Wall Thickness Of Spheres Research Articles

Mechanical performance of hexagonal close-packed hollow sphere infill structures with shared walls under compression load

Infill structures of additive manufactured components give not only stability, but can be used as a design feature regarding lightweight and mechanical properties. In this study, an infill structure was investigated which consists of hollow spheres in a hexagonal closed packing. An additional characteristic is, that the contact between the spheres is modelled as an intersection. A script-based design approach was used for generating the structure within a cylinder. Thus, the sphere diameter, the sphere wall thickness and the outer shell thickness can be varied. The deformation behavior was studied using the Finite Element Method (FEM). Compression tests on additive manufactured cylindrical specimens verify the FEM results: (1) appropriate modelling of the contact between the spheres enhances the stability to the structure. (2) Increasing the relative density increases the mechanical properties. (3) Lower values for the relative sphere wall thickness result in an improved ductility.

In situ decoration of Co3O4 on N-doped hollow carbon sphere as an effective bifunctional oxygen electrocatalyst for oxygen evolution and oxygen reduction reactions

Transition metal oxide based materials are believed as a sustainable and effective electrocatalysts for oxygen evolution and oxygen reduction reactions (OER/ORR). However, poor conductivity, specific surface area, and tunable crystallography are major bottlenecks. To alleviate such issues, we developed a highly active spinel Co3O4 decorated N-doped hollow carbon sphere (Co3O4/NHCS) by single step decoration using cobalt phthalocyanine (CoPc) precursor for the first time. The introduction of various extents of CoPc significantly affects the sphere wall thickness, defect sites, doping amount of cobalt content, and the concentration of Co3+ and Co2+ sites. The resulting optimum loading of 0.2 g of Co3O4/NHCS-0.2, exhibits a highly uniform hollow carbon sphere with a high wall thickness (61 nm), better surface area (445 m2 g−1), and moderate defect sites. Notably, an exterior concentration of octahedral Co3+ (35.50%) and tetrahedral Co2+ (26.54%) sites serve as the active centres for OER and ORR, respectively. Remarkably, the obtained material exhibits exceptional OER performance with a potential of 1.80 V vs. RHE in 0.1 M KOH medium for achieving a current density of 10 mA cm−2, outperforming the benchmark RuO2 material. In addition, Co3O4/NHCS-0.2 demonstrates an impressive ORR electrocatalytic activity with onset potential of 0.89 V vs. RHE, excellent current density of 5.0 mA cm−2, lower Tafel slope of 60 mV dec−1 and close to four electron transfer. Moreover, the moderate carrier concentration, flat band potential, higher tetrahedral Co2+ and pyridinic N sites significantly improved the ORR activity and methanol oxidation tolerance ability.

Researches on compressive mechanical property of thin‐walled hollow spheres structure

AbstractThe compressive mechanical property of thin‐walled hollow spheres structure is researched by experiment and finite element method in this paper. Due to the ideal elastic‐plastic material and extremely thin but uniform wall thickness, Ping‐Pong balls are bonded together with a linking neck to comprise the ideal model of thin‐walled hollow spheres structure. The experimental result validates the effectiveness of the finite element model. The effects of the material and geometry parameters of the spheres and linking neck are then investigated by finite element method. The results reveal that: 1) The deformation process of the two‐ball bonding structure includes four stages: elastic deformation, axisymmetric buckling, forming non‐axisymmetric polygon and transforming to axisymmetric mode (or structural self‐contact behavior); 2) the Young's modulus and initial yield stress are basically unaffected by the linking neck center thickness, but they increase linearly with the hollow sphere wall thickness and linking neck radius as well as the Young's modulus and yield stress of material, and the linear correlation of the material yield stress is the lowest; 3) the strain of structural self‐contact behavior increases with the linking neck center thickness and radius.

Transient sound radiation from an impulsively excited piezoelectric composite hollow sphere in a wedge-shaped acoustic domain

The exact 3D linear piezoelasticity theory, the linear acoustic wave equation, and the classical method of images are employed for the coupled acousto-elastodynamic time response analysis of an arbitrarily thick two-layered elasto-piezoelectric composite hollow sphere that is freely suspended in a perfect acoustic wedge with impenetrable (rigid/compliant) boundaries, while subjected to arbitrary (non-axisymmetric) non-stationary electro-mechanical excitations. Problem solution is attained by application of the method of eigen-function expansion, a revised form of translational addition theorems for modified spherical Bessel functions in Laplace transform domain, and Durbin’s numerical inversion algorithm with an advanced (modified Cesàro) convergence improvement scheme. Numerical simulations include selected radiated pressure time signatures of a water-submerged air-filled PZT4/aluminum spherical shell driven by a pair of external diametrical short duration mechanical pulses. The effects of sphere wall thickness, wedge opening (apex) angle (γ=π/6,π/4,π/2) and surface condition (hard or pressure-release) are examined. Also, some noteworthy features of the transient fluid/structure interaction are recognized through proper 2D visualizations of the internal and external sound fields. Lastly, accuracy of the proposed acousto-elastic model is confirmed with the help of a commercial FEA software in addition to comparison with the available data.

