Search Results (689)

Thin wall composite fan blades in aircraft engines demand designs that ensure structural integrity under operational loads while resisting foreign object damage and bird strikes. This study presents a finite element investigation of thin wall composite blades with metal leading edge caps, modeled through parametric coupon analyses under static flexure loading using ANSYS APDL. Three metallic leading edge caps, Ti-6Al-4V, Inconel 718, and 15-5 PH stainless steel, were combined with IM7/8551-7 carbon fiber composites. Parametric variations included changes in metal cap material, geometric designs of the joint, and other things. Performance was evaluated in terms of failure stress, interlaminar shear strains, interface integrity, and failure margins. Results reveal that cap design and cap material critically govern structural response, with distinct interchanges between strength-to-weight efficiency, interface stresses, and interlaminar shear strain. Optimal designs reduced interlaminar shear strain levels in thin wall composite blades, while retaining adequate stiffness and strength. The results underscore the importance of interface design for effective load transfer and provide design guidelines for lightweight, damage-tolerant thin wall composite fan blade structures. Full article

To address the inherent inaccuracies of the classical beam theory (which overestimates the flexural stiffness) and the “quasi-plane section method” (which neglects the shear deformation) in the deflection analysis of steel truss web–concrete composite beams, this study homogenizes discrete steel truss web members into a continuous steel web with equivalent thickness based on the strain energy equivalence principle. This homogenization is conducted under the assumption of fixed-end constraints for web members, thus establishing a sandwich laminated beam model. Incorporating the assumptions of zigzag axial displacement and layer-wise quadratic parabolic transverse shear stress, this study adopts the governing equations for static bending of composite beams derived via Hamilton’s mixed energy variational principle—this theory eliminates the need for an artificial shear correction factor, as the transverse shear stress naturally satisfies the zero boundary conditions at the upper and lower surfaces and the continuity condition at the interlayers. Analytical solutions for bending deflection under uniformly distributed loads are derived and validated against three-dimensional (3D) finite element (FE) models. The analysis results of a 45-meter-span beam demonstrate that the relative error in the maximum deflection of both simply supported beams and cantilever beams calculated by the proposed method is approximately 5%, which is significantly superior to the classical beam theory; the deflection induced by the zigzag effect at the mid-span of simply supported beams accounts for 15% of the total deflection, making it an indispensable key component in structural design. This method enables accurate deflection prediction and provides reliable technical guidance for the preliminary design of steel truss web–concrete composite beam bridges. Full article

The performance of polymer nanocomposites is governed primarily by the structure and properties of the matrix–filler interphase. This study presents a quantitative Raman spectroscopy analysis of interphase evolution in epoxy nanocomposites reinforced with two-dimensional WS₂, whose surface chemistry was systematically tuned via grafting of aminoacetic acid (AA) at concentrations of 2.5, 5.0, and 7.5 wt.%. By tracking peak shifts, linewidths, intensity ratios, and integrated areas of the characteristic WS₂ phonon modes (2LA(M) + E₂g¹, A₁g, and defect-related bands), we establish a non-linear, concentration-dependent interfacial response. Minor spectral variations at 2.5 wt.% AA indicate limited interfacial interaction. At 5.0 wt.% AA, suppression of the A₁g mode and significant band broadening reflect increased structural disorder. At 7.5 wt.% AA, coordinated red shifts (~−1.8 cm⁻¹) and the appearance of an additional band near 432.8 cm⁻¹ suggest the development of a strain-mediated interfacial state. Overall, increasing AA concentration leads to a non-linear evolution of the WS₂–epoxy interface, as reflected in peak positions, linewidths and intensity ratios. These Raman-derived descriptors correlate directly with enhanced mechanical properties (flexural and tensile strength) and thermal stability (Vicat softening point) of the composites. The results demonstrate that effective interfacial coupling requires a critical surface coverage and that Raman spectroscopy serves as a powerful tool for non-destructively probing and optimizing interphase architecture in TMD/polymer systems. Full article

