Browsing by Author "Chiu, WK"

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    Comparative study between FEA, trepanning and neutron strain diffraction on residual stresses in flash-butt welded rails
    (Taylor & Francis, 2007-06) Tawfik, D; Mutton, PJ; Kirstein, O; Chiu, WK
    This paper compares three independent methods for deriving the residual stresses distribution in AS60 normal cooled flash-butt welded rail. A numerical technique utilised a sequentially coupled thermo-mechanical analysis with representative temperature dependent and phase transformation properties of the rail steel. The numerical model also incorporated an element removal regime to assess the effect of stress relaxation when slicing a plate section from a welded rail section for neutron stress mapping. Two experimental techniques were used to quantify the magnitude of residual stresses in the weld; these were strain gauging and trepanning, and neutron diffraction (ND). The results showed satisfactory correlation between the residual stress distribution obtained from the numerical analysis and the strain gauge/trepanning data and ND stress mapping, respectively. The ND and numerical analysis both confirmed that the tensile residual stresses in both vertical and longitudinal directions are concentrated in the web region, despite a significant relaxation as a result of the sectioning method used to obtain the plate section for neutron stress mapping. © 2007, Taylor & Francis Ltd.
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    Verification of residual stresses in flash-butt-weld rails using neutron diffraction
    (Elsevier B. V., 2006-11-15) Tawfik, D; Kirstein, O; Mutton, PJ; Chiu, WK
    Residual stresses developed during flash-butt welding may play a crucial role in prolonging the fatigue life of the welded tracks under service loading conditions. The finished welds typically exhibit high levels of tensile residual stresses in the web region of the weld. Moreover, the surface condition of the web may contain shear drag or other defects resulting from the shearing process which may lead to the initiation and propagation of fatigue cracks in a horizontal split web failure mode under high axle loads. However, a comprehensive understanding into the residual stress behaviour throughout the complex weld geometry remains unclear and is considered necessary to establish the correct localised post-weld heat treatment modifications intended to lower tensile residual stresses. This investigation used the neutron diffraction technique to analyse residual stresses in an AS60 flash-butt-welded rail cooled under normal operating conditions. The findings will ultimately contribute to developing modifications to the flash-butt-welding procedure to lower tensile residual stresses which may then improve rail performance under high axle load. © 2006 Elsevier B.V.
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    Verification of residual stresses in flash-butt-weld rails using neutron diffraction
    (The Bragg Institute, Australian Nuclear Science and Technology Organisation, 2005-11-27) Tawfik, D; Kristein, O; Mutton, PJ; Chiu, WK
    Residual stresses developed during flash-butt welding may play a crucial role in prolonging the fatigue life of the welded tracks under service loading conditions. The finished welds typically exhibit high levels of tensile residual stresses in the web region of the weld. Moreover, the surface condition of the web may contain shear drag or other defects resulting from the shearing process which may lead to the initiation and propagation of fatigue cracks in a horizontal split web failure mode under high axle loads. However, a comprehensive understanding into the residual stress behaviour throughout the complex weld geometry remains unclear and is considered necessary to establish the correct localised post-weld heat treatment modifications intended to lower tensile residual stresses. This investigation used the neutron diffraction technique to analyse residual stresses in an AS60 flash-butt-welded rail cooled under normal operating conditions. The findings will ultimately contribute to developing modifications to the flash-butt-welding procedure to lower tensile residual stresses which may then improve rail performance under high axle load conditions. © The Authors