Size effects on residual stress and fatigue crack growth in friction stir welded 2195-T8 aluminium - Part II: Modelling

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.