Shells Of Variable Thickness Research Articles

Effect of pH on the fabrication of lauric acid/Ag phase change nanocapsules via liquid-phase reduction

Phase change nanocapsules can be dispersed in fluids to form latant functional thermal fluids (LFTFs), which can serve as effective coolants for extending the lifespan of electronic devices. For this purpose, it is significant to prepare phase change capsules that possess excellent heat storage capacity, thermal conductivity, and suspension stability. In this paper, lauric acid/silver composite phase change nanocapsules were prepared by liquid-phase reduction method. To investigate the effect of pH value on capsule synthesis, six phase change capsule samples were prepared between pH values of 2.6–4.6. The results indicate that the prepared nanocapsules exhibited good heat storage capacity and thermal conductivity under different pH values. However, as pH increases, the silver shell thickness on the nanocapsule surface initially decreases and subsequently increases. The silver shell thickness of L3 is the thinnest, measuring 12.5 nm. Correspondingly, the enthalpy and volume encapsulation rate of the phase change capsules first increase and then decrease. The lauric acid/Ag nanocapsules possess a thermal conductivity in the 1.77–4.32 W/(m∙K) range. Further, it is found that pH affects the formation of silver shell on the surface of lauric acid/Ag phase change nanocapsules by influencing the electrostatic interactions between particles, and diffusion in the system, which explains the variation of silver shell thickness with pH value for the six capsule samples. We also found that the thinner the silver shell of the nanocapsules, the more advantageous it is to reduce the density of the capsules, thereby improving their suspension. Therefore, controlling the pH value during the preparation to obtain lauric acid/Ag phase change nanocapsules with thin silver shell thickness plays an important role in improving the overall performance of phase change nanocapsules used for preparing latent functionally thermal fluid.

Investigated numerically nanoshell thickness on photothermal response of hybrid nanostructures in an aqueous medium

The current study describes the effect of changing a shell thickness on photothermal response of a hybrid nanostructures, using theoretical investigation based on the Finite Element Method (FEM) of the COMSOL multi-physics program. The hybrid nanostructures are the Core/Shell nanoparticles (C/S NPs) and the Core/Multi-Shell nanoparticles (C/MS NPs), with fixed core diameter (30 nm) and variable shell thickness (10–20 nm) to create a new type of hybrid nanostructures usable in photonic and optoelectronic applications. For these hybrid nanostructures, gold (Au) and silver (Ag) as a partner of titanium dioxide (TiO2) were used in thermo-plasmonic part. Hybrid multi-shell nanostructures consist of silver-gold and gold-silver sandwich with titanium dioxide shell in between, all of which are dispersed in an aqueous medium (n = 1.33). The optical properties, the local field distribution, and local heating control of plasmonic nanostructures have been studied under the influence of illumination at plasmonic wavelengths (405, and 532 nm). The results revealed to a clear tunable and adjustable optical and thermo-plasmonic properties by controlling the structure of the core/shell NPs. This results can be enhanced by changing the shell thickness, shape, size, and the nanostructure. The temperature elevation of the core/shell NPs was about 1–5 °C under different wavelengths of laser irradiation. Based on those results, there is possibility of using the core/shell nanoparticles as an efficient heat source in many applications, such as in the sterilization and disinfection of medical equipments.

Analytical Study on the Buckling of Cylindrical Shells With Circumferential Thickness Variation Under Varying External Pressure

Abstract In this article, the analytical buckling load coefficient formula for a cylinder with circumferential thickness variation subjected to varying external pressure is established for the first time by developing a quadratic perturbation method. Based on the presented formula, some specific examples that consider either circumferential shell thickness variation or varying lateral pressure are studied and compared with those in the published literature. First, classical cosine thickness variation is analyzed. The computed results of buckling load coefficients indicate that most of differences between the proposed formula and finite element (FE) analyses in previous literature are less than 5%. Second, wind-type pressure load is discussed, and the maximum difference of predicted buckling load coefficients between our formula and results in published article is 2.3%. Third, both circumferential thickness variation and linear liquid pressure are analyzed by the proposed analytical formula and validated by the Galerkin method when both thickness and load variations are small. Therefore, accuracy and reliability of the established formula are validated. For the purpose of engineering application, buckling of a circular shell with local circumferential thickness variation due to weld shrinkage under wind-type pressure is analytically investigated. The effects of thickness variation amplitude, load parameter, half angle of thickness variation, and shell dimensions on buckling load coefficients are studied in detail.

