Archives of Civil and Mechanical Engineering最新文献

The unusually fast diffusional layer growth which observed in some solid-state reactions can be linked to the superlattice formation in the product phase. The reaction product layer in such diffusion zone composes numerous antiphase domains separated by antiphase boundaries. These planar defects provide short-circuit diffusion paths leading to very fast growth, while the overall reaction kinetics is found to follow parabolic law. Formation of intermetallic phases in diffusion couples based on Sn and Cu-Ni alloys containing up to 25 at% of Ni and interdiffusion in ordered Fe(Si)-solid solutions were discussed to illustrate this peculiar reaction behaviour. When a superlattice occurs in the product phase, diffusion along the antiphase boundaries can be a dominant mass-transport mechanism in the intermetallic layer. Since the generally accepted treatment of the Kirkendall effect assumes that mass-transport through the reaction zone is controlled by a vacancy-mediated (lattice) diffusion, it is not clear whether it is still possible to obtain meaningful information about relative mobilities of species by monitoring behaviour (migration) of fiducial markers initially introduced at the contact surface of the diffusion couple.

Heat treatment induced micro residual stress accelerating subsurface spalling in bearing raceways, significantly limiting the service life of high-performance bearings. In this study, the evolution of interphase stress between primary carbides and the matrix in 8Cr4Mo4V steel during quenching and tempering is systematically investigated via a combined finite element method and nanoindentation approach. The submodel method is adopted to simulate the local stress field around carbides embedded in the raceway, accounting for phase transformation kinetics and transformation-induced plasticity. Residual stress is quantified using nanoindentation tests in continuous stiffness measurement mode at the carbide interfaces. Based on the load-displacement curves obtained by nanoindentation simulations, a linear relationship between indentation work and residual stress is established. Results of submodel method indicate that quenching introduces significant stress concentrations at carbide interfaces, with effective stress exceeding the macroscopic level by 250 MPa. Tempering homogenizes the stress distribution but induces a transition from compressive to tensile stress in the matrix adjacent to carbides due to volume shrinkage during martensite tempering. EBSD analysis confirms strain localization near interfaces, consistent with simulation predictions. This work provides a validated strategy for analyzing heat treatment micro residual stresses and offers insights for optimizing heat treatment processes to increase bearing service life.

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Current density (CD) played a critical role in the performance of micro–arc oxidation (MAO) coatings on magnesium (Mg) alloy, which influenced their tribocorrosion and electrochemical properties. In this study, MAO coatings were prepared under the different current densities on AZ31B Mg alloy, and their tribocorrosion and electrochemical behaviors in 3.5% NaCl solution were evaluated to elucidate the wear and corrosion mechanisms. The results demonstrate that the average coefficients of friction (COFs) are increased with the CD, whereas the wear rates are opposite. The MAO coating prepared at 6 A•dm^–2 has the lowest wear rate, demonstrating the enhanced tribocorrosion performance. The abrasive wear and oxidative wear dominate the wear mechanism, which are correlated with the increased hardness by the optimal CD. Moreover, the MAO coating prepared at 5 A•dm^–2 with the lowest corrosion current density exhibits superior anti–corrosion performance.

Recycled aggregate concrete (RAC) suffers from significantly inadequate mechanical properties and durability due to the high porosity and weak interface transition zone (ITZ) of RCA, severely limiting its engineering applications. To address this issue, this study systematically investigates the coupled effects of basalt fiber (BF) dosage (volume fractions of 0.05%, 0.1%, 0.2%, and 0.3%) and RCA replacement rate (volume fractions of 40%, 60%, 80%, and 100%) on the performance of basalt fiber-reinforced recycled aggregate concrete (BFRAC). Results indicate that, regarding mechanical properties, considering combined splitting tensile, flexural, and compressive strengths, 0.2% BF reinforcement yields optimal performance. Compared to C40 concrete, splitting tensile strength increases by 29.7%, flexural strength by 15.1%, and compressive strength by 24.8% with compressive strength peaking at 88.06 MPa at 0.05% BF content. Overall mechanical performance remained optimal at 0.2% BF. 2. For durability, 0.1% BF demonstrated the best improvement, reducing chloride ion permeability by 83% and sulfate erosion-induced strength loss by 8.99%. 3. When the RCA replacement rate increased to 100%, the BFRAC compressive strength decreased by up to 27.4%, and the chloride ion diffusion increased by 72%. However, the synergistic effect of 40% RCA combined with 0.1–0.2% BF enabled BFRAC’s comprehensive performance to approach that of ordinary concrete. This study quantifies the relationships between BF dosage, RCA replacement rate, and BFRAC’s macroscopic properties. It provides a reliable scientific basis for optimizing BFRAC mix designs and scaling up its application in civil engineering, holding significant implications for advancing sustainable development in the construction industry.

