A multi-axial Fatigue Damage Spectrum for the evaluation of the fatigue damage potential of multi-axis random vibration environments

The Fatigue Damage Spectrum (FDS) method has been a cornerstone in the characterization and evaluation of vibrational loads. However, the formulation of the FDS requires to simplify the Device Under Test (DUT) as a Single-Input-Single-Output system, while real components are, in general, Multi-Input Multi-Output (MIMO) systems. This strict assumption neglects the possibility of multi-axis testing. In MIMO random tests, one critical aspect is the phase and coherence between each pair of single-axis excitation. Nevertheless, the FDS is still used to define test-tailored specifications. In this context, this paper proposes an improved version of the traditional FDS to be used to classify multi-axis random vibration environments. In particular, the proposed approach improves the traditional formulation of the FDS by incorporating the correlation of multi-axial vibration environments, enabling a better evaluation of the fatigue damage potential of multi-axis random vibration environments. This paper provides the theoretical formulation of the proposed methodology as well as its experimental verification. The experimental verification showcases the capability of the method to evaluate the damage potential of different multi-axis and single-axis vibration environments. In the experiments, the MI-FDS has been able to identify the damage potential of different vibration environments and allow to synthesize a new damage equivalent vibration environment. The evaluation of the MI-FDS aligns with the actual time to failure of the tested specimens.