Browsing by Author "Du Plessis, Anton"
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- ItemAccurate Laboratory Wavelengths of the A1Π(υ' = 0-5)-X1Σ+(υ'' = 0) Vibronic Bands of 12C17O and 12C18O(IOP Science, 2006) Du Plessis, Anton; Rohwer, Erich G.; Steenkamp, Christine M.Twenty nine rovibronic lines of 12C17O for which laboratory wavelengths were previously unavailable were detected in laser-induced fluorescence excitation spectra of the six vibronic bands A1Π(υ' = 0-5)-X1Σ+(υ'' = 0). Rovibronic lines of 12C16O, 13 C16O, 12C17O, and 12C 18O were detected in each band, allowing accurate determination of the unknown wavelengths using neighboring 12C16O and 13C16O lines as reference. The new wavelength data yield consistent heliocentric velocity values when applied to vacuum ultraviolet observations of 12C17O and 12C 18O in the interstellar medium.
- ItemAdvancing X-ray micro computed tomography in Africa : going far, together(Elsevier, 2019) Du Plessis, Anton; Le Roux, Stephan G.; Tshibalanganda, MuofheX-ray micro computed tomography (microCT) is a high resolution non-destructive materials imaging technology and is emerging as a powerful tool for industrial and scientific research applications. The aim of this review paper is to present the capabilities and potential of this technique within an African context. This is done using a representative sample: all work done at the Stellenbosch CT facility during 2018 is used as an overview of the type of work done at such a facility in Africa. Besides the plethora of academic research topics, the most important industrial applications are also discussed, which assisted to keep the Stellenbosch CT facility financially operational. This provides a wider understanding of the opportunities and capabilities of this technique and how it can benefit African researchers and local industries. The question “what is it used for?”, and more specifically “what is it used for in Africa?” is therefore answered. The availability of such X-ray tomography facilities helps to fast-track research by providing local expertise and support in Africa for advancing African science. This model is not only applicable to microCT but applies to any collaborative scientific endeavor in Africa, with success rates depending on the efficient sharing of resources, providing expert skills and advancing African science in Africa. There is an African proverb “if you want to go fast – go alone; if you want to go far – go together”. Clearly, African science will go far by working together in such facilities.
- ItemA characterization of beam shaping devices and a tunable Raman laser(Stellenbosch : University of Stellenbosch, 2003-04) Du Plessis, Anton; Rohwer, Erich G.; Von Bergmann, H. M.; University of Stellenbosch. Faculty of Science. Dept. of Physics.ENGLISH ABSTRACT: The efficient manipulation of various nonlinear optical processes frequently requires the shaping of the laser beams used for these processes. Three beam shaping techniques were investigated in this thesis. The focussing of Gaussian laser beams was investigated analytically, in order to efficiently manipulate the focussed beam characteristics. The beam-shaping characteristics of a diffractive optical element (DOE) was investigated numerically, which illustrates the beamshaping capability of the DOE, and identifies the critical parameters in experimental situations. The use of a waveguide as beam shaping device was investigated analytically and experimentally, and characterized for use with the available tunable laser sources. A Raman laser, or Raman shifter, employs stimulated vibrational Raman scattering to generate laser radiation at shifted frequencies. The waveguide was successfully applied as a beam shaping device in the Raman laser system, for optimisation of the process. The Raman laser system was investigated experimentally and characterized for use with the available tunable laser sources. The successful generation of laser radiation at shifted frequencies illustrates the usefulness of the system for generating tunable red-shifted frequencies. The results of this work allow the simple and efficient application of the Raman laser to generate laser radiation at shifted frequencies, in particular tunable infrared laser radiation which is desirable for molecular spectroscopy.
- ItemCharacterization of coloured gemstones by X-ray micro computed tomography(MDPI, 2021-02-08) Heyn, Rene; Rozendaal, Abraham; Du Plessis, Anton; Mouton, CareneThe monetary value of gemstones is based on five variables: rarity, cut, weight, color and clarity. The latter refers to internal impurities and defects. Fashion may also dictate demand and price. To enhance some of these features and value, gemstones are treated. Disclosure or nondisclosure thereof has been controversial and affected consumer confidence. Most of these treatments are difficult to detect with the naked eye and accurately quantify with traditional optical and analytical methods. X-ray micro computed tomography (micro-CT or μCT) is proposed as a relatively low cost, physically non-destructive and complementary method to detect and quantify clarity enhancement and also to provide a unique 3D fingerprint of each gemstone. A collection of 14 cut colored gemstones was selected. Micro-CT scans allowed fracture detection, their distribution and calculation of filler volume as well as 3D mapping of inclusions, surface and internal imperfections and artificially induced modifications. As a result the method allows the construction of a digital twin. X-ray exposure could however induce unwanted color changes. This effect was minimized or eliminated by optimizing dosage and exposure time.
