I12-JEEP: Joint Engineering, Environmental and Processing
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Diamond Proposal Number(s):
[16188]
Abstract: In die-casting processes, the high cooling rates and pressures affect the alloy solidification and deformation behavior, and thereby impact the final mechanical properties of cast components. In this study, isothermal semi-solid compression and subsequent cooling of aluminum die-cast alloy specimens were characterized using fast synchrotron tomography. This enabled the investigation and quantification of gas and shrinkage porosity evolution during deformation and solidification. The analysis of the 4D images (3D plus time) revealed two distinct mechanisms by which porosity formed; (i) deformation-induced growth due to the enrichment of local hydrogen content by the advective hydrogen transport, as well as a pressure drop in the dilatant shear bands, and (ii) diffusion-controlled growth during the solidification. The rates of pore growth were quantified throughout the process, and a Gaussian distribution function was found to represent the variation in the pore growth rate in both regimes. Using a one-dimensional diffusion model for hydrogen pore growth, the hydrogen flux required for driving pore growth during these regimes was estimated, providing a new insight into the role of advective transport associated with the deformation in the mushy region.
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Aug 2019
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I12-JEEP: Joint Engineering, Environmental and Processing
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Ramzi
Al-agele
,
Emily
Paul
,
Sophie
Taylor
,
Charlotte
Watson
,
Craig
Sturrock
,
Michael
Drakopoulos
,
Robert C.
Atwood
,
Catrin S.
Rutland
,
Nicola
Menzies-gow
,
Edd
Knowles
,
Jonathan
Elliott
,
Patricia
Harris
,
Cyril
Rauch
Open Access
Abstract: Global inequalities in economic access and agriculture productivity imply that a large number of developing countries rely on working equids for transport/agriculture/mining. Therefore, the understanding of hoof conditions/shape variations affecting equids' ability to work is still a persistent concern. To bridge this gap, using a multi-scale interdisciplinary approach, we provide a bio-physical model predicting the shape of equids’ hooves as a function of physical and biological parameters. In particular, we show (i) where the hoof growth stress originates from, (ii) why the hoof growth rate is one order of magnitude higher than the proliferation rate of epithelial cells and (iii) how the soft-to-hard transformation of the epithelium is possible allowing the hoof to fulfil its function as a weight-bearing element. Finally (iv), we demonstrate that the reason for hoof misshaping is linked to the asymmetrical design of equids' feet (shorter quarters/long toe) together with the inability of the biological growth stress to compensate for such an asymmetry. Consequently, the hoof can adopt a dorsal curvature and become ‘dished’ overtime, which is a function of the animal's mass and the hoof growth rate. This approach allows us to discuss the potential occurrence of this multifaceted pathology in equids.
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Jun 2019
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I12-JEEP: Joint Engineering, Environmental and Processing
Optics
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Diamond Proposal Number(s):
[14033]
Open Access
Abstract: High energy X-ray phase contrast tomography is tremendously beneficial to the study of thick and dense materials with poor attenuation contrast. Recently, the X-ray speckle-based imaging technique has attracted widespread interest because multimodal contrast images can now be retrieved simultaneously using an inexpensive wavefront modulator and a less stringent experimental setup. However, it is time-consuming to perform high resolution phase tomography with the conventional step-scan mode because the accumulated time overhead severely limits the speed of data acquisition for each projection. Although phase information can be extracted from a single speckle image, the spatial resolution is deteriorated due to the use of a large correlation window to track the speckle displacement. Here we report a fast data acquisition strategy utilising a fly-scan mode for near field X-ray speckle-based phase tomography. Compared to the existing step-scan scheme, the data acquisition time can be significantly reduced by more than one order of magnitude without compromising spatial resolution. Furthermore, we have extended the proposed speckle-based fly-scan phase tomography into the previously challenging high X-ray energy region (120 keV). This development opens up opportunities for a wide range of applications where exposure time and radiation dose are critical.
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Jun 2019
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I12-JEEP: Joint Engineering, Environmental and Processing
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Liya
Guo
,
Na
Mi
,
Haval
Mohammed-ali
,
Majid
Ghahari
,
Andrew
Du Plessis
,
Angus
Cook
,
Steven
Street
,
Christina
Reinhard
,
Robert C.
Atwood
,
Trevor
Rayment
,
Alison J.
Davenport
Diamond Proposal Number(s):
[7412]
Open Access
Abstract: Atmospheric corrosion of stainless steel can take place when airborne salt particles deposit on the metal surface, forming droplets when the relative humidity (RH) reaches a critical value: the deliquescence relative humidity of the salt. Most work to date has focused on single salts such as MgCl2 or NaCl. In the present work, the effect of mixed salts is investigated at 45% RH, above the deliquescence relative humidity of MgCl2 but below that of NaCl. Dish-shaped pits were found in pure MgCl2 solutions and mixed solutions. Crevice corrosion takes place under NaCl crystals. This is shown both with ex situ measurements and in situ time-dependent measurements using X-ray microtomography, where pit growth was also monitored.
