Search Results (80)

Microorganisms present in asphalt pavement service environments can alter the composition of asphalt through metabolic activities, thereby affecting its rheological properties. To investigate this influence and compare performance variations across asphalt types, two asphalt-degrading bacterial strains were isolated from in-service pavements. Following 16S rRNA gene sequencing and phylogenetic analysis, the strains were identified as Pseudomonas putida and a putative novel species within the Citrobacter genus. Using a custom-designed thin-film inoculation system, the performance evolution of base asphalt and styrene-butadiene-styrene (SBS) modified asphalt was systematically evaluated after microbial activity periods of 5, 10, and 15 days. Conventional property tests and multi-temperature rheological analyses (temperature sweep, multiple stress creep recovery test, linear amplitude sweep, 4 mm DSR) were conducted. Results demonstrated that microbial action reduced penetration, elevated softening point, and decreased ductility in both asphalt types, with more pronounced changes observed in base asphalt. High-temperature rheological parameters (G*/sinδ), recovery rate, and non-recoverable creep compliance indicated compromised resistance to permanent deformation. SBS-modified asphalt substantially mitigated these detrimental effects. Fatigue life of base asphalt decreased overall with periodic fluctuations, whereas SBS-modified asphalt exhibited superior fatigue stability: after an initial decline at 5 days, performance recovered and stabilized between 10 and 15 days. Low-temperature performance showed slight improvement in base asphalt, while SBS-modified asphalt demonstrated significant enhancement during later activity stages. Full article

CoCrFeNiMn high entropy alloy (HEA) fabricated via laser-based powder bed fusion (PBF-LB/M) exhibits exceptional mechanical properties, including high strength, better ductility than titanium alloy, and superior corrosion resistance. This study simulates the intergranular fracture behavior of PBF-LB/M CoCrFeNiMn HEA under tensile loading by embedding cohesive elements with damage mechanisms into polycrystalline representative volume elements based on the crystal plasticity finite element method. The simulation results show good agreement with reported experimental stress–strain curves, demonstrating that the crystal plastic constitutive model combined with the cohesive constitutive model can accurately describe both the macroscopic response behavior and fracture failure behavior of the CoCrFeNiMn HEA. Furthermore, this work investigates the mechanical properties of the HEA in different tensile directions, the improvement of anisotropy through columnar-to-equiaxed grain transition, and the effect of texture strength on crack initiation and propagation. The results show that the polycrystalline CoCrFeNiMn HEA exhibits anisotropic mechanical properties: simulated yield strengths (YSs) are 436.9 MPa (in the scanning direction) and 484.7 MPa (in the building direction), tensile strengths (TSs) reach 639 MPa and 702.5 MPa, and elongations (ELs) are 10.6% and 21.8%, respectively. After equiaxed grain formation, the EL in the scanning direction increased from 10.6% to 17.2%, while the EL in the building direction decreased from 21.8% to 20.3%. Concurrently, the anisotropy coefficients of YS, TS, and EL decreased by 1.8%, 2.2%, and 36.1%, respectively. The cracks initiate at stress concentrations and subsequently propagate along grain boundaries until final fracture. Variations in texture strength significantly influence the crack initiation location and propagation path in the CoCrFeNiMn HEA. Full article

To reduce the carbon footprint of the concrete industry and promote a circular economy, this study explores the reuse of waste materials such as glass powder (GP) and nitrile rubber (NR) fibres in concrete. However, the inclusion of these waste materials results in lower compressive strength compared to conventional concrete, limiting their application to non-structural elements. To overcome this limitation, this study adopts the concept of confined concrete by developing concrete-filled steel tube (CFST) stub columns. In total, twelve concrete mix variations were developed, with and without steel tube confinement. GP was utilised at replacement levels of 10–30% by weight of cement, while NR fibres were introduced at 0.5% and 1% by volume of concrete. The findings demonstrate that the incorporation of GP and NR fibres leads to a reduction in compressive strength, with a compounded effect observed when both materials are combined. Steel confinement within CFST columns effectively mitigated the strength reductions, restoring up to 17% of the lost capacity and significantly improving ductility and energy absorption capacity. All CFST columns exhibited consistent local outward buckling failure mode, irrespective of the concrete mix variations. A comparison with predictions from existing design codes and empirical models revealed discrepancies, underscoring the need for refined design approaches for CFST columns incorporating sustainable concrete infill. This study contributes valuable insights into the development of eco-friendly, high-performance structural systems, highlighting the potential of CFST technology in facilitating the adoption of waste materials in the construction sector. Full article

