High Strength Research Articles

The influence of carbon content gradient and carbide precipitation on the microstructure evolution during carburizing-quenching-tempering of 20MnCr5 bevel gear

Due to the mechanism of microstructural transition, high-strength low-carbon alloy steel gears exhibit high strength and surface hardness after Carburizing-Quenching-Tempering (CQT) combined heat treatment, while maintaining good toughness in the core. The carbon potential gradient and the precipitation of carbides are the main factors affecting the final microstructure, yet there is a shortage of related research. To address this gap, this study developed a multi-physics coupled model considering the impact of carbon content to simulate microstructural transformation. Using finite element analysis, we simulated the microstructural evolution during the CQT heat treatment of 20MnCr5 bevel gear. By comparing the simulation results with the calculations from the commercial heat treatment software DANTE®, the accuracy of this model in predicting microstructural distribution and hardness has been validated. Furthermore, the study established a carbide precipitation kinetics model that takes into account the influence of grain size, to investigate the precipitation behavior of carbides within the matrix during the tempering stage. The cellular automaton method was applied to demonstrate the evolution process of the quenched microstructure during tempering. The study shows that during tempering, carbides primarily precipitate in areas with higher carbon content, preferentially at the boundaries of fine grains with a high density of lattice defects. As the carbon content increases, the number density of precipitates rises, while their average radius decreases. The reduction in matrix supersaturation due to carbide precipitation is one of the causes for the reduction of tooth surface hardness during tempering. The model constructed in this study provides a new perspective for understanding the laws governing material microstructural evolution and offers a solid theoretical foundation for the study of stress and deformation during the heat treatment process.

Strength and ductility of concrete columns reinforced with hybrid steel-fiber reinforced polymer composite bars

Using hybrid reinforcement scheme, comprising steel-FRP composite bar (SFCB) and FRP tie, holds great promise in developing seawater sea-sand concrete (SSC) columns with high strength and ductility for marine infrastructures. However, the impacts of FRP tie configurations on hybrid-reinforced SSC columns have not been thoroughly investigated, which hinders their application. To fill this research gap, this study conducted axial compression tests on hybrid-reinforced SSC columns to assess the impacts of tie type, tie size, tie spacing, and tie size/spacing configuration. The failure mechanism of columns, compressive contribution of SFCBs, and confinement mechanism of FRP ties were revealed. The results show that within the tie spacing limit, the failure mode, elastic modulus, yield strength, and ultimate strength of SFCBs are similar. Longitudinal SFCBs effectively resist compression until concrete crushing, providing considerable compressive contributions. However, the confinement efficiency of pultruded FRP ties is limited by the slip of lap splice and the inferior bent portions. In contrast, the closed-type FRP ties exhibit significantly higher confinement efficiency, which increases the load capacity and ductility of columns by 13.6% and 82.8%, respectively. The tie spacing limit was determined and a prediction model of load capacity was proposed based on theoretical analysis and experimental validation.

Turning waste concrete powder into high calcium alkali-activated cementitious materials and artificial aggregates

In order to handle the environmental pollution caused by waste concrete powder, recycled concrete powder (RCP) is utilized to prepare high calcium alkali-activated cementitious materials and artificial aggregates. This study first investigates the high calcium alkali-activated cementitious materials, exploring the effects of different mineral admixtures, liquid-to-solid ratios (L/S), RCP/slag, Na2SiO3 modulus, and Na2O content. The results illustrate that slag powder is the best mineral admixture and the most critical factor affecting cementitious materials. Increasing the slag dosage enhances the generation of C-(A)-S-H, improves the microstructure, and increases compressive strength, with a maximum compressive strength reaching 68.42MPa. According to these test results, the impact of various factors on RCP aggregates is further explored. The results illustrate that the L/S and slag content are primary factors influencing particle size distribution and strength. Increasing these factors leads to larger aggregate particle sizes and higher strength. The compressive strength of the aggregates at 7d reaches 93.24%-99.5% of that at 28d, with a maximum strength of 8.2MPa. Additionally, slag content (10%-30%) and Na2O content significantly impact the physical properties of aggregates, improving apparent density and bulk density while reducing water absorption. To verify the applicability of RCP aggregates, they were used in concrete, and the effects of aggregate strength and replacement rate on concrete performance were explored. The results display that as aggregate strength rises, the mechanical properties of the concrete improve. When RCP aggregates are incorporated, the mechanical properties of the natural concrete decline only slightly (<16.70%). The probability of aggregate damage increases with decreased RCP aggregate strength or increased RCP aggregate content under pressure. RCP aggregate concrete exhibits better shrinkage resistance compared to natural concrete. The process of utilizing RCP is low-energy, non-polluting, and results in high-performance products, making the large-scale effective utilization of RCP feasible.

