Publications
520 results found
Chen Y, Clark SJ, Collins DM, et al., 2021, Correlative synchrotron X-ray imaging and diffraction of directed energy deposition additive manufacturing, Acta Materialia, Vol: 209, Pages: 1-13, ISSN: 1359-6454
The governing mechanistic behaviour of Directed Energy Deposition Additive Manufacturing (DED-AM) is revealed by a combined in situ and operando synchrotron X-ray imaging and diffraction study of a nickel-base superalloy, IN718. Using a unique DED-AM process replicator, real-space imaging enables quantification of the melt-pool boundary and flow dynamics during solidification. This imaging knowledge was also used to inform precise diffraction measurements of temporally resolved microstructural phases during transformation and stress development with a spatial resolution of 100 µm. The diffraction quantified thermal gradient enabled a dendritic solidification microstructure to be predicted and coupled to the stress state. The fast cooling rate entirely suppressed the formation of secondary phases or recrystallisation in the solid-state. Upon solidification, the stresses rapidly increase to the yield strength during cooling. This insight, combined with the large solidification range of IN718 suggests that the accumulated plasticity exhausts the ductility of the alloy, causing liquation cracking. This study has revealed the mechanisms that govern the formation of highly non-equilibrium microstructures during DED-AM.
Nelson M, Li S, Page SJ, et al., 2021, 3D printed silica-gelatin hybrid scaffolds of specific channel sizes promote collagen Type II, Sox9 and Aggrecan production from chondrocytes, Materials Science and Engineering: C, Vol: 123, Pages: 1-12, ISSN: 0928-4931
Inorganic/organic hybrids have co-networks of inorganic and organic components, with the aim of obtaining synergy of the properties of those components. Here, a silica-gelatin sol-gel hybrid “ink” was directly 3D printed to produce 3D grid-like scaffolds, using a coupling agent, 3-glycidyloxypropyl)trimethoxysilane (GPTMS), to form covalent bonds between the silicate and gelatin co-networks. Scaffolds were printed with 1 mm strut separation, but the drying method affected the final architecture and properties. Freeze drying produced <40 μm struts and large ~700 μm channels. Critical point drying enabled strut consolidation, with ~160 μm struts and ~200 μm channels, which improved mechanical properties. This architecture was critical to cellular response: when chondrocytes were seeded on the scaffolds with 200 μm wide pore channels in vitro, collagen Type II matrix was preferentially produced (negligible amount of Type I or X were observed), indicative of hyaline-like cartilaginous matrix formation, but when pore channels were 700 μm wide, Type I collagen was prevalent. This was supported by Sox9 and Aggrecan expression. The scaffolds have potential for regeneration of articular cartilage regeneration, particularly in sports medicine cases.
Couperthwaite FK, Morgan DJ, Pankhurst MJ, et al., 2021, Reducing epistemic and model uncertainty in ionic inter-diffusion chronology: A 3D observation and dynamic modeling approach using olivine from Piton de la Fournaise, La Reunion, American Mineralogist: an international journal of earth and planetary materials, Vol: 106, Pages: 481-494, ISSN: 0003-004X
Modeling of ionic diffusion in natural crystals has been developed over the last three decades to calculate timescales of geological processes. As the number of studies and the size of data sets have expanded, improvements in the precision of the general technique are needed to resolve temporal patterns that would otherwise be masked by large uncertainties. This contribution examines fundamental aspects of timescale calculation uncertainty using Mg-Fe zonation in olivine crystals from a Piton de la Fournaise oceanite erupted in 2002 CE. First, we quantitatively consider the role of geometric uncertainty in data sets from the perspectives of sectioning angle, crystal shape, and crystal agglomeration. Second, we assess how crystal growth and changing boundary conditions during diffusion pose problems for simplistic, 1D, diffusion-only modeling.An initial database of 104 timescales (7–45 days) was generated using typical, 1D, isothermal diffusion-only methods for profiles taken from 30 compositionally and texturally zoned crystals of olivine. This simplistic modeling yields poor model fits and imprecise timescales; prior to this work, we would have rejected >60% of these data. Universal-stage measurements of crystal boundary angles and three-dimensional (3D) X-ray microcomputed tomography observations of crystal shape address geometric uncertainties. U-stage measurements show that, contrary to expectations of random sectioning, most boundaries modeled initially were close to the ideal sectioning plane. Assessment of crystal morphology from 2D thin sections suggests olivine crystals are dominantly euhedral; however, 3D imaging reveals that they are significantly subhedral and often exist as agglomerates, an observation that underscores both the potential for diverse crystal interactions through time in the magma (Wieser et al. 2019) and out-of-plane effects capable of influencing calculations of diffusion profiles.Refinements to timescale determination can be m
