Browsing by Author "Lin, J"

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    Effect of weld residual stresses and their re-distribution with crack growth during fatigue under constant amplitude loading
    (Elsevier, 2010-04) Liljedahl, CDM; Zanellato, O; Fitzpatrick, ME; Lin, J; Edwards, L
    In this work the evolution of the residual stresses in a MIG-welded 2024-T3 aluminium alloy M(T) specimen during in situ fatigue crack growth at constant load amplitude has been measured with neutron diffraction. The plastic relaxation and plasticity-induced residual stresses associated with the fatigue loading were found to be small compared with the stresses arising due to elastic re-distribution of the initial residual stress field. The elastic re-distribution was modelled with a finite element simulation and a good correlation between the experimentally-determined and the modelled stresses was found. A significant mean stress effect on the fatigue crack growth rate was seen and this was also accurately predicted using the measured initial residual stresses. © 2010, Elsevier Ltd.
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    An investigation of inconsistent projections and artefacts in multi-pinhole SPECT with axially aligned pinholes
    (IOP Publishing Ltd, 2011-12-07) Kench, PL; Lin, J; Grégoire, MC; Meikle, SR
    Multiple pinholes are advantageous for maximizing the use of the available field of view (FOV) of compact small animal single photon emission computed tomography (SPECT) detectors. However, when the pinholes are aligned axially to optimize imaging of extended objects, such as rodents, multiplexing of the pinhole projections can give rise to inconsistent datawhich leads to ‘ghost point’ artefacts in the reconstructed volume. A novel four pinhole collimator with a baffle was designed and implemented to eliminate these inconsistent projections. Simulation and physical phantom studies were performed to investigate artefacts from axially aligned pinholes and the efficacy of the baffle in removing inconsistent data and, thus, reducing reconstruction artefacts. SPECT was performed using a Defrise phantom to investigate the impact of collimator design on FOV utilization and axial blurring effects. Multiple pinhole SPECT acquired with a baffle had fewer artefacts and improved quantitative accuracy when compared to SPECT acquired without a baffle. The use of four pinholes positioned in a square maximized the available FOV, increased acquisition sensitivity and reduced axial blurring effects. These findings support the use of a baffle to eliminate inconsistent projection data arising from axially aligned pinholes and improve small animal SPECT reconstructions. © 2011 IOP Publishing LTD
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    Projection process modelling for iterative reconstruction of Pinhole SPECT
    (IEEE, 2010-10-01) Lin, J; Kench, PL; Grégoire, MC; Meikle, SR
    In iterative reconstruction of pinhole SPECT data, the forward and back projection processes are often performed using the ray tracing method. Ray tracing is computationally efficient, but it has the drawback of poor reconstruction quality due to the missing voxel effect and textural artefacts. In this paper, the pinhole projection process was modelled starting from consideration of all the main factors affecting pinhole projection, such as voxel shape, penetration of the pinhole edges and detector response. Next, approximations were made to reduce the computational speed and the effect of the approximations on reconstructed image accuracy was evaluated in simulation and phantom experiments and compared with the ray tracing algorithm. When used in conjunction with the ML-EM algorithm, the proposed model improved reconstructed image accuracy compared with the ray tracing method and achieved comparable computational efficiency. Therefore, the proposed projection model is a practical alternative to the ray tracing algorithm for pinhole SPECT reconstruction.© 2010, Institute of Electrical and Electronics Engineers (IEEE)
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    Synthesis, structure and conductivity of BaIn0.8Mn0.2O3 − δ
    (Elsevier, 2014-04-01) Yang, C; Shu, T; Zhang, H; Dong, J; Zhiwen, S; Xiong, C; Sihai, Y; Guobao, L; Liao, F; Lin, J
    Green BaIn0.80Mn0.20O2.70 (S1) has been synthesized by solid-state reaction under high temperature, and black BaIn0.80Mn0.20O2.60 (RS1) is obtained by treating S1 under vacuum at 500 °C. They were characterized by powder X-ray and neutron diffraction, selected area electron diffraction, magnetic measurement, and impedance spectrum. S1 and RS1 crystallize in Cmcm (a = 5.9722(3), b = 5.9664(3), c = 8.4511(4) Å) and P21/c (a = 5.9328(7), b = 5.9445(11), c = 16.8154(14) Å, β = 90.02(2)°), respectively. Oxide ion vacancies are confirmed to exist in S1 and RS1 by the neutron diffraction data. © 2014, Elsevier B.V.
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    Weld residual stress effects on fatigue crack growth behaviour of aluminium alloy 2024-T351
    (Elsevier, 2009-06) Liljedahl, CDM; Brouard, J; Zanellato, O; Lin, J; Tan, ML; Ganguly, S; Irving, PE; Fitzpatrick, ME; Zhang, X; Edwards, L
    The interaction between residual stress and fatigue crack growth rate has been investigated in middle tension and compact tension specimens machined from a variable polarity plasma arc welded aluminium alloy 2024-T351 plate. The specimens were tested at three levels of applied constant stress intensity factor range. Crack closure was continuously monitored using an eddy current transducer and the residual stresses were measured with neutron diffraction. The effect of the residual stresses on the fatigue crack behaviour was modelled for both specimen geometries using two approaches: a crack closure approach where the effective stress intensity factor was computed; and a residual stress approach where the effect of the residual stresses on the stress ratio was considered. Good correlation between the experimental results and the predictions were found for the effective stress intensity factor approach at a high stress intensity factor range whereas the residual stress approach yielded good predictions at low and moderate stress intensity factor ranges. In particular, the residual stresses accelerated the fatigue crack growth rate in the middle tension specimen whereas they decelerated the growth rate in the compact tension sample, demonstrating the importance of accurately evaluating the residual stresses in welded specimens which will be used to produce damage tolerance design data. © 2009, Elsevier Ltd.