Search Results (957)

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

Salt stress significantly reduces plant growth and yield, which has led to extensive research on the mechanisms underlying plant salinity tolerance. Carrot (Daucus carota ssp. sativus) is a glycophyte highly sensitive to soil salinity. We investigated root and leaf anatomical, histological, and immunohistological alterations in two carrot accessions, previously identified as salt-sensitive (DH1) and salt-tolerant (DLBA), growing under control and salt stress conditions. The results demonstrate that the salt-tolerant DLBA growing under control conditions has trichome-rich leaves, high starch reserves and a hydraulically safer root xylem. Under salt stress, DLBA maintains mesophyll integrity, and increases the number of vessels and deposition of highly esterified pectins, hemicelluloses and spatially regulated AGPs in cell walls. In contrast, DH1 develops thinner, trichome-free leaves, and roots almost free of starch with fewer cambial cells and vessels. Salt stress induces overexpansion of palisade parenchyma, excess starch accumulation, loss of arabinan epitopes, disappearance of extensins in vascular bundles, and changes in hemicellulose and AGP distribution. These findings indicate that salt tolerance of DLBA plants results from the combination of constitutive anatomical characteristics and adaptive responses that together support tissue hydration, wall elasticity and stable water transport when plants are growing in saline soil. Full article

This study investigates the impact of ultrasonic treatment on the deagglomeration of aggregates of single-walled carbon nanotubes (SWCNTs) and reduced graphene oxide (rGO). The aim of the research is to enhance the electrical conductivity of a biopolymer hydrogel designed for coating metallic neurostimulation electrodes. Biocompatible coating materials are essential for the safe long-term function of implants within the body, enabling the transmission of nerve impulses to external devices for signal conversion and neurostimulation. Dynamic light scattering (DLS) was employed to monitor the dispersion state, in conjunction with measurements of specific electrical conductivity. The mass loss and swelling capacity were evaluated over an 80-day period to account for the effects of degradation during in vitro studies. Samples of flexible–elastic hydrogels for electrodes with complex geometry were formed by the photopolymerization of a photopolymerizable medium, similar to a photoresist. Analysis of the dependence of temperature and normalized optical transmittance on the duration of laser photopolymerization made it possible to determine the optimal polymerization temperature for the photopolymerizable medium as −28 °C. This temperature regime ensures maximum reproducibility of hydrogel formation and eliminates the presence of unpolymerized areas. The article presents a biopolymer hydrogel with SWCNTs and rGO nanoparticles in a 1:1 ratio. It was found that sufficient specific electrical conductivity is achieved using SWCNTs with a characteristic hydrodynamic radius of R = 490 nm and rGO with R = 210 nm (sample Col/BSA/CS/Eosin Y/SWCNTs (490 nm)/rGO 4). The photopolymerized hydrogel 4 demonstrated sufficient biocompatibility, exceeding the control sample by 16%. According to the results of in vitro studies over 80 days, this sample exhibited moderate degradation of 45% while retaining its swelling ability. The swelling degree decreased by 50% compared to the initial value of 170%. The presented hydrogel 4 is a promising coating material for implantable metallic neurostimulation electrodes, enhancing their stability in the physiological environment. Full article

This study investigates the long-term service effects on Chinese fir (Cunninghamia lanceolata) components from ancient timber buildings in southern China. Anisotropic mechanical tests were performed to examine the evolution of mechanical properties from the perspectives of moisture absorption behavior, chemical composition, and microstructural characteristics. The results show that, after approximately 217 ± 12 years (Lvb specimens) and 481 ± 23 years (Xuc specimens) of service, the longitudinal compressive strength and corresponding elastic modulus of Chinese fir increased by about 11% and 15% and 33% and 71%, respectively, compared with fresh timber. The bending strength of the Lvb sample exhibited a slight reduction (approximately 6%), whereas the Xuc specimens showed the highest increase (33%). This difference is mainly attributed to long-term bending loads that caused structural damage in the Lvb beam specimens. In contrast, changes in lateral mechanical properties were negligible. Chemical composition analysis revealed an increase in extractive content and a reduction in cellulose and hemicellulose, leading to a notable rise in crystallinity. Scanning electron microscopy (SEM) observations further showed interlayer separation, wrinkling, and local collapse of the cell walls, suggesting significant cell wall densification. Overall, the evolution of mechanical properties is governed by the combined effects of increased crystallinity and microstructural densification, which together enhance the longitudinal and bending performance of aged timber with increasing service time. The findings provide a scientific basis for evaluating the performance and structural safety of aged timber components in the conservation of ancient timber buildings. Full article