Chen Y, Clark SJ, Huang Y, et al., 2021, In situ X-ray quantification of melt pool behaviour during directed energy deposition additive manufacturing of stainless steel, Materials Letters, Vol: 286, ISSN: 0167-577X
The Directed Energy Deposition Additive Manufacturing (DED-AM) of SS316L was studied using in situ and operando synchrotron X-ray imaging to quantitively understand the effect of processing parameters on the melt-pool morphology and surface quality. It was found that surface roughness of DED-AM builds can result from melt pool surface perturbations caused by changes in the melt flow and build stage motion perturbations. Process maps are developed that quantitatively correlate build quality to process parameters including powder feed rate, laser power and traverse speed. How the AM process parameters control build efficacy is clarified, and the processing conditions required to dampen surface perturbations leading to roughness were determined.
Walsh C, Tafforeau P, Wagner WL, et al., 2021, Multiscale three-dimensional imaging of intact human organs down to the cellular scale using hierarchical phase-contrast tomography., bioRxiv
Human organs are complex, three-dimensional and multiscale systems. Spatially mapping the human body down through its hierarchy, from entire organs to their individual functional units and specialised cells, is a major obstacle to fully understanding health and disease. To meet this challenge, we developed hierarchical phase-contrast tomography (HiP-CT), an X-ray phase propagation technique utilising the European Synchrotron Radiation Facility's Extremely Brilliant Source: the world's first high-energy 4 th generation X-ray source. HiP-CT enabled three-dimensional and non-destructive imaging at near-micron resolution in soft tissues at one hundred thousand times the voxel size whilst maintaining the organ's structure. We applied HiP-CT to image five intact human parenchymal organs: brain, lung, heart, kidney and spleen. These were hierarchically assessed with HiP-CT, providing a structural overview of the whole organ alongside detail of the organ's individual functional units and cells. The potential applications of HiP-CT were demonstrated through quantification and morphometry of glomeruli in an intact human kidney, and identification of regional changes to the architecture of the air-tissue interface and alveolar morphology in the lung of a deceased COVID-19 patient. Overall, we show that HiP-CT is a powerful tool which can provide a comprehensive picture of structural information for whole intact human organs, encompassing precise details on functional units and their constituent cells to better understand human health and disease.
Ma L, Fauchille A-L, Chandler MR, et al., 2021, In-situ synchrotron characterisation of fracture initiation and propagation in shales during indentation, Energy, Vol: 215, Pages: 1-11, ISSN: 0360-5442
The feasibility and advantages of synchrotron imaging have been demonstrated to effectively characterise fracture initiation and propagation in shales during indentation tests. These include 1) fast (minute-scale) and high-resolution (μm-scale) imaging of fracture initiation, 2) concurrent spatial and temporal information (4D) about fracture development, 3) quantification and modelling of shale deformation prior to fracture. Imaging experiments were performed on four shale samples with different laminations and compositions in different orientations, representative of three key variables in shale microstructure. Fracture initiation and propagation were successfully captured in 3D over time, and strain maps were generated using digital volume correlation (DVC). Subsequently, post-experimental fracture geometries were characterised at nano-scale using complementary SEM imaging. Characterisation results highlight the influence of microstructural and anisotropy variations on the mechanical properties of shales. The fractures tend to kink at the interface of two different textures at both macroscale and microscale due to deformation incompatibility. The average composition appears to provide the major control on hardness and fracture initiation load; while the material texture and the orientation of the indentation to bedding combine to control the fracture propagation direction and geometry. This improved understanding of fracture development in shales is potentially significant in the clean energy applications.