- ItemThe CT scanner facility at Stellenbosch University : an open access X-ray computed tomography laboratory(Elsevier, 2016-10) Du Plessis, Anton; Le Roux, Stephan Gerhard; Guelpa, AninaThe Stellenbosch University CT Scanner Facility is an open access laboratory providing non-destructive Xray computed tomography (CT) and a high performance image analysis services as part of the Central Analytical Facilities (CAF) of the university. Based in Stellenbosch, South Africa, this facility offers open access to the general user community, including local researchers, companies and also remote users (both local and international, via sample shipment and data transfer). The laboratory hosts two CT instruments, i.e. a micro-CT system, as well as a nano-CT system. A workstation-based Image Analysis Centre is equipped with numerous computers with data analysis software packages, which are to the disposal of the facility users, along with expert supervision, if required. All research disciplines are accommodated at the X-ray CT laboratory, provided that non-destructive analysis will be beneficial. During its first four years, the facility has accommodated more than 400 unique users (33 in 2012; 86 in 2013; 154 in 2014; 140 in 2015; 75 in first half of 2016), with diverse industrial and research applications using X-ray CT as means. This paper summarises the existence of the laboratory’s first four years by way of selected examples, both from published and unpublished projects. In the process a detailed description of the capabilities and facilities available to users is presented.
- ItemA dataset describing brooding in three species of South African brittle stars, comprising seven high-resolution, micro X-ray computed tomography scans(BioMed Central, 2015) Landschoff, Jannes; Du Plessis, Anton; Griffiths, Charles L.Background: Brooding brittle stars have a special mode of reproduction whereby they retain their eggs and juveniles inside respiratory body sacs called bursae. In the past, studying this phenomenon required disturbance of the sample by dissecting the adult. This caused irreversible damage and made the sample unsuitable for future studies. Micro X-ray computed tomography (μCT) is a promising technique, not only to visualise juveniles inside the bursae, but also to keep the sample intact and make the dataset of the scan available for future reference. Findings: Seven μCT scans of five freshly fixed (70 % ethanol) individuals, representing three differently sized brittle star species, provided adequate image quality to determine the numbers, sizes and postures of internally brooded young, as well as anatomy and morphology of adults. No staining agents were necessary to achieve highresolution, high-contrast images, which permitted visualisations of both calcified and soft tissue. The raw data (projection and reconstruction images) are publicly available for download from GigaDB. Conclusions: Brittle stars of all sizes are suitable candidates for μCT imaging. This explicitly adds a new technique to the suite of tools available for studying the development of internally brooded young. The purpose of applying the technique was to visualise juveniles inside the adult, but because of the universally good quality of the dataset, the images can also be used for anatomical or comparative morphology-related studies of adult structures.
- ItemEffects of defects on mechanical properties in metal additive manufacturing : a review focusing on X-ray tomography insights(Elsevier, 2019) Du Plessis, Anton; Yadroitsava, Ina; Yadroitsev, IgorENGLISH ABSTRACT: X-ray tomography has emerged as a uniquely powerful and non-destructive tool to analyze defects in additive manufacturing. Defects include unintended porosity, rough surfaces and deviations from design, which can have different root causes and can vary significantly among samples. Powder material properties, non-uniform delivery of the powder layer, deformation during manufacturing, deviations from optimal process-parameters caused by changes in the laser beam, the optical components and the scanning system operation, may result in lack of fusion pores, metallurgical pores, keyhole pores, etc. These different types of pores have different typical sizes, shapes and 3D distributions. All types of defects have effects on the mechanical properties of a final part. The use of X-ray tomography to visualize pores in parts (non-destructively) prior to mechanical testing has allowed us to improve our understanding of the effect of this porosity on the mechanical properties of the part (also referred to as “effect of defect”). This can provide the possibility to discriminate critical defects from harmless ones, and thereby build confidence in additivemanufacturing processes. This paper reviews the current state of knowledge with regard to the “effect of defect” in metal additivemanufacturing, and highlights some relevant examples from our recent work.
