Analogies between spectral methods and multiaxial criteria in fatigue damage evaluation

This work aims at providing some analogies among existing multiaxial criteria and spectral methods, used in frequency domain approach to estimate the fatigue damage of uniaxial stochastic loadings. In particular, among existing multiaxial criteria it will be analysed the co-called "projection-by-projection" approach, in which fatigue damage is estimated by assuming a quadratic sum of single damage contributions of uncorrelated projected loadings. This work will mathematically demonstrate that the theoretical framework behind the "projection-by-projection" method could be used to providing a theoretical basis to the so-called "single moment" (SM) method, proposed in the nineties as an "empirical" approach. Once the formal analogy between the two methods has been established, numerical simulations will be used to evaluate the accuracy of SM method, with reference to different types of stochastic processes with bimodal spectral density