Search Results (1,073)

Traditional brick masonry buildings in China are commonly constructed using fired clay grey bricks bonded with glutinous rice mortar, forming a unique historical masonry system with significant cultural value. During long-term service, these structures are vulnerable to environmental deterioration, material aging, and seismic actions, resulting in cracking, deformation, and degradation of structural integrity and load-carrying capacity. Carbon fiber-reinforced polymer (CFRP) sheets have been increasingly applied for strengthening masonry structures due to their high strength-to-weight ratio, corrosion resistance, and convenient installation. However, most existing studies on Fiber-reinforced polymer (FRP)–masonry interfaces have focused on conventional masonry systems, while the interfacial bond behavior and load-transfer characteristics between CFRP sheets and traditional grey brick masonry bonded with glutinous rice mortar remain insufficiently investigated. This study investigates the interfacial bond behavior of CFRP-strengthened traditional grey brick masonry through combined experimental testing and numerical analysis. First, uniaxial compression tests were conducted to determine the mechanical properties of glutinous rice mortar and fired clay grey bricks. Subsequently, double-shear tests considering different CFRP bond widths, bond lengths, and interface integrity conditions were performed to characterize the failure modes, force–displacement responses, and interfacial load-carrying behavior. The effects of interface geometric and integrity conditions were considered to evaluate the load-transfer characteristics of the strengthened interface. Based on the experimental results, a finite element model considering interface behavior was established and verified through comparison with the experimental results, which was subsequently employed to investigate the influence of bond width on interfacial stress transfer behavior beyond the experimental conditions. The results show that interfacial debonding accompanied by near-surface masonry damage dominates the failure process of CFRP–glutinous rice mortar masonry interfaces. Increasing the CFRP bond width enhances the interfacial load-carrying capacity and initial stiffness, while the ultimate capacity exhibits an approximately linear relationship with bond width within the investigated range. Numerical analyses further demonstrate that increasing bond width expands the effective load-transfer region, redistributes interfacial stresses, and delays stiffness degradation. These findings improve the understanding of interfacial bond behavior and load-transfer characteristics in CFRP-strengthened traditional masonry systems and provide references for the design and performance evaluation of strengthening applications in historic masonry structures. Full article

Carbon-fiber-reinforced polymer (CFRP) reinforcement is a potential alternative to steel in corrosive environments. However, CFRP is elastic without ductility, and the seismic performance of CFRP-reinforced concrete (RC) columns is inadequately understood. This study characterizes the intrinsic seismic response of concrete columns reinforced with CFRP cable-type bars and spirals under recorded near-fault ground motions. Three reference steel-RC columns are designed as seismic-resistant, non-seismic-resistant, and with post-cracking stiffness equivalent to the CFRP-RC column. The CFRP-RC and seismic-resistant steel-RC columns were tested under cyclic loading, and the results validated finite element (FE) models. Validated models simulated four columns under cyclic loading, and under 11 near-fault records matched to a capacity-derived elastic target spectrum. The results, bounded by selected ground motions and material constitutive models, show that: (1) The tested CFRP-RC column dissipated about 50% less energy than the steel-RC reference; (2) No material-level failure criterion was met under the suite, although peak base shears exceeded the nominal quasi-static capacities; (3) The CFRP-RC column developed the largest transient drift but minimal residual drift, whereas the steel-RC columns limited transient amplitude via hysteretic dissipation yet accumulated permanent offsets; (4) Response of the CFRP-RC column depends on ground motion energy delivery characteristics: concentration, symmetry, and duration. Full article

The compressive behavior of carbon fiber-reinforced polymer (CFRP)-confined ultra-high-performance concrete (UHPC) short columns involves nonlinear interactions among concrete properties, confinement characteristics, and specimen geometry. In this study, a database of 144 circular specimens was compiled using nine input variables: specimen diameter ($D$), height ($H$), CFRP thickness ($t$), number of CFRP layers ($Layers$), unconfined concrete compressive strength ($f_{co}^{\prime }$), concrete ultimate strain (${\epsilon }_{co}$), CFRP tensile strength ($f_f$), CFRP ultimate strain (${\epsilon }_f$), and CFRP elastic modulus ($E_f$). Eight regression algorithms were evaluated using an 80:20 training–test split, with ten-fold cross-validation conducted within the training subset for hyperparameter selection. ANN achieved the best test performance, with an $R^2$ of 0.96, an MAE of 8.37 MPa, and an RMSE of 11.32 MPa, while SVM and CatBoost also showed competitive predictive accuracy. The selected ML models exhibited substantially lower prediction errors than seven existing empirical equations. SHAP analysis further identified CFRP layer number, unconfined concrete strength, specimen height, and CFRP thickness as influential predictors and revealed interactions among confinement, matrix deformability, and specimen geometry. The proposed framework provides an accurate and interpretable supplementary approach for assessing the compressive strength of CFRP-confined UHPC within the parameter range represented by the database. Full article

