Publications
521 results found
Geng H, Todd NM, Devlin-Mullin A, et al., 2016, A correlative imaging based methodology for accurate quantitative assessment of bone formation in additive manufactured implants, Journal of Materials Science-Materials in Medicine, Vol: 27, ISSN: 1573-4838
A correlative imaging methodology was developed to accurately quantify bone formation in the complex lattice structure of additive manufactured implants. Micro computed tomography (μCT) and histomorphometry were combined, integrating the best features from both, while demonstrating the limitations of each imaging modality. This semi-automatic methodology registered each modality using a coarse graining technique to speed the registration of 2D histology sections to high resolution 3D μCT datasets. Once registered, histomorphometric qualitative and quantitative bone descriptors were directly correlated to 3D quantitative bone descriptors, such as bone ingrowth and bone contact. The correlative imaging allowed the significant volumetric shrinkage of histology sections to be quantified for the first time (~15 %). This technique demonstrated the importance of location of the histological section, demonstrating that up to a 30 % offset can be introduced. The results were used to quantitatively demonstrate the effectiveness of 3D printed titanium lattice implants.
Wang J, Yue S, Fautrelle Y, et al., 2016, Refinement and growth enhancement of Al2Cu phase during magnetic field assisting directional solidification of hypereutectic Al-Cu alloy., Scientific Reports, Vol: 6, ISSN: 2045-2322
Understanding how the magnetic fields affect the formation of reinforced phase during solidification is crucial to tailor the structure and therefor the performance of metal matrix in situ composites. In this study, a hypereutectic Al-40 wt.%Cu alloy has been directionally solidified under various axial magnetic fields and the morphology of Al2Cu phase was quantified in 3D by means of high resolution synchrotron X-ray tomography. With rising magnetic fields, both increase of Al2Cu phase's total volume and decrease of each column's transverse section area were found. These results respectively indicate the growth enhancement and refinement of the primary Al2Cu phase in the magnetic field assisting directional solidification. The thermoelectric magnetic forces (TEMF) causing torque and dislocation multiplication in the faceted primary phases were thought dedicate to respectively the refinement and growth enhancement. To verify this, a real structure based 3D simulation of TEMF in Al2Cu column was carried out, and the dislocations in the Al2Cu phase obtained without and with a 10T high magnetic field were analysed by the transmission electron microscope.
Reyes-Davila GA, Arambula-Mendoza R, Espinasa-Perena R, et al., 2016, Volcán de Colima dome collapse of July, 2015 and associated pyroclastic density currents, Journal of Volcanology and Geothermal Research, Vol: 320, Pages: 100-106, ISSN: 1872-6097
During July 10th–11th 2015, Volcán de Colima, Mexico, underwent its most intense eruptive phase since its Subplinian–Plinian 1913 AD eruption. Production of scoria coincident with elevated fumarolic activity and SO2 flux indicate a significant switch of upper-conduit dynamics compared with the preceding decades of dome building and vulcanian explosions. A marked increase in rockfall events and degassing activity was observed on the 8th and 9th of July. On the 10th at 20:16 h (Local time = UTM − 6 h) a partial collapse of the dome generated a series of pyroclastic density currents (PDCs) that lasted 52 min and reached 9.1 km to the south of the volcano. The PDCs were mostly channelized by the Montegrande and San Antonio ravines, and produced a deposit with an estimated volume of 2.4 × 106 m3. Nearly 16 h after the first collapse, a second and larger collapse occurred which lasted 1 h 47 min. This second collapse produced a series of PDCs along the same ravines, reaching a distance of 10.3 km. The total volume calculated for the PDCs of the second event is 8.0 × 106 m3. Including associated ashfall deposits, the two episodes produced a total of 14.2 × 106 m3 of fragmentary material. The collapses formed an amphitheater-shaped crater open towards the south. We propose that the dome collapse was triggered by arrival of gas-rich magma to the upper conduit, which then boiled-over and sustained the PDCs. A juvenile scoria sample selected from the second partial dome collapse contains hornblende, yet at an order of magnitude less abundant (0.2%) than that of 1913, and exhibits reaction rims, whereas the 1913 hornblende is unreacted. At present there is no compelling petrologic evidence for imminent end-cycle activity observed at Volcán de Colima.