To address the shortage of natural sand and the unclear mechanism of lithology’s influence on the application of manufactured sand, this study explores the applicability of neutral rock manufactured sand in asphalt mixtures. Taking neutral diabase manufactured sand as the research object, a series of tests including the Marshall test, water stability test, high- and low-temperature stability test, and surface free energy (SFE) test were conducted to systematically analyze the effects of aggregate lithology on the volumetric indicators, road performance, and interface adhesion of asphalt mixtures. Additionally, the improvement effect of cement as an anti-stripping agent was verified. The results show that lithology of manufactured sand significantly regulates the performance of asphalt mixtures. In terms of volumetric indicators, the limestone manufactured sand mixture has the smallest void ratio (3.81%), while the diabase manufactured sand mixture has the largest (5.81%), requiring an appropriate increase in the mixing ratio of diabase manufactured sand to optimize the compaction effect. For water stability, the short-term performance ranks as diabase ≈ limestone > granite, and the long-term durability ranks as limestone > diabase > granite. A least-squares linear regression model demonstrated that the polar component of aggregate surface free energy exhibits a strong positive correlation with asphalt–aggregate adhesion work (R² = 0.92), which quantitatively explains variations in the 48 h immersed Marshall residual stability ratio among different lithologies. Regarding high-temperature stability, the order is diabase > limestone > granite. Thanks to its low crushing value and strong angularity, the diabase manufactured sand mixture achieves a dynamic stability of 12,629 times/mm at 60 °C, showing the best rutting resistance. In terms of low-temperature performance, the diabase manufactured sand mixture exhibits the optimal initial crack resistance (maximum flexural strain of 2757 με) and long-term durability (strain attenuation rate of 11.7% after 30 cycles), while the granite manufactured sand mixture fails to meet the design requirements. Adding 1.5%~2.0% cement can significantly improve the adhesion between manufactured sand and asphalt, with more obvious enhancement effects on granite and diabase, thereby optimizing water stability and high-temperature stability. The research results provide theoretical support and technical reference for the scientific selection and engineering application of fine aggregates in asphalt pavements. Full article

Offshore reinforced concrete (RC) structures, such as bridges and high-piled wharves, are frequently subjected to the coupled action of steel corrosion and ship collision loads. However, existing studies lack systematic quantification and in-depth revelation of the synergistic degradation mechanism under this coupling effect, resulting in an insufficient scientific basis for engineering design and reinforcement. To address this gap, this study established a refined three-dimensional numerical model of drop hammer-reinforced concrete beams based on ABAQUS, comprehensively considering the strain rate effects of steel and concrete, steel–concrete bond–slip behavior, and the trilinear constitutive model of corroded steel. After validating the model’s reliability against experimental data from the existing literature, parametric simulations were conducted to investigate the coupled effects of different corrosion rates and drop heights (0.25–1.5 m). Key findings include: (1) corrosion reduces the peak impact force by 9.7–58.9% and increases the maximum mid-span displacement by 6.6–35.7%, with this effect amplified by higher drop heights; (2) shear performance degradation (16.14–35.19%) is significantly more severe than flexural performance degradation (13.28–28.93%), confirming that shear performance is more sensitive to corrosion; (3) corrosion causes cracks to propagate from a localized distribution to a global distribution, while higher drop heights accelerate structural evolution toward brittle failure; (4) the synergistic degradation law of “corrosion exacerbates impact damage, and impact amplifies corrosion defects” is revealed. By quantifying the corrosion–impact coupling effect, this study advances research in the field and provides critical technical support for damage assessment and service life prediction for offshore RC structures. In engineering practice, it is recommended that offshore structures in high-corrosion environments prioritize shear resistance enhancement and adopt targeted protective measures for high-impact-risk areas to mitigate the risk of brittle failure. Full article

Bacteria-based self-healing concrete is extensively shown to improve strength and durability; yet, the mechanistic relationship among microbial activity, damage progression, and transport resistance is still ambiguous. This study examines the interrelated mechanical and transport properties of concrete that incorporates Bacillus subtilis by directly substituting mixing water. Concrete mixtures with 0%, 5%, and 10% bacterial solution were assessed for compressive strength, complete stress–strain response, split tensile strength, flexural toughness, fast chloride ion penetration, and capillary sorptivity. X-ray diffraction was employed for microstructural validation. Results indicate a dose-dependent shift from brittle to quasi-ductile behavior, marked by augmented strain capacity, postponed crack localization, and improved post-cracking energy absorption. The mechanical alterations resulted in substantial decreases in chloride ion penetrability (up to 57%) and capillary sorptivity (up to 60%), signifying a drop in crack-assisted transport. X-ray diffraction verified the production of calcite resulting from microbial-induced calcium carbonate precipitation. The results indicate that the improvement in durability of bacterial concrete is attributable not only to pore filling but also to altered damage mechanisms that diminish the connectedness of transport channels, underscoring the potential of Bacillus subtilis as a bio-admixture for resilient structural concrete. Full article

