Browsing by Author "Ma, Yu E."
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Item Open Access Size effects on residual stress and fatigue crack growth in friction stir welded 2195-T8 aluminium - Part I: Experiments(Elsevier Science B.V., Amsterdam., 2011-11-30T00:00:00Z) Ma, Yu E.; Staron, P.; Fischer, T.; Irving, Phil E.Residual stress fields were measured in three different sizes of Compact-Tension (C(T)) and eccentrically loaded single edge notch (ESE(T)) specimens containing transverse or longitudinal welds. The effect of size on residual stress profiles was studied. Fatigue crack growth tests were carried out with cracks growing into or away from the weld line, as well as growing along the weld centre line. Effects of weld residual stresses on fatigue crack growth rates parallel and perpendicular to the friction stir welds were studied. It was found that compressive residual stresses around the sample notch had significant retarding effects on both crack initiation and crack growth rates for cracks growing towards the weld line. Effects of residual stress on crack growth rates declined with increasing crack length. When cracks grew parallel to the weld line in C(T) samples the crack growth rate was around 20% lower than in parent material.Item Open Access Size effects on residual stress and fatigue crack growth in friction stir welded 2195-T8 aluminium - Part II: Modelling(Elsevier Science B.V., Amsterdam., 2011-12-31T00:00:00Z) Ma, Yu E.; Staron, P.; Fischer, T.; Irving, Phil E.The use of residual K (Kres) approaches for prediction of fatigue crack growth rates in residual stress fields was studied. Finite element models of the samples were built and the measured residual stress data put into the model. The virtual crack closure technique (VCCT) was used to calculate (stress intensity factor from residual stress) together with its changes with crack length using data from the part I paper. Local Kres values were used to calculate effective R values. Kop and ΔKeff values throughout the crack path in the weld were calculated. The master curve approach was used to relate these to corresponding values for crack growth rates. Predicted crack growth rates were compared with experimental results. Changes in crack growth rate found as the crack grows through the weld can successfully be predicted via application of this closure based model. Agreement between predictions and experimental data was best for tensile residual stress fields and was not as exact in compression. Possible reasons for this discrepancy are discussed.