Coir ropes as a low-tech circular alternative to synthetic ropes in French Polynesia pearl farming

Local coir rope production utilises waste from copra cultivation and could provide a natural alternative to synthetic ropes in French Polynesia’s pearl farming industry. This research aimed to enhance the understanding of coir rope production for pearl farming in the region. Initially, the mechanical properties of coconut fibres were analysed, as well as the construction of ropes made from these fibres. To determine the impact of retting on the mechanical properties of ropes and to assess the relevance of this process, ropes with different retting times in seawater and/or freshwater were tested. A life cycle analysis was also conducted to compare the benefits of locally producing a coir fibre rope versus importing a commercial HDPE rope. Results showed that retting did not significantly affect rope mechanical properties, this polluting process could then be avoided. However, the braiding processes used to make the ropes was proven to influence both mechanical properties and water resistance. It should then be optimised to have coir ropes with higher strength and mechanical properties retention in water, which would also improve their environmental performance, and make them suitable for use as ropes in pearl farming in French Polynesia.

Enhancing Leachate Management with Antibacterial Nanocomposites Incorporating Plant-Based Carbon Dots and Satureja Khuzestanica Essential Oils

Landfill leachate, a complex mixture of pollutants, poses a significant environmental hazard. This study reports the synthesis and characterization of superabsorbent nanocomposites (SANs) designed for enhanced performance in waste management applications. SANs were prepared using carboxymethyl cellulose (CMC) and sodium polyacrylate (SPA) as the main components, carbon dots (CDs) to improve absorption, and Satureja Khuzestanica essential oil (SEO) for antibacterial performance. The results demonstrated that the addition of CDs significantly increased the absorption capacity and liquid retention of the samples, with a water absorption capacity reaching up to 8621%. Furthermore, the samples exhibited high mechanical strength, with tensile strength improving by over 100% in the presence of CDs. The inclusion of SEO provided strong antibacterial activity against Escherichia coli and Staphylococcus aureus, with inhibition zones measuring up to 26mm. These SANs, with their high absorption capacity, mechanical robustness, and antibacterial properties, show great potential for improving waste management practices, particularly in leachate absorption strategies.

Characterization and life cycle assessment of alkali treated abaca fibers: the effect of reusing sodium hydroxide

The increasing demand for natural fibers, driven by their advantageous attributes such as low density, sustainability, and high specific strength, has promoted the adoption of sustainable alternatives in composites. Although alkali treatments are known to improve fiber properties, they entail challenges regarding NaOH consumption and environmental impact, making it necessary to explore cleaner production strategies. This study evaluated the effects of implementing a circular economy approach through the recirculation of an NaOH solution on the treatment of abaca fibers. The fiber properties were assessed using thermogravimetric analysis (TGA), scanning electron microscopy (SEM), and tensile strength testing, along with an evaluation of the carbon footprint through a life cycle assessment. New life cycle inventories were developed to reflect the NaOH recirculation process. Comparative analyses were conducted using polypropylene fibers. The findings indicate that the recirculation of the NaOH solution remains effective for up to eight cycles, producing consistent TGA, SEM, and tensile strength results while achieving a 25 % reduction in the carbon footprint compared to conventional treatment. Additionally, this study highlights the environmental advantages of abaca over synthetic fibers, with increased tensile strength (8–46 %) and carbon footprint reduction (55–86 %) compared to polypropylene fibers. These results highlight the potential of abaca fibers to contribute to the circular economy, enhance resource efficiency, and mitigate climate change.

