Boundary Structure Research Articles

Analysis of Vibration Characteristics for Rotating Braided Fiber-Reinforced Composite Annular Plates with Perforations

In the current study, a comprehensive numerical model for analyzing the vibrational characteristics of braided fiber-reinforced composite (BFRC) rotating annular plate with perforations under diverse boundary constraints was introduced. This model employs the differential quadrature finite element method (DQFEM), which was developed based on the first-order shear deformation theory (FSDT) and coordinate transformation approach. The BFRC material, specifically a two-dimensional biaxial orthogonal fabric, was utilized to fabricate the annular plate with two distinct types of holes: circular and sector-shaped. The model’s convergence, accuracy, numerical stability, and reliability were confirmed through comparative assessments utilizing data from the literature, from ABAQUS software, and from experimental findings. The analysis focuses on studying the influences of structural properties, material parameters, and boundary restraints on the frequencies of vibration for BFRC rotating annular plates with holes. This theoretical model helps provide scientific basis and technical guidance for the stability and lightweight design of rotating annular plates, such as rotor structures in aircraft engines.

Metaharvesting: emergent energy harvesting by piezoelectric metamaterials

Vibration energy harvesting is a technology that enables electric power generation by augmenting vibrating materials or structures with piezoelectric elements. In a recent work, we quantified the intrinsic energy-harvesting availability (EHA) of a piezoelectric phononic crystal (Piezo-PnC) by calculating its damping ratio across the Brillouin zone and subtracting off the damping ratio of the corresponding non-piezoelectric version of the phononic crystal. It was highlighted that the resulting quantity indicates the amount of useful energy available for harvesting and is independent of the finite structure size and boundary conditions and of any forcing conditions. Here, we investigate the intrinsic EHA of two other material systems chosen to be statically equivalent to a given Piezo-PnC: a piezoelectric locally resonant metamaterial (Piezo-LRM) and a piezoelectric inertially amplified metamaterial (Piezo-IAM). Upon comparing with the intrinsic EHA of the Piezo-PnC, we observe an emergence of energy-harvesting capacity, a phenomenon we refer to as metaharvesting. This is analogous to the concept of metadamping, except the quantity evaluated is associated with piezoelectric energy harvesting rather than raw dissipation. Our results show that the intrinsic EHA is enhanced by local resonances and enhanced further by inertial amplification. These findings offer a new paradigm for the design—at the fundamental level—of architectured piezoelectric materials with superior energy-harvesting capacity.

Correlations between local chemical fluctuations and grain boundary strength in Ti-Zr-Nb-Ta-Mo refractory multi-principal element alloys

Ti-Zr-Nb-Ta-Mo refractory multi-principal element alloys typically exhibit high yield strength while tensile ductility tends to be poor. In this study, we found that even after solid solution treatment of Ti-Zr-Nb-Ta-Mo alloys, significant change in ductility occur due to the local chemical fluctuations. Ta's dramatic chemical fluctuations cause variations in atomic-scale strain fields, leading to reduced grain boundary strength and brittle fracture. First-principles calculations show that (Ti, Zr)-rich at the grain boundaries increases the delocalization of valence electrons, leading to longer bond lengths and reduced crystal orbital bond index values, thereby causing grain boundary embrittlement. Our findings explore the root causes of brittleness in Ti-Zr-Nb-Ta-Mo alloys at the atomic and electronic scales, providing not only a method to analyze grain boundary embrittlement using bond length, electronic localization function and crystal orbital bond index, but also a theoretical guidance for improving the mechanical properties via grain boundary structure optimization.

