I13-2-Diamond Manchester Imaging
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Clara
Anduix-Canto
,
Mark A.
Levenstein
,
Yi-Yeoun
Kim
,
Jose R. A.
Godinho
,
Alexander N.
Kulak
,
Carlos
Gonzalez Nino
,
Philip J.
Withers
,
Jonathan P.
Wright
,
Nikil
Kapur
,
Hugo K.
Christenson
,
Fiona C.
Meldrum
Diamond Proposal Number(s):
[13578, 17314]
Open Access
Abstract: Characterizing the pathways by which crystals form remains a significant challenge, particularly when multiple pathways operate simultaneously. Here, an imaging-based strategy is introduced that exploits confinement effects to track the evolution of a population of crystals in 3D and to characterize crystallization pathways. Focusing on calcium sulfate formation in aqueous solution at room temperature, precipitation is carried out within nanoporous media, which ensures that the crystals are fixed in position and develop slowly. The evolution of their size, shape, and polymorph can then be tracked in situ using synchrotron X-ray computed tomography and diffraction computed tomography without isolating and potentially altering the crystals. The study shows that bassanite (CaSO4 0.5H2O) forms via an amorphous precursor phase and that it exhibits long-term stability in these nanoscale pores. Further, the thermodynamically stable phase gypsum (CaSO4 2H2O) can precipitate by different pathways according to the local physical environment. Insight into crystallization in nanoconfinement is also gained, and the crystals are seen to grow throughout the nanoporous network without causing structural damage. This work therefore offers a novel strategy for studying crystallization pathways and demonstrates the significant impact of confinement on calcium sulfate precipitation, which is relevant to its formation in many real-world environments.
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Sep 2021
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I12-JEEP: Joint Engineering, Environmental and Processing
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Ying
Wang
,
Xu
Xu
,
Wenxia
Zhao
,
Nan
Li
,
Samuel A.
Mcdonald
,
Yuan
Chai
,
Michael D.
Atkinson
,
Katherine J.
Dobson
,
Stefan
Michalik
,
Yingwei
Fan
,
Philip J.
Withers
,
Xiaorong
Zhou
,
Timothy L.
Burnett
Diamond Proposal Number(s):
[20226]
Open Access
Abstract: The damage mechanisms and load redistribution taking place under high temperature (350°C), high cycle fatigue (HCF) of TC17 titanium alloy/unidirectional SiC fibre composites have been investigated in situ using synchrotron X-ray computed tomography (CT) and X-ray diffraction (XRD) under two stress amplitudes. The three-dimensional morphology of the fatigue crack and fibre fractures has been mapped by CT. At low stress amplitude, stable growth occurs with matrix cracking deflecting by 50-100 µm in height as it bypasses the bridging fibres. At higher stress amplitude, loading to the peak stress led to a burst of fibre fractures giving rise to rapid crack growth. Many of the fibre fractures occurred 50-300 µm above/below the matrix crack plane during rapid growth, contrary to that in the stable growth stage, leading to extensive fibre pull-out on the fracture surface. The changes in fibre loading, interfacial stress, and the extent of fibre-matrix debonding in the vicinity of the crack have been mapped over the fatigue cycle and after the rapid growth by XRD. The fibre/matrix interfacial sliding extends up to 600 µm (in the stable-growth zone) or 700 µm (in the rapid-growth zone) either side of the crack plane. The direction of interfacial shear stress reverses over the loading cycle, with the maximum frictional sliding stress reaching ∼55 MPa in both regimes. In accordance with previous studies, it is possible that a degradation in fibre strength at elevated temperature is responsible for bursts of fibre fracture and rapid crack growth under higher stress amplitude.
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May 2021
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I13-2-Diamond Manchester Imaging
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Diamond Proposal Number(s):
[13704, 18197]
Open Access
Abstract: The torsional performance of bi-axially braided carbon fibre reinforced polymer (CFRP) tubes as a function of braid architecture is investigated. It is found that for a given braid pattern, the 45° braided CFRP tubes have higher shear moduli and lower shear strength than the 35° braids. In general, 2/2 (regular) braided CFRP tubes exhibit both higher shear strength and higher shear modulus than 1/1 (diamond) braids. However, beyond the peak load, the shear strength of 2/2 braided CFRPs exhibits sudden, steep drops, resulting in a lower remnant shear strength than 1/1 structures after the shear strain exceeds 4.5%. Moreover, the damage evolution is monitored in-situ by synchrotron X-ray computed tomography during torsional straining. It showed that for a 2/2 structure, inter-tow debonded regions are vertically interconnected allowing rapid crack propagation and strength drops, whereas for the 1/1 braid they are distributed in a chequer board causing more gradual loss of strength. The fibre/matrix interfacial strength and tow cross-over density play key roles in the torsional failure of 1/1 and 2/2 braided CFRP tubes, as the former controls damage initiation and the latter controls damage propagation.
