A nanocrystalline CoCrNi alloy of ~50 nm grain size with the ultra-high ultimate tensile strength of ~2.2 GPa and fracture strain of ~9% was fabricated using high-pressure torsion. The presence of ...high density of nano-twins, stacking faults, dislocations, and nano-grains is attributed to the superior mechanical properties.
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IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UM, UPCLJ, UPUK, ZRSKP
Tensile strength of rocks is an important parameter involved in the design and stability analysis of rock structures. The present paper is devoted to develop a new experimental method to investigate ...tensile strength, and the effect of confining pressure (Pc) on tensile behavior of rocks in underground rock engineering. A triaxial direct tension (noted as TDT) apparatus was developed based on the conventional triaxial compression (noted as CTC) device with the inspiration of the glue on steel cap type of method. TDT tests were carried out on the Fontainebleau quartz sandstone specimens under four different confining pressures. CTC tests under nine confining pressures were also carried out in order to compare the tension and compression behavior of the tested quartz sandstone. Tensile stress-strain curves were obtained during the CTC and TDT tests. Post-failure specimen analysis was also carried out to identify the failure mode in TDT test. The triaxial tension failed surfaces was sampled and scanned with the optical microscopy to obtain three dimensional images to show the effect of the confining stress on the failed surface roughness. The relationship between tensile and compressive strength and the strength criteria were analyzed with the experimental data. The results show the failure mechanism under TDT loading is different from that under CTC. The inter-grain cement is the dominant factor that contributes to the triaxial tensile strength of the quartz sandstone although the increase of confining pressure can induce a decrease of the triaxial direct tensile strength. It is suggested that the direct tensile strength of rocks should be tested directly for underground structures that confining pressure exists since uniaxial tensile strength can induce overestimate of the triaxial tensile strength.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Nanostructured metals are usually strong because the ultrahigh density of internal boundaries restricts the mean free path of dislocations. Usually, they are also more brittle because of their ...diminished work-hardening ability. Nanotwinned materials, with coherent interfaces of mirror symmetry, can overcome this inherent trade-off. We show a bulk nanostructuring method that produces a multiscale, hierarchical twin architecture in a hexagonal closed-packed, solute-free, and coarse-grained titanium (Ti), with a substantial enhancement of tensile strength and ductility. Pure Ti achieved an ultimate tensile strength of almost 2 gigapascals and a true failure strain close to 100% at 77 kelvin. The multiscale twin structures are thermally stable up to 873 kelvin, which is above the critical temperature for many applications in extreme environments. Our results demonstrate a practical route to achieve attractive mechanical properties in Ti without involving exotic and often expensive alloying elements.
Chitosan was modified with thioctic acid and used to prepare soft films. As confirmed by FTIR and XPS measurements, a condensation reaction occurred between the amino groups in the chitosan and the ...carboxyl groups in the lipoic acid to form amide bonds in the modified chitosan. Films were then prepared by casting at ambient conditions, and the effects of the chemical modification on the physical-mechanical, antibacterial, and thermal properties of the films were investigated. The results showed that the tensile strength, flexibility and recovery performance of the modified films were significantly different from those of the unmodified films. For example, the Young's modulus of a pure chitosan film was 2600 MPa, while the modified films were much more flexible with a Young's modulus as low as 32.5 MPa. Moreover, the modified chitosan films were not dissolved or damaged by common organic solvents or in highly acidic (pH 1) or highly basic (pH 13) conditions. The modified films also showed good antibacterial activity against both E coli and S aureus with inhibition rates of almost 100 %. These desirable properties suggest that the modified chitosan films prepared here have possible application prospects in flexible devices and packaging.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Mechanically interlocked molecules (MIMs) possess unique architectures and nontraditional degrees of freedom that arise from well-defined topologies that are achieved through precise mechanical ...bonding. Incorporation of MIMs into materials can thus provide an avenue to discover new and emergent macroscale properties. Here, the synthesis of a phenanthroline-based 2catenane crosslinker and its incorporation into polyacrylate organogels are described. Specifically, Cu(I) metalation and demetalation was used as a postgelation strategy to tune the mechanical properties of a gel by controlling the conformational motions of integrated MIMs. The organogels were prepared via thermally initiated free radical polymerization, and Cu(I) metal was added in MeOH to the pretreated, swollen gels. Demetalation of the gels was achieved by adding lithium cyanide and washing the gels. Changes in Young’s and shear moduli, as well as tensile strength, were quantified through oscillatory shear rheology and tensile testing. The reported approach provides a general method for postgelation tuning of mechanical properties using metals and well-defined catenane topologies as part of a gel network architecture.
