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

Orest Pavlosiuk, Marcin Matusiak, Andrzej Ptok et al.

Topologically trivial and non-trivial semimetals with a high degree of carrier compensation are well known for demonstrating large transverse magnetothermopower ($S_{yx}$). However, in such systems, the longitudinal magnetothermopower ($S_{xx}$) is typically suppressed due to nearly perfect electron-hole compensation. Here, we show that the half-Heusler topological semimetal DyPtBi exhibits simultaneously large $S_{xx}$ and $S_{yx}$ magnetothermopowers, defying this conventional trade-off. In $B=14$\,T, thermopower of DyPtBi reaches peak values of $S_{xx}=131\,μ\rm{V/K}$ at $T=149$\,K and $S_{yx}=-297\,μ\rm{V/K}$ at $T=200$\,K, and transverse component remains significantly large even at $290$\,K ($S_{yx}=-213\,μ\rm{V/K}$). Remarkably, at $T=290$\,K and in relatively weak magnetic field of $1$\,T, both relevant for practical applications, DyPtBi shows $S_{yx}=-18\,μ\rm{V/K}$, which is one of the largest values reported under such conditions. The large transverse thermopower originates from an ambipolar effect associated with thermal excitation occurring in zero-gap semiconductors. Due to the imperfect electron-hole compensation, an intrinsic asymmetry between hole- and electron-type carriers enables pronounced values of both $S_{xx}$ and $S_{yx}$, resulting in high effective thermopower ($S_{xx}+|S_{yx}|=379\,μ\rm{V/K}$) in DyPtBi at 200\,K. A comparative analysis with DyPdBi, another half-Heusler material that demonstrates large $S_{xx}=123\,μ\rm{V/K}$ but small $S_{yx}=-16\,μ\rm{V/K}$ (both values obtained at $T=293$\,K and $B=14$\,T), highlights the critical role of band structure and compensation tuning. These findings underscore the potential of chemical doping and band engineering in rare-earth-based half-Heusler materials for optimizing both transverse and longitudinal thermoelectric properties.

Yun Li, Youxiang Si, Ke Zhang et al.

Yuntian Liu, Jiayu Li, Pengfei Liu et al.

Abstract Spin textures, i.e., the distribution of spin polarization vectors in reciprocal space, exhibit diverse patterns determined by symmetry constraints, resulting in a variety of spintronic phenomena. Here, we propose a universal theory to comprehensively describe the nature of spin textures by incorporating three symmetry flavors of reciprocal wavevector, atomic orbital, and atomic site. Such an approach enables us to establish a complete classification of spin textures constrained by the little co-group and predict some exotic spin texture types, such as Zeeman-type spin splitting in antiferromagnets and quadratic spin texture. To illustrate the influence of atomic orbitals and sites on spin textures, we predict orbital-dependent spin texture and anisotropic spin-momentum-site locking effects, and corresponding material candidates validated through first-principles calculations. The comprehensive classification and the predicted new spin textures in realistic materials are expected to trigger future spin-based functionalities in electronics.

Sanfeng Wu

In strongly correlated quantum materials, electrons behave in ways that often extend beyond the confines of conventional Fermi-liquid theory. Interesting results include the observation of low-temperature metallic behavior in systems that are highly resistive. Here we provide an overview of experiments in which insulators exhibit characteristics of a metal such as the Shubnikov de Haas like quantum oscillations, focusing on recent findings in the correlated insulating states of two-dimensional WTe2. We discuss the status of current research, clarify the debates and challenges in interpreting the experiments, rule out extrinsic explanations and discuss promising future directions.

Marcilei A. Guazzelli, Luis H. Avanzi, Vitor A. P. Aguiar et al.

Highly Ordered Pyrolytic Graphite (HOPG) has been extensively researched due to its chemical and physical properties that make it suitable for applications in several technologies. Its high thermal conductivity makes HOPG an excellent heat sink, a crucial characteristic for manufacturing targets used in nuclear reactions, such as those proposed by the NUMEN project. However, when subjected to different radiation sources, this material undergoes changes in its crystalline structure, which alters its intended functionality. This study examined HOPG sheets before and after exposure to a 14 MeV neutron beam. Morphological and crystallographic analyses reveal that even minor disruptions in the high atomic ordering result in modifications to its thermal properties. The results of this study are essential to establish the survival time of the HOPG used as thermal interface material to improve heat dissipation of a nuclear target to be bombarded by an intense high-energy heavy-ion beam.

