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 wan 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.

The use of residual K (K res) 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 res K (stress intensity factor from residual stress) together with its changes with crack length using data from the part I paper. Local K res values were used to calculate effective R values. K op and ΔK eff 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.

Applications of friction stir welding in a fuselage structure were studied. Samples with two different friction-stirweld orientations in the fuselage panel were tested: one is along the fuselage longitudinal direction and the other one is along the fuselage circumferential direction. Then fatigue cracks were investigated that were set in three different types: parallel and perpendicular to friction stir welds and between double welds. Sample geometries were machined from identical welds in order to remove the effect of the weld process on fatigue behavior. Tests were conducted on M (T) specimens with either longitudinal or transverse welds. Cracks growing into or growing away from the weld center, as well as in the nugget zone, were investigated. It is shown that fatigue crack growth for cracks growing away from the center seems similar to that of the parent material; for crack growing in the nugget, crack grows slower than in the parent material; and for cracks starting between double welds, the crack grows slower than in the other two types. The virtual crack-closure technique method was used to calculate stress intensity factor from residual stress (K res ) and effective R ratio in an attempt to explain the experimental findings.Nomenclature a = crack length da=dN = crack growth rate E = Young's modulus of elasticity F j = reaction force on the jth node G = strain-energy release rate K = stress intensity factor K res = stress intensity factor from residual stress N = cycle (fatigue load) R eff = R ratio with the presence of residual stress R nom = applied load R ratio t = thickness of samples u i = total displacement from the ith node c = element size