Strategies for Developing High-Volume Fly Ash Concrete with High Early-Age Strength for Precast Applications

Strategies for Developing High-Volume Fly Ash Concrete with High Early-Age Strength for Precast Applications

Marine sulfated polysaccharide affects the formation mechanism of gelatin emulsion-based oleogels

Protein-polysaccharide delivery systems function as a promising tool to deliver bioactive ingredients aiming to improve their solubility and bioavailability. In this study, gelatin (Gel) and κ-carrageenan (Car) were used to evaluate the characteristics of the Gel-Car emulsion and the emulsion-templated oleogels. Results showed that Car addition significantly reduced the particle size and increased the potential absolute value during emulsion storage, especially for Gel-0.5% Car and Gel-1.0% Car emulsions, indicating Car addition enhanced the emulsion’s stability. The emulsions’ rheological results indicated that all the emulsions exhibited weak gel-like behavior dominated by elasticity, suggesting Car addition improved the emulsions’ shear resistance and viscoelasticity. The emulsions’ instability indices were Gel (0.034), Gel-0.1% Car (0.026), Gel-0.5% Car (0.013), and Gel-1.0% Car (0.011), indicating Car addition enhanced the emulsions’ stability. For oleogels, Car addition significantly reduced the oil loss rate, delayed the thermal degradation, and improved the viscoelasticity, shear resistance, thixotropic recovery properties, and high-temperature resistance, especially for Gel-1.0% Car oleogel. The stability analysis exhibited that Car addition improved the oleogels’ stability, with Gel-0.5% Car oleogel showing the best stability. FFA release was Gel (25.22%), Gel-0.1% Car (26.86%), Gel-0.5% Car (31.38%), and Gel-1.0% Car (39.57%), suggesting Car addition promoted the rapid release of FFA during oleogels digestion. Results above indicated that Gel-Car oleogels exhibited good structural stability and high gel strength, which provide a theoretical basis and new ideas for the preparation of oleogels from protein-marine sulfated polysaccharides using the emulsion template method for food industrial application.

Differential associations of physical job demands with cognitive impairment in Korean workers aged 45 and older: a 14-year longitudinal study using the Korean Longitudinal Study of Aging (KLoSA)

ObjectivesTo investigate the association between subelements of physical job demands and cognitive impairment risk in middle-aged and older workers in Korea.DesignLongitudinal study using eight waves (2006–2020) of the Korean Longitudinal...

Dual-mode immunochromatography based on Ti3C2Tx functionalized CdTe quantum dots for chloramphenicol detection in animal-derived foods

In this study, Ti3C2Tx was coupled with CdTe quantum dots via plyethylenimine (PEI) mediation to form composite nanomaterials with dual colorimetric and fluorescent properties, which had strong pH, high ion strength, and organic solvent resistance. Then, this novel Ti3C2Tx@CdTe was firstly applied to develop a dual-mode immunochromatographic assay (ICA) for chloramphenicol (CAP) detection in animal-derived foods. The limits of detection of the colorimetric and fluorescent modes for CAP in milk/chicken/fish were 0.01 and 0.005 μg/kg, the limits of quantification were 0.025 and 0.016 μg/kg, the recovery rates were between 85.7% and 129.0% and 84.0%-119.2%, with the corresponding variations ranged from 6.5% to 14.8% and 6.4%-14.9%, respectively. The sensitivity of fluorescence mode was up to 100-fold higher than that of the reported ICA for CAP detection. The results of the confirmatory experiment on 30 samples showed good consistency with that of our established method (R2>0.93). The above results indicated that Ti3C2Tx@CdTe had superior detection performance and can provide a dual-mode signal calibration, high stability and sensitivity selection for immunoassay detection platforms.

Direct Ink Writing 3D Printing Elastomeric Polyurethane Aided by Cellulose Nanofibrils.

