Metallic Hollow Sphere Structures Research Articles

Thermal conductivity of metallic hollow sphere structures: An experimental, analytical and comparative study

The thermal conductivity of metallic hollow sphere structures is analyzed in terms of their main structural parameters (sphere diameter, shell thickness and constituent metal) by using analytical/empirical models to estimate the relative density and admitted scaling laws to determine the thermal conductivity. These results are compared with experimental values of such structures determined by the transient plane source method. In addition, a thermal conductivity map comparing these results with the typical thermal conductivity of other cellular metallic materials is provided.

On the acoustical properties of metallic hollow sphere structures (MHSS)

Well-known advantages of cellular metals are their high ability for energy absorption, good damping behavior and sound absorption at a high specific stiffness. This paper has a focus on the absorption coefficient representing the acoustical property. The absorption coefficient is analysed experimentally by an impedance tube. Results fit well to theoretical investigations described by Champoux and Allard.

Recent Advances in the Prediction of the Thermal Properties of Syntactic Metallic Hollow Sphere Structures

Metallic hollow sphere structures (MHSS) constitute a group of innovative materials which are characterised by more constant material properties compared to classical cellular metals. Their big potential lies within multifunctional applications where combinations of their properties yield symbiotic advantages. In this paper, the effective thermal conductivity of MHSS materials is investigated. Three different approaches, namely a Finite Element Method, a Lattice Monte Carlo Method and an analytical Maxwell model, are used. It is shown that all approaches complement each other and that the results are in excellent agreement.

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.

Calculations of the Effective Thermal Conductivity in a Model of Syntactic Metallic Hollow Sphere Structures Using a Lattice Monte Carlo Method

In this paper, a Lattice Monte Carlo method is used to determine the effective thermal conductivity in two dimensional models of adhesively bonded metallic hollow sphere structures (MHSS). In contrast to earlier approaches, more realistic distributions of spheres without the simplification of cubic symmetric arrangements are considered in this study. For the Monte Carlo analyses, two-dimensional periodic lattices representing different cutting planes through MHSS are generated. Therefore, an algorithm is used which sequentially fills the lattice by adding cut spherical shells and inclusions in the matrix. Another focus of this work is the analysis of the influence of different geometric circle distributions on the effective thermal conductivity. The findings of the random arrangements are also compared to a regular primitive cubic arrangement and with a Maxwell-type approach.

Experimental analysis of the flexural properties of sandwich panels with cellular core materials

AbstractThis paper addresses the flexural properties of sandwich structures with cellular core materials. Experimental three point bending tests are conducted in order to determine the flexural stiffness and the load‐carrying capacity of these advanced composites. In addition, the significant failure modes after exceeding the load‐carrying capacity are identified. The results of these analyses are compared for sandwich structures containing various core materials. These core materials comprise two aluminium foams, namely M‐Pore® and Alporas®, honeycomb structures and novel metallic hollow sphere structures (MHSS).

On the anisotropy of adhesively bonded metallic hollow sphere structures

This paper addresses the mechanical properties of adhesively bonded metallic hollow sphere structures (MHSS). Finite element analyses are conducted in order to determine Young's modulus and the initial yield stress dependence on the loading direction. Therefore, three dimensional unit cell models with a primitive cubic arrangement of hollow spheres are analysed. Within the numerical analyses, two different morphologies, namely syntactic MHSS and partially-bonded MHSS, are considered.

Experimental Investigation of Mechanical Properties of Metallic Hollow Sphere Structures

Metallic foam was fabricated from 316L stainless steel spheres, where the bonding of the spheres was achieved by a sintering process. The mechanical behavior of a low-density material (0.3 g/cm3) with 2- and 4-mm sphere diameter and a high-density material (0.6 g/cm3) with 4-mm sphere diameter was investigated in compression and tension. The cell wall material of this hollow sphere structure (HSS) had different morphologies: dense and porous sintered walls were investigated. The cell wall morphology affects the Young’s modulus (stiffness) and the ductility of the HSS material. Defects, such as the cell wall porosity, lower the ductility of the material. Besides the quasi-static measurements, the HSS material was tested with a resonance frequency method (dynamic measurement), to obtain detailed information on the stiffness at different temperatures up to 700 °C. In-situ compression and tension tests were carried out to understand the deformation mechanisms on the scale of the single hollow spheres. The failure mechanisms in the vicinity of the sintering neck of the spheres was investigated. A doubling of the density leads to an increase of the plateau stress and the ultimate tensile stress of the material, whereas the ductility (strain to fracture) depended mainly on the cell wall morphology. Due to the mainly tensile loading of the cell walls in the vicinity of the sinter neck, the ultimate tensile strength doubled for the high-density HSS, in good agreement with theoretical considerations. In compression, the gain in the plateau stress was not as distinctive compared with the theoretical considerations assuming a bending dominated deformation. The influence of structural parameters, such as cell wall morphology, cell wall thickness, and sphere diameter, on the mechanical behavior is discussed.

Finite element analysis of the temperature dependent conductivity of metallic hollow sphere structures

In the scope of this study, finite element analysis is applied in order to determine the effective thermal conductivity of periodic metallic hollow sphere structures (MHSS). Two different joining technologies for the connection of the hollow spheres, namely sintering and adhesive bonding, are considered. For the determination of the thermal conductivity of the MHSS, the temperature dependence of the thermal conductivities of the base materials, i.e. hollow spheres and joining element, are considered. Two different cases, a low and a high temperature gradient within the structure are distinguished. Furthermore, the overall thermal conductivities of sandwich panels with an insulating MHSS core in dependence on the relative face sheet thickness are investigated.

Numerical and experimental analysis of the thermal conductivity of metallic hollow sphere structures

Numerical, analytical and experimental analyses are performed in order to determine the thermal conductivity of Metallic Hollow Sphere Structures (MHSS). Therefore, the geometry of this composite material is discretised and finite element analysis is performed. Furthermore, the thermal conductivity is estimated using Misnar's analytical model. Additionally, the Transient Plane Source method (TPS) is applied in order to perform thermal measurements on experimental samples. The findings of these approaches are compared and a good agreement is observed.

Uniaxial Elasto-Plastic Behaviour of Adhesively Bonded Hollow Sphere Structures (HHS): Numerical Simulations and Experiments

This paper is on the investigation of adhesively bonded metallic hollow sphere structures. Two different approaches, namely experimental analysis and finite element cal- culations are applied and the findings of both attempts are compared. In the scope of the numerical approach the influence of the mechanical properties of the adhesive on the me- chanical response of the structure is analysed. Based on these results, suggestions for design parameters are derived.

接着剤固化による超軽量MHS成形体の特性(S17-1 環境調和型加工技術とその材料特性(1),S17 環境調和型加工技術とその材料特性)

接着剤固化による超軽量MHS成形体の特性(S17-1 環境調和型加工技術とその材料特性(1),S17 環境調和型加工技術とその材料特性)

Novel Metallic Hollow Sphere Structures

The obvious advantages of metallic hollow sphere materials have lead to several attempts to produce such structures. None of these approaches has gained practical significance owing to the very high cost of the methods. A new powder metallurgical process using styrofoam spheres allows for the production of hollow spheres from arbitrary metals and alloys. The IFAM Department of Powder Metallurgy and Composite Materials, Dresden, has developed this process and added a method that produces random hollow sphere structures (RHS) directly from the green spheres.

Novel Metallic Hollow Sphere Structures

Novel Metallic Hollow Sphere Structures

Novel Metallic Hollow Sphere Structures

Novel Metallic Hollow Sphere Structures