Search Results (3,281)

Magnesium phosphate cement (MPC) exhibits brittleness when utilized as a repair material for bridge decks. To address this issue, this study employs nano-TiO₂ (NT) and a novel material (basalt fiber bar) as modifiers. A double-K fracture model is developed for the modified MPC to quantitatively evaluate the enhancement of fracture toughness induced by NT and basalt fiber bars. The cracking behavior and toughening mechanisms of the NT and basalt fiber bar reinforced MPC are investigated using extended finite element theory and composite material theory. Additionally, a formula is proposed to calculate the incremental fracture toughness of NT and basalt fiber bar reinforced MPC. The results indicated that NT and basalt fiber bar can effectively enhance the ultimate bending capacity of MPC. The improvement increases with the fiber volume fraction, and noticeable bending hardening occurs when the fiber content exceeds 2%. With the same fiber volume fraction, the peak load can be increased by up to 11.7% with the addition of NT. The crack initiation toughness of the NT group without basalt fiber bars is 58% higher than that of the CC group. The content and diameter of basalt fiber bar are critical parameters affecting the toughness of the NT and basalt fiber bar reinforced MPC. Full article

Research on raw materials for Al₂O₃-SiC-C refractory castables used in blast furnace troughs is relatively well established. However, gaps remain in both laboratory and industrial trials concerning the performance of castables incorporating SiC-modified flake graphite and alternative carbon sources. This study investigated the sintering behavior, mechanical properties, and service performance of Al₂O₃-SiC-C castables utilizing varying contents of modified flake graphite, pitch, and carbon black as carbon sources. Samples were characterized using SEM, XRD, and EDS for phase composition and microstructural morphology analysis. Key findings revealed that the thermal expansion mismatch between the SiC coating and flake graphite in SiC-modified graphite generated a microcrack-toughening effect. This effect, combined with the synergistic reinforcement from both components, enhanced the mechanical properties. The SiC modification layer improved the wettability and oxidation resistance of the flake graphite. This modified graphite further contributed to enhanced erosion resistance through mechanisms of matrix pinning and crack deflection within the microstructure. However, the microcracks induced by thermal mismatch concurrently reduced erosion resistance, resulting in an overall limited net improvement in erosion resistance attributable to the modified graphite. Specimens containing 1 wt.% modified flake graphite exhibited the optimal overall performance. During industrial trials, this formulation unexpectedly demonstrated a water reduction mechanism requiring further investigation. Full article

The superb dynamic performance of steel-plate composite (SC) structures under unexpected impact loading depends on the good design of the connection between the SC wall and foundation. This study investigated the flexural behavior and dynamic responses of SC wall-to-foundation connections subjected to low-velocity impact. Impact tests were performed on three SC connection specimens to evaluate failure mode, impact force, deflection, and strain responses. The effects of concrete strength grade and impact energy were analyzed in detail. All specimens exhibited flexural failure, with three distinct stages observed during impact. The experimental results demonstrated that compared to the specimen with C30 concrete, the specimen with C50 concrete significantly reduced wall damage, decreased deflections, and enhanced deflection recovery ability. It can be concluded that increasing the concrete strength grade effectively improves the impact resistance of SC wall-to-foundation connections. In addition, peak impact force, global deflection response, residual strains, and interface crack length were highly sensitive to changes in impact energy, whereas deflection recovery exhibited lower sensitivity. Furthermore, a finite element model was developed and validated against experimental results. Parametric studies explored the influence of key parameters with expanded ranges on the impact responses of SC wall-to-foundation connections. Full article

This study evaluates the influence of fiber type, geometry, and interfacial behavior on the physical and mechanical performance of cementitious composites reinforced with recycled pulp from beverage cartons (RPBC), bamboo fiber (BF), and eucalyptus fiber (EF) as the sole reinforcing agents. The BF was rounded in shape and had the highest aspect ratio, while the ribbon-shaped EF exhibited the highest tensile strength index. The RPBC fibers were fibrillated and the shortest, with a ribbon shape. Flexural strength results showed that RPBCC achieved a maximum strength that was 47.6% higher than the control specimen (0% fiber), outperforming both BF- and EF-reinforced counterparts. This superior performance is attributed to the higher fibrillation level of the ribbon-shaped RPBC fibers, which promoted better fiber–matrix bonding. As the fiber content increased, the bulk density of EFC and BFC decreased linearly, while RPBC composites showed only a modest decrease in density. Porosity steadily increased in EFC and BFC, whereas a non-linear trend was observed in RPBCC, likely due to its unique morphology and fibrillation. Conversely, EFC exhibited significantly higher maximum fracture toughness (3600 J/m² at 10 wt.%) compared to PBFCC (1600 J/m² at 14 wt.%) and BFC (1400 J/m² at 14 wt.%). This enhancement is attributed to extensive fiber pullout mechanisms and increased energy absorption during crack propagation. Overall, all composite types demonstrated flexural strength values above 4 MPa, placing them in the Grade I category. Those reinforced with 10–14% RPBC exhibited strengths of 11–12 MPa, categorizing them as Grade II according to ASTM C1186-02. Full article