3D printing of a flexible polyurethane elastomer is highly demandable for its potential to revolutionize industries ranging from footwear to soft robotics thanks to its exceptional design flexibility and elasticity performance. Nevertheless, conventional methods like fused deposition modeling (FDM) and vat photopolymerization (VPP) polyurethane 3D printing typically limit material options to thermoplastic or photocurable polyurethanes. In this research, a water-borne polyurethane ink was synthesized for direct ink writing (DIW) 3D printing through the incorporation of cellulose nanofibrils (CNFs), enabling direct printing of complex, monolithic elastomeric structures at room temperature that can maintain the designed structure. Additionally, a solvent-induced fast solidification (SIFS) method was introduced to facilitate room-temperature curing and enhance mechanical properties. The 3D-printed WPU structures demonstrated strong interfacial adhesion, exhibiting high ultimate tensile strength of up to 22 MPa and an elongation at break of 951%. The 3D-printed WPU structures also demonstrated outstanding resilience and durability, capable of enduring more than 100 cycles of compression and tension as well as withstanding vehicle crushing and heavy lifting. This method also shows suitability for 3D printing complex structures such as a vase and an octopus.

Nanobubble-enabled foam fractionation to remove algogenic odorous micropollutants

Due to climate change and environmental pollution, natural lakes and reservoir water suffer increasingly serious algal blooms and associated water quality problems due to the presence of algal or algogenic organic matter (AOM) such as algal odour and toxins. Effective removal of these micropollutants, especially in the event of algal blooms, is critical to aesthetic values of water bodies, drinking water security and human health. The study investigated the removal efficiency of two common odorous compounds, trans-1,10-dimethyl-trans-9-decalol (geosmin) and 2-Methylisoborneol (2-MIB), using foam fractionation enabled by air nanobubbles with addition of two common cationic and anionic surfactants, sodium dodecyl sulfate (SDS) and cetyltrimethylammonium bromide (CTAB), to enhance foaming ability and stability. The results showed that the cationic surfactant (i.e., CTAB), a low pH, and high ionic strength significantly promoted the removal of geosmin and 2-MIB. For example, the removal tests using the synthetic water determined that the conditions of pH = 7, [CTAB] = 20 mg·L−1 and IS = 10 mM as NaCl resulted in both the highest geosmin removal rate of 91.81% and highest 2-MIB removal rate of 85.0%. The removal of two odorous compounds in real lake water was evaluated, which yielded removal rates of 83.2% for geosmin and 48.1% for 2-MIB, highlighting the minor inhibition from water matrixes on the removal performances. Compared to microbubbles, nanobubbles enabled greater surface areas of foam and higher removal efficiencies. The study provided new insights into the use of foam fractionation with air nanobubbles to enhance the removal of odorous compounds from impaired water and mitigate the negative environmental and health impacts of harmful algal blooms (HABs).

Evaluation of extraction and storage conditions for quantification and characterization of silver nanoparticles in complex samples by single particle-ICP-MS

The extraction of nanoparticles (NPs) from complex matrices and subsequent storage can potentially alter the NPs physicochemical properties and hinder cross-study comparisons. Most NP extraction methods are designed and tested at high nanoparticle concentrations, although (eco)toxicological and regulatory monitoring programs require methods capable of analyzing NPs at environmentally relevant concentrations (lower ppb range). In this study, we investigated how extraction methods affect the characteristics of PVP coated and citrate-stabilized silver NPs (AgNPs) spiked into soil, sewage sludge, and biological samples at environmentally relevant concentrations using Single Particle Inductively Coupled Plasma Mass Spectrometry spICP-MS). Further we investigated the impact of storage temperature (-80°C to 21°C) and storage duration (1-28 days) on the particle characteristics such as particle size.We found that aqueous AgNPs samples with low ionic strength media retained their original characteristics (like particle size, particle concentration and particle-based Ag mass) when preserved at 4°C for up to 28 days. AgNPs dispersed in high ionic strength media were however better preserved at -80°C. Among the extraction agents, tetrasodium pyrophosphate was more efficient in extracting AgNPs from soil and sewage sludge matrices, while Proteinase K was more suitable for biological samples from organisms (earthworms or fish).Although our study focused only on AgNPs, it provides crucial information to aid interlaboratory comparisons and data interpretation for (eco)toxicological studies.

