Hasil untuk "Materials of engineering and construction. Mechanics of materials"

Weitong Lin, Liutao Chen, Si-Mian Liu et al.

In-situ nanopillar compression tests were conducted to evaluate slip strengths of prismatic <a> and pyramidal <c+a> in Zr-Nb alloys. The resolved shear stress (RSS) for prismatic <a> slip in Zr-2.5Nb is about five times that of Zr-1.0Nb at 298 K, and RSS for pyramidal <c+a> slip of Zr-2.5Nb is about twice that of Zr-1.0Nb at 623 K, indicating that a higher density of β-Nb precipitates can appreciably enhance slip resistance. Moreover, RSS for prismatic <a> slip in Zr-2.5Nb at 623 K is approximately one-tenth of that at 298 K, suggesting that the strengthening effect substantially reduces at reactor operating temperatures.

Ayenew Amare, Mezigebu Belay, Zewudu Wondimagegn

Abstract The use of aluminium matrix composites (AMCs) in advanced engineering applications has increased due to their improved mechanical properties, such as hardness, ultimate tensile strength, toughness, wear, and corrosion resistance. Although synthetic ceramic particles enhance the mechanical properties of aluminium matrix composites, they also increase weight and cost due to their high density. Using inexpensive and lightweight reinforcements like industrial and agro-waste can reduce cost and weight, but may compromise some mechanical properties. This study investigates the mechanical properties and microstructure of AA6063 aluminium alloy reinforced with corn cob ash (CCA) and Al2O3 particles. The composites were produced using the two-step stir casting method, incorporating varying weight fractions of CCA and Al2O3 (ranging from 5% to 15% in 5% intervals). Optimal properties were achieved using Taguchi with grey relational analysis. Mechanical testing was carried out, such as tensile, compression, and hardness. Microstructural analysis and phase identification were performed using an optical microscope and X-ray diffraction (XRD), respectively. The findings demonstrate that incorporating CCA and Al2O3 reinforcements leads to significant improvements in the mechanical properties of AA6063 aluminium alloy, with ultimate tensile strength increasing by 49% at 10% CCA and Al2O3, compressive strength by 44.4% at 15% CCA and Al2O3, and hardness by 31% at 15% CCA and Al2O3. Although there was a slight decrease in ultimate tensile strength at 15% CCA and Al2O3, it remained higher than that of the unreinforced AA6063 alloy. The microstructural analysis images revealed the uniform distribution of the reinforcements and the positive influence of Al2O3-CCA reinforcements on the mechanical properties. Furthermore, XRD confirmed the presence of reinforced Al2O3-CCA particles in the produced composite samples. Therefore, the mechanical properties of AA6063 aluminium alloy were significantly improved by incorporating Al2O3-CCA reinforcements, suggesting its potential for enhanced applications in engineering.

Liangliang Huang, Xiangang Wan, Feng Tang

The scarcity of predicted magnetic topological materials (MTMs) by magnetic space group (MSG) hinders further exploration towards realistic device applications. Here, we propose a new scheme combining spin space groups (SSGs)--approximate symmetry groups neglecting spin-orbit coupling (SOC)--and MSGs to diagnose topology in collinear magnetic materials based on symmetry-indicator theory, enabling a systematic classification of the electronic topology across 484 experimentally synthesized collinear magnets from the MAGNDATA database. This new scheme exploits a symmetry-hierarchy due to SOC induced symmetry-breaking, so that nontrivial band topology can be revealed by SSG, that is yet invisible by the conventional MSG-based method, as exemplified by real triple points in ferromagnetic CaCu$_3$Fe$_2$Sb$_2$O$_{12}$, Dirac nodal lines at generic $k$-points in antiferromagnetic FePSe$_3$ and Weyl nodal lines in altermagnetic Sr$_4$Fe$_4$O$_{11}$. Notably, FePSe$_3$ is topologically trivial under MSG but hosts Dirac nodal lines within the SSG framework. Upon including SOC, these nodal lines are gapped and generate a sizable anomalous Hall conductivity. Despite a vanishing bulk net magnetism, FePSe$_3$ can host topologically protected surface states with large non-relativistic band spin-splitting. Moreover, topology in MTMs is tunable by rotating the magnetic moment direction once SOC is included, as exemplified in Sr$_4$Fe$_4$O$_{11}$.The interplay of topology with non-relativistic and SOC-induced control of properties via magnetic moment reorientation in the predicted MTMs is worthy of further studies in future.

