Showing papers on "Shell (structure) published in 2017"

Dynamic crash responses of bio-inspired aluminum honeycomb sandwich structures with CFRP panels

Abstract: Nature has provided us with extraordinary resources to tackle design challenges facing in modern society nowadays. The multistate structures inspired by animal shell have proven effective to improve the impact resistance of composite laminate. This study aims to identify the crash responses and crashworthiness characteristics of bio-inspired sandwich structures composed of carbon fiber reinforced plastic (CFRP) panels and aluminum honeycomb. The crash responses, failure mode as well as the effects of core side length, height and impact velocity on peak load and energy absorption were explored herein. The differences of crashworthiness characteristics between the CFRP aluminum honeycomb sandwiches and bare CFRP panel were quantified. Two typical load-displacement relations, namely single-peak and double-hump curves, were observed in the tests. It was noted in the energy-displacement curve, where the slopes corresponding to the failure stages of the upper and lower face-sheets, were greater than that in the honeycomb failure stage, indicating that the bare aluminum honeycomb was of lower energy absorption capacity than the CFRP face-sheet. By comparison, the honeycomb filling was an effective way to improve the impact resistance of CFRP structure, yielding higher energy absorption and lower peak load during the impact. It was also found that the crashworthiness characteristics were more sensitive to the core length than to the core height; and the specific energy absorption (SEA) varied insignificantly with the increase in the core height. It was noted that the peak load, absorbed energy and SEA increased significantly under high impact velocity.

Thermal and mechanical stability of functionally graded carbon nanotubes (FG CNT)-reinforced composite truncated conical shells surrounded by the elastic foundations

Abstract: The thermal and mechanical stability of a functionally graded composite truncated conical shell reinforced by carbon nanotube fibers and surrounded by the elastic foundations are studied in this paper. Distribution of reinforcements across the shell thickness is assumed to be uniform or functionally graded. The equilibrium and linearized stability equations for the shells are derived based on the classical shell theory. Using Galerkin method, the closed – form expression for determining the linear thermal and mechanical buckling load is obtained. The paper also analyzed and discussed the effects of semi-vertex angle, shell length, volume fraction of fibers, distribution pattern of fibers, temperature, elastic foundations on the linear thermal and mechanical buckling loads of the functionally graded carbon nanotube fibers-reinforced composite (FG CNTRC) truncated conical shell in thermal environment.

Interfacial Design in Dielectric Nanocomposite Using Liquid-Crystalline Polymers

Abstract: The interfacial region plays a critical role in determining the electrical properties of dielectric nanocomposites. The current state-of-the-art interfacial modification is predominantly based on utilizing flexible organic molecules, which are random polymer coils and generally collapse on the surface of any modified nanoparticles. This work focused on engineering the interfacial region between Na2Ti3O7 nanofibers and polymer matrix and, for the first time, utilized the liquid-crystalline polymer poly{2,5-bis[(4-methoxyphenyl)oxycarbonyl]styrene} (PMPCS) to modulate the interface where the rigid polymer was forced to form a straight conformation. Owing to the rigidity and orientation of PMPCS, a series of core–shell structured Na2Ti3O7@PMPCS nanofibers with finely tuned shell thickness were prepared. The prepared Na2Ti3O7@PMPCS/P(VDF-HFP) nanocomposites showed significantly different permittivity from 10.7 to 69.6 at 1 kHz with the gradient thicknesses of PMPCS shell. These results effectively proved that...

A Numerical Investigation on the Natural Frequencies of FGM Sandwich Shells with Variable Thickness by the Local Generalized Differential Quadrature Method

Abstract: The main aim of the present paper is to solve numerically the free vibration problem of sandwich shell structures with variable thickness and made of Functionally Graded Materials (FGMs). Several Higher-order Shear Deformation Theories (HSDTs), defined by a unified formulation, are employed in the study. The FGM structures are characterized by variable mechanical properties due to the through-the-thickness variation of the volume fraction distribution of the two constituents and the arbitrary thickness profile. A four-parameter power law expression is introduced to describe the FGMs, whereas general relations are used to define the thickness variation, which can affect both the principal coordinates of the shell reference domain. A local scheme of the Generalized Differential Quadrature (GDQ) method is employed as numerical tool. The natural frequencies are obtained varying the exponent of the volume fraction distributions using higher-order theories based on a unified formulation. The structural models considered are two-dimensional and require less degrees of freedom when compared to the corresponding three-dimensional finite element (FE) models, which require a huge number of elements to describe the same geometries accurately. A comparison of the present results with the FE solutions is carried out for the isotropic cases only, whereas the numerical results available in the literature are used to prove the validity as well as accuracy of the current approach in dealing with FGM structures characterized by a variable thickness profile.

