Isotropic Core Research Articles

Hysteretic behavior of the segmented buckling‐resistant braces with LYP160

AbstractThe goal was to evaluate the hysteretic performance of buckling‐resistant braces with low yield point steel LYP160, the monotonic tensile and cyclic loading tests of LYP160 test specimens were conducted and the cyclic constitutive relationship was obtained. According to the load–displacement curves of the specimens, the low‐yield point steel was characterized by good ductility and energy absorption ability. With consideration of the Chaboche model for the materials, the cyclic hardening parameters of low‐yield point steel were obtained. On this basis, the hysteretic properties of buckling‐resistant braces under cyclic loads were simulated and analyzed. After the analysis and comparison of buckling‐resistant braces specimens with isotropic core plate and segmented variable section core plate, it can be found that: when the conventional buckling‐resistant braces with an isotropic core plate were loaded to L/100, the lateral deformation of the buckling‐resistant brace (BRB) would reach 17 mm. Additionally, serious squeezing could be observed on the lateral restraining members. The conventional BRB would become ineffective due to the accumulation of deformation at both ends of the BRB. When the segmented buckling‐resistant brace was applied, the core plate with variable section would buckle first in the middle area, other parts could continue to consume energy thanks to the action of the limit plate. It would avoid the situation that other areas would be unable to consume energy after the core plate yields at one area first. Under the action of cyclic loads, no stiffness degradation was noted in the segmented buckling‐resistant brace. Segmented buckling‐resistant braces demonstrated superior ductility and energy dissipation capacity.

Radially transverse isotropic inclusions in isotropic elastic media: Local fields, neutral inclusions, effective elastic properties

Radially transverse isotropic inclusions in homogeneous isotropic elastic host media are considered. Mellin transform method is used for solution of the volume integral equation of the problem for an isolated inclusion subjected to a constant external stress (strain) field. The tensor structure of the solution is revealed with precision to three scalar functions of the radial coordinate, and the system of ordinary differential equations for these functions is derived. For multilayered radially transverse isotropic inclusions with constant elastic coefficients inside layers, explicit solution of these equations is obtained. An efficient numerical algorithm of solution for inclusions with an arbitrary number of the layers is proposed. Neutral inclusions that do not disturb homogeneous external fields applied to the medium are considered. It is shown that an inclusion with an isotropic core and radially transverse isotropic external layer can be weak neutral by appropriate choice of the layer elastic constants. The effective field method is used for determination of the effective elastic stiffness tensor of a homogeneous isotropic medium containing a random set of radially transverse isotropic inclusions.

Rupture of thin nematic walls between isotropic droplets of the same mesogenic material

ABSTRACT We prepared isotropic droplets surrounded by nematic fringes in smectic A freely suspended films. During their coalescence, a thin nematic film is formed that acts as a barrier and separates the isotropic cores of these droplets. This film ruptures in the course of the droplet merging process. The observation of the film dynamics provides an exceptional opportunity to study the rupture of a thin liquid barrier embedded in a surrounding viscous liquid. A detailed dynamic characterisation of the nematic walls is performed. Qualitatively similar observations have been reported in 3D for oil drops coalescing in water and vice versa, where the rupture of an intermediate thin fluid film retards the merging process. The peculiarity of the system reported here is that the material of the droplets and the membrane is identical.

Multistage mineralizing episodes of the Proterozoic world-class Volta Grande gold deposit, Amazonian Craton, northern Brazil: Implications for the Bacajá Domain metallogenesis