Aluminum matrix composites provide an ideal solution for lightweight brake disks, but conventional casting processes are prone to crack initiation due to inhomogeneous reinforcement dispersion, gas porosity, and inadequate toughness. To break the conventional trade-off between high wear resistance and low toughness of brake disks, this study fabricated a bimetallic structure of SiC_p/Al–Fe–V–Si aluminum matrix composite and cast ZL101 alloy using friction stir lap welding (FSLW). Then, the microstructural evolution, mechanical properties, and tribological behavior of the FSLW joints were studied by XRD, SEM, TEM, tensile testing, and tribological tests. The results showed that the FSLW process homogenized the distribution of SiC particle reinforcements in the SiC_p/Al–Fe–V–Si composites. The Al₁₂(Fe,V)₃Si heat-resistant phase was not decomposed or coarsened, and the mechanical properties were maintained. The FSLW process refined the grains of the ZL101 aluminum alloy through recrystallization and fragmented eutectic silicon, improving elongation to 22%. A metallurgical bond formed at the joint interface. Tensile fracture occurred within the ZL101 matrix, demonstrating that the interfacial bond strength exceeded the alloy’s load-bearing capacity. In addition, the composites exhibited significantly enhanced wear resistance after FSLW, with their wear rate reduced by approximately 40% compared to the as-received materials, which was attributed to the homogenized SiC particle distribution and the activation of an oxidative wear mechanism. Full article

In this study, the atmospheric corrosion behavior of AZ31 magnesium alloy exposed in Sanya and Nansha for one year was investigated. While existing studies have characterized marine corrosion of magnesium alloys, the synergistic corrosion mechanisms under extreme tropical marine conditions (simultaneous high Cl⁻, rainfall, and temperature fluctuations) remain poorly understood—particularly regarding dynamic corrosion–product evolution. The corrosion characteristics and behavior of AZ31 magnesium alloy exposed in Sanya and Nansha were evaluated using X-ray photoelectron spectroscopy, X-ray diffraction, electrochemical measurements, scanning electron microscopy, and weight loss tests. The results showed that the main components of corrosion products were MgCO₃·xH₂O(x = 3, 5), Mg₅(CO₃)₄(OH)₂·4H₂O, Mg₂Cl(OH)₃·4H₂O, and Mg(OH)₂. The corrosion rate exposed in the Nansha was 26.5 μm·y⁻¹, which was almost two times than that in Sanya. Localized corrosion is the typical corrosion characteristic of AZ31 magnesium alloy in this tropical marine atmosphere. This study exposes the dynamic crack–regeneration mechanism of corrosion products under high-Cl⁻-rainfall synergy. The corrosion types of AZ31 magnesium alloy in this tropical marine atmosphere were mainly represented by pitting corrosion and filamentous corrosion. Full article

This investigation employs focused ion beam (FIB) and transmission electron microscopy (TEM) techniques to systematically analyze the distribution characteristics of fission products in medium-burnup (40.6 GWd/tU) UO₂ fuel and their impact on fuel cracking behavior. The findings indicate that grain boundary embrittlement is predominantly attributed to the accumulation of spherical particles of solid fission products, including Mo, Ru, Rh, and Pd, which preferentially segregate around impurity particles, leading to localized stress concentration. Intragranular cracks are associated with the strip-like segregation of fission elements and the amorphization process. It also reveals that the size and number density of intragranular Xe bubbles are ~6.24 ± 0.24 nm and 5.2 × 10²² m⁻³, respectively, while Xe did not, under the analyzed conditions, significantly influence crack nucleation. This research elucidates the correlation mechanism between fission product distribution and fuel cracking behavior at medium burn up, offering experimental evidence to enhance the reliability and safety of nuclear fuel assemblies. Full article