Notley S, Chen Y, Lee PD, et al., 2021, Variance Stabilised Optimisation of Neural Networks: A Case Study in Additive Manufacturing, International Joint Conference on Neural Networks (IJCNN), Publisher: IEEE, ISSN: 2161-4393
Sinclair L, Leung CLA, Marussi S, et al., 2020, In situ radiographic and ex situ tomographic analysis of pore interactions during multilayer builds in laser powder bed fusion, Additive Manufacturing, Vol: 36, Pages: 1-14, ISSN: 2214-8604
Porosity and high surface roughness can be detrimental to the mechanical performance of laser powder bed fusion (LPBF) additive manufactured components, potentially resulting in reduced component life. However, the link between powder layer thickness on pore formation and surface undulations in the LPBF parts remains unclear. In this paper, the influence of processing parameters on Ti-6Al-4 V additive manufactured thin-wall components are investigated for multilayer builds, using a custom-built process replicator and in situ high-speed synchrotron X-ray imaging. In addition to the formation of initial keyhole pores, the results reveal three pore phenomena in multilayer builds resulting from keyhole melting: (i) healing of the previous layers' pores via liquid filling during remelting; (ii) insufficient laser penetration depth to remelt and heal pores; and (iii) pores formed by keyholing which merge with existing pores, increasing the pore size. The results also show that the variation of powder layer thickness influences which pore formation mechanisms take place in multilayer builds. High-resolution microcomputed tomography images reveal that clusters of pores form at the ends of tracks, and variations in the layer thickness and melt flow cause irregular remelting and track height undulations. Extreme variations in height were found to lead to lack of fusion pores in the trough regions. It is hypothesised that the end of track pores were augmented by soluble gas which is partitioned into the melt pool and swept to track ends, supersaturating during end of track solidification and diffusing into pores increasing their size.
Cai B, Kao A, Boller E, et al., 2020, Revealing the mechanisms by which magneto-hydrodynamics disrupts solidification microstructures, Acta Materialia, Vol: 196, Pages: 200-209, ISSN: 1359-6454
A key technique for controlling solidification microstructures is magneto-hydrodynamics (MHD), resulting from imposing a magnetic field to solidifying metals and alloys. Applications range from bulk stirring to flow control and turbulence damping via the induced Lorentz force. Over the past two decades the Lorentz force caused by the interaction of thermoelectric currents and a magnetic field, a MHD phenomenon known as Thermoelectric Magnetohydrodynamics (TEMHD), was also shown to drive inter-dendritic flow altering microstructural evolution. In this contribution, high-speed synchrotron X-ray tomography and high-performance computational simulation are coupled to reveal the evolution, dynamics and mechanisms of solidification within a magnetic field, resolving the complex interplay and competing flow effects arising from Lorentz forces of different origins. The study enabled us to reveal the mechanisms disrupting the traditional columnar dendritic solidification microstructure, ranging from an Archimedes screw-like structure, to one with a highly refined dendritic primary array. We also demonstrate that alloy composition can be tailored to increase or decrease the influence of MHD depending on the Seebeck coefficient and relative density of the primary phase and interdendritic liquid. This work paves the way towards novel computational and experimental methods of exploiting and optimising the application of MHD in solidification processes, together with the calculated design of novel alloys that utilise these forces.
Chen Y, Clark SJ, Leung CLA, et al., 2020, In-situ Synchrotron imaging of keyhole mode multi-layer laser powder bed fusion additive manufacturing, Applied Materials Today, Vol: 20, Pages: 1-8, ISSN: 2352-9407
The keyhole mode in laser powder bed fusion (LPBF) additive manufacturing can be associated with excessive porosity and spatter, however, the underlying physics in multilayer build conditions remain unclear. Here, we used ultra-fast synchrotron X-ray imaging to reveal this phenomena. We in investigated melt pool dynamics, keyhole porosity and spatter formation mechanisms and their impact in all layers of the build. We observed that the transient melt pool dynamics associated with the keyhole include: (I) keyhole initiation, (II) keyhole development, and (III) melt pool recovery. Porosity and spatter were associated with stages (II) and (III). We also discovered that droplet spatter can form due to the collapse of the keyhole recoil zone, causing molten particle agglomeration and ejection during stage (III). Our results clarify the transient dynamics behind the keyhole mode in a multi-layer LBPF process and can be used to guide the reduction in porosity and spatter in additive manufacturing.