Insights from the Shell Proteome: Biomineralization to Adaptation.

Abstract: Bivalves have evolved a range of complex shell forming mechanisms that are reflected by their incredible diversity in shell mineralogy and microstructures. A suite of proteins exported to the shell matrix space plays a significant role in controlling these features, in addition to underpinning some of the physical properties of the shell itself. Although, there is a general consensus that a minimum basic protein tool kit is required for shell construction, to date, this remains undefined. In this study the shell matrix proteins (SMPs) of four highly divergent bivalves (The Pacific oyster, Crassostrea gigas; the blue mussel, Mytilus edulis; the clam, Mya truncata and the king scallop, Pecten maximus) were analyzed in an identical fashion using proteomics pipeline. This enabled us to identify the critical elements of a “basic tool kit” for calcification processes, which were conserved across the taxa irrespective of the shell morphology and arrangement of the crystal surfaces. In addition, protein domains controlling the crystal layers specific to aragonite and calcite were also identified. Intriguingly, a significant number of the identified SMPs contained domains related to immune functions. These were often are unique to each species implying their involvement not only in immunity, but also environmental adaptation. This suggests that the SMPs are selectively exported in a complex mix to endow the shell with both mechanical protection and biochemical defense.

Phase field modeling of brittle fracture for enhanced assumed strain shells at large deformations: formulation and finite element implementation

Abstract: Fracture of technological thin-walled components can notably limit the performance of their corresponding engineering systems. With the aim of achieving reliable fracture predictions of thin structures, this work presents a new phase field model of brittle fracture for large deformation analysis of shells relying on a mixed enhanced assumed strain (EAS) formulation. The kinematic description of the shell body is constructed according to the solid shell concept. This enables the use of fully three-dimensional constitutive models for the material. The proposed phase field formulation integrates the use of the (EAS) method to alleviate locking pathologies, especially Poisson thickness and volumetric locking. This technique is further combined with the assumed natural strain method to efficiently derive a locking-free solid shell element. On the computational side, a fully coupled monolithic framework is consistently formulated. Specific details regarding the corresponding finite element formulation and the main aspects associated with its implementation in the general purpose packages FEAP and ABAQUS are addressed. Finally, the applicability of the current strategy is demonstrated through several numerical examples involving different loading conditions, and including linear and nonlinear hyperelastic constitutive models.

Selective Cation Exchange Enabled Growth of Lanthanide Core/Shell Nanoparticles with Dissimilar Structure

Abstract: Core/shell nanostructure is versatile for improving or integrating diverse functions, yet it is still limited to homeomorphism with isomorphic core and shell structure. Here, we delineate a selective cation exchange strategy to construct lanthanide core/shell nanoparticles with dissimilar structure. Hexagonal NaLnF4, a typical photon conversion material, was selected to grow cubic CaF2 shell to protect surface exposed Ln3+. Preferential cation exchange between Ca2+ and Na+ triggered the surface hexagonal-to-cubic structure evolution, which remediated the large barrier for heteroepitaxy of monocrystalline CaF2 shell. The heterostructured CaF2 shell leads to greatly enhanced upconversion emission with increased absolute quantum yield from 0.2% to 3.7%. Moreover, it is advantageous in suppressing the interfacial diffusion of Ln3+, as well as the leakage of Ln3+ from nanoparticle to aqueous system. These findings open up a new avenue for fabricating heterostructured core/shell nanoparticles, and are instructi...

Controlled Isotropic and Anisotropic Shell Growth in β-NaLnF4 Nanocrystals Induced by Precursor Injection Rate

Abstract: Precise morphology and composition control is vital for designing multifunctional lanthanide-doped core/shell nanocrystals. Herein, we report controlled isotropic and anisotropic shell growth techniques in hexagonal sodium rare-earth tetrafluoride (β-NaLnF4) nanocrystals by exploiting the kinetics of the shell growth. A drastic change of the shell morphology was observed by changing the injection rate of the shell precursors while keeping all other reaction conditions constant. We obtained isotropic shell growth for fast sequential injection and a preferred growth of the shell layers along the crystal’s c-axis [001] for slow dropwise injection. Using this slow shell growth technique, we have grown rod-like shells around different almost spherical core nanocrystals. Bright and efficient upconversion was measured for both isotropic and rod-like shells around β-NaYF4 nanocrystals doped with Yb3+/Er3+ and Yb3+/Tm3+. Photoluminescence upconversion quantum yield and lifetime measurements reveal the high quality...