The easternmost region of the Amazonian Craton in northern Brazil has been the focus of several mining exploration surveys, which led to the identification of the world-class Volta Grande gold deposit (∼6.0 Moz@1.02 g/t). The deposit is inserted in the Bacajá Domain (2.24–2.0 Ga), and part of the mineralization occurs in Proterozoic mylonite, gneiss, and associated metamafic rocks that underwent greenschist to amphibolite-facies metamorphism. Electrum (Au–Ag) occurs as grains in cm-sized quartz high-grade veins and veinlets (up to 34.1 g/t in some rock intervals) that follow the mylonitic foliation and are associated with pervasive carbonate alteration, synchronous with the dynamic metamorphism. Disseminated electrum grains, pyrite, chalcopyrite, arsenopyrite, tellurides, and galena occur associated with potassic, argillic, propylitic, and silicic alteration types mainly in fracture-controlled or pervasive styles. These geological features as a whole suggest an orogenic high-tonnage orogenic gold system. Isotropic core samples along a stratigraphic profile reveal late andesite, dacite, rhyodacite, and rhyolite lava flows and dikes and plutonic rocks such as quartz monzonite, granodiorite, monzodiorite, and subordinate microgranite crosscutting the older metamorphic rocks. These rocks reveal potassic, propylitic, argillic, silicic, and sericitic alteration types. Electrum grains, possibly related to boiling deposition, occur along cm-sized quartz, calcite, and adularia high-grade veins (up to 29.5 g/t in some rock intervals) with chalcopyrite, pyrite, arsenopyrite, tetradymite, and tellurobismuthite. Such mineralogy is compatible with a low-sulfidation epithermal system. Data integration points to at least two distinct mineralizing events leading to the Volta Grande gold deposit – orogenic gold and low-sulfidation epithermal – which explains such large-tonnage and high-grade ore accumulation. It configures a new exploration guide for the Bacajá Domain of the Amazonian Craton, attested by other worldwide regions with similar metamorphic, magmatic, and hydrothermal alteration characteristics.

Elastodynamic Green's functions for sandwich panels with aluminum foam core and transversely isotropic face sheets using potential functions method

Green's functions of stress and displacement due to wave propagation in a sandwich panel consisting of transversely isotropic face-sheets and aluminum foam core are developed in the present paper. Dynamic partial differential equations of equilibrium for the considered face-sheets and core are expressed in cylindrical coordinates (r, θ, z), and converted into two separate equations using two unknown potential functions. Then, by writing the potential functions as Fourier series in the circumferential direction and using Hankel transform in the radial direction, an analytical solution to the potential functions in Hankel transformed space is developed. Using the boundary conditions and continuity of the problem as well as the place of application of harmonic forces, Green's functions for displacements and stresses in the frequency domain are derived using Hankel's inverse integral transform. These functions are expressed as complex integrals and calculated numerically. To verify the methodology and results, a comparison study is performed for particular cases showing a high level of the accuracy. Green's functions obtained from this paper will give information about the loading models or materials causing the maximum normal stress, shear stress, vertical and radial displacements. In addition, based on the results, with an increase in the core thickness compared to that of face-sheets in a Sandwich panel, an increment in Green's functions of stress and displacement is observed in both real and imaginary parts.

Coalescence of biphasic droplets embedded in free standing smectic A films.

We investigate micrometer-sized flat droplets consisting of an isotropic core surrounded by a nematic rim in freely suspended smectic A liquid-crystal films. In contrast to purely isotropic droplets which are characterized by a sharp edge and no long-range interactions, the nematic fringe introduces a continuous film thickness change resulting in long-range mutual attraction of droplets. The coalescence scenario is divided in two phases. The first one consists in the fusion of the nematic regions. The second phase involves the dissolution of a thin nematic film between the two isotropic cores. The latter has many similarities with the rupture of thin liquid films between droplets coalescing in an immiscible viscous liquid.

Heterogeneous Integration of Isotropic and Anisotropic Magnetic Cores for Inductive Power Transfer

Heterogeneous Integration of Isotropic and Anisotropic Magnetic Cores for Inductive Power Transfer

Variable kinematics finite plate elements for the buckling analysis of sandwich composite panels

This paper extends sublaminate-based variable kinematics plate finite elements towards the buckling analysis of composite structures. Robust locking-free 4-node and 8-node interpolations are used to build the finite element matrices in terms of fundamental nuclei, invariant with respect to the employed kinematic model of the composite plate. Geometric nonlinearities are accounted for in the von Kármán sense. The classical linearized stability analysis is mainly conducted for sandwich panels, for which different kinematic assumptions are employed for the skins and the core. Global buckling of the sandwich panel as well as short-wavelength wrinkling of the skins are investigated by referring to a variety of case studies, including homogeneous and laminated skins as well as isotropic and orthotropic cores. Convergence studies are performed to establish the minimum number of elements for the local instabilities to be grasped. The proposed computational framework requires a simple 2D mesh and is capable of providing quasi-3D response patterns. This is as demonstrated by numerous case studies that address the transition from global to local buckling, the onset of wrinkling in flat sandwich panels with anisotropic skins under various loading conditions as well as the local face sheet instability occurring in sandwich panels working in bending. It is concluded that he proposed FEM-based tool is computationally efficient and can be advantageously employed in pre-sizing design phases without resorting to full 3D models.