To address issues such as web and bottom plate cracking and insufficient bending capacity in in-service prestressed concrete box girder bridges, this study proposes internal prestressing and section enlargement composite reinforcement. Firstly, taking a bridge of Shenhai Expressway as the background project, the combined reinforcement method is designed and the reinforcement effect is analyzed by MIDAS/Civil. Secondly, through numerical analysis, the influence of the bond shrinkage of self-compacting concrete with different mix ratios on the stress of the web of the original box girder is analyzed, and the interface between the new and old concrete is carried out. The analysis of the loss of the new prestress on the bonding surface of the new and old concrete is carried out by parameters such as the interface planting rate, the interface shear stiffness and the reinforcement structure. Furthermore, the theoretical calculation method of prestress loss rate of new and old concrete bonding interface is obtained. The results show that the flexural capacity of the normal section of the main beam is significantly improved after reinforcement, and the surplus coefficient is 1.18, which meets the requirements of the secondary safety level, and the mid-span deflection is improved by 34.28%, which verifies the effectiveness and feasibility of the combined reinforcement method. When the content of fly ash is 54%, the bond shrinkage strain and shrinkage stress of self-compacting concrete are reduced to the lowest level, which has the least influence on the existing box girder structure. It is suggested that the reinforcement ratio between the new and old concrete interface is 0.6%, and the interface roughness is 0.9 mm, which can increase the shear resistance of the new and old concrete interface and effectively reduce the transfer loss of prestress at the interface. Error analysis shows that the proposed semi-empirical calculation method has high accuracy with a deviation of less than 10%. Full article

This study investigates the seismic behavior of reinforced concrete (RC) columns with hollow rectangular cross-sections through experimental testing and analytical evaluation. A series of hollow-sectioned column specimens with different shear span ratios and failure modes were tested under cyclic lateral loading to examine their flexural and shear performance. The results demonstrated that flexure-dominated columns exhibited stable load-deformation responses and sustained seismic performance, even with the reduced shear span ratio. The experimental results also showed that the presence of the hollow cross-section had minimal influence on flexural strength and bar strain distribution. The shear strength of RC columns with hollow cross-sections tended to be underestimated by the conventional equation; however, improved accuracy was achieved by applying an equivalent cross-sectional area in the calculation. A nonlinear finite element analysis successfully reproduced the flexural load-deformation response of the specimens. While some discrepancies were observed in the shear-dominated cases, the analytical model provided conservative estimates under positive loading. These findings provide new insights into the seismic design of RC columns with hollow cross-sections, highlighting their potential applicability in building structures when flexural and shear behaviors are properly considered. Full article

To address the engineering challenges of frequent flexural deformation and instability of composite roadway roofs and the difficulty in accurately controlling the support strength range during deep coal mining, this study takes the soft–hard interbedded composite roof of the working face in the West No. 1 Mining Area of Shuangyang Coal Mine in Shuangyashan as the engineering background. Typical fine sandstone (hard rock) and tuff (soft rock) from the on-site roof were selected to prepare layered composite specimens, and indoor four-point bending tests were conducted. Combined with theoretical calculations, strain monitoring, and acoustic emission (AE) real-time localization technology, the regulatory mechanisms of three key factors—lithological combination, loading rate, and span—on the flexural mechanical properties, deformation and failure modes, and fracture evolution laws of layered composite rock masses were systematically investigated. The research results show the following: (1) The flexural performance of layered composite rock masses is dominated by the interlayer interface effect. Their flexural strength is 46.7% and 41.1% lower than that of single hard rock and soft rock specimens, respectively, and the competitive mechanism between interface slip and delamination fracture is the core inducement of strength deterioration. (2) The strength and deformation characteristics of layered composite rock masses exhibit a significant loading rate effect. When the loading rate increases from 0.002 mm/s to 0.02 mm/s, the flexural strength decreases by 51.8% and the mid-span deformation deflection reduces by 50.1%. High loading rates will exacerbate the deformation mismatch between soft and hard rock layers, trigger premature failure of interface bonding, and inhibit the full development of structural plastic deformation. (3) Increasing the span significantly optimizes the flexural bearing performance of layered composite rock masses. When the span increases from 170 mm to 190 mm, the flexural strength increases by 65.7% and the mid-span deformation deflection synchronously increases by 65.7%. A large span can extend the flexural deformation path, promote the coordinated deformation of rock layers, and suppress local stress concentration. (4) The flexural failure of layered composite rock masses is dominated by Mode II shear cracks, while single-lithology specimens are mainly dominated by Mode I tensile cracks. Loading rate and span significantly change the crack propagation mode and energy release law. This study establishes a calculation method for the equivalent flexural stiffness of layered composite rock masses and reveals the mesoscopic mechanism of flexural failure of heterogeneous layered rock masses. The research results can provide a theoretical basis and experimental support for the optimization of support schemes and the prevention and control of roof collapse hazards for composite roofs of deep coal mine roadways. Full article