Synthesis and Quasi-Static Compressive Properties of Mg-AZ91D-Al₂O₃ Syntactic Foams.

Magnesium alloys have considerably lower density than the aluminum alloy matrices that are typically used in syntactic foams, allowing for greater specific energy absorption. Despite the potential advantages, few studies have reported the properties of magnesium alloy matrix syntactic foams. In this work, Al2O3 hollow particles of three different size ranges, 0.106–0.212 mm, 0.212–0.425 mm, and 0.425–0.500 mm were encapsulated in Mg-AZ91D by a sub-atmospheric pressure infiltration technique. It is shown that the peak strength, plateau strength and toughness of the foam increases with increasing hollow sphere wall thickness to diameter (t/D) ratio. Since t/D was found to increase with decreasing hollow sphere diameter, the foams produced with smaller spheres showed improved performance—specifically, higher energy absorption per unit weight. These foams show better performance than other metallic foams on a specific property basis.

Model-based analysis of thermal insulation coatings

Thermal insulation properties of coatings based on selected functional filler materials are investigated. The underlying physics, thermal conductivity of a heterogeneous two-component coating, and porosity and thermal conductivity of hollow spheres (HS) are quantified and a mathematical model for a thermal insulation coating developed. Data from a previous experimental investigation with hollow glass sphere-based epoxy and acrylic coatings were used for model validation. Simulations of thermal conductivities were in good agreement with experimental data. Using the model, a parameter study was also conducted exploring the effects of the following parameters: pigment (hollow spheres) volume concentration (PVC), average sphere size or sphere size distribution, thermal conductivities of binder and sphere wall material, and sphere wall thickness. All the parameters affected the thermal conductivity of an epoxy coating, but simulations revealed that the most important parameters are the PVC, the sphere wall thickness, and the sphere wall material. The model can be used, qualitatively, to get an indication of the effect of important model parameters on the thermal conductivity of an HS-based coating and thereby be used as a specification tool or as a help in the planning of relevant experiments to conduct. Further work with the model must involve additional experiments to secure a general verification of important underlying model assumptions.

Effect of hollow sphere size and size distribution on the quasi-static and high strain rate compressive properties of Al-A380–Al2O3 syntactic foams

Metal matrix syntactic foams are promising materials for energy absorption; however, few studies have examined the effects of hollow sphere dimensions and foam microstructure on the quasi-static and high strain rate properties of the resulting foam. Aluminum alloy A380 syntactic foams containing Al2O3 hollow spheres sorted by size and size range were synthesized by a sub-atmospheric pressure infiltration technique. The resulting samples were tested in compression at strain rates ranging from 10−3 s−1 using a conventional load frame to 1720 s−1 using a Split Hopkinson Pressure-bar test apparatus. It is shown that the quasi-static compressive stress–strain curves exhibit distinct deformation events corresponding to initial failure of the foam at the critical resolved shear stress and subsequent failures and densification events until the foam is deformed to full density. The peak strength, plateau strength, and toughness of the foam increases with increasing hollow sphere wall thickness to diameter (t/D) ratio. Since t/D was found to increase with decreasing hollow sphere diameter, the foams produced with smaller spheres showed improved performance. The compressive properties did not show measurable strain rate dependence.

Dynamic Properties of Density Graded Thin-Walled Metal Hollow Sphere Arrays

In order to improve the dynamic properties of uniform cellular materials, a 2D density graded metal hollow sphere (MHS) array is investigated by explicit finite element method (FEM) simulation of in-plane crushing of sphere systems. The grading is established by changing sphere wall thickness. Pattern transformation from a square lattice to a hexagonal one is formed at a low impact velocity as observed in experiments. The emphasis is placed on the influence of gradient profile on the energy absorption of materials under high impact velocities. The relation between material dynamic responses and gradients as well as impact velocities is established for design purpose.

