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Instruments / Technical Area	Publication Details	Published
B16-Test Beamline	Investigations into the interface failure of yttria partially stabilised zirconia - porcelain dental prostheses through microscale residual stress and phase quantification Alexander Lunt , Enrico Salvati , Nikolaos Baimpas , Igor Dolbnya , Tee Khin Neo , Alexander Korsunsky Dental Materials DOI: 10.1016/j.dental.2019.08.098 Diamond Proposal Number(s): [8823] Show Abstract ▼ Abstract: Objectives: Yttria Partially Stabilised Zirconia (YPSZ) is a high strength ceramic which has become widely used in porcelain veneered dental copings due to its exceptional toughness. Within these components the residual stress and crystallographic phase of YPSZ close to the interface are highly influential in the primary failure mode; near interface porcelain chipping. In order to improve present understanding of this behaviour, characterisation of these parameters is needed at an improved spatial resolution. Methods: In this study transmission micro-focus X-ray Diffraction, Raman spectroscopy, and focused ion beam milling residual stress analysis techniques have, for the first time, been used to quantify and cross-validate the microscale spatial variation of phase and residual stress of YPSZ in a prosthesis cross-section. Results: The results of all techniques were found to be comparable and complementary. Monoclinic YPSZ was observed within the first 10 μm of the YPSZ-porcelain interface with a maximum volume fraction of 60%. Tensile stresses were observed within the first 150μm of the interface with a maximum value of ≈300MPa at 50μm from the interface. The remainder of the coping was in mild compression at ≈ − 30 MPa, with shear stresses of a similar magnitude also being induced by the YPSZ phase transformation. Significance: The analysis indicates that the interaction between phase transformation, residual stress and porcelain creep at YPSZ-porcelain interface results in a localised porcelain fracture toughness reduction. This explains the increased propensity of failure at this location, and can be used as a basis for improving prosthesis design.	Sep 2019
I15-Extreme Conditions	Residual strain mapping through pair distribution function analysis of the porcelain veneer within a yttria partially stabilised zirconia dental prosthesis Alexander J. G. Lunt , Philip Chater , Annette Kleppe , Nikolaos Baimpas , Tee K. Neo , Alexander M. Korsunsky Dental Materials DOI: 10.1016/j.dental.2018.11.013 Diamond Proposal Number(s): [9106] Show Abstract ▼ Abstract: Objective. Residually strained porcelain is influential in the early onset of failure in Yttria Partially Stabilised Zirconia (YPSZ) – porcelain dental prosthesis. In order to improve current understanding it is necessary to increase the spatial resolution of residual strain analysis in these veneers. Methods. Few techniques exist which can resolve residual stress in amorphous materials at the microscale resolution required. For this reason, recent developments in Pair Distribution Function (PDF) analysis of X-ray diffraction data of dental porcelain have been exploited. This approach has facilitated high-resolution (70 μm) quantification of residual strain in a YPSZ-porcelain dental prosthesis. In order to cross-validate this technique, the sequential ring-core focused ion beam and digital image correlation approach was implemented at a step size of 50 μm. This semi-destructive technique exploits microscale strain relief to provide quantitative estimates of the near-surface residual strain. Results. The two techniques were found to show highly comparable results. The residual strain within the veneer was found to be primarily tensile, with the highest magnitude stresses located at the YPSZ-porcelain interface where failure is known to originate. Oscillatory tensile and compressive stresses were also found in a direction parallel to the interface, likely to be induced by the multiple layering used during fabrication. Significance. This study provides the insights required to improve prosthesis modelling, to develop new processing routes that minimise residual stress and ultimately to reduce prosthesis failure rates. The PDF approach also offers a powerful new technique for microscale strain quantification in amorphous materials.	Nov 2018