Fe3O4/CoFe2O4 core-shell nanoparticles with enhanced magnetic properties for hyperthermia application

Fe3O4/CoFe2O4 core/shell nanoparticles with varying shell thickness were fabricated by seed-mediated growth via thermal decomposition method. Ligand exchange process using poly(maleic anhydride-alt-1-octadecene) (PMAO) was performed to prepare the aqueous magnetic fluids from the as-synthesised nanoparticles. X-ray diffraction (XRD), transmission electron microscopy (TEM) and Quantum Design PPMS VersaLab were utilised to characterise morphological and magnetic properties of the sample. XRD results showed that all the particles were single phase with spinel structure and the average crystallite size in the range of 11–17 nm. All particles were spherical in TEM images with similar size compared to results calculated from XRD. Magnetic measurements were performed at different temperatures (50 − 300 K) at 30 kOe. The result showed that the saturation magnetisation (M s) and coercivity (H C) were significantly increased with the formation of hard magnetic shell with varying thickness. The dynamic light scattering (DLS) analysis presented a narrow distribution and zeta potential of −16 to −35 mV, indicating a good stability of the ferrofluids. The cytotoxicity of the FOC3/PMAO ferrofluid, which has the highest SAR value of 372.02 W g−1, was tested on Hep-G2 cell line at different concentrations from 10 to 100 μg ml−1. Less than 30% of the cell was inhibited, indicating that the FOC3/PMAO particles have low toxicity at these tested concentrations. Thus, these as-synthesised core/shell nanoparticles with uniform particle size, high saturation magnetisation, good stability and five-time increased specific absorption rate (SAR) compared to the Fe3O4 core nanoparticles are very promising in hyperthermia and magnetic resonance imaging (MRI) applications.

Enhancing Mechanical Characteristics of PETG Carbon Fiber Composite through Various Shell Thickness in FDM Processing

The utilization of PETG (Polyethylene Terephthalate Glycol) carbon fiber composites in Fused Deposition Modelling (FDM) processes has gained significant attention due to their enhanced mechanical properties compared to traditional PETG filaments. This study focuses on investigating the impact of varying shell thickness on the mechanical characteristics of PETG carbon fiber composites fabricated through FDM. The objective is to optimize the shell thickness to achieve superior mechanical performance while maintaining printing efficiency. A series of PETG carbon fiber composites with different shell thicknesses were manufactured using an FDM 3D printer. Mechanical tests, including tensile strength, flexural strength, and impact resistance, were conducted to evaluate the performance of the fabricated specimens. Additionally, micro-structural analysis was performed to understand the influence of shell thickness on the interfacial bonding between PETG matrix and carbon fibers. Preliminary results indicate that increasing shell thickness positively affects the mechanical properties of PETG carbon fiber composites. Tensile and flexural strength show a noticeable improvement with an increase in shell thickness, attributed to enhanced interlayer adhesion and improved load-bearing.

Quantifying tidal versus non-tidal stresses in driving time-varying fluxes of Enceladus' plume eruptions

