A. du Plessis

Microfocus X-ray computed tomography (CT) analysis of laser sintered parts

Microfocus X-ray computed tomography (CT) scanning is a three-dimensional (3D) nondestructive technique that is useful in many research and technology fields. Similar to twodimensional (2D) X-ray inspections, this 3D technology allows the investigation of almost any material down to 1 micron spatial resolution and higher. In this paper we present a characterisation and demonstration of the use of CT to analyse the 3D volume of laser sintered parts including analyses of porosity, dimensional measurement of cracks and other features, and a demonstration of quality testing methods which can be used to quickly identify problems in production. OPSOMMING

Visualising and quantifying thermal degradation of wood by computed tomography

Wood samples from South African pine were subjected to thermal degradation of varying degrees, and their dimensional change as well as changes in cell wall density were determined with a micro CT scanner. It was possible to visualise and quantify those changes and also determine a temperature threshold above which the degradation seemed to be too severe to use this wood for any structural purposes. Below this threshold, however, wood properties changed little and the wood may still be of economic value.

Looking inside votive creatures : computed tomography (CT) scanning of ancient Egyptian mummified animals in Iziko Museums of South Africa : a preliminary report

The ancient Egyptians mummified many more animals than humans. The study of ancient Egyptian animal mummies is varied and extensive. Currently new methodologies and modern technology are being used to unlock the secrets of animal mummies. Recently five animal mummies housed in the Egyptian collection of Iziko Museums of South Africa in Cape Town were scanned using a state of the art computed tomography (CT) scanner at Stellenbosch University. Preliminary results revealed two complete bird skeletons, a claw, a fake and the partial skeleton of what appears to be a cat.

Numerical comparison of lattice unit cell designs for medical implants by additive manufacturing

ABSTRACT The aim of this study was to compare traditional strut-based lattices with minimal surface designs using morphological analysis and image-based simulations of design files. While the two types have been studied widely, no direct comparison has ever been done. Surprisingly, there are no major differences in performance between the two types generally, but minimal surface designs do outperform slightly on angular load simulation. However, minimal surface designs in this density range are shown to have very thin walls, potentially making their accurate production more challenging, or more suitable for applications where larger pore sizes and sheet thicknesses may be applicable. Interesting results such as dual pore size distributions and variations in tortuosity of pore networks are demonstrated, with differences between various designs. The results show that all the tested designs are suitable for bone implants, but the best design might be selected based on its specialised performance requirements.

Non-destructive, high-resolution X-ray micro-CT of a Hairy Stalagmite: investigating the structural details of a biogenic speleothem

Three-dimensional X-ray micro-computed tomography permits to investigate the internal structure of objects at a high resolution without altering its original form. It also facilitates the rendering and visualization of a virtual replica, which can be subjected to rigorous and complex analyses. In the present study, micro-computed tomography was used to investigate a unique and fragile speleothem (cave formation) named a “Hairy Stalagmite”. Non-destructive analyses have revealed the calcareous internal structure of this speleothem, which consists of hollow, interconnected tubes. Rendered two-dimensional cross-sections also clearly revealed the outline of a once dense root nest that formed part of the speleothem’s biogenic origin. The internal structure was further visualized using an image sequence of two-dimensional cross-sections to create a video that “brings the speleothem to life”, also illustrating its complexity and variability. Statistical analyses revealed structural variability in void fraction, which is likely related to changing environmental conditions. In addition, the micro-computed tomography data were used as input for additive manufacturing (three-dimensional printing) in order to produce an enlarged replica of the Hairy Stalagmite sample, which made physical inspection possible. This combined approach represents the first of its kind and provides much benefit for future studies.

Determining tactical operational planning policies for an auto carrier - A case study

This study was done to assist a local auto carrier company with tactical operational planning. The objective of the planning process is to maximise the number of vehicles delivered while being on time and adhering to staff and maintenance schedule constraints. We investigated the feasibility of allowing part of the fleet to roam the closed spatial network, as opposed to the traditional assignment of the complete fleet to fixed routes. We developed decision-making rules for roaming and fixed-to-route auto carriers, and evaluated the quality of these proposed rules, in combination with different fleet compositions, using discrete event simulation and four performance measures. We found that the auto carrier company should adopt a tactical operations policy where at least 50% of the fleet is allowed to roam, while roaming auto carriers pick vehicles to transport according to specific rules. OPSOMMING Hierdie studie is gedoen om ’n plaaslike motorvervoer-onderneming te help met taktiese bedryfsbeplanning. Die doelwit van die beplanningsproses is om die aantal voertuie wat betyds afgelewer word te maksimeer met inagneming van personeel- en instandhoudingbeperkings. Ons het die moontlikheid dat ’n deel van die vragmotorvloot swerwend in die geslote ruimtelike roete-network moet opereer, ondersoek. Dit is in teenstelling met die tradisionele vaste toedeling van vragmotors aan roetes. Besluitnemingreels vir swerwende en vaste-roete vragmotors is ontwikkel, en die gehalte van die reels is met diskrete simulasie en vier prestasiemaatstawwe evalueer. Ons het bevind dat die vervoeronderneming ’n bedryfsbeleid behoort te aanvaar wat toelaat dat ten minste 50% van die vloot swerf, terwyl hierdie swerwende vragmotors voertuie volgens spesifieke reels by oplaaipunte moet kies.