Carbon-fiber-reinforced polymer (CFRP) composites fabricated with bio-based epoxy resins represent a promising approach for sustainable lightweight structures produced by out-of-autoclave (OoA) technologies. The curing schedule influences the state of the epoxy matrix and, consequently, can affect the fiber–matrix interaction and laminate performance. This study investigates the effect of practical curing conditions on 2 × 2 twill woven carbon fiber laminates fabricated by vacuum infusion using a commercially available bio-based epoxy resin IB2. The manufacturer’s recommended room-temperature conditions (25 °C for 24 h) were compared with accelerated mold heating schedules at 40, 50, 60, and 70 °C for 12 h. The laminates were characterized by three-point tensile and flexural tests, heat deflection temperature (HDT) measurements, differential scanning calorimetry (DSC), and SEM fractography. The tensile response showed limited sensitivity to the investigated curing conditions, with mean tensile strengths ranging from 634.01 to 672.95 MPa; T60 exhibited the highest mean numerical tensile strength (672.95 ± 53.60 MPa) and tensile modulus (53.39 ± 11.53 GPa), although the differences were small relative to the experimental spread. In contrast, the flexural response was more sensitive to the processing conditions. T70 exhibited the highest average flexural strength (980.60 ± 129.03 MPa), strain at maximum flexural stress, and strain energy density to maximum stress (8.75 ± 1.89 MJ/m³). The heat deflection temperature (HDT) systematically increased from 65.20 °C for T25 to 85.83 °C for T70. DSC revealed clear differences in the calorimetric response after curing during the first heating cycle, while the glass transition temperatures at the middle of the second heating occupied a relatively narrow range of 80.9–85.6 °C. SEM fractography revealed mixed tensile failure mechanisms related to fibers, matrix, and interface under all curing conditions. Overall, the results demonstrate that accelerated 12 h heated mold programs can reduce cure time while maintaining tensile performance generally comparable to the 24 h room-temperature IB2 reference condition and providing higher average flexural performance and thermal deformation resistance under load. These findings establish processing–property relationships relevant to the development of biomass-based CFRP OoA laminates for lightweight aerospace applications. Full article

To enhance the mechanical properties of carbon-fiber-reinforced polymer composites (CFRPs), this study devised a novel three-dimensional web-like “rigid–flexible” surface modification strategy. The synergistic incorporation of carbon nanotubes (CNTs), polydopamine (PDA), and cellulose nanofibers (CNFs) constructed a “three-dimensional nanospider web” modulus transition layer. The modified carbon-fiber (CF-0.1%CNT-PDA-CNF) surface exhibits a three-dimensional network structure, with significantly increased surface roughness. The surface energy increased by 128.60% compared to the desized carbon fiber, thereby improving the wettability of the carbon-fiber surface. The results of both PeakForce-Quantitative Nanomechanical Mapping (PF-QNM) and EDS analyses indicate that a transition layer of a certain thickness initially formed at the interface. At the interface, the modulus exhibits a gradual gradient decrease from carbon fiber to epoxy resin, achieving more efficient stress transfer. The interfacial shear strength (IFSS, 95.71 MPa), interlaminar shear strength (ILSS, 73.19 MPa), tensile strength (701.08 MPa), and flexural strength (934.41 MPa) of the CF-0.1%CNT-PDA-CNF/EP composite material increased by 38.39%, 54.93%, 51.74%, and 64.98%, respectively, compared to the composite material made from desized carbon fiber. Through hydrogen bonding, covalent bonding, and π-π interactions, CNTs, CNFs and PDA formed a “rigid–flexible” transition layer with a modulus gradient at the CF-epoxy interface, achieving a significant enhancement in the mechanical properties of the composite material. Full article

