Search Results (477)

This study investigates the fracture initiation and propagation mechanisms of continuously reinforced concrete–asphalt (CRC+AC) composite pavements under the synergistic effects of diurnal temperature fluctuations and non-uniform tire loading. A three-dimensional (3D) thermo-mechanical coupled finite element (FE) model was developed, with its underlying mechanical framework validated through laboratory-scale model tests conducted at 20 °C. The experimental results, involving strain monitoring at varying depths, demonstrated a high degree of consistency with numerical predictions in terms of spatial strain distribution, thereby ensuring the model’s reliability in capturing interlayer load-transfer efficiency. Building upon this validated mechanical foundation, numerical simulations were extended to analyze the low-temperature fracture response. The numerical results indicate that the maximum longitudinal and transverse tensile stresses in the asphalt layer are concentrated at the pavement surface, whereas the maximum shear stress occurs at a depth of 2–3 cm near the leading and trailing edges of the wheel load. Under low-temperature gradients, the Mode I stress intensity factor (K_I) at the crack tip exhibits a distinct diurnal opening–closing–reopening pattern, peaking at approximately 220 kPa·m^1/2 during the early morning hours (05:00–06:00). Furthermore, numerical simulations reveal the significant sensitivity of shear-sliding to axle loads; specifically, the peak Mode II stress intensity factor (K_II) increases monotonically from 190 to 230 kPa·m^1/2 as the axle load rises from 10 t to 16 t. Under non-uniform contact pressure, longitudinal cracking is primarily characterized by a mixed Mode I and Mode II mechanism driven by coupled tensile and shear stresses, whereas transverse cracking is dominated by Mode II shear failure. These findings suggest that implementing targeted traffic restrictions for overloaded vehicles during identified high-risk time windows can significantly enhance the structural durability and service life of composite pavements in cold regions. Full article

This paper presents a nonlinear time-history reassessment of an existing reinforced concrete frame building originally designed in 2007 according to the Romanian seismic code P100-1/2006 and re-evaluated under current seismic demand. Two three-dimensional solid finite-element models were developed in ANSYS Workbench 2025 R2: a bare reinforced concrete frame and an infilled frame with masonry panels. A distinctive feature of the modelling strategy is the explicit representation of longitudinal and transverse reinforcement embedded in the concrete solids, which allows direct tracking of steel stress demand and post-cracking load transfer. The models were subjected to bidirectional ground motions from the Vrancea 1977 and 1990 earthquakes and the Türkiye 2023 earthquake, scaled to the P100-1/2013 target spectrum for the investigated site. The results show that masonry infills markedly increase global stiffness and reduce displacement-related demand, with substantially lower roof displacements and interstorey drift measures in the infilled configuration. The bidirectional response remains predominantly translational, while the local stress and inelasticity fields indicate qualitative concentration zones in the frame, masonry panels, and staircase region. Overall, the study shows that masonry infills can strongly modify the actual seismic response of existing reinforced concrete frame buildings and should be considered explicitly in performance assessment. Full article

This study predicts expressway asphalt pavement maintenance decisions using machine learning to overcome the information loss inherent in traditional composite indices like PQI and PCI. Using ten years of inspection data from the G3012 Expressway in Xinjiang, an interpretable Random Forest (RF) model was developed. The methodology integrates permutation-based feature selection, three imbalance mitigation strategies (Balanced Weighting, SMOTE, and Cost-Sensitive Learning), and a rigorous time-aware validation framework. Results indicate that raw distress features—specifically strip repairs, block cracking, transverse and longitudinal cracking—are the most influential predictors, significantly outperforming aggregated indices. The optimized model, using Balanced Weighting and mean imputation, achieved an accuracy of 0.826 and ROC-AUC of 0.853 under strict temporal validation, effectively identifying the minority “repair” class. This research demonstrates that leveraging raw distress data through an interpretable ensemble framework provides a robust, data-driven alternative to threshold-based planning, supporting the transition from reactive to preventive maintenance in complex infrastructure management. Full article

This study clarifies the catalytic role of chloride ions on the corrosion performance of SS316L alloy immersed in molten LiNaK carbonate salt at 700 °C. Accordingly, isothermal static immersion corrosion tests were systematically conducted under different experimental conditions. Our results revealed that the presence of Cl significantly accelerates the corrosion process: the rate constant of the corroded samples increased from 11.3 × 10⁻² mg/cm² to 13.8 × 10⁻² mg/cm² with the addition of Cl. Continuous migration of Cl₂ and volatile metal chlorides leads to the formation of obvious pores, transverse cracks along grain boundaries, surface wrinkles, and partial spalling of the oxide scale, thereby severely aggravating substrate degradation. Notably, no chlorine-containing compounds or chlorine-rich regions were detected in the corroded samples, confirming that chlorine is not consumed in the corrosion process, rather it acts as an autocatalyst through the cyclic process of “oxidation–diffusion–reaction–regeneration”. Full article