Polarization Pinning at Antiphase Boundaries in Multiferroic YbFeO3

Abstract The switching characteristics of ferroelectrics and multiferroics are influenced by the interaction of topological defects with domain-walls. We report on the pinning of polarization due to antiphase boundaries in thin films of the multiferroic hexagonal YbFeO3. We have directly resolved the atomic structure of a sharp antiphase boundary (APB) in YbFeO3 thin films using a combination of aberrationcorrected scanning transmission electron microscopy (STEM) and total energy calculations based on density-functional theory (DFT). We find the presence of a layer of FeO6 octahedra at the APB that bridge the adjacent domains. STEM imaging shows a reversal in the direction of polarization on moving across the APB, which DFT calculations confirm is structural in nature as the polarization reversal reduces the distortion of the FeO6 octahedral layer at the APB. Such APBs in hexagonal perovskites are expected to serve as domain-wall pinning sites and hinder ferroelectric switching of the domains.

Correlation between microstructure properties and the effect of WC addition on the interface, hardness and corrosion performance of thermally sprayed NiCrBSi-WC coating

ABSTRACT Ni super-alloy is based on a powder coating of NiCrBSi – WC from flexicord wire feedstock material. The role of the CMoAlNi thick layer on the microstructure and interface properties of the coating was examined. The microstructure and interface properties were analyzed for both NiCrBSi-WC and NiCrBSi-WC/CMoAlNi thick layer using optical microscopy (OM), scanning electron microscopy (SEM) coupled with energy dispersive X-ray spectroscopy (EDS), X-ray diffraction analysis (XRD). The mechanical property was evaluated by a Vickers hardness and nano-indentation measurement under 3N and 100mN, respectively. The performance of corrosion interface coatings was investigated in 3.5% of bentonite solution. The applied layer has a flame-spray morphology with unmelted and deformed particles associated with voids and porosities. In contrast, after CMoAlNi under-layers, the interface is a more compact boundary structure with no porosity or cracks. The as-sprayed NiCrBSi-WC coating exhibits high hardness (HIT≈6 GPa), and high Young's modulus (EIT≈ 240 GPa) The ability to resist cracking is significantly higher for the NiCrBSi-WC coating concerning the NiCrBSi-WC/CMoAlNi coating, 7.21 compared to 2.88 (GPA−3) x106. The electrochemical potentiodynamic polarisation results show that the NiCrBSi-WC coating's corrosion resistance is higher than that of the NiCrBSi-WC / CMoAlNi coating.

Intrinsic symmetry-protected topological mixed state from modulated symmetries and hierarchical structure of boundary anomaly

Intrinsic symmetry-protected topological mixed state from modulated symmetries and hierarchical structure of boundary anomaly

Freestanding Penta-Twinned Pd-Ag Nanosheets.

2D metal nanosheets have attracted significant attention as efficient catalysts for various important chemical reactions. However, the development of metal nanosheets with controlled compositions and morphologies has been slow due to the challenges associated with synthesizing thermodynamically unfavorable 2D structures. Herein, we report a synthesis route of freestanding Pd-Ag penta-twinned nanosheets (Pd-Ag ptNSs) with distinct 5-fold twin boundaries. Through the coreduction of Ag and Pd precursors on presynthesized Pd ptNSs, Ag could be homogeneously alloyed with Pd, leading to the formation of well-defined Pd-Ag ptNSs. The promotional effects of the bimetallic composition, 2D structure, and twin boundaries on catalysis were studied by using Pd-Ag ptNS-catalyzed H2 production from formic acid decomposition as a model reaction. Notably, the catalytic activity of the Pd-Ag ptNSs drastically outperformed those of monometallic, bimetallic, and 3D counterparts, such as Pd ptNSs, Pd-Ag nanosheets without a TB, and Pd-Ag octahedral nanocrystals, demonstrating the promising potential of the integration of twin boundaries and multiple compositions in the development of high-performance 2D nanocatalysts.

Misorientations across interfaces in spark plasma–sintered WC–Co cemented carbides

AbstractThis interdisciplinary work concerns misorientations across various interfaces in spark plasma–sintered (SPSed) WC–Co cemented carbides, as well as how these misorientations affect the intergranular fracture. The whole boundaries in cemented carbides were divided according to the phases on the two sides of the boundary plane, and carbide/carbide grain boundaries were further divided according to the misorientation across the boundary plane. Stereological statistics and five‐parameter analysis were comprehensively performed on the concerned boundary types. For Σ2 carbide/carbide boundaries, multiple boundary structures are observed. How Σ2 twist inhibits intergranular fracture and how such boundary structure is formed are analyzed. For random carbide/carbide boundaries, the habit planes that they are terminated by are calibrated, and their responses to intergranular fracture are examined according to their energy anisotropy. For WC/α‐cobalt and WC/β‐cobalt phase boundaries, misorientations across these boundary planes and the corresponding crack propagation routines are illustrated. On these bases, approaches to improve the fracture strength of SPSed cemented carbides are suggested.