Nonlinear thermoelastic frequency analysis of functionally graded CNT-reinforced single/doubly curved shallow shell panels by FEM

Abstract: In this article, the nonlinear vibration frequencies of functionally graded carbon nanotube-reinforced composite doubly curved shell panels under elevated thermal environment are numerically investigated using finite element method. The doubly curved carbon nanotube-reinforced shell panel has been modeled mathematically using higher-order kinematics theory and Green–Lagrange geometrical nonlinear strains. The properties of the individual constituents of the graded composite are assumed to be temperature dependent. In addition, the properties of the media are obtained based on the modified rule of mixture. The carbon nanotubes are dispersed nonuniformly through the thickness direction. The large deformation kinematic effects on the structural responses are counted by including all the nonlinear higher-order terms in the formulation. The desired nonlinear responses are computed numerically using our in-house computer code in conjunction with the direct iterative scheme. The convergence and the accur...

Improving the triethylamine sensing performance based on debye length: A case study on α-Fe2O3@NiO(CuO) core-shell nanorods sensor working at near room-temperature

Abstract: Metal oxide semiconductor (MOS) based gas sensors for triethylamine (TEA) are anticipated with low operating temperature, high response, and robust manufacturing process. TEA sensors with the α-Fe2O3@NiO or α-Fe2O3@CuO core-shell nanorods (NRs) heterostructure are successfully fabricated and their sensing performance is optimized by controlling the shell thickness based on Debye length. Porous α-Fe2O3 NRs are directly prepared on flat Al2O3 substrates by convenient hydrothermal process. The p-type shell layer is deposited by pulsed laser deposition (PLD) method, which width is controlled by changing the applied laser pulses. Due to the formation of PN heterojunction, the core-shell NR heterostructures show enhanced performances than pristine α-Fe2O3 NRs at near room-temperature, e.g. 40 °C. Moreover, such heterostructural sensor performances also exhibit a strong dependence on the shell thickness. When the p-type shell thickness is close to its Debye length (λd), the core-shell sensor of the highest response is realized. The enhanced sensing properties of this core-shell NR heterostructure toward TEA can be explained by the increase of initial resistance (Ra) due to the modulation of depletion layer through optimizing the p-type shell thickness.

Single Nozzle Electrospinning Synthesized MoO2@C Core Shell Nanofibers with High Capacity and Long-Term Stability for Lithium-Ion Storage

Abstract: MoO2@C core shell nanofibers are synthesized via a simple electrospinning method with a single nozzle. The formation mechanism of MoO2@C core shell nanofibers is investigated in detail and it is discovered that the phase-segregation phenomenon may be the main driving force of thermodynamics to form MoO2@C core shell nanofibers, and the high temperature as the dynamic factor can accelerate the formation of these core shell nanofibers. The carbon shell of the MoO2@C core shell nanofibers acts as both conductive bond to increase electrical conductivity and structural skeleton to maintain the integrity of MoO2 during Li+ insertion/extraction to achieve both high specific capacity and good cyclic stability. So as an anode for lithium-ion batteries, the MoO2@C core shell nanofiber electrode exhibits high specific capacity and extraordinary lifetime even at a large current density. Their reversible capacities are 665 mA h g−1 in the 600th cycle at 0.5 A g−1. Even at a high current density of 1 A g−1, a capacity of 537 mA h g−1 is obtained after 600 cycles. The present work may provide a facile and broadly applicable way for the fabrication and utilization of metal oxide/carbon core shell composites in fields of batteries, catalysts, and fuel cells.