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Jan 2019
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I12-JEEP: Joint Engineering, Environmental and Processing
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Diamond Proposal Number(s):
[13641, 16214]
Abstract: Understanding defect formation during laser additive manufacturing (LAM) of virgin, stored, and reused powders is crucial for the production of high quality additively manufactured parts. We investigate the effects of powder oxidation on the molten pool dynamics and defect formation during LAM. We compare virgin and oxidised Invar 36 powder under overhang and layer-by-layer build conditions using in situ and operando X-ray Imaging. The oxygen content of the oxidised powder was found to be ca. 6 times greater (0.343 wt.%) than the virgin powder (0.057 wt.%). During LAM, the powder oxide is entrained into the molten pool, altering the Marangoni convection from an inward centrifugal to an outward centripetal flow. We hypothesise that the oxide promotes pore nucleation, stabilisation, and growth. We observe that spatter occurs more frequently under overhang conditions compared to layer-by-layer conditions. Droplet spatter can be formed by indirect laser-driven gas expansion and by the laser-induced metal vapour at the melt surface. In layer-by-layer build conditions, laser re-melting reduces the pore size distribution and number density either by promoting gas release from keyholing or by inducing liquid flow, partially or completely filling pre-existing pores. We also observe that pores residing at the track surface can burst during laser re-melting, resulting in either formation of droplet spatter and an open pore or healing of the pore via Marangoni flow. This study confirms that excessive oxygen in the powder feedstock may cause defect formation in LAM.
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Dec 2018
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I12-JEEP: Joint Engineering, Environmental and Processing
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Michael R.
Chandler
,
Anne-laure
Fauchille
,
Ho Kyeom
Kim
,
Lin
Ma
,
Julian
Mecklenburgh
,
Roberto
Rizzo
,
Mahmoud
Mostafavi
,
Sebastian
Marussi
,
Robert
Atwood
,
Steven
May
,
Mohammed
Azeem
,
Ernie
Rutter
,
Kevin
Taylor
,
Peter
Lee
Diamond Proposal Number(s):
[13824]
Abstract: Mode‐I Fracture Toughness, KIc, was measured in six shale materials using the double torsion technique. During loading, crack propagation was imaged both using twin optical cameras, and with fast X‐Ray radiograph acquisition. Samples of Bowland, Haynesville, Kimmeridge, Mancos, Middlecliff and Whitby shales were tested in a range of orientations. The measured fracture toughness values were found to be in good agreement with existing literature values. The two imaging techniques improve our understanding of local conditions around the fracture tip, through in‐situ correlation of mechanical data, inelastic zone size and fracture‐tip velocity. The optical Digital Image Correlation (DIC) technique proved useful as a means of determining the validity of individual experiments, by identifying experiments during which strains had developed in the two "rigid" specimen halves. Strain maps determined through DIC of the optical images suggest that the scale of the inelastic zone is an order of magnitude smaller than the classically used approximation suggests. This smaller damage region suggests a narrower region of enhanced permeability around artificially generated fractures in shales. The resolvable crack‐tip was tracked using radiograph data and found to travel at a velocity around 470μm.s−1 during failure, with little variation in speed between materials and orientations. Fracture pathways in the bedding parallel orientations were observed to deviate from linearity, commonly following layer boundaries. This suggests that while a fracture travelling parallel to bedding may travel at a similar speed to a bedding perpendicular fracture, it may have a more tortuous pathway, and therefore access a larger surface area.
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Dec 2018
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I12-JEEP: Joint Engineering, Environmental and Processing
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Lee
Aucott
,
Hongbiao
Dong
,
Wajira
Mirihanage
,
Robert
Atwood
,
Anton
Kidess
,
Shian
Gao
,
Shuwen
Wen
,
John
Marsden
,
Shuo
Feng
,
Mingming
Tong
,
Thomas
Connolley
,
Michael
Drakopoulos
,
Chris R.
Kleijn
,
Ian M.
Richardson
,
David J.
Browne
,
Ragnvald H.
Mathiesen
,
Helen
Atkinson
Diamond Proposal Number(s):
[8218, 7855]
Open Access
Abstract: Internal flow behaviour during melt-pool-based metal manufacturing remains unclear and
hinders progression to process optimisation. In this contribution, we present direct timeresolved
imaging of melt pool flow dynamics from a high-energy synchrotron radiation
experiment. We track internal flow streams during arc welding of steel and measure
instantaneous flow velocities ranging from 0.1ms−1 to 0.5ms−1. When the temperaturedependent
surface tension coefficient is negative, bulk turbulence is the main flow
mechanism and the critical velocity for surface turbulence is below the limits identified in
previous theoretical studies. When the alloy exhibits a positive temperature-dependent
surface tension coefficient, surface turbulence occurs and derisory oxides can be entrapped
within the subsequent solid as result of higher flow velocities. The widely used arc welding and the emerging arc additive manufacturing routes can be optimised by controlling internal
melt flow through adjusting surface active elements.
