Evaluation of residual stresses during fatigue test in an FSW joint

This paper shows an application of the adjusted compliance ratio method (ACR), and the on-line crack-compliance technique for determination of the effects of the residual stress during a fatigue test. The fatigue crack growth tests were carried out on a friction stir welded (FSW) joint in Ti-6Al-4V titanium alloy. On-line crack compliance enables the determination of the residual stress intensity factor in real time from a fatigue test. The ACR methodology was used to separate the residual stress effects from the crack growth rate data. Finally, the residual stress distribution of the FSW joint was found from the knowledge of the residual stress intensity factor through an integral solution. It would have to be noted that both methods are based on ratios of displacements; therefore, the practical application does not require the use of the influence functions needed for the cut-compliance method. Moreover, a specific test, which determines residual stresses, can be avoided because the effect of the same residual stresses on the crack growth is evaluated during the fatigue test. This methodology is more accurate than cut compliance because it reflects the real crack growth behaviour.