Search Results (97)

To achieve the same service life of glass fiber reinforced polymer (GFRP) connectors and precast concrete sandwich panels, ensuring the structural stability and safety of the walls during long-term service, it is necessary to research the durability of GFRP connectors. In accordance with the ACI 440.3R-12 test method, an accelerated aging study was conducted by immersing 90 GFRP connectors in a simulated concrete pore solution at temperatures of 40 °C, 60 °C, and 80 °C for durations of 3.65, 18, 36.5, 92, and 183 days. This investigation aimed to analyze the effects of temperature and exposure time on the shear strength of the GFRP connectors. Scanning Electron Microscopy (SEM) was employed to analyze the micro-morphology of the specimens before and after exposure. The SEM observations revealed that after 183 days at 40 °C, the fiber-matrix interface remained relatively intact without significant debonding. However, at 60 °C, noticeable degradation occurred, characterized by corrosion of fibers and evident debonding from the surrounding matrix. At 80 °C, the GFRP specimens were severely damaged, precluding the extraction of viable samples for SEM analysis. The results further indicated that the most rapid decline in the shear strength occurred within the initial 3.65 days of exposure, with reductions of 8.62%, 10.12%, and 10.77% at 40 °C, 60 °C, and 80 °C, respectively. The degradation rate subsequently decelerated with prolonged exposure. After 183 days, the residual shear strength retention rates decreased by 21.03% and 26.89% at 40 °C and 60 °C, respectively. This behavior is primarily attributed to a high moisture absorption rate driven by a significant humidity gradient between the surface and the interior, leading to rapid swelling and plasticization of the vinyl ester resin matrix, which consequently reduced the stiffness and strength of the GFRP connectors. Finally, a predictive model for the time-dependent shear strength of GFRP connectors under various temperature conditions was developed based on Fick’s law. Full article

To prevent corrosion in humid environments and electrical failure under loads, we developed a highly durable corrosion-resistant flexible strain sensor with a patterned sandwich structure. The effects of film dimensions and ambient temperature on the sensor’s electrical conductivity were investigated separately. The patterned flexible strain sensor demonstrated exceptional durability, maintaining stability after multiple tensile cycles and large deformations. The PDMS coating effectively protected the conductive layer from external environmental factors. Experimental results revealed that the sensor could efficiently block the corrosive effects of humid environments. Furthermore, when applied to real-time micro-strain detection in steel plate tensile tests, the relationship between ΔR/R₀ and strain exhibited high linearity and sensitivity. The conductive film shows excellent durability and corrosion resistance, demonstrating significant application potential as a flexible strain sensor in humid conditions. Full article

The improper management of fats, oils, and grease (FOG) from food services is a major cause of sewer blockages and environmental damage. This study examines FOG management in the restaurant sector of the Guadalajara Metropolitan Area, Mexico, from three complementary perspectives: the performance of the authorized formal collection system, management practices in food establishments, and the physicochemical characteristics of grease trap residues. These perspectives were addressed using official administrative records and reports from environmental authorities, structured surveys applied to kitchen staff, and laboratory analyses of grease trap samples collected in restaurants. The results reveal important institutional and structural constraints affecting FOG management. Only a limited number of authorized collectors operate actively, serving a small fraction of potential generators, while most food service establishments are micro- or small-sized businesses with limited technical and financial capacity to comply with regulations. A large portion of the sector consists of small, low-cost food service establishments with intensive oil use (e.g., street food vendors, sandwich shops, and set-menu restaurants), which contribute to widespread oil reuse and inadequate disposal practices. Laboratory analyses showed a high free fatty acids (FFAs) content and compositional profiles consistent with repeated oil use, with negative implications for sewer systems and waste management. Overall, the findings highlight the need for stronger regulatory enforcement, collection schemes tailored to micro-scale generators, and awareness campaigns while also indicating opportunities for FOG valorization within circular economy approaches, particularly through energy recovery pathways. Full article

Sandwich panels with trapezoidal (corrugated) cores combine low weight, high specific stiffness, and energy absorption capability. This study analyzes four configurations with different core heights by means of microstructural analyses (optical microscopy, SEM/EDS, XRD) and quasi-static compression tests. The tests yield stress–strain curves with an initial linear stage, a peak, a plateau, and a densification stage. Peak stresses range from 0.5 MPa for the thickest core (P1) to 6.2 MPa for the thinnest core (P4), while the energy absorbed density (EAD) increases with strain: at ε = 30% it varies from 0.031 to 0.670 J/cm³, and at ε = 50% the thin-core configuration reaches ≈1.113 J/cm³. The face sheets and the core are both manufactured from AA 3000 series (Al–Mn) aluminum alloy; widespread micro-porosity and Fe/Mn-rich phases are observed by SEM/EDS. XRD confirms aluminum with different peak intensities ascribable to the manufacturing texture. Increasing the core height promotes earlier local/global instabilities and reduces the peak stress; the thinnest core displays higher stiffness and peak loads. These findings support the use of trapezoidal corrugation where low weight and progressive strain are required. Full article

