Predicting the fatigue life of threaded bolts is crucial in aerospace and mechanical assemblies where cyclic loading can cause early joint failure. Existing studies, like [1], have created S-N curves for high-strength bolts under different pretension and temperature conditions through experimentation. However, there are few numerical methods that can replicate these results, especially for bolts without pretension.
This study develops and validates a finite element analysis (FEA) methodology to predict the fatigue performance of pretensioned threaded bolts under axial loading, using the experimentally derived Series-2 S-N data for M20 high-strength bolts with pretension. The approach employs a detailed 3D solid model with explicit thread geometry and a two-step transient structural analysis. This first simulates the bolt tightening process to establish a realistic preload, followed by the application of a service tensile load. Local stress distributions are analyzed to extract peak stress amplitudes, which are then used with the Basquin relation and the ASME Elliptic failure criterion to estimate fatigue life. The FEA-predicted results are compared against the published experimental dataset.
Preliminary results show that the proposed FEA method aligns with the observed fatigue lives within the experimental variability, confirming its effectiveness for directly assessing the fatigue of threaded bolts with pretension. This method provides a practical, experimentally based simulation framework for aerospace bolt design, enabling engineers to incorporate validated fatigue predictions into digital engineering processes for ensuring structural integrity.