Geng Wei, Zhu Zhibao, Ma Jinhui et al.

Steam oxidation corrosion resistance is an important index to evaluate boiler steel. In this study 9Cr-3Co-2W martensitic heat-resistant steel （/% 0.08C， 0.40Si， 0.40Mn， 9.00Cr， 0.20Ni， 0.50Mo， 1.50 W. 0.05Nb， 0.20V， 0.07N， 0.030Al， 0.0012B， S≤0.010， P≤0.020）， the oxidation kinetics curves of the two groups without rare earth and with rare earth <italic>w</italic>［Ce］ 0.03% in 625 ℃ water vapor environment were carried out， and the morphology and structure of the oxide film were analyzed by SEM and XRD. The results show that the outer layer of iron oxide scale in both sets of experimental steel are mainly rich in Fe oxide Fe₃O₄ or Fe₂O₃， and the inner layer is rich in Cr and Fe oxides （Fe，Cr）₂O₃ and （Fe，Cr）₃O₄ in the 625 ℃ water vapor environment. However， the outer layer of iron oxide scale in the experimental steel without rare earth addition has poor density ， and even cracks appear. The experimental steel with rare earth added has dense outer oxide layer and large chromium-rich oxide layer thickness. On the surface of the oxidation kinetics curve， at the initial stage of oxidation （0 h-200 h）， with the extension of oxidation time， the oxidation rate of the test steel is large. After the oxidation time exceeds 200 h， the oxidation rate gradually decreases， and after 2 000 h， the oxidation rate approaches the level， and the oxidation rate continues to decline and gradually becomes stable. The addition of a small amount of rare earth Ce can help to form a dense oxide film and improve the oxidation resistance of the steel.

Tim Heitkamp, Marijn Goutier, Karl Hilbig et al.

Recent advancements in fiber reinforced additive manufacturing leverage the piezoresistivity of continuous carbon fibers. This effect enables the fabrication of structural components with inherent piezoresistive properties suitable for load measurement or structural monitoring. These are achieved without necessitating additional manufacturing or assembly procedures. However, there remain unexplored variables within the domain of continuous fiber-reinforced additive manufacturing. Crucially, the roles of fiber curvature radii and sensing fiber bundle counts have yet to be comprehensively addressed. Additionally, the compression-sensitive nature of printed carbon fiber-reinforced specimens remains a largely unexplored research area. To address these gaps, this study presents experimental analyses on tensile and three-point flexural specimens incorporating sensing carbon fiber strands. All specimens were fabricated with three distinct curvature radii. For the tensile specimens, the number of layers was also varied. Sensing fiber bundles were embedded on both tensile and compression sides of the flexural specimens. Mechanical testing revealed a linear-elastic behavior in the specimens. It was observed that carbon fibers supported the majority of the load, leading to brittle fractures. The resistance measurements showed a dependence on both the number of sensing layers and the radius of curvature, and exhibited a slight decreasing trend in the cyclic tests. Compared with the sensors subjected to tensile stress, the sensors embedded on the compression side showed a lower gauge factor.

Sandeep Kumar Sahoo, Jogendra Majhi, Suresh Chandra Patnaik et al.

Abstract Aluminium matrix composites (AMCs) are well known for their excellent wear resistance and low weight. In the present work, in-situ synthesis of Al-Si-TiB2 composites with near eutectic and hypereutectic compositions of Al-Si alloys has been attempted through salt-metal reaction (K2TiF6 and KBF4 halide salts) by stir casting route. The fabricated composites were subjected to microstructure analysis, XRD study, sliding wear test, hardness and density measurements. The combined effect of Si and TiB2 is the novelty of this investigation to alter the structure–property correlation as well as hardness and tribological properties. Optical Emission Spectroscopy analysis indicated some amount of Si loss during stir casting and revealed the final composition of the cast composites. Though the increase in the density of the composite was not considerable due to incorporation of TiB2 particles, there was remarkable improvement in hardness and tribological properties attributed to clear interface between the matrix and the reinforcement as a result of in-situ process of fabrication. Wear resistance was found to be improved with increasing amount of Si content with a fixed TiB2 content in the composites under a constant load. TiB2 acts as a good grain refiner and improves the wear properties of the hypereutectic Al-Si alloy composites by decreasing the brittle primary silicon particle size.

