybrid scheme using EB-SFPSG in the middle row with EB-MECC in the side rows exhibited favorable mechanical performance. The latter, however, was achieved at a lower construction cost. Another hybrid scheme that further replaced the middle row with enlarged-borehole conventional pressure grouting (EB-CPG) provided limited reinforcement and poorer uniformity. Full article

Coalbed methane development is constrained by reservoir characteristics including high gas adsorption, high salinity, and high closure pressure, which impose significant limitations on conventional polymer fracturing fluids regarding viscosity enhancement, proppant transport, and fracture maintenance. In this study, a novel polymer fracturing fluid system, Z-H-PAM, was designed and synthesized to achieve strong salt tolerance, low adsorption affinity, and high elasticity to withstand closure pressure. This was accomplished through the molecular integration of a zwitterionic monomer ZM-1 and a hydrophobic associative monomer HM-2, forming a unified structure that combines rigid hydrated segments with a hydrophobic elastic network. The results indicate that ZM-1 provides a stable hydration layer and low adsorption tendency under high-salinity conditions, while HM-2 contributes to a high-storage-modulus, three-dimensional physically cross-linked network via reversible hydrophobic association. Their synergistic interaction enables Z-H-PAM to retain viscoelasticity that is significantly superior to conventional HPAM and to achieve rapid structural recovery in high-mineralization environments. Systematic evaluation shows that this system achieves a static sand-suspension rate exceeding 95% in simulated flowback fluid, produces broken gel residues below 90 mg/L, and results in a core damage rate of only 10.5%. Moreover, it maintains 88.8% of its fracture conductivity under 30 MPa closure pressure. Notably, Z-H-PAM can be prepared directly using high-salinity flowback water, maintaining high elasticity and sand-carrying capacity while enabling fluid recycling and reducing reservoir damage. This work clarifies the multi-scale mechanisms of strongly hydrated and highly elastic polymers in coalbed methane reservoirs, offering a theoretical and technical pathway for developing efficient and low-damage fracturing materials. Full article

Most insects secrete special fluids from their tarsal pads which are essential for the function of their attachment systems. Previous studies investigated several physical and chemical characteristics of this pad fluid in different insect species. However, there is not much known about the mechanical properties of fluid from smooth adhesive pads. In this study, we used the stress–relaxation nanoindentation method to examine the viscoelastic properties of pad fluid from Sungaya aeta. Force–displacement and stress–relaxation curves on single fluid droplets were recorded with an atomic force microscope (AFM) and analyzed using Johnson–Kendall–Roberts (JKR) and generalized Maxwell models for determination of effective elastic modulus (E), work of adhesion (Δγ) and dynamic viscosity (η). In addition, we used white light interferometry (WLI) to measure the maximal height of freshly acquired droplets. Our results revealed three different categories of droplets, which we named “almost inviscid”, “viscous” and “rigid”. They are presumably determined at the moment of secretion and retain their characteristics even for several days. The observed mechanical properties suggest a non-uniform composition of different droplets. These findings provide a basis for advancing our understanding about the requirements for adaptive adhesion-mediating fluids and, hence, aid in advancing technical solutions for soft or liquid temporal adhesives and gripping devices. Full article

Due to their superior tribological properties compared to conventional materials, the use of functionally graded materials (FGMs) has long become indispensable in mechanical engineering. The wide variety of in-depth gradings means that solving contact problems requires specific, complex numerical analysis. In many cases, however, the spatial change in Young’s modulus can be approximated by a power law, which allows closed-form analytical solutions. In the present work, integral equations for solving tangentially loaded power-law graded elastic half-planes are derived by using the Mossakovskii–Jäger procedure. In this way, the application of highly complicated singular integrals arising from a superposition of fundamental solutions is avoided. A distinction is made between different mixed boundary conditions. The easy tractability of the novel equations is substantiated by solving the plane strain fretting contact of a rigid parabolic cylinder and a power-law graded (PLG) elastic half-space. The effect of the type of in-depth grading on the dissipated energy density and the total energy lost per cycle is investigated in detail. A comparison of the total dissipated energy per cycle shows that, for very thin stiff layers on soft substrates, the total dissipated energy exceeds that of a homogeneous material. The same trend is observed for thick layers of a functionally graded material whose Young’s modulus gradually increases with depth, matching that of the underlying substrate at the bonded interface. In addition, a closed-form analytical solution for the total dissipated energy per cycle for plane strain parabolic contact of elastically homogeneous material is presented for the first time. Full article