This study investigates the impact of partially replacing cement with fly ash (FA) on the mechanical performance of fiber-reinforced rubberized concrete (FRRC) incorporating waste tyre rubber and recycled macro-synthetic fibers (MSF). FRRC mixtures were prepared with varying fly ash replacement levels (0%, 25%, and 50%), rubber aggregate contents (0%, 10%, and 20% by volume of fine aggregate), and macro-synthetic fiber dosages (0% to 1% by total volume). The fresh properties were evaluated through slump tests, while hardened properties including compressive strength, splitting tensile strength, and flexural strength were systematically assessed. Results demonstrated that fly ash substitution up to 25% improved the interfacial bonding between rubber particles, fibers, and the cementitious matrix, leading to enhanced tensile and flexural performance without significantly compromising compressive strength. However, at 50% replacement, strength reductions were more pronounced due to slower pozzolanic reactions and reduced cement content. The inclusion of MSF effectively mitigated strength loss induced by rubber aggregates, improving post-cracking behavior and toughness. Overall, an optimal balance was achieved at 25% fly ash replacement combined with 10% rubber and 0.5% fiber content, producing a more sustainable composite with favorable mechanical properties while reducing carbon and ecological footprints. These findings highlight the potential of integrating industrial by-products and waste materials to develop eco-friendly, high-performance FRRC for structural applications, supporting circular economy principles and reducing the carbon footprint of concrete infrastructure. Full article

Railway axles are among the most safety-critical components in rolling stock, as their failure can lead to catastrophic consequences. One of the most subtle damage mechanisms affecting these components is fretting fatigue, which is a particularly challenging damage mechanism in these components, as it can initiate cracks under real service conditions and is difficult to detect in its early stages, which is vital to ensure operational safety and to optimize maintenance strategies. This paper focuses on the development of fretting fatigue damage in solid railway axles under realistic service-like conditions. Full-scale axle specimens with artificially induced notches were subjected to loading conditions that promote fretting fatigue crack initiation and growth. Acoustic emission techniques were used to monitor the damage progression, and post-processing of the emitted signals, by using wavelet-based tools, was conducted to identify early indicators of crack formation. The experimental findings demonstrate that the proposed approach allows for reliable identification of fretting-induced crack initiation, contributing valuable insights into the in-service behavior of railway axles under this damage mechanism. Full article

The study investigates the influence of microstructures on fatigue behavior and failure mechanisms of the α-β titanium alloy Ti6246, fabricated via Powder Bed Fusion-Laser Beam (PBF-LB). In particular, the investigation assesses the effect of two post-processing heat treatments, namely α-β annealing at 875 °C (AN875) and solution treatment at 825 °C followed by aging at 500 °C (STA825), on the alloy’s rotating and bending fatigue behavior. The results indicate that the STA825 condition provides superior fatigue resistance (+25%) compared to AN875, due to the presence of a finer bilamellar microstructure, characterized by thinner primary α lamellae (α_p) and a more homogeneous distribution of secondary α lamellae (α_s) within the β matrix. Additionally, an investigation conducted using the Kitagawa–Takahashi (KT) approach and the El-Haddad model, based on the relationship between the fatigue limit and defect sensitivity, revealed improved crack propagation resistance from pre-existing defects (ΔK_th) for the STA825 condition compared to AN875. Notably, the presence of fine α_s after aging for STA825 is effective in delaying crack nucleation and propagation at early stages, while refined α_p contributes to hindering macrocrack growth. The fatigue behavior of the STA825-treated Ti6246 alloy was even superior to that of the PBF-LB-processed Ti64, representing a viable alternative for the production of high-performance components in the automotive and aerospace sectors. Full article

This review presents a comprehensive synthesis of recent advances in the tensile performance of adhesively bonded joints, focusing on applied aspects and modeling developments rather than providing a full theoretical analysis. Although many studies have addressed individual joint types or modeling techniques, an integrated review that compares joint configurations, modeling strategies, and performance optimization methods under tensile loading remains lacking. This work addresses that gap by examining the mechanical behavior of key joint types, namely, single-lap, single-strap, and double-strap joints, and highlighting their differences in stress distribution, failure mechanisms, and structural efficiency. Modeling and simulation approaches, including cohesive zone modeling, extended finite element methods, and virtual crack closure techniques, are assessed for their predictive accuracy and applicability to various joint geometries. This review also covers material and geometric enhancements, such as adherend tapering, fillets, notching, bi-adhesives, functionally graded bondlines, and nano-enhanced adhesives. These strategies are evaluated in terms of their ability to reduce stress concentrations and improve damage tolerance. Failure modes, adhesive and adherend defects, and delamination risks are also discussed. Finally, comparative insights into different joint configurations illustrate how geometry and adhesive selection influence strength, energy absorption, and weight efficiency. This review provides design-oriented guidance for optimizing bonded joints in aerospace, automotive, and structural engineering applications. Full article