Shi X, Nommeots-Nomm A, Todd NM, et al., 2020, Bioactive glass scaffold architectures regulate patterning of bone regeneration in vivo, Applied Materials Today, Vol: 20, Pages: 1-11, ISSN: 2352-9407
The architecture of bone scaffolds, such as pore dimensions, connectivity and orientation can regulate osteogenic defect repair, as can their rate of degradation. Synthetic bone grafts have historically been developed with foam structures to mimic trabecular bone. Now, Additive Manufacturing techniques enable production of open and regular pore architectures with improved compressive strengths. Here, we compare two types of bioactive glass scaffolds, made of the highly biodegradable ICIE16 composition, with distinctively different architectures but matched interconnect sizes (~150 µm), produced via two different techniques: gel-cast foaming and direct ink writing. A rabbit lateral femoral defect model was used to compare the effect of their architecture on in vivo bone regeneration, relative to a defect only control group, after 4 and 10 weeks of implantation. 3D X-ray microcomputed tomography (micro-CT), correlated to histology and back-scatter electron microscopy (BS-SEM) permitted quantitative evaluation of new bone ingrowth and degradation of the scaffolds. Both foam and printed scaffolds showed equal or higher bone ingrowth compared to the control group. After 4 weeks, the foam group showed the highest osteogenesis, with 51% more bone ingrowth than the defect only controls, but after 10 weeks the defect treated with the printed scaffold had the most bone ingrowth (40% more than the empty defect). Energy dispersive X-ray (EDS) mapping revealed degradation of the glass and calcium-phosphate deposition. The foam group showed more rapid degradation than the printed group, due to higher total porosity (even though interconnected pore size was equivalent). The foam scaffold appeared to allow rapid bone ingrowth and cancellous bone formation, whereas the printed scaffold seemed to provoke cortical-like bone formation, while remaining in place for longer than the 10 week study. While the foam's concave architectures promote initial bone ingrowth, the higher stren
Kao A, Shevchenko N, He S, et al., 2020, Magnetic effects on microstructure and solute plume dynamics of directionally solidifying Ga-In alloy, JOM Journal of the Minerals, Metals and Materials Society, Vol: 72, Pages: 3645-3651, ISSN: 1047-4838
The effects of applying a 0.2-T transverse magnetic field on a solidifying Ga-25 wt%In alloy have been investigated through a joint experimental and numerical study. The magnetic field introduced significant changes to both the microstructure and the dynamics of escaping high-concentration Ga plumes. Plume migration across the interface was quantified and correlated to simulations to demonstrate that thermoelectric magnetohydrodynamics (TEMHD) is the underlying mechanism. TEMHD introduced macrosegregation within the dendritic structure, leading to the formation of a stable “chimney” channel by increasing the solutal buoyancy in the flow direction. The resulting pressure difference across the solidification front introduced a secondary hydrodynamic phenomenon that subsequently caused solute plume migration.
Lee PD, 2020, Peter Lee answers questions about additive manufacturing, NATURE COMMUNICATIONS, Vol: 11, ISSN: 2041-1723
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Prasad A, Yuan L, Lee P, et al., 2020, Towards understanding grain nucleation under Additive Manufacturing solidification conditions, Acta Materialia, Vol: 195, Pages: 392-403, ISSN: 1359-6454
This paper provides insights into the effect of high thermal gradients and cooling rates on equiaxed grain nucleation and growth in conditions similar to those experienced during Additive Manufacturing (AM) processes. Bridgman type solidification is numerically simulated with columnar grains growing at a fixed pull rate under a user-imposed thermal gradient. Controlled inoculants of known nucleation undercooling were placed ahead of the growing columnar grains to allow quantitative analysis of nucleation events. At low thermal gradient and cooling rate only the inoculants with low nucleation undercooling were activated due to low melt undercooling driven by constitutional supercooling (CS). As the cooling rate is increased, for a given thermal gradient, a larger number of inoculants with higher nucleation undercoolings were activated. At higher cooling rates, thermal undercooling was generated by a lag in the growth rate of the solid-liquid (S–L) interface compared to the theoretical pull rate. Thus, thermal undercooling becomes dominant leading to the facilitation of nucleation on less potent substrates requiring higher undercooling. The results show a transition from solute-driven undercooling to cooling rate driven thermal undercooling which contributes to the undercooling that activates the nucleation events. Invoking the Interdependence model, it is also shown that the high cooling rate induced thermal undercooling reduces the size of the nucleation free zone substantially.