Wearing D, Horsfield AP, Xu W, et al., 2016, Corrigendum to 'Which wets TiB2 inoculant particles: Al or Al3Ti?' [J. Alloys Compd. 664 (2016) 460-468], Journal of Alloys and Compounds, Vol: 677, Pages: 302-303, ISSN: 1873-4669
TiB2 particles are proven effective nucleants of commercial purity aluminium, resulting in smaller grains and hence greater desired mechanical properties; however, there is uncertainty as to the mechanism by which it operates. Here we clarify what happens in the initial stages by computing the total Gibbs energy change associated with four possible nucleation mechanisms, each characterised by the termination of the TiB2(0001) substrate (Ti or B) and the solid that forms on it (Al or Al3Ti). The appropriate solid//solid interfacial energies are derived from Density Functional Theory (DFT) calculations, while the bulk energies are derived from thermodynamic data, supplemented with strain energies calculated from DFT. Solid//liquid interfacial energies are estimated using simple models with parameters based on the literature and DFT calculations. The results suggest that the Ti termination of TiB2 is more stable than the B termination in the melt, and that the direct formation of Al off a Ti-terminated TiB2 substrate is the most favourable mechanism for the nucleation of Al rather than the previously proposed formation of a Al3Ti interlayer. On the B termination of TiB2, Al formation is more stable for thick solid layers, but this is much more uncertain for thin solid layers where it is possible that Al3Ti formation is more stable.
Prasad A, Yuan L, Lee PD, et al., 2016, The effect of the melt thermal gradient on the size of the constitutionally supercooled zone, 4th International Conference on Advances in Solidification Processes (ICASP-4), Publisher: IOP Publishing, ISSN: 1757-8981
Recent verification of the analytical Interdependence model by a numerical solidification model (μMatIC) confirmed the critical role of constitutional supercooling (CS) in achieving sufficient undercooling to trigger successful nucleation events. The location of the maximum amount of CS (ΔT CSmax ) is some distance from the interface of the previously growing grain and this distance contributes to the final as-cast grain size. The effect of the thermal gradient, G, on the size of the CS zone (CSZ) was neglected in that work. However, G is expected to affect the size of the CSZ (i.e. the length of the CSZ, x' CSZ , and the location of ΔTCSmax, x' CSmax ). This investigation assesses the effect of G on x'csz and x' CSmax . A range of G values is introduced into both the analytical and the numerical models to obtain a correlation between the value of G and the dimensions of the CSZ. The result of a test case from the analytical model shows that x' CSmax initially decreases rapidly and then decreases gradually approaching zero at very high values of G. Independent of the analytical model, the results from the numerical model replicate the trend obtained from the analytical model.
Staines KA, Madi K, Mirczuk SM, et al., 2016, Endochondral Growth Defect and Deployment of Transient Chondrocyte Behaviors Underlie Osteoarthritis Onset in a Natural Murine Model, Arthritis & Rheumatology, Vol: 68, Pages: 880-891, ISSN: 2326-5191
ObjectiveTo explore whether aberrant transient chondrocyte behaviors occur in the joints of STR/Ort mice (which spontaneously develop osteoarthritis [OA]) and whether they are attributable to an endochondral growth defect.MethodsKnee joints from STR/Ort mice with advanced OA and age-matched CBA (control) mice were examined by Affymetrix microarray profiling, multiplex polymerase chain reaction (PCR) analysis, and immunohistochemical labeling of endochondral markers, including sclerostin and MEPE. The endochondral phenotype of STR/Ort mice was analyzed by histologic examination, micro–computed tomography, and ex vivo organ culture. A novel protocol for quantifying bony bridges across the murine epiphysis (growth plate fusion) using synchrotron x-ray computed microtomography was developed and applied.ResultsMeta-analysis of transcription profiles showed significant elevation in functions linked with endochondral ossification in STR/Ort mice (compared to CBA mice; P < 0.05). Consistent with this, immunolabeling revealed increased matrix metalloproteinase 13 (MMP-13) and type X collagen expression in STR/Ort mouse joints, and multiplex quantitative reverse transcriptase–PCR showed differential expression of known mineralization regulators, suggesting an inherent chondrocyte defect. Support for the notion of an endochondral defect included accelerated growth, increased zone of growth plate proliferative chondrocytes (P < 0.05), and widespread type X collagen/MMP-13 labeling beyond the expected hypertrophic zone distribution. OA development involved concomitant focal suppression of sclerostin/MEPE in STR/Ort mice. Our novel synchrotron radiation microtomography method showed increased numbers (P < 0.001) and mean areal growth plate bridge densities (P < 0.01) in young and aged STR/Ort mice compared to age-matched CBA mice.ConclusionTaken together, our data support the notion of an inherent endochondral defect that is linked to growth dynamics and s
Kazantsev D, Guo E, Kaestner A, et al., 2016, Temporal sparsity exploiting nonlocal regularization for 4D computed tomography reconstruction, Journal of X-Ray Science and Technology, Vol: 24, Pages: 207-219, ISSN: 1095-9114
X-ray imaging applications in medical and material sciences are frequently limited by the number of tomographic projections collected. The inversion of the limited projection data is an ill-posed problem and needs regularization. Traditional spatial regularization is not well adapted to the dynamic nature of time-lapse tomography since it discards the redundancy of the temporal information. In this paper, we propose a novel iterative reconstruction algorithm with a nonlocal regularization term to account for time-evolving datasets. The aim of the proposed nonlocal penalty is to collect the maximum relevant information in the spatial and temporal domains. With the proposed sparsity seeking approach in the temporal space, the computational complexity of the classical nonlocal regularizer is substantially reduced (at least by one order of magnitude). The presented reconstruction method can be directly applied to various big data 4D (x, y, z+time) tomographic experiments in many fields. We apply the proposed technique to modelled data and to real dynamic X-ray microtomography (XMT) data of high resolution. Compared to the classical spatio-temporal nonlocal regularization approach, the proposed method delivers reconstructed images of improved resolution and higher contrast while remaining significantly less computationally demanding.
