Browsing by Author "Zanellato, O"

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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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    Load partitioning and evidence of deformation twinning in dual-phase fine-grained Zr-2.5%Nb alloy
    (Elsevier, 2012-03-01) Muránsky, O; Daymond, MR; Bhattacharyya, D; Zanellato, O; Vogel, SC; Edwards, L
    In situ neutron diffraction loading experiments were carried out on a cold-rolled dual-phase (α-phase, ∼10% β-phase) Zr–2.5%Nb alloy at room temperature. The specimens were cut at different angles from the rolling direction (RD) towards the transverse direction (TD), thus the loading axis changes gradually from the rolling to transverse direction. Due to the strong texture of the studied alloy, and unidirectional nature of deformation twinning, the changing loading direction with respect to initial texture has a significant impact on the collaborative slip-twinning deformation mode in the hexagonal close-packed (hcp) α-phase. The present neutron diffraction results provide direct evidence of {1−1.2}〈1−1.−1〉 “tensile” twins in the α-phase of dual-phase Zr–2.5%Nb alloy at room temperature. Additionally, TEM analysis was employed to confirm the presence of “tensile” twins, and determine if other type of twins were present. It is further clear from the neutron diffraction results that applied load is gradually transferred from the plastically softer α-phase to the plastically harder β-phase which acts as a reinforcing phase having a yield strength in the range 750–900 MPa depending on the loading direction. © 2012, 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.