Search Results (2,036)

Prefabricated steel–concrete composite bridge decks are widely used in the construction of long-span bridges due to their excellent mechanical performance and rapid construction speed. However, the joints in these decks are prone to tensile failure under negative bending moments, which limits the overall mechanical behavior of the structure. To improve the flexural–tensile performance of joints in prefabricated steel–concrete composite bridge decks under negative bending moments, a novel prefabricated steel grid–hybrid fiber concrete (PSG-HFC) composite bridge deck with closed-loop steel bar joints is proposed. Basic unit specimens of the composite bridge deck with closed-loop steel bar joints were designed and fabricated. Both physical and numerical experiments, including finite element modeling and model refinement, were conducted to clarify the mechanical response and failure mode of closed-loop steel bar joints under negative bending moments and to identify their rational structural parameters. Theoretical formula for calculating the flexural capacity of the closed-loop steel bar joints based on the strut-and-tie model theory was derived and verified. The results indicate that the failure mode of the novel PSG-HFC composite bridge deck under negative bending moments is typical plastic failure, with the ultimate failure mode being flexural–tensile failure at the joint section. The loading process includes elastic, elastoplastic, and plastic stages. From the perspectives of improving flexural capacity and fully utilizing high-strength materials, the rational structural parameters for the closed-loop steel bar joints are as follows: lap length of closed-loop steel bars of 230~250 mm, spacing of closed-loop steel bars of 130~150 mm, and bending radius of closed-loop steel bars of 70~90 mm. The maximum deviation between the theoretical formula results and the experimental and finite element numerical simulation results is 8.21%, indicating that the proposed formula is suitable for calculating and analyzing the flexural capacity of the joints in this novel composite bridge deck. This study reveals that the proposed closed-loop steel bar joint enables a ductile flexural–tensile failure mode in PSG-HFC composite deck under negative bending moments, and provides a validated theoretical formula for advancing the understanding of joint design in fiber-reinforced concrete structures. Full article

Accurately predicting the mechanical response and failure of composite–metal hybrid bolted joints under thermo-mechanical coupled loads remains a critical challenge in aerospace engineering. This paper develops a temperature-dependent multi-scale progressive failure analysis model based on micromechanical failure theory. A hexagonal representative volume element (RVE) incorporating fibers, matrix and interphase is constructed, with a stress amplification factor enabling macro–meso stress–strain transformation. Dimensionless temperature corrections are applied to resin and interphase mechanical properties, and temperature-influenced mesoscopic failure criteria with corresponding stiffness degradation schemes are proposed. The nonlinear progressive damage simulation is implemented via the ABAQUS/UMAT subroutine. Static tensile tests on AC531/CCF800H composite-7075 aluminum alloy three-bolt double-shear joints are conducted at −70 °C, 20 °C and 120 °C. The results show excellent agreement between the simulations and experiments, with ultimate load errors < 5%. Low temperature increases load capacity by 3.91% via resin hardening and enhanced interfacial bonding, while high temperature reduces it by 9.07% due to resin softening. Failure modes shift from end-hole tensile fracture (−70 °C, 20 °C) to full-hole bearing failure (120 °C), governed by altered bolt load distribution and damage evolution paths. The proposed model provides reliable support for thermo-mechanical design and strength verification of aerospace composite structures. Full article

Engineered cementitious composites (ECCs) reinforced with imported polyvinyl alcohol (PVA) or polyethylene (PE) fibers exhibit high tensile deformability, but the fiber cost limits the wider application of ECCs. In this study, locally produced PVA and PE fibers were used to develop lower-cost ECC, and PVA–PE fiber hybridization was adopted to improve tensile deformability. Based on matrices with various fly ash volumes, the single-fiber pullout behavior was first investigated at the micromechanical level. The results showed that PVA and PE fibers failed mainly by rupture and pullout, respectively, and that the chemical bonding between PVA fibers and the surrounding matrix decreased with increasing fly ash volume. The effects of single-fiber addition and hybrid-fiber addition on the macromechanical properties of ECC were then examined. The results indicated that ECC reinforced with hybrid PVA–PE fibers exhibited enhanced tensile performance compared with ECC reinforced with either PVA or PE fibers alone, with an ultimate tensile strain exceeding 5.3%, an average crack width below 39 μm, and hybrid reinforcing effect coefficients of 1.17–1.30, indicating a positive hybrid effect. Overall, the lower-cost ECC incorporating hybrid local fibers developed in this study demonstrates promising tensile deformability and crack-control capacity. Full article

