This work presents a new methodology for evaluating crack initiation under biaxial conditions. The
methodology consists of evaluating a number of crack parameters automatically with digital processing
of high-magnification images of the crack. Five different strain conditions were evaluated on a low carbon
ferritic–pearlitic steel specimen with tubular shape. A hole of 150 lm diameter was drilled to enforce the
crack to initiate at a particular spot. Different combinations of axial and torsional strains were analysed
during the initiation stage of the crack. Fatigue crack propagation curves clearly showed oscillations due
to microstructure. It was also observed that these oscillations decreased as the torsional component of
the strain was increased. Driving force was also evaluated in crack opening and sliding direction through
crack opening displacement and crack sliding displacement. The results demonstrate that crack opening
displacement is sensitive to microstructural barriers and crack sliding displacement is sensitive to crack
deviations caused by the microstructure.