- ItemInfluence of large artificial porosity on bending behaviour of TI6AL4V ELI additively manufactured specimens subjected to typical loads during mastication(Southern African Institute for Industrial Engineering, 2020) Wessels, Adriaan; Du Plessis, Anton; Yadroitsava, Ina; Els, Johan; Yadroitsev, IgorEffective quality control of implants made using additive manufacturing is an important task for suppliers to comply fully with existing regulations and certifications. To study the influence of porosity on the mechanical behaviour of mandibular implants produced by additive manufacturing, preliminary tests with longitudinal flat samples were performed with 3D point bending tests. Ti6Al4V Extra Low Interstitial (ELI) specimens with artificial porosity were designed and subjected to typical loads during mastication. In this work, a finite element simulation was constructed to investigate the bending behaviour of samples, which was consistent with the experimental results. The work shows that even large artificial cavities (designed up to 0.42 mm) do not significantly affect the strength of additively manufactured 2.5 mm-thick Ti6Al4V ELI specimens under typical static loads of mandibular implants, in the considered loading conditions, and for samples subjected to appropriate surface finishing and annealing heat treatment.
- ItemInvestigation of four carbon monoxide isotopomers in natural abundance by laser-induced fluorescence in a supersonic jet(Elsevier, 2007) Du Plessis, Anton; Rohwer, Erich G.; Steenkamp, Christine M.The four carbon monoxide (CO) isotopomers 12C16O, 13C16O, 12C18O and 12C17O have been detected simultaneously in a CO gas sample of natural isotopic abundance by measuring rovibronic excitation spectra of six vibronic bands in the Fourth Positive System. The CO sample was flow cooled by adiabatic expansion in a pulsed supersonic jet. The rovibronic excitation spectra were obtained using a novel pulsed laser source (pulse duration ∼25 ns, spectral bandwidth ∼5 GHz) continuously tunable in the 139–155 nm vacuum ultraviolet wavelength region for excitation and recording the total fluorescence. In the present paper we report on the spectroscopic results obtained, including transition wavelengths of three forbidden rovibronic bands (e3Σ− − X1Σ+(1, 0), d3Δ − X1Σ+(5, 0), a′3Σ+ − X1Σ+(14, 0)) of 12C16O and band origins of six rovibronic bands (A1Π(v′ = 0–5) − X1Σ+(v″ = 0)) of the rare isotopomer 12C17O, and on the experimental conditions facilitating the high sensitivity of the measurements. The exceptional sensitivity demonstrated by the results has been achieved by fine tuning experimental conditions including the conditions in the supersonic expansion, the jet pulse duration and the laser pulse timing.
- ItemLaboratory X-ray micro-computed tomography : a user guideline for biological samples(Oxford University Press, 2015) Du Plessis, Anton; Broeckhoven, Chris; Guelpa, Anina; Le Roux, Stephan GerhardLaboratory X-ray micro-computed tomography (micro-CT) is a fast growing method in scientific research applications that allows for non-destructive imaging of morphological structures. This paper provides an easily operated “how-to” guide for new potential users and describes the various steps required for successful planning of research projects that involve micro-CT. Background information on micro-CT is provided, followed by relevant set-up, scanning, reconstructing and visualization methods and considerations. Throughout the guide, a Jackson’s chameleon specimen, which was scanned at different settings, is used as an interactive example. The ultimate aim of this paper is make new users familiar with the concepts and applications of micro-CT, in an attempt to promote its use in future scientific studies.