The microstructural evolution during friction stir welding (FSW) of martensitic steel is difficult to interpret, primarily due to the austenite-to-martensite transformation that occurs during post-weld cooling. This study utilized electron backscatter diffraction (EBSD) data to reconstruct prior austenite grains (PAGs) from the martensitic microstructure, enabling detailed evaluation of the laser scanning speed’s impact on the FSW process. The results indicate that lower laser scanning speeds lead to larger PAGs and higher aspect ratios of lath martensite in laser-treated steel plates. Compared with conventional FSW (FSW-C), laser pre-treatment reduces the axial force (Fz) exerted on the welding tool. In the stir zone (SZ), PAG size decreases with slower scanning speeds, and the shear texture comprises A and C components. At the highest scanning speed (120 cm/min), a thermo-mechanically affected zone (TMAZ) exhibits the lowest ferrite content, and increased carbide precipitation is observed throughout the heat-affected zone (HAZ). Analysis of martensitic variants reveals that severe plastic deformation during FSW suppresses variant selection, leading to a predominance of close-packed (CP) variants. The joint welded at the highest scanning speed exhibits the greatest ultimate tensile strength (UTS), attributed to the minimal ferrite content at the fracture location.

The partial replacement of natural aggregates with bamboo aggregates leads to a reduction in the compressive strength of concrete. Hence, a pivotal research question lies in whether the superior strength and ductility of steel can effectively compensate for this strength loss while concurrently enhancing the cooperative load-bearing behavior of the composite structural system. Bamboo aggregates were incorporated into conventional concrete mixtures, which was then cast into circular steel tubes to fabricate bamboo aggregate concrete-filled steel tube (BACFST) stub columns. An experimental program was conducted on 30 circular BACFST specimens, with the primary variables being the steel tube wall thickness (T) and the bamboo aggregate replacement rate (r). The study quantitatively evaluated the monotonic axial compressive behavior, including failure modes and stress–strain responses. The stub columns were mainly damaged by lumbar bulge flexure, and the stress–strain curves can be categorized into two kinds: medium constraint and strong constraint. Moreover, after analyzing the key mechanical indexes, it can be concluded that when the properties of the steel tube are maintained constant, with the increase of r, peak stress (f_cc), strength index (SI), and initial stiffness (E) decrease to different degrees; however, the ductility index (DI) was positively correlated with r, and the value of DI increases about 80.4% at the maximum. Based on experimental data, this study systematically investigated the influence of parameter r on the compressive strength of bamboo-aggregate concrete and proposes a BACFST bearing capacity model. A comprehensive assessment was conducted comparing the proposed model with existing code-specified models, with validation results demonstrating the enhanced rationality and improved predictive accuracy of the proposed model.

The simultaneous use of Coarse Recycled Aggregate (CRA) and Raw-Crushed Wind-Turbine Blade (RCWTB) in concrete enables the recycling and revaluation of two wastes from wind-farm decommissioning. Verification of the validity of Non-Destructive Testing (NDT) for field control of the concrete mixes produced with these wastes is key to extending its possibilities of use, as is the application of NDT in concrete monitoring. This research evaluates the suitability of Ultrasonic Pulse Velocity (UPV) and rebound index to estimate the mechanical properties of concrete made with up to 100% CRA and 10% RCWTB. From an experimental approach, both NDT properties decreased when adding both wastes, although rebound index exhibited a higher experimental variability. These experimental results were subsequently analyzed through two statistical procedures. First, an analysis through response surface methodology was conducted, whose models revealed that the directions of maximum variation (gradients) for UPV, modulus of elasticity, compressive strength and tensile splitting strength were aligned, especially for high waste contents. Second, a regression analysis determined that only these three mechanical properties could be properly estimated using these NDT properties, since Poisson’s coefficient and flexural strength largely depended on the stitching of the cementitious matrix, influenced by the fibers from glass fiber-reinforced polymer contained in RCWTB. UPV was always the NDT property that yielded more accurate estimations, while rebound index only improved the estimation quality of compressive strength, although a reduction of its measured value is recommended to avoid strength overestimations. In general, non-linear multiple regression models provided accurate and reliable predictions.

