Traditional fatigue analysis relies on time-domain methods like to identify individual stress cycles from a known time history. Spectral methods, however, characterize random loads as stationary Gaussian processes represented by Power Spectral Density (PSD) .

An "ideal" spectral method accurately predicts the cycle distribution of a random process. Prominent methods include: Vibration Fatigue by Spectral Methods - ScienceDirect.com

: Most spectral methods aggregate damage using Palmgren-Miner's rule , which assumes that the total damage is the sum of damage from individual cycles.

: Spectral analysis accounts for dynamic amplification factors by relating the excitation frequency to the structure's natural frequencies and modes. Why Use Spectral Methods?

Vibration Fatigue by Spectral Methods: A Comprehensive Technical Guide

: Instead of tracking instantaneous amplitude, PSD shows the distribution of vibration energy across different frequencies.