In this study we investigate the relative importance of endogenic vs. exogenic stresses in controlling the location and timing of active ice-shell deformation on Enceladus, which is expressed by cyclic plume eruptive flux along active fault zones (i.e., the tiger stripes). Although the variation of the eruption flux on Enceladus follows the periodicity of the diurnal tide, it remains unclear why there is a consistent phase delay of the observed peak eruption when compared to the predicted peak tidal stress. Here, we explore whether endogenic stresses in the ice shell are capable of explaining this observed phase delay. To achieve this goal, we performed geologic mapping along the tiger-stripe faults that host the erupting plumes. Using the fault kinematics established from our mapping, we determine the general stress state (i.e., the principal-stress directions) along the tiger-stripe faults. This knowledge in turn forms the basis for inferring the most likely plume-eruption mechanism. Our mapping shows that the tiger-stripe fractures are not tensile cracks but are instead left-slip fault zones locally displaying extensional fissures. This insight leads to a hypothesis that strike-slip faults and their local tensile cracks experience simultaneous shear and tensile failure, and that the tensional opening reaches maximum at the time of the peak plume flux. We quantified this hypothesis using a stress decomposition model that assesses (1) the relative importance in magnitude between the tectonic stress and tidal stress exerted on the tiger-stripe faults and (2) the role of ice shell properties such as the shear strengths, tensile strengths, and ice shell thickness in controlling the eruption phase delay. Using laboratory-determined ice strengths and the best estimate of the ice shell thickness at the South Polar Terrain of Enceladus, which hosts the tiger-stripe faults, our model results indicate that the endogenic tectonic stress is comparable in magnitude to the tidal stress. Although we cannot rule out warm-ice convection, true polar wander, and non-synchronous rotation as causes of endogenic stresses, the large variation in ice shell thickness makes the lateral gravitational-potential gradient the most plausible source of the endogenic stress required by our model results.

A hierarchic isogeometric hyperelastic solid-shell

The present study aims to develop an original solid-like shell element for large deformation analysis of hyperelastic shell structures in the context of isogeometric analysis (IGA). The presented model includes a new variable to describe the thickness change of the shell and allows for the application of unmodified three-dimensional constitutive laws defined in curvilinear coordinate systems and the analysis of variable thickness shells. In this way, the thickness locking affecting standard solid-shell-like models is cured by enhancing the thickness strain by exploiting a hierarchical approach, allowing linear transversal strains. Furthermore, a patch-wise reduced integration scheme is adopted for computational efficiency reasons and to annihilate shear and membrane locking. In addition, the Mixed-Integration Point (MIP) format is extended to hyperelastic materials to improve the convergence behaviour, hence the efficiency, in Newton iterations. Using benchmark problems, it is shown that the proposed model is reliable and resolves locking issues that were present in the previously published isogeometric solid-shell formulations.

Microcapsule Triggering Mechanics in Cementitious Materials: A Modelling and Machine Learning Approach.

Self-healing cementitious materials containing microcapsules filled with healing agents can autonomously seal cracks and restore structural integrity. However, optimising the microcapsule mechanical properties to survive concrete mixing whilst still rupturing at the cracked interface to release the healing agent remains challenging. This study develops an integrated numerical modelling and machine learning approach for tailoring acrylate-based microcapsules for triggering within cementitious matrices. Microfluidics is first utilised to produce microcapsules with systematically varied shell thickness, strength, and cement compatibility. The capsules are characterised and simulated using a continuum damage mechanics model that is able to simulate cracking. A parametric study investigates the key microcapsule and interfacial properties governing shell rupture versus matrix failure. The simulation results are used to train an artificial neural network to rapidly predict the triggering behaviour based on capsule properties. The machine learning model produces design curves relating the microcapsule strength, toughness, and interfacial bond to its propensity for fracture. By combining advanced simulations and data science, the framework connects tailored microcapsule properties to their intended performance in complex cementitious environments for more robust self-healing concrete systems.

A facile synthetic approach for TiO2@NiO core‐shell nanoparticles using TiO2@Ni(OH)2 precursors and their photocatalytic application

AbstractThe current study presents a simple and an efficient chemical method for the synthesis of TiO2@NiO core‐shell nanoparticles (CSNPs) as photocatalyst for effective degradation of rhodamine B (RhB) in an aqueous solution upon sunlight irradiation. First, TiO2 spheres were synthesized using a wet chemical method. Then, TiO2@Ni(OH)2 precursors were prepared via homogeneous precipitation and TiO2@NiO core‐shell nanoparticles were obtained on calcination of the precursors. The synthesized precursors and the TiO2@NiO CSNPs were analyzed using XRD, FT‐IR, FESEM and DRS. XRD data shows the presence of both TiO2 and NiO phases in the TiO2@NiO samples. FE‐SEM and TEM analyses confirm coating of NiO NPs on TiO2 spheres with varying shell thickness (40 nm to 170 nm). Optical studies reveal that TiO2@NiO CSNPs possess band gap of about 3.7 eV. Photoluminescence (PL) results show lower recombination rate of e− and h+ pairs in the TiO2@NiO CSNPs. XPS studies confirm the presence of different elements in the TiO2@NiO CSNPs. Magnetic investigations reveal ferromagnetic behavior of the core‐shell NPs at 5 K. The TiO2@NiO CSNPs were explored as photocatalyst for the degradation of rhodamine B in water under natural sunlight. The TiO2@NiO CSNPs exhibit better photocatalytic activity compared to TiO2 and NiO nanoparticles.

