Towards a probabilistic concept of the Kitagawa-Takahashi diagram

The Kitagawa-Takahashi (K-T) diagram, implemented by the El Haddad equation, relates the conventional fatigue limit to the crack size, enabling a boundary for the cyclic stress range to be established, below which an infinite life of the structural component may be, theoretically, ensured for any crack size due to the non-propagation of micro- and macrocracks. In order to account for the inherent random character of the fatigue phenomenon in real materials and the need of extending the K-T applicability to any prefixed number of cycles, advanced probabilistic S-N models should be considered to define the fatigue limit. In this way, a new basis towards a probabilistic Kitagawa-Takahashi-El Haddad approach is provided in agreement with the asymptotic matching proposed by Ciavarella-Monno.