In this work, we optimized three key factors for rotational molding composites: the recycled polyethylene (rPE) content, the pigment (Cp) content, and the process parameter-peak internal air temperature (PIAT). We studied the influence of rPE, Cp, and PIAT on various composite properties. These included mechanical properties (e.g., elastic modulus E), impact strength (MFEsp), surface characteristics (wettability measured by contact angle θ and IR spectroscopy), thermal stability (by DTA–TG analysis), environmental stress cracking resistance (ESCR in hours), and the amplitude of the third harmonic β of the ultrasonic back-wall signal. The IR spectroscopy and contact angle results indicate that adding rPE and pigment slightly increases the composite’s surface hydrophilicity. The results show that PIAT strongly influences all the characteristics of the composites studied. Depending on its percentage, the introduction of rPE can either improve or worsen these composite properties. A correlation was found between β, ESCR, MFEsp, and E, demonstrating that β can serve as a quantitative indicator of internal stress (IS) in rotomolded parts. The recommended optimal composition is rPE 30%, Cp 0.5%, and PIAT 195 °C. Under these conditions, the composite exhibits minimal internal stress and optimal performance, which in turn extends the service life of rotomolded products. Four nomograms were developed: rPE = f(MFEsp, Cp, PIAT) and rPE = f(β, Cp, PIAT), which make it possible to quickly determine MFEsp and β of a product based on the actual PIAT, taking into account rPE and pigment content in the composite (they also allow selecting the rPE and pigment content in the composition depending on the required MFEsp). Full article

Background: Soft actuation relies on materials that are lightweight, flexible, and responsive to external stimuli. In biomedical applications, miniaturization and biocompatibility are key requirements for developing smart devices. Thermoplastic polyurethane (TPU) is particularly attractive due to its elasticity, processability, and biocompatibility; however, an improvement in its shape-recovery performance would significantly enhance its suitability for actuation systems. This study aims to develop TPU-based shape memory polymer (SMP) composites with improved functional behavior for biomedical applications. Methods: TPU was modified with aluminum nanoparticles (AlNPs) and multi-walled carbon nanotubes (MWCNTs), incorporated individually (1 wt.% and 3 wt.%) and in hybrid combinations (MWCNT:AlNP ratios of 2:1, 5:1, and 10:1). Samples were produced by compression molding and characterized through thermal, mechanical, electrical, and shape-recovery tests, supported by morphological analysis. Results: AlNPs moderately improved thermal conductivity, while MWCNTs significantly enhanced electrical conductivity and doubled the recovery force compared with neat TPU. Hybrid composites showed intermediate properties, with the 5:1 MWCNT:AlNP ratio offering the best balance between recovery force and activation speed. Conclusions: The synergistic combination of MWCNTs and AlNPs effectively enhances TPU’s multifunctional behavior, demonstrating strong potential for soft actuation in biomedical devices. Full article

Compared to traditional single/double-row concrete cast-in-place piles or concrete walls commonly used in foundation pit engineering, pre-tensioned prestressed hollow concrete-filled steel tube piles (referred to as prestressed Steel Cylinder Piles, or prestressed SC piles) demonstrate superior advantages including high bearing capacity, light weight, enhanced stiffness, excellent crack resistance, and cost-effectiveness, indicating a promising future in foundation pit engineering. However, current research has paid limited attention to such piles. Only a few experimental studies have focused on their flexural performance. No studies have presented bearing behavior investigations considering soil–pile interactions and the differences between these kinds of piles and traditional piles. To address this gap, this paper conducts a systematic investigation into the bearing performance of prestressed SC piles. A refined finite element analysis model capable of accurately characterizing pile–soil interactions is developed to analyze the mechanical behavior. Subsequently, the elastic foundation beam method recommended by design codes is employed to analyze the internal forces and displacement variations of these piles during excavation. Finally, the predictions by the design code are compared against those from the refined model. Results shows that the established finite element model presents reasonable predictions on monitoring data and experimental results, with deviations in bending moments and deformations within the range of 10–15%; a comparative analysis of different pile types reveals that prestressed SC piles exhibit smaller horizontal displacements and higher bearing capacities; the bending moments and deformations predicted by design methods (elastic foundation beam method) are conservative, with the predicted values significantly higher than those predicted by the refined model. Full article

This paper addresses the seismic retrofitting of masonry churches with timber roofs by designing a ductile roof diaphragm with a new energy-based methodology. The proposed approach relies on nonlinear dynamic analyses conducted on an equivalent structural model. In this model, masonry nonlinearity is represented by rotational plastic hinges at the base of the equivalent wall elements. Roof system nonlinearity is modeled by shear plastic hinges simulating the energy dissipation of steel connections. In the equivalent model, the earthquake is implemented using a set of spectrum-compatible accelerograms. The dynamic response of the aforementioned plastic hinges is analyzed in terms of equivalent damping during the seismic events by extracting the relevant hysteresis cycles. This allows for the evaluation of both dissipated and strain energy. The estimation of the equivalent damping ratio provided by the roof diaphragm is based on multiple design configurations. After identifying the maximum achievable damping ratio, the study suggests ways to determine the corresponding roof stiffness, which defines the optimal retrofit configuration. This configuration is then implemented in a three-dimensional model that includes nonlinear properties for both masonry and connection elements, allowing a validation of the seismic response obtained from the initial equivalent model with a more complex and detailed model. Finally, a seismic response comparison is conducted between the optimized dissipated energy configuration, based on damping ratio evaluation, and an overstrength design variant determined considering the elastic behavior of the roof connections. Full article