Cameron J. Hargreaves, Michael W. Gaultois, Luke M. Daniels et al.

Abstract The application of machine learning models to predict material properties is determined by the availability of high-quality data. We present an expert-curated dataset of lithium ion conductors and associated lithium ion conductivities measured by a.c. impedance spectroscopy. This dataset has 820 entries collected from 214 sources; entries contain a chemical composition, an expert-assigned structural label, and ionic conductivity at a specific temperature (from 5 to 873 °C). There are 403 unique chemical compositions with an associated ionic conductivity near room temperature (15–35 °C). The materials contained in this dataset are placed in the context of compounds reported in the Inorganic Crystal Structure Database with unsupervised machine learning and the Element Movers Distance. This dataset is used to train a CrabNet-based classifier to estimate whether a chemical composition has high or low ionic conductivity. This classifier is a practical tool to aid experimentalists in prioritizing candidates for further investigation as lithium ion conductors.

Shixiong Liao, Kun Ma, Lei Wu et al.

The research and development of new building materials such as phosphorous building gypsum is crucial to promote the utilisation of phosphogypsum resources by improving their value. This study developed a new type of shape-stabilised energy storage phosphorus building gypsum aggregate (ES-PBGA). The mechanical and thermal properties of ES-PBGA with Paraffin were investigated. The results indicate that the matrix of ES-PBGA had a good microstructure, and the optimal paraffin-embedding rate of ES-PBGA was 31.08%. The phase transition temperature and enthalpy of the endothermic and exothermic stages were 17.6 and 27.14 ℃, and 33.02 and 31.62 J/g, respectively. The cylinder pressure strength of ES-PBGA with paraffin (31.08%) was 4.32 MPa, which meets the requirements of artificial aggregate application. To verify the practicability of ES-PBGA, energy storage lightweight aggregate concrete was prepared with 0%, 25%, 50%, and 100% ES-PBGA to replace the lightweight shale ceramsite. The results show that ES-PBGA can improve the interface transition zone between cement-based materials and energy storage aggregates, thereby improving the strength, and has a relatively suitable thermal conductivity, thermal diffusion coefficient, and specific heat capacity. Furthermore, it is also a type of low-carbon energy storage aggregate, and its application in the field of energy storage composite building materials is a relatively new concept.

W.P. Cathie Lee, Shunnian Wu, Franklin Anariba et al.

This study introduces a novel method for mica exfoliation using biaxial straining principles through H2 and N2 intercalation. Our two-stage approach combines microwave irradiation with biaxial straining triggered by H2 and N2. Our first principles simulations showed that N2 leads to a larger drop in bulk modulus per tensile strain than H2, resulting in decreased mica strain entropy (or less disordering) and ineffective exfoliation due to the resulting positive (H2) and negative (N2) Poisson ratio. Therefore, we applied H2 and performed SEM, FT-IR, and XRD analyses. The results indicate that our pre-treatment methods did not alter the mica's crystalline structure, and our two-step treatment method increased the interlayer distances of bulk mica particles. TEM analysis revealed the presence of mica nanosheets in single layers. This study represents a significant breakthrough in 2D exfoliation research not only for mica but also for non-van der Waals bonded crystals. By utilizing innovative biaxial straining principles through H2 and N2 interclation, our approach offers a promising avenue for achieving enhanced layer separation in layered materials.

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Nicholas Ng, Tyrel M. McQueen

Building on discoveries in graphene and two-dimensional (2D) transition metal dichalcogenides, van der Waals (VdW) layered heterostructures - stacks of such 2D materials - are being extensively explored with resulting new discoveries of novel electronic and magnetic properties in the ultrathin limit. Here we review a class of naturally occurring heterostructures - so called misfits - that combine disparate VdW layers with complex stacking. Exhibiting remarkable structural complexity and diversity of phenomena, misfits provide a platform on which to systematically explore the energetics and local bonding constraints of heterostructures and how they can be used to engineer novel quantum fabrics, electronic responsiveness, and magnetic phenomena. Like traditional classes of layered materials, they are often exfoliatable and thus also incorporatable as units in manually or robotically stacked heterostructures. Here we review the known classes of misfit structures, the tools for their single crystal and thin film synthesis, the physical properties they exhibit, and computational and characterization tools that are unraveling their complexity. Directions for future research are also discussed.

Stefan Jacob, Shilpi Pandey, Jaime Del Moral et al.

