Browsing by Author "Kisi, EH"

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    Ab initio phonon dispersion curves used to check experimentally determined elastic constants of the MAX phase Ti3SiC2
    (Trans. Tech Publication Inc., 2011-07-04) Kirstein, O; Zhang, JF; Kisi, EH; Riley, DP
    The ternary carbide Ti3SiC2 is the archetype of MAX phases. To date, MAX phases have proven difficult to synthesize as sufficiently large single crystals from which single crystal elastic constants might be obtained. Therefore, the elastic properties not only of Ti3SiC2 but other MAX phases are extensively studied by ab initio methods. Recently single crystal elastic constants were experimentally determined for the first time using neutron diffraction. The experiment revealed extreme shear stiffness which is not only quite rare in hexagonal materials but also strongly contradicts the predictions of all published MAX phase elastic constants from ab initio calculations. In the present paper we would like to show that such shear stiffness can possibly be supported by ab initio calculations and the calculated phonon dispersion along high symmetry directions.© 2011, Trans Tech Publications
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    Bragg-edge elastic strain tomography
    (Engineers Australia, 2017-11-27) Wensrich, CM; Gregg, AWT; Hendriks, JN; Aggarwal, R; Tremsin, AS; Shinohara, T; Luzin, V; Meylan, MH; Kisi, EH; Kirstein, O
    Time-of-flight neutron imaging has now progressed to the point where high-resolution energy-resolved imaging is possible. Among many other applications, this technology allows the imaging of elastic strain fields within polycrystalline solids using a geometry identical to a traditional radiograph. 3D strain tomography from measurements such as these has been a current topic of research over the past decade. The authors recently solved this tomography problem and provided a reconstruction algorithm for the set of all systems subject to external loads in the absence of residual or eigenstrain. In this paper we provide an overview of the recent experiment carried out at the J-PARC pulsed neutron source in Japan focused on demonstrating this algorithm. This now represents the first-ever practical demonstration of Bragg-edge neutron transmission strain tomography in a non-axisymmetric system. The results of the experiment are presented along with the validation of the reconstructed field through Digital Image Correlation and traditional constant wavelength neutron strain scanning within the Australian Centre for Neutron Scattering at ANSTO. An outlook on potential strategies for reconstruction in the general case is also provided. © 2017 Engineers Australia
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    Bragg-edge neutron strain imaging and tomography
    (Australian Institute of Nuclear Science and Engineering (AINSE), 2018-11-18) Wensrich, C; Gregg, AWT; Hendriks, JN; Luzin, V; Shinohara, T; Kirstein, O; Meylan, MH; Kisi, EH
    For more than 10 years, time-of-flight detectors at pulsed neutron sources have been capable of providing high-resolution images of strain fields through Bragg-edge analysis [1]. With a geometry akin to a traditional radiograph, these images represent a projection of the full 3D tensor strain distribution to a scalar field. This poses a rich tomography problem based on a generalised version of the Radon transform known as the Longitudinal Ray Transform (LRT). The solution to this Bragg-edge strain tomography problem promises a new approach by which the full triaxial elastic strain (and hence stress) distribution could be observed within crystalline solids over the scale of centimetres. This presentation will provide an overview of Bragg-edge imaging and strain measurement before outlining recent work by the Authors focused on solving the associated tomography problem. The central issue that rendered the problem ill-posed will be discussed before introducing a range of approaches based on equilibrium constraints. A two dimensional experimental demonstration based on data from the RADEN energy-resolved imaging instrument (at J-PARC in Japan) will be presented with comparisons to detailed constant wavelength strain scans from the KOWARI diffractometer (ANSTO). The generalisation of this approach to three-dimensions will also be discussed. [1] Tremsin et al. “High-resolution strain mapping through time-of-flight neutron transmission diffraction with a microchannel plate neutron counting detector”, Strain, v48 pp296-305, 2012. © The Authors
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    Elastic constants of oriented Ti3AlC2 and Ti3SiC2 obtained via coherent inelastic neutron scattering
    (International Conference on Neutron Scattering, 2017-07-12) Kirstein, O; Gray, V; Stampfl, APJ; Kisi, EH