Molecular Dynamics Analysis of Hydrogen Diffusion Behavior in Alpha-Fe Bi-Crystal Under Bending Deformation

The hydrogen embrittlement (HE) phenomenon occurring in drawn pearlitic steel wires sometimes results in dangerous delayed fracture and has been an important issue for a long time. HE is very sensitive to the amount of plastic deformation applied in the drawing process. Hydrogen (H) atom diffusion is affected by ambient thermal and mechanical conditions such as stress, pressure, and temperature. In addition, the influence of stress gradient (SG) on atomic diffusion is supposed to be crucial but is still unclear. Metallic materials undergoing plastic deformation naturally have SG, such as residual stresses, especially in inhomogeneous regions (e.g., surface or grain boundary). In this study, we performed molecular dynamics (MD) simulation using EAM potentials for Fe and H atoms and investigated the behavior of H atoms diffusing in pure iron (α-Fe) with the SG condition. Two types of SG conditions were investigated: an overall gradient established by a bending deformation of the specimen and an atomic-scale local gradient caused by the grain boundary (GB) structure. A bi-crystal model with H atoms and a GB structure was subjected to bending deformation. For a moderate flexure, bending stress is distributed linearly along the thickness of the specimen. The diffusion coefficient of H atoms in the bulk region increased with an increase in the SG value. In addition, it was clearly observed that the direction of diffusion was affected by the existence of the SG. It was found that diffusivity of the H atom is promoted by the reduction in its cohesive energy. From these MD results, we recognize an exponential relationship between the amount of H atom diffusion and the intensity of the SG in nano-sized bending deformation.

Ultrahigh thermal stability and piezoelectricity of lead-free KNN-based texture piezoceramics

The contradiction between high piezoelectricity and uniquely poor temperature stability generated by polymorphic phase boundary is a huge obstacle to high-performance (K, Na)NbO3 -based ceramics entering the application market as Pb-based substitutes. We possess the phase boundary by mimicking Pb(Zr, Ti)O3’s morphotropic phase boundary structure via the synergistic optimization of diffusion phase boundary and crystal orientation in 0.94(Na0.56K0.44)NbO3−0.03Bi0.5Na0.5ZrO3−0.03(Bi0.5K0.5)HfO3 textured ceramics. As a result, a prominent comprehensive performance is obtained, including giant d33 of 550 ± 30 pC/N and ultrahigh temperature stability (d33 change rate less than 1.2% within 25-150 °C), representing a significant breakthrough in lead-free piezoceramics, even surpassing the Pb-based piezoelectric ceramics. Within the same temperature range, the d33 change rate of the commercial Pb(Zr, Ti)O3−5 ceramics is only about 10%, and more importantly, its d33 (~ 350 pC/N) is much lower than that of the (K, Na)NbO3-based ceramics in this work. This study demonstrates a strategy for constructing the phase boundary with MPB feature, settling the problem of temperature instability in (K, Na)NbO3-based ceramics.