The long-term behavior of reinforced concrete (RC) structures under sustained loading is strongly affected by creep and cracking, particularly under service conditions where tension stiffening and curvature changes are significant. This study investigates the flexural response of cracked RC beams through combined numerical and experimental analyses. A new 1D finite element model is proposed, integrating nonlinear material behavior, damage mechanics, and time-dependent effects, including creep in both compression and tension. The model relies on a layered fiber section approach and uses a Newton–Raphson iterative procedure to solve equilibrium, allowing accurate prediction of strain, curvature, and internal force evolution over time. The model shows excellent agreement with experimental observations and ABAQUS simulations, accurately capturing deflection trends and crack development. Its performance is further validated using a database of 55 RC beams, including specimens with recycled aggregates and fiber reinforcement. Across this dataset, 84.5% of predicted deflections fall within ±1 mm of measured values, with an R² of 0.960, demonstrating strong reliability. A Sobol-based sensitivity analysis identifies load ratio as the most influential parameter on long-term deflection, followed by concrete strength and humidity. Overall, the model offers an efficient and robust tool for long-term deflection prediction, bridging simplified design rules and complex 3D simulations. Full article

Flexible concrete blankets (FCBs) are emerging as a promising material for slope protection and surface stabilization, offering advantages of light weight, ease of installation, and environmental adaptability. This study investigates the mechanical properties, freeze–thaw resistance, and microstructural evolution of FCBs fabricated with varying cement–sand ratios and high alumina cement dosages. A series of mechanical tests, including compressive, flexural, and tensile strength evaluations, were conducted alongside freeze–thaw cycling tests (up to 125 cycles) to assess mass loss and strength retention. X-ray diffraction (XRD) and scanning electron microscopy (SEM) analyses were employed to elucidate the hydration mechanisms and damage evolution at the microstructural level. The results demonstrate that FCBs exhibit ductile failure behavior, with peak tensile strengths ranging from 3.1 to 4.5 MPa and tensile strain capacities ranging from 5 to 16%. The optimal mix achieved a compressive strength of 51.2 MPa after 28 days of curing. Freeze–thaw cycling induced a two-stage degradation pattern, with damage initiation occurring at approximately 50 cycles and significant deterioration beyond 75 cycles. After 125 cycles, mass loss ranged from 4.39% to 4.99%, and compressive strength retention varied between 78% and 83%, depending on the mix composition. Mixtures with balanced cement–sand ratios (1:1) and moderate Portland cement content demonstrated superior frost resistance, whereas high alumina cement-rich mixtures exhibited pronounced structural loosening due to phase transformations of unstable hydration products. These findings provide a theoretical and experimental basis for optimizing the composition of FCBs to achieve enhanced mechanical performance and durability in cold-region engineering applications. Full article