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This paper presents the proof of concept for a facile sulfation-disintegration approach toward generating sulfated cellulose nanofibrils (SCNF) via direct sulfation of rice straw cellulose with ...chlorosulfonic acid (HSO3Cl) followed by blending. The direct sulfation of cellulose with chlorosulfonic acid (HSO3Cl) was optimized at acid ratios of 1–1.5 HSO3Cl per anhydroglucose unit (AGU) and short reaction times (30–60 min) at ambient temperature to produce SCNF with tunable charges of 1.0–2.2 mmol/g, all in impressively high yields of 94–97%. SCNF were characterized via AFM, TEM, FTIR, and XRD. SCNF lengths (L: 0.75–1.24 μm) and widths (W: 3.9–5.9 nm) decreased with harsher sulfation, while heights (H: 1.23–1.32 nm) remained relatively static. The SCNF had uniquely anisotropic cross sections (W/H: 3.0–4.7) and high aspect ratios (L/H: 568–984) while also exhibiting amphiphilicity, thixotropy, and shear thinning behaviors that closely followed a power law model. Aqueous SCNF dispersions could be wet spun into organic and mixed organic/ionic coagulants, producing continuous fibers possessing an impressively high tensile strength and Young’s modulus of up to 675 ± 120 MPa and 26 ± 5 GPa, respectively.
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High-entropy alloys (HEAs) are multi-component systems based on novel alloy composition designs with entropy maximization. They feature an array of unique mechanical properties when compared with ...traditional alloys. In this study, HEA fibers with diameters ranging from 1 to 3.15 mm in diameter, with the composition of Al0.3CoCrFeNi (atomic percent, at.%), were successfully fabricated by hot-drawing, followed by microstructural characterization using scanning-electron microscopy (SEM) and transmission-electron microscopy (TEM). The compositional variations within and between fibers were determined using energy-dispersive X-ray spectroscopy in TEM along with atomic-probe tomography (APT). These analyses revealed a homogeneous face-centered cubic (FCC) structure in the as-cast material, while post processing (e.g., forging and wire drawing) produced nanosized B2 particles in an FCC matrix. Electron back-scatter diffraction (EBSD) was used to determine the evolution of the texture and grain boundary character after processing of the fibers. The tensile strength and plasticity of the fibers were determined at both 298 K (1207 MPa/7.8%) and 77 K (1600 MPa/17.5%). Detailed TEM analyses revealed that the improvement of mechanical properties at 77 K (i.e. increased strength and ductility) is due to a change in deformation mechanisms from the planar slip of dislocations to nano-twinning. Such properties could be beneficial for cryogenic applications.
The map of tensile strength and ductility combinations of various phases of high entropy alloys. Display omitted
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•A small amount (0.25%) of fiber showed a positive influence on compressive strength.•Fiber length (FL) and volume (FV) contributed equal amount (40%) to concrete slump.•Jute fiber showed no ...significant impact on the split tensile strength of concrete.•FL, FV & their interaction contributed 17, 36 & 47% to flexural tensile strength.
The purpose of this study is to evaluate the addition of jute fibers on the fresh and hardened properties of concrete. Locally produced jute fibers having two different lengths of 10 mm and 20 mm and four different volumes of 0.00%, 0.25%, 0.50%, and 1.00% were added to prepare concrete cylinders and beams. The cylinder specimens were tested for the compressive strength at 7, 28 and 90 days and for the split tensile test at 28 and 90 days, whereas the beam specimens were assessed for the flexural tensile strength at 28 days. Additionally, various factorial analyses were conducted on the experimental results to detect the effect of the volume and size of jute fibers on concrete properties. The experimental results revealed that the addition of 0.50% jute fiber had an adverse impact on the fresh properties of concrete. However, a smaller dosage (0.25%) of jute fiber showed a positive influence on the hardened properties of concrete. The results obtained from factorial analysis demonstrated that the fiber length and volume showed a positive influence on hardened concrete properties at early and extended curing ages, respectively.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
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•GEP algorithm is utilized for predicting mechanical properties of concrete incorporating WFS.•Simple and accurate formulations with a wide range of applicability have been ...proposed.•Proposed models can promote the re-utilization of hazardous WFS for development of green concrete.
Waste foundry sand (WFS) is a major pollutant generated from metal casting foundries and is classified as a hazardous material due to the presence of organic and inorganic pollutants which can cause adverse environmental impact. In order to promote the re-utilization of WFS, gene expression programming (GEP) has been employed in this study to develop empirical models for prediction of mechanical properties of concrete made with WFS (CMWFS). An extensive and reliable database of mechanical properties of CMWFS is established through a comprehensive literature review. The database comprises of 234 compressive strength, 163 split tensile strength and 85 elastic modulus results. The four most influential parameters i.e. water-to-cement ratio, WFS percentage, WFS-to-cement content ratio and fineness modulus of WFS are considered as the input parameters for modelling. The mechanical properties can be estimated by the application of proposed simplified mathematical expressions. The performance of the models is assessed by conducting parametric analysis, applying statistical checks and comparing with regression models. The results reflected that the proposed models are accurate and possess a high generalization and prediction capability. The findings of this study can enhance the re-usage of WFS for development of green concrete leading to environmental protection and monetary benefits.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
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