Conventional deposition techniques hinder the integration of high-performance lead-free piezoelectric thick films on silicon substrates due to slow growth kinetics and complex processing. Herein, dense, crack–free Ba(Zr_xTi_1−x)O₃ (BZT, x = 0–0.10) thick films (~2 μm) were fabricated via aerosol deposition (AD) followed by annealing, forming a nanocrystalline microstructure with an average grain size of ~78 nm. Compositional tuning showed optimal electromechanical performance at x = 0.03, attributed to the coexistence of tetragonal and orthorhombic phases near room temperature that reduce the phase transformation energy barrier. The optimized BZT films exhibit excellent electrical properties: saturation polarization of 31.3 μC/cm², relative permittivity of 430, dielectric tunability figure of merit (FOM) of 155, and a large transverse piezoelectric coefficient |e_31, f| of 1.01 C/m²—comparable to textured magnetron–sputtered BaTiO₃ films but with higher deposition efficiency. This work provides a high-throughput route for fabricating piezoelectric thick films, highlighting the potential of compositionally engineered AD–processed BZT in lead-free MEMS applications. Full article

Steel jackets are widely used for the seismic retrofitting of reinforced concrete (RC) beam–column joints. However, the details and efficiencies of steel jackets are directly impacted by the presence of transverse beams. An in-depth understanding of this issue has been lacking so far. In this study, using realistic configurations of transverse beams, the seismic performance of exterior RC beam–column joints retrofitted according to the modified steel jacketing method were investigated numerically and theoretically. The refined nonlinear three-dimensional finite element approach was adopted and verified against experimental observations. A series of parameters were considered, including the number of transverse beams; the thickness, width and spacing of the steel strips at joint panels; and the axial compression ratio of columns. The results obtained from twenty specimens in terms of load response, cracking pattern, stress distribution, stiffness degradation and energy dissipation confirmed the effectiveness of the modified steel jacketing method. Significant differences among the roles of the parameters were revealed, and the reasons behind the differences were analyzed. Moreover, by means of significance analysis, the width and thickness of the steel strips were identified as the most influential parameters on the shear capacities of the joint panels with single- and double-sided transverse beams, respectively. Furthermore, based on the softened strut-and-tie model, a design approach for predicting the shear contribution of steel jackets in the presence of transverse beams was proposed for engineering applications. Full article

Design guidance for headed-bar development remains uncertain for large-diameter bars at cutoff points, where bar termination increases anchorage demand and confinement is often limited. This study quantified the anchorage behavior of 43 and 57 mm headed bars and established a regression-based strength model grounded in a splitting-controlled bond–bearing mechanism. Nineteen reinforced concrete beam specimens were tested under four-point loading configured to place the bending-moment inflection point at the head location. The primary variables were the development length (l_dt = 12–28d_b), concrete compressive strength (f_c′ = 42 and 70 MPa), clear side cover, clear spacing, and transverse reinforcement index (K_tr/d_b = 0–2.0). All the specimens failed by splitting prior to bar yielding, characterized by longitudinal cracking along the development region and cover spalling near the head. The anchorage strength increased with concrete compressive strength and development length and was most strongly enhanced by transverse reinforcement (up to ~60%). At failure, the bond contributed 70–86% of the developed stress, while the head-bearing contribution increased with confinement. Existing ACI 318-19 and KDS-2021 provisions were generally unconservative, particularly for unconfined specimens. The proposed bond–bearing model showed a close agreement with the test database (mean test/prediction = 0.99; COV = 4.72%) within stated parameter limits. Full article

