Examples exist aplenty in nature - the quill of a bird’s feather is hollow, yet sturdy. Similarly, bone is not solid, but contains a pored inner structure. This light, yet strong style of structure is also now used in industry - for example metal foams are used in the manufacture of lightweight yet stiff components for cars. Like the examples in nature, the metal foams possess filigree three dimensional structures made of pores, hollow cavities and bridges, all of which do more than just determine their macroscopic mechanical behaviour. However, if closer examination is required, optical microscopes only reveal two dimensional views of the sample’s microsections.
In the case of highly porous or soft materials, this process can fail entirely as the samples may be deformed when sliced and polished.
As a result researchers have turned to X-ray based micro computer tomography, which is increasingly being used to perform detailed examinations of the inner structures of foamed materials in 3D. To visualise tomographic data on a monitor, there are a variety of programs.
‘To display such pictures is only the beginning,’ says Dr Joachim Ohser from the Fraunhofer Institute for Industrial Mathematics, ITWM. ‘Until now, researchers have lacked sufficiently advanced software to accurately analyse data and images.’ In Ohser’s department - Models and Algorithms in Image Processing - researchers have developed a set of software programs in cooperation with Berlin based aquinto AG. Called ‘a4i 3D’ the process combines a base image processing program with various analysis modules, enabling flexible, computer based examination of many geometrical parameters.
The program has already been comprehensively tested. In many industrial processes particles are filtered from gases and liquids, but until now developers, manufacturers and users have had no way to rationally analyse materials like open cell ceramics. ‘With a4i 3D we can start to accurately determine the shape, size and distribution of the pores,’ says Jorg Adler, who works with the ceramic filters group at the Fraunhofer Institute for Ceramic Technologies and Sintered Materials, IKTS. ‘For our project partners this is a prerequisite to understanding and optimising the properties of their products.’
Another application area is the food industry. ‘We even analysed marshmallows for a US confectioner. Apparently, the structure of the sugary foam influences their taste,’ concluded Ohser.