Wang W, Guo E, Phillion AB, et al., 2020, Semi-solid compression of nano/micro-particle reinforced Al-Cu composites: An in situ synchrotron tomographic study, Materialia, Vol: 12, Pages: 1-8, ISSN: 2589-1529
Four-dimensional fast synchrotron X-ray tomography has been used to investigate the semi-solid deformation of nano- and micro-particle reinforced aluminum-copper composites (Al-10 wt% Cu alloy with ~1.0 wt% Al2O3 nano and ~1.0 wt% Al2O3 micro particles). Quantitative image analysis of the semi-solid deformation behavior of three alloys (base, nano- and micro-particle reinforced) revealed the influence of the particulate size on both microstructural formation and dominant deformation mechanisms. The results showed that initial void closure and incubation period were present in the particle-free and nano-particle reinforced Al-Cu composite during semi-solid compression, while the micro-particle reinforced alloy only showed continual void growth and coalescence into cracks. The results suggest that the nano-particle reinforced composite has the best hot-tearing resistance amongst the three alloys. Improved hot-tear performance with nano-particulate reinforcement was attributed to the small liquid channel thickness, fine grain size which alters the distribution/morphology of the liquid channels, more viscous inter-dendritic liquid, and fewer initial voids.
Chen Y, Clark S, Leung ACL, et al., 2020, Melt pool morphology in directed energy deposition additive manufacturing process, MCWASP XV: International Conference on Modelling of Casting, Welding and Advanced Solidification Processes, Publisher: IOP Publishing, Pages: 1-6
Directed Energy Deposition Additive Manufacturing (DED-AM) is one of the principal AM techniques being explored for both the repair of high value components in the aerospace industry as well as freeform fabrication of large metallic components. However, the lack of fundamental understanding of the underlying process-structure-property relationships hinders the utilisation of DED-AM for the production or repair of safety-critical components. This study uses in situ and operando synchrotron X-ray imaging to provide an improved fundamental understanding of laser-matter interactions and their influence on the melt pool geometry. Coupled with process modelling, these unique observations illustrate how process parameters can influence the DED-AM melt pool geometry. The calibrated simulation can be used for guidance in an industrial additive manufacturing process for microstructure and quality control.
Yuan L, Sabau AS, StJohn D, et al., 2020, Columnar-to-equiaxed transition in a laser scan for metal additive manufacturing, MCWASP XV: International Conference on Modelling of Casting, Welding and Advanced Solidification Processes, Publisher: IOP Publishing, Pages: 1-8
In laser powder bed fusion additive manufacturing (LPBFAM), different solidification conditions, e.g., thermal gradient and cooling rate, can be achieved by controlling the process parameters, such as laser power and laser speed. Tailoring the behaviour of the columnar to equiaxed transition (CET) of the printed alloy during fabrication can facilitate the production of highly customized microstructures. In this study, effective analytical solutions for both thermal conduction and solidification are employed to model solidifying melt pools. Microstructure textures and solidification conditions are evaluated for numerous combinations of laser power and laser speed under bead-on-plate conditions. This analytical-based high-throughput tool was demonstrated to select specific process parameters that lead to desired microstructures. Two selected process conditions were examined in detail by a highly parallelized microstructural solidification model to reveal both nucleation and grain growth. Both numerical solutions agree well with experiments that are performed based on bead-on-plate conditions, indicating that these numerical models aid evaluation of the nucleation parameters, providing insights for controlling CET during the LPBFAM processing.