In nature, organisms have evolved unique structures that feature low weight, high strength, and damage resistance. The Eurasian eagle-owl serves as a representative example, with specialized feather architectures that enable stable flight in intense and turbulent airflow conditions. Herein, driven by classical design layup guidelines, and inspired by the distinctive fiber architecture of the feather shaft cortex, we propose a regionally tailored layup (RTL) design to enable mass-efficient composite beams with high load-bearing capacity and enhanced damage tolerance. The feather shaft reference lay-up rectangular beam (FSRB) adopts the RTL, and a flange overlap is introduced to preserve the integrity and strength of the flange–web interface; it is then manufactured using inner–outer matched molds in conjunction with vacuum bag molding. Three-point bending shows that the FSRB achieves a flexural strength of 180 MPa and a flexural modulus of 12.1 GPa. Relative to conventional axial (ALRB), Cross-ply (CPRB), single-helix (SLRB), and quasi-isotropic (QLRB) lay-up rectangular beams, the FSRB improves strength by 59.5%, 46.6%, 26.8%, and 21.2%, and increases modulus by 81.7%, 34.7%, 25.1%, and 10.8%, respectively. FEA and SEM observations confirm an RTL architecture in the rectangular beams, characterized by differentiated fiber arrangements in the flange and web. Flanges with an axially dominated layup provide high initial flexural strength and stiffness. The web, formed by a crossed-ply/axial hybrid layup, provides transverse support and redirects crack/delamination growth, thereby promoting progressive failure and enhancing energy dissipation. Overall, this RTL design enables concurrent improvements in load-carrying capacity and damage tolerance. This study offers a design perspective for high-performance load-bearing components. Full article

As a critical barrier for power network safety, insulating materials are susceptible to internal microcracks, delamination, and other hidden defects that can trigger dielectric strength degradation and space charge accumulation, ultimately leading to insulation breakdown. Ultrasonic shear wave non-destructive testing enables defect identification without damaging the material. Therefore, this paper focuses on the identification and imaging of internal defects in insulating components using ultrasonic shear waves. First, a physical model for ultrasonic shear wave NDT is established. Based on the refraction and reflection characteristics of ultrasonic waves in materials with different acoustic impedances, a defect localization formula is derived. Through simulation verification, for the three defects set at different positions in the defect model, the positioning error is less than 0.5 mm. Subsequently, defects such as circular holes, triangular shapes, cracks, and bottom grooves were simulated. Analysis of the echo data revealed a correlation between the distance from the sensor to the defect and the echo amplitude. For groove defect imaging, the differential SAFT algorithm was employed, achieving a width error of 1 mm for imaging a 2 mm wide by 5 mm high groove, clearly presenting the defect morphology. Finally, an imaging software program for defect structure reconstruction was developed based on the simulation model presented in this article. We collected side and back view data through the constructed ultrasonic transverse wave non-destructive testing experimental platform, and visualized defects in insulation materials with grooves using this ultrasonic imaging program. This study achieved defect localization and imaging through simulation of various defect types combined with synthetic aperture focused imaging algorithms, providing a reference for visualization and industrial application of ultrasonic shear wave non-destructive testing technology. Full article

In this study, an annular laser beam shaping optics and a wire feeding system are used for additive manufacturing. A discrete concentric layering trajectory strategy (DCL-TS) and a continuous deposition trajectory strategy (CD-TS) for the laser-directed energy deposition (WL-DED) of aluminum alloy stud structures are developed. Initially, combinations of parameters, such as laser power, transverse speed, and wire feeding speed, which lead to a process that produces a single-layer structure with good morphology and no visible pores and cracks, are identified. Then, DCL-TS and CD-TS manufacturing strategies are used to produce aluminum alloy studs of similar dimensions. The EBSD results indicate that the CD-TS produces finer grains in the aluminum alloy studs compared to the DCL-TS; correspondingly, mechanical testing reveals superior microhardness and tensile strength in the circularly fabricated studs. The latter tensile value testing verifies that aluminum alloy studs using WL-DED on the substrate can meet the requirements for practical application in mobile phones, computers, etc. This research method enhances the mechanical properties of additively manufactured items. Consequently, manufacturing efficiency is significantly improved, providing a promising solution for rapid production. Full article

To evaluate the cracking characteristics of asphalt pavements under thermal stresses, the finite element (FE) software ABAQUS 2021 was used in this paper to establish thermal and mechanical parameter models, respectively. The temperature field distributions in winter and summer were analyzed according to the actual situation based on fracture mechanics theory and the extended FE method, as well as the most unfavorable crack type for crack propagation was also studied. Further, the impact of the propagation of transverse cracks on the road surface was investigated by changing the solar radiation, sunshine duration, and wind speed. Finally, the propagation pattern of reflective cracks was observed under the cyclic temperature field. The results show that under the action of the temperature field alone, type I cracks, which are cracks that undergo opening displacement due to the vertical tensile stress acting on the crack surface, are the main type of cracks, while the trend of crack propagation was much higher in winter than in summer. It was also found that changing the parameters of solar radiation, sunshine duration, and wind speed could significantly impact cracking. Under the cyclic temperature field, the length of reflective cracks was proportional to time, and the initial crack length significantly affected the pavement life. Therefore, pavement inspection should be more stringent in winter, and initial cracks should be avoided as much as possible during paving. Full article

