Averaged strain energy density-based synthesis of crack initiation life of notched titanium and steel bars under uniaxial and multiaxial fatigue

The fatigue behaviour of circumferentially notched specimens made of titanium alloy, Ti-6Al-4V, and austenitic stainless steel, AISI 304L, is investigated in the present paper. Fatigue crack initiation and subsequent propagation are accurately monitored by using the electrical potential drop technique. This method allows to define the crack initiation life in correspondence of a given increase of the electrical potential drop. The experimental results of each material is re-analysed using the strain energy density (SED) averaged over a structural volume having radius R0 and surrounding the notch tip. To exclude extrinsic mechanisms acting during the crack propagation phase, the crack initiation life is herein considered. A physical definition of the initiation life in relation to the SED-approach is related to an initiated crack depth equal to R0. With the aim to to estimate the increase of the potential drop at the initiation time defined by a physical crack depth equal to R0, the calibration curves of the potential drop method, i.e. potential drop change as a function of crack depth, are derived in the present contribution by means of electrical FE analyses.