Search Results (40)

In this study, lanthanum–nitrogen co-doped titanium dioxide (La-N-TiO₂) thin films were fabricated using Ion Beam Assisted Deposition (IBAD) and subjected to accelerated ultraviolet (UV) aging experiments to systematically investigate the impact of co-doping on the films’ resistance to UV aging. X-ray diffraction (XRD) analysis revealed that La-N co-doping inhibits the phase transition from anatase to rutile, significantly enhancing the phase stability of the films. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) characterizations indicated that co-doping increased the density and surface uniformity of the films, thereby delaying the expansion of cracks and increase in roughness induced by UV exposure. Energy-dispersive X-ray spectroscopy (EDS) results confirmed the successful incorporation of La and N into the TiO₂ lattice, enhancing the chemical stability of the films. Contact angle tests demonstrated that La-N co-doping markedly improved the hydrophobicity of the films, inhibiting the rapid decay of hydrophilicity during UV aging. After three years of UV aging, the co-doped films maintained high structural integrity and photocatalytic performance, exhibiting excellent resistance to UV aging. These findings offer new insights into the long-term stability of photovoltaic self-cleaning materials. Full article

Geopolymer concrete (GPC) offers reduced carbon emissions and employs industrial by-products such as fly ash and ground granulated blast furnace slag (GGBFS). In this study, the synergistic augmentation of shear carrying capacity in steel-fiber-reinforced rubberized geopolymer concrete (FRGC) incorporating industrial by-products such as fly ash, GGBFS, and recycled rubber for sustainable construction is investigated. The reinforced rubberized geopolymer concrete (RFRGC) mixtures contained 20% rubber crumbs as a partial replacement for fine aggregate, uniform binder, and alkaline activator. The findings revealed that 1.25% steel fiber achieved optimal hardened properties (compressive strength, flexural, and split tensile strength), with 12 M sodium hydroxide and oven curing achieving maximum values. An increase in molarity improved geopolymerization, with denser matrices, while oven curing boosted polymerization, enhancing the bonding between the matrix and the fiber. The effect of steel fiber on the shear carrying capacity of RFRGC beams without stirrups is also discussed in this paper. An increased fiber content led to an increased shear carrying capacity, characterized by an improvement in first crack load and a delayed ultimate failure. These results contribute to sustainable concrete technologies for specifically designed FRGC systems that can balance structural toughness, providing viable alternatives to traditional concrete without compromising strength capacity. Full article

The beam–column connection is an important element in frame construction. Despite numerous studies, there is still no uniform procedure for shear force design across countries. We continue to witness serious problems and even collapse of buildings under seismic activity caused by failures in the beam–column connection of the frame. During the last 60 decades, a large number of experimental studies have been carried out on frame assemblies, where various parameters and their compatibility under cyclic activities have been investigated. What remains misunderstood is the magnitude and distribution of the forces passing through the joint and their involvement in the magnitude of the shear force. Here, the creation of a new mathematical model for the beam and column contributes significantly to our understanding of the flow of forces in the frame connection. For this purpose, the full dimensions of the beam and its material properties are taken into account. All investigations were carried out before crack initiation and after crack propagation along the face of the column, where it separates from the beam. In the present work, the beam is subjected to two symmetrical, transverse, uniformly distributed loads. Expressions are derived to determine the magnitudes of the support reactions from the beam, as a function of the height of its lateral edge. The load positions corresponding to the extreme values of the support reactions are determined. Numerical results are presented for the effect over the magnitudes of the support reactions from different strengths of concrete and steel on the beam. The results are compared with those given in the Eurocode for shear force calculation. It is found that the shear force determined by the proposed new model exceeds the force calculated by Eurocode by 4–62.5%, depending on the crack development stage and the beam materials. Full article