Clark SJ, Leung CLA, Chen Y, et al., 2020, Capturing Marangoni flow via synchrotron imaging of selective laser melting, MCWASP XV: International Conference on Modelling of Casting, Welding and Advanced Solidification Processes, Publisher: IOP Publishing, Pages: 1-6
Marangoni flow has a substantial influence on the quality of components fabricated via laser powder bed fusion (LPBF). However, Marangoni flow in melt pools is rarely quantified due to the opacity of liquid metals and the necessity for in situ evaluation. Here we report the findings of high-temporal-resolution synchrotron x-ray radiography experiments tracking the flow in the melt-pool. Dense, highly attenuating tungsten carbide particles are seeded within an elemental powder blend of aluminium and copper of varying composition. Due to the extremely high temporal resolution of greater than 50 kfps at the 31-ID-B beamline at the Advanced Photon Source, USA, we can track the position of tracer particles from frame to frame. This data provides valuable process guidance for optimising mixing and informs the development and validation of multiphysics models.
Golkhosh F, Sharma Y, Martinez DM, et al., 2020, 4D synchrotron tomographic imaging of network and fibre level micromechanics in softwood paper, Materialia, Vol: 11, Pages: 1-11, ISSN: 2589-1529
A 4D imaging study (3D + time) combining synchrotron tomography with in situ tensile testing has been carried out to observe the fibre and network level micromechanics of paper made from northern bleached softwood kraft (NBSK). Quantitative image analysis and digital volume correlation is used to characterize local deformation, the evolution of fibre-fibre contacts, and fibre straightening in a ”freeze-dried” handsheet as well as standard handsheets low consistency refined at different refining energies. In the freeze-dried handsheet having low fibre conformability, the results show that deformation at the network level occurs because of fibre straightening and possible inter-fibre bond breakage. Further, significant out-of-plane deformation near the failure regions was observed, which led to auxetic behaviour. In the refined handsheets, a strong inverse correlation is seen between refining energy, thickness expansion, and the number of broken fibres. The use of out-of-plane strain norms is proposed as a method to determine network efficiency (i.e. the ratio of the network’s elastic modulus to that of the constituent fibres) as well as the relative contribution of fibre pull-out to the overall failure of the handsheet.
Østergaard MB, Zhang M, Shen X, et al., 2020, High-speed synchrotron X-ray imaging of glass foaming and thermal conductivity simulation, Acta Materialia, Vol: 189, Pages: 85-92, ISSN: 1359-6454
Glass foams are attractive thermal insulation materials, thus, the thermal conductivity (λ) is crucial for their insulating performance. Understanding the foaming process is critical for process optimization. Here, we applied high-speed synchrotron X-ray tomography to investigate the change in pore structure during the foaming process, quantifying the foam structures and porosity dynamically. The results can provide guidance for the manufacturing of glass foams. The 3D pore structures were also used to computationally determine λ of glass foams using image-based modelling. We then used the simulated λ to develop a new analytical model to predict the porosity dependence of λ. The λ values of the glass foams when the porosity is within 40% to 95% predicted by the new model are in excellent agreement with the experimental data collected from the literature, with an average error of only 0.7%, which performs better than previously proposed models.
Nelson T, Cai B, Warnken N, et al., 2020, Gravity effect on thermal-solutal convection during solidification revealed by four-dimensional synchrotron imaging with compositional mapping, Scripta Materialia, Vol: 180, Pages: 29-33, ISSN: 1359-6462
The effect of gravity on thermo-solutal convection and its impact on solidification dynamics of an Al-15 wt%Cu alloy were studied using high speed synchrotron tomography. A method for mapping the composition of the solidifying samples was developed, enabling three-dimensional quantification of the time evolved solute concentration and dendrite morphology. Differences in solute segregation, dendrite morphology and fragmentation between upwards and downwards solidification were identified, which were attributed to buoyancy-modulated thermal-solutal convection.