This study conducted an experimental investigation of the flexural behavior of reinforced concrete beams strengthened using externally bonded and near-surface-mounted techniques. The strengthening materials consisted of carbon fiber-reinforced polymer (CFRP) sheets, carbon fiber plates, and textile-reinforced mortar (TRM) with carbon, basalt, and glass textiles, as well as near-surface-mounted (NSM) glass and carbon bars. Twenty-two reinforced concrete beams were tested, comprising one reference specimen and 21 strengthened specimens with different strengthening techniques, numbers of layers, and anchorage conditions. The results showed a marked improvement in the flexural performance of the strengthened specimens compared with the reference specimen, which had an ultimate load capacity of 60.01 kN. CFRP strengthening achieved the highest increase in ultimate load capacity and stiffness, with the best specimen recording 110.44 kN and a stiffness value of 18.83 kN/mm. Carbon fiber plates also exhibited a significant improvement in strength. In contrast, TRM and NSM systems produced comparatively lower strength gains but offered superior ductility and more gradual failure behavior. In terms of TRM strengthening, carbon textiles demonstrated the highest ultimate load capacity, whereas basalt and glass textiles enhanced deformation capacity. The use of fan-type anchors further enhanced the efficiency of externally bonded strengthening systems by delaying premature debonding. Within the scope of the present experimental program, the findings provide a direct comparison of the investigated carbon fiber-reinforced polymer (CFRP), carbon-plate (CP), textile-reinforced mortar (TRM), and near-surface-mounted (NSM) strengthening configurations under identical testing conditions and demonstrate their relative effects on strength, stiffness, ductility, energy dissipation, and failure behavior. These results provide comparative experimental evidence that may assist in selecting strengthening strategies for RC beams with comparable characteristics; however, broader generalization requires consideration of additional member geometries, material properties, reinforcement configurations, and loading conditions. Full article

Carbon-fiber-reinforced polymer (CFRP) composites are widely used in lightweight aerospace structures because their mechanical performance can be adapted to different structural requirements through appropriate manufacturing conditions. This study investigates the influence of curing temperature applied using temperature-controlled heated molds on the mechanical and thermo-mechanical behavior of vacuum-infused CFRP laminates manufactured with an IN2 epoxy infusion resin. Laminates were cured at room temperature (25 °C) and at 40, 50, 60, and 70 °C using heated molds. Their performance was evaluated by tensile testing, three-point bending, and heat deflection temperature (HDT) measurements. The highest tensile strength (675.06 MPa) was obtained for laminates cured at 40 °C, whereas increasing the curing temperature beyond this value did not provide further improvement in tensile performance. The highest flexural stress at the first peak (983.36 MPa) and flexural modulus (67.17 GPa) were obtained for laminates cured at 70 °C, while the highest energy absorption during bending (0.57 J) was measured for laminates cured at 40 °C. The HDT increased from 59.77 °C for room-temperature curing to 87.60 °C for laminates cured at 70 °C, indicating improved thermo-mechanical stability with increasing curing temperature. The results indicate that no single curing temperature simultaneously maximized the tensile, flexural, and thermo-mechanical properties. Instead, the optimum curing temperature depended on the specific mechanical and thermo-mechanical requirements of the intended application. The results further indicate that controlling the temperature of heated molds during manufacturing provided a practical approach for tailoring the mechanical and thermo-mechanical performance of CFRP laminates without modifying the reinforcement architecture, laminate stacking sequence, or constituent materials. Full article

Valued for their lightweight, high strength-to-weight ratio, and energy absorption, sandwich composites were adopted across multiple industries. This paper evaluates the static and dynamic mechanical performances of sandwich configurations exploiting carbon fiber-reinforced polymer (CFRP) and quartz fiber-reinforced polymer (QFRP) composite skins bonded to hexagonal Nomex^® or compliant Flex-Core^® cores. Skin thickness varied negligibly; therefore, this study focused on skin type and particularly core architecture influence on mechanical behavior. Three-point bending and flatwise compression tests evaluated flexural stiffness, core shear strength, and core compressive strength. DMA analysis was used to characterize their temperature-dependent viscoelastic response through the storage modulus, loss modulus, and damping factor. QFRP/Nomex emerged as the optimal configuration achieving the highest flexural stress, outperforming CFRP/Nomex by 14%, while restricting strain to 2.4% (compared to 7% for CFRP). DMA (Dynamic Mechanical Analyzer) analysis showed that QFRP/Nomex exhibits the highest storage and loss moduli. Observing the energy at break, CFRP/Nomex^® sandwiches stand out in their ability to absorb 60% more energy than QFRP/Nomex^® before total failure occurs, showing an overall superior energy absorption of CFRP skins. Conversely, flatwise compression tests revealed that QFRP/Flex-Core^® excelled in yield and compressive strengths, outperforming CFRP/Nomex by 10% and 8%, respectively, due to superior elastic matching. DMA damping profiles confirmed that the geometric compliance of curved Flex-Core^® cell walls in conjunction with QFRP skins accelerates structural yielding under shear and viscoelastic energy dissipation prior to chemical softening. This work highlights that sandwich structure design critically depends on managing core architecture and skin-to-core stiffness mismatch. Full article