This study investigated the effects of Auricularia auricula Polysaccharide (AAP) concentrations on the rheological and thermal properties of gluten and its subunit components. We used multiple techniques, including dynamic rheology, differential scanning calorimetry (DSC), Fourier-transform infrared spectroscopy (FT-IR), free thiol group analysis, and scanning electron microscopy (SEM). The results revealed that AAP increased the storage (G′) and loss (G″) modulus of gluten, glutenin, and gliadin, promoting compact elastic protein networks. DSC and free thiol group analysis demonstrated that AAP enhanced thermal stability and disulfide bond cross-linking in gluten and glutenin, but reduced thermostability and inhibited disulfide formation in gliadin. Secondary structure analysis showed 31.93% and 17.72% increases in α-helix and β-sheet content, respectively, in glutenin at 8% AAP, thereby enhancing the orderliness of the gluten structure and improving structural rigidity, while reducing gliadin’s structural order. Microscopy confirmed AAP narrowed gluten matrix pores, forming uniform honeycomb structures (though high concentrations caused disruption). In summary, AAP primarily stabilizes gluten conformation by modulating glutenin structure, thereby enhancing rheological and thermal properties. Full article

This study investigates the mechanical performance of three temperature-resistant 3D-printable polymer composites for turbine impellers used in district heating networks for pressure reduction. Using fused deposition modeling (FDM), tensile strength and deformation of ASA-X CF10, PA6-GF30, and ePAHT-CF15 were evaluated at temperatures representative of real operating conditions (60–130 °C). These polymer composites were systematically tested, with particular emphasis on annealed ePAHT-CF15. Results demonstrated that annealing significantly improved mechanical performance, yielding higher tensile strength, Young’s modulus, and reduced deformation. Structural analyses confirmed that ePAHT-CF15, particularly when annealed at 200 °C, exhibited superior thermal stability and rigidity, making it the optimal material choice for high-temperature turbine impeller applications. These findings support the design of 3D-printed composite impellers for pump-as-turbine applications in district heating systems, where high stiffness and heat resistance are required. Full article

Most polymeric plastics used as food packaging are obtained from petroleum or made with non-biodegradable synthetic molecules, which slowly degrade and leach into the environment, resulting in the accumulation of microplastics along the trophic chains. To mitigate these impacts, biodegradable packaging derived from agro-industrial biomass residues has emerged as a promising alternative. In this study, bio-based methylcellulose films reinforced with cellulose nanocrystals (CNCs) extracted from low-quality coffee beans were developed and fully characterized. The extracted CNCs presented a needle-like morphology, with an average height of 7.27 nm and a length of 221.34 nm, with 65.75% crystallinity, were stable at pH 7–8, and presented thermogravimetric mass loss of 8.0%. Methylcellulose films containing 0.6% w/w of CNC were produced by casting and characterized in terms of thermal, mechanical, and optical properties. Notably, the incorporation of CNCs resulted in significantly more flexible and less rigid films, as evidenced by the higher elongation at break (57.90%) and lower Young’s modulus (0.0015 GPa) compared to neat methylcellulose film. The tensile strength was not affected (p > 0.05). Additionally, the MCNC 0.6% films effectively blocked UV light in the 200–300 nm range without compromising transparency. Altogether, these findings underscore the MCNC 0.6% film as a flexible, biodegradable packaging material suitable for food industry application. Full article

Biocomposite films based on polylactic acid (PLA) reinforced with cellulose nanofibers (CNFs) extracted from Salicornia ramosissima by-products were developed and characterised using solvent casting (SC) and electrospinning (ES) techniques. The primary objective was to assess their suitability as sustainable food packaging materials that are compatible with high-pressure processing (HPP). The SC films exhibited a transparent, homogeneous morphology with superior ductility and water vapour barrier performance, whereas the ES films displayed a fibrous, porous structure with enhanced tensile strength and rigidity. The incorporation of CNFs significantly improved the mechanical properties, particularly the tensile strength and Young’s modulus, with optimal reinforcement achieved at a loading of 0.5%. Thermal and spectroscopic analyses confirmed the effective integration of CNF without compromising the thermal stability of PLA. Pouch-type packages from CNF-reinforced SC films withstood industrial HPP conditions without rupture or leakage, demonstrating their technical feasibility for food packaging applications. This study presents the first demonstration of Salicornia ramosissima by-product valorisation for CNF production and its application in HPP-compatible food packaging, addressing both circular economy goals and emerging food processing technologies. Full article

Natural fillers have been widely explored to enhance the mechanical and barrier properties of biodegradable films. In this study, a mineral-rich powder obtained from the solid components of Ucides cordatus crab shells was processed (washing, drying, milling, and sieving at 75 µm) and extensively characterized using SEM, FTIR XRD, EDX, mineral analysis, hygroscopicity, density, and particle size distribution. The powder exhibited heterogeneous morphology and contained 22.52 g·kg⁻¹ of calcium carbonate, along with other trace minerals; its crystalline profile indicated the presence of both calcite and aragonite. Low hygroscopicity (1.76%) and a true density of 2.11 g/cm³ were also observed. When incorporated into pectin-based films at 1–5%, the filler promoted a reduction in film thickness, indicating enhanced structural compaction. Solubility increased linearly with filler content, whereas water vapor permeability (WVP) decreased at 1% and 2% but rose again at 4% and 5%, correlating positively with solubility (r = 0.895). Films containing 4% and 5% exhibited higher tensile strength and elastic modulus, confirming increased rigidity. At elevated concentrations, the films also became less luminous and more chromatic. Overall, the findings demonstrate that crab-shell mineral powder is a viable and sustainable reinforcement capable of tailoring the structural, mechanical, and barrier performance of biodegradable films. Full article