Evans L, Lee P, Javaheri B, et al., 2020, Identifying novel osteoarthritis (OA) biomarkers via anatomical discrepancies between OA-predisposed and OA-protected murine knee joints., Publisher: WILEY, Pages: 143-144, ISSN: 0021-8782
Javaheri B, Razi H, Gohin S, et al., 2020, Lasting organ-level bone mechanoadaptation is unrelated to local strain, Science Advances, Vol: 6, Pages: 1-13, ISSN: 2375-2548
Bones adapt to mechanical forces according to strict principles predicting straight shape. Most bones are, however, paradoxically curved. To solve this paradox, we used computed tomography–based, four-dimensional imaging methods and computational analysis to monitor acute and chronic whole-bone shape adaptation and remodeling in vivo. We first confirmed that some acute load-induced structural changes are reversible, adhere to the linear strain magnitude regulation of remodeling activities, and are restricted to bone regions in which marked antiresorptive actions are evident. We make the novel observation that loading exerts significant lasting modifications in tibial shape and mass across extensive bone regions, underpinned by (re)modeling independent of local strain magnitude, occurring at sites where the initial response to load is principally osteogenic. This is the first report to demonstrate that bone loading stimulates nonlinear remodeling responses to strain that culminate in greater curvature adjusted for load predictability without sacrificing strength.
Madi K, Staines KA, Bay BK, et al., 2020, In situ characterization of nanoscale strains in loaded whole joints via synchrotron X-ray tomography, Nature Biomedical Engineering, Vol: 4, Pages: 343-354, ISSN: 2157-846X
Imaging techniques for quantifying changes in the hierarchical structure of deforming joints are constrained by destructive sample treatments, sample-size restrictions and lengthy scan times. Here, we report the use of fast low-dose pink-beam synchrotron X-ray tomography in combination with mechanical loading at nanometric precision for in situ imaging, at resolutions below 100 nm, of the mechanical strain in intact untreated joints under physiologically realistic conditions. We show that in young, older and osteoarthritic mice, hierarchical changes in tissue structure and mechanical behaviour can be simultaneously visualized, and that the tissue structure at the cellular level correlates with the mechanical performance of the whole joint. We also use the tomographic approach to study the colocalization of tissue strains to specific chondrocyte lacunar organizations within intact loaded joints and to explore the role of calcified-cartilage stiffness on the biomechanics of healthy and pathological joints.
Bhartiya A, Madi K, Disney CM, et al., 2020, Phase-contrast 3D tomography of HeLa cells grown in PLLA polymer electrospun scaffolds using synchrotron X-rays, Journal of Synchrotron Radiation, Vol: 27, Pages: 158-163, ISSN: 0909-0495
Advanced imaging is useful for understanding the three-dimensional (3D) growth of cells. X-ray tomography serves as a powerful noninvasive, nondestructive technique that can fulfill these purposes by providing information about cell growth within 3D platforms. There are a limited number of studies taking advantage of synchrotron X-rays, which provides a large field of view and suitable resolution to image cells within specific biomaterials. In this study, X-ray synchrotron radiation microtomography at Diamond Light Source and advanced image processing were used to investigate cellular infiltration of HeLa cells within poly L-lactide (PLLA) scaffolds. This study demonstrates that synchrotron X-rays using phase contrast is a useful method to understand the 3D growth of cells in PLLA electrospun scaffolds. Two different fiber diameter (2 and 4 µm) scaffolds with different pore sizes, grown over 2, 5 and 8 days in vitro, were examined for infiltration and cell connectivity. After performing visualization by segmentation of the cells from the fibers, the results clearly show deeper cell growth and higher cellular interconnectivity in the 4 µm fiber diameter scaffold. This indicates the potential for using such 3D technology to study cell-scaffold interactions for future medical use.
Wang YQ, Clark SJ, Cai B, et al., 2020, Small-angle neutron scattering reveals the effect of Mo on interphase nano-precipitation in Ti-Mo micro-alloyed steels, Scripta Materialia, Vol: 174, Pages: 24-28, ISSN: 1359-6462
Ti-containing micro-alloyed steels are often alloyed with molybdenum (Mo) to reduce nano-precipitate coarsening, although the mechanism is still disputed. Using small angle neutron scattering we characterised the precipitate composition and coarsening of Ti-alloyed and Ti-Mo-alloyed steels. The results demonstrate ~25 at.% of Ti is substituted by Mo in the (Ti, Mo)C precipitates, increasing both the precipitate volume percent and average size. Mo alloying did not retard precipitation coarsening, but improved lattice misfit between precipitate and matrix, contributing to better ageing resistance of the Ti-Mo-alloyed steel. This new understanding opens opportunities for designing ageing-resistant micro-alloyed steels with lean alloying elements.