Thermally assisted optical processes in InP/ZnS quantum dots.

The utilization of InP-based biocompatible quantum dots (QDs) necessitates a comprehensive understanding of the structure-dependent characteristics influencing their optical behavior. The optimization of core/shell QDs for practical applications is of particular interest due to their reduced toxicity, enhanced photostability, and improved luminescence efficiency. This optimization involves analyzing thermally activated processes involving exciton and defect-related energy levels. This study investigates water-soluble colloidal InP/ZnS QDs with varying shell thicknesses and stabilizing coatings using temperature-dependent optical absorption (OA) and photoluminescence (PL). Our results indicate that all samples experience temperature-induced shifts in exciton absorption and luminescence peaks due to interactions with acoustic phonons. Despite the wide size distribution of nanocrystals, the halfwidth of the bands remains constant. We observe a temperature-dependent Stokes shift in InP/ZnS QDs, revealing the fine structure of exciton states across different configurations. Furthermore, our findings demonstrate common mechanisms underlying PL thermal quenching in these QDs, regardless of the shell thickness or coating type. Specifically, defect-related emissions arise from localized energy levels at the core/shell interface. At the same time, exciton PL quenching primarily occurs through thermally activated electron migration from the InP core to the ZnS shell. Overall, our study highlights the potential for tailoring the temperature response of InP/ZnS QDs by adjusting shell thickness, offering opportunities to optimize their performance for specific applications.

Analysis of the Dynamic Characteristics of Conical Shells of Variable Thickness on an Elastic Bed Under Unsteady Loading

Analysis of the Dynamic Characteristics of Conical Shells of Variable Thickness on an Elastic Bed Under Unsteady Loading

Core atoms escape from the shell: reverse segregation of Pb–Al core–shell nanoclusters via nanoscale melting

Melting is a phase transition that profoundly affects the fabrication and diverse applications of metal nanoclusters. Core–shell clusters offer distinctive properties and thus opportunities compared with other classes of nano-alloys. Molecular dynamics simulations have been employed to investigate the melting behaviour of Pb–Al core–shell clusters containing a fixed Pb147 core and varying shell thickness. Our results show that the core and shell melt separately. Surprisingly, core melting always drives the core Pb atoms to break out the shell and coat the nanoclusters in a reversed segregation process at the nanoscale. The melting point of the core increases with the shell thickness to exceed that of the bare core cluster, but the thinnest shell always supresses the core melting point. These results can be a reference for the future fabrication, manipulation, and exploitation of the core–shell nanoalloys chosen. The system chosen is ideally suited for experimental observations.

Rational construction of hollow ZnO@SnS2 core-shell nanorods: A way to boost catalytic removal of Cr (VI) ions, antibiotic and industrial dyes

Herein, the novel hollow ZnO@SnS2 core-shell nanorods with variable shell thickness have been synthesized by a chemical synthesis approach. The transmission electron microscopy (TEM) images signified the creation of a hollow core-shell nanostructure. The SnS2 layer coating on ZnO nanorods broadens visible light absorption and suppresses near-band edge emission of ZnO nanorods. Interestingly, the band gap (optical) of the developed ZnO nanorods decreased from 3.3 eV to 2.1 eV after the coating of SnS2 shell. Consequently, the coated hollow ZnO@SnS2 core-shell nanorods displayed a significant enhancement in catalytic activity for the decomposition of toxic industrial dyes, pharmaceutical pollutant tetracycline, and Cr(VI) ion in comparison to hollow ZnO NRs. The photon-induced charge carrier generation and separation were confirmed by the three-electrode electrochemical amperometric analysis and impedance analysis under illumination of simulated solar light (AM 1.5, One Sun). Moreover, an exceptionally higher photocurrent generation (∼10 times higher than ZnO nanorod). The improved ZnO@SnS2 core shell NRs catalytic activity was attributed to its core-shell structure, proper band structure, and effective charge carrier transfer across the core shell interface. This work offers new insights for the design and growth of visible light-active core shell nanorods for resolving environmental pollution and photocurrent generation.

