  A new fatigue life prediction method using the energy-based approach under
uniaxial and multiaxial random loadings is proposed in this paper. One unique
characteristic of the proposed method is that it uses time-derivative damage
accumulation model compared to the classical cycle-based damage accumulation
model. Thus, damage under arbitrary random loading can be directly obtained
using time-domain integration without cycle counting (e.g., rain-flow cycle
counting method in classical fatigue analysis). First, a brief review of
existing models is given focusing on their applicability to
uniaxial/multiaxial, constant/random, and high cycle fatigue/low cycle fatigue
loading regimes. It is observed that most existing models are only applicable
to certain loading conditions and many of them are not applicable/validated
under random loadings. Next, a time-derivative damage accumulation model under
uniaxial random loading is proposed. The proposed damage function is inspired
by a time-domain fatigue crack growth model. The fatigue life is obtained by
integrating the damage function following random energy loading histories.
Following this, an equivalent energy concept for general multiaxial loading
conditions is used to convert the random multiaxial loading to an equivalent
random uniaxial loading, where the time-derivative damage model can be used.
Finally, the proposed model is validated with extensive experimental data from
open literature and in-house testing data under various constant and random
spectrum loadings. Conclusions and future work are suggested based on the
findings from this study.