One-pot template-free preparation of mesoporous TiO2 hollow spheres and their photocatalytic activity

Mesoporous TiO2 hollow spheres were prepared in a solvothermal process, which did not involve any templates and surfactants. Meanwhile, the photocatalytic activity of TiO2 hollow spheres was studied using methyl orange as a probe. The results indicate that the anatase TiO2 hollow spheres with mesoporous walls and high specific surface area (141m2g−1) can be obtained using this simple method. The mean diameter and wall thickness of spheres are about 700nm and 90nm, respectively. Moreover, the as-prepared TiO2 hollow spheres display high photocatalytic activity with 98% of degradation ratio of methyl orange after 30min irradiation.

Thermal Conductivity Computations of Sintered Hollow Sphere Structures

The thermal conductivity of sintered hollow sphere structures (HSS) is investigated within the scope of this paper. For this purpose, finite element analyses based on micro-computed tomography images are performed on HSS structures. The complex geometry of the real sintered HSS sample is accurately captured with this new hybrid method. The numerical computations are investigated in three perpendicular directions (i.e., x, y and z) in order to examine the anisotropic material behaviour. The results indicate that sintered HSS reveals quasi-isotropic behaviour in terms of effective thermal conductivity. For the first time, the influence of the sphere wall thickness of real HSS is investigated. To this end, the computed tomography data is carefully manipulated by changing the thickness of the hollow sphere wall. The variation of the wall thickness alters the relative density and has a significant influence on the thermal conductivity. The influence of the relative density on the thermal conductivity reveals a linear dependency.

Finite Element Parametric Analysis on Bearing Capacity of Cast Steel Spherical Joint

Nonlinear finite element analysis of the cast steel spherical joint is performed by using ANSYS program. The deformation process, the failure mode and the effects of parameters on bearing capacity for the joint are analyzed. The results show that the outer diameter of sphere D, wall thickness of sphere t, external diameter of cast steel tube d, radius of outer fillet r which is located in the connection of sphere to cast steel tube, material strength f have remarkable effects on the bearing capacity of the joint. The results also show that with the increasing of parameter t, d, r, and f, the bearing capacity increases, and with the increasing of parameter D, the bearing capacity decreases.

Impact Behavior of Composite Hollow Sphere Structures

Porous composite materials constitute an innovative group of lightweight materials which combine high specific stiffness, good damping properties, and thermal insulation with the ability to absorb large amounts of energy at a low constant stress level. In the scope of this study, adhesively bonded metallic hollow sphere structures (MHSS) fully embedded within the adhesive matrix are considered with aim to determine their macroscopic behavior under uniaxial impact loading conditions by means of parametric computational simulations. The base material properties have been determined by quasi-static and dynamic experiments. Three topologies of syntactic hollow sphere structures of various dimensions are considered, namely the cubic primitive, the body centered cubic and the face centered cubic topology. Results of computational simulations show significant influence of topology and strain rate sensitivity on the composite structure behavior, while the influence of metallic hollow sphere wall thickness is less pronounced. Computational simulations show that it is possible to combine the MHSS topology, metallic hollow sphere wall thickness and strain rate sensitivity to achieve any desired dynamic response of MHSS adapted to a given engineering problem.

Fatigue in aluminum–steel and steel–steel composite foams

The compression–compression fatigue behavior of two classes of composite metal foams (CMF) manufactured using different processing techniques, was investigated experimentally. Aluminum–steel composite foam processed using gravity casting technique comprises of steel hollow spheres and a solid aluminum alloy matrix. Steel–steel composite foam, processed using powder metallurgy (PM) technique consists of steel hollow spheres packed in a steel matrix. Under compression fatigue loading, the composite foam samples showed a high cyclic stability at maximum stress levels as high as 90 MPa. The deformation of the composite foam samples was divided into three stages – linear increase in strain with fatigue cycles (stage I), minimal strain accumulation in large number of cycles (stage II) and rapid strain accumulation within few cycles culminating in complete failure (stage III). Composite foams under cyclic loading undergo a uniform distribution of deformation, unlike the regular metal foams, which deform by forming collapse bands at weaker sections. As a result, the features controlling the fatigue life of the composite metal foams have been considered as sphere wall thickness and diameter, sphere and matrix materials, processing techniques and the bonding strength between the spheres and matrix.

Behaviour of Syntactic and Partial Hollow Sphere Structures under Dynamic Loading

The paper investigates the macroscopic behaviour of adhesively bonded metallic hollow sphere structures fully and partially embedded within an adhesive matrix subjected to compressive dynamic loading by means of computational simulations. Different influences e.g. morphology, topology, sphere wall thickness and strain rate sensitivity have been analyzed.

