X-ray computed tomography of a titanium aerospace investment casting

AbstractThis case study demonstrates the type of non-destructive analysis possible using X-ray micro computed tomography (microCT) for a titanium aerospace investment casting of 225 mm in its longest axis. The advantages of the method are highlighted while the limitations are also discussed. Recently the method has become more accessible and affordable due to multi-user service facilities and the analysis has become simpler due to software and hardware improvements. This case study demonstrates a typical analysis including defect detection, wall thickness and part to CAD comparison, which can be done in less than 4 h, while simpler results are possible in under 1 h. This will be particularly useful for industries requiring quick but detailed non-destructive analysis

WHEN CAN I FIRE? Use of lethal force to defend property

Can you use lethal force to protect your property, and if so, when? South Africans are confused about how much force they can use in defending themselves from crime, and mistakes in this area could have disastrous consequences. While the law remains unclear, the constitutional right to life is likely to be given precedence over the right to protect property

The feasibility of punishing negligent assault

LawIn this essay I consider whether or not there is a need for the creation of the crime of negligent assault. I start off by giving a brief exposition of the current position in South Africa with regard to assault. From this exposition it becomes clear that negligent assault is not recognised in South African law. I give a brief summary of the concepts of intention and negligence. After this I briefly discuss what criteria should be considered before invoking the criminal sanction. In the next section of the essay I consider the need for, and the benefits of, creating the crime of negligent assault. Lastly, I critically analyse whether the legislature should intervene or not. My conclusion is that the social benefits of criminalising the conduct do in fact outweigh the negative implications of not criminalising it, and that the legislature would not err if it were to create the crime of negligent assault.LL.M

THE TIDE IS TURNING: The 2003/04 SAPS crime statistics

The latest official crime statistics, for the financial year 2003/04, are encouraging because they show a decrease in levels of most serious crimes, including murder, car hijacking, burglary and farm attacks. But the good news has yet to hit home for many South Africans. In fact, most people are more afraid of crime today than they were in 1998. It is likely that only sustained decreases in violent crime over several years, coupled with better service delivery, will make a difference

Interview with Shaun Abrahams, National Director of Public Prosecutions

Executive Director of Institute for Security Studies, Anton du Plessis, and Senior Researcher, Ottilia Maunganidze, sat down with the National Prosecuting Authority’s (NPA) National Director of Public Prosecutions, Shaun Abrahams to discuss life, presidents, politics and prosecutions in South Africa. Du Plessis and Abrahams have known each other for many year

Quality Control of a Laser Additive Manufactured Medical Implant by X-Ray Tomography

Published ArticleQuality control of laser additive manufactured medical implants is of interest, especially if nondestructive quality control can be performed on parts before implantation. X-ray micro-computed tomography (microCT or CT) can be used for defect/porosity analysis as well as for comparing the part surface with its computer-aided design (CAD) file. In both cases, the limited use of CT is partly due to the variation in scan types and the quality of scans that can occur. We present a simple method demonstrating the use of a light metal casting as a reference porosity sample, to confirm good CT image quality and to quantify minimum detectable pore size for the selected CT scan settings. This makes a good comparison for additive manufactured parts, since castings generally contain more porosity. A full part-to-CAD comparison shows how the part is compared with its CAD file, as a second-quality control. The accuracy of the CAD variance is given by the minimum detectable pore size. Finally, the part is sectioned and scanned at two higher resolution settings showing small porosity (10–50 lm diameter) present but well distributed, as expected

Directionality of Cavities and Porosity Formation in Powder-Bed Laser Additive Manufacturing of Metal Components Investigated Using X-Ray Tomography