Stiffness optimisation of sandwich structures with elastically isotropic lattice core

This study concerns homogenisation-based stiffness optimisation with elastically isotropic plate and truss-based lattice structures. Due to the lattices’ isotropy, an optimised design can be obtained without including each lattice's rotational degree of freedom (DOF) as a design variable. Stiffness optimisation was performed on sandwich structures with lattice cores. Two optimised sandwich structures were fabricated using material extrusion additive manufacturing, and their deformation behaviour was studied using digital image correlation (DIC). DIC results revealed that when using a truss-based lattice as the core, certain trusses were susceptible to local strain concentration. On the other hand, sandwich structures with a plate-based lattice as the core showed an evenly distributed strain field, indicating loads can be more efficiently carried. Optimisation results in a maximum increase of 14.0 % for bending stiffness and 24.2 % for energy absorption. This research stands out for its novel selection of lattices and in-depth analysis of the full-field strain distribution in optimised sandwich lattice structures during bending. Combining experimental and numerical methods, the study sheds light on the deformation mechanism of these additively manufactured lattices, offering additional insights.

Dynamic Analysis of Elastically Supported Functionally Graded Sandwich Beams Resting on Elastic Foundations Under Moving Loads

Vibration behaviors of elastically supported functionally graded (FG) sandwich beams resting on elastic foundations under moving loads are investigated. The transformed-section method is first applied to establish the bending vibration equations of FG sandwich beams, then the Chebyshev collocation method is used to study free and forced vibrations. Two types of sandwich beams with FG faces-isotropic core and isotropic faces-FG core are considered. The material properties of FG materials are assumed to vary across the beam thickness according to a simple power function. Regarding the free vibration analysis, bending vibration frequencies are calculated numerically by forming a matrix eigenvalue equation. As for the forced vibration analysis, the backward differentiation formula method is employed to solve the time-dependent ordinary differential equations to obtain the dynamic deformations of the beam. To ensure the accuracy of the proposed model, some calculated results are compared with those in the published literature. Parametric studies are then performed to demonstrate the effects of material gradient indexes, stack types, layer thickness ratios, slenderness ratios, excitation frequency and speed of moving loads, and foundation and support stiffness parameters on the dynamic characteristics of FG sandwich beams.

Dynamic Instability of Sandwich Beams Made of Isotropic Core and Functionally Graded Graphene Platelets-Reinforced Composite Face Sheets

In this study, dynamic instability of a sandwich beam made of an isotropic core and functionally graded (FG) graphene platelets-reinforced composite (GPLRC) face sheets is investigated for the first time. A Frostig theory for soft core and third-order shear deformation theory (TSDT) for sheets are used. Hamilton’s principle is used to derive the governing equations of motion, and by applying Bolotin’s approach, the dynamic instability regions (DIRs) are investigated. A comprehensive investigation is conducted to assess the effects of different weight fractions of nanofiller, various GPL patterns, boundary conditions, slenderness ratio, the thickness of face sheet and static load factors on the DIRs of the beam.

Nonlocal strain gradient IGA numerical solution for static bending, free vibration and buckling of sigmoid FG sandwich nanoplate

For the first time, a numerical isogeometric numerical solution based on the nonlocal strain gradient elasticity theory for static bending, free vibration, and buckling of sigmoid functionally graded (S-FG) nanoplate is presented. Two configurations of S-FG sandwich material, including isotropic core and FG core, are considered. A parameter is proposed to define the location of the neutral axis through the cross-section. The simple Reissner-Mindlin plate theory, the nonlocal strain gradient theory, and Hamilton's principle are employed to establish the general equilibrium of S-FG nanoplate that contains two small size coefficients, including nonlocal and strain gradient parameters. The static bending, free vibration, and buckling responses of S-FG nanoplate are explored using isogeometric analysis with a NURBS basic function. The accuracy of the presented model is verified through the comparison with other solutions for nanoplate. As a result of numerical investigation studies, the static bending, free vibration, and buckling responses of S-FG are significantly affected by the material variation along the thickness direction, the neutral axis location, nonlocal parameter, strain gradient parameter, and material index.

