Papers by Keyword: Computed Tomography

Abstract: This study investigates the impact of voids on the precision and dimensional stability of bonded joints in hybrid CFRP–aluminum assemblies for optical applications. Six CFRP samples were fabricated using filament winding and bonded to anodized aluminum alloy sleeves with DP 190 epoxy. Four samples were cured at 70 °C and two at 20 °C. Dimensional stability was assessed through radial runout measurements at three stages: post-manufacture, after environmental conditioning (including thermal cycling between +70 °C and –40 °C and six thermal shock cycles), and following mechanical resistance tests (shock, bump, and vibration per ISO 9022-3:2015). X-ray computed tomography (CT) revealed frequent defects such as adhesive starvation at joint edges, overflow, and a significant number of voids introduced during mixing. Porosity analysis showed that the presence of voids with equivalent diameters ≥0.5 mm strongly correlated with increased changes in radial runout, suggesting reduced dimensional stability.

Abstract: An effective powder consumption is indispensable for enlarging the diameter and thickness of SiC crystals. We employed three types of filling designs for SiC source powder with different distances between the surface of the seed and the source powder. To maintain the shape of the designs, the SiC source powder was heat-treated in an Ar atmosphere at 680 torr within a temperature range of 1500 to 1600°C. The SiC source powder consumption and contribution to growth in well-structured layouts increased due to the increase in the surface area of SiC source powder, despite its lower initial powder filling. The numerical simulation showed that the well-structured layouts with a higher surface area of SiC source powder have a higher partial pressure of Si and SiC₂ gases (supersaturation of these gas phases) near the seed region compared to the without well-structured layouts. The computed tomography (CT) analysis of the cross-section of SiC source powder after the growth run clearly showed that the source powder was previously sublimated at the region of the crucible wall, and recrystallization at the surface region of the source powder physically retarded the pathway of SiC source gases to the region of the SiC seed crystal. The newly designed well-structured layouts of the source powder have an economical advantage in achieving effective powder consumption during crystal growth.

Abstract: Positron annihilation spectroscopy (PAS) offers a transformative approach to medical imaging, providing detailed insights into molecular structures. Although PAS has been extensively applied in studying defects in semiconductors and synthetic materials—yielding quantitative data on their microscopic properties—its potential in medical imaging could significantly enhance diagnostic methodologies. The application of positrons and other forms of radiation in analyzing living tissues necessitates careful consideration of potential damage. In this work, a model method designed to determine the optimal dose for experimental measurements is introduced. While Positron Emission Tomography (PET) has been instrumental in clinical diagnostics using radiopharmaceuticals to visualize metabolic processes, PAS presents a cutting-edge tool for improving the specificity and accuracy of biological imaging. Its capability to non-destructively explore structural transformations and micro-environmental changes in biological samples positions it as a promising innovation in diagnostics, paving the way for enhanced healthcare outcomes globally.

Abstract: The limitations of iodinated-based contrast media in computed tomography (CT) imaging have prompted studies into alternative contrast agents. Bismuth oxide nanoparticles (BiONPs) have emerged as a potential contrast agent due to their high X-ray attenuation, low toxicity, and cost-effectiveness. This study evaluates the efficacy of BiONPs as a contrast agent in CT imaging compared to traditional iodine-based contrast agents. A phantom study was conducted using synthesized BiONPs and iodine contrast agents (ICA) at a range of concentrations (0.05 to 1.0 mmol/L). The phantom was scanned with a CT scanner using 120 kVp tube potential and the contrast-to-noise ratio (CNR) was calculated to determine the contrast enhancement. The findings show that BiONPs demonstrated superior CNR values compared to iodine contrast agents at all concentrations tested. Specifically, at 0.5 mmol/L, BiONPs achieved a mean CNR of 161.70, significantly higher than iodine’s 51.47 (p < 0.05). Similar trends were observed at lower concentrations, with BiONPs consistently outperforming ICA. The findings highlight the BiONPs as an effective alternative to ICA, particularly at lower concentrations. This study highlights the capability of BiONPs to provide superior image contrast in CT imaging compared to conventional ICA. Its consistent performance across variations of concentration emphasizes its potential for improving diagnostic accuracy in CT imaging.

Abstract: Pores are the inevitable concomitant in the current state of laser powder bed fusion (PBF-LB/M) of AlSI10Mg components. Various pore characteristics, such as pore size and pore shape, influence the quality and affect the intended functionality of the component. Today, the experimental effort to find the appropriate process parameters for additive manufacturing (AM) results in high costs and long time-to-market. Pore formation is highly dependent on the applied process parameters. Consequently, pores can also be seen as an individual process fingerprint. Computed tomography is a commonly used measurement tool for AM components and can be used to comprehensively investigate process-induced defects. Furthermore, X-ray data allows an accurate categorisation of pores and provides a large amount of labelled data for supervised learning applications. The applied classification method classifies the pores into six classes (A-F) according to their shape and size. A total number of 3,066,249 pores detected in cylindrical samples were categorised and used for machine learning. The purpose of this work is to demonstrate an approach for predicting AM process parameters depending on the resulting pore distribution using supervised learning methods. The result is an expandable machine learning model based on an artificial neural network.