This study investigates hybrid fiber-reinforced polymer (FRP)–steel-reinforced concrete (RC) beams by using three-dimensional finite element models. The research systematically analyzes the influence of key parameters, including FRP type, FRP bar ratio (ρ_f), the ratio of FRP to total reinforcement (ρ_f/ρ_t), and concrete strength. The load–deflection response of the hybrid RC beams is analyzed in detail. The results show that the investigated parameters have a relatively limited influence on the cracking moment, but significantly affect both the yield and ultimate moments. When ρ_f/ρ_t increases from 0 to 0.75, the yield moment decreases by up to 44.34%. When ρ_f increases from 0.55% to 0.88%, the yield moment increases by 50.63%. Meanwhile, increasing the concrete strength significantly enhances the ultimate moment, with a maximum increase of 38.46%. In addition, an energy ductility index is adopted to quantitatively evaluate the structural ductility. The results indicate that the energy ductility index is consistently lower than the conventional ductility index. Finally, to improve the accuracy of theoretical predictions, a semi-empirical simplified formula is proposed for estimating the FRP bar stress at the ultimate state of hybrid beams. The verification results show that the proposed prediction method agrees well with the experimental data, demonstrating that the simplified formula has good applicability and reliability within the parameter range investigated in this study. Full article

Basalt fiber (BF) is an effective reinforcement for improving concrete’s mechanical properties and crack resistance due to its high tensile strength and bridging ability. To investigate the influence of fiber length combinations on the mechanical performance of concrete, basalt fiber-reinforced concrete (BFRC) specimens were prepared using single and hybrid blending methods. Compressive and splitting tensile tests, scanning electron microscopy, and numerical simulations were conducted to evaluate the effects of fiber content and length hybridization, and analyze the possible reinforcement mechanisms. Results showed that for single-blended BFRC with 18 mm BF, both compressive and tensile strengths peaked at a 0.2% dosage, then declined. Conversely, the strengths of hybrid BFRC continuously increased with fiber content, reaching 33.00 MPa and 2.38 MPa at a 0.3% dosage, significantly outperforming the single-length fiber systems. Microstructural observations and numerical analyses suggested that fibers with different lengths contributed to complementary reinforcement effects during the loading process. The improved performance was attributed to the combined effects of crack bridging and stress redistribution provided by fibers with different lengths. Full article

Distributed optical fiber acoustic sensing (DAS) has become an important technology for production logging because it can record dense strain or strain-rate responses along an optical fiber under high-temperature, high-pressure, and corrosive downhole conditions. This single-well field case study investigated a hybrid low-frequency DAS processing framework for distributed optical fiber production logging. First, a finite impulse response (FIR)-based preprocessing step was used for low-pass smoothing before an F–K domain analysis. The DAS records were then transformed into the frequency–wavenumber (F–K) domain, where particle swarm optimization (PSO) was used to tune the nu parameter of a one-class support vector machine (OCSVM) for automatic feature extraction. Rule-based feature enhancement and a small-sample support vector classifier (SVC) were then applied to suppress residual F–K domain noise and retain the V-shaped features associated with upgoing and downgoing waves. Finally, linear regression was applied to the enhanced F–K domain branches to estimate the apparent propagation velocities and derive the flow velocity through the field interpretation relationship. The workflow was demonstrated using 15 s field DAS segments from an oil–water two-phase production well, and the six-window validation showed errors below 3.13% relative to the field-reference values. These results demonstrate the feasibility of the proposed workflow for the investigated well, but do not constitute general validation across different wells or acquisition conditions. Full article