Arzilli F, La Spina G, Burton MR, et al., 2019, Magma fragmentation in highly explosive basaltic eruptions induced by rapid crystallization, Nature Geoscience, Vol: 12, Pages: 1023-1028, ISSN: 1752-0894
Basaltic eruptions are the most common form of volcanism on Earth and planetary bodies. The low viscosity of basaltic magmas inhibits fragmentation, which favours effusive and lava-fountaining activity, yet highly explosive, hazardous basaltic eruptions occur. The processes that promote fragmentation of basaltic magma remain unclear and are subject to debate. Here we used a numerical conduit model to show that a rapid magma ascent during explosive eruptions produces a large undercooling. In situ experiments revealed that undercooling drives exceptionally rapid (in minutes) crystallization, which induces a step change in viscosity that triggers magma fragmentation. The experimentally produced textures are consistent with basaltic Plinian eruption products. We applied a numerical model to investigate basaltic magma fragmentation over a wide parameter space and found that all basaltic volcanoes have the potential to produce highly explosive eruptions. The critical requirements are initial magma temperatures lower than 1,100 °C to reach a syn-eruptive crystal content of over 30 vol%, and thus a magma viscosity around 105 Pa s, which our results suggest is the minimum viscosity required for the fragmentation of fast ascending basaltic magmas. These temperature, crystal content and viscosity requirements reveal how typically effusive basaltic volcanoes can produce unexpected highly explosive and hazardous eruptions.
Bhagavath S, Cai B, Atwood R, et al., 2019, Combined deformation and solidification-driven porosity formation in aluminum alloys, Metallurgical and Materials Transactions A, Vol: 50, Pages: 4891-4899, ISSN: 1073-5623
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.
Ostergaard MB, Cai B, Petersen RR, et al., 2019, Impact of pore structure on the thermal conductivity of glass foams, Materials Letters, Vol: 250, Pages: 72-74, ISSN: 0167-577X
The thermal conductivity (λ) of glass foams is thought to depend on pore size. We report on the impact of pore size, determined using X-ray microtomography, and percentage porosity on the λ of glass foams. Glass foams were prepared by heating powder mixtures of obsolete cathode ray tube (CRT) panel glass, Mn3O4 and carbon as foaming agents, and K3PO4 as additive, to a suitable temperature above Tg, and subsequent cooling. Here, we report for the first time a correlation between λ and pore size in the range 0.10–0.16 mm showing a decrease from 57 to 49 mW m−1 K−1 with increasing the pore size for glass foams with porosities of 87–90%. This indicates that the pore structure should be optimized in order to improve the insulating performance of glass foams.
Ma L, Dowey PJ, Rutter E, et al., 2019, A novel upscaling procedure for characterising heterogeneous shale porosity from nanometer-to millimetre-scale in 3D, Energy, Vol: 181, Pages: 1285-1297, ISSN: 0360-5442
Microstructures and pore systems in shales are key to understanding the role of shale in many energy applications. This study proposes a novel multi-stage upscaling procedure to comprehensively investigate the heterogeneous and complex microstructures and pore systems in a laminated and microfractured shale, utilising 3D multi-scale imaging data. Five imaging techniques were used for characterisation from sub-nanoscale to macroscale (core-scale), spanning four orders of magnitude. Image data collected using X-ray tomography, Focused Ion Beam, and Electron Tomography techniques range in voxel size from 0.6 nm to 13 μm. Prior to upscaling, a novel two-step analysis was performed to ensure sub-samples were representative. Following this, a three-step procedure, based on homogenising descriptors and computed volume coefficients, was used to upscale the quantified microstructure and pore system. At the highest resolution (nanoscale), four distinct pore types were identified. At the sub-micron scale equations were derived for three pore-associated phases. At the microscale, the volume coefficients were recalculated to upscale the pore system to the millimetre- scale. The accuracy of the upscaling methodology was verified, predicting the total porosity within 7.2% discrepancy. The results provide a unique perspective to understand heterogeneous rock types, breaking though prior scale limitations in the pore system.
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