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Dec 2018
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I12-JEEP: Joint Engineering, Environmental and Processing
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Matthew J.
Pankhurst
,
Nghia T.
Vo
,
Alan R.
Butcher
,
Haili
Long
,
Hongchang
Wang
,
Sara
Nonni
,
Jason
Harvey
,
Guđmundur
Guđfinnsson
,
Ronald
Fowler
,
Robert
Atwood
,
Richard
Walshaw
,
Peter D.
Lee
Diamond Proposal Number(s):
[14033]
Abstract: Olivine is a key constituent in the silicate Earth; its composition and texture informs petrogenetic understanding of numerous rock types. Here we develop a quantitative and reproducible method to measure olivine composition in three dimensions without destructive analysis, meaning full textural context is maintained. The olivine solid solution between forsterite and fayalite was measured using a combination of three-dimensional (3D) X-ray imaging techniques, 2D backscattered electron imaging, and spot-analyses using wavelength-dispersive electron probe microanalysis. The linear attenuation coefficient of natural crystals across a range of forsterite content from ∼73–91 mol% were confirmed to scale linearly with composition using 53, 60, and 70 kV monochromatic beams at I12-JEEP beamline, Diamond Light Source utilizing the helical fly-scan acquisition. A polychromatic X-ray source was used to scan the same crystals, which yielded image contrast equivalent to measuring the mol% of forsterite with an accuracy of <1.0%. X-ray tomography can now provide fully integrated textural and chemical analysis of natural samples containing olivine, which will support 3D and 3D+time petrologic modeling. The study has revealed >3 mm domains within a large crystal of San Carlos forsterite that varies by ∼2 Fo mol%. This offers a solution to an outstanding question of inter-laboratory standardization, and also demonstrates the utility of 3D, non-destructive, chemical measurement. To our knowledge, this study is the first to describe the application of XMT to quantitative chemical measurement across a mineral solid solution. Our approach may be expanded to calculate the chemistry of other mineral systems in 3D, depending upon the number, chemistry, and density of end-members.
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Nov 2018
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I12-JEEP: Joint Engineering, Environmental and Processing
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Open Access
Abstract: Synchrotron-based X-ray micro-tomography systems often suffer severe ring artifacts in reconstructed images. In sinograms the artifacts appear as straight lines or stripe artifacts. These artifacts are caused by the irregular response of a detecting system giving rise to a variety of observed types of stripes: full stripes, partial stripes, fluctuating stripes, and unresponsive stripes. The use of pre-processing techniques such as distortion correction or phase retrieval blurs and enlarges these stripes. It is impossible for a single approach to remove all types of stripe artifacts. Here, we propose three techniques for tackling all of them. The proposed techniques are easy to implement; do not generate extra stripe artifacts and void-center artifacts; and give superior quality on challenging data sets and in comparison with other techniques. Implementations in Python and a challenging data set are available for download.
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Oct 2018
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I12-JEEP: Joint Engineering, Environmental and Processing
I13-2-Diamond Manchester Imaging
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Diamond Proposal Number(s):
[13641, 15250]
Abstract: Laser-matter interactions in laser additive manufacturing (LAM) occur on short time scales (10-6 - 10-3 s) and have traditionally proven difficult to characterise. We investigate these interactions during LAM of stainless steel (SS316 L) and 13-93 bioactive glass powders using a custom built LAM process replicator (LAMPR) with in situ and operando synchrotron X-ray radiography. This reveals a range of melt track solidification phenomena as well as spatter and porosity formation. We hypothesise that the SS316 L powder absorbs the laser energy at its surface while the trace elements in the 13-93 bioactive glass powder absorb the laser energy by radiation conduction. Our results show that a low viscosity melt, e.g. 8 mPa s for SS316 L, tends to generate spatter with a diameter up to 250 µm and an average spatter velocity of 0.26 m s-1 and form a melt track by molten pool wetting. In contrast, a high viscosity melt, e.g. 2 Pa s for 13-93 bioactive glass, inhibits spatter formation by damping the Marangoni convection, forming a melt track via viscous flow. The viscous flow in 13-93 bioactive glass resists pore transport; combined with the reboil effect, this promotes pore growth during LAM, resulting in a pore size up to 500 times larger than that exhibited in the SS316 L sample.
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Aug 2018
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