I15-Extreme Conditions	A state-of-the-art review of micron-scale spatially resolved residual stress analysis by FIB-DIC ring-core milling and other techniques Alexander Lunt , Nikolaos Baimpas , Enrico Salvati , Igor Dolbnya , Tan Sui , Siqi Ying , H. Zhang , Annette Kleppe , J. Dluhos , Alexander Korsunsky The Journal Of Strain Analysis For Engineering Design DOI: 10.1177/0309324715596700 Show Abstract ▼ Abstract: Quantification of residual stress gradients can provide great improvements in understanding the complex interactions between microstructure, mechanical state, mode(s) of failure and structural integrity. Highly focused local probe non-destructive techniques such as X-ray diffraction, electron diffraction or Raman spectroscopy have an established track record in determining spatial variations in the relative changes in residual stress with respect to a reference state for many structural materials. However, the interpretation of these measurements in terms of absolute stress values requires a strain-free sample often difficult to obtain due to the influence of chemistry, microstructure or processing route. With the increasing availability of focused ion beam instruments, a new approach has been developed which is known as the micro-scale ring-core focused ion beam-digital image correlation technique. This technique is becoming the principal tool for quantifying absolute in-plane residual stresses. It can be applied to a broad range of materials: crystalline and amorphous metallic alloys and ceramics, polymers, composites and biomaterials. The precise nano-scale positioning and well-defined gauge volume of this experimental technique make it eminently suitable for spatially resolved analysis, that is, residual stress profiling and mapping. Following a summary of micro-stress evaluation approaches, we focus our attention on focused ion beam-digital image correlation methods and assess the application of micro-scale ring-core methods for spatially resolved residual stress profiling. The sequential ring-core milling focused ion beam-digital image correlation method allows micro- to macro-scale mapping at the step of 10–1000 μm, while the parallel focused ion beam-digital image correlation approach exploits simultaneous milling operation to quantify stress profiles at the micron scale (1–10 μm). Cross-validation against X-ray diffraction results confirms that these approaches represent accurate, reliable and effective residual stress mapping methods.	Aug 2015
B16-Test Beamline	Multiple-length-scale deformation analysis in a thermoplastic polyurethane Tan Sui , Nikolaos Baimpas , Igor Dolbnya , Cristina Prisacariu , Alexander Korsunsky Nature Communications 6 DOI: 10.1038/ncomms7583 PMID: 25758945 Diamond Proposal Number(s): [5038] Open Access Show Abstract ▼ Abstract: Thermoplastic polyurethane elastomers enjoy an exceptionally wide range of applications due to their remarkable versatility. These block co-polymers are used here as an example of a structurally inhomogeneous composite containing nano-scale gradients, whose internal strain differs depending on the length scale of consideration. Here we present a combined experimental and modelling approach to the hierarchical characterization of block co-polymer deformation. Synchrotron-based small- and wide-angle X-ray scattering and radiography are used for strain evaluation across the scales. Transmission electron microscopy image-based finite element modelling and fast Fourier transform analysis are used to develop a multi-phase numerical model that achieves agreement with the combined experimental data using a minimal number of adjustable structural parameters. The results highlight the importance of fuzzy interfaces, that is, regions of nanometre-scale structure and property gradients, in determining the mechanical properties of hierarchical composites across the scales.	Mar 2015
B16-Test Beamline	Nano-scale mapping of lattice strain and orientation inside carbon core SiC fibres by synchrotron X-ray diffraction Nikolaos Baimpas , Alexander Lunt , Igor Dolbnya , Jiri Dluhos , Alexander Korsunsky Carbon 79, 85 - 92 DOI: 10.1016/j.carbon.2014.07.045 Diamond Proposal Number(s): [9318] Show Abstract ▼ Abstract: The strongest fibres available today are carbon-based, made from carbon nanotubes (CNTs) or reduced graphene oxide flakes (RGOFs). Carbon fibres (CFs) were first developed half a century ago. Control of the thermal, chemical and mechanical processing allows obtaining desired combination of structure, strength and stiffness. In practical use, CFs are typically incorporated into larger scale systems that require multi-scale characterisation. In the present study we considered an aerospace composite consisting of titanium alloy matrix reinforced with unidirectional silicon carbide fibres with carbon monofilament core. By combining synchrotron-based imaging and nano-focused X-ray beam scattering with Focused Ion Beam stress evaluation, we construct detailed maps of structure and strain inside this material. Eigenstrain modelling was used to reconstruct the full residual strain state within the fibre cross-section. The joined-up experimental and theoretical approach allows extracting information about fibre structure down to the nanoscale, developing insight into its processing history, and revealing the existence of significant residual strains that have a strong effect on the performance of CFs in service.	Nov 2014