Younouss Dıéye, Vincent Sambou, Pape Moussa Touré et al.

This work deals with characterizing concrete based on baobab trunk fibers for thermal in- sulation in buildings. The aim is to study the effect of the fiber content and the type of fiber treatment on the hygroscopic and thermo-physical properties of the concrete. Therefore, two types of treatment were carried out: an alkaline treatment and a thermo-alkaline treatment. Hygroscopic test results (34.25% to 54.92% for fiber content ranging from 14% to 28%) show that adding fibers to concrete makes them more sensitive to water. However, thermochemical treatment of the fibers reduces this water sensitivity. The thermal conductivities of concrete range from 0.202 to 0.086 W/m.K for the same fiber content. These results show that these biomaterials can be used in construction to improve building insulation.

Guanghong Lai, Xiao Liu, Shiyu Li et al.

This study aims to achieve further progress in application performance of polymers in cement-based materials. The objective is to establish the research direction of superplasticizers with ordered micro-sequence via the innovation of synthesis technology and to clarify the correlation between the specific motifs in the microstructures of superplasticizers and the properties of cement pastes. In this study, a novel comb-like polycarboxylate superplasticizer (PCE) was synthesized using isobutenyl polyethylene glycol (IPEG) and hydroxyethyl acrylate (HEA) by atom transfer radical polymerization (ATRP) (defined as A-CPCE). Comb-like PCE with the same molecular weight as A-CPCE was also produced via conventional free radical polymerization (defined as CPCE). The molecular properties of both polymers and the structural motifs of monomers therein were characterized via size exclusion chromatography (SEC), 1H nuclear magnetic resonance (1H NMR), 13C nuclear magnetic resonance (13C NMR) and MATLAB, and furthermore the adsorption behavior of PCE polymers on cement particles was analyzed. Together with the rheological and mechanical properties of cement-based materials, the relationship between micro-sequence distribution and macro-performance of PCEs was investigated. The results showed that the monomer sequence distribution in A-CPCE was AAE and AAA, and the probability of the acid-ether ratio of 4:1 was 16.54%, meaning that relatively uniform polymer species were obtained. The A-CPCE molecules exhibited the smaller hydrodynamic radius (Rh=11.7 nm) and stronger adsorption capacity (maximum was 2.3618 mg·g−1) in cement pastes, which was in good accordance with Langmuir isotherm model and pseudo-second order kinetic model. The dispersing power of PCEs correlated with the specific motifs in the microstructures, thus indicating that A-CPCE enhanced the rheological performances of cement paste and concrete. In addition, the compressive strengths of concrete containing A-CPCE after 3 d, 7 d and 28 d were 16.00 MPa, 28.30 MPa and 52.9 MPa, respectively, which were significantly higher than those of concrete with CPCE.

Chia-Jui Chang, Lih-Ren Chen, Kuo-Bin Hong et al.

Abstract Photonic-crystal surface-emitting lasers have many promising properties over traditional semiconductor lasers and are regarded as the next-generation laser sources. However, the minimum achievable lasing threshold of PCSELs is still several times larger than that of VCSELs, and limiting its applications especially if the required power is small. Here, we propose a new design that reduces the gain region in the lateral plane by using selective quantum-well intermixing to reduce the threshold current of PCSELs. By performing theoretical calculations, we confirmed that the threshold current can be lowered by a factor of two to three while keeping the PCSEL’s advantage of small divergence angle.

Daisuke Tashima, Takuhiro Kashio, Takuya Eguchi et al.

In this study, a method was developed for the management of marine plastic waste via the production of activated carbon. The specific surface area, micropore volume, and mesopore volume of marine-plastic-based activated carbon prepared at selected temperatures and using selected activator weight ratios were measured, and the specific capacitance and supercapacitor electrode performance were evaluated. At an activation temperature of 800 °C and a raw material to 8 M KOH weight ratio of 1:7, a specific capacitance of 201F/g and a high surface area of 2389 m2/g were obtained. Therefore, marine plastic waste-based activated carbon can be used as the electrode material in supercapacitors.

Yueshan Xu, Junjie Wang, Bo Su et al.