This study aims to develop a stress-optimized ultra-broadband beam-splitting coating that integrates four spectral bands by analyzing the beam-splitting properties of coatings spanning visible to medium and long-wave infrared regions. A beam-splitting coating was deposited on a Ge substrate using ion-beam-assisted thermal evaporation, employing Ge, ZnS, and YbF₃ as coating materials. The designed coating exhibits high reflectance in the 0.5–0.8 μm and 0.9–1.7 μm wavelength bands while maintaining high transmittance in the 3–5 μm and 8–12 μm bands. The optimal deposition process for a single-layer coating was established, at a 45° incidence angle, the beam-splitting coating achieved an average reflectance (Rave) of 86.6% in the 0.9–1.7 μm band and 93.7% in the 0.9–1.7 μm band, alongside an average transmittance (Tave) of 91.36% in the 3–5 μm band and 91.3% in the 8–12 μm band. The antireflection coating achieved a single-side Tave of 98.5% in the 3–5 μm band and 97% in the 8–12 μm band. The coating uniformity exceeded 99.6%. To optimize the surface profile, a single-layer Ge coating was added to the rear surface, resulting in a root mean square deviation of less than 0.0007 μm, achieved the same precision of the surface profile successfully. The deposited beam-splitting coating possessed high surface profile precision, and successfully achieved high reflectance in the visible to short-wave infrared range and high transmittance in the medium- and long-wave infrared range. The coating demonstrated excellent adhesion, abrasion resistance, and structural integrity, with no wrinkling, cracking, or delamination. Full article

Taking AC-13 asphalt mixture as the matrix, this research delves into the impacts of assorted steel fibers on AC-13 asphalt mixture, especially the influence of 17.5 mm × 17.5 mm L-shaped steel fibers. A gradient design with mass dosages of 0%, 1%, 2%, and 3% was employed to evaluate the reinforcement effect of L-shaped steel fiber-reinforced asphalt mixture compared with conventional mixture. Also, comparative analysis between L-shaped and straight steel fibers was conducted through comprehensive mechanical performance tests, including the Marshall stability test, high-temperature wheel tracking test, low-temperature beam bending test, freeze–thaw splitting strength test, and immersion Marshall test. The results demonstrate that L-shaped steel fibers significantly improve the comprehensive mechanical properties of asphalt mixture compared to conventional asphalt mixture, showing remarkable improvements in high-temperature stability, low-temperature crack resistance, and water stability. The overall performance enhancement effect increases by approximately 20%. Compared with straight steel fibers, the performance improvement of the mixtures is slightly greater, with the optimal performance achieved at 2% mass dosage. The standard deviation and coefficient of variation are used to reflect the degree of data dispersion. The results show that the data of L-shaped steel fibers have relatively smaller fluctuations, being more uniform and stable. Full article

During use, titanium alloy structural components may experience sudden overloads or occasional loads, which can reduce their fatigue life and accelerate structural failure. To study the fatigue behavior of TC4/Ti60 joints, this paper uses electron beam welding technology to obtain TC4/Ti60 dissimilar joints. The results show that the microstructure changes during the welding process, with the weld zone being relatively uniform, primarily consisting of coarse α′ phase. The near heat-affected zone on the TC4 side consists of α′, while on the Ti60 side, in addition to the α′ phase, there is a small amount of residual α phase. Fatigue tests reveal that as the pre-deformation increases, the fatigue life gradually decreases. During the early stages of fatigue, the joint exhibits cyclic hardening, which transitions to cyclic softening as the test progresses, ultimately leading to failure. Fatigue fracture analysis reveals that all fatigue samples failed on the TC4 side, with no failure observed in the weld zone. This is likely due to the presence of martensite, which gives the weld zone higher strength than the TC4 base materials. Additionally, fatigue cracks initiated from surface or near-surface defects, with ductile fractures being predominant. Full article