Taiwo OO, Finegan DP, Eastwood DS, et al., 2016, Comparison of three-dimensional analysis and stereological techniques for quantifying lithium-ion battery electrode microstructures, Journal of Microscopy, Vol: 263, Pages: 280-292, ISSN: 1365-2818
Lithium-ion battery performance is intrinsically linked to electrode microstructure. Quantitative measurement of key structural parameters of lithium-ion battery electrode microstructures will enable optimization as well as motivate systematic numerical studies for the improvement of battery performance. With the rapid development of 3-D imaging techniques, quantitative assessment of 3-D microstructures from 2-D image sections by stereological methods appears outmoded; however, in spite of the proliferation of tomographic imaging techniques, it remains significantly easier to obtain two-dimensional (2-D) data sets. In this study, stereological prediction and three-dimensional (3-D) analysis techniques for quantitative assessment of key geometric parameters for characterizing battery electrode microstructures are examined and compared. Lithium-ion battery electrodes were imaged using synchrotron-based X-ray tomographic microscopy. For each electrode sample investigated, stereological analysis was performed on reconstructed 2-D image sections generated from tomographic imaging, whereas direct 3-D analysis was performed on reconstructed image volumes. The analysis showed that geometric parameter estimation using 2-D image sections is bound to be associated with ambiguity and that volume-based 3-D characterization of nonconvex, irregular and interconnected particles can be used to more accurately quantify spatially-dependent parameters, such as tortuosity and pore-phase connectivity.
Sloof WG, Pei R, McDonald SA, et al., 2016, Repeated crack healing in MAX-phase ceramics revealed by 4D in situ synchrotron X-ray tomographic microscopy, Scientific Reports, Vol: 6, ISSN: 2045-2322
MAX phase materials are emerging as attractive engineering materials in applications where the material is exposed to severe thermal and mechanical conditions in an oxidative environment. The Ti2AlC MAX phase possesses attractive thermomechanical properties even beyond a temperature of 1000 K. An attractive feature of this material is its capacity for the autonomous healing of cracks when operating at high temperatures. Coupling a specialized thermomechanical setup to a synchrotron X-ray tomographic microscopy endstation at the TOMCAT beamline, we captured the temporal evolution of local crack opening and healing during multiple cracking and autonomous repair cycles at a temperature of 1500 K. For the first time, the rate and position dependence of crack repair in pristine Ti2AlC material and in previously healed cracks has been quantified. Our results demonstrate that healed cracks can have sufficient mechanical integrity to make subsequent cracks form elsewhere upon reloading after healing.