Cellulose and chitosan are biopolymers widely used to prepare composites due to their complementary charges and intrinsic biocompatibility. While they are mainly of interest for medical applications, they are also suitable for water remediation. In their native states both biopolymers are non-porous; however, after dissolution and subsequent regeneration they can form porous structures that are better suited for such applications. In this work, cellulose pulp and chitosan were dissolved in an ionic liquid and regenerated in water at different mass ratios to produce hydrogels and their corresponding aerogels. The materials were structurally characterized and evaluated for dye adsorption and antimicrobial performance. Methylene blue and Congo red were selected as cationic and anionic dyes, respectively. The concentrations went from 5 to 80 mg/L in 24 h batch adsorption experiments. Chitosan-rich and intermediate cellulose–chitosan hydrogels preferentially removed Congo red, reaching 27 ± 1 mg/g and 24 ± 1 mg/g at 80 mg/L, respectively; the fully cellulose hydrogel maximized methylene blue uptake, achieving 23 ± 1 mg/g under the same conditions. SEM and XRD analyses revealed a hybrid architecture in which chitosan coats cellulose fibers and becomes more amorphous, while cellulose preserves crystalline domains that act as a rigid, highly porous backbone. Aerogels derived from freeze-dried hydrogels exhibited high porosity and water uptake, together with broad-spectrum antimicrobial activity, achieving bactericidal levels (≥99.9% inhibition) against Staphylococcus aureus for all compositions and against Escherichia coli for selected cellulose–chitosan ratios. These results demonstrate that cellulose–chitosan hydrogels and aerogels function as multifunctional bio-based materials whose supramolecular organization, surface charge distribution, and porosity can be tuned to balance adsorption selectivity and antimicrobial performance for advanced environmental applications. Full article

Battery housings are critical structural and safety components in electric vehicles, fulfilling multiple functions related to mechanical protection, crashworthiness, thermal management, fire resistance, electromagnetic shielding, and integration of battery modules into the vehicle body. While metallic housings, particularly aluminum and steel, remain dominant in industrial applications, increasing attention is being given to composite materials as lightweight alternatives capable of improving energy efficiency and extending driving range. However, the growing use of composites in battery enclosures raises important questions regarding recyclability, end-of-life management, and compatibility with circular economy principles. This review critically examines the current state of the art in composite materials used for electric vehicle battery housings, with particular emphasis on glass- and carbon-fiber-reinforced thermoplastics, thermoset composites, sandwich structures, and hybrid multi-material systems. The paper discusses the functional requirements imposed on battery housings and analyzes how these requirements influence material selection and design strategies. Particular attention is devoted to recycling pathways applicable to composite battery enclosures, including mechanical recycling, thermal treatment, chemical recycling, and reuse-oriented approaches, as well as to the limitations associated with mixed-material assemblies, adhesives, coatings, and integrated functions. The review also addresses circular design strategies for battery housings, including design for disassembly, material traceability, modularity, and the incorporation of recycled polymers and secondary reinforcements into new housing systems. Current research gaps are identified in the integration of structural performance, fire safety, manufacturability, and recyclability within a single design framework. The analysis shows that thermoplastic composites currently offer the most promising route toward circular battery enclosures, while thermoset-based systems still face significant challenges in high-value recycling. The paper concludes by outlining future research directions required for the development of lightweight, safe and recyclable composite battery housings aligned with sustainable mobility and circular economy goals. Full article

The ballistic impact behavior of soft body armor is governed by complex interactions between material architecture and projectile characteristics. This review provides a critical overview of the evolution of textile and composite-based armor materials developed for ballistic protection. Emphasis is placed on experimental and analytical methodologies used to elucidate impact energy dissipation, deformation mechanisms, and failure modes. Key material-related parameters influencing ballistic performance including areal density, weave architecture, yarn crimp, twist, and thread density are systematically discussed, along with assembly variables such as ply orientation, layer number, and hybrid configurations. In parallel, the influence of projectile mass, velocity, and geometry on impact resistance is examined. The review also summarizes internationally adopted ballistic and stab-resistance standards employed for soft armor evaluation. Various assessment techniques, including yarn–yarn friction analysis, puncture resistance testing, ballistic limit velocity determination, and back-face signature measurement, are critically reviewed. Strategies aimed at enhancing impact performance, such as rubber or latex impregnation, fiber surface modification, and the incorporation of shear thickening fluids, are comprehensively discussed. Attention is given to shear thickening fluids due to their significant role in improving energy absorption and flexibility. The fundamental mechanisms governing shear thickening behavior and the parameters affecting their performance are analyzed. Overall, this review highlights emerging material design strategies and performance optimization approaches for next-generation soft body armor systems. Full article

