Browsing by Author "Edwards, L."

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    The effect of weld residual stresses and their re-distribution with crack growth during fatigue under constant amplitude loading
    (Elsevier, 2010-04) Liljedahl, C. D. M.; Zanellato, O.; Fitzpatrick, M. E.; 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.
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    The Effects of Residual Stress and HAZ on Fatigue Crack Growth in MIG Welded 2024 and 7150 Aluminium
    (2003-01-01T00:00:00Z) Lin, J.; Ganguly, Supriyo; Edwards, L.; Irving, Phil E.
    The effect of weld residual stress, and hardness profile on fatigue crack propagation in MIG welded 2024 and 7150 aluminium joints was studied. Residual stress fields in the weld were measured using neutron diffraction. Tests were performed using a range of mean stresses and on different starting defect shapes. It was found that fatigue crack propagation in weld metal and HAZ is influenced by crack morphology and also the distribution of residual stress and hardness. Control of these parameters will optimise damage tolerance capability in welded safety critical structures.
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    An Integrated Approach to the Determination and Consequences of Residual Stress on the Fatigue Performance of Welded Aircraft Structures.
    (2006-02-01T00:00:00Z) Edwards, L.; Fitzpatrick, M. E.; Irving, Phil E.; Sinclair, I.; Zhang, X.; Yapp, David
    Although residual stress in welded structures and components has long been known to have an effect on their fatigue performance, access to reliable, spatially accurate residual stress field data has been limited. Recent advances in neutron and synchrotron X-ray diffraction allow a far more detailed picture of weld residual stress fields to be obtained that permits the development and use of predictive models that can be used for accurate design against fatigue in aircraft structures. This paper describes a fully integrated study of the three- dimensional residual stress distribution accompanying state-of-the-art fusion welds in 2024-T4 aluminum alloy, and how it is affected by subsequent machining and service loading. A particular feature of this work has been the development of techniques allowing the nondestructive evaluation of the residual stress field in the full range of specimens used to provide the design data required for welded aircraft structures and the integration of this information into all aspects of damage tolerant design.
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    Problems in using a comb sample as a stress-free reference for the determination of welding residual stress by diffraction
    (Elsevier Science B.V., Amsterdam., 2010-12-31T00:00:00Z) Ganguly, Supriyo; Edwards, L.; Fitzpatrick, M. E.
    Precise measurement of a stress-free reference lattice parameter is vital in the determination of residual stress by diffraction techniques using θ/2θ-based analyses. For the evaluation of the residual strain profile in fusion-welded material, it is particularly important to correct the measured strain point-by-point by a stress-free reference for each spatial location across the weld. This is to take into account the compositional and microstructural variation across the weld caused by the thermal cycle of welding, as local changes in solute content of the parent alloy cause changes in the stress-free lattice parameter. Although ideally such measurements should be obtained from small cubes machined from the weld, the use of a comb sample has previously been proposed as a macro-stress-free reference, with the assumption that each finger of the comb is of insufficient dimension to hold a macro-stress field. This paper presents an approach towards analysis of the stress-free reference values using a comb sample extracted from a variable polarity plasma arc (VPPA) welded plate. It is shown that there is inter-granular stress and retained macro-stress within the comb teeth, and an experimental approach to deal with the problem is proposed.
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    Weld residual stress effects on fatigue crack growth behaviour of aluminium alloy 2024-T351
    (Elsevier Science B.V., Amsterdam., 2009-06-30T00:00:00Z) Liljedahl, C. D. M.; Brouard, J.; Zanellato, O.; Lin, J.; Tan, M. L.; Ganguly, Supriyo; Irving, Phil E.; Fitzpatrick, M. E.; 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.