A computational study of the effects of graphene additions on electrical properties of polycrystalline copper

The addition of graphene has recently shown promise as a route for the significant improvement of the bulk electrical properties of metallic materials. We explore the effects these additions have on the net electrical conductivity of fabricated copper-graphene (Cu-Gr) nanocomposites as a function of grain structure and grain boundary properties. Synthetic 3D microstructures were generated to represent polycrystalline copper with different average grain diameters and twinned grain boundary fractions. Then, the Poisson equation of electrical transport was solved using a finite difference method in order to predict the net electrical conductivity of each microstructure. In this context, the potential effect of graphene on the conductivity of the composite was evaluated as a function of the number of affected grain boundaries. The results of these calculations indicate that 1.) as supported by literature, net electrical conductivity decreases with decreasing grain size, 2.) the presence of twinned grain boundaries results in smaller loss of conductivity than would otherwise be expected, and 3.) the presence of graphene on the grain boundaries can be expected to lead to improvements in net electrical conductivity. However, we also find that 4.) when the Cu grain structure becomes sufficiently refined, the addition of graphene could conceivably result in significant improvements in electrical conductivity over and above coarse-grained Cu. It is estimated from our calculations that, assuming microstructures with average grain sizes between 100 nm and 100 μm and graphene conductivity 1000 to 10,000 that of a typical Cu grain boundary, an improvement in electrical conductivity of approximately 17 % over that of bulk Cu may be attainable. Therefore, by performing this study we suggest a possible route for the improvement of Cu electrical properties through the addition of graphene.

Thermodynamic properties and structure of interfacial boundaries in nonionic fluids from the multilayer quasichemical model

The interfacial properties and structure of nonuniform fluids containing complex chainlike molecules and associating species are very much needed in a variety of different fields, including enhanced oil recovery, drug delivery, pharmacy, cosmetics, food processing, etc.Recently, we described the Multilayer Quasichemical Model (MQuM) of a nonuniform fluid that provides a remarkably detailed structural information, including the local concentration and orientation of functional groups of the molecules, the orientation profiles of the chemical bonds in molecular chains and the orientation profiles of the hydrogen bonds in the mixture.In this work, we focus on the description of thermodynamic properties with the aid of MQuM, including the interfacial tension and the profiles of normal and transverse pressures. Before proceeding to more complex systems, a test is performed through comparison with the previously known results from the Scheutjens-Fleer theory for the planar liquid–vapor interface and spherical droplet in one-component fluid of nonpolar monomeric molecules. The model is applied then for planar interfaces between the liquid phases in mixtures of water with n-alkanes of different chain length and for spherical drops in model systems that contain an associating solvent, a nonpolar chain and a nonionic amphiphile. Our theoretical results are compared with experiment, predictions from iSAFT and MD simulation data from the literature. For the spherical droplets, we discuss the model description of the dependence of the interfacial tension on the curvature and estimate the Tolman length. For the planar interface between the equilibrium liquid phases in water – n-alkane mixtures, the interfacial tensions predicted from the model are in good agreement with experiment.

Critical Review of Physical-Mechanical Principles in Geostructure-Soil Interface Mechanics

AbstractDue to the relatively different mechanical and physical properties of soils and structures, the interface plays a critical role in the transfer of stress and strain between them. The stability and safety of geotechnical structures are thus greatly influenced by the behavior at the soil–structure interface. It is therefore important to focus on the unique characteristics that set the interface apart from other geomaterials while examining the interface behaviour. Understanding the physical mechanism and modelling principles of these interfaces becomes a crucial step for the secure design and investigation of soil-structure interaction (SSI) issues. Moreover, to deal with this soil-environment interaction problem, the classical soil mechanics formulation must be progressively generalised in order to incorporate the effects of new phenomena and new variables on SSI behaviour. Considering the variety of energy geostructures that are emerging nowadays, it is crucial to comprehend the thermo-hydro-mechanical (THM) behaviour of the interface. The objective of this study is to fill this information gap as concisely as possible. A critical review is provided along with the state-of-the-art information on the thermo-hydro-mechanical behaviour of the soil-structure interface, including testing tools and measurement methods, basic principles and deformation mechanisms, constitutive models, as well as their applications in numerical simulations. This study explains how loading influences the mechanisms at the interface and critically examines the effects of boundary conditions, soil properties, environmental factors, and structure type on the THM behaviour of interface zones between soils and structural elements. The validity and reliability of the interface shear stress-displacement models are also covered in this paper. Lastly, the trends and recent advancements are also recommended for the interface research.

