Multifunctional Metallic Hollow Sphere Structures




Introduction

Andreas Ochsner and Christian Augustin 2

Technical University of Malaysia, Faculty of Mechanical Engineering,

81310 UTM Skudai, Johor, Malaysia and

The University of Newcastle, Callaghan, New South Wales 2308,

hollomet GmbH, Grunaer Weg 26, D-01277 Dresden, Germany and

University of Konstanz, Faculty of Humanities, Department of History,

D-78457 Konstanz, Germany



Nature frequently uses cellular and porous materials for creating load-carrying and

weight-optimized structures. Thanks to their cellular design, natural materials such as

wood, cork, bones, and honeycombs fulfill structural as well as functional demands. For

a long time, the development of artificial cellular materials has been aimed at utilizing

the outstanding properties of biological materials in technical applications. As an example,

the geometry of honeycombs was identically converted into aluminum structures

which have been used since the 1960s as cores of lightweight sandwich elements in the

aviation and space industries. Nowadays, in particular, foams made of polymeric materials

are widely used in all fields of technology. For example, Styrofoam

and hard

polyurethane foams are widely used as packaging materials. Other typical application

areas are the fields of heat and sound absorption. During the last few years, techniques

for foaming metals and metal alloys and for manufacturing novel metallic cellular structures

have been developed. Owing to their specific properties, these cellular materials

have considerable potential for applications in the future. The combination of specific

mechanical and physical properties distinguishes them from traditional dense metals,

and applications with multifunctional requirements are of special interest in the context

of such cellular metals. Their high stiffness, in conjunction with a very low specific

weight, and their high gas permeability combined with a high thermal conductivity

can be mentioned as examples. Cellular materials comprise a wide range of different

arrangements and forms of cell structures. Metallic foams are being investigated intensively,

and they can be produced with an open- or closed-cell structure, cf. Fig. 1.1.

Their main characteristic is their very low density. The most common foams are made

of aluminumalloys. Essential limiting factors for the utilization are unevenly distributed

material parameters and relatively high production costs.


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