This study investigates the effects of repeated mechanical recycling on the structural, thermal, mechanical, and aesthetic properties of poly(butylene succinate) (PBS), a commercially available bio-based and biodegradable aliphatic polyester. PBS production scraps were subjected to five consecutive recycling cycles through semi-industrial extrusion compounding followed by injection molding to simulate realistic mechanical reprocessing conditions. Melt mass-flow rate (MFR) analysis revealed a progressive increase in melt fluidity. Initially, the trend of viscosity followed the melt flow rate; however, increasing the reprocessing number (up to 5) resulted in a partial recovery of viscosity, which was caused by chain branching mechanisms. The phenomenon was also confirmed by data of molecular weight evaluation. Differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) confirmed the thermal stability of the polymer, with minimal shifts in glass transition, crystallization, and degradation temperatures during the reprocessing cycles. Tensile tests revealed a slight reduction in strength and stiffness, but an increase in elongation at break, indicating improved ductility. Impact resistance declined moderately from 8.7 to 7.3 kJ/m² upon reprocessing; however, it exhibited a pronounced reduction to 1.8 kJ/m² at −50 °C, reflecting brittle behavior under sub-ambient conditions. Despite these variations, PBS maintained excellent color stability (ΔE < 1), ensuring aesthetic consistency while retaining good mechanical and thermal properties. Full article

Although asphalt mixtures can be applied to railway tracks due to their viscoelastic properties, caution is required, as their ductility and brittleness are highly sensitive to temperature variations. In recent years, interest in the application of asphalt in railway infrastructure has increased, driven by the development of modified mixtures and the broader availability of performance-enhancing additives. Additionally, evaluation methods for railway tracks should be adapted to account for the distinct loading mechanisms involved, which differ from those of conventional roadways. In this study, the comprehensive properties of asphalt binders, mixtures, and testing methods—including physical and engineering characteristics—were assessed to improve the performance of asphalt concrete layers for potential applications in railroad infrastructure. The results of this study indicate that (1) the higher the performance grade (PG), the higher the indirect tensile strength (ITS) value achieved by the 13 mm mixture using PG76-22, which is higher than that of the PG64-22 mixture. This indicates that higher PG grades and modification contribute to improved tensile strength, beneficial for upper layers subjected to dynamic railroad loads. (2) The tensile strength ratio (TSR) increased from the unmodified mixture to over 92% in mixtures containing crumb rubber modifier (CRM) and styrenic thermoplastic elastomer (STE), demonstrating enhanced durability under freeze–thaw conditions. (3) Wheel tracking test results showed that modified mixtures exhibited more than twice the rutting resistance compared to PG64-22. The 13 mm aggregate mixtures also generally performed better than the 19 mm mixtures, indicating reduced permanent deformation under repeated loading. (4) It was concluded that asphalt is a suitable material for railroads, as its overall characteristics comply with standard specifications. Full article