Uniaxial compression performance of anti-tetrachiral structures considering the effects of cell size and boundary conditions

Anti-tetrachiral structures (AS) are typical metamaterials known for their negative Poisson's ratio. The existing analysis of the mechanical properties of AS is conducted by applying the energy method to a unit cell with periodic boundary conditions (PBC). In available works, the shear force at the structure's boundaries is neglected. But is it permissible to disregard the impact of shear forces at the boundaries on the structure's equivalent mechanical properties? By examining the deformation relationship between the ribs and the nodal rings, we developed a uniaxial compression model for AS under both free and constrained boundary conditions, which accurately predicts the mechanical properties of the AS structure. This model was validated through numerical simulations and experiments. The findings reveal that the equivalent mechanical properties of AS exhibit a size dependence related to the cell size. For example, for AS with equivalent density and identical overall dimensions, the equivalent Young's modulus of an AS with 2×2 cells will be twice that of an AS with 4×4 cells. Furthermore, the size effect of the structure can be neglected when the number of cells larger than 8×8. Moreover, it is found that the present model considering boundary conditions exhibits an equivalent Young's modulus 25% higher than the model neglecting boundary conditions. The study's findings indicate that the presence of boundary conditions can disrupt PBC, leading to significant discrepancies between theoretical derivations and practical applications.

Self-diffusion in < 100 > symmetrical tilt grain boundaries in tungsten: Molecular dynamics simulation

The structure and energy of grain boundaries, the energies of point defects formation in them and grain-boundary self-diffusion coefficients in 18 < 100 > symmetrical tilt grain boundaries in tungsten have been determined by atomistic simulation. The dependences of grain boundary energies, defect formation energies in them and activation energy of grain-boundary self-diffusion on the misorientation angle have been calculated. A structural phase transformation has been discovered in Σ5(310) and Σ5(210) boundaries, which affected the diffusion properties of these grain boundaries. The calculations performed are compared with the available experimental data on self-diffusion in grain boundaries of tungsten.

Effect of alloying element segregation on theoretical strength and structural low-energy transition of Ni grain boundaries: A first-principles computational tensile test study

Enhancing the stability and strength of nanocrystalline metals through the manipulation of grain boundary (GB) chemistry and structure is crucial for their engineering applications. In this study, first-principle computational tensile tests on Ni Σ5 [001] (210) GBs were conducted with considering Poisson's ratio and strengthening effect of alloying elements B, W, Zr, Ta, B-W and Zr-Ta segregation. The results indicate that the Zr-Ta co-segregated GB shows a remarkable increase in theoretical tensile strength by 195 % compared to the clean GB under small strain conditions. As tensile strain increases, both clean and segregated GBs undergo a low-energy structural transition from the Σ5 [001] (210) to the more stable Σ11 [110] (113). This work presents a promising approach for enhancing the stability of Ni nanograined materials through tensile deformation and GB segregation.

Prediction of automotive body-in-white distortion in paint baking process

Thermal-induced distortion prediction of thin shell structures is a challenging task. It often involves highly nonlinear buckling behaviour, where the critical buckling temperature and post-buckling deformations are very sensitive not only to structural stiffness and boundary conditions but also minute geometric imperfections (a.k.a., “surface quality”) of the incoming parts. In the present work, novel Computer Aided Engineering (CAE) methods were developed to predict the thermal-induced distortion of automotive Body-in-White (BIW) panels during paint shop oven-baking processes. The CAE methodology consist of a set of three Finite Element Analysis (FEA) procedures, i.e., thermal-buckling mode analysis, thermo-structural analysis, and imperfection analysis. Two vehicle level case studies showed that simulations successfully predicted the thermal-induced distortion for panels such as the Body Side Outer (BSO) header. It was concluded that the distortion depends primarily on the temperature difference between the BSO and the rest of the BIW during the oven-baking process, rather than the temperatures themselves. Body panel forming quality (e.g., residual stresses and thickness thinning) and assembly dimensional quality were also found to impact the distortions.