Lin Q, Barker DJ, Dobson KJ, et al., 2016, Modelling particle scale leach kinetics based on X-ray computed micro-tomography images, Hydrometallurgy, Vol: 162, Pages: 25-36, ISSN: 1879-1158
The apparent leach kinetics for an ore particle within a heap leaching system depend on the chemical conditions in the fluids around the particle, the mass transport within the particle and the reaction kinetics at the surface of each mineral grain. The apparent rate kinetics thus depend upon the distribution of the mineral grains, in terms of both size and position, within the individual ore particles, as well as the evolution of this distribution. Traditionally this behaviour has been modelled using simplified relationships such as the shrinking core model. In this paper a method for simulating this evolution and the resultant kinetics based directly on 3D XMT images of the internal structure of the particles is presented. The model includes mass transport through the gangue matrix, surface reaction kinetics and the dissolution and subsequent evolution of the individual mineral grains within the ore particle. Different minerals and mineral associations will result in different surface reaction kinetics. One of the key inputs into this model is thus the distribution of the surface rate kinetics. A method for experimentally determining this distribution is presented. The simulation results are compared to the evolution of real particles as they undergo leaching as measured using a time sequence of 3D XMT images of a leaching column. It was found that these simulations are able to accurately predict both the overall leaching trends, as well as the leaching behaviour of mineral grains in classes based on their size and distance to the particle surface. The leaching behaviour did not follow that of a simple shrinking core approximation, with the actual spatial and size distribution of the grains, as well as the distribution of their surface rate kinetics, all impacting the apparent leach kinetics. For the copper ore particles used in this work the best fit to the experiments was achieved at an intermediate value of the dimensionless group that characterises the relativ
Ma L, Taylor KG, Lee PD, et al., 2016, Novel 3D centimetre-to nano-scale quantification of an organic-rich mudstone: the Carboniferous Bowland Shale, Northern England, Marine and Petroleum Geology, Vol: 72, Pages: 193-205, ISSN: 1873-4073
X-ray computed tomography and serial block face scanning electron microscopy imaging techniques were used to produce 3D images with a resolution spanning three orders of magnitude from ∼7.7 μm to 7 nm for one typical Bowland Shale sample from Northern England, identified as the largest potential shale gas reservoir in the UK. These images were used to quantitatively assess the size, geometry and connectivity of pores and organic matter. The data revealed four types of porosity: intra-organic pores, organic interface pores, intra- and inter-mineral pores. Pore sizes are bimodal, with peaks at 0.2 μm and 0.04 μm corresponding to pores located at organic–mineral interfaces and within organic matter, respectively. These pore-size distributions were validated by nitrogen adsorption data. The multi-scale imaging of the four pore types shows that there is no connected visible porosity at these scales with equivalent diameter of 20 nm or larger in this sample. However, organic matter and clay minerals are connected and so the meso porosity (<20 nm) within these phases provides possible diffusion transport pathways for gas. This work confirms multi-scale 3D imaging as a powerful quantification method for shale reservoir characterisation allowing the representative volumes of pores, organic and mineral phases to be defined to model shale systems. The absence of connected porosity at scales greater than 20 nm indicates the likely importance of the organic matter network, and associated smaller-scale pores, in controlling hydrocarbon transport. . The application of these techniques to shale gas plays more widely should lead to a greater understanding of properties in the low permeability systems.
Abolghasemi S, Williamson J, Lindley TC, et al., 2016, Embrittlement of alloy 625 and effect of remedial treatments, PROCEEDINGS OF THE INSTITUTION OF MECHANICAL ENGINEERS PART L-JOURNAL OF MATERIALS-DESIGN AND APPLICATIONS, Vol: 230, Pages: 328-331, ISSN: 1464-4207
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- Citations: 3
Xu WW, Tzanakis I, Srirangam P, et al., 2016, Synchrotron quantification of ultrasound cavitation and bubble dynamics in Al-10Cu melts., Ultrasonics Sonochemistry, Vol: 31, Pages: 355-361, ISSN: 1350-4177
Knowledge of the kinetics of gas bubble formation and evolution under cavitation conditions in molten alloys is important for the control casting defects such as porosity and dissolved hydrogen. Using in situ synchrotron X-ray radiography, we studied the dynamic behaviour of ultrasonic cavitation gas bubbles in a molten Al-10wt%Cu alloy. The size distribution, average radius and growth rate of cavitation gas bubbles were quantified under an acoustic intensity of 800W/cm(2) and a maximum acoustic pressure of 4.5MPa (45atm). Bubbles exhibited a log-normal size distribution with an average radius of 15.3±0.5μm. Under applied sonication conditions the growth rate of bubble radius, R(t), followed a power law with a form of R(t)=αt(β), and α=0.0021 &β=0.89. The observed tendencies were discussed in relation to bubble growth mechanisms of Al alloy melts.
Mills KC, Karagadde S, Lee PD, et al., 2016, Calculation of Physical Properties for Use in Models of Continuous Casting Process-Part 1: Mould Slags, ISIJ International, Vol: 56, Pages: 264-273, ISSN: 0915-1559
Physical properties of both steels and mould slags are needed as input data for the mathematical modelling of the continuous casting process. Routines for calculating the properties of mould slags and for estimating steel properties have been developed and are described in Parts 1 and 2, respectively. Many mould powders, with differing compositions, are used in casting practice and their properties vary significantly. Reliable models have been developed to calculate these property values as a function of temperature from their chemical composition since this is available on a routine basis. Models have been developed to calculate the following properties: heat capacities, enthalpies, thermal expansion coefficient, density, viscosity, thermal conductivity and surface tension. Solid mould slags can exist as glassy or crystalline phases or as mixtures of the two (i.e. slag films) and the properties for the various phases can vary considerably; methods have been developed to calculate property values for these various states. The software used to calculate the properties is available via the link (i) http://www.mxif.manchester.ac.uk/resources/software (ii) https://sites.google.com/site/shyamkaragadde/software/thermophysical-properties.