Cemented carbides, renowned for their exceptional strength, hardness, elastic modulus, wear resistance, corrosion resistance, low coefficient of thermal expansion, and chemical stability, have long been indispensable tooling materials in metal cutting, oil drilling, and engineering excavation. The advent of additive manufacturing (AM), commonly known as “3D printing”, has sparked considerable interest in the processing of cemented carbides. Among the various AM techniques, Selective Laser Melting (SLM), Selective Laser Sintering (SLS), Selective Electron Beam Melting (SEBM), and Binder Jetting Additive Manufacturing (BJAM) have garnered frequent attention. Despite the great application potential of AM, no single AM technique has been universally adopted for the large-scale production of cemented carbides yet. The SLM and SEBM processes confront substantial challenges, such as a non-uniform sintering temperature field, which often result in uneven sintering and frequent post-solidification cracking. SLS notably struggles with achieving a high relative density of carbides. While BJAM yields WC-Co samples with a lower incidence of cracking, it is not without flaws, including abnormal WC grain growth, coarse WC clustering, Co-rich pool formation, and porosity. Three-dimensional gel-printing, though possessing certain advantages from its sintering performance, falls short in dimensional and geometric precision control, as well as fabrication efficiency. Cemented carbides produced via AM processes have yet to match the quality of their traditionally prepared counterparts. To date, the specific densification and microstructure evolution mechanisms during the AM process, and their interrelationship with the feedstock carbide material design, printing/sintering process, and resulting mechanical behavior, have not been thoroughly investigated. This gap in our knowledge impedes the rapid advancement of AM for carbide processing. This article offers a succinct overview of additive manufacturing of cemented carbides, complemented by an analysis of the current research landscape. It highlights the benefits and inherent challenges of these techniques, aiming to provide clarity on the present state of the AM processing of cemented carbides and to offer insights into potential future research directions and technological advancements. Full article

The key structural components of a wind turbine blade, such as the skin, spar cap, and shear web, are fabricated from fiber-reinforced composite materials. The spar, predominantly manufactured via resin infusion—a process of resin injection and curing in carbon fibers—is prone to initial defects, such as pores, wrinkles, and delamination. This study suggests employing the pultrusion technique for spar production to consistently obtain a uniform cross-section and augment the reliability of both the manufacturing process and the design. In this context, this study introduces carbon fiber-reinforced polymer (CFRP/CFRP) and glass fiber-reinforced polymer (GFRP/CFRP) test specimens, which mimic the bonding structure of the spar cap, utilizing pultruded CFRP in accordance with ASTM standards to analyze the delamination traits of the spar. Delamination tests—covering Mode I (double cantilever beam), Mode II (end-notched flexure), and mixed mode (mixed-mode bending)—were performed to gauge displacement, load, and crack growth length. Through this crack growth mechanism, the interlaminar fracture toughness derived was examined, and the stiffness and strength changes compared to CFRP based on the existing prepreg manufacturing method were analyzed. In addition, the interlaminar fracture toughness for GFRP, which is a material in contact with the spar structure, was analyzed, and through this, it was confirmed that the crack behavior has less deviation compared to a single CFRP material depending on the stiffness difference between the materials when joining dissimilar materials. This means that the higher the elasticity of the high-stiffness material, the higher the initial crack resistance, but the crack growth behavior shows non-uniform characteristics thereafter. This comparison provides information for predicting interlaminar delamination damage within the interior and bonding area of the spar and skin and provides insight for securing the reliability of the design life. Full article

Alkali–silica reaction (ASR) is an important factor that seriously affects the durability of reinforced concrete (RC) structures. The current research on alkali-aggregate mainly focuses on the deterioration mechanism of materials and the mechanical properties of standard specimens. However, there is a gap in the field of research on the effect of alkali-aggregate damage on the level of RC structures. In this study, five RC beams were tested, and the depth and location of alkali solution immersion were used as the test variables, with the aim of investigating how the steel reinforcement suppresses the expansion caused by ASR and evaluating the shear behavior of RC beams after non-uniform ASR damage. The results of the study showed that immersion in an alkali solution and an increase in immersion depth accelerated the rate of expansion development, while steel reinforcement inhibited the rate of expansion development. Compared with undamaged RC beams, ASR initially generates expansion stresses within the concrete, which increase the cracking and yield loads of RC beams and delay the cracking of RC beams, and ASR reduces the ultimate load-carrying capacity and ductility of RC beams due to the disruption of the concrete microstructure. Finally, a chemo-mechanical analysis method is proposed based on experimental results, which incorporate an ASR expansion model and a pore mechanics model. The efficacy and precision of this model are validated through comparison with experimental results. Full article