Damage performance and failure analysis of reinforced concrete doubly curved shells under seismic excitations considering curvature and thickness variation

Most of the past investigations on the structural response of the doubly curved shell (DCS) roofs under seismic excitation were limited to linear dynamic analysis, whereas nonlinear dynamic analysis was rarely introduced, making it difficult to understand their dynamic behavior and draw general conclusions. Therefore, in the current study, linear dynamic analysis (LDA) and nonlinear dynamic analysis (NLDA) are conducted in tandem to fill the gap in the literature and give a complete perception of how these roofs respond to earthquakes. To this end, an innovative automatic finite element-based design algorithm is developed to obtain the steel reinforcement in preparation for the NLDA. Accordingly, the current study exploits the multi-layered shell element incorporated with the multi-axial concrete damage plasticity model (implemented via VUMAT subroutine) and the developed design algorithm (via Python script) to perform the NLDA and accurately capture the structural response and damage performance of these roofs. Unlike most common structures, the results demonstrated that DCS is highly affected by the vertical component of the earthquake rather than the horizontal component. The NLDA revealed that the shell exhibits severe damage and a high displacement response under strong seismic excitations, which could not be captured via the LDA. Additionally, the failure analysis is performed for the studied roof, considering the variation in shell curvature and thickness. This analysis shows a notable decrease in the demand-capacity ratio and steel rebar’s stress with increasing the shell curvature. Consequently, according to the proposed performance levels, the shell’s state changed from the initial failure to the elastic state. In contrast, slight changes in the overall behavior are observed due to the variation in the shell thickness. Finally, a new formula is proposed to predict the damage induced in the DCS under seismic excitations.

Free Vibration Analysis of a Cylindrical Shell of Variable Thickness Partially Filled with Fluid

Free Vibration Analysis of a Cylindrical Shell of Variable Thickness Partially Filled with Fluid

Quantitative Elasticity Mapping of Submicron Silica Hollow Particles by PeakForce QNM AFM Mode.

Silica hollow spheres with a diameter of 100-300 nm and a shell thickness of 8±2 nm were synthesized using a self-templating amphiphilic polymeric precursor, i.e., poly(ethylene glycol)-substituted hyperbranched polyethoxysiloxane. Their elastic properties were addressed with a high-frequency AFM indentation method based on the PeakForce QNM (quantitative nanomechanical mapping) mode enabling simultaneous visualization of the surface morphology and high-resolution mapping of the mechanical properties. The factors affecting the accuracy of the mechanical measurements such as a local slope of the particle surface, deformation of the silica hollow particles by a solid substrate, shell thickness variation, and applied force range were analysed. The Young's modulus of the shell material was evaluated as E=26±7 GPa independent of the applied force in the elastic regime of deformations. Beyond the elastic regime, the buckling instability was observed revealing a non-linear force-deformation response with a hysteresis between the loading and unloading force-distance curves and irreversible deformation of the shell at high applied forces. Thus, it was demonstrated that PeakForce QNM mode can be used for quantitative measurements of the elastic properties of submicon-sized silica hollow particles with nano-size shell thickness, as well as for estimation of the buckling behaviour beyond the elastic regime of shell deformations.

Inferring the Mean Thickness of the Outer Ice Shell of Enceladus From Diurnal Crustal Deformation