Analysis of FG-CNT reinforced composite conical panel subjected to moving load using Ritz method

Abstract: Forced vibration response of a conical panel subjected to the action of a moving load is investigated in the current research Panel is made from a carbon nanotube (CNT) reinforced composite where the CNTs as reinforcements are distributed either uniformly or functionally graded across the panel thickness Panel is formulated using the first order shear deformation shell theory and the Donnell kinematic assumptions It is subjected to a moving load whose path and velocity are both arbitrary The properties of the composite media are estimated according to a refined rule of mixtures approach The governing equations of motion of the shell are obtained according to the Ritz method where the shape functions are obtained according to the Gram-Schmidt process The developed equations with the aid of Ritz method are transformed into time-dependent ordinary differential equations whose solution is traced in time by means of the Newmark time marching scheme Numerical results are provided to explore the influences of semi-vertex and opening angles of the cone, geometrical parameters and also CNT characteristics of the shell It is shown that, dynamic deflection of the shell decreases significantly with the introduction of FG-X pattern of CNTs Furthermore, enrichment of the matrix with more CNTs alleviates the dynamic deflection of the conical shell

Free Vibration Analysis of Functionally Graded Porous Doubly-Curved Shells Based on the First-Order Shear Deformation Theory

Abstract: Due to some technical issues that can appear during the manufacturing process of Functionally Graded Materials (FGMs), it can be extremely difficult to produce perfect materials. Indeed, one of the biggest problems is the presence of porosities. For this purpose, the vibrational behavior of doubly-curved shells made of FGM including porosities is investigated in this paper. With respect to previous research, the porosity has been added to the mechanical model that characterizes the through-the-thickness distribution of the graded constituents and applied to doubly-curved shell structures. Few papers have been published on this topic. In fact, it is easier to find works related to one-dimensional structures and beam models that take account the effect of porosities. The First-order Shear Deformation Theory (FSDT) is considered as the theoretical framework. In addition, the mechanical properties of the constituents vary along the thickness direction. For this purpose, two power-law distributions are employed to characterize their volume fraction. Strain components are established in an orthogonal curvilinear coordinate system and the governing equations are derived according to the Hamilton’s principle. Finally, Navier’s solution method is used and the numerical results concerning three different types of shell structures are presented.

The nonlinear vibration of orthotropic functionally graded cylindrical shells surrounded by an elastic foundation within first order shear deformation theory

Abstract: The non-linear free vibration behavior of functionally graded (FG) orthotropic cylindrical shell interacting with the two-parameter elastic foundation is investigated. The major goal of this research was to obtain a solution for the non-linear frequencies associated with the problem outlined above. The dynamic stability and compatibility equations of FG orthotropic cylindrical shells surrounded by an elastic foundation are derived within the first order shear deformation theory (FSDT) and von Karman strain displacement relationships, and then superposition and Galerkin methods are adopted to convert the above equations into a nonlinear ordinary differential equation. The expression for non-linear frequency of FG orthotropic cylindrical shell surrounded by an elastic foundation within the FSDT is obtained using the homotopy perturbation method (HPM). In particular, similar expression in the framework of the classical shell theory (CST) is obtained, also. The results are compared and validated with the results available in the literature. Finally, the calculation and presentation of the effect of many parameters included in the analysis conclude the goals to be reached in the study.

In-medium similarity renormalization group for closed and open-shell nuclei

Abstract: We present a pedagogical introduction to the In-Medium Similarity Renormalization Group (IM-SRG) framework for ab initio calculations of nuclei. The IM-SRG performs continuous unitary transformations of the nuclear many-body Hamiltonian in second-quantized form, which can be implemented with polynomial computational effort. Through suitably chosen generators, it is possible to extract eigenvalues of the Hamiltonian in a given nucleus, or drive the Hamiltonian matrix in configuration space to specific structures, e.g., band- or block-diagonal form. Exploiting this flexibility, we describe two complementary approaches for the description of closed- and open-shell nuclei: The first is the Multireference IM-SRG (MR-IM-SRG), which is designed for the efficient calculation of nuclear ground-state properties. The second is the derivation of nonempirical valence-space interactions that can be used as input for nuclear Shell model (i.e., configuration interaction (CI)) calculations. This IM-SRG+Shell model approach provides immediate access to excitation spectra, transitions, etc., but is limited in applicability by the factorial cost of the CI calculations. We review applications of the MR-IM-SRG and IM-SRG+Shell model approaches to the calculation of ground-state properties for the oxygen, calcium, and nickel isotopic chains or the spectroscopy of nuclei in the lower $sd$ shell, respectively, and present selected new results, e.g., for the ground- and excited state properties of neon isotopes.