    Effort has gone into understanding the properties of MAX phases and their archetypes, Ti3SiC2,and Ti3AlC2, is as these materials exhibit a desirable combination of metallic and ceramic properties [1]. Single crystal elastic constants(SEC), usually obtained using ab-initio calculations in combination with crystallographic information, indicate the materials to be isotropic [2]. While it is difficult to obtain single crystals it is possible to produce highly textured specimens. Using a method developed by Buchenau [3] allows using coherent inelastic neutron scattering to obtain an estimation of the SEC, and such an experiment was performed using the three-axis spectrometer TAIPAN at ANSTO [4]. Results for Ti3AlC2 agree with ab-initio calculations and the assumption of isotropy. For Ti3SiC2 experimental results of c44 = 402.7 GPa do not support isotropic values obtained from ab-initio calculations. Molecular dynamics simulations combined with inelastic neutron scatteringexperiments support the initial diffraction experiment and hence themicromechanical model that was used [5]. We present here a self-consistentdescription of the mechanical properties of the MAX phases Ti3SiC2and Ti3AlC2. [1] M. W. Barsoum et al. Annual Rev.Mat. Res. 41(2011); [2] M. F. Cover et al., J. Phys.Conds. Matt., 21(2009) 305403; [3] U. Buchenau, Sol. St. Comm.,Vol.32(12), 1979 ; [4] V. Gray et al.. J. Am. Ceram. Soc.1-6, 2016; [5] E.H. Kisi et al, J. of Phys.: Cond.Matter 22 (2010) 162202
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    Energy-resolved neutron imaging options at a small angle neutron scattering instrument at the Australian Center for Neutron Scattering
    (AIP Publishing, 2019-03-26) Tremsin, AS; Sokolova, AV; Salvemini, F; Luzin, V; Paradowska, AM; Muránsky, O; Kirkwood, HJ; Abbey, B; Wensrich, CM; Kisi, EH
    Energy-resolved neutron imaging experiments conducted on the Small Angle Neutron Scattering (SANS) instrument, Bilby, demonstrate how the capabilities of this instrument can be enhanced by a relatively simple addition of a compact neutron counting detector. Together with possible SANS sample surveying and location of the region of interest, this instrument is attractive for many imaging applications. In particular, the combination of the cold spectrum of the neutron beam and its pulsed nature enables unique non-destructive studies of the internal structure for samples that are opaque to other more traditional techniques. In addition to conventional white beam neutron radiography, we conducted energy-resolved imaging experiments capable of resolving features related to microstructure in crystalline materials with a spatial resolution down to ∼0.1 mm. The optimized settings for the beamline configuration were determined for the imaging modality, where the compromise between the beam intensity and the achievable spatial resolution is of key concern. © 2020 AIP Publishing LLC
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    Force chains in monodisperse spherical particle assemblies: three-dimensional measurements using neutrons
    (American Physical Society, 2014-10-03) Wensrich, CM; Kisi, EH; Luzin, V; Garbe, U; Kirstein, O; Smith, AL; Zhang, JF
    The full triaxial stress state within individual particles in a monodisperse spherical granular assembly has been measured. This was made possible by neutron imaging and computed tomography combined with neutron diffraction strain measurement techniques and associated stress reconstruction. The assembly in question consists of 549 precision steel ball bearings under an applied axial load of 85 MPa in a cylindrical die. Clear evidence of force chains was observed in terms of both the shape of the probability distribution function for normal stresses and the network formed by highly loaded particles. An extensive analysis of the source and magnitude of uncertainty in these measurements is also presented.©2014 American Physical Society.
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    Measurement and analysis of the stress distribution during die compaction using neutron diffraction
    (Springer, 2012-11-01) Wensrich, CM; Kisi, EH; Zhang, JF; Kirstein, O
    The full axisymmetric stress state of a granular material undergoing compaction in a cylindrical die has been measured using a technique based on neutron powder diffraction. This technique allowed the detailed distribution of stress to be measured in situ, deep within a copper powder inside a solid die. Four components of normal strain were measured over a radial cross section. These components consisted of the axial, radial, hoop and an off-axis strain in the axial-radial direction. This allowed for the reconstruction of the full axisymmetric stress tensor as a distribution over the radial cross section. Many interesting features were observed in this distribution, such as exponential decay of the axial stress (described by Janssen in Zeitschrift des Vereines duetscher Ingenieure 39:1045, 1895), and highly localised regions of high shear stress. The potential of this type of data in the validation of numerical models is discussed. © 2012, Springer.