Chloride permeation resistance of sulphoaluminate cement-based composite characterized by both alternating current section and RCM methods

Sulphoaluminate cement (SAC) was widely used for rapid repair and strengthening of building structures due to its excellent quick hardening and high early strength behavior. This study developed a SAC-based engineering cement composites (ECC) with ultra-high molecular weight polyethylene (UHMWPE) and investigated its mechanical properties. Chloride ion permeability coefficient were evaluated by new alternating-current sectioning and rapid chloride migration (RCM). The mechanism of the SAC-ECC against chloride erosion were quantified using nitrogen isothermal adsorption. The results show that the fracture energy, tensile strength and strain of SAC-ECC samples are higher than that of normal ECC. The polyethylene (PE) fiber could significantly improve the flexural strength and toughness with PE fiber content of 0.75% by volume. The hydration products generated could react with chloride ion to make it chemically stabilized, leading to reduce the chloride ion diffusion coefficient significantly. Based on microscopic analysis (SEM), the pore structure in SAC-ECC composite improved remarkedly while the volume of harmful pore decreased evidently as well. SAC-ECC developed in this paper could be poetically applied to strengthening and repair of marine concrete structures.

Development of Geopolymer and Cement-based Shotcrete Mortar: Impact of Mix Design Parameters and Spraying Process

Shotcrete mortar is used in various construction works, including repair, tunneling, mining, and slope stabilization, among others. Traditionally, cement is used to produce shotcrete mortars with high viscosity, flowability, and early strength. Geopolymers (GP) have the potential to replace cement in shotcrete mortars, owing to their ability to reduce the material’s environmental footprint without compromising performance. This investigation assesses the feasibility of utilizing fly ash and blast furnace slag-based GP mortars produced with dune sand in shotcrete applications while comparing them to cement-based mixtures. The GP and cement-based shotcrete mortars were designed to have similar yield stress values. The evaluated properties included the initial flow, thickness layer, rebound material, rheological properties, setting time, compressive strength, ultrasonic pulse velocity, and pull-off bonding strength. Test results showed direct relationships between the yield stress and initial flow values, as well as between the buildup thickness and plastic viscosity, revealing that GP mortars were suitable for shotcrete applications, specifically those produced with flow values of 18.5cm or less. GP mixtures produced with higher slag content than fly ash, higher sand content compared to binder, higher SH molarity, and lower solution content achieved higher buildup thickness owing to their higher viscosity. In the second phase, the performance of four mixes with different initial flows was assessed at various pumping flow rates and distances between the wall and machine pipe nozzle. The findings confirmed that these spraying parameters are crucial to improve the shotcrete performance of GP mortar with varying fresh behaviors.

Influence of ground slag and dune sand behavior of binary and ternary cement

This study examines the effect of slag and dune sand replacement (binary and ternary) in cement production, focusing on key mechanical properties and chemical behavior, especially on fire loss and residual an insoluble examined at different curing times ranging from 2 to 210 days. The findings show that the addition of slag and dune sand powder significantly influences the mechanical and thermal properties of mortar mixtures replaced by slag the compressive strength increases up to 30% and a slight decrease up to 40 is observed %. Ternary mixes show improved long-term compressive strength, especially after 120, 210 days, although generally young strength is lower than control When binary and ternary are combined with high flexural strength, ternary mixes exhibit good long-term performance, especially in mixtures of 20-30% slag and 10% dune sand lime (ACHOURA, D and al. 2008). From a thermal perspective, the replacement of slag with dune sand lime reduces losses during combustion, indicating excellent thermal stability. The addition of dune sand lime increases the proportion of impervious residue, indicating stability and durability of the cement. Overall, the study concludes that the proper use of slag and dune sand lime especially in ternary mixes can significantly improve the long-term mechanical and thermal performance of cement mortars Thus these findings provide valuable insights for designing building materials with higher durability and strength to suit specific construction application applications.