Excitons, which represent a type of quasi-particles consisting of electron-hole pairs bound by the mutual Coulomb interaction, were often observed in lowly-doped semiconductors or insulators. However, realizing excitons in the semiconductors or insulators with high charge carrier densities is a challenging task. Here, we perform infrared spectroscopy, electrical transport, ab initio calculation, and angle-resolved-photoemission spectroscopy studies of a van der Waals degenerate-semiconductor Bi4O4SeCl2. A peak-like feature (i.e., alpha peak) is present around ~ 125 meV in the optical conductivity spectra at low temperature T = 8 K and room temperature. After being excluded from the optical excitations of free carriers, interband transitions, localized states and polarons, the alpha peak is assigned as the exciton absorption. Moreover, assuming the existence of weakly-bound excitons--Wannier-type excitons in this material violates the Lyddane-Sachs-Teller relation. Besides, the exciton binding energy of ~ 375 meV, which is about an order of magnitude larger than those of conventional semiconductors, and the charge-carrier concentration of ~ 1.25 * 10^19 cm^-3, which is higher than the Mott density, further indicate that the excitons in this highly-doped system should be tightly bound. Our results pave the way for developing the optoelectronic devices based on the tightly-bound and room-temperature-stable excitons in highly-doped van der Waals degenerate semiconductors.

Prashant Singh, Manoj K Harbola

This article is part-I of a review of density-functional theory (DFT) that is the most widely used method for calculating electronic structure of materials. The accuracy and ease of numerical implementation of DFT methods has resulted in its extensive use for materials design and discovery and has thus ushered in the new field of computational material science. In this article we start with an introduction to Schrödinger equation and methods of its solutions. After presenting exact results for some well-known systems, difficulties encountered in solving the equation for interacting electrons are described. How these difficulties are handled using the variational principle for the energy to obtain approximate solutions of the Schrödinger equation is discussed. The resulting Hartree and Hartree-Fock theories are presented along with results they give for atomic and solid-state systems. We then describe Thomas-Fermi theory and its extensions which were the initial attempts to formulate many-electron problem in terms of electronic density of a system. Having described these theories, we introduce modern density functional theory by discussing Hohenberg-Kohn theorems that form its foundations. We then go on to discuss Kohn-Sham formulation of density-functional theory in its exact form. Next, local density approximation is introduced and solutions of Kohn-Sham equation for some representative systems, obtained using the local density approximation, are presented. We end part-I of the review describing the contents of part-II.

Hui-Ke Jin, Wilhelm Kadow, Michael Knap et al.

We study the effect of hole doping on the Kitaev spin liquid (KSL) and find that for ferromagnetic (FM) Kitaev exchange $K$ the system is very susceptible to the formation of a FM spin polarization. Through density matrix renormalization group (DMRG) simulations on finite systems, we uncover that the introduction of a single hole with a hopping strength of just $t\sim{}0.28K$ is enough to disrupt fractionalization and polarize the spins in the [001] direction due to an order-by-disorder mechanism. Taking into account a material relevant FM anisotropic spin exchange $\varGamma$ drives the polarization towards the [111] direction via a reorientation transition into a topological FM state with chiral magnon excitations. We develop a parton mean-field theory incorporating fermionic holons and bosonic spinons/magnons, which accounts for the doping induced FM phases and topological magnon excitations. We discuss experimental signatures and implications for Kitaev candidate materials.

Fan Wu, Marco Gibertini, Kenji Watanabe et al.

Using field-effect transistors (FETs) to explore atomically thin magnetic semiconductors with transport measurements is difficult, because the very narrow bands of most 2D magnetic semiconductors cause carrier localization, preventing transistor operation. Here, we show that exfoliated layers of CrPS$_4$ -- a 2D layered antiferromagnetic semiconductor whose bandwidth approaches 1 eV -- allow the realization of FETs that operate properly down to cryogenic temperature. Using these devices, we perform conductance measurements as a function of temperature and magnetic field, to determine the full magnetic phase diagram, which includes a spin-flop and a spin-flip phase. We find that the magnetoconductance depends strongly on gate voltage, reaching values as high as 5000 % near the threshold for electron conduction. The gate voltage also allows the magnetic states to be tuned, despite the relatively large thickness of the CrPS$_4$ multilayers employed in our study. Our results show the need to employ 2D magnetic semiconductors with sufficiently large bandwidth to realize properly functioning transistors, and identify a candidate material to realize a fully gate-tunable half-metallic conductor.

