A spectral fatigue method incorporating non-proportional multiaxial loading

A frequency domain method incorporating multiaxial non-proportional loading conditions is presented in this paper. The non-proportionality is modelled by implementing a multiaxial cycle counting procedure of path dependent maximum range\moment of load path proposed recently by Mei and Dong (2016) in frequency domain through a formulation of an effective equivalent structural stress (EESS) transfer function. Additionally, the formulation through transfer functions and the treatment of phase differences between normal and shear stresses represents a unique approach to multiaxial fatigue analysis in frequency domain. The numerous test studies performed on a representative structural detail in marine structure showed rather promising results. Reasonable multiaxial fatigue damage estimations have been obtained through the developed method by comparing the fatigue damages computed with time domain methods.