Atomic-scale revelation of Cu diffusion mechanism in high-performance Pr-doped 2:17-type SmCo magnets

The coercivity of 2:17-type SmCo magnets is mainly determined by the gradient distribution of Cu within the cell boundary phase. However, the fundamental migratory behavior and driving force causing such Cu distribution remains unclear. In this work, the phenomenon of Cu enrichment at the lamellar/intracellular interface is reported at the atomic scale, and a new Cu diffusion mechanism of 2:17-type SmCo magnets is proposed via combining microstructure characterization with first-principles calculation. Our study indicates that Cu will migrate from the intracellular phase to the lamellar/intracellular phase interface following the migration of twin boundary, and then diffuses further along the lamellar phase interface to the cell boundary, achieving the expected Cu-rich cell boundary structure. Doping Pr results in a reduction of Cu substitution energy in the lamellar phase, leading to a decreased driving force during the subsequent Cu diffusion. As a result, the Cu does not completely diffuse into the cell boundary phase there is Cu enrichment at the interface between lamellar and intracellular phases. The Cu concentration of the cell boundaries could be increased in 2:17-type SmCo magnets by reasonable designing the substitution energy difference of intracellular phase, lamellar phase and cell boundary phase that promote Cu diffusion to cell boundary. Our study sheds light on the control of Cu segregation in magnets and a new strategy for enhancing the magnetic performance of 2:17-type SmCo magnets.

Relationships Between Upper-Plate Structure, Mantle Wedge Melting, and Fore-Arc Sliver Transport in the Nicaraguan Subduction Zone

Abstract This study images the base of the upper-plate lithosphere in the Nicaraguan subduction zone using common conversion point stacking of Sp phases and explores the relationships between deep upper-plate structure, subduction zone melting processes, and the arc-parallel transport of the Central American fore-arc sliver. We observe the negative velocity gradient associated with the upper-plate lithosphere–asthenosphere boundary in the Nicaraguan back-arc at depths of 60–80 km. However, the amplitude of the lithosphere–asthenosphere velocity gradient diminishes beneath the arc, consistent with a reduction in the shear-wave velocity of the deep upper-plate lithosphere. This zone lies above mantle wedge velocity anomalies which indicate upward-migrating partial melt, suggesting that ascending melt has altered and weakened the lithospheric mantle of the upper plate. In northwestern Nicaragua, the boundary of the Central American fore-arc sliver and the Caribbean plate, which is marked by a northeast decrease in geodetically measured arc-parallel surface velocities, lies above the northeast increase in the amplitude and localization of the lithosphere–asthenosphere velocity gradient. This correlation indicates that the kinematic margin of the Central American fore-arc sliver corresponds to a structural boundary that extends throughout the upper plate, and that is influenced by melt ascending from the mantle wedge.

Level-set based shape optimization for plane elastic structures using radial basis functions and Hilbertian descent direction

Structural optimization problems are often associated with the so-called shape functionals depending on a shape through its geometry and the state being a solution of given partial differential equation. In such a framework it is convenient to work with the gradient-like method based on a concept of a shape derivative and level set method. The key idea of level set method is to represent the structural boundary with zero level set of given function (level set function—LSF). Now, changing the shape of a structure under optimization is equivalent to transport the LSF in such a direction that ensures decreasing the value of the objective functional. To this end, we make use of coercive bilinear form taken from the weak formulation of elasticity problem to obtain descent direction at each iteration. This descent direction is a solution of an additional variational problem, involving the bilinear form mentioned above and the volumetric expression of the shape derivative plays the role of a linear form. In this paper, we combine level set method with radial basis functions (RBFs) used to approximate LSF. We focus on the so-called multiquadric RBFs, but other classes of RBFs are also briefly considered. This eventually leads to transformation of partial differential equation (linear transport equation governing the evolution of shapes) to a system of linear ordinary differential equations which admits analytical formula for the solution. We apply our method to compliance minimization of a cantilever problem as well as to total potential energy minimization of a structure with kinematic loading. To run all the numerical experiments, we wrote our own code in Wolfram Mathematica environment.