The lightweight design of modern aircraft necessitates efficient optimization of complex thin-walled structures to improve performance and minimize mass. This paper proposes an Elastic Boundary Sub-model Optimization (EBSO) algorithm for accurately predicting and optimizing local buckling behavior in aerospace thin-walled structures. The method partitions the global structure into substructures and incorporates elastic boundary conditions to realistically simulate interaction effects between adjacent components. By establishing a direct mapping between substructural design parameters and critical buckling loads, an iterative optimization framework is developed to enable concurrent design of multiple thin-walled segments. A numerical case study involving an aircraft fuselage panel demonstrates that the EBSO algorithm significantly improves the accuracy of local buckling predictions. The results confirm that the method achieves a substantial weight reduction while maintaining structural stability, greatly enhancing the efficiency of lightweight design optimization. Full article

This work introduces a block-coupled finite volume method for simulating the large-strain deformation of incompressible hyperelastic solids. Conventional displacement-based finite-volume solvers for incompressible materials often exhibit stability and convergence issues, particularly on unstructured meshes and in finite-strain regimes typical of biological tissues. To address these issues, a mixed displacement–pressure formulation is adopted and solved using a block-coupled strategy, enabling simultaneous solution of displacement and pressure increments. This eliminates the need for under-relaxation and improves robustness compared to segregated approaches. The method incorporates several enhancements, including temporally consistent Rhie–Chow interpolation, accurate treatment of traction boundary conditions, and compatibility with a wide range of constitutive models, from linear elasticity to advanced hyperelastic laws such as Holzapfel–Gasser–Ogden and Guccione. Implemented within the solids4Foam toolbox for OpenFOAM, the solver is validated against analytical and finite-element benchmarks across diverse test cases, including uniaxial extension, simple shear, pressurised cylinders, arterial wall, and idealised ventricle inflation. Results demonstrate second-order spatial and temporal accuracy, excellent agreement with reference solutions, and reliable performance in three-dimensional scenarios. The proposed approach establishes a robust foundation for fluid–structure interaction simulations in vascular and soft tissue biomechanics. Full article

Hollow microneedle (HMN) systems can deliver insulin with minimal pain, but most rely on external pumps that add bulk, cost, and failure modes. This paper reports the design, fabrication, and mechanical characterisation of a pump-free, refillable HMN patch that integrates a syringe-loadable, self-sealing reservoir and delivers by passive diffusion. A 3 × 4 array of side-orifice conical HMNs with a target height of 1 mm and a bore of 0.8 mm was stereolithography-printed in dental-grade resin and coupled to an elastic-grade resin septum that maintains a leak-free seal after repeated needle puncture. A surface-response design of experiments (DoE) probed wall thickness of 0.10–0.20 mm, post-cure time of 20–60 min, and temperatures of 35–80 °C. The microneedle characteristics include geometric fidelity, insertion into multilayer Parafilm, and axial compression to 150 N. All patches were printed with a hollow channel and side orifices with tips were slightly blunted. Relative to the original design, height undershoot was from −24.5% to −60.5% while base diameters were within −11% to +20%. Parafilm insertion exhibited a peak then force drop at about 0.22 mm displacement with 1.2–1.5 N pierced the first layer. It was found that about 90% of needles penetrated about 381 µm and more than 20% reached 635 µm. Patches withstood 150 N without fracture with strains of 9.7–15.6% and modulus of 8–48 MPa. ANOVA identified wall thickness as a significant factor, with curing temperature not being significant. Contour analysis defined an operating window near a 0.15 mm wall and about 40 min post-cure balancing dimensional fidelity and post-compression height retention. These results define a manufacturable path to compact, pump-free insulin patches with low insertion force and robust mechanics, opening a clinically scalable route to simpler everyday insulin therapy. Full article