Cracks and holes are commonly found in wooden components, and ancient Chinese wooden buildings, represented by the Yingxian Wooden Pagoda, demonstrate the ability to work with defects. This study systematically investigated the effects of longitudinal cracks and circular holes on the load-bearing capacity of wooden beams through four-point bending experiments on 1580 specimens. The study focuses on load-bearing capacity as the core indicator and provides calculation formulas for the section weakening coefficient and damage tolerance coefficient to quantitatively evaluate the impact of defects. Research has found that the harmfulness of a defect strongly depends on its position within the wooden beam. In the horizontal direction, when the longitudinal crack is located in the pure bending section of the wooden beam, it has little effect on the load-bearing capacity of the wooden beam. Once it deviates to the transverse bending section, the load-bearing capacity of the wooden beam significantly decreases. The hole is most dangerous when it is located in the horizontal center of the wooden beam, and it is also dangerous when it is near the loading point. In the vertical direction, the crack has the greatest impact on the load-bearing capacity of the wooden beam when it is located in the middle-height layer or its vicinity, while its impact decreases when it is close to the top and bottom surfaces of the wooden beam. Holes have the least impact when approaching the middle-height layer, which is different from the impact pattern of cracks. In addition, the hazard increases when the hole is located in the tension zone of the wooden beam, and decreases when it is located in the compression zone. The anisotropy and fiber structure of wood are the microscopic basis for the damage-tolerance mechanical behavior of timber beams. Full article

This study investigates the shear performance of high-strength concrete (HSC) beams reinforced with steel, fiber composite grids (CFRP and GFRP), and their hybrid configurations in the absence of transverse reinforcement. A total of six full-scale beams with varying reinforcement configuration and shear span-to-depth (a/d) ratios were experimentally tested under monotonic loading to evaluate their load capacity, cracking characteristics, failure modes, and serviceability behavior. The results revealed that beams reinforced solely with fiber grids exhibited significantly reduced strength and brittle shear failure. Hybrid systems incorporating both steel and fiber grids demonstrated improved strength and ductility, closely matching or surpassing control specimens with conventional steel reinforcement. Key structural parameters such as effective moment of inertia, cracking moment, shear strength, and midspan deflection were compared against analytical predictions based on ACI 318-16 and the Canadian Education Module code. While predictions generally aligned for hybrid beams, notable discrepancies were found for FRP-only systems, particularly in serviceability performance. The findings highlight the potential of hybrid reinforcement as a viable design strategy for HSC beams, offering a balance between strength, ductility, and service performance. Full article

The performance of Zr-2.5Nb alloy pressure tubes in nuclear reactors is critically dependent on the behavior of precipitated hydrides. In this study, a hydrogen-charged Zr-2.5Nb alloy pressure tube was subjected to in situ tensile testing combined with electron backscatter diffraction to elucidate microcrack evolution and microstructural adaptation. Initially, longitudinal hydride–hydride interface cracks nucleated at non-coherent interfaces of two types of hydrides due to the inherent brittleness. Subsequently, stress redistribution by a small proportion of hydride–hydride interface cracks resulted in the emergence of microcracks at the transverse hydride–matrix interfaces, accompanied by partial hydride phase transformation. Finally, under high strain conditions, increased dislocation movement in the matrix triggered a single slip system, leading to the formation of numerous low-angle grain boundaries. As strain further increased, multiple slip systems were activated, and longitudinal matrix–matrix interface cracks began to nucleate at certain grain boundary locations. Full article

Early age cracking induced by cement hydration heat in a 37.6 m-wide PK-section concrete box girder was investigated through full-scale field testing and numerical simulation. Material properties, temperature, and strain were measured, and the obtained thermal and mechanical parameters were used to simulate temperature and stress distributions during cantilever casting. Results show that direct casting on the foundation cap led to extensive vertical cracking in diaphragms, where tensile stresses exceeded concrete strength, corresponding to a cracking index of approximately 1.8, with thermal-to-shrinkage stress ratios up to 3:1 in critical regions. Under cantilever construction conditions, significant transverse stress occurred only at the diaphragm bottom, reaching a cracking index of about 1.6, with a thermal-to-shrinkage ratio of 2:1. Reducing casting temperature lowered thermal stress by 0.1 MPa/°C, while adding 0.9 kg/m³ polypropylene fibers increased early-age tensile strength by 15%. Optimized mix design or the inclusion of mineral admixtures such as silica fume further reduced shrinkage. The combined application of these measures effectively mitigated early-age cracking risk, providing practical guidance for the construction of wide-box girders in subtropical climates. Full article