Mills KC, Karagadde S, Lee PD, et al., 2016, Calculation of Physical Properties for Use in Models of Continuous Casting Process-Part 2: Steels, ISIJ International, Vol: 56, Pages: 274-281, ISSN: 0915-1559
The objective of the present study was to calculate physical property values for steels from their chemicalcompositions for subsequent use in mathematical models of the fluid flow, heat transfer and shellsolidification in the continuous casting mould. Values of the following properties of steels are calculatedfor temperatures between 298 K and 2 000 K; Heat Capacity (Cp) Density (ρ) Thermal conductivity (k) anddiffusivity (a) Electrical resistivity (R) Viscosity (η) Surface (γm) and Interfacial tension (γmsl). In addition temperaturesof transitions (Liquidus Tliq, Solidus Tsol) and various solid state transitions were also calculated.Ferritic and austenitic phases of Carbon - and stainless steels are both covered. The associated softwareis available on the following websites (i) http://www.mxif.manchester.ac.uk/resources/software (ii) https://sites.google.com/site/shyamkaragadde/software/thermophysical-properties.
Cai B, Lee PD, Karagadde S, et al., 2016, Time-resolved synchrotron tomographic quantification of deformation during indentation of an equiaxed semi-solid granular alloy, Acta Materialia, Vol: 105, Pages: 338-346, ISSN: 1873-2453
Indentation is a well-established technique for measuring mechanical properties, such as hardness and creep, in solid materials at a continuum level. In this study, we performed indentation of a semi-solid granular alloy with an equiaxed dendritic microstructure. The resulting microstructural effects were quantified using a novel thermo-mechanical setup combined with 4D (three spatial dimensions plus time) synchrotron tomography and digital volume correlation. The experiments not only revealed the multitude of deformation mechanisms occurring at a microstructural level, (e.g. dilatancy, liquid flow, macrosegregation, shrinkage voids, and intra-granular deformation), but also allowed quantification of the evolution of the strain fields within the material. The resulting methodology is a powerful tool for assessing the evolution of localized deformation and hence material properties.
Wearing D, Horsfield AP, Xu W, et al., 2015, Which wets TiB2 inoculant particles: Al or Al3Ti?, Journal of Alloys and Compounds, Vol: 664, Pages: 460-468, ISSN: 0925-8388
TiB2 particles are proven effective nucleants of commercial purity aluminium, resulting in smaller grains and hence greater desired mechanical properties; however, there is uncertainty as to the mechanism by which it operates. Here we clarify what happens in the initial stages by computing the total Gibbs energy change associated with four possible nucleation mechanisms, each characterised by the termination of the TiB2(0001) substrate (Ti or B) and the solid that forms on it (Al or Al3Ti). The appropriate solid//solid interfacial energies are derived from Density Functional Theory (DFT) calculations, while the bulk energies are derived from thermodynamic data, supplemented with strain energies calculated from DFT. Solid//liquid interfacial energies are estimated using simple models with parameters based on the literature and DFT calculations. The results suggest that the Ti termination of TiB2 is more stable than the B termination in the melt, and that the direct formation of Al off a Ti-terminated TiB2 substrate is the most favourable mechanism for the nucleation of Al rather than the previously proposed formation of a Al3Ti interlayer. On the B termination of TiB2, Al formation is more stable for thick solid layers, but this is much more uncertain for thin solid layers where it is possible that Al3Ti formation is more stable.
Fielding LCD, Jones NG, Walsh J, et al., 2015, Synchrotron analysis of toughness anomalies in nanostructured bainite, Acta Materialia, Vol: 105, Pages: 52-58, ISSN: 1873-2453
High-resolution synchrotron X-ray diffraction has been used to characterise the notch root regions of Charpy impact test specimens of a superbainitic steel, both before and after loading. The changes in the volume fraction of austenite induced by the application of a three-point-bending load were quantified. Analysis of diffraction peak shifts revealed the extent of residual tensile and compressive strains present due to both machining and an applied load. The results lend support to the hypothesis that the comparatively low energies absorbed during Charpy impact testing of superbainitic steels, <7 J, are due to the formation of stress-induced martensite at the notch root, prior to crack initiation.