AbstractThe thickness of the outer ice shell plays an important role in several geodynamical processes at ocean worlds. Here, we show that observations of tidally driven diurnal surface displacements can constrain the mean ice shell thickness, . Such estimates are sensitive to any significant structural features that break spherical symmetry such as faults and lateral variation in ice shell thickness and structure. We develop a finite‐element model of Enceladus to calculate diurnal tidal displacements for a range of values in the presence of such structural heterogeneities. Consistent with results from prior studies, we find that the presence of variations in ice shell thickness can significantly amplify deformation in thinned regions. If major faults are also activated by tidal forcing—such as Tiger Stripes on Enceladus—their characteristic surface displacement patterns could easily be measured using modern geodetic methods. Within the family of Enceladus models explored, estimates of that assume spherical symmetry a priori can deviate from the true value by as much as ∼41% when structural heterogeneities are present. Additionally, we show that crustal heterogeneities near the South Pole produce differences of up to 35% between Love numbers evaluated at different spherical harmonic orders. A ∼41% range in estimates of from Love numbers is smaller than that found with approaches relying on static gravity and topography (∼250%) or analyzing diurnal libration amplitudes (∼85%) to infer at Enceladus. As such, we find that analysis of diurnal tidal deformation is a relatively robust approach to inferring mean crustal thickness.

Fluidic microencapsulation of calcium chloride hexahydrate phase change material in resorcinol formaldehyde shell

Phase change material, encapsulated in micro-particles are required extensively in temperature control and heat storage applications. The encapsulation through random mixing and chemical emulsification does not allow use of inorganic salt as PCM that is otherwise known to be safe and effective. Microencapsulation of an inorganic phase change material in resorcinol resin shell is demonstrated here by co-flowing the two phases in a fluidic device, and inducing instability driven disintegration of core-sheath filament. Highly unimodal sized microcapsules with diameter of 978 µm ± 75 µm and uniform coating thickness were evident from the optical microscope as well as scanning electron microscope images. The heat absorption and release characteristics of microcapsules with varied shell thickness of 1.57 µm, 4.05 µm and 12.8 µm were studied by differential scanning calorimetry. The integrity of the shell was evaluated through sustained dipping of microcapsules in water, and measuring the electrical conductivity. The fractional release was restricted to about 10% of in-place PCM after 30 days. The results serve as proof of concept for the fluidic microencapsulation in general, and inorganic material in particular, which in spite of possessing many favourable aspects has not been studied till date for thermal control and energy harvesting applications.

Buckling Behavior Analysis of Thin-Walled Cylindrical Shell Structure Under Localized Axial Compression Load Based on Initial Imperfection Sensitivity

In practical engineering, a thin-walled cylindrical shell structure is more easily subjected to localized axial compression loads caused by external adjacent structures or devices. However, until now there are few studies to reveal the buckling behavior of cylindrical shells under such nonuniform loading conditions based on initial imperfection sensitivity. Therefore, buckling analysis of cylindrical shell under localized axial compression loads is investigated in this paper. Based on the buckling test, the influence of the morphology and amplitude of measured initial geometric imperfection are studied using the finite element method. Meanwhile, the inherent reason for initial geometric imperfection affecting the buckling load is elaborated. The influence of amplitude, distribution range, and different combinations of local dent imperfections are also elucidated. In addition, the effects of inclined loading imperfection and uneven shell thickness distribution imperfection are analyzed in the form of deterministic numerical simulation. Finally, a new buckling load knockdown factor that can reasonably consider the influence of loading imperfection and shell thickness variation imperfection is proposed. This work elucidates the initial imperfection sensitivity of the thin-walled cylindrical shell structures under localized axial compression load and can provide useful guidance for the buckling design and preventing buckling failure of these structures.

Machine learning-based optimization design of bistable curved shell structures with variable thickness

The mechanical performance of curved shell structures is difficult to predict due to their complex geometric nonlinearity. There have been many efforts to improve the mechanical property of curved shell structures by designing the thickness distributions. However, due to the nonlinear characteristics of variable-thickness shells, it is impossible to exhaust all possible structural forms through experimental and theoretical approaches. In this paper, we report a new machine learning (ML)-based approach to design and optimize bistable curved shell structures. The ML model is used to establish the underlying mapping relationship between structural parameters and specific performance. Nonlinear shell structures are efficiently and accurately designed and optimized with optimal backward snapping forces (B). The results demonstrate an effective approach for the design and optimization of curved shell structures and provide a valuable reference for future study of nonlinear structures. Moreover, this approach presents an efficient means of designing advanced metamaterials. The modular design of meta-atoms based on ML has the potential to construct metamaterials with specific properties and functionalities, which will lead to extensive applications in different fields.