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    Non-contact stress measurement in granular materials via neutron and x-ray diffraction: theoretical foundations
    (Springer, 2013-06-01) Wensrich, CM; Kisi, EH; Luzin, V
    Model validation remains a serious problem within the field of computational granular materials research. In all cases the rigor of the validation process is entirely dependent on the quality and depth of the experimental data that forms the point of comparison. Neutron and X-ray diffraction methods offer the only quantitative non-contact method for determining the spatially resolved triaxial stress field within granular materials under load. Measurements such as this can provide an unprecedented level of detail that will be invaluable in validating many models. In this paper the theoretical foundation underpinning diffraction-based strain measurements, their conversion to local stress in the particles and ultimately into the bulk stress field is developed. Effects such as elastic anisotropy within the particles of the granular material, particle plasticity and locally inhomogeneous stress distribution are shown to not offer any obstacles to the method and a detailed treatment of the calculation of the bulk stresses from the particle stresses is given. © 2013, Springer.
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    Quantitative neutron diffraction texture measurement applied to alpha-phase alumina and Ti(3)AlC(2)
    (Wiley-Blackwell, 2011-10-01) Zhang, JF; Kisi, EH; Kirstein, O
    Orientation distribution functions, essential for making a quantitative connection between single-crystal and polycrystal properties, have been determined for extruded [alpha]-phase alumina, hot-pressed Ti3AlC2 and cold isostatically pressed Ti3AlC2 using experimental pole figures recorded on the fixed-wavelength neutron diffractometer KOWARI. Some practical improvements to the calculation of the pole-figure density from the raw area-detector data, and for constructing pole figures on an n x ndegrees hemispherical grid, are presented. The textures give some insight into particle flow during manufacture. Directly measured material textures were compared with one-dimensional pole density functions, such as the March and Rietveld functions commonly used for the correction of preferred orientation in Rietveld refinements, as a means of assessing the utility of the latter for the computation of diffraction elastic constants and other polycrystal properties from a given set of single-crystal properties. © 2011, Wiley-Blackwell
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    Shear stiffness in nanolaminar Ti3SiC2 challenges ab initio calculations
    (Institute of Physics, 2010-04-28) Kisi, EH; Zhang, JF; Kirstein, O; Riley, DP; Styles, MJ; Paradowska, AM
    Nanolaminates such as the Mn + 1AXn (MAX) phases are a material class with ab initio derived elasticity tensors published for over 250 compounds. We have for the first time experimentally determined the full elasticity tensor of the archetype MAX phase, Ti3SiC2, using polycrystalline samples and in situ neutron diffraction. The experimental elastic constants show extreme shear stiffness, with c44 more than five times greater than expected for an isotropic material. Such shear stiffness is quite rare in hexagonal materials and strongly contradicts the predictions of all published MAX phase elastic constants derived from ab initio calculations. It is concluded that second order properties such as elastic moduli derived from ab initio calculations require careful experimental verification. The diffraction technique used currently provides the only method of verification for the elasticity tensor for the majority of new materials where single crystals are not available. © 2010, Institute of Physics
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    Single crystal elastic constants of the MAX phase Ti3AlC 2 determined by neutron diffraction
    (Trans Tech Publications, 2010-01-01) Kirstein, O; Zhang, JF; Kisi, EH; Riley, DP; Styles, MJ; Paradowska, AM
    The ternary ceramic Ti3AlC2 has an interesting combination of electrical, thermal and mechanical properties. Single crystal elastic constants under the Reuss approximation for the micromechanical state were obtained by analysing the shifts of neutron diffraction peaks while a polycrystalline sample was subjected to a compressive load varying from 5 to 300 MPa. The values of Young’s modulus and Poisson’s ratio computed from the single crystal compliances are in good agreement with those obtained directly from strain gauges and from the average changes in the a and c unit cell parameters.
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    Stress distribution in iron powder during die compaction
    (Trans Tech Publications Ltd, 2014-02) Kisi, EH; Wensrich, CM; Luzin, V; Kirstein, O
    The unique and unusual state of matter represented by granular materials has historically made it very difficult to develop models of stress distributions and was previously not able to be explored experimentally in the required detail. This paper reports the application of the neutron diffraction strain scanning method, originally developed for residual stress measurements within engineering components, to the problem of the stress distribution in granular Fe under a consolidating pressure. Strains were measured in axial, radial, circumferential and an oblique direction using the neutron strain scanning diffractometer KOWARI at ANSTO (Sydney). The full stress tensor as a function of position was able to be extracted for both straight walled, converging and stepped dies. © 2014, Trans Tech Publications.