Finegan DP, Tudisco E, Scheel M, et al., 2015, Quantifying bulk electrode strain and material displacement within lithium batteries via high-speed operando tomography and digital volume correlation, Advanced Science, Vol: 3, ISSN: 2198-3844
Tracking the dynamic morphology of active materials during operation of lithium batteries is essential for identifying causes of performance loss. Digital volume correlation (DVC) is applied to high-speed operando synchrotron X-ray computed tomography of a commercial Li/MnO2 primary battery during discharge. Real-time electrode material displacement is captured in 3D allowing degradation mechanisms such as delamination of the electrode from the current collector and electrode crack formation to be identified. Continuum DVC of consecutive images during discharge is used to quantify local displacements and strains in 3D throughout discharge, facilitating tracking of the progression of swelling due to lithiation within the electrode material in a commercial, spiral-wound battery during normal operation. Displacement of the rigid current collector and cell materials contribute to severe electrode detachment and crack formation during discharge, which is monitored by a separate DVC approach. Use of time-lapse X-ray computed tomography coupled with DVC is thus demonstrated as an effective diagnostic technique to identify causes of performance loss within commercial lithium batteries; this novel approach is expected to guide the development of more effective commercial cell designs.
Mirihanage W, Xu W, Tamayo-Ariztondo J, et al., 2015, Synchrotron radiographic studies of ultrasonic melt processing of metal matrix nano composites, Materials Letters, Vol: 164, Pages: 484-487, ISSN: 1873-4979
Fast synchrotron radiography was used to investigate ultrasonic cavitation bubble formation and their dynamics during liquid metal processing of Al–Cu metal matrix nano composites (MMNC) in comparison with conventional alloys. The experimental observations showed enhanced cavitation potential in MMNC melts, due to the presence of Al2O3 nano particles which were believed to be acting as heterogeneous nuclei for bubble formation. Quantitative image analysis demonstrates that the addition of nano particles increases melt agitation partially, while introducing higher flow velocity variations across the melt. This suggests that the presence of nano particles may substantially alter propensity for ultrasonic treatment effects during solidification processing of MMNCs.
Chapman TP, Kareh KM, Knop M, et al., 2015, Characterisation of short fatigue cracks in titanium alloy IMI 834 using X-ray microtomography, Acta Materialia, Vol: 99, Pages: 49-62, ISSN: 1359-6454
A first attempt at the three-dimensional evaluation of naturally initiated surface connected and internal fatigue cracks is presented. Fatigue crack initiation and growth in air and vacuum environments have been investigated through X-ray microtomography in air and vacuum environments at elevated temperatures (350 °C), accompanied by post-mortem electron microscopy of the fracture surfaces. In vacuum (<10⁻⁵ mbar), multiple internal and surface-connected crack initiation was observed, but only the surface-connected cracks grew. In contrast, fewer cracks formed in air, these were mostly surface-connected and all were observed to grow. In all instances the initiation features were associated with globular primary α. An improved fatigue life was found in vacuum, which was mostly a consequence of delayed initiation, but was also due to slower fatigue crack propagation. The non-propagation of internal cracks was taken to imply that even the good laboratory vacuum obtained here was insufficient to simulate the conditions obtained for an internal crack in a component. The crack shape evolved towards a semi-circular shape a/c=1 in air during fatigue crack growth, whilst the vacuum cracks remained semi-elliptical (a/c≃1.4). This was taken to imply that oxide-induced crack closure played a role in fatigue crack growth in air.
Tzanakis I, Xu WW, Lebon GSB, et al., 2015, In Situ Synchrotron Radiography and Spectrum Analysis of Transient Cavitation Bubbles in Molten Aluminium Alloy, Proceedings of the 2015 ICU International Congress on Ultrasonics, Publisher: Elsevier, Pages: 841-845, ISSN: 1875-3892
The melt processing of conventional and advanced metallic materials with high-intensity ultrasonic vibrations significantly improves the quality and properties of molten metals during their solidification. These improvements are primarily attributed to ultrasonic cavitation: the creation, growth, pulsation, and collapse of bubbles in the liquid. However, the development of practical applications is limited by the lack of fundamental knowledge on the dynamics of the cavitation bubbles; it is very difficult to directly observe ultrasonic cavitation using conventional techniques in molten metals due their high temperature and opaqueness.In this study, an in situ synchrotron radiography experiment was performed to investigate bubble dynamics in an Al-10 wt.% Cu alloy under an external ultrasound field at 30 kHz. Radiographs with an exposure time of 78 ms were collected continuously during the sonication of molten alloys at temperatures of 660±10 °C. To the best of our knowledge, this is the first time that transient cavitation bubbles have been observed in liquid aluminium. Quantification of bubble parameters such as average size and time of collapse were evaluated from radiographs using advanced image analysis. Additionally, broadband noise associated with the acoustic emissions from shock waves of transient cavitation bubbles and estimation of the real-time acoustic pressure at the driving frequency were assessed using an advanced high-temperature cavitometer in separate bulk experiments.
