Fatigue assessment of friction stir channels

Uniaxial and biaxial fatigue tests were carried out with a stress ratio of R = −1. The FSC specimens used in this study were specially designed for the purpose. The fatigue behaviour was investigated by load controlled tests under uniaxial tension/compression loading and combined axial and torsional proportional loading. Metallographic analysis of the channel microstructure and fractograph analysis of the fracture surfaces were performed by optical microscope and SEM, respectively. For all tests carried out, the first crack always has initiated at the top of the advancing side namely in the boundary between the nugget and the thermo-mechanically affected zone.