The extreme environment of aerospace requires severe material properties, and in situ autogenous ZrC–NbC dual-phase reinforced titanium matrix composites have attracted much attention. In this study, TiC/Ti composites (TMC1–TMC4) with different NbC contents (0–9 wt%) were prepared and investigated in depth by various means and ANSYS simulations. The results show that the variation in NbC content significantly changes the TiC morphology from fine needles at 0 wt% to needles with a small amount of ellipsoidal grains at 3 wt%, to an ideal uniform distribution (mostly granular or nearly spherical) at 6 wt%, and to a large number of aggregates (dendritic or coarse rod-like) at 9 wt%. In terms of mechanical properties, the compressive strength and elongation firstly increased and then decreased, and reached the optimum at 6 wt% NbC, with the ultimate compressive strength as high as 1379.50 MPa, the compressive yield strength at 817.3 MPa, the compressive strain up to 38.73%, and typical ductile fracture characteristics; at 9 wt%, it transformed into a mixed fracture mode, with a decrease in performance. ZrC and NbC synergistically stabilize the microstructure, with the best synergistic effect at 6 wt% NbC, which effectively improves the overall performance and meets the requirements of aerospace applications. The simulation is highly compatible with the experiment and verifies the experiment; this helps to reveal the mechanism, provides guidance for the design of high-performance materials, and promotes the development of materials technology in the aerospace field. Full article

This study investigates the effects of post-curing temperatures on the tensile properties of hybrid basalt-jute-glass-carbon fiber-reinforced polymers (FRPs). Composite specimens were post-cured at 60 °C and 100 °C for 60 min, and their tensile behavior was assessed using a servo-hydraulic testing machine. Numerical simulations using the Abaqus software V6.14 were also conducted to compare experimental and computational results. The findings indicate that post-curing heat treatment enhances ductility due to increased polymer cross-linking, but excessive heat treatment at 100 °C negatively impacts elongation at fracture. The results revealed that specimens post-cured at 60 °C exhibited the optimal balance between strength and ductility, with increased elongation and moderate tensile strength. However, at 100 °C, while tensile strength improved in some cases, a significant decrease in elasticity and an increased risk of brittleness were observed, suggesting that extreme heat treatment may degrade polymer integrity. Natural fiber composites, particularly jute-based samples, outperformed synthetic composites in terms of elongation and overall mechanical stability. The numerical simulations provided further insights but showed discrepancies with experimental results, mainly due to fiber property variations and fabric waviness, underscoring the challenges of accurately modeling woven composites. The study highlights the importance of controlled post-curing temperatures in optimizing the mechanical performance of FRP composites, with 60 °C identified as the most effective condition for achieving a favorable balance between tensile strength, flexibility, and material durability. These findings offer valuable insights for material scientists and engineers working on the development of high-performance composite materials for structural and industrial applications. Full article

The finite-element model was developed using ABAQUS to investigate the hysteretic properties of space joints. This study examined the effects of axial compression ratio, T-plate stiffness, column wall thickness, and bolt-preload on the joint’s hysteretic behavior. The model was verified by comparing the failure modes, hysteresis curves, and skeleton curves of the specimens with the test results of the relevant literature, ensuring the reliability of the research. The results reveal three primary failure modes: beam flange buckling, T-plate buckling, and column-wall buckling; increasing the thickness of the T-plate web or column wall significantly enhances joint stiffness and mitigates brittle failure. Specifically, the stiffness of T-plate 1 has a substantial impact on joint performance, and it is recommended that its web thickness be no less than 18 mm. In contrast, variations in the thickness of T-plate 2 have negligible effects on seismic performance. Increasing the column wall thickness improves the bearing capacity and stiffness of the joint, with a recommended minimum thickness of 12 mm, which should not be less than the flange thickness of the steel beam. While an increase in the axial compression ratio reduces the bearing capacity and stiffness, it enhances the energy dissipation capacity and ductility of the joint. Notably, variations in bolt-preload were found to have minimal influence on joint performance. These findings provide valuable insights for optimizing the design of unilateral bolted joints in steel structures to improve seismic resilience. Full article