Cellulose nanofibers (CNFs) have significant potential in composites as additives to improve mechanical properties, melt rheology, and more. However, agglomeration of CNFs is a key challenge in composite melt processing as obtaining nano-level dispersion of CNFs often requires cost- and energy-intensive processes (e.g., solvent exchange or freeze drying) due to the strong hornification tendencies of CNF. Herein, we avoid these challenges by using a natural fiber carrier method to integrate CNF into thermoplastic composites. Fibers are co-dried to create a hybrid fiber feedstock for compounding in which natural fibers are decorated with dispersed nanofibers. The hybridized fibers result in up to a 24% increase in tensile strength and up to a 35% increase in Young’s modulus compared to composites only containing natural fibers. The lignocellulosic nanofibers are found to outperform their purely cellulosic counterpart, which is theorized to be due to either an increased propensity for fibrillation of the lignocellulosic fibers or the increased hydrophobicity of the fibers due to the presence of lignin. Surface analysis of fiber feedstocks, via streaming potential measurements and dynamic light scattering (DLS), confirmed a significant change in the feedstock hydrophobicity before and after hybridization. While mild additions of CNF (1 wt.% on the macroscale fiber) do not impact the composite melt viscosity, the viscosity is found to increase at higher CNF loadings (5 wt.% on the macroscale fiber), indicating its utility as a rheology modifier. Lastly, use of these materials as novel feedstocks for medium-scale additive manufacturing in high-fidelity part production was demonstrated. Full article

Reusing industrial byproducts to prepare recycled aggregate concrete (RAC) is a sustainable approach that can protect the ecological environment. This study tested the possibility of preparing an eco-efficient recycled concrete containing steel slag (SS), ground-granulated blast-furnace slag (GGBS), and polypropylene (PP) fibers to avoid resource waste and depletion and decrease CO₂ emissions. To this end, 12 mix proportions were designed to analyze the effects of SS, GGBS, and PP fibers on the macro- and micro-performances of the developed RAC. The experimental results showed that increasing the SS content decreased the RAC mechanical strength, whereas partially substituting SS with GGBS in the RAC improved the mechanical properties, especially at a later stage. Adding PP fibers to the RAC containing SS and GGBS significantly increased the splitting tensile strength. However, it had little effect on the compressive strength as the PP fiber content was less than 0.6%. The microscopic experiment revealed that adding GGBS promoted the degree of hydration of SS, reduced the Ca (OH)₂ content, made the ITZ structure more compact, and optimized the pore characteristics of the RAC. Furthermore, according to the raw materials and results of mechanical properties, a hybrid Genetic Algorithm/Artificial Neural Network (GA-ANN) technique was proposed to predict the compressive strength of the RAC containing SS, GGBS, and PP fibers. We found that the proposed GA-ANN model effectively predicts the compressive strength. The findings of this study demonstrate that preparing RAC incorporating SS, GGBS, and PP fibers is promising for the reuse of industrial byproducts and construction waste. Full article

The synergistic use of natural bamboo fiber and synthetic aramid fiber in asphalt mixtures has received limited research attention, particularly regarding the optimal blending ratio under a constant total fiber content and the underlying reinforcement mechanisms. This study systematically investigated the co-blending of bamboo and aramid fibers in SMA-13 asphalt mixtures with a fixed total fiber content of 0.3%. Five mixture groups were prepared, LF (0.3% lignin fiber, control), BF (0.3% bamboo fiber), as well as three hybrid groups: ABF-1 (0.27% bamboo + 0.03% aramid, 9:1), ABF-2 (0.24% bamboo + 0.06% aramid, 4:1), and ABF-3 (0.21% bamboo + 0.09% aramid, 7:3). The mixtures were evaluated using rutting tests, low-temperature flexural beam tests, moisture stability tests, and AMPT dynamic modulus testing. The results demonstrate that hybrid-fiber mixtures outperform single-fiber mixtures, with ABF-2 exhibiting the best overall performance. Compared with LF and BF, ABF-2 achieved a dynamic stability of 6921 passes/mm (increases of 97.7% and 52.7%, respectively); flexural tensile strength increased by 43.1% and 32.1%; maximum flexural tensile strain increased by 42.6% and 35.0%; and retained stability improved by 10.8% and 12.5%. AMPT results indicated a higher dynamic modulus and lower phase angle for the hybrid system, suggesting an enhanced elastic response. The superior performance of ABF-2 is attributed to the complementary adsorption–stabilization effect of bamboo fiber and bridging–reinforcement effect of aramid fiber. This study provides quantitative evidence for the beneficial combination of natural and synthetic fibers in asphalt mixtures and identifies key limitations that warrant future investigation. Full article