B16-Test Beamline I12-JEEP: Joint Engineering, Environmental and Processing I22-Small angle scattering & Diffraction	'Hybrid' non-destructive imaging techniques for engineering materials applications Nikolaos Baimpas Show Abstract ▼ Abstract: The combination of X-ray imaging and diffraction techniques provides a unique tool for structural and mechanical analysis of engineering components. A variety of modes can be employed in terms of the spatial resolution (length-scale), time resolution (frequency), and the nature of the physical quantity being interrogated. This thesis describes my contributions towards the development of novel X-ray “rich” imaging experimental techniques and data interpretation. The experimental findings have been validated via comparison with other experimental methods and numerical modelling. The combination of fast acquisition rate and high penetration properties of X-ray beams allows the collection of high-resolution 3-D tomographic data sets at submicron resolution during in situ deformation experiments. Digital Volume Correlation analysis tools developed in this study help understand crack propagation mechanisms in quasi-brittle materials and elasto-plastic deformation in co-sprayed composites. For the cases of crystalline specimens where the knowledge of “live” or residual elastic strain distributions is required, diffraction techniques have been advanced. Diffraction Strain Tomography (DST) allows non-destructive reconstruction of the 2-D (in-plane) variation of the out-of-plane strain component. Another diffraction modality dubbed Laue Orientation Tomography (LOT), a grain mapping approach has been proposed and developed based on the translate-rotate tomographic acquisition strategy. It allows the reconstruction of grain shape and orientation within polycrystalline samples, and provides information about intragranular lattice strain and distortion. The implications of this method have been thoroughly investigated. State-of-the-art engineering characterisation techniques evolve towards scrutinising submicron scale structural features and strain variation using the complementarity of X-ray imaging and diffraction. The first successful feasibility study is reported of in operando stress analysis in an internal combustion engine. Finally, further advancement of ‘rich’ imaging techniques is illustrated via the first successful application of Time-of-Flight Neutron Diffraction Strain (TOF-NDST) tomography for non-destructive reconstruction of the complete strain tensor using an inverse eigenstrain formulation.	Sep 2014
I22-Small angle scattering & Diffraction	In situ X-ray scattering evaluation of heat-induced ultrastructural changes in dental tissues and synthetic hydroxyapatite Tan Sui , Michael Sandholzer , Alexander Lunt , Nikolaos Baimpas , Andy Smith , Gabriel Landini , Alexander Korsunsky Journal Of The Royal Society Interface DOI: 10.1098/rsif.2013.0928 PMID: 24718447 Open Access Show Abstract ▼ Abstract: Human dental tissues consist of inorganic constituents (mainly crystallites of hydroxyapatite, HAp) and organic matrix. In addition, synthetic HAp powders are frequently used in medical and chemical applications. Insights into the ultrastructural alterations of skeletal hard tissues exposed to thermal treatment are crucial for the estimation of temperature of exposure in forensic and archaeological studies. However, at present, only limited data exist on the heat-induced structural alterations of human dental tissues. In this paper, advanced non-destructive small- and wide angle X-ray scattering (SAXS/WAXS) synchrotron techniques were used to investigate the in situ ultrastructural alterations in thermally treated human dental tissues and synthetic HAp powders.	Apr 2014
B16-Test Beamline	A study of phase transformation at the surface of a zirconia ceramic Oliver Roberts , Alexander Lunt , Siqi Ying , Tan Sui , Nikolaos Baimpas , Igor Dolbnya , Maria Parkes , Daniele Dini , Sergei M. Kreynin , Tee Khin Neo , Alexander Korsunsky World Congress on Engineering 2014 Diamond Proposal Number(s): [8823] Show Abstract ▼ Abstract: Yttria Partially Stabilized Zirconia (YPSZ) is one of the most important engineering ceramic materials in that it displays a whole host of outstanding structural and functional properties. Of particular importance for load bearing applications is the remarkable fracture toughness of YPSZ that arises from its ability to undergo martensitic transformation , a phase transformation that is dependent on stress, temperature, time, humidity, grain size, and the proximity of an interface. The present study was aimed at revealing the influence of the thermal ageing on the tetragonal to monoclinic phase transformation in the near surface regions of YPSZ. In order to perform qualitative and quantitative characterisation of the phase composition, three principal microscopic techniques were employed: atomic force microscopy, depth resolved Raman microspectroscopic scanning, and synchrotron X-ray diffraction. Satisfactory consistency was achieved between the results obtained using different techniques. Moreover, the data obtained in this way displayed complementarity that provided valuable input for the development of thermodynamic.	Apr 2014