Abstract: Two common types of internal defects of additively manufactured (AM) samples are lack-of-fusion and gas-entrapped porosities. These internal defects can have different physical origins and particular local characteristics (e.g., different shape, size). Thus, the use of reliable non-destructive inspection techniques is essential for the accurate assessment of integrity, allowing the applicable AM processing parameters correction. To overcome this challenge, this work aims to evaluate the accuracy of volumetric characteristics measured by computed tomography for porosity evaluations in AM samples, including assessment of measurement uncertainty. The effect of different cumulative thickness on the evaluated measurements accuracy is also assessed. The results show that deviations of defect size measurements can be below 2% if the proposed procedure is followed. In addition, the expanded uncertainty can be up to 10% of the measured magnitude when the cumulative thickness is increased to 70 mm. The physical relationships obtained between the cumulative thickness and the individual measurements are also presented.

Abstract: Within the technologies that make up Additive Manufacturing (AM), one of the ones that have taken the greatest prominence in recent times is DED (Direct Energy Deposition), particularly that of wire feedstock. The W-DED/LB technique has some benefits compared to other AM methods, such as the fabrication of relatively larger parts, repair capabilities of the damaged areas of a component, cladding of different materials on existing parts, and reduced material waste.This study describes the optimisation of processing parameters for the manufacturing stainless steel (SS316L) and Inconel 718 alloys (INC718) using W-DED/LB. This is performed by modifying processing aspects like deposition trajectories, laser power, displacement speeds of the DED head, etc, with the aim of obtaining high deposition rates and a density above 99.5%. Once the alloy systems are optimised, a characterisation campaign has been performed, which includes a series of tests as well for defectology analysis using X-ray Computed Tomography (CT). Finally, the influence of different heat treatments on the tensile behaviour is analysed.This work has developed the technology of DED assembling in a Kuka-robot, so the challenge has not only been to control the DED system, but also the communication with the robotic arm to guarantee perfect harmony between all the parts that make up the W-DED/LB system.

Abstract: In this paper, both thixocasting and rheocasting of Al-7Si-0.6Mg alloy (EN AC 42200) for the same part was performed. It was found that rheocasting of Al-7Si-0.6Mg alloy show a smaller primary Al grain size and significant improvement of cast defects compared with thixocasting of Al-7Si-0.6Mg alloy. This paper demonstrates that rheocasting of Al-7Si-0.6Mg alloy is more beneficial in terms of microstructure and cast defects compared with thixocasting of Al-7Si-0.6Mg alloy.

Abstract: In the simulation of bulk forming processes the validation of the applied simulation models is necessary. Then, predictive simulations are possible. A visualisation method is an advanced way to create additional evaluation parameters. In this work, the upscaling of a newly developed non-destructive method from semi-industrial to near-industrial scale for metal extrusion of aluminium alloys is presented. A copper coating, which deforms with the billet material, was applied to one half (in the longitudinal direction) of a cast billet and detected by computed tomography (CT). The copper pattern was applied by a plasma coating technology to determine the deformation of the billet material during the process until the final profile. A detailed analysis of the upscaled method with improved geometric setup shows the superiority of the newly chosen properties enabling a complete determination of strain state also in the profile.

Abstract: Industrial X-ray computed tomography (XCT) is a tool for non-destructive testing and a volumetric analysis method with the ability to measure dimensions and geometry inside a component without destroying it. However, XCT is a relatively young technology in the field of dimensional metrology and thus faces several challenges. The achievement of a high measurement resolution, which is re-quired to detect small geometrical features, depends on a variety of influencing factors. In this arti-cle, the interface structural resolution (ISR) as one of the key challenges will be investigated. The two-sphere standard called the hourglass standard allows the determination of the structural resolu-tion by evaluation of the surrounding area of an ideal point contact of two spheres after the CT re-construction in form of a neck-shaped transition. Close to the contact point of the two spheres two opposing surfaces exist. Their distances from each other increase as the distance from the contact point of the two spheres increase. The determination of the distances between the spheres’ surface allows a statement about the ISR. A new developed specimen or standard with a variable gap size consisting of calibrated parallel gauge blocks allows statements about the ISR, too. Because of the higher number of probing points of the gauge block standard the results of the determined ISR are more stable compared to the hourglass standard. This paper compares the results of the computed tomography measurements for the designed interface structural resolution standard with those of the hourglass standard.