Amine-impregnated elastic carbon nanofiber aerogel templated by bacterial cellulose for CO2 adsorption and separation

Carbon aerogel has become a promising electrode material for CO2 capture and capacitor due to its large specific surface area, well-developed pore structure, adjustable porosity and ultra-high specific power. However, most of the carbon-based materials suffer from poor mechanical properties, low recycling efficiency, and low adsorption capacity, making it difficult to be put into industrial applications on a large scale. Bacterial cellulose (BC) has an ultra-fine reticular structure, a modulus of elasticity that is several to more than ten times that of typical plant fibers, and high tensile strength. In this paper, BC was treated by unidirectional freeze-drying method, and the aerogels with ordered honeycomb pore structure were constructed by unidirectional growth of ice crystals, and the pyrolytic chemical properties of BC were adjusted by using (NH4)2SO4, which effectively prevented the shrinkage and deformation of materials during carbonization, and successfully prepared elastic nanocarbon fiber aerogels. At the same time, the introduction of (NH4)2SO4 made the material realize N doping in the carbonization process, providing more adsorption sites, which was conducive to the adsorption of CO2. Finally, the carbon fiber nanoaerogel was modified by TEPA to further improve its adsorption selectivity for CO2. The prepared elastic carbon nanofiber aerogel (CBCNT) has high CO2 adsorption performance and high selectivity, and its CO2 capture capacity is up to 4.88 mmol/g. At the same time, its capacitance also reached 246F/g.

The evolution and toughening mechanism of austenite in high Co-Ni ultrahigh strength steel

The evolution and toughening mechanism of austenite in high Co-Ni ultrahigh strength steel

Curved surface coupled structural battery composites manufactured by resin transfer molding process: Microstructure and multifunctional performance

To bridge industrial production and lab-scale research, this work demonstrates a technology to manufacture curved surface structural battery composites (CSBCs) that can simultaneously achieve electrochemical energy storage and load-bearing. The curved-surface carbon fiber structural anode and cathode are fabricated by coating the active materials on carbon fiber fabric with a vacuum-bag-assisted technique. The resin transfer molding (RTM) process is conducted to manufacture the coupled CSBCs by infusing bi-continuous phase epoxy resin electrolyte and curing at high temperatures. The microstructure of structural electrodes and CSBCs is characterized by scanning electron microscopy (SEM). Due to good interfacial compatibility between high mechanical strength carbon fiber structural electrode and high ionic conductivity solid polymer electrolyte bulk for load support, the fabricated CSBCs demonstrate a high density of 294 mWh kg−1 based on the whole mass of devices, a tensile strength of 257.4 MPa with Young's modulus of 12.9 GPa and a flexural strength of 194.1 MPa with flexural modulus of 11.1 GPa. In situ electrochemical-mechanical tests further confirm the durability of CSBCs under mechanical loads with a multifunctional efficiency of 1.07, suggesting the effectiveness of the introduced manufacturing techniques for coupled structural battery composites.

Effect of Stretching Orientation on the Crystalline Structure and Energy Storage Properties of Poly(vinylidene fluoride) Films

Poly(vinylidene fluoride) (PVDF) with a high content of β phase shows great potential for applications in the pulse energy storage field because of its high dielectric constant and breakdown strength. The stretching process can significantly induce the crystal phase transformation and change the structure of the aggregated state. To deeply investigate the influence mechanism of the fabrication process, solution casting (SC), melt stretching (MS), static biaxial orientation (SBO), and continuous biaxial orientation (CBO) were used to fabricate PVDF films. The essential difference between the four technological routes lies in the different forms of tensile orientation imposed. Stretching perpendicular to the machine direction promotes the transition of the original α phase crystals to the β phase. Stretching orientation can regulate the crystalline phase structure of the film and its applicability. The relative fraction of β phase crystals in the PVDF-CBO film reaches 84.1%, resulting in a much higher dielectric constant (12.22 @1kHz) than that of the PVDF-SC film (7.16). The continuous biaxially oriented PVDF exhibited excellent insulation properties with a breakdown strength of 759.21kV/mm. Meanwhile, the CBO film obtained an energy storage density of 16.76J/cm3 with a charge-discharge efficiency of 80.13% at 675kV/mm. This work is of great scientific significance for the in-depth study of the influence of different film-forming processes on the internal structure of films, ranging from laboratory fabrication to industrialized production.