FATIGUE PERFORMANCE OF PRELOADED ULTRA HIGH STRENGTH THREADED FASTENERS

This experimental study investigates the high cycle fatigue (HCF) performance of preloaded ultra-high strength (UHS) threaded fasteners. Every sample is subjected to a cyclic uniaxial stress additional to a mean stress, which is arbitrarily set as half of the static tensile strength. Experimental results of UHS fasteners (Classes 14.9 and 15.9) and commercially available (CA) fasteners (Class 10.9) are analyzed: S-N curves are constructed following the ASTM standards and compared after normalization. Results indicate that the normalized fatigue strength of UHS threaded fasteners is lower than that of CA threaded fasteners. For each class, the experimental S-N curves are compared with the estimation obtained using Marin equation adjusted by mean stress criteria. It is concluded that the estimation by Marin equation did not show acceptable consistency to experimental data.