Natural frequency analysis of imperfect FG sandwich plates resting on Winkler-Pasternak foundation

The present research analyzes the natural frequencies of the imperfect functionally graded sandwich plate (FGSP) comprised of porous face sheets made of functionally graded materials (FGMs) and an isotropic homogeneous core resting on the elastic foundation. To accomplish this, the material characteristics of the FGSP are taken to be changed incessantly along the thickness direction based on the volume fraction of constituents expressed by the modified rule of the mixture, which includes porosity volume fraction with three diverse kinds of porosity distribution models. Furthermore, to describe the two-parameter elastic foundation's response on the imperfect FGSP, the medium is supposed to be linear, homogenous, and isotropic, and it has been modelled using the Winkler-Pasternak model. Moreover, in the kinematic relationship of the imperfect FGSP resting on the Winkler-Pasternak foundation, third-order shear deformation theory (TSDT) is used, and the motion equations are set up employing Hamilton's principle. For natural frequency analysis of imperfect FGSPs resting on the Winkler-Pasternak foundation with simply supported edges, an analytical solution is obtained. To verify the current formulation, comprehensive comparisons are performed with the available data. The impacts of the two-parameter elastic foundation, porosity volume fraction, porosity distribution types, lay-up scheme, and side to thickness ratio, on the values of the non-dimensional fundamental natural frequency (NDFNF) of the imperfect FGSPs, are investigated, thoroughly.

Free vibration analysis of annular sector sandwich plates using first-order shear deformation theory

The present paper is concerned with the analysis of free transverse vibration of moderately thick annular sandwich sector plates of uniform thickness consisting of isotropic facings and core based on first-order shear deformation theory. The radial edges of the plate are taken as simply-supported (S) while the other two edges are considered to be under three combinations of clamped (C), and free (F) boundary conditions. The effects of transverse shear and rotatory inertia are included in the governing equations which are derived from Hamilton's principle. The differential quadrature method is used to discretise these equations and compute the lowest three eigenvalues of frequency parameter reported as the first three modes of vibration. The influence of boundary conditions, core thickness, facing thickness, inner-to-outer radii ratio, and sector angle on the frequency parameter of the plate is presented. Convergence of the results is also presented. Results are compared in special cases. Three-dimensional mode shapes for the first three modes are plotted.

Carbon fiber reinforced plastics with aluminum honeycomb core design methodology for space and surface mining applications

The space mining market is expected to grow in the future with water, gold, and platinum as just a few of the resources that could be accessible in the Moon or in near-Earth asteroids. To achieve this mining capability, sandwich composites offer an optimum structure for space mining vehicles due to their relatively high strength and stiffness compared to their weight. The challenge of designing such structures is often hampered by the lack of design approaches for practicing engineers in the mining industry usually lacking the composite material expertise or access to significant test capabilities. Expanding the use of sandwich composite materials into this industry requires selection charts that fully define the material system for a design engineer. Currently there is no methodology that systematically allows a design engineer to define a material system that uses carbon fiber reinforced plastics with aluminum honeycomb cores. The purpose of this paper is to introduce novel selection charts that allow an engineer to define the number of plies, stacking sequence, core thickness, and core density of a sandwich composite based off the moment carrying capacity. An example implementation of this approach is conducted using a carbon-fiber/epoxy with an aluminum alloy 5052 core. The selection charts developed with this approach are than validated with experimental analysis in accordance with ASTM D7249 (Standard Test Method for Facing Properties of Sandwich Construction by Long Beam Flexure). Experimental results show strong correlation with the selection charts by predicting the available moment and the mode of failure. Such selection charts will help facilitate wider use of these materials into industries that do not currently use them. Additionally, a novel numerical modeling approach for thick section sandwich composites using 3D finite elements is introduced. This approach shows how sandwich composite facesheets can be modeled with standard 3D elements instead of elements that support layers. Such an approach allows access to a wider variety of elements and is conducive to rapid design iterations when topological changes are occurring such as in a research and development environment. It is shown that numerical results correlate well with experimental data when using a linear-elastic isotropic core model with bilinear isotropic plasticity.

Evidence of topological boundary modes with topological nodal-point superconductivity

The extension of the topological classification of band insulators to topological semimetals gave way to the topology classes of Dirac, Weyl, and nodal line semimetals with their unique Fermi arc and drum head boundary modes. Similarly, there are several suggestions to employ the classification of topological superconductors for topological nodal superconductors with Majorana boundary modes. Here, we show that the surface 1H termination of the transition metal dichalcogenide compound 4Hb-TaS$_2$, in which 1T-TaS$_2$ and 1H-TaS$_2$ layers are interleaved, has the phenomenology of a topological nodal point superconductor. We find in scanning tunneling spectroscopy a residual density of states within the superconducting gap. An exponentially decaying bound mode is imaged within the superconducting gap along the boundaries of the exposed 1H layer characteristic of a gapless Majorana edge mode. The anisotropic nature of the localization length of the edge mode aims towards topological nodal superconductivity. A zero-bias conductance peak is further imaged within fairly isotropic vortex cores. All our observations are accommodated by a theoretical model of a two-dimensional nodal Weyl-like superconducting state, which ensues from inter-orbital Cooper pairing. The observation of an intrinsic topological nodal superconductivity in a layered material will pave the way for further studies of Majorana edge modes and its applications in quantum information processing.