Externally bonded carbon fiber-reinforced polymer (CFRP) systems are used to improve the flexural performance of reinforced concrete members. However, premature debonding, particularly intermediate crack-induced (IC) debonding, limits CFRP utilization and may lead to sudden failure. This study experimentally and numerically investigates the effectiveness of CFRP patch anchors with different anchorage configurations in improving the flexural behavior and failure mode of CFRP-strengthened reinforced concrete slabs. Nine reinforced concrete slabs were tested under four-point bending, including one reference slab, two slabs strengthened with longitudinal CFRP strips without anchorage, and six slabs strengthened with CFRP strips and transverse patch anchors. The experimental results showed that CFRP increased the ultimate load by about 30–61% compared with the reference slab. The unanchored specimens failed mainly by IC debonding. In contrast, the patch-anchored specimens showed better strain distribution, delayed debonding, and a shift toward CFRP rupture. The numerical results showed good agreement with the experimental results, with ultimate-load prediction errors below 7%. Changing the patch area did not significantly increase the ultimate load, with about 0.8% difference between the mean capacities of the anchored groups, while end anchors alone were insufficient to prevent debonding. CFRP patch anchors effectively delayed premature debonding and improved CFRP utilization. Full article

Carbon fiber-reinforced polymer (CFRP) composites are widely used in curved aerospace structures, where riveting-induced interlaminar damage is a critical concern. Most existing studies have focused on flat laminates, while the influence of structural curvature on rivet load transfer and delamination tendency remains insufficiently understood. This study develops a three-dimensional finite element model in ANSYS Workbench to investigate the curvature–interference coupling effect on CFRP/Al single-lap riveted joints. Four curvature configurations with identical arc lengths (C0, C45, C90, and C180) are established, and riveting is simulated with upsetting displacements of 1.5–3.0 mm. Results show that curvature shifts the contact pressure from an axisymmetric pattern to a localized distribution on the convex side, while the deformation mode transitions from isotropic expansion to hoop-dominated behavior. The equivalent interlaminar shear stress increases nonlinearly with curvature and displacement. At 3.0 mm, the peak stress in C180 reaches 415.9 MPa, 1.86 times that of the flat laminate. Further analysis reveals that curvature induces membrane-bending coupling, which amplifies ply deformation incompatibility and increases delamination tendency. These findings indicate that riveting parameters developed for flat laminates cannot be directly transferred to curved structures, and curvature–interference coupling should be considered in damage-tolerant design. Full article

This study addresses the inherently low damping and vibration susceptibility of carbon fiber reinforced polymer (CFRP) laminated cantilever plates by developing a comprehensive dynamic modeling and active vibration control framework. An electromechanical coupling model incorporating macro-fiber composite (MFC) actuators and sensors is established using the first-order shear deformation theory (FSDT) and the assumed mode method, with virtual springs introduced to account for non-ideal clamped boundary conditions. A reduced-order state-space model is then derived through model reduction, and a linear quadratic Gaussian (LQG) controller is designed for optimal state estimation and feedback control. The theoretical model is systematically validated via convergence analysis, ANSYS finite element simulations, and LMS impact hammer testing. The results demonstrate that, with the relative errors of the first four natural frequencies controlled within 2%, the theoretical mode shapes are highly consistent with those obtained from ANSYS simulations. An active vibration control experimental platform is established, and the effectiveness of the control strategy is verified under dual-spectrum harmonic and impact excitations. The results show that the designed LQG controller can effectively suppress multi-modal vibrations, substantially attenuating the response amplitudes of dominant modes and significantly accelerating the transient vibration convergence. This study addresses the challenge of precisely characterizing actual non-ideal clamped boundary conditions. Through model order reduction and closed-loop LQG control experiments, it provides a comprehensive set of theoretical methodologies, numerical solution strategies, and engineering-oriented experimental schemes for the electromechanical coupling dynamic modeling and optimal vibration suppression of CFRP thin-walled composite structures. Full article