Inconel 718 is a widely popular aerospace superalloy known for its high-temperature performance and resistance to oxidation, creep, and corrosion. Traditional manufacturing methods, like casting and powder metallurgy, face challenges with intricate shapes that can result in porosity and uniformity issues. On the other hand, Additive Manufacturing (AM) techniques such as Powder Bed Fusion (PBF) and Direct Energy Deposition (DED) can allow the creation of intricate single-part components to reduce weight and maintain structural integrity. However, AM parts often exhibit directional solidification, leading to anisotropic properties and potential crack propagation sites. To address this, post-processing treatments like HIP and heat treatment are necessary. This study explores the effects of the raster and stochastic spot melt scanning strategies on the microstructural and mechanical properties of IN718 parts fabricated using Electron Beam Powder Bed Fusion (EB-PBF). This research demonstrates that raster scanning produces columnar grains with higher mean aspect ratios. Stochastic spot melt scanning facilitates the formation of equiaxed grains, which enhances microstructural refinement and lowers anisotropy. The highest microstructural values were recorded in the raster-produced columnar grain structure. Conversely, the stochastic melt-produced transition from columnar to equiaxed grain structure demonstrated increased hardness with decreasing grain size; however, the hardness of the smallest equiaxed grain structure was slightly less than that of the columnar grain structure. These findings underscore the vital importance of scanning strategies in optimizing the EB-PBF process to enhance material properties. Full article

The marine atmospheric corrosion behavior of 700L high-strength automotive beam steel exposed for 36 months was investigated by scanning electron microscopy, energy dispersive spectroscopy, X-ray diffraction, and electrochemical technology. The corrosion kinetics of 700L steel followed the exponential function: D = 4.85t^1.23. The rust layers were mainly composited of γ-FeOOH, α-FeOOH, γ-Fe₂O₃, and Fe₃O₄, regardless of the exposure duration. With an extended exposure time, the porosity, cracking, and spalling of the rust layers increased, and the densification and thickness uniformity decreased. Electrochemical measurements displayed that the corrosion resistance of the rusted 700L steel gradually decreased with increasing exposure time. A good correlation was found between rust layer composition, microstructure, and corrosion resistance. Full article

The beam-to-column connection is a particularly vulnerable element in frame structures under seismic action and is often responsible for building damages. Experimental investigations carried out over the past six decades on shear strength in frame joints have not led to the establishment of a uniform procedure in the design codes of different countries. The reason lies probably in the varied nature of the investigated parameters and in the varied configurations of beam–column connections. A good knowledge of the forces passing through the frame joints in the beam–beam and column–column direction would allow both their adequate computation in new buildings and the verification of existing ones without requiring experimental studies. In the design codes of the leading countries in seismic engineering, the shear force is determined by the capacitive method, considering only the area of the longitudinal reinforcement of the beam passing through the column. This method shows us how much shear force the beam reinforcement can take, but not what the magnitude of the resulting forces actually is as a result of the acting loads. In addition, the method of the codes does not indicate the contribution of the concrete to the total magnitude of the shear force in the beam–column connection. In the proposed mathematical model for calculating the forces that leave the beam, the full dimensions of the cross-section of the beam were taken into account. The material properties and cross-sectional shape were also taken into account. A determining factor for the magnitude of forces entering the beam–column joint is the acting load on the beam. In this paper, the load of two transverse forces was considered. The forces are applied in different possible positions, while remaining symmetrically located on the beam. The calculations are based on Menabrea’s theorem to determine the hyperstatic unknowns. The results of the proposed method for the considered beam show that the magnitude of the shear force differs from that accepted in the literature and the norms by 2% to 27%, depending on the stage of development of the crack. In comparison, the Eurocode-recommended method shows differences in the order of 27% to 40% for the adopted beam under static loads. Full article

