Multi-axial fatigue behavior of high-strength structural bolts

In this study, the fatigue failure of high-strength bolts (galvanized and regular) was experimentally and analytically explored under different tension-to-shear cyclic loading ratios. The observed cracking mechanisms were found to be a function of the bolt types and loading conditions. Though the cracks in the galvanized bolts followed the helical shape of the threads, the cracks for the regular bolts were parallel to the shear plan. The predicted fatigue lives under the combined tension and shear loads using the analytical approach matched the experimental results. Utilizing Eurocode SN curves for independent tension and shear demands overestimated the fatigue life of bolts under multi-axial stresses. The resulting SN curves obtained from this study can aid engineers in designing connections where bolts are subjected to multi-axial fatigue load.