Samantha Mora, Nicola M. Pugno, Diego Misseroni

High-precision 3D printing technology opens to almost endless opportunities to design complex shapes present in tailored architected materials. The scope of this work is to review the latest studies regarding 3D printed lattice structures that involve the use of photopolymers fabricated by Material Jetting (MJ), with a focus on the widely used Polyjet and MultiJet techniques. The main aspects governing this printing process are introduced to determine their influence during the fabrication of 3D printed lattices. Performed experimental studies, considered assumptions, and constitutive models for the respective numerical simulations are analyzed. Furthermore, an overview of the latest extensively studied 3D printed architected lattice materials is exposed by emphasizing their achieved mechanical performances through the use of Ashby plots. Then, we highlight the advantages, limitations, and challenges of the material jetting technology to manufacture tunable architected materials for innovative devices, oriented to several engineering applications. Finally, possible approaches for future works and gaps to be covered by further research are indicated, including cost and environmental-related issues.

María Camarasa-Gómez, Ashwin Ramasubramaniam, Jeffrey B. Neaton et al.

The accurate description of electronic properties and optical absorption spectra is a long-standing challenge for density functional theory. Recently, the introduction of screened range-separated hybrid (SRSH) functionals for solid-state materials has allowed for the calculation of fundamental band gaps and optical absorption spectra that are in very good agreement with many-body perturbation theory. However, since solid-state SRSH functionals are typically tuned to reproduce the properties of bulk phases, their transferability to low-dimensional structures, which experience substantially different screening than in the bulk, remains an open question. In this work, we explore the transferability of SRSH functionals to several prototypical van der Waals materials, including transition-metal sulfides and selenides, indium selenide, black phosphorus, and hexagonal boron nitride. Considering the bulk and a monolayer of these materials as limiting cases, we show that the parameters of the SRSH functional can be determined systematically, using only the band-edge quasiparticle energies of these extremal structural phases as fitting targets. The resulting SRSH functionals can describe both electronic bandstructures and optical absorption spectra with accuracy comparable to more demanding ab initio many-body perturbation theory (GW and Bethe-Salpeter equation) approaches. Selected examples also demonstrate that the SRSH parameters, obtained from the bulk and monolayer reference structures, display good accuracy for bandstructures and optical spectra of bilayers, indicating a degree of transferability that is independent of the fitting procedure.

Youssef AbouelNour, Nikhil Gupta

Additive Manufacturing (AM), or 3D printing, processes depend on a user-defined set of optimized process parameters to create a component. Monitoring and control of AM processes in real-time can help achieve process stability and repeatability to produce high quality parts. By applying in-situ monitoring methods to the AM process, defects in the printed parts can be detected. In this review, application of both imaging and acoustic methods for the detection of sub-surface and internal defects is discussed. Imaging methods consist of visual and thermal monitoring techniques, such as optical cameras, infrared (IR) cameras, and X-ray imaging. Many studies have been conducted that prove the reliability of imaging methods in monitoring the printing process and build area, as well as detecting defects. Acoustic methods rely on acoustic sensing technologies and signal processing methods to acquire and analyze acoustic signals, respectively. Raw acoustic emission signals can correlate to particular defect mechanisms using methods of feature extraction. In this review, representation and analysis of the acquired in-situ data from both imaging and acoustic methods is discussed, as well as the means of data processing. Ex-situ testing techniques are introduced as methods for verification of results gained from in-situ monitoring data.

David F. Williams

This essay analyzes the scientific evidence that forms the basis of bioactive materials, covering the fundamental understanding of bioactivity phenomena and correlation with the mechanisms of biocompatibility of biomaterials. This is a detailed assessment of performance in areas such as bone-induction, cell adhesion, immunomodulation, thrombogenicity and antimicrobial behavior. Bioactivity is the modulation of biological activity by characteristics of the interfacial region that incorporates the material surface and the immediate local host tissue. Although the term ‘bioactive material’ is widely used and has a well understood general meaning, it would be useful now to concentrate on this interfacial region, considered as ‘the bioactivity zone’. Bioactivity phenomena are either due to topographical/micromechanical characteristics, or to biologically active species that are presented in the bioactivity zone. Examples of topographical/micromechanical effects are the modulation of the osteoblast – osteoclast balance, nanotopographical regulation of cell adhesion, and bactericidal nanostructures. Regulation of bioactivity by biologically active species include their influence, especially of metal ions, on signaling pathways in bone formation, the role of cell adhesion molecules and bioactive peptides in cell attachment, macrophage polarization by immunoregulatory molecules and antimicrobial peptides. While much experimental data exists to demonstrate the potential of such phenomena, there are considerable barriers to their effective clinical translation. This essay shows that there is solid scientific evidence of the existence of bioactivity mechanisms that are associated with some types of biomaterials, especially when the material is modified in a manner designed to specifically induce that activity.

