Browsing by Author "Lim, B"

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    Additively manufactured Haynes-282 monoliths containing thin wall struts of varying thicknesses
    (Elsevier, 2022-09-01) Lim, B; Chen, H; Nomoto, K; Chen, Z; Saville, AI; Vogel, SC; Clarke, AJ; Paradowska, AM; Reid, M; Primig, S; Liao, XZ; Babu, SS; Breen, AJ; Ringer, SP
    Magnitude and distribution of residual stresses in additively manufactured Ni-based superalloys may impact the mechanical performance of as-fabricated parts. Though electron beam powder bed fusion (E-PBF) can produce components with minimal defects and residual stresses compared to laser powder bed fusion and directed energy deposition, variations of them may occur within the complex geometry of a component, due to inherent variations of thermal signatures and the evolution of section modulus along the build direction. This work reveals the residual stress distribution, characterised from neutron diffraction, of an as-fabricated Haynes 282 monolith containing internal cube voids and thin wall struts of varying thicknesses. Complementary local hardness measurements and multi-scale microscopy were used to investigate the geometry-structure-property relationships. Observed variations in hardness were attributed to a combination of type I macro-scale residual stresses and variations in bimodal γ′ precipitation behaviour. The results highlight the influence of residual stresses and microstructure on the mechanical properties of E-PBF Haynes 282. © 2022 The Author(s). Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license
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    Energy optimisation of propagation-based phase-contrast computed tomography: a quantitative image quality assessment
    (SPIE, 2022-04-04) Lim, B; Lewis, S; Arhatari, BD; Nesterets, YI; Mayo, SC; Fox, J; Thomposon, D; Kumar, B; Häusermann, D; Maksimenko, A; Hall, C; Dimmock, M; Lockie, D; Rickard, M; Giannoitti, N; Peele, AG; Quiney, HM; Gureyev, TE; Brennan, PC; Taba, ST
    Purpose: This study aims at establishing the optimum x-ray energy for synchrotron acquired propagation-based computed tomography (PB-CT) images to obtain highest radiological image quality of breast mastectomy samples. It also examines the correlation between objective physical measures of image quality with subjective human observer scores to model factors impacting visual determinants of image quality. Approach: Thirty mastectomy samples were scanned at Australian Synchrotron’s Imaging and Medical Beamline. Samples were scanned at energies of 26, 28, 30, 32, 34, and 60 keV at a standard dose of 4mGy. Objective physical measures of image quality were assessed using signal-to-noise ratio (SNR), contrast-to-noise ratio (CNR), SNR/resolution (SNR/res), CNR/resolution (CNR/res) and visibility. Additional calculations for each measure were performed against reference absorption-based computer tomography (AB-CT) images scanned at 32 keV and 4mGy. This included differences in SNR (dSNR), CNR (dCNR), SNR/res (dSNR/res), CNR/res (dCNR/res), and visibility (dVis). Physical measures of image quality were also compared with visual grading analysis data to determine a correlation between observer scores and objective metrics. Results: For dSNR, dCNR, dSNR/res, dCNR/res, and dVis, a statistically significant difference was found between the energy levels. The peak x-ray energy for dSNR and dSNR/res was 60 keV. For dCNR and dCNR/res 34 keV produced the highest measure compared to 28 keV for dVis. Visibility and CNR correlate to 56.8% of observer scores. Conclusion: The optimal x-ray energy differs for different objective measures of image quality with 30-34 keV providing optimum image quality for breast PB-CT. Visibility and CNR correlate highest to medical imaging expert scores. © (2022) Society of Photo-Optical Instrumentation Engineers (SPIE).