Concrete-filled steel tube (CFST) columns reinforced with latticed steel angles (LSA), referred to as CFST-LSA columns, have been widely adopted in practical engineering. Understanding their mechanical behavior under eccentric loading is crucial for ensuring structural safety and performance in engineering applications. Previous experimental studies have demonstrated that the incorporation of steel angles substantially improves both the axial capacity and ductility of CFST-LSA columns. Existing methods for determining the eccentric bearing capacity of CFST-LSA columns primarily rely on the normalized N/N_u-M/M_u interaction curve. However, this approach involves a complex calculation procedure for evaluating the eccentric bearing capacity. To address this limitation, this study proposes a theoretical model based on the limit equilibrium method to predict the eccentric bearing capacity of CFST-LSA columns. The proposed model explicitly integrates fundamental geometric and material parameters, thereby enabling a more efficient and programmable calculation of the eccentric bearing capacity. Comparisons between the proposed model and experimental results show good agreement, with a tested-to-predicted eccentric resistance ratio of 1.085 and a coefficient of variation (COV) of 0.022. The proposed model can serve as a practical calculation method for eccentric loading of CFST-LSA columns, facilitating their application in high-rise buildings and long-span bridges. Full article

The seismic performance assessment of timber structures and topology optimization have been widely researched in recent years. Furthermore, the use of wood as a construction material has increased due to new sustainability challenges. This research assesses the seismic performance of a topologically optimized timber building located in Concepcion, Chile. The structure is a five-story glulam braced frame, designed following current Chilean standards. The structural configuration was obtained through a topology optimization process using a variation of a soft-kill BESO algorithm implemented in MATLAB R2015a, obtaining topologies with low structural redundancy. For the analysis, a full 3D nonlinear model was prepared using OpenSees (Version 3.7.1), and the nonlinear behavior of the structure was only considered at joints using the backbone curves introduced in ASCE 41-13. Six different study cases were analyzed, varying joint strengths and ductility. The fragility curves were determined from a static pushover analysis (SPO) using SPO2FRAG (V1.1), considering the performance levels established in ASCE 41-13. The seismic hazard of the building’s site is estimated through a probabilistic seismic hazard analysis (PSHA), and the seismic performance of each case is determined by computing the probabilities of exceedance of the considered limit states. Analysis results show that wood braced-frame structures with low structural redundancy (and fewer main joints to dissipate energy), such as those obtained from topology optimization algorithms, exhibit a markedly brittle behavior with almost no displacement ductility. This undesirable behavior does not improve by providing more deformation capacity to this structure’s reduced number of main joints. Currently, the Chilean standard for seismic design requires a unique response modification factor R for wood structures. This research suggests that this requirement should be revisited, specifying different R values depending on the wood structure’s redundancy, considering that its displacement ductility comes almost exclusively from the nonlinear deformation capacity of joints. Full article

Establishing dependable and resilient methodologies for identifying damage that may compromise the integrity of reinforced concrete (RC) infrastructures is imperative for preventing potential catastrophic failures. Continuous evaluation and Structural Health Monitoring (SHM) can play a key role in extending the lifespan of new or existing buildings. At the same time, early crack detection in critical members prevents bearing capacity loss and potential failures, enhancing safety and reliability. Furthermore, implementing discrete fibers in concrete has significantly improved the ductility and durability of Fiber-Reinforced Concrete (FRC). The present study employs a hierarchical clustering analysis (HCA) to identify damage in FRC by analyzing the raw Electromechanical Impedance (EMI) signature of piezoelectric lead zirconate titanate (PZT) transducers. The experimental program consisted of three FRC standard cylinders subjected to repeated loading. The loading procedure consists of 6 incremental steps carefully selected to gradually deteriorate FRC’s structural integrity. Additionally, three PZT patches were adhered across the height of its specimen using epoxy resin, and their EMI response was captured between each loading step. Subsequently, the HCA was conducted for each PZT transducer individually. The experimental investigation demonstrates the efficacy of HCA in detecting load-induced damage in FRC through the variations in the EMI signatures of externally bonded PZT sensors. Full article

