Prof Thomas Seifert (NRF grantholder) and Dr Anton du Plessis (CT scanner facility manager) demonstrate the CT scanning capabilities on a sample while Amanda van der Westhuizen (General Electric representative for Africa and Middle East) looks on.
Egyptologists struggle with the temptation to unwrap rare intact mummies in order to discover more about the individual’s identity, diet, cause of death and the precious treasures that accompanied it into the afterlife. However, mummies deteriorate quickly once exposed to the elements and expensive specialist preservation measures have to be taken. At the other end of the scale, medical implants such as hip joints manufactured from advanced nanomaterials by cutting-edge laser additive technology need to be inspected for potential structural problems before being implanted into the recipient. X-ray computed tomography (CT) scanning techniques and 3D image generation eliminate the challenges of these very divergent disciplines of science. The newly established Computed Tomography Scanner Facility of the Stellenbosch University was officially launched on 12 April 2010, based at the Department of Forestry and Wood Science, and was funded jointly by the university and the NRF through a grant obtained by Prof Thomas Seifert. This multi-user facility forms part of the Central Analytical Facility (CAF) of the university and is available to both academics and commercial clients.
Micro-focus x-ray CT scanners allow for 2D or 3D material properties investigations at a high spatial resolution based on density variations. This ensures non-destructive slicing and imaging of the material interiors. Similar in technology to the medical CT-scanners, industrial CT scanners allow penetration of much denser objects, including steel and rock samples, providing much higher spatial resolution than medical scanners (in the region of 1-5 microns vs 250-500 microns). The General Electric Phoenix model installed at the university is one of the most versatile on the market, offering different penetration and resolution capabilities and thus able to cover a larger range of sample sizes (up to 0.5 m by 1 m). Potential applications are limitless and include engineering, agriculture, art, archaeology, civil, structural and mechanical engineering and zoology.
Forestry and Wood Science
Grantholder Prof Thomas Seifert’s particular field of interest is the scanning of wood samples from trees, having obtained his unique expertise in Germany. A variety of projects are currently being undertaken such as scanning wood disks and drill cores to relate tree ring density variations to climate change and tree stress induced by environmental conditions. Applications in wood science include the quantification of growth stress induced by fire damage, the quantification and distribution of resin pockets while structures in wood can be assessed on the macroscopic and the anatomic level. The main objectives are to investigate the structural variability of wood as a response to environmental, pathological and silvicultural changes and to obtain a better understanding of the tree-environment interaction of indigenous and introduced commercial species. Further work will be conducted to assess and improve the quality of wood based products.
CT Scanning techniques are particularly beneficial in the viticulture investigations undertaken at Stellenbosch University, in particular the scanning of vine grafts. Because the technique is non-destructive and various 2D slices can be made from the 3D data set, increased information on the internal structure of the vine graft can be obtained and the connections of xylem between the old to new sections can be extracted.
Engineering and Materials Analysis
The inspection of mechanical components is performed to check for porosity and micro-cracks. In one such example, a medical implant (jawbone) produced using laser additive manufacturing by the Central University of Technology’s Centre for Rapid Prototyping and Manufacturing, was scanned. No structural problems were evident even though it was produced in its entirety in one single process. Future work in this direction will involve the use of CT scanning to quantify the porosity and structural integrity of components in order to improve the process especially where new materials and new processes are being developed. Quality control is also possible with either the fast 2D inspection or a full 3D inspection.
The dimensional measurement of objects is a niche application area and includes the dimensional measurement of distances and interiors in enclosed objects, the accurate measurement of enclosed volumes and even the surface measurement of objects producing surface file output such as STL format. This dimensional control is particularly relevant in reverse engineering and rapid prototyping processes
Researchers requiring high resolution non-destructive 2D or 3D inspection would find the technology particularly beneficial to their research projects.