Influence of the Morphology of Joining on the Heat Transfer Properties of Periodic Metal Hollow Sphere Structures

Hollow sphere structures (HSS) constitute a group of innovative materials which are characterised by more constant material properties compared to classical cellular metals [1]. Their big potential lies within multifunctional applications where combinations of their proper- ties yield symbiotic advantages. In the scope of this paper their effective thermal conductivity is investigated. In addition to the analysis of the dependency of this material parameter on the conductivities of the base materials and the sphere wall thickness, special focus is given to the influence of the morphology of joining.

New Composite Metal Foams under Compressive Cyclic Loadings

New composite metal foams are processed using powder metallurgy (PM) and gravity casting techniques. The foam is comprised of steel hollow spheres, with the interstitial spaces occupied by a solid metal matrix (Al or steel alloys). The cyclic compression loading of the products of both techniques has shown that the composite metal foams have high cyclic stability at very high maximum stress levels up to 68 MPa. Under cyclic loading, unlike other metal foams, the composite metal foams do not experience rapid strain accumulation within collapse bands and instead, a uniform distribution of deformation happen through the entire sample until the densification strain is reached. This is a result of more uniform cell structure in composite metal foams compared to other metal foams. As a result, the features controlling the fatigue life of the composite metal foams have been considered as sphere wall thickness and diameter, sphere and matrix materials, and processing techniques as well as bonding strength between the spheres and matrix.

Compressive Properties and Energy Absorption of Hollow Sphere Aluminum

Manufactured cellular aluminums have been developed for a wide range of automotive applications where weight savings, improved safety, crashworthiness and comfort are required. The plateau deformation behavior of cellular aluminums under compressive loading makes this new class of lightweight materials suitable for energy absorption and comes close to ideal impact absorbers. In the present study, aluminum hollow hemispheres were firstly processed by pressing. Hollow sphere aluminum samples with a body-centered cubic (BCC) packing were then fabricated by bonding together single hollow spheres, which were prepared by adhering together hollow hemispheres. Hollow sphere aluminum samples with various kinds of sphere wall thicknesses of 0.1 mm, 0.3 mm and 0.5 mm but the same outside diameter of 4 mm were investigated by compressive tests. The effects of the sphere wall thickness on the mechanical properties and energy absorption characteristics were investigated.

Hollow Titania Spheres from Layered Precursor Deposition on Sacrificial Colloidal Core Particles

The preparation of monodisperse hollow titania spheres with defined diameter, wall thickness and crystal phase is reported. The hollow spheres have been produced by the layered deposition of a water-soluble titania precursor, e.g. titanium(IV) bis (ammonium lactato) dihydroxide (TALH), in alternation with poly(diallydimethylammonium chloride) (PDADMAC) onto submicrometer-sized template particles e.g. polystyrene (PS) particles, followed by calcination at elevated temperatures. the layer-by-layer growth of the coating on the colloid particles was observed by microelectrophoresis and transmission electron microscopy (TEM). Calcination of the TALH/PDADMAC-coated particles resulted in intact, hollow titania spheres, as confirmed by scanning electron microscopy (SEM) and TEM. Calcining the coated particles at 450 or 950° C resulted in hollow sphere consisting of titania in anatase or rutile form, respectively. Nanometer-level control over the sphere wall thickness was achieved by varying the number of layers deposited on the PS particles. The hollow titania spheres produced can be used in photonic applications, where hollow spheres of high refractive index materials are desired, and in catalysis.

Fabrication and Properties of Syntactic Magnesium Foams

ABSTRACTSyntactic magnesium foams which consist of thin-walled hollow alumina spheres embedded in a magnesium matrix were fabricated by infiltrating a three-dimensional array of hollow spheres with a magnesium melt by using a gas pressure-assisted casting technique.The resulting composite contains closed cells of homogeneous and isotropic morphology. The densities of the syntactic magnesium foams were between 1.0 and 1.4 g/cm3. The densities were controlled by variations in the bulk density of the hollow spheres with the volume fraction of spheres kept constant at approximately 63 %.Compressive deformation characteristics of the composites were evaluated with respect to the influence of matrix strength and sphere wall thickness on characteristic variables such as compressive strength, plateau stress and energy absorption efficiency. Differences in the strength of the magnesium-based matrix materials investigated (cp-Mg, AM20, AM50, AZ91) had little influence on the compressive strength of the syntactic foam. However, an increasing relative wall thickness of the hollow ceramic spheres led to a significant strength enhancement. In all cases the ratio between compressive and plateau strength rose with increasing composite strength resulting in decreasing energy absorption efficiency.