Browsing by Author "Xu, A"

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    A comparative study of two nanoindentation approaches for assessing mechanical properties of ion-irradiated stainless steel
    (The Minerals, Metals & Materials Society, 2020-02-26) Bhattacharyya, D; Saleh, M; Xu, A; Zaidi, Z; Hurt, C; Ionescu, M
    Not available
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    Deformation behaviour of hexagonal- and circular-patterned Ni single-crystal 2D micro-lattices via in situ micro-tensile testing and computational analysis
    (Springer Nature Limited, 2022-04-22) Xu, A; Saleh, M; Bhattacharyya, D
    The effects of hole shape and orientation on the mechanical properties of micro-scale 2D honeycomb structures, fabricated using a focused ion beam equipment, have been investigated using an in situ micro-mechanical testing machine inside the scanning electron microscope . The material used was single-crystal Ni oriented in the < 100 > direction, with the plane of the 2D micro-lattice having a {001} normal direction. The hole shapes explored were hexagonal and circular, while two different orientations of the hexagonal holes were also compared. One of these orientations had a horizontal arm (designated 0° orientation), while the other had a vertical arm (30° orientation) in each hexagon. The results indicate that there is substantial change in strength and ductility depending on the orientation and shape of the holes with respect to the tensile axis. The samples with 30° oriented hexagonal holes had the lowest strength and highest ductility, while the samples with circular holes showed the greatest yield and tensile strength. The samples with the 0° orientated hexagonal holes had much higher strength and lower ductility than the 30° orientated ones. Moreover, the samples with 0° orientated hexagonal holes, which had a similar hole pattern arrangement to the ones with circular holes, had a similar strength to those of the latter type. Thus, it is apparent from this study that the orientation or arrangement of the holes is more important in determining the properties of the 2D microlattice than the shape of the holes. Finite element simulation of the lattice structures utilised the GTN (Gurson, Tvergaard and Needleman) model to evaluate the failure modes under uniaxial tension. The lattice structure has been shown, in a previous paper by the authors, to exhibit composite like behaviour with strength differences in various parts arising from size effects. These size effect variations were incorporated into the model, and a generalised formulation for the GTN parameters was proposed on the basis of one of the experimental configurations and subsequently applied to the other geometries. The models were in good quantitative agreement with the experimental results with accurate representation of the flows stress and failure modes. © 2022, The Author(s), under exclusive licence to Springer Science Business Media, LLC, part of Springer Nature
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    Investigating bulk mechanical properties on a micro-scale: micro-tensile testing of ultrafine grained Ni–SiC composite to determine its fracture mechanism and strain rate sensitivity
    (The Minerals, Metals & Materials Society, 2020-02-25) Bhattacharyya, D; Xu, A; Yang, C; Thorogood, GJ
    In this study, in-situ micro-tensile testing technique was used to investigate the mechanical properties of ultrafine grained Ni-3wt% SiC composite the size effect on the mechanical properties of the ultrafine grained Ni-3wt% SiC composite, and to further reveal the reasons for the low ductility of the bulk Ni-3wt%SiC composite. Dog-bone micro-tensile samples were manufactured using a Focused Ion Beam (FIB) milling machine to 15 μm length with a cross sectional area of 5 μm by 5 μm. The micro-tensile samples are pulled in tension at a quasi-static strain rate of 0.000087/s (LSR) and a relatively faster strain rate of 0.011/s (HSR). Analysis of experimental stress-strain plots for the LSR tests measured yield stress, ultimate tensile stress and modulus values that approach values previously reported for bulk/macro-level tensile tests. However, the elongation and fracture energy at the micro-level is approximately half that at the bulk scale. This discrepancy is attributed to the presence of unwanted carbon and silicon oxide impurities ∼1.5 μm in diameter which act as stress concentrators especially given their large size relative to the width of the tensile specimens. The composition of these impurities was validated by transmission electron microscopy, and they seem to be the most likely cause of low ductility of the Ni-3wt% SiC composite. In all, the study undertaken here was able to replicate mechanical properties observed at the macro scale as well as reproduce a strain rate effect. Furthermore, the failure mode of Ni-3wt% SiC composite was identified and analysed in detail.
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    Investigating bulk mechanical properties on a micro-scale: micro-tensile testing of ultrafine grained Ni–SiC composite to determine its fracture mechanism and strain rate sensitivity
    (Elsevier, 2020-03-15) Xu, A; Yang, C; Thorogood, GJ; Bhattacharyya, D
    In this study, in-situ micro-tensile testing technique was used to investigate the mechanical properties of ultrafine grained Ni-3wt% SiC composite the size effect on the mechanical properties of the ultrafine grained Ni-3wt% SiC composite, and to further reveal the reasons for the low ductility of the bulk Ni-3wt%SiC composite. Dog-bone micro-tensile samples were manufactured using a Focused Ion Beam (FIB) milling machine to 15 μm length with a cross sectional area of 5 μm by 5 μm. The micro-tensile samples are pulled in tension at a quasi-static strain rate of 0.000087/s (LSR) and a relatively faster strain rate of 0.011/s (HSR). Analysis of experimental stress-strain plots for the LSR tests measured yield stress, ultimate tensile stress and modulus values that approach values previously reported for bulk/macro-level tensile tests. However, the elongation and fracture energy at the micro-level is approximately half that at the bulk scale. This discrepancy is attributed to the presence of unwanted carbon and silicon oxide impurities ∼1.5 μm in diameter which act as stress concentrators especially given their large size relative to the width of the tensile specimens. The composition of these impurities was validated by transmission electron microscopy, and they seem to be the most likely cause of low ductility of the Ni-3wt% SiC composite. In all, the study undertaken here was able to replicate mechanical properties observed at the macro scale as well as reproduce a strain rate effect. Furthermore, the failure mode of Ni-3wt% SiC composite was identified and analysed in detail. Crown Copyright © 2019 Published by Elsevier B.V
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    Studies of high dpa ion beam irradiation fcc-bcc duplex steel 2205: micromechanical testing and nanoindentation examination of hardness variations
    (The Minerals, Metals & Materials Society, 2020-02-26) Saleh, M; Xu, A; Munroe, P; Bhattacharyya, D
    Not available.