In this paper, a nano-layered transmission GaAs photocathode structure is proposed. The near-infrared absorption of the photocathode is enhanced by inserting a “sandwich” structure of nano-SiO₂ layer + Si₃N₄ nanopillar array + nano-SiO₂ layer between the cathode optical window and the photocathode. Compared with the flat film structure GaAs photocathode used in the current third-generations image intensifiers, the optical absorption of the optimized “sandwich” structure GaAs photocathode in the near-infrared band has been significantly improved: when the wavelength λ is 868 nm and 896 nm, the optical absorption is increased by 41.69%, 55.08%, respectively. The effects of structural parameters including film thickness and grating filling medium on the light absorption of photocathode are investigated. The results show that the near-infrared light absorption enhancement is the most obvious when Si₃N₄ is selected as the grating filling medium for the current design, and the deposition of SiO₂ film with 10 nm thickness could effectively prevent the damage of Si₃N₄ during bonding with the photocathode. The theoretical analyses offer important guidance in material selection and structural optimization in the grating cathode optical window used in the third-generation image intensifier for improving performance. Full article

In recent years, honeycomb sandwich structures have seen continuous development due to their excellent structural performance and design flexibility in heat dissipation. However, their complex heat transfer mechanisms and diverse modes of thermal exchange necessitate research on the air flow behavior and temperature distribution characteristics of micro-channels and lattice pores. This study investigates the internal flow field within a ventilated honeycomb sandwich structure through numerical simulation. The spatial flow characteristics and temperature distribution are analyzed, with a focus on the effects of turbulent kinetic energy, heat flux distribution on the heated surface, and varying pressure drop conditions on the thermal performance. The results indicate that the micro-channels inside the honeycomb core lead to a strong correlation between temperature distribution, flow velocity, and turbulence intensity. Regions with higher flow velocity and turbulent kinetic energy exhibit lower temperatures, confirming the critical role of flow motion in heat transfer. Heat flux analysis further verifies that heat is primarily removed by airflow, with superior heat exchange occurring inside the honeycomb cells compared to the solid regions. The intensive mixing induced by highly turbulent flow within the small cells enhances contact with the solid surface, thereby improving heat conduction from the solid to the flow. Moreover, as the inlet pressure increases, the overall temperature gradually decreases but exhibits a saturation trend. This indicates that beyond a certain pressure level, further increasing the inlet pressure yields diminishing returns in heat dissipation enhancement. Full article

Reinforced concrete walls (RC walls) are widely used in transportation, building structures, and civil air defence engineering. RC walls are vulnerable to low-velocity impact, such as the fall of components caused by earthquakes or explosions, for example, and the impact from road objects, such as vehicles, during their service life. When subjected to instantaneous high-energy impact, RC walls at key positions are prone to severe damage, which can further lead to structural collapse. Therefore, it is necessary to consider improving the impact resistance of key RC walls in a structure. Using a porous honeycomb structure with excellent energy absorption performance to provide impact protection for key RC walls is an effective way to reduce the damage of RC walls and thereby enhance the impact resistance of a structure. Therefore, based on the author’s previous series of experimental and numerical studies on the impact resistance of RC walls, as well as the high-mass pendulum impact experimental study on the honeycomb sandwich panel composite RC wall (HSP-RC wall), this paper adopts a multi-scale modelling method in micro-mechanics and macro-mechanics to establish a pendulum impact finite element model (FEM) for the HSP-RC wall. The representative volume element (RVE) and periodic boundary condition (PBC) are used to calculate the elastic property parameters of the honeycomb, which guide the establishment of the FEMs for the HSP-RC wall. The FEMs can avoid the computational difficulty caused by refined simulation, analyse the impact damage of the HSP-RC walls more accurately, quantify the impact protection effect of the honeycomb sandwich panel, and thus facilitate the parametric analysis of the impact resistance of HSP-RC walls with different honeycomb panel structural parameters in subsequent studies. Full article

