A threshold in metal fatigue

Abstract Three possible mechanisms for non-propagating cracks were proposed with one being at least partially eliminated when a test run in dry argon on Ti-6Al-4V produced little or no change in the threshold compared to that in air. WOL type compact tension specimens of 9310 steel, 4340 steel, and Ti-6Al-4V were cyclically loaded at frequencies up to 200 cps for long periods of time to obtain extremely slow crack propagaion data down to 5 x 10-9 inches per cycle. Fracture mechanics was used to analyze the data in terms of K, the alternating stress intensity parameter, and da/dn, the fatigue crack growth rate.