This study reveals that degradation in load-carrying capacity owing to sustained-load cracking (SLC) can occur in alloys of the Ti-6Al-4V family. Each of eight alloys tested with fatigue-precracked specimens in ambient room air exhibited the phenomenon, with degradations ranging from 11 to 35 percent. The degree of susceptibility to SLC was seen to be dependent upon crack orientation in rolled plate materials. The threshold stress-intensity factor below which SLC failures will not occur in these alloys, KIt, appears to represent a more conservative fracture-safe design parameter than the plane-strain fracture toughness KIc, which cannot account for time-delayed failures owing to SLC.

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