Conventional Fiber-Reinforced Polymer (FRP) materials may exhibit certain performance uncertainties in harsh environments, limiting their reliability for structural strengthening. To address this, Basalt Fiber-Reinforced Polymer (BFRP) plates fabricated with silicate-modified epoxy resin are proposed for the flexural strengthening of reinforced concrete (RC) beams. The research aims to evaluate their short-term strengthening performance and establish a reliable calculation method for flexural capacity. Four-point bending tests were conducted to investigate the effects of BFRP plate thickness and end anchorage configuration on failure modes, flexural capacity, and ductility. Finite element simulations incorporating interfacial bond–slip behavior reproduced typical debonding failures, followed by a comprehensive parametric analysis. Based on the experimental and numerical results, a modified BFRP plate strain formula at debonding was proposed to establish a calculation method for the flexural capacity of BFRP-strengthened beams governed by debonding failure. The results indicate that beams without end anchorage were prone to interfacial debonding, where increasing the plate thickness from 0.5 mm to 2 mm raised the flexural capacity gain from 4.5% to 15% but intensified the ductility reduction from 42.9% to 64.9%. Conversely, applying mechanical anchorage improved the ductility index by over 20% compared to unanchored counterparts. The adopted FRP–concrete bond–slip constitutive model accurately characterizes interfacial debonding behavior, and the proposed flexural capacity model demonstrates high accuracy with overall deviations within 5%. It can be concluded that the novel BFRP plates exhibit strengthening behavior comparable to existing FRP systems. Effective end anchorage further enhances flexural capacity and prevents brittle failure. The proposed debonding strain formula for the novel BFRP system offers a reliable basis for capturing the critical onset of interfacial failure. Building upon this, the developed flexural capacity model provides a reliable theoretical basis for the design and assessment of RC beams strengthened with the novel BFRP plates. Full article

Through static bending tests on two full-scale specimens of a new steel grating–UHPC (ultra-high-performance concrete) composite bridge deck, the load–displacement curves, crack propagation, strain distribution, and failure characteristics were analyzed. According to the experimental results, a numerical model was established using ABAQUS software 2021, in which two contact methods were employed to simulate the interfacial connection between UHPC and steel. The results indicate that the surface-to-surface contact method provides better agreement with the experimental data. Subsequently, conducted parameter studies using this model to investigate the impact of key geometric parameters, including section height, flange width, flange thickness, steel bottom plate thickness, and steel web plate thickness, on the flexural performance of the structure. The results demonstrated that the section height and the steel bottom plate thickness had a significant effect on the load-bearing capacity and overall stiffness of the component, while the influence of other parameters was comparatively minor. Finally, based on both experimental and numerical results, a formula for calculating the flexural bearing capacity of steel grating–UHPC composite bridge slabs was proposed, providing a reference for the structural design and promotion of the new composite bridge deck. Full article

In this study, the flexural behavior of notched steel beams retrofitted with CFRP is investigated. Two series of tests, including W200 × 22 and W14” wide-flange notched beams rehabilitated with externally bonded (EB) CFRP are evaluated under static loading. The W200 × 22 beams were received directly from a factory, whereas the W14” wide-flange beams were extracted from the Original Champlain Bridge after roughly 60 years in service. The parameters considered include the CFRP elastic modulus, CFRP configuration, notch depth, anchorage system, and adhesive type. The effect of the CFRP elastic modulus on the rehabilitation technique is examined by using Normal Modulus (NM) and Ultra-High Modulus (UHM) CFRP with approximately the same tensile capacity. Failure modes, load–deflection behavior, strain distributions along the CFRPs, and Crack Mouth Opening Displacement (CMOD) are thoroughly discussed in this study. The results reveal that both UHM and NM CFRP significantly enhance the load-carrying capacity. However, specimens retrofitted with UHM CFRP exhibit a brittle behavior, whereas those strengthened with NM CFRP show a more ductile behavior. Full article

Delamination is a critical failure mode in composite laminates that degrades the structural performance and load-carrying capacity. This study investigates the improvement of Mode I and Mode II interlaminar fracture toughness of carbon fiber-reinforced polymer (CFRP) laminates through the interleaving of electrospun thermoplastic nanofiber mats. Nanofiber veils were inserted between carbon fiber plies to enhance resistance to delamination under tensile opening (Mode I) and in-plane shear (Mode II) loading. The effects of nanofiber interleaving were evaluated using double cantilever beam (DCB) tests for Mode I and end notch flexure (ENF) tests for Mode II. Both tests were conducted on a symmetric quasi-isotropic laminate [-45/45/90/0₅]_s containing a thick unidirectional 0° ply at the mid-plane. Thermally induced residual stresses resulting from mismatches in ply coefficients of thermal expansion and unsymmetric arm lay-ups were accounted for in the experimental determination of fracture toughness. These stresses, generated during cooling from the cure temperature, influence the effective strain energy release rate and were included in the fracture toughness calculations to ensure accurate toughness evaluation and consistency with numerical predictions. The results demonstrate improved delamination fracture toughness, highlighting the potential of nanofiber interleaving for aerospace and wind energy applications. Full article