With the advancement of construction development, urban renewal, and urbanization, engineering appraisal and structural reinforcement will become crucial tasks in the construction industry, thus presenting both significant challenges and long-term responsibilities. The concept of “partial strengthening and replacement composite shear walls without support roof” refers to a structural system that utilizes the existing load-bearing capacity of RC shear walls. In this method, high-performance materials are used to locally remove and replace critical load-bearing sections of the wall to be strengthened, resulting in a “composite shear wall” structure composed of both strengthened replacement areas and non-replaced sections. This study proposes the concept of composite shear walls, conducts simulation analysis and exploratory research on their bearing performance, and explores engineering applications based on engineering examples. The research conclusions include the following: Compared to only one batch of replacement reinforcement, partial strengthening and replacement in batches can significantly improve the bearing performance of composite shear walls. The use of steel-reinforced concrete for local strengthening and replacement can significantly improve the bearing performance of composite shear walls, and the magnitude of the improvement in bearing performance decreases with the increase in the initial vertical stress level of the components. The overall structural stress condition after local strengthening and replacement reinforcement is good, and its vertical and horizontal bearing capacity can meet the original design requirements (after reinforcement, the vertical bearing capacity of the overall structure increased by about 6.3% compared to the original design, and the horizontal ultimate bearing capacity is about 1.4 times larger compared to the elastic–plastic “large earthquake” effect of the original design). Compared with conventional replacement methods, the unsupported-roof local reinforcement replacement method has the advantages of using high-performance materials, reducing reinforcement engineering, minimizing resource waste, and simplifying construction procedures, and has good application prospects. Full article

This study examines the thermal modification (TM) of European black alder (Alnus glutinosa) wood boards measuring 1000 × 100 × 32 mm. The TM was carried out in a nitrogen atmosphere under an initial pressure of 4 bar at 160 °C for 60, 120, and 180 min, as well as at 170 °C for 30 and 60 min. The TM process resulted in mass loss and volumetric changes with shrinkage observed across all anatomical directions. Water uptake decreased significantly, with the cell wall’s total water capacity dropping from 35% to a range of 14%–27%. Dimensional stability was improved by between 21% and 61%. The TM wood showed a reduction exceeding 50% in both volumetric swelling and equilibrium moisture content relative to the unmodified specimens. A marked decline in the modulus of rupture was observed, especially in samples treated at 160 °C for 180 min and at 170 °C. Conversely, the modulus of elasticity exhibited a slight upward trend, though the changes were not statistically significant. Brinell hardness revealed a pronounced difference between the tangential and radial orientations, with the tangential surface displaying distinctly lower hardness. Chemical analysis indicated a notable increase in acetone-soluble extractives and reductions in the xylan, mannan, and acetyl groups, reflecting structural alterations in hemicelluloses. Full article

Recent advances in computer vision and artificial intelligence have enabled new approaches for non-destructive post-earthquake assessment of masonry structures. This study proposes a hybrid AI–FEA framework that integrates a MobileNetV2 convolutional neural network for crack-image-based material property inference with nonlinear finite element analysis (FEA) of confined masonry walls. The model predicts key mechanical parameters, including elastic modulus, compressive and tensile strengths, and fracture energies, directly from crack morphology, and these parameters are subsequently used as input for DIANA FEA to simulate the wall’s seismic response. The framework is validated against reference experimental data, achieving a strong parametric correlation (R² = 0.91) and accurately reproducing characteristic nonlinear behavior such as stiffness degradation, diagonal cracking, and post-peak softening in pushover analysis. Photographs from the Limatambo urban area in Lima, Peru, are included to illustrate typical damage patterns in a high-seismic-risk context, although the numerical model represents a standardized confined masonry wall typology rather than site-specific buildings. The proposed methodology offers a consistent, non-destructive, and efficient tool for seismic performance evaluation and supports the digital modernization of structural diagnostics in earthquake-prone regions. Full article

Aortic valve calcification is the process of calcium buildup on the leaflets of the aortic valve, preceding functional insufficiency. Calcification underlies the development of aortic stenosis by stiffening the valve leaflets, leading to restricted aortic valve opening during systole and obstructed blood flow. However, a more comprehensive understanding of the hemodynamic effects of altered valve properties is required. Therefore, it is crucial to investigate the biomechanical properties of aortic valve leaflets susceptible to calcification. To examine fluid flow in an aorta segment with leaflets of different stiffness, a two-way fluid–structure interaction model was developed. The leaflet’s behavior was modeled using two constitutive laws—linear-elastic and isotropic hyperelastic—followed by numerical testing and comparative analysis. Using the material parameter values $c_{01}$ and $c_{10}$ within the ranges of 22–60 and 22–60 kPa, respectively, the hyperelastic model was examined. The valve leaflets’ Young’s modulus ranged from 1 to 22 MPa, while their Poisson’s ratio ranged from 0.35 to 0.45. A high correlation between Poisson’s ratio and wall shear stress was found. With an elastic modulus of 22 MPa and the highest Poisson’s ratio of 0.45, the maximum wall shear stress was 81.78 Pa during peak flow velocity and complete valve opening, while the lowest wall shear stress was 0.38 Pa. We can infer from the study’s results that, when considering the isotropic structure and nonlinear characteristics of valve leaflets, the Delfino hyperelastic model more accurately depicts their complex behavior. Full article