Duplex LCF-VHCF P-S-N design curves: a methodology based on the Maximum Likelihood Principle

Probabilistic-S-N (P-S-N) curves are commonly employed to model the fatigue response of specimens and components and are generally obtained by assuming the statistical distribution of the fatigue life. In industrial applications, starting from the P-S-N curves, the so-called “design curves” or “lower bound S-N curves” are defined for the design of components, in order to ensure a safety margin against fatigue failures. Due to the growing interest in the Very High Cycle Fatigue (VHCF) response of materials, methodologies for the estimation of the design curves should not be limited to the Low Cycle Fatigue (LCF)-High Cycle Fatigue (HCF) life range but should also cover the VHCF region. In this work, the Maximum Likelihood Principle is exploited for the assessment of the design curves of datasets obtained through tests in the LCF-VHCF range, with the P-S-N curves showing a duplex trend. First, the model for the P-S-N curves with duplex trend is defined. Then the proposed methodology for the design curves is described and finally validated with literature datasets.