Font Size: 

This paper describes results from Fatigue Crack Growth (FCG) tests onFriction Stir (FS) welded aluminium alloys. Main focus is on the crack paths which, insome cases, is dramatically changed. The most extreme case is of a fatigue crack whichrotates 90o upwards and continues to growth in that direction parallel to the appliedload. To visualise the influence of the material behaviour in the FS Weld on the FCGproperties, Digital Image Correlation (DIC) was used during the tests to visualise thestrain field around the crack tip. From the strain fields, the size and geometry of theplastic zone is obtained, which can help to understand how the yield strength and theresidual stresses in the FS weld influence the FCG behaviour.