Corrosion of steel reinforcement is a major cause of deterioration in reinforced concrete (RC) structures exposed to aggressive environments. Although fiber-reinforced polymer (FRP) reinforcement provides excellent corrosion resistance, its confinement effectiveness in RC columns has not been fully understood. This study experimentally investigated the axial compressive behavior of rectangular RC short columns reinforced with steel, carbon fiber-reinforced polymer (CFRP), and glass fiber-reinforced polymer (GFRP) bars. Ten specimens with different reinforcement types and stirrup configurations were tested under monotonic axial compression to evaluate compressive strength, axial strain response, deformation behavior, failure mechanisms, and confinement performance. The results indicated that the contribution of FRP reinforcement depended on the reinforcement configuration and confinement mechanism. Specimens reinforced with CFRP longitudinal bars exhibited higher axial capacity than the steel-reinforced control specimen within the tested configurations; however, the influence of the longitudinal reinforcement ratio should also be considered. GFRP stirrups exhibited confinement behavior comparable to CFRP stirrups, whereas CFRP stirrups experienced premature fracture at bent corner regions, which reduced their confinement effectiveness and deformation capacity. Reducing stirrup spacing from 150 mm to 75 mm provided limited improvement in compressive strength because of premature stirrup failure and insufficient development of confinement effects. Existing confinement models tended to overestimate the post-peak response of FRP-reinforced columns. These preliminary findings provide experimental insights into the confinement behavior of FRP-reinforced concrete columns and contribute to the development of improved analytical models. Full article

In recent years, premature fatigue issues in heavy-duty steel crane girders have occurred frequently, underscoring an urgent need to establish targeted life extension methods. Compared with post-crack repair after macroscopic fatigue cracks have appeared, it is more practical to delay or even prevent the formation of such cracks in fatigue-sensitive zones of the crane girder. Extensive research has demonstrated that bonding Carbon Fiber-Reinforced Polymer (CFRP) plates can significantly enhance the fatigue life of defective components. However, most existing studies focus on thin plates with pre-existing macroscopic cracks, with limited attention given to scenarios involving thick plates or intervention before crack initiation. Therefore, this study focuses on the fatigue problem around bolt holes in the lower flange of heavy-duty steel crane girders. It investigates the life extension method of bonding CFRP plates prior to macroscopic crack formation. Through finite element analysis and comparative fatigue tests, the fatigue life enhancement mechanism was preliminarily interpreted. The effectiveness of this method is validated, and a practical CFRP bonding strategy is proposed to significantly improve the fatigue life of the lower flange in heavy-duty steel crane girders. Full article

Given that large-scale storage and transportation of liquid hydrogen are key to realizing the hydrogen economy, tank containers have attracted much attention for their flexibility. To minimize evaporation losses, efficient support structures are essential for these liquid hydrogen tank containers. Herein, a carbon fiber-reinforced polymer (CFRP) suspension ring is developed to support the inner vessel of liquid hydrogen tank containers. By using a special resin matrix and optimizing its curing process, the suspension ring capitalizes on a small cross-sectional area and low thermal conductivity, thereby significantly mitigating the cold-bridge heat transferred from the outer vessel to the inner vessel. Experimental results demonstrate that the tensile strength, outgassing rate, and fatigue performance of the suspension ring at both 77 K (liquid nitrogen temperature) and 4 K (liquid helium temperature) can meet the design targets. Notably, its equivalent thermal conductivity was approximately 88% lower than that of a stainless steel structure of the same size. With the integration of this suspension ring into a 40 ft liquid hydrogen tank container, the daily liquid nitrogen evaporation rate was recorded below 0.082%/d. Furthermore, the holding time before the pressure reached 0.14 MPa exceeded 192 h with a 90% liquid hydrogen filling ratio. This work provides key technical support for high thermal insulation, long-endurance liquid hydrogen storage and transportation equipment. Full article