Migrating active deicing capabilities to transparent materials with low thermal conductivity has a high potential to improve the operations of several seminal industries in the automotive, robotic, energy, and aerospace sectors. However, the development of efficient and environmentally friendly deicing methods is yet in its infancy regarding their compatibility with end-user surfaces at relevant scales and real-world operations. Herein, we approach deicing through nanoscale surface activation enabled by surface acoustic waves (SAWs), allowing efficient on-demand deicing of surface areas spanning several square centimeters covered with thick layers of glace ice. We contemplate SAW-based deicing from a twofold perspective: First, we demonstrate its functionality both with a bulk piezoelectric material (LiNbO3) and a piezo-electric film (ZnO), the latter proving its versatile applicability to a large variety of functional materials with practical importance; second, we gain fundamental knowledge of the mechanisms responsible for efficient deicing using SAWs. In particular, we show that SAW vibrational modes easily transport energy over greater distances outside the electrode areas and efficiently melt large ice aggregates covering the materials' surfaces. In addition, the essential physics of SAW-based deicing is inferred from a carefully designed experimental and numerical study. We support our findings by providing macroscopic camera snapshots captured in situ inside a climate chamber during deicing and highly resolved laser-doppler vibrometer scans of the undisturbed wavefields at room temperature. Great care was taken to deposit the interdigital transducers (IDTs) used for SAW excitation only on ice-free areas close to the chip edges, leaving most of the substrate used for deicing unaltered and, as a matter of fact, demonstrating transparent deicing solutions.

Joel Davidsson, Fabian Bertoldo, Kristian S. Thygesen et al.

Doping of a two-dimensional (2D) material by impurity atoms occurs \textit{via} two distinct mechanisms: absorption of the dopants by the 2D crystal or adsorption on its surface. To distinguish the relevant mechanism, we systematically dope 53 experimentally synthesized 2D monolayers by 65 different chemical elements in both absorption and adsorption sites. The resulting 17,598 doped monolayer structures were generated using the newly developed ASE \texttt{DefectBuilder} -- a Python tool to set up point defects in 2D and bulk materials -- and subsequently relaxed by an automated high-throughput density functional theory (DFT) workflow. We find that interstitial positions are preferred for small dopants with partially filled valence electrons in host materials with large lattice parameters. On the contrary, adatoms are favored for dopants with a low number of valence electrons due to lower coordination of adsorption sites compared to interstitials. The relaxed structures, characterization parameters, defect formation energies, and magnetic moments (spins) are available in an open database to help advance our understanding of defects in 2D materials.

Ufaith Qadiri

In this contribution two Alternative fuels in fixed proportions were compared with conventional 100% gasoline fuel on a constant Speed single cylinder based generator. This work defines the complete state of the art work done on computational Simulation Software on AVL Boost. In this work, we have compared the performance and emission characteristics of single cylinder spark Ignition engine constant speed of 3000 rpm fuelled conventional Gasoline 100% with blended Alternative fuel Ethanol15% with 85% Gasoline, and water-Ethanol based micro-emulsion fuel Gasoline 85% Ethanol 10% and H2O 5% on licence based Simulation Software AVL Boost. The performance parameters were checked for all the three types of fuels and emission characteristics were compared with all the three types of fuels. The results were very promising for water-Ethanol based micro-emulsion fuel as far as the emission characteristics are concerned. Ethanol 15% blends with 85% Gasoline also showed very less emissions as compared to conventional 100% Gasoline. The power &amp; Torque has shown slightly more increase for conventional 100% Gasoline fuel as compared to other two Alternative Fuels. However, emissions were far lesser for water-Ethanol based micro-emulsion and Ethanol blended fuel. The main aim of this investigation is to reduce the emissions and trying to meet the future emission standards Euro 7.

Cong Gao, Yucai Shen, Tingwei Wang

A cost-efficient and practical strategy was developed for preparing high thermal conductive epoxy packaging composites. The effective conductive network was constructed by the bridging effect between boron nitride (BN) and spherical silica (SiO _2 ). Compared to the epoxy (EP) composites with randomly dispersed BN and SiO _2 , the EP/SiO _2 @BN showed a great enhancement in thermal conduction. The thermal conductivity of EP/SiO _2 @BN reached to 0.86 W m ^−1  K ^−1 with 60 wt% content of hybrid filler, which was 91% higher than that of EP/SiO _2 samples and was around 12% higher than that of epoxy composites with unmodified BN and SiO _2 . In addition, the EP/SiO _2 @BN exhibited lower thermal interface resistance in comparison with EP/SiO _2 &BN composites according to the effective medium theory (EMT). The encapsulation of BN on the surface of SiO _2 greatly enhanced the thermal transfer efficiency of the epoxy matrix and showed great potential in the epoxy packaging practical application.