B16-Test Beamline	Hierarchical modelling and X-ray analysis of human dentine and enamel Tan Sui , Michael Sandholzer , Nikolaos Baimpas , Alexander Lunt , Igor Dolbnya , Jianan Hu , Anthony D. Walmsley , Philip J. Lumley , Gabriel Landini , Alexander Korsunsky International MultiConference of Engineers and Computer Scientists 2014 Diamond Proposal Number(s): [7981, 7989, 9318, 9261] Show Abstract ▼ Abstract: Human teeth consist of enamel, dentine and cementum, hierarchical mineralised tissues with a two - level composite structure. The understanding of the mechanical behaviour of dentine and enamel in terms of their micro - and nano - scale structure has been somewhat limited. Here we present an overview of our recent work aimed at improving the understanding of the internal lattice strain response of the mineral crystallites of diffe rent orientations under external in situ loading. A range of experimental techniques was employed for the purpose of this analysis. Small - and Wide - Angle X-ray Scattering (SAXS/WAXS) were used to determine the internal lattice strain and orientational distribution of HAp crystals, while quantitative stress distribution evaluation in the birefringent mounting epoxy surrounding the sample was carried out in parallel using photoelasticity. Finite element analysis and advanced multi-scale Eshelby inclusion modelling were used to interpret the data. The satisfactory agreement achieved between the model and the experimental data, in terms of the values of multidirectional strain components under the action of differently orientated loads, demonstrates that our multiscale approach captures successfully the structure - property relationships between the hierarchical architecture of human dental tissues and their response to the applied forces. Our systematic approach can be used to improve the insight into the mechanical properties of dentine and enamel, and of textured hierarchical biomaterials (such as bones) in general.	Mar 2014
I22-Small angle scattering & Diffraction	Structure-mechanical function relations at nano-scale in heat-affected human dental tissue Tan Sui , Michael Sandholzer , Eric Le Bourhis , Nikolaos Baimpas , Gabriel Landini , Alexander Korsunsky Journal Of The Mechanical Behavior Of Biomedical Materials DOI: 10.1016/j.jmbbm.2013.12.014 Open Access Show Abstract ▼ Abstract: The knowledge of the mechanical properties of dental materials related to their hierarchical structure is essential for understanding and predicting the effect of microstructural alterations on the performance of dental tissues in the context of forensic and archaeological investigation as well as laser irradiation treatment of caries. So far, few studies have focused on the nano-scale structure-mechanical function relations of human teeth altered by chemical or thermal treatment. The response of dental tissues to thermal treatment is thought to be strongly affected by the mineral crystallite size, their spatial arrangement and preferred orientation. In this study, synchrotron-based small and wide angle X-ray scattering (SAXS/WAXS) techniques were used to investigate the micro-structural alterations (mean crystalline thickness, crystal perfection and degree of alignment) of heat-affected dentine and enamel in human dental teeth. Additionally, nanoindentation mapping was applied to detect the spatial and temperature-dependent nano-mechanical properties variation. The SAXS/WAXS results revealed that the mean crystalline thickness distribution in dentine was more uniform compared with that in enamel. Although in general the mean crystalline thickness increased both in dentine and enamel as the temperature increased, the local structural variations gradually reduced. Meanwhile, the hardness and reduced modulus in enamel decreased as the temperature increased, while for dentine, the tendency reversed at high temperature. The analysis of the correlation between the ultrastructure and mechanical properties coupled with the effect of temperature demonstrates the effect of mean thickness and orientation on the local variation of mechanical property. This structural–mechanical property alteration is likely to be due to changes of HAp crystallites, thus dentine and enamel exhibit different responses at different temperatures. Our results enable an improved understanding of the mechanical properties correlation in hierarchical biological materials, and human dental tissue in particular.	Dec 2013

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