A new higher order shear and normal deformation theory for FGM sandwich shells

Static and free vibration analysis of simply supported FGM sandwich shells is presented in this paper using a new higher order shear and normal deformation theory. The higher order theory developed herein considers the effects of transverse normal stresses. The theory uses higher order variations of in-plane as well as transverse displacements. Hamilton’s principle is used to formulate the equations of motion. Solutions of simply supported cylindrical and spherical shells are obtained using Navier’s solution technique. Different types of sandwich shells with FGM face sheets and isotropic core are considered for the numerical problems. The present results are compared with previously published results wherever possible to prove the validity of the present theory.

On Wrinkling in Sandwich Panels with an Orthotropic Core.

This paper deals with the local loss of stability (wrinkling) problem of a thin facing of a sandwich panel. Classical solutions to the problem of a facing instability resting on a homogeneous and isotropic substructure (a core) are compared. The relations between strain energy components associated with different forms of core deformations are discussed. Next, a new solution for the orthotropic core is presented in detail, which is consistent with the classic solution for the isotropic core. Selected numerical examples confirm the correctness of the analytical formulas. In the last part, parametric analyses are carried out to illustrate the sensitivity of wrinkling stress to a change in the material parameters of the core. These analyses illustrate the possibility of using the equations derived in the article for the variability of Poisson’s ratio from −1 to 1 and for material parameters strongly deviating from isotropy.

Dynamics of colloidal cubes and cuboids in cylindrical nanopores

Understanding how colloidal suspensions behave in confined environments has a striking relevance in practical applications. Despite the fact that the behavior of colloids in the bulk is key to identifying the main elements affecting their equilibrium and dynamics, it is only by studying their response under confinement that one can ponder the use of colloids in formulation technology. In particular, confining fluids of anisotropic particles in nanopores provides an opportunity to control their phase behavior and stabilize a spectrum of morphologies that cannot form in the bulk. By properly selecting the pore geometry, particle architecture, and system packing, it is possible to tune their thermodynamic, structural, and dynamical properties for ad hoc applications. In the present contribution, we report Grand Canonical and Dynamic Monte Carlo simulations of suspensions of colloidal cubes and cuboids constrained into cylindrical nanopores of different sizes. We first study their phase behavior, calculate the chemical potential vs density equation of state, and characterize the effect of pore walls on particle anchoring and layering. In particular, at large enough concentrations, we observe the formation of concentric nematic-like coronas of oblate or prolate particles surrounding an isotropic core, whose features resemble those typically detected in the bulk. We then analyze the main characteristics of their dynamics and discover that these are dramatically determined by the ability of particles to diffuse in the longitudinal and radial directions of the nanopore.

Cylindrical Confinement of Nanocolloidal Cholesteric Liquid Crystal.

The organization of nanocolloidal liquid crystals in constrained geometries has fundamental and practical importance, since under confinement, liquid crystals contain stable topological defects that can serve as templates for nanoparticle organization. Three-dimensional confinement of cholesteric (Ch) liquid crystals formed by cellulose nanocrystals (CNCs) have been extensively studied; however, their two-dimensional confinement remains under-investigated. Here, we report the results of systematic experimental studies of two-dimensional confinement of Ch-CNC liquid crystal in cylindrical capillaries with varying inner diameters. Confinement resulted in phase separation of the Ch-CNC liquid crystal into a Ch shell formed by concentric CNC pseudolayers with the helicoidal axis perpendicular to the inner surface of the capillary walls, and a micrometer-diameter isotropic core thread running parallel to the long axis of the capillary. The morphology of the confined Ch-CNC liquid crystal varied when progressively increasing the degree confinement. Finally, we show that phase separation of the Ch-CNC liquid crystal into a Ch shell and an isotropic core is preserved in flexible capillary tubing, suggesting the applicability of this system for the fabrication of flexible optical waveguides.