To determine the effects of various factors on low-cycle fatigue phenomena in connection with space vehicle design, axial tension fatigue tests up to 2000 cycles were conducted on titanium alloy, Ti-6Al-4V, at −423 F. The effects of changing the minimum-to-maximum load ratio and cycling speed for the range tested were slight. The fatigue strength of pressure-welded specimens was within 1 per cent of that of the base metal. Fatigue strengths at −423 F were 65 to 68 per cent higher than those at room temperature.

Two types of fractures were observed, depending on the fatigue life. A transition in the fracture appearance occurred between 700 and 2000 cycles in which the fracture changed from a cup-and-cone to a more typical surface-initiated fatigue fracture. Cycling below the ultimate tensile strength tended to raise the fatigue strength above the static tensile strength. Possible mechanisms are discussed.