In this paper, we propose and experimentally demonstrate a dual-parameter fiber optic sensor, which combines a Fabry–Perot interferometer (FPI) and a Mach–Zehnder interferometer (MZI) for simultaneous pressure and temperature sensing. The Fabry–Perot (FP) cavity is formed by sandwiching a capillary fiber between a single-mode fiber and a dual-core fiber (DCF). A fluid channel is very close to the central core of the DCF. By precisely drilling micro-air chambers in the annular cladding of a capillary fiber (CF) using a femtosecond laser, external air pressure can directly affect the capillary fiber and induce changes in the refractive index of the air in the CF. The F-P cavity achieves a pressure sensitivity of 3.67 nm/MPa with a temperature cross-sensitivity of 2.82 pm/°C. The MZI is constructed using a dual-core fiber filled with silicone oil in the fluidic channel, which enhances temperature sensitivity through the thermo-optic effect. The MZI sensor exhibits a nonlinear temperature response with an average sensitivity of 103.43 pm/°C. The corresponding pressure cross-sensitivity is about –0.11 nm/MPa. Due to very low cross-sensitivity, simultaneous measurement of temperature and gas pressure is feasible. In addition, we implement a variant by replacing silicone oil with a UV-curable adhesive, which delivers a comparable FP-based pressure sensitivity of ~3.93 nm/MPa while yielding an MZI-based temperature sensitivity of 71.7 pm/°C and potentially improved long-term stability. Full article

With the extensive application of 3D-printed composites across multiple industries, the investigation into their structural reliability under complex loading conditions has become a critical research focus. This study comprehensively employs acoustic emission (AE) monitoring, digital image correlation (DIC) measurement, and micro-computed tomography (Micro-CT) visualization techniques to explore the progressive damage behavior of 3D-printed sandwich-structured composites reinforced with continuous carbon fiber sheets under three-point bending. Mechanical tests show that increasing the fiber content of face sheets from 10% to 20% enhances average bending strength by 56%, while low fiber content compromises stiffness and load-bearing capacity. AE analysis categorizes damage modes into matrix cracking (<50 kHz), debonding/delamination (50–150 kHz), and fiber breakage (>150 kHz) using k-means clustering algorithms. DIC measurement reveals significant structural deformation processes during damage progression. The AE-DIC-Micro-CT combination demonstrates an initial undamaged state, followed by damage initiation and propagation in the subsequent stages. This integrated approach provides an effective method for damage assessment, guiding the design and reliability improvement of 3D-printed composites. Full article

The development of metal–organic framework (MOF)-based composites for photocatalytic hydrogen evolution has garnered significant attention due to their tunable structures, high surface area, and abundant active sites. Recent advancements focus on enhancing light absorption, charge separation, and catalytic efficiency through strategies such as ligand functionalization, metal doping, heterojunction formation, and plasmonic coupling effects. For instance, modifications with Ir (III) complexes and Pt nanoparticles have significantly improved hydrogen evolution rates, while sandwich-structured MOF composites demonstrate optimized charge separation through tailored micro-environments and proton reduction efficiency. Additionally, integrating MOFs with semiconductors (e.g., CdS, g-C₃N₄) or plasmonic metals (e.g., Au) enhances visible-light responsiveness and stability. This review highlights key design principles, performance metrics, and mechanistic insights, providing a roadmap for future research in MOF-based photocatalysts for sustainable hydrogen production. Challenges such as long-term stability and scalable synthesis are also discussed to guide further innovations in this field. Full article

Based on time-averaged digital holography, a vibration deformation measurement system was designed and a full process reconstruction and identification strategy was developed for detecting the micro-defects in optical materials. Through the double beam expansion setting and off-axis imaging adjustments, it is suitable for measuring optical materials with non-specular surfaces by double exposure shots. The scheme was applied to optical sandwich composites and 3D printed glass. Abnormal amplitudes occur at the defects due to different resonance frequencies, resulting in anomalous vibrations under excitation, and the differences in the amplitudes and phases before and after vibration can effectively characterize vibration amplitude and subsurface defects, proving that this method has a high detecting sensitivity. Full article

The vibration of porous Al–Al₂O₃ micro-cantilever sandwich beams in fluids was studied utilizing the modified couple stress theory and the scale distribution theory (MCST and SDT). Four types of porosity distributions were defined; the uniform distribution of pores was defined as U-type, while O-type, V-type and X-type represented non-uniform distributions of pores. The material properties of different porous sandwich beams were calculated. The properties of the micro-cantilever sandwich beams were adjusted to account for scale effects according to MCST. With the fluid driving force taken into consideration, the amplitude-frequency response, and resonant frequencies of the FGM sandwich beams in three different fluids were calculated using the Euler–Bernoulli beam theory. The computational studies showed that the presence of gradient factor p and the pores in the micro-cantilever sandwich beams affect the temperature field distribution and amplitude-frequency response in fluids. Increasing gradient factor p leads to a more obvious thermal concentration of the one-dimensional temperature field and migrates the resonance peaks to lower frequencies. In contrast to the uniform distribution type, the non-uniformly distributed pores also cause a decrease in the resonance frequency. Full article