High-performance concrete (HPC) is commonly used in the main structures of bridges. HPC is widely applied in the main structures of bridges, yet some skepticism remains with integrating fly ash and mineral powder as admixtures into prestressed HPC bridges. To address this, this study conducted scaled-model experiments to analyze the flexural fatigue behavior of prestressed HPC bridges with double-mineral fine powder admixtures (PB-DA). This study derives the similarity criteria for a simply supported beam bridge under a concentrated load based on similarity theory. Subsequently, in following these criteria, a 30 m long actual bridge is scaled down to a 6 m PB-DA at a 1:5 scale. For this scaled PB-DA, the concentrated load is reduced to 1/25 of the actual bridge, while the strain remains the same as in the actual bridge. The double-mineral fine powder admixture (D-A) was produced and used to fabricate PB-DA by mixing fly ash and mineral powder. Five PB-DAs were constructed, with C50 and C80 concrete strength grades, and admixture ranges from 10% to 32%. Sinusoidal half-wave constant stress amplitude loading at 5 Hz frequency was applied, with 2 million fatigue loading cycles. After fatigue loading, a continuously increasing static load was applied until the PB-DA failed. The experimental results show that the upper part of the PB-DA is compressed, and the lower part is in tension. The PB-DA strain distribution from top to bottom generally conforms to the plane section assumption. During 2 million fatigue loading cycles, 200,000 cycles mark the beam strain and stiffness evolution boundary. Below 200,000 cycles, the PB-DA strain rapidly increases, and flexural stiffness quickly decreases. Beyond 200,000 cycles, the rate of increase in strain and the rate of decrease in flexural stiffness significantly slow down. After fatigue loading, the PB-DA displacement increases exponentially under a continuously increasing static load. The crack distribution is uniform across all PB-DA, with the cracks being sparsest at a 30% admixture. A comprehensive analysis shows that all PB-DAs demonstrate good flexural fatigue behavior. Notably, when D-A content reaches 30%, strain increases, but reductions in flexural stiffness and damage in PB-DA significantly decrease. This paper’s conclusions provide a reference for applying D-A at PB-DA. Full article

On the basis of existing experimental studies on web-opening wood composite beams, six new types of reinforcement were proposed in this study. The effects of different reinforcement measures on mechanical properties such as the load-carrying capacity, deformation capacity, internal force distribution law, and force transfer mechanism of web-opening wood composite beams were investigated. The results show that the stress distribution in the opening area is more uniform after reinforcement, and the influence of different reinforcement measures changes the damage mode of the whole beam. The setting of reinforcement measures in the opening area can effectively inhibit and slow down the generation and development of the cracks in the opening area of the web opening and reduce the negative influence of the composite beam caused by the opening. With reinforcement, the allowable and ultimate bearing capacity of wood composite beams can be increased by 3%~21% and 28%~59%; the redistribution of shear force occurs in the opening area after reinforcement, and plywood and cold-formed thin-walled section (CFTWS) help to bear 14%~76% of the value of shear force in the opening area. The most effective reinforcement measures are bolts–epoxy–CFTWS. Full article

The crack resistance of concrete structures with low reinforcement ratios requires a broader examination. It is particularly important in the case of foundations working in changing subsoil conditions. Unfavorable phenomena occurring in the subsoil (e.g., ground subsidence, landslips, non-uniform settlement) can lead to unexpected cracking. Therefore, it is necessary to check the effectiveness of the low reinforcement provided. As there are limited studies on lightly reinforced concrete structures, we performed our own experimental investigation and numerical calculations. In the beams analyzed, the reinforcement ratio varied from 0.05% to 0.20%. It was found that crack resistance in concrete members depends on the reinforcement ratio and steel bar distribution. A comprehensive method was proposed for estimating the crack resistance of lightly reinforced concrete members in which both the reinforcement ratio and the reinforcement dispersion ratio were taken into account. Furthermore, the method considered the size effect and the fracture properties of concrete. The proposed method provides the basis for extrapolation of the test results obtained for small elements and conclusions for members with large cross-sections, such as foundations, which frequently use lightly reinforced concrete. Full article