M. Zheng, S. Zhang, X.J. Peng et al.

In the present paper, the excavation of the energetic approach that estimates the fatigue crack initiation life of metal is conducted for H62 brass. The benefit of the energetic approach is the division of the actual applied strain range Δε into two parts, that is, a damage strain range Δεd that induces fatigue damage within the metal, and an undamaged strain range Δεc, which does not produce fatigue damage of the metal and corresponds to theoretical strain fatigue limit. The brightness of this approach is that the undamaged strain range Δεc can be estimated by the fundamental conventional parameters of metal in tensile test. The result indicated that the fatigue crack initiation life of H62 brass can be estimated by this approach successfully.

Jian Jiang, Zhifang Zhang, Jiyang Fu et al.

The lightweight design of railway vehicle components using fiber reinforced polymers (FRPs) has become a research hotspot due to the strong need for energy saving and environmental protection. This paper aims to evaluate the impact damage behavior of a carbon fiber reinforced polymers (CFRP) protection suspender, which is a component on railway vehicles to prevent the falling joist and bolster from touching the rails and to avoid the derailment of trains. A finite element (FE) model of the CFRP protection suspender, which considered varying bolt preloads was established in ABAQUS/Explicit. The bolt preload was successfully applied around the installation holes on the protection suspender by deliberately reducing the local temperature of the bolt shank to create shrinkage. The impact behavior of the protection suspender was then analyzed, and the impact-induced damage was governed by the Continuum Damage Mechanics (CDM) models, which include both intra-laminar damage and inter-laminar damage. The low-velocity impact response of the CFRP protection suspender was investigated with the lay-ups of [0]10 and [0/90/0/90/0]S under different bolt preloads (i.e. 0, 5 and 20 kN). The results showed that the vulnerable positions of the protection suspenders included the contact edge between the protection suspender and the impactor, the curved corner of the suspender, and the areas around the bolt holes. In addition, the protection suspender with the lay-up of [0]10 had better impact resistance than that with the lay-up of [0/90/0/90/0]S. By applying different preloads, it showed that the increase of bolt preloads could help to prevent the occurrence of crack damage around the installation holes, thus improving the structural safety when subjected to low-velocity impact. The present simulation results offered great value for the lightweight design and structural optimization of a protection suspender on railway vehicles that had to survive from sudden impact loads in service.

Matheus I. N. Rosa, Bruce L. Davis, Liao Liu et al.

While resonant modes do not exist within band gaps in infinite periodic materials, they may appear as in-gap localized edge modes once the material is truncated to form a finite periodic structure. Here, we provide an analysis framework that reveals the topological origins of truncation resonances, elucidating formally the conditions that influence their existence and properties. Elastic beams with sinusoidal and step-wise property modulations are considered as classical examples of periodic structures. Their non-trivial topological characteristics stem from the consideration of a phason parameter that produces spatial shifts of the property modulation while continuously varying how the boundaries are truncated. In this context, non-trivial band gaps are characterized by an integer topological invariant, the Chern number, which is equal to the number of truncation resonances that traverse a band gap as the phason is varied. We highlight the existence of multiple chiral edge states that may be localized at opposite boundaries, and illustrate how these can be independently tuned by modified boundary-specific phason parameters. Furthermore, we show that the frequency location of a truncation resonance is influenced by the modulation volume fraction, boundary conditions, and number of cells comprising the finite structure, thus quantifying its robustness to these factors. Non-topological in-gap resonances induced by a defect are also demonstrated, showing that these can be coupled with topological modes when the defect is located at an edge. Finally, experimental investigations on bi-material phononic-crystal beams are conducted to support these findings. The tunability of truncation resonances by material-property modulation may be exploited in applications ranging from vibration attenuation and thermal conductivity reduction to filtering and flow control by phononic subsurfaces.