MicroRNA122 (miR-122) is a microRNA that is highly expressed in hepatocytes and has been identified as a prospective therapeutic target and biomarker for liver injury. An expanding body of research has demonstrated that miR-122 is a critical regulator in both the initiation and progression of a wide range of liver diseases. Traditional methods for detecting miR-122 mainly include Northern blotting and qRT-PCR, but they are technically complex and cumbersome, requiring expensive instruments and high technical requirements. In this paper, we present a novel rapid testing method utilizing a lateral flow nucleic acid biosensor (LFNAB) for the sensitive and time-efficient detection of miR-122. This approach offers several advantages, including a high specificity for miR-122, the ability to detect low concentrations of the target molecule, and a significantly reduced testing time compared to conventional detection methods. In this study, a thiol-modified single-stranded detection DNA probe (Det-DNA), a biotinylated single-stranded capture DNA probe (Cap-DNA), and a biotinylated single-stranded control DNA probe (Con-DNA) are used to construct the LFNAB. A gold nanoparticle (AuNP) is a colored tag, which is used to label the Det-DNA probe. The principle of detecting miR-122 is based on dual DNA-miRNA hybridization reactions on the LFNAB to form sandwich-type AuNP-Det-DNA-miR-122-Cap-DNA complexes, which are captured on the test area of LFNAB for visualization and quantification. After systematic optimization of conditions of experiment, the response of LFNAB was highly linear within the scope of 0 pM-100 pM miR-122, and the detection limit in 15 min was 3.90 pM. The use of LFNAB to detect miR-122 in serum and fingertip blood has yielded satisfactory results. This successful application indicates the effectiveness of LFNAB in detecting miR-122 in both serum and fingertip blood samples, showcasing its potential utility in clinical and research settings for assessing miR-122 levels in different biological samples. Full article

This study investigates the flexural behavior of three sandwich panels composed of an agglomerated cork core and skins made up of cross-ply [0,90]₂ flax or glass layers with areal densities of 100 and 300 g/m². They are designated by SF100, SF300, and SG300, where S, F, and G stand for sandwich material, flax fiber, and glass fiber, respectively. The three sandwich materials were fabricated in a single step using vacuum infusion with the liquid thermoplastic resin Elium^®. Specimens of these sandwich materials were subjected to three-point bending tests at five span lengths (80, 100, 150, 200, and 250 mm). Each specimen was equipped with two piezoelectric sensors to record acoustic activity during the bending, facilitating the identification of the main damage mechanisms leading to flexural failure. The acoustic signals were analyzed to first track the initiation and propagation of damage and, second, to correlate these signals with the mechanical behavior of the sandwich materials. The obtained results indicate that SF300 exhibits 60% and 49% higher flexural and shear stiffness, respectively, than SG300. Moreover, a comparison of the specific mechanical properties reveals that SF300 offers the best compromise in terms of the flexural properties. Moreover, the acoustic emission (AE) analysis allowed the identification of the main damage mechanisms, including matrix cracking, fiber failure, fiber/matrix, and core/skin debonding, as well as their chronology during the flexural tests. Three-dimensional micro-tomography reconstructions and scanning electron microscope (SEM) observations were performed to confirm the identified damage mechanisms. Finally, a correlation between these observations and the AE signals is proposed to classify the damage mechanisms according to their corresponding amplitude ranges. Full article

Based on the basic theoretical framework of the Bi-directional Evolutionary Structural Optimization method (BESO) and the Solid Isotropic Material with Penalization method (SIMP), this paper presents a multiscale topology optimization method for concurrently optimizing the sandwich structure at the macro level and the core layer at the micro level. The types of optimizations are divided into macro and micro concurrent topology optimization (MM), macro and micro gradient concurrent topology optimization (MMG), and macro and micro layered gradient concurrent topology optimization (MMLG). In order to compare the multiscale optimization method with the traditional macroscopic optimization method, the sandwich simply supported beam is illustrated as a numerical example to demonstrate the functionalities and superiorities of the proposed method. Moreover, several samples are printed through micro-nano 3D printing technology, and then the static three-point bending experiments and the numerical simulations are carried out. The mechanical properties of the optimized structures in terms of deformation modes, load-bearing capacity, and energy absorption characteristics are compared and analyzed in detail. Finally, the multiscale optimization methods are extended to the design of 2D sandwich cantilever beams and 3D sandwich fully clamped beams. Full article