Distinguishing between human-made interferences and natural background disturbances is of great significance for the safe operation of terrestrial optical cables because human-caused damage can be halted through timely intervention. To address the problem of small-sample disturbance recognition in distributed acoustic sensing (DAS) systems, this paper proposes a fused CNN–SVM classification model based on hybrid features. A convolutional neural network is employed to extract the high-level spatiotemporal features of disturbance signals, which are subsequently fused with statistical features and fed into a support vector machine for classification. Evaluated on open-source data, the proposed model achieves accuracy improvements of 9.1%, 8.7%, and 2.7% over the conventional CNN, the statistical-feature-based SVM, and the conventional CNN-SVM model, respectively. Furthermore, based on field-measured data, a dataset comprising 5664 samples was constructed, covering four typical disturbance-event types: background noise, drilling, knocking, and digging. The field classification results demonstrate that the three-layer convolutional structure of the model achieves a recognition accuracy of 98.5%. Both the ROC curves and multiple evaluation metrics indicate that the proposed three-layer fused CNN–SVM model delivers better classification performance and more balanced category recognition, offering a feasible reference for similar fiber disturbance engineering tasks. Full article

A Q-switched pulsed laser based on a coupled 7-core Yb-doped fiber with a cavity based on a fiber Bragg grating array has been demonstrated with a maximum energy of microsecond pulses up to 15 μJ at a 1 kHz repetition rate. The lasing spectrum is hybridized so that the laser line maxima of each core are nearly the same, having a negligible spread relative to each other, which is much lower than the wavelength shifts between individual FBGs in the cores. At the same time, the generated power is nearly the same in all the cores. However, when increasing the power beyond the stimulated Raman scattering threshold, the supermodes are destroyed so that the spectra in the cores become increasingly different and less stable, and the output power is mainly concentrated in one of the cores, whereas the pulse shortens significantly to a sub-microsecond duration (300 ns), with damped oscillations appearing at the beginning. The new regimes we demonstrated of the multicore fiber laser are promising for creating powerful pulsed radiation sources with a narrow spectrum. Full article

To investigate the impact resistance of hybrid fiber-reinforced recycled aggregate concrete (RAC) under dry–wet cycles and sulfate attack, hybrid fiber-reinforced recycled aggregate concrete (RAC) was prepared. Dynamic impact compression experiments were conducted using an SHPB test device with a 50 mm diameter. The microstructure of recycled aggregate concrete (RAC) within dry–wet cycles and sulfate attack was examined using SEM. The results indicate that the dynamic compressive strength first rises and then declines with the rise in dry–wet cycles, and increases with the increase in the average strain rate. When the number of dry–wet cycles reaches 16, the dynamic compressive strength reaches its peak, with the B4S6 group achieving a maximum dynamic compressive strength of 59.02 MPa. The dynamic elastic modulus follows a good quadratic parabolic function distribution with respect to the number of dry–wet cycles. Both the incident energy and dissipated energy density initially rise and then reduce with increasing dry–wet cycles. The energy values of RAC with different fiber types follow the order: B4S6 > S6 > B4 > RAC. Under impact loading, the strain rate–strain time history curve of recycled aggregate concrete (RAC) exhibits the change of “increase–decrease–stable–decrease”. With increasing dry–wet cycles, the degree of fragmentation of recycled aggregate concrete (RAC) first increases and then decreases, the fractal dimension first decreases and then increases, and the average particle size first increases and then decreases. SEM results and microscopic reaction mechanisms reveal that in the early stage of dry–wet cycles, sulfate ions generate ettringite and gypsum within the recycled aggregate concrete (RAC), which fill internal cracks and pores, making the concrete denser and enhancing its mechanical properties. Towards the end of the dry–wet cycle, the amount of expansive ettringite and gypsum inside the recycled aggregate concrete (RAC) increases, leading to a sharp increase in pore wall stress, which induces new microcracks in the specimens, manifesting as a decline in mechanical properties at the macroscopic level. Full article