Published ArticleEnsuring additive manufactured metal components are free of major defects is crucial to the application of this new technology in medical and aerospace industries. One source of defects in such parts is lack of fusion in individual locations or specific layers. Such lack of melting or fusion could be the result of a nonflat powder bed due to an imperfect recoating blade or loose support structures causing recoating problems. Another possible source is laser power fluctuations or beam size fluctuations, or even ambient humidity or temperature changes, among others. The aims of this article are to investigate lack of fusion with planned induced defects (cavities) with different three-dimensional (3D) geometries and analyze these using nondestructive 3D X-ray tomography. It is found that some fusion occurs in induced defect layers and lines perpendicular to the build direction (XY) up to 180 lm in height. This means fusion occurs through fused layers above cavities, minimizing defect formation in the plane of the build platform. In contrast, in the case of vertical cavities (cavity walls) parallel to the build direction, much larger defects are observed compared to the above case. This result may point to the build direction (vertical) being more favorable for porosity formation under nonideal conditions (i.e., a preferred directionality). An example of unexpected porosity trail formation in the build direction is also reported from such nonideal conditions for a real part in contrast to a designed cavity

TENSILE PROPERTIES AND MICROSTRUCTURE OF DIRECT METAL LASER-SINTERED TI6AL4V (ELI) ALLOY

Published ArticleDirect metal laser sintering (DMLS) is an additive manufacturing technology used to melt metal powder by high laser power to produce customised parts, light-weight structures, or other complex objects. During DMLS, powder is melted and solidified track-by-track and layer-by-layer; thus, building direction can influence the mechanical properties of DMLS parts. The mechanical properties and microstructure of material produced by DMLS can depend on the powder properties, process parameters, scanning strategy, and building geometry. In this study, the microstructure, tensile properties, and porosity of DMLS Ti6Al4V (ELI) horizontal samples were analysed. Defect analysis by CT scans in pre-strained samples was used to detect the crack formation mechanism during tensile testing of as-built and heat-treated samples. The mechanical properties of the samples before and after stress relieving are discussed

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

CITATION: Du Plessis, A., Seifert, T., Booysen, G. & Els, J. 2014. Microfocus X-ray computed tomography (CT) analysis of laser sintered parts. South African Journal of Industrial Engineering, 25(1):39-49, doi:10.7166/25-1-663.The original publication is available at http://sajie.journals.ac.zaMicrofocus X-ray computed tomography (CT) scanning is a three-dimensional (3D) non-destructive technique that is useful in many research and technology fields. Similar to two-dimensional (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.Mikrofokus X-straal rekenaar-tomografie (RT) is ‘n drie-dimensionele (3D) nie-destruktiewe tegniek wat bruikbaar is in baie navorsing en tegnologie velde. Soortgelyk aan twee dimensionele (2D) X-straal inspeksies, laat hierdie 3D tegnologie dit toe om enige materiaal in 3D te ondersoek tot 1 mikron (en hoër) ruimtelike resolusie. In hierdie artikel word ‘n karakterisering en demonstrasie van die gebruik van RT aangebied om die 3D volume van laser-gesinterde onderdele te analiseer, insluitend die analise van porositeit, dimensionele metings van krake en ander eienskappe en ‘n demonstrasie van kwaliteit toets metodes wat gebruik kan word om vinnig probleme in produksie te identifiseer.http://sajie.journals.ac.za/pub/article/view/663Publisher's versio

Three-dimensional model of an ancient Egyptian falcon mummy skeleton

Published ArticlePurpose – The purpose of this paper is to present the first detailed three-dimensional (3D) print from micro-computed tomography data of the skeleton of an ancient Egyptian falcon mummy. Design/methodology/approach – Radiographic analysis of an ancient Egyptian falcon mummy housed at Iziko Museums of South Africa was performed using non-destructive x-ray micro-computed tomography. A 1:1 physical replica of its skeleton was printed in a polymer material (polyamide) using 3D printing technology. Findings – The combination of high-resolution computed tomography scanning and rapid prototyping allowed us to create an accurate 1:1 model of a biological object hidden by wrappings. This model can be used to study skeletal features and morphology and also enhance exhibitions hosted within the museum. Originality/value – This is the first replica of its kind made of an ancient Egyptian falcon mummy skeleton. The combination of computed tomography scanning and 3D printing has the potential to facilitate scientific research and stimulate public interest in Egyptology