The study presented an analysis of the behaviour of cellular structures under bending, produced using the PolyJet Matrix (PJM) additive manufacturing method with photopolymer resin. Structures with regular cell geometry were designed to achieve a balance between stiffness, weight reduction, and energy absorption capacity. The aim of this study was to investigate the influence of unit-cell topology (quasi-similar, spiral, hexagonal honeycomb, and their core–skin hybrid combinations) on the flexural properties and deformation mechanisms of PolyJet-printed photopolymer beams under three-point bending. Additionally, all cellular configurations were fully infiltrated with a low-modulus platinum-cure silicone to evaluate the effect of complete polymer–elastomer interpenetration on load-bearing capacity, stiffness, ductility, and energy absorption. All tests were performed according to bending standard on specimens fabricated using a Stratasys Objet Connex350 printer with RGD720 photopolymer at 16 µm layer thickness. The results showed that the dominant failure mechanism was local buckling and gradual collapse of the cell walls. Among the silicone-filled cellular beams, the QS-Silicone configuration exhibited the best overall flexural performance, achieving a mean peak load of 37.7 ± 4.2 N, mid-span deflection at peak load of 11.4 ± 1.1 mm, and absorbed energy to peak load of 0.43 ± 0.06 J. This hybrid core–skin design (quasi-similar core + spiral skin) provided the optimum compromise between load-bearing capacity and deformation capacity within the infiltrated series. In contrast, the fully dense solid reference reached a significantly higher peak load of 136.6 ± 10.2 N, but failed in a brittle manner at only ~3 mm deflection, characteristic of UV-cured rigid photopolymers. All open-cell silicone-filled lattices displayed pseudo-ductile behaviour with extended post-peak softening, enabled by large-scale elastic buckling and silicone deformation and progressive buckling of the thin photopolymer struts. The results provided a foundation for optimising the geometry and material composition of photopolymer–silicone hybrid structures for lightweight applications with controlled stiffness-to-weight ratios. Full article

In this work, microfibrillated cellulose (MFC) from ash branch wood was used as reinforcement in a thermoplastic starch matrix to develop environmentally friendly materials. Pulp fibers and MFCs were characterized by SEM, TEM, and FTIR. Corn starch biofilms were prepared via casting, formulating eight biofilms with 5 and 10 wt% of MFC. Also, extracts of Muicle and Hibiscus were added to incorporate antibacterial properties. The biofilms were evaluated for mechanical, thermal, and antibacterial properties. Also, properties such as color, opacity, morphology, electrical conductivity, contact angle, and solubility, among others, were evaluated. The reinforced biofilms were homogeneous, dimensionally stable, and transparent with slight color changes. MFC incorporation enhanced hydrogen bonding, which increased the ultimate tensile strength from 11.2 MPa to approximately 19–21 MPa and the Young’s modulus from 809 MPa to 1034–1192 MPa. The presence of MFC also reduced solubility from 48.7% to 38.7–39.8% and decreased water vapor permeability by about 20–23% in biofilms with 10 wt% MFC. Gas barrier properties and the glass transition temperature depended on extract type and fiber content, indicating greater rigidity. The use of ash-based MFC encourages the implementation of circular economy strategies and the development of sustainable biocomposites. Full article

Filling-type large-size cement-stabilized macadam (F-LSBC) is a promising base material for mitigating reflection cracking in semi-rigid pavements. However, its engineering application is hindered by the challenge of balancing strength, crack resistance, and construction adaptability. More fundamentally, the relationship between micromechanical features—especially the interfacial transition zone (ITZ)—and the macroscopic behavior of filling-type cement-stabilized composites remains insufficiently understood. This study used conventional cement-stabilized macadam (CSM) as a reference and combined nanoindentation with macro-scale mechanical, fatigue, and drying shrinkage tests to clarify the micro–macro mechanisms of F-LSBC. Results show that the ITZ in F-LSBC exhibits substantially lower elastic modulus (reduced by 60–75%) and hardness (reduced by 55%), along with greater porosity and phase volume fraction than CSM. Cluster analysis revealed a thicker ITZ (55–90 μm vs. 40 μm), indicating notable interfacial weakening. These microstructural features lead to reduced strength and fatigue life. Nevertheless, due to its high coarse aggregate content and weak-interface-induced “crack-without-displacement” mechanism, F-LSBC demonstrates enhanced shrinkage resistance, with drying shrinkage reduced to 81.36% of that of CSM at 180 days. The findings emphasize the key role of ITZ characteristics in determining performance and suggest that improved interface engineering could enhance durability and shrinkage control in pavement bases. Full article