Wei Ning, Zhiqiang Mao

The studies of topological insulators and topological semimetals have been at frontiers of condensed matter physics and material science. Both classes of materials are characterized by robust surface states created by the topology of the bulk band structures and exhibit exotic transport properties. When magnetism is present in topological materials and breaks the time-reversal symmetry, more exotic quantum phenomena can be generated, e.g. quantum anomalous Hall effect, axion insulator, large intrinsic anomalous Hall effect, etc. In this research update, we briefly summarize the recent research progresses in magnetic topological materials, including intrinsic magnetic topological insulators and magnetic Weyl semimetals.

X Lin, JC Lu, Y Shao et al.

Two-dimensional (2D) materials have been studied extensively as monolayers 1-5, vertical or lateral heterostructures 6-8. To achieve functionalization, monolayers are often patterned using soft lithography and selectively decorated with molecules 9,10. Here we demonstrate the growth of a family of 2D materials that are intrinsically patterned. We demonstrate that a monolayer of PtSe2 can be grown on a Pt substrate in the form of a triangular pattern of alternating 1T and 1H phases. Moreover, we show that, in a monolayer of CuSe grown on a Cu substrate, strain relaxation leads to periodic patterns of triangular nanopores with uniform size. Adsorption of different species at preferred pattern sites is also achieved, demonstrating that these materials can serve as templates for selective self-assembly of molecules or nanoclusters, as well as for the functionalization of the same substrate with two different species.

M.J. Hashemi, M. Jamshidi, J. Hassanpour Aghdam

Alexander Potapov

We proposed a method for calculating statical indeterminacy frames taking into account plastic defor­mations, which is based on the use of a schematized diagram of material with hardening. Two types of standard beams with supports are used during the implementation of the displacement method (DM) and the elastic solu­tion of the problem: “fixed” - “pinned” and “fixed” - “fixed”, but unlike the elastic solution, standard beams con­tain plastic zones (PZs). So as the stresses in these zones did not exceed the limit of yielding in the nonlinear frame calculation, we took measures to transform the PZs into equal strength plastic zones (ESPZ). The calcula­tions were made for both types of beams for all single and load impacts. The frame calculation consists of two stages (elastic and plastic). At the elastic stage, we determine an elastic moment diagram and the corresponding load. For a practical use of the DM in a nonlinear frame calculation, we introduced a simplifying prerequisite sup­plementing the well-known hypotheses of the classical version of the method, and formulated a Statement of the limiting load. According to the Statement, each length of the PZ can correspond to the lower boundary of the lim­iting load. The plastic stage of the calculation is performed at a given length of the PZ using the method of se­quential loadings. At each loading stage, incremental equations are written using the DM equations, which estab­lish relations between incremental moments and the incremental load, that allows you to get the resulting moment diagram. This diagram represents a sum of the elastic diagram and the diagrams of incremental moments at all previous loading stages. According to the resulting diagram, we calculate the length of the PZ, together with the limiting load. The calculation is considered complete if the length of the PZ does not exceed the specified value within the margin of error.

Che-Min Chiu, Shuo-Wen Chen, Yu-Ping Pao et al.

Flexible electronics with great functional characteristics have proved to be a stepping stone in the field of wearable devices. Amongst all, gesture-sensing techniques have been widely studied for human-machine interfaces. In this paper, we propose a self-powered gesture-sensing system attached to the back of the hands, which has the capability of distinguishing hand gestures by measuring the triboelectric nanogenerator output signal. By attaching the sensor on the back of the hand, we can sense the displacement of tendons to detect the gestures. In addition, humidity resistance and durability of the device were tested and validated. Furthermore, we have established a set of rules to define the relationship between gestures and corresponding English letters. Therefore, the proposed sensor can further serve as an electronic sign language translator by converting gestures into words. Finally, we can integrate this system into gloves to enhance the applicability and utility. Overall, we have developed a real-time self-powered back-of-hand sensing system which can recognize various hand gestures.