High-temperature-resistant materials, such as stainless steel and cast steel, are widely used in industrial applications. While cast steel has a lower casting ability, cast iron demonstrates a superior casting performance but suffers from structural instability in thin sections, in which its phase structure tends to shift from graphite to cementite. This limits its applicability in thin-walled components. This study aims to characterize thin-walled ductile cast iron with improved high-temperature resistance. The focus is on evaluating the effects of Fe-Mg inoculation with the addition of nickel on the microstructure and mechanical properties of the material. Gray cast iron was cast and inoculated with Fe-Mg and nickel. Mold designs incorporated thickness variations of two, three, four, and five mm. Chemical composition testing was performed in the liquid state using a CE meter and in the solid state using a spectrometer, following ASTM A536 standards for ductile cast iron. A microstructural analysis was conducted using a scanning electron microscope (SEM) JEOL JSM-IT500 SEM (JEOL Ltd., Tokyo, Japan), and hardness was measured using the Vickers method. The results demonstrated that Fe-Mg inoculation with the nickel addition improved the microstructure and hardness of the thin-walled ductile cast iron. These enhancements contribute to increased high-temperature resistance and structural integrity, providing significant benefits for industrial casting processes. The findings have implications for improving the quality of small and medium industry (SMI) products, including the development of advanced metal molds. Full article

AISI 304L is a low-carbon austenitic stainless steel widely used in common engineering applications, according to its good mechanical properties such as high ductility, corrosion resistance, and easy weldability. This material is adopted in various environmental conditions, such as pressure vessels or in pipelines where fluid temperature variations occur and affect its mechanical behavior. Nowadays, the applications of advanced investigation methodologies, such as infrared thermography, are widely adopted for the rapid analysis of the fatigue properties of common materials, especially metals. In this work, fatigue properties were evaluated on AISI304L specimens having two different microstructural states, one in the as-received condition and the other one after solution annealing. Fatigue test campaigns were performed with the application of the Risitano Thermographic Method. The microscopic analysis highlights the differences in the microstructure before and after the heat treatment. The characteristics of the microstructures are the main ones responsible for the different fatigue behavior obtained with experimental tests. The Thermographic Method proved to be a valid rapid approach for the fatigue analysis, confirming that the annealing process led to an improvement in the fatigue strength of the material. Full article

Flat slabs supported by columns without beams are widely used in construction owing to their economy and efficiency. However, brittle punching shear failure at slab–column connections can cause progressive collapse. UHPC has a higher tensile strength than NSC and, when appropriately reinforced with steel fibers, exhibits strain hardening after initial cracking. These properties make Ultra-High-Performance Concrete (UHPC) ideal for durable, thin, low-cost bridge decking and heavily loaded elements and an excellent choice for improving slab–column connections that have experienced punched shear failure. This study explores the impact of UHPC layers on the punching shear behavior of reinforced concrete slabs. Sixteen slab specimens were tested with variations in UHPC layer thickness, placement, and column shape. Results demonstrate that incorporating UHPC layers significantly enhances punching shear resistance, increasing ultimate load capacity by 27–91% compared to reference specimens. Notably, thicker UHPC layers (75 mm) and bottom-placed layers exhibited superior performance in terms of ductility and toughness. Square columns outperformed circular ones in resisting punching shear. Additionally, thicker layers reduced initial stiffness, while debonding issues in 25 mm layers adversely affected structural performance. This research provides valuable insights for optimizing UHPC configurations to improve the punching shear resistance of concrete slabs, offering promising solutions for high-load structures in modern construction. Full article

This research presents a simplified approach using a uniaxial restoring force model to analyze the seismic response of recycled aggregate concrete (RAC) frames. Nonlinear simulations were conducted to explore how factors like axial compression ratio, reinforcement ratio, and cross-sectional geometry affect the ductility and seismic performance of RAC sections. The findings reveal that a reduction in the axial compression ratio from 0.60 to 0.57 results in a 15% increase in ductility, while a higher reinforcement ratio leads to a 20% enhancement. In addition, rectangular sections were found to be more sensitive to variations in material strength than square sections, offering key insights for structural optimization. The method proposed here also enhances computational efficiency by minimizing resource consumption and improving the convergence of nonlinear iterative procedures. These findings provide a theoretical foundation for optimizing the design and seismic evaluation of RAC structures, promoting their broader application in engineering practice. Full article