Karagadde S, Lee PD, Cai B, et al., 2015, Transgranular liquation cracking of grains in the semi-solid state, Nature Communications, Vol: 6, ISSN: 2041-1723
Grain refinement via semi-solid deformation is desired to obtain superior mechanical properties of cast components. Using quantitative in situ synchrotron X-ray tomographic microscopy, we show an additional mechanism for the reduction of grain size, via liquation assisted transgranular cracking of semi-solid globular microstructures. Here we perform localized indentation of Al-15wt.%Cu globular microstructures, with an average grain size of ~480 μm, at 555 °C (74% solid fraction). Although transgranular fracture has been observed in brittle materials, our results show transgranular fracture can also occur in metallic alloys in semi-solid state. This transgranular liquation cracking (TLC) occurs at very low contact stresses (between 1.1 and 38 MPa). With increasing strain, TLC continues to refine the size of the microstructure until the grain distribution reaches log-normal packing. The results demonstrate that this refinement, previously attributed to fragmentation of secondary arms by melt-shearing, is also controlled by an additional TLC mechanism.
Wang D, Romer F, Connell L, et al., 2015, Highly flexible silica/chitosan hybrid scaffolds with oriented pores for tissue regeneration, Journal of Materials Chemistry B, Vol: 3, Pages: 7560-7576, ISSN: 2050-7518
Inorganic/organic sol–gel hybrids have nanoscale co-networks of organic and inorganic components that give them the unique potential of tailored mechanical properties and controlled biodegradation in tissue engineering applications. Here, silica/chitosan hybrid scaffolds with oriented structures were fabricated through the sol–gel method with a unidirectional freeze casting process. 3-Glycidoxypropyl trimethoxysilane (GPTMS) was used to obtain covalent inorganic/organic coupling. Process variables were investigated such as cooling rate, GPTMS and inorganic content, which can be used to tailor the mechanical properties and hybrid chemical coupling. Structural characterization and dissolution tests confirmed the covalent cross-linking of the chitosan and the silica network in hybrids. The scaffolds had a directional lamellar structure along the freezing direction and a cellular morphology perpendicular to the freezing direction. Compression testing showed that the scaffolds with 60 wt% organic were flexible and elastomeric perpendicular to the freezing direction whilst behaving in an elastic-brittle fashion parallel to the freezing direction. The compressive strengths are about one order of magnitude higher in the latter direction reaching values of the order of 160 kPa. This behaviour provides potential for clinicians to be able to squeeze the materials to fit tissue defect sites while providing some mechanical support from the other direction.
Van Eyndhoven G, Batenburg KJ, Kazantsev D, et al., 2015, An iterative CT reconstruction algorithm for fast fluid flow imaging, IEEE Transactions on Image Processing, Vol: 24, Pages: 4446-4458, ISSN: 1941-0042
The study of fluid flow through solid matter by computed tomography (CT) imaging has many applications, ranging from petroleum and aquifer engineering to biomedical, manufacturing, and environmental research. To avoid motion artifacts, current experiments are often limited to slow fluid flow dynamics. This severely limits the applicability of the technique. In this paper, a new iterative CT reconstruction algorithm for improved a temporal/spatial resolution in the imaging of fluid flow through solid matter is introduced. The proposed algorithm exploits prior knowledge in two ways. First, the time-varying object is assumed to consist of stationary (the solid matter) and dynamic regions (the fluid flow). Second, the attenuation curve of a particular voxel in the dynamic region is modeled by a piecewise constant function over time, which is in accordance with the actual advancing fluid/air boundary. Quantitative and qualitative results on different simulation experiments and a real neutron tomography data set show that, in comparison with the state-of-the-art algorithms, the proposed algorithm allows reconstruction from substantially fewer projections per rotation without image quality loss. Therefore, the temporal resolution can be substantially increased, and thus fluid flow experiments with faster dynamics can be performed.