Implementing machine learning (ML) methods in performance level assessment of reinforced concrete (RC) shear walls can considerably enhance the speed and accuracy of performance evaluations, which are traditionally time-consuming and require extensive expertise. However, due to the effects of many input features in the seismic behavior of RC shear walls, several challenges, e.g. overfitting, increased complexity and computational cost, sparsity of data, and difficulty in feature selection can lead to low effectiveness of ML models for real-world examples. Therefore, this research is focused on reducing the number of input features effectively while maintaining high prediction accuracy. According to the results, optimizing extreme gradient boosting (XGBoost) and random forest (RF) models with the adaptive tree of Parzen estimators can boost the performance of ML models without the need for hyperparameter tuning. However, by providing the ML models based on two main input features of wall length and period of structure, the coefficients of A, B, and C can be determined for predicting the median of incremental dynamic analysis (M_IDA) curve of RC shear wall based on the maximum interstory drift ratio threshold. Proposed ML models predicted the M_IDA values of a 5-story case study RC shear wall with an accuracy of 97.2% and 96.5% for near-field records, then, the graphical user interface (GUI) is introduced to be used by researchers for preliminary seismic performance assessment.

The paper presented an investigation into the rheological and physical properties and durability of concrete treated with anticorrosive coatings. The primary materials utilized include organosilicon compounds, silanes, methacrylic resin (MR), and epoxy resin (ER) modified with stearic acid (STA) or methyl esters (ME). A total of ten different resins were developed. The fundamental characteristics of the coated concrete were assessed, including watertightness, water absorptivity, water vapor diffusion, frost and salt crystallization resistance. Following a curing period of 28 days, the concrete samples were coated with the newly formulated coatings. Notably, the concrete treated with ER2 + SA demonstrated the lowest water absorptivity (1.76%) among all samples tested. Following 50 freezing-thawing cycles, the concrete with epoxy resins showed minimal mass change, ranging from 0.01 to 0.2%, whereas the reference concrete samples experienced a mass change of 3.11%. The concrete with the new coatings exhibited excellent resistance to salt crystallization, in contrast to the reference concrete, which suffered a 15% weight loss. The findings suggest that ME and STA derivatives can effectively serve as coatings for concrete used in cooling towers.

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Under the trend of high-speed lightweight design for aero-engines, turbine fan blades face dynamic instability risks in complex aerothermal-rotational coupled environments. While annular sector plates optimize aerodynamic adaptability and centrifugal stress distribution via curvature effects, traditional homogeneous and composite materials struggle to meet the demands of matching the 3D stress field. Furthermore, existing research often neglects the coupling effects between variable thickness and multidimensional functionally graded materials (MDFGM), and lacks systematic analysis of blade dynamic responses under transonic flow fields. ‌This paper establishes a coupled aero-thermal-elastic model for annular sector plates with variable thickness made of MDFGM. Based on the First-order Shear Deformation Theory (FSDT), the rotational-thermal field coupled governing equations are derived by combining artificial spring boundary conditions with Hamilton’s principle. The Generalized Differential Quadrature Method (GDQM) is employed to efficiently discretize the spatially varying gradient coefficients, coupled with the Runge–Kutta method to solve ‌forced vibration amplitude-frequency response under subsonic unsteady aerodynamics and transient flutter limit cycle oscillation (LCO) and chaotic evolution in supersonic flow fields. ‌The study reveals the synergistic control mechanisms of gradient parameters and elucidates the influence laws of variable thickness, material gradation, and multi-physics coupling on structural stability. It fills the research gap concerning the dynamic characteristics analysis of MDFGM blades under complex operating conditions, providing theoretical foundations for the design of high-reliability engine blades.