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Sep 2020
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I13-2-Diamond Manchester Imaging
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Diamond Proposal Number(s):
[18165]
Abstract: Environment Induced Cracking (EIC) has been observed in three dimensions (3D) at high spatial and temporal resolution for AA5083 H131 alloy using in situ synchrotron X-ray CT. The initiation of EIC cracks occurred in humid air at ∼0.5σy and started from corrosion sites associated with intermetallic particle clusters. Time-resolved monitoring of the crack growth confirmed cracks grow below threshold KIEIC and are susceptible to arrest under fixed displacement conditions. Even when the cracks exceed threshold KIEIC and enter sustained propagation they exhibit very uneven growth rates. Failure occurs when the K of the largest crack exceeds the fracture toughness KIC.
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Jun 2020
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I13-2-Diamond Manchester Imaging
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Diamond Proposal Number(s):
[10456]
Abstract: This paper is the first to predict and then validate the overall stress-strain curve and the damage sequence comprising matrix cracking, interface debonding and fibre fracture against X-ray Computed Tomography (CT) observations for a multidirectional laminate. Until recently, numerical modelling of multi-directional multi-ply composites required idealised continuum mechanics models or idealised unit cell approaches (or homogenisation method) that cannot reliably capture property variations and the complex sequence of damage events that occur upon tensile loading. Here a multiscale image-based model is used to simulate stochastic crack growth in a double-notch (-45°/90°/+45°/0°/-45°/90°/+45°/0°)s carbon fibre reinforced polymer (CFRP) composite specimen subjected to tensile loading monitored by time-lapse X-ray CT. The data integration approach involves: (1) parallel simulations of meso-scale elements (MeEs) for each ply for which the orientation of the individual fibres has been extracted from an X-ray CT image, (2) local hierarchical coupling of the MeEs into a macro-scale mechanical model of the test piece, and (3) the use of a random variation in material properties where microstructural details are not revealed by the X-ray CT characterisation method.
Cohesive interface elements (CIEs) are used at both scales to predict the accumulation of interface damage and crack growth. The fibre-level modelling captures the detailed damage sequence and crack morphology including fibre/matrix debonding, sliding, matrix cracking and fibre fracture events. The multiscale model is validated by comparison with the measured tensile loading curve and the damage evolution recorded by the X-ray CT.
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May 2020
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I12-JEEP: Joint Engineering, Environmental and Processing
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Diamond Proposal Number(s):
[16647]
Open Access
Abstract: The fatigue overload behaviours of coarse grain (~30 μm), ultrafine grain (360 nm) and nanocrystalline (~30 nm) Ni are compared under constant amplitude loading at R = 0.1 after a 100% overload. Synchrotron X-ray diffraction is applied to map the elastic crack-tip strain fields at the mid-thickness of a compact tension specimen of nanocrystalline Ni at various stages through the loading cycles, from which the variation in stress before, during and after overload is estimated. Digital image correlation is used to measure the crack length and the displacement fields at the specimen surfaces for both grain sizes, from which the fatigue crack growth (FCG) rate, crack opening displacement and stress intensity factor range are determined. The FCG for coarse grain Ni is most significantly retarded whereas the nanocrystalline Ni is least affected by the overload due to an increased yield stress and a more planar crack surface morphology. As a result, FCG retardation by plasticity, surface roughness and residual stress-induced crack closure are reduced.
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Apr 2020
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I13-2-Diamond Manchester Imaging
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Diamond Proposal Number(s):
[13704, 18197]
Abstract: Here we present the first real-time three dimension (3D) observations of damage evolution in a composite tube under torsion. An in-situ torsion test of 1/1 45° (diamond) braided carbon fibre-epoxy circular composite tube was performed on a loading rig and the damage process was characterised by synchrotron X-ray computed tomography (CT). A number of damage modes and their damage sequence has been identified and monitored globally and in more detail within a representative region of interest. In particular, intra-tow cracks and inter-tow debonding have been found to occur almost simultaneously at low shear strains (1.5%). It is noteworthy that inter-tow debonding was initially trapped/limited within repeated braid units before propagating and connecting with other damage modes in 3D. The area fraction of inter-tow debonds was quantified at different stages and it was found to dramatically increase with increasing shear strain beyond 1.5%. The total volume fraction of the observed intra-tow cracks of various forms was seen to grow rapidly beyond shear strain of 2.0%. Beyond the peak shear stress (at shear strain of 2.5%), fibre micro-buckling and kink bands occur in the tows subjected to torsion induced axial compression at crimped regions close to tow crossovers. Tow crossovers control many aspects of damage propagation under torsion, positively by localising inter-tow debonds and negatively by initiating fibre micro-buckling.