Xu W, Horsfield AP, Wearing D, et al., 2015, First-principles calculation of Mg/MgO interfacial free energies, Journal of Alloys and Compounds, Vol: 650, Pages: 228-238, ISSN: 1873-4669
Interfacial free energies strongly influence many materials properties, especially for nanomaterials that have very large interfacial areas per unit volume. Quantitative evaluation of interfacial free energy by means of computer simulation remains difficult in these cases, especially at finite temperature. Density Functional Theory (DFT) simulation offers a robust way to compute both the energies and structures of the relevant surfaces and interfaces at the atomic level at zero Kelvin, and can be extended to finite temperatures in solids by means of the harmonic approximation (HA). Here we study the Mg/MgO interface, employing DFT calculations within the HA to obtain its key physical properties. We calculate the free energies of several key surfaces/interfaces when the temperature (T) increases from 0 K to 800 K, finding that all free energies decrease almost linearly with T. We have considered two surfaces, Mg(0001) (0.520–0.486 J/m2), and MgO(100) (0.86–0.52 J/m2), and two Mg(0001)//MgO(100) interfaces with the Mg–Mg and Mg–O stacking sequences at the interface planes (1.048–0.873 J/m2 and 0.910 to 0.743 J/m2 respectively). Using these values we determine the interfacial free energy as a function of temperature and size for MgO nanoparticles in solid Mg, an important metal matrix nanocomposite material.
Qiu C, Yue S, Adkins NJE, et al., 2015, Influence of processing conditions on strut structure and compressive properties of cellular lattice structures fabricated by selective laser melting (vol 628, pg 188, 2015), MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING, Vol: 638, Pages: 228-231, ISSN: 0921-5093
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- Citations: 6
Rockett P, Karagadde S, Guo E, et al., 2015, A 4-D dataset for validation of crystal growth in a complex three-phase material, ice cream, 14th International Conference on Modeling of Casting, Welding and Advanced Solidification Processes (MCWASP), Publisher: IOP Publishing: Conference Series, ISSN: 1757-899X
Four dimensional (4D, or 3D plus time) X-ray tomographic imaging of phase changes in materials is quickly becoming an accepted tool for quantifying the development of microstructures to both inform and validate models. However, most of the systems studied have been relatively simple binary compositions with only two phases. In this study we present a quantitative dataset of the phase evolution in a complex three-phase material, ice cream. The microstructure of ice cream is an important parameter in terms of sensorial perception, and therefore quantification and modelling of the evolution of the microstructure with time and temperature is key to understanding its fabrication and storage. The microstructure consists of three phases, air cells, ice crystals, and unfrozen matrix. We perform in situ synchrotron X-ray imaging of ice cream samples using in-line phase contrast tomography, housed within a purpose built cold-stage (-40 to +20oC) with finely controlled variation in specimen temperature. The size and distribution of ice crystals and air cells during programmed temperature cycling are determined using 3D quantification. The microstructural evolution of three-phase materials has many other important applications ranging from biological to structural and functional material, hence this dataset can act as a validation case for numerical investigations on faceted and non-faceted crystal growth in a range of materials.
Carr J, Milhet X, Gadaud P, et al., 2015, Quantitative characterization of porosity and determination of elastic modulus for sintered micro-silver joints, Journal of Materials Processing Technology, Vol: 225, Pages: 19-23, ISSN: 1873-4774
High resolution serial block-face scanning electron microscopy has been performed on sintered micro-silver pastes that are used as lead replacement joints for die bonding. The size and spatial distributions of the porosity before and after ageing were determined by quantification of the segmented 3D images. The elastic modulus was determined by an image-based finite element model and validated by results obtained from a dynamical resonance method. In agreement with contemporary analytical models on the elastic behaviour of porous materials, the elastic modulus was found to be a function of pore fraction only. Ageing the specimens does not alter the density or Young's modulus.
Robinson JB, Brown LD, Jervis R, et al., 2015, Investigating the effect of thermal gradients on stress in solid oxide fuel cell anodes using combined synchrotron radiation and thermal imaging, Journal of Power Sources, Vol: 288, Pages: 473-481, ISSN: 1873-2755
Thermal gradients can arise within solid oxide fuel cells (SOFCs) due to start-up and shut-down, non-uniform gas distribution, fast cycling and operation under internal reforming conditions. Here, the effects of operationally relevant thermal gradients on Ni/YSZ SOFC anode half cells are investigated using combined synchrotron X-ray diffraction and thermal imaging. The combination of these techniques has identified significant deviation from linear thermal expansion behaviour in a sample exposed to a one dimensional thermal gradient. Stress gradients are identified along isothermal regions due to the presence of a proximate thermal gradient, with tensile stress deviations of up to 75 MPa being observed across the sample at a constant temperature. Significant strain is also observed due to the presence of thermal gradients when compared to work carried out at isothermal conditions.
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