This study investigates the impact of two comminution technologies—Vertical Shaft Impactors (VSI) and High-Pressure Grinding Rolls (HPGR)—on gold flotation performance, using ore samples from the Ballarat Gold Mine, Australia. The motivation stems from the growing need to improve energy efficiency and flotation recovery in mineral processing, particularly under increasing economic and environmental constraints. Despite the widespread use of HPGR and VSI in the industry, limited comparative studies have explored their effects on downstream flotation behavior. Laboratory-scale experiments were conducted across particle size fractions (300–600 µm) using two collector types—Potassium Amyl Xanthate (PAX) and DSP002 (a proprietary dithiophosphate collector) to assess differences in flotation recovery, concentrate grade, and specific energy consumption. The results reveal that HPGR produces more fines and micro-cracks, enhancing liberation but also increasing gangue entrainment and energy demand. Conversely, VSI produces coarser, cubical particles with fewer slimes, achieving higher flotation grades and recoveries at lower energy input. VSI at 600 µm demonstrated the highest flotation efficiency (4241) with only 9.79 kWh/t energy input. These findings support the development of hybrid or tailored comminution strategies for improved flotation selectivity and sustainable processing. Full article

This study introduces a time-efficient rotating bending fatigue testing system featuring 11 dual-end spindles, enabling simultaneous testing of 22 specimens. Designed for high-throughput fatigue life (S–N curve) assessment, the system theoretically allows over 93% reduction in total test duration, with 87.5% savings demonstrated in validation experiments using AISI 304 stainless steel. The PLC-based architecture provides autonomous operation, real-time failure detection, and automatic cycle logging. ER16 collet holders are easily replaceable within one minute, and all the components are selected from widely available industrial-grade parts to ensure ease of maintenance. The modular design facilitates straightforward adaptation to different station counts. The validation results confirmed an endurance limit of 421 MPa, which is consistent with the established literature and within ±5% deviation. Fractographic analysis revealed distinct crack initiation and propagation zones, supporting the observed fatigue behavior. This high-throughput methodology significantly improves testing efficiency and statistical reliability, offering a practical solution for accelerated fatigue life evaluation in structural, automotive, and aerospace applications. Full article

HIV disproportionately affects key populations (MSM, transgender people, sex workers and psychoactive substance users), who face greater social vulnerability and limited healthcare access. This study aimed at analyzing sexual orientation and gender identity and their association with sexual practices, sexually transmitted infections and psychoactive substance use among PrEP users. Method: A cross-sectional study was conducted between January 2018 and June 2021 with 736 Brazilian PrEP users from a health service in São Paulo. Sociodemographic data, sexual behaviors, STI history (past 3 months) and psychoactive substances use (past 3 months) were extracted from clinical records. The associations were analyzed using binomial logistic regression (p < 0.05). Results: Most of the participants were cisgender men (93.4%) and homosexual (84.8%), with a mean age of 34.9 years old. Condomless sex was reported by 98.5%, and 18.4% had some recent sexually transmitted infection, mainly syphilis. Psychoactive substance use was reported by 55.4%, especially marijuana, club drugs, erectile stimulants and poppers. Transgender and cisgender women were more likely to report sex work and crack use. Homosexual and bisexual participants had higher odds of using erectile stimulants. Conclusions: The study reveals key links between gender, sexual orientation and risk behaviors, highlighting the need for inclusive, targeted prevention. Full article

This paper evaluates the synergistic effect of polyvinyl alcohol (PVA) fibers and nanosilica (nS) on the mechanical behavior and deformation properties of engineered cementitious composites (ECCs). ECCs have gained a reputation for high ductility, crack control, and strain-hardening behavior. Nevertheless, the next step is to improve their performance even more through nano-modification and fine-tuning of fiber dosage—one of the major research directions. In the experiment, six types of ECC mixtures were made by maintaining constant PVA fiber content (0.5, 1.0, 1.5, and 2.0%), while the nanosilica contents were varied (0, 1, 2, 3, and 5%). Stress–strain tests carried out in the form of compression, together with unrestrained shrinkage measurement, were conducted to test strength, strain capacity, and resistance to deformation, which was highest at 80 MPa, recorded in the concrete with 2% nS and 0.5% PVA. On the other hand, the mixture of 1.5% PVA and 3% nS had the highest strain result of 2750 µm/m, which indicates higher ductility. This is seen to be influenced by refined microstructures, improved fiber dispersion, and better fiber–matrix interfacial bonding through nS. In addition to these mechanical modifications, the use of nanosilica, obtained from industrial byproducts, provided the possibility to partially replace Portland cement, resulting in a decrease in the amount of CO₂ emissions. In addition, the enhanced crack resistance implies higher durability and reduced long-term maintenance. Such results demonstrate that optimized ECC compositions, including nS and PVA, offer high performance in terms of strength and flexibility as well as contribute to the sustainability goals—features that will define future eco-efficient infrastructure. Full article