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Dec 2019
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I12-JEEP: Joint Engineering, Environmental and Processing
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Diamond Proposal Number(s):
[16647]
Abstract: Changes in crack growth rate associated with overload events during fatigue are poorly understood, especially for materials with anisotropic microstructures. Here overload fatigue tests are reported for compact tension samples cut in two different orientations from high pressure torsion disc samples. During growth the crack planes reoriented either slightly, or significantly, to align with the elongated grain structure leading to low, and high, levels of mixed mode fatigue loading respectively. In both cases the ultrafine grained microstructure led to macroscopically flat crack faces. The fatigue crack growth rate was around 3.4 times slower for the case with the high mode II component than for the low. A 100% overload was then introduced and synchrotron X-ray diffraction and digital image correlation (DIC) were applied in-situ to map the bulk crack-tip elastic strain field (plane strain) and surface displacement field (plane stress) respectively prior to, during and after overload. The high mode II case displayed a larger degree of retardation after overload. Residual stress and plasticity-induced crack closure were found to be the primary causes for the retardation as the crack grows into the overload plastic zone. Significant crack face contact was observed for the high mode II case along with significant levels of compressive stress transferred across the crack faces at minimum load. Compared with conventional (coarse) grain Ni, the ultrafine grained Ni is less retarded by overload, because of its relatively flatter crack path and higher yield stress and thus less plasticity and residual stress induced closure.
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Nov 2019
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I13-2-Diamond Manchester Imaging
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Diamond Proposal Number(s):
[4022]
Open Access
Abstract: Structural polymeric materials incorporating a microencapsulated liquid healing agent demonstrate the ability to autonomously heal cracks. Understanding how an advancing crack interacts with the microcapsules is critical to optimizing performance through tailoring the size, distribution and density of these capsules. For the first time, time-lapse synchrotron X-ray phase contrast computed tomography (CT) has been used to observe in three-dimensions (3D) the dynamic process of crack growth, microcapsule rupture and progressive release of solvent into a crack as it propagates and widens, providing unique insights into the activation and repair process. In this epoxy self-healing material, 150 µm diameter microcapsules within 400 µm of the crack plane are found to rupture and contribute to the healing process, their discharge quantified as a function of crack propagation and distance from the crack plane. Significantly, continued release of solvent takes place to repair the crack as it grows and progressively widens.
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Nov 2019
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I13-2-Diamond Manchester Imaging
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Rafael
Leiva-Garcia
,
Adam
Anders
,
Tony
Cook
,
Grace
Burke
,
Chris
Muryn
,
Mary
Ryan
,
Malte
Storm
,
Silvia
Vargas
,
Philip
Withers
,
Brian
Connolly
,
James
Carr
,
Sheetal
Handa
Diamond Proposal Number(s):
[21142]
Abstract: Thick corrosion scales form within carbon steel oilfield pipelines in sweet (CO2 saturated) environments. The morphology and the extent of the resultant pseudo-protective nature of these scales has been seen to be dependent on multiple factors including solution pH, temperature, flow rate, and partial pressure of CO2 present. Different techniques (SEM, XRD, FIB, etc.) have been used in the past to characterise these corrosion scales. However, limitations in these techniques occur due to the fact that only small regions of the scale can be characterised in a feasible time. Further limitations may result in difficulty to relate local scale features with corrosion morphology on the evolving metal surface (i.e. localised corrosion) as the morphology of the substrate surface can only be characterised once the scale is removed. The aim of this work is to address this issue through the use of high resolution x-ray absorption tomography to characterise the internal morphology of the corrosion scales from ex situ specimens exposed to CO2 environments as a function of pH and temperature.
X-65 pipeline steel, high purity 99.99 Fe and low purity 99.0 Fe pins were used in these experiments. Specimens were exposed to CO2saturated solutions using two different methods, notably open circuit potential (OCP) immersion for 7-12 days and electrochemical polarisation for two hours at 200 mV(vs OCP). After the scaling experiments, samples were characterised using XRD and SEM. X-ray tomography was subsequently performed at the University of Manchester X-ray Imaging Facilities to characterise the corrosion morphology. Transmission X-ray microscopy (TXM) was used in absorption mode and phase contrast mode to obtain three dimensional reconstructions of the specimens, where the different features of the scale and the internal corroded substrate were imaged and characterised simultaneously.
Results indicate differences in the morphology of the corrosion scale depending on the method that was used to corrode the samples. As a consequence of the supersaturation in Fe2+, polarised samples present a thicker scale than the scales obtained by immersion at OCP conditions. The polarisation process also produces a less uniform corroded substrate than when the sample is immersed for 7 days at open circuit in the corroding environments used. In this work high resolution X-ray tomography has been proven to be a very powerful technique to study the scale morphology as well as the features of localised corrosion occurring under scale in the substrate.
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Sep 2019
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