Effect of Basic Thread Parameters on Fatigue Life

The effect of basic thread parameters on the fatigue performance of high fatigue strength fasteners is discussed. Fatigue data were obtained in a carefully controlled experiment and statistically analyzed to present a comparison between ISO metric threads and nonsymmetric threads. The bolts tested were made to ISO aircraft standards for high strength fasteners of steel and titanium. Available fastener design theory is correlated with the fatigue strength improvements obtained from changes in thread parameters such as root radius, flank angle, and controlled lead compensation.