- ItemLaser spectroscopy of the Fourth Positive System of carbon monoxide isotopomers(Stellenbosch : University of Stellenbosch, 2006-03) Du Plessis, Anton; Rohwer, Erich G.; Steenkamp, Christine M.; University of Stellenbosch. Faculty of Science. Dept. of Physics.Carbon monoxide (CO) is a diatomic molecule of particular interest in astrophysics, due to its high abundance in interstellar space. The Fourth Positive System A1Π−X1Σ+ of CO is an important feature in the vacuum ultraviolet (VUV) region of the electromagnetic spectrum in astronomical observations, especially in high-resolution spectra recorded by satellite-based spectrographs. The interpretation of these astronomically detected spectra requires accurate laboratory wavelengths to serve as rest wavelengths and to resolve possible Doppler-shifts. Such rest wavelengths are known for the 12C16O, 13C16O and 12C18O isotopomers for all astronomically observed spectral lines of the Fourth Positive System. The only laboratory wavelengths currently available for the Fourth Positive System of the 12C17O isotopomer have been determined in a previous work carried out in our laboratory for the vibronic band A1Π(v0 = 3)−X1Σ+(v00 = 0). The present study continues this work for the other vibronic bands which have been detected astronomically, namely A1Π(v0 = 2 − 5)−X1Σ+(v00 = 0). The A1Π(v0 = 0− 1)−X1Σ+(v00 = 0) vibronic bands have also been investigated due to their probability for future astronomical detection. Rotationally-resolved spectra of these six vibronic bands were obtained by selective rovibronic laser excitation, and subsequent detection of the undispersed fluorescence, observed as a function of the excitation wavelength in the VUV. A tunable narrow-bandwidth VUV laser source is used for excitation, and the CO gas sample is introduced by supersonic expansion. Flow-cooling in the supersonic expansion to rotational temperatures roughly corresponding to temperatures in the interstellar medium simplifies and aids the spectral analysis of the spectral lines of interest. The cold conditions in the supersonic expansion facilitates a high sensitivity for detection of the low-J lines, and allows the detection of rare isotopomers of CO in natural abundance. The experimental setup has been improved in the present study by the addition of a vacuum monochromator, facilitating an improved characterisation of the VUV source. Furthermore, a number of experimental conditions have been optimised for the detection of rare CO isotopomers, significantly increasing the signals of these lines in the spectra. The combination of this increase in sensitivity and the addition of the vacuum monochromator to the experimental setup, allowed the simultaneous detection of absorption spectra with the fluorescence spectra as an additional source of information in spectral analysis. The increased sensitivity also contributed to the detection of a large number of spectral lines of interest, with some additional lines identified in the previously studied vibronic band. Spectral lines of 12C16O, 13C16O, 12C18O and 12C17O were detected in each vibronic band, allowing accurate calibration of the spectra. A total of 29 new lines of 12C17O were recorded in the six vibronic bands investigated. Additionally, 10 new singlet-triplet lines of 12C16O were recorded in the wavelength regions investigated. The new wavelengths of 12C17O have been applied to calculate consistent heliocentric velocities of a gas cloud toward the star X Persei, obtained from spectra of the different CO isotopomers taken by the Hubble space telescope.
- ItemMechanical properties and in situ deformation imaging of microlattices manufactured by laser based powder bed fusion(MDPI, 2019-09-09) Du Plessis, Anton; Kouprianoff, Dean-Paul; Yadroitsava, Ina; Yadroitsev, IgorENGLISH ABSTRACT: This paper reports on the production and mechanical properties of Ti6Al4V microlattice structures with strut thickness nearing the single-track width of the laser-based powder bed fusion (LPBF) system used. Besides providing new information on the mechanical properties and manufacturability of such thin-strut lattices, this paper also reports on the in situ deformation imaging of microlattice structures with six unit cells in every direction. LPBF lattices are of interest for medical implants due to the possibility of creating structures with an elastic modulus close to that of the bones and small pore sizes that allow effective osseointegration. In this work, four different cubes were produced using laser powder bed fusion and subsequently analyzed using microCT, compression testing, and one selected lattice was subjected to in situ microCT imaging during compression. The in situ imaging was performed at four steps during yielding. The results indicate that mechanical performance (elastic modulus and strength) correlate well with actual density and that this performance is remarkably good despite the high roughness and irregularity of the struts at this scale. In situ yielding is visually illustrated.
- ItemA micro X-ray computed tomography dataset of fossil echinoderms in an ancient obrution bed : a robust method for taphonomic and palaeoecologic analyses.(Oxford University Press, 2019-03) Reid, Mhairi; Bordy, Emese M.; Taylor, Wendy L.; Le Roux, Stephan G.; Du Plessis, AntonBackground: Taphonomic and palaeoecologic studies of obrution beds often employ conventional methods of investigation such as physical removal and extraction of fossils from their host rock (matrix) by mechanical preparation. This often-destructive method is not suitable for studying mold fossils, which are voids left in host rocks due to dissolution of the original organism in post-depositional processes. Findings: Microcomputed tomography (µCT) scan data of 24 fossiliferous rock samples revealed thousands of Paleozoic echinoderms. Digitally "stitching" together individually µCT scanned rock samples within three-dimensional (3D) space allows for quantifiable taphonomic data on a fossil echinoderm-rich obrution deposit from the Devonian (Emsian) of South Africa. Here, we provide a brief step-by-step guide on creating, segmenting, and ultimately combining sections of richly fossiliferous beds to create virtual models suited for the quantitative and qualitative taphonomic analyses of fossil invertebrate assemblages. Conclusions: Visualizing the internal features of fossiliferous beds in 3D is an invaluable taphonomic tool for analyzing delicate fossils, accounting for all specimens irrespective of their preservation stages and with minimal damage. This technique is particularly useful for analyzing fossiliferous deposits with mold fossils that prove to be difficult to study with traditional methods, because the method relies on the large density contrast between the mold and host rock.