Nonlinear dynamic analysis and vibration of eccentrically stiffened S-FGM elliptical cylindrical shells surrounded on elastic foundations in thermal environments

Abstract: Elliptical cylindrical shell is one of shells with special shape. Up to date, there is no publication on vibration and dynamic of functionally graded elliptical cylindrical shells. Therefore, the purpose of the present study is to investigate the nonlinear dynamic response and vibration of imperfect eccentrically stiffness functionally graded elliptical cylindrical shells on elastic foundations using both the classical shell theory (CST) and Airy stress functions method with motion equations using Volmir's assumption. The material properties are assumed to be temperature - dependent and graded in the thickness direction according to a Sigmoid power law distribution (S-FGM). The S-FGM elliptical cylindrical shell with metal-ceramic-metal layers are reinforced by outside metal stiffeners. Both the S-FGM elliptical shell and metal stiffeners are assumed to be in thermal environment and both of them are deformed under temperature simultaneously. Two cases of thermal loading (uniform temperature rise and temperature variation through thickness) are considered. The nonlinear motion equations are solved by Galerkin method and Runge-Kutta method (nonlinear dynamic response, natural frequencies). The effects of geometrical parameters, material properties, elastic foundations Winkler and Pasternak, the nonlinear dynamic analysis and nonlinear vibration of the elliptical cylindrical shells are studied. The some obtained results are validated by comparing with those in the literature.

Core–Shell Structure of Palladium Hydride Nanoparticles Revealed by Combined X-ray Absorption Spectroscopy and X-ray Diffraction

Abstract: We report an in situ, temperature and H2 pressure-dependent, characterization of (2.6 ± 0.4) nm palladium nanoparticles supported on active carbon during the process of hydride phase formation. For the first time the core–shell structure is highlighted in the single-component particles on the basis of a different atomic structure and electronic configurations in the inner “core” and surface “shell” regions. The atomic structure of these particles is examined by combined X-ray powder diffraction (XRPD), which is sensitive to the crystalline core region of the nanoparticles, and by first shell analysis of extended X-ray absorption fine structure (EXAFS) spectra, which reflects the averaged structure of both the core and the more disordered shell. In the whole temperature range (0–85 °C), XRPD analysis confirms the existence of two well-separated α- and β-hydride phases with the characteristic flat plateau in the phase transition region of the pressure-lattice parameter isotherms. In contrast, first shell in...

Static stability behavior of aluminum alloy single-layer spherical latticed shell structure with Temcor joints

Abstract: In recent years, aluminum alloy single-layer latticed shell has been extensively used in civil and industrial infrastructure. The elasticity modulus of aluminum alloy is low, the rigidity of aluminum joints are weak and the roof load transmission path is different. Therefore, the stability performance of this dome is unique. To clarify the stability performance of aluminum alloy single-layer latticed shell, over 500 aluminum alloy single-layer spherical latticed shells were analyzed with nonlinear finite method. The suggested values of rise/span ratio and initial imperfection were presented. The influencing coefficients of initial imperfection, material nonlinearity and stressed skin effect on stability bearing capacity were obtained. And the structural stability safety coefficient and the approximate calculation formula for stability bearing capacity of aluminum alloy single-layer spherical latticed shell were derived. The influences of joint semi-rigidity were investigated. All the aforementioned results provide a scientific basis for future stability design of aluminum alloy single-layer spherical latticed shell structure.

Dynamic stability analysis of a pressurized FG-CNTRC cylindrical shell interacting with supersonic airflow

Abstract: The objective of this research is to investigate the aeroelastic buckling and flutter instability of a pressurized functionally graded carbon nanotube reinforced composite (FG-CNTRC) cylindrical shell subjected to supersonic airflow. The dynamic model of the FG-CNTRC cylindrical shell is established in accordance with the first-order shear deformation theory, Donnell kinematic theory along with the von Karman geometrical nonlinearity. The quasi-steady Krumhaar's modified piston theory by considering the effect of the panel curvature is used to estimate the aerodynamic pressure induced by the supersonic airflow. The dynamic equations are discretized using trigonometric expansion through the circumferential direction and harmonic differential quadrature (HDQ) method through the meridional direction. Effects of boundary conditions, geometrical parameters, volume fraction and distribution of CNTs and the Mach number on the flutter instability, onset of the buckling and deformation shapes of the cylindrical shell are put into evidence through a set of parametric studies. The simulation indicates that the critical flutter dynamic pressure may be significantly enhanced through functionally graded distribution of CNTs in a polymer matrix. Furthermore, it is found that presence of the aerodynamic pressure may completely change deformation shapes of the FG-CNTRC cylindrical shell.