A Comparative Analysis: Time vs. Frequency Domain Definitions of the Fatemi-Socie Criterion

The article aims to adapt the Fatemi-Socie criterion (FSC) to the frequency domain and compare it with the time domain approach to evaluate fatigue life. Key challenges include determining the critical plane position, replacing cycle counting methods with models estimating rainflow amplitude distributions, and defining a probability density function for strain amplitude and maximum normal stress. The methodology involves defining the maximum variance method to locate the critical plane and using moments of PSD to establish a twodimensional probability distribution function for shear strain and normal stress. The study verifies the proposed method against known solutions and applies it to random load cases to demonstrate its effectiveness. Results indicate a strong correlation between fatigue life predictions in both domains, confirming the robustness and versatility of the FSC. The findings suggest that the proposed frequency domain approach, utilizing statistical models, can reliably extend FSC applications to complex loading scenarios, offering a valuable tool for fatigue analysis in engineering applications.