- ItemA micro X-ray computed tomography dataset of South African hermit crabs (Crustacea: Decapoda: Anomura: Paguroidea) containing scans of two rare specimens and three recently described species(Oxford University Press, 2018-03-14) Landschoff, Jannes; Du Plessis, Anton; Griffiths, Charles L.Background: Along with the conventional deposition of physical types at natural history museums, the deposition of 3-dimensional (3D) image data has been proposed for rare and valuable museum specimens, such as irreplaceable type material. Findings: Micro computed tomography (μCT) scan data of 5 hermit crab species from South Africa, including rare specimens and type material, depicted main identification characteristics of calcified body parts. However, low-image contrasts, especially in larger (>50 mm total length) specimens, did not allow sufficient 3D reconstructions of weakly calcified and fine characteristics, such as soft tissue of the pleon, mouthparts, gills, and setation. Reconstructions of soft tissue were sometimes possible, depending on individual sample and scanning characteristics. The raw data of seven scans are publicly available for download from the GigaDB repository. Conclusions: Calcified body parts visualized from μCT data can aid taxonomic validation and provide additional, virtual deposition of rare specimens. The use of a nondestructive, nonstaining μCT approach for taxonomy, reconstructions of soft tissue structures, microscopic spines, and setae depend on species characteristics. Constrained to these limitations, the presented dataset can be used for future morphological studies. However, our virtual specimens will be most valuable to taxonomists who can download a digital avatar for 3D examination. Simultaneously, in the event of physical damage to or loss of the original physical specimen, this dataset serves as a vital insurance policy.
- ItemMicroCT imaging applied to description of a new species of Pagurus Fabricius, 1775 (Crustacea: Decapoda: Anomura: Paguridae), with selection of three-dimensional type data(Public Library of Science, 2018) Landschoff, Jannes; Komai, Tomoyuki; Du Plessis, Anton; Gouws, Gavin; Griffiths, Charles L.A new species of hermit crab, Pagurus fraserorum n. sp. (family Paguridae) is described from rocky subtidal reefs off KwaZulu-Natal, South Africa, and illustrated using both conventional drawings and colour photographs, and via three-dimensional (3D) X-ray micro-computed tomography (μCT). Because of the limitation μCT has in detecting very fine and soft structures, a novel approach of manually drawing setation and spinulation onto the twodimensional images of the 3D visualizations was used to illustrate the pereopods. In addition, an interactive figure and rotation movie clips in the supplement section complement the species description, and the 3D raw data of the 3D type data are downloadable from the Gigascience Database repository. The new species is the sixth species of Pagurus Fabricius, 1775 reported from South Africa and is closely allied to the Indo-Pacific P. boriaustraliensis Morgen, 1990 and P. pitagsaleei McLaughlin, 2002, from which it differs by its shorter ocular peduncles, by the armature of the carpus of the right cheliped, and also in colouration. This study presents the first description of a hermit crab in which a majority of taxonomic details are illustrated through 3D volume-rendered illustrations. In addition, colour photographs and COI molecular barcodes are provided, and the latter compared to COI sequences of specimens from Western Australia previously identified as P. boriaustraliensis and of specimens of P. pitagsaleei from Taiwan, as well as to three additional South African members of the genus. The South African taxon was confirmed to be genetically distinct from all species tested.
- ItemMicrofocus X-ray computed tomography (CT) analysis of laser sintered parts(Southern African Institute for Industrial Engineering, 2014-05) Du Plessis, Anton; Seifert, T.; Booysen, G.; Els, J.Microfocus 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.
- ItemPhysico-elemental analysis of roasted organic coffee beans from Ethiopia, Colombia, Honduras, and Mexico using X-ray micro-computed tomography and external beam particle induced X-ray emission(MDPI, 2019) Cloetea, Karen J.; Smit, Ziga; Minnis-Ndimba, Roya; Vavpetic, Primoz; Du Plessis, Anton; Le Roux, Stephan G.; Pelicon, PrimozThe physico-elemental profiles of commercially attained and roasted organic coffee beans from Ethiopia, Colombia, Honduras, and Mexico were compared using light microscopy, X-ray micro-computed tomography, and external beam particle induced X-ray emission. External beam PIXE analysis detected P, S, Cl, K, Ca, Ti, Mn, Fe, Cu, Zn, Br, Rb, and Sr in samples. Linear discriminant analysis showed that there was no strong association between elemental data and production region, whilst a heatmap combined with hierarchical clustering showed that soil-plant physico-chemical properties may influence regional elemental signatures. Physical trait data showed that Mexican coffee beans weighed significantly more than beans from other regions, whilst Honduras beans had the highest width. X-ray micro-computed tomography qualitative data showed heterogeneous microstructural features within and between beans representing different regions. In conclusion, such multi-dimensional analysis may present a promising tool in assessing the nutritional content and qualitative characteristics of food products such as coffee.
- ItemSnake fangs : 3D morphological and mechanical analysis by microCT, simulation, and physical compression testing(Oxford University Press, 2018) Du Plessis, Anton; Broeckhoven, Chris; Le Roux, Stephan G.This Data Note provides data from an experimental campaign to analyse the detailed internal and external morphology and mechanical properties of venomous snake fangs. The aim of the experimental campaign was to investigate the evolutionary development of 3 fang phenotypes and investigate their mechanical behaviour. The study involved the use of load simulations to compare maximum Von Mises stress values when a load is applied to the tip of the fang. The conclusions of this study have been published elsewhere, but in this data note we extend the analysis, providing morphological comparisons including details such as curvature comparisons, thickness, etc. Physical compression results of individual fangs, though reported in the original paper, were also extended here by calculating the effective elastic modulus of the entire snake fang structure including internal cavities for the first time. This elastic modulus of the entire fang is significantly lower than the locally measured values previously reported from indentation experiments, highlighting the possibility that the elastic modulus is higher on the surface than in the rest of the material. The micro–computed tomography (microCT) data are presented both in image stacks and in the form of STL files, which simplifies the handling of the data and allows its re-use for future morphological studies. These fangs might also serve as bio-inspiration for future hypodermic needles.
- ItemStandard method for microCT-based additive manufacturing quality control 1 : porosity analysis(Elsevier, 2018) Du Plessis, Anton; Sperling, Philip; Beerlink, Andre; Tshabalala, Lerato; Hoosain, Shaik; Mathe, Ntombi; Le Roux, Stephan G.ENGLISH ABSTRACT: MicroCT is a well-established technique that is used to analyze the interior of objects non-destructively, and it is especially useful for void or porosity analysis. Besides its widespread use, few standards exist and none for additive manufacturing as yet. This is due to the inherent differences in part design, sizes and geometries, which results in different scan resolutions and qualities. This makes direct comparison between different scans of additively manufactured parts almost impossible. In addition, different image analysis methodologies can produce different results. In this method paper, we present a simplified 10 mm cube-shaped coupon sample as a standard size for detailed analysis of porosity using microCT, and a simplified workflow for obtaining porosity information. The aim is to be able to obtain directly comparable porosity information from different samples from the same AM system and even from different AM systems, and to potentially correlate detailed morphologies of the pores or voids with improper process parameters. The method is applied to two examples of different characteristic types of voids in AM: sub-surface lack of fusion due to improper contour scanning, and tree-like pores growing in the build direction. This standardized method demonstrates the capability for microCT to not only quantify porosity, but also identify void types which can be used to improve AM process optimization.
- ItemStandard method for microCT-based additive manufacturing quality control 2 : density measurement(Elsevier, 2018) Du Plessis, Anton; Sperling, Philip; Beerlink, Andre; Tshabalala, Lerato; Hoosain, Shaik; Mathe, Ntombi; Le Roux, Stephan G.ENGLISH ABSTRACT: MicroCT is best known for its ability to detect and quantify porosity or defects, and to visualize its 3D distribution. However, it is also possible to obtain accurate volumetric measurements from parts – this can be used in combination with the part mass to provide a good measure of its average density. The advantage of this density-measurement method is the ability to combine the density measurement with visualization and other microCT analyses of the same sample. These other analyses may include detailed porosity or void analysis (size and distribution) and roughness assessment, obtainable with the same scan data. Simple imaging of the interior of the sample allows the detection of unconsolidated powder, open porosity to the surface or the presence of inclusions. The CT density method presented here makes use of a 10 mm cube sample and a simple data analysis workflow, facilitating standardization of the method. A laboratory microCT scanner is required at 15 μm voxel size, suitable software to allow sub-voxel